abcArquivos Brasileiros de CardiologiaArq. Bras. Cardiol.0066-782X1678-4170Sociedade Brasileira de Cardiologia - SBCSão Paulo, SP, BrazilWNnrtXPvCwtwgMMgmByTGbt00001S0066-782X2007001500001S0066-782X(07)0890030110.1590/S0066-782X2007001500001Artigos OriginaisAblação da fibrilação atrial por cateter com radiofreqüência guiada por mapeamento espectral endocárdico dos "ninhos de FA" em ritmo sinusalMateosJosé Carlos PachónMateosEnrique I. PachónLoboTasso J.PachónMaria Zélia C.MateosJuán Carlos PachónPachónDenilda Queiroz V.VargasRemy Nelson A.PiegasLeopoldo S.JateneAdib D.Hospital do CoraçãoSão PauloSão PauloInstituto Dante Pazzanese de CardiologiaBrazil092007893140150010320072502200707032007This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
FUNDAMENTO: Através de mapeamento espectral-(ME) endocárdico em ritmo sinusal, observam-se dois tipos de miocárdio atrial: o compacto de espectro liso e o fibrilar de espectro segmentado ("Ninho de FA" [NFA]). Durante a FA o compacto tem ativação organizada e baixa freqüência (passivo) enquanto o fibrilar apresenta ativação bastante desorganizada e alta freqüência (ativo/ressonante) sendo ambos ativados por uma taquicardia protegida de alta freqüência, taquicardia de background (TB). OBJETIVO: Descrever o tratamento da FA pela ablação dos NFA e da TB. MÉTODOS: 1) Ablação por cateter-RF [4/8mm-60º/30-40J/30s] dos NFA guiada por ME em ritmo sinusal, fora das veias pulmonares; 2) Estimulação atrial-300ppm; 3) Ablação adicional de NFA se induzida FA; 4) Ablação focal se induzida TB e/ou Flutter; 5) Seguimento clínico+ECG+Holter. RESULTADOS: Foram tratados 50±18 NFA/paciente. Após 11,3±8m 81p (88%) estavam sem FA (28,3% com antiarrítmico). Após a ablação dos NFA: a FA não foi reinduzida em 61p(71%); TB foi induzida e tratada em 24p(26%). Ocorreram 2 sangramentos pericárdicos (1 tratado clinicamente e 1 cirurgicamente) ocasionados por bainhas não mais utilizadas. CONCLUSÃO: O ME em ritmo sinusal ablaciona os NFA. Durante a FA os NFA apresentam um padrão reativo-ressonante e o miocárdio compacto apresenta-se passivo, estimulados pela alta freqüência da TB. Após a ablação dos NFA e da TB não foi possível reinduzir FA sustentada. A ablação dos NFA fora das VP se mostrou segura e altamente eficiente para a cura e/ou o controle clínico da FA.
Ablação por cateterfibrilação atrialanálise espectralfreqüência cardíaca25092007
ARTIGO ORIGINAL
Ablação da fibrilação atrial por cateter com radiofreqüência guiada por mapeamento espectral endocárdico dos "ninhos de FA" em ritmo sinusal
José Carlos Pachón Mateos; Enrique I. Pachón Mateos; Tasso J. Lobo; Maria Zélia C. Pachón; Juán Carlos Pachón Mateos; Denilda Queiroz V. Pachón; Remy Nelson A. Vargas; Leopoldo S. Piegas; Adib D. Jatene
Hospital do Coração (HCor) e Instituto Dante Pazzanese de Cardiologia - São Paulo, SP - Brasil
Correspondência
RESUMO
FUNDAMENTO: Através de mapeamento espectral-(ME) endocárdico em ritmo sinusal, observam-se dois tipos de miocárdio atrial: o compacto de espectro liso e o fibrilar de espectro segmentado ("Ninho de FA" [NFA]). Durante a FA o compacto tem ativação organizada e baixa freqüência (passivo) enquanto o fibrilar apresenta ativação bastante desorganizada e alta freqüência (ativo/ressonante) sendo ambos ativados por uma taquicardia protegida de alta freqüência, taquicardia de background (TB).
OBJETIVO: Descrever o tratamento da FA pela ablação dos NFA e da TB.
MÉTODOS: 1) Ablação por cateter-RF [4/8mm-60º/30-40J/30s] dos NFA guiada por ME em ritmo sinusal, fora das veias pulmonares; 2) Estimulação atrial-300ppm; 3) Ablação adicional de NFA se induzida FA; 4) Ablação focal se induzida TB e/ou Flutter; 5) Seguimento clínico+ECG+Holter.
RESULTADOS: Foram tratados 50±18 NFA/paciente. Após 11,3±8m 81p (88%) estavam sem FA (28,3% com antiarrítmico). Após a ablação dos NFA: a FA não foi reinduzida em 61p(71%); TB foi induzida e tratada em 24p(26%). Ocorreram 2 sangramentos pericárdicos (1 tratado clinicamente e 1 cirurgicamente) ocasionados por bainhas não mais utilizadas.
CONCLUSÃO: O ME em ritmo sinusal ablaciona os NFA. Durante a FA os NFA apresentam um padrão reativo-ressonante e o miocárdio compacto apresenta-se passivo, estimulados pela alta freqüência da TB. Após a ablação dos NFA e da TB não foi possível reinduzir FA sustentada. A ablação dos NFA fora das VP se mostrou segura e altamente eficiente para a cura e/ou o controle clínico da FA.
Palavras-chave: Ablação por cateter, fibrilação atrial, análise espectral, freqüência cardíaca.
Introdução
O estudo eletrofisiológico convencional baseia-se na análise das variações de amplitude no tempo (domínio do tempo). Todavia, a análise espectral de uma onda relaciona amplitude e/ou potência com as freqüências intrínsecas do sinal (domínio da freqüência), fornecendo grande número de informações adicionais. A freqüência cardíaca é medida em batimentos por minuto (freqüência extrínseca do sinal), ou seja, domínio do tempo, ao passo que o pico da onda R normal, por exemplo, muda de voltagem de forma brusca pelo fato de ter altas freqüências espectrais intrínsecas (domínio da freqüência), medidas em hertz (Hz, ciclos por segundo). Dessa forma, o termo freqüência poderá estar relacionado a grandezas temporais ou espectrais. Utilizando a análise espectral em tempo real e em ritmo sinusal, verifica-se que as paredes atriais são constituídas por dois tipos distintos de miocárdio, o compacto e o fibrilar (fig. 1). O primeiro apresenta espectro contínuo e organizado, com a maior parte da potência agrupada à esquerda (baixas freqüências), e o segundo tem espectro segmentado, com boa parte de segmentos desviada à direita (altas freqüências, > 80 Hz)1. O miocárdio fibrilar geralmente está agrupado em pequenas áreas mais ou menos extensas. Durante a fibrilação atrial (FA), o miocárdio compacto apresenta comportamento organizado e ativação elétrica de grande amplitude, baixa freqüência e discretamente irregular, sugerindo comportamento passivo. Contrariamente, o miocárdio fibrilar apresenta atividade elétrica de baixa amplitude, altamente desorganizada e de alta freqüência, denotando, do ponto de vista elétrico, comportamento ressonante. Ressonante é o sistema que apresenta ressonância. Ressonância: estado de um sistema que vibra numa freqüência própria, com amplitude geralmente decremental, como resultado de estímulos externos - pode ser: mecânica, como a do diapasão; elétrica, como a de indutores, sintonizadores e osciladores; eletromagnética, como a de forno de microondas e ressonância nuclear magnética; etc.
Tem-se observado que a eliminação do miocárdio fibrilar torna progressivamente mais difícil a reindução da FA. Além disso, essas áreas apresentam as maiores freqüências durante essa arritmia. Por essa razão, os pontos com alta densidade de miocárdio fibrilar foram denominados "ninhos de FA"1,2. Adicionalmente, após a eliminação dos "ninhos de FA", tem sido possível induzir taquicardia atrial muito rápida e altamente protegida de reversão. Diversas evidências têm demonstrado que essa taquicardia existe em segundo plano durante a FA (taquicardia de background), sendo seu elemento mantenedor. Neste estudo, são descritos o mapeamento e a ablação dos "ninhos de FA", seguidos de indução e ablação da taquicardia de background.
Hipótese - Os "ninhos de FA" podem ser facilmente identificados, por meio do mapeamento espectral durante o ritmo sinusal, e eliminados com ablação por radiofreqüência. Isso poderia enfraquecer um dos mecanismos de manutenção da FA, contribuindo para seu tratamento definitivo. Além disso, permitiria visualizar a taquicardia de background2, possibilitando seu mapeamento e a respectiva ablação.
Objetivos - Propor uma nova alternativa para o tratamento da FA baseada em mapeamento espectral durante o ritmo sinusal e descrever novos achados para melhor entendimento da fisiopatologia dessa arritmia.
Casuística - Foram incluídos 92 pacientes, 76 do sexo masculino, com média de idade de 52,4 ± 11 anos. Todos eram portadores de FA freqüente e refratária a pelo menos duas drogas antiarrítmicas, e 51 (55,4%) relatavam pelo menos uma cardioversão elétrica. Nesse grupo, todos os antiarrítmicos disponíveis em nosso meio, assim como a flecainamida, mostraram-se ineficazes em um ou mais pacientes. Com relação ao tipo de FA, 56 casos (61%) eram da forma paroxística (3,6 ± 1,3, com duas a sete crises por ano), 25 (27%) eram da forma persistente (2,6 ± 1,2, com uma a seis crises por ano), e 11 (12%) eram da forma permanente. Episódios muito freqüentes de FA não-sustentada ou incessante foram observados em nove pacientes. A maioria dos pacientes não apresentava cardiopatia significativa. O diâmetro do átrio esquerdo era normal ou moderadamente aumentado (41,9 ± 5 mm). A média da fração de ejeção era de 0,61 ± 0,8. As etiologias mais relevantes foram: idiopática, 42%; hipertensão, 22%; cardiopatias congênitas, 11%; cardiopatia reumática, 10%; coronariopatia, 9%; e outras, 6%.
Métodos
Os pacientes em uso de anticoagulantes orais foram internados 24 ou 48 horas antes para ajustar o International Normalized Ratio (INR) para < 1,4. Todos os casos, principalmente aqueles com história de tromboembolismo, somente foram tratados após confirmação da ausência de trombos cardíacos por meio de ecocardiografia transesofágica3-5. Utilizou-se monitoração convencional, com eletrocardiografia (ECG) de superfície, placas adesivas radiotransparentes de desfibrilação, entubação orotraqueal com ventilação mecânica e anestesia inalatória, além de passagem de transdutor de ecocardiografia transesofágica. Após assepsia, foram realizadas cinco punções venosas (uma subclávia e quatro femorais). Foi introduzido um cateter decapolar pela veia subclávia para cateterizar o seio coronariano. Pela veia femoral foram introduzidos dois cateteres quadripolares para átrio e ventrículo direitos, um cateter octapolar posicionado no His, sendo realizada punção transeptal (cinco pacientes tinham forame oval patente). Foram utilizados os seguintes equipamentos: equipamento de anestesia Cícero EM (Dräger); monitor multiparamétrico HP/Philips M1026A; ecocardiógrafo HP/Philips modelo Sonos 2500; polígrafo de 32 canais TEB com software modificado para pós-análise espectral (TEB-Pachón); espectrômetro computadorizado (Pachón®) para análise espectral em tempo real (fig. 2); radioscopia Digital Siemens; gerador de radiofreqüência Biotronik Abcontrol MDS; desfibrilador bifásico Philips Heartstart XL com marcapasso transcutâneo; espectrômetro de atividade cerebral-BIS (nos casos de maior risco tromboembólico). As ablações foram realizadas com cateter Blazer EPT 4 mm ou 8 mm ou Medtronic Conductor 4 mm ou 8 mm. Todos os pacientes incluídos foram informados sobre os métodos e as potenciais complicações e concordaram com os procedimentos por meio de consentimento escrito.
Por meio de punção transeptal foram introduzidos um cateter espiral (Supreme St. Jude ou Biotronik Lexx) e o cateter de ablação. Foi utilizada heparina por via endovenosa para manter o tempo de coagulação ativado entre 300 s e 400 s. Os endocárdios atriais foram escaneados com análise espectral em tempo real. Foram eliminados todos os "ninhos de FA" encontrados com aplicação de radiofreqüência (30-40 W/30 s/60ºC) até o desaparecimento do padrão fibrilar (fig. 3). Não foi realizado isolamento completo intencional das veias pulmonares ou das linhas de bloqueio conforme as técnicas convencionais existentes6. O cateter espiral foi utilizado para identificar com segurança os limites atriais e para detectar "ninhos de FA" que são menos evidentes com cateter de 8 mm.
Reestudo pós-ablação - Após ablação dos "ninhos de FA", foi realizada estimulação atrial tanto programada (até três extra-estímulos) como progressiva (até 300 ppm). Se fosse induzida FA, novos "ninhos de FA" eram procurados e tratados. Caso fosse induzida taquicardia residual (taquicardia de background2), esta era mapeada e tratada em seu foco de origem. Os autores deste estudo optaram pela denominação taquicardia de background em detrimento de taquicardia de segundo plano, pelo fato de a palavra background já ter sido incorporada à língua portuguesa, conforme versão 5.11 do Novo Dicionário Aurélio. Caso houvesse história ou indução de flutter era realizada ablação específica. Os critérios para encerrar a ablação foram: 1) impossibilidade de reinduzir FA ou taquicardias; 2) indução somente de taquicardia/FA não-sustentada inferior a 10 segundos; e 3) impossibilidade de eliminar taquicardia residual ou procedimento prolongado (mais de cinco horas), caso em que era feita cardioversão torácica externa.
Medicação pós-ablação - Mesmo sendo ineficaz ou pouco eficaz na fase pré-ablação, a medicação antiarrítmica foi utilizada durante dois meses para reduzir a excitabilidade atrial em decorrência do processo de resolução cicatricial. Anticoagulantes warfarínicos foram administrados durante três meses pós-ablação, mantendo-se o tempo de protrombina entre 2 e 3 INR. Após esse período, foram utilizados antiagregantes nos casos com risco de tromboembolismo (idade, insuficiência cardíaca, disfunção mitral, átrio esquedo dilatado, etc.), inclusive naqueles com recidiva sustentada ou não-sustentada da FA e resposta farmacológica adequada. Os antiarrítmicos foram retirados, exceto em 23 casos nos quais se mostraram necessários para manter o ritmo sinusal.
Seguimento pós-ablação - Foi constituído de controle clínico e ECG (alta hospitalar, um mês, três e seis meses, e um ano) e Holter (um mês, seis meses e um ano) ou sempre que ocorressem sintomas. Adicionalmente, foi realizado controle constante por contato telefônico.
Resultados
Em média, foram tratados 50 ± 18 "ninhos de FA" por paciente. Após a ablação, não foi possível induzir FA sustentada em 65 (71%) casos. Em 27 (29%) pacientes foi possível induzir episódio não-sustentado de taquicardia atrial ou FA (< 10 s). Em 24 pacientes (26%) foi possível induzir taquicardia atrial com características peculiares (induzida por estimulação atrial programada ou progressiva, alta freqüência, altamente protegida por bloqueio de entrada, difícil de induzir e muito difícil de reverter por estimulação atrial), a qual foi denominada taquicardia de background2. Em 18 pacientes (19%), havia antecedente de flutter comum ou o mesmo foi induzido, sendo tratado com bloqueio bidirecional do istmo cavotricúspide. Após seguimento médio de 11,3 ± 8 meses, 81 pacientes (88%) estavam em ritmo sinusal, 23 casos (28%) utilizando antiarrítmicos previamente ineficazes em doses reduzidas (amiodarona, 100 mg/dia a 300 mg/dia; sotalol, 60 mg/dia a 160 mg/dia; propafenona, 150 mg/dia a 600 mg/dia; quinidina, 200 mg/dia a 400 mg/dia). Em nove pacientes (9,8%) foram realizadas reablações, em decorrência de dificuldade de controle clínico da FA ou de taquicardias atriais na fase tardia pós-ablação (mais de seis meses de evolução).
Na fase inicial desse método, ocorreram dois sangramentos pericárdicos (sendo um de resolução clínica e outro drenado cirurgicamente), provavelmente relacionados à manipulação simultânea de múltiplas bainhas dentro do átrio esquerdo, já que a ponta dos eletrodos envolvidos (EPT 4 mm large), ao contrário das bainhas, é bastante macia, sendo improvável que tivesse ocasionado a lesão. Além do mais, essa complicação não mais ocorreu depois que as bainhas passaram a ser retiradas do átrio esquerdo durante a ablação, mesmo quando foram utilizados eletrodos mais rígidos de 8 mm. Nenhuma outra complicação foi observada.
As localizações mais freqüentes dos "ninhos de FA" estão demonstradas na tabela 1.
Em 11 pacientes (46%) dos 24 casos nos quais foi induzida taquicardia de background, o local de origem foi bem definido pelo mapeamento, sendo obtida reversão da taquicardia com aplicação de radiofreqüência no local de melhor mapeamento (tab. 2). Nos outros 13 casos (54%) foi realizada cardioversão torácica externa (10) ou reversão por overdrive (3), em decorrência de mapeamentos inconsistentes, freqüência muito alta da taquicardia, mais de um foco de origem ou duração prolongada dos procedimentos.
Os tempos médios de procedimento e de radioscopia foram, respectivamente, de 4,3 ± 1,2 horas e de 53,8 ± 19 minutos.
Discussão
Este estudo demonstra a aplicação do mapeamento espectral em tempo real, em ritmo sinusal, na identificação e na ablação dos "ninhos de FA". Foi possível observar que quanto mais extensa a ablação dos "ninhos de FA" menor a possibilidade de indução dessa arritmia por meio de estimulação. Além do mais, elevada proporção desses pacientes (88%) permaneceu sem FA ou com FA controlada durante o seguimento, apesar dos 39% de casos de FA persistente e permanente, tipos normalmente relacionados a piores resultados7. Esses dados sugerem que, aparentemente, quanto menor o número de "ninhos de FA" mais estáveis se tornam as paredes atriais, do ponto de vista elétrico. Além disso, sua eliminação permitiu identificar taquicardia com propriedades muito específicas, constituindo, provavelmente, um elo fundamental na fisiopatologia da FA.
Substrato da FA - Grandes contribuições foram feitas na identificação de deflagradores da FA8-10 assim como no tratamento dessa arritmia pela ablação ou pelo isolamento desses deflagradores11,12. Entretanto, pouco tem avançado a identificação do substrato. É relativamente fácil entender uma arritmia como a FA em átrio dilatado com fibrose e degeneração significativas; entretanto, como explicar essa arritmia em corações aparentemente normais? As observações iniciais deste estudo apontam para os "ninhos de FA" e para as taquicardias de background. Comparando pacientes normais com e sem FA paroxística, verificou-se que o número de "ninhos de FA" é significativamente maior nos casos com FA espontânea ou induzida em laboratório1,13.
Miocárdio fibrilar e "ninhos de FA": Os diferentes espectros dos miocárdios compacto e fibrilar sugerem que a grande diferença entre os dois tipos reside no grau de conexão entre as células, o que lhes confere freqüências de ressonância elétrica muito distintas. O miocárdio compacto é muito bem conectado e funciona como uma "grande célula", ao passo que o fibrilar se comporta como um conjunto de feixes com velocidades de condução e refratariedades diversas. Do ponto de vista espectral, os miocárdios fibrilar e compacto têm alta e baixa freqüências de ressonância, respectivamente. Dessa forma, ao se estimular as paredes atriais com freqüência progressiva, verifica-se que o miocárdio fibrilar apresenta respostas repetitivas autolimitadas em freqüência muito menor que o miocárdio compacto (234 ± 28 x > 300 ppm; p = 0,018), ou seja, o miocárdio compacto é muito mais resistente à estimulação atrial rápida. Por causa dessa propriedade, durante a FA o miocárdio fibrilar se mantém constantemente com freqüência muito alta, irregular e desorganizada (elemento multiplicador), justificando a denominação "ninho de FA", ao passo que o compacto mantém despolarização organizada, freqüência muito mais baixa e sem respostas repetitivas (elemento passivo) (fig. 4).
Ressonância dos "ninhos de FA" - Durante a FA, freqüentemente, os "ninhos de FA" alternam períodos de baixa amplitude e alta-freqüência-desorganizada com grande amplitude e baixa-freqüência-organizada (fig. 4). Isso acontece por causa de uma instabilidade elétrica periódica que promove alternância de altas e baixas freqüências. Nesse caso, "ninhos de FA" próximos e em fases diferentes podem se realimentar, favorecendo a manutenção da FA (fig. 5). Essa periodicidade de organização/desorganização elétrica é denominada ressonância elétrica (propriedade biológica conhecida observada em algumas células do sistema nervoso de mamíferos e anfíbios), já que seu comportamento é comparável ao de um ressonador eletrônico14, capaz de multiplicar o estímulo inicial. A microrreentrada e/ou a reflexão entre feixes celulares próximos, assim como períodos de atividade deflagrada autolimitada decorrente de fenômeno transiente de cálcio, podem explicar essa propriedade dos "ninhos de FA"15,16.
Provável origem dos "ninhos de FA" - No grupo de pacientes avaliado neste estudo foi possível relacionar os "ninhos de FA" com as seguintes condições:
1. Congênita: entrada da inervação (interpolação de fibras)20.
2. Constitucional: redução de conexinas, com predomínio de conexões término-terminais (crista terminalis)21.
3. Transição atriovenosa (interpolação de tecidos na inserção das veias pulmonares).
4. Estiramento mecânico do miocárdio atrial (separação das células por condições patológicas, tais como aneurisma do septo interatrial, etc.).
5. Redução da expressão das conexinas (insuficiência cardíaca congestiva, envelhecimento, condições congênitas).
6. Patológica: degeneração, isquemia, inflamação ou doença infiltrativa com remodelação e redução das conexinas.
Recentemente foi observado que a eliminação dos "ninhos de FA" torna negativa a resposta à atropina em pacientes que antes apresentavam resposta normal, denotando estreita relação entre "ninhos de FA" e inervação vagal20 (fig. 6).
Tratando a fibrilação atrial em ritmo sinusal por meio de ablação com radiofreqüência dos "ninhos de FA" - A vantagem do conceito dos "ninhos de FA" foi permitir a ablação por cateter durante o ritmo sinusal1 (fig. 4) sem realizar as clássicas linhas de bloqueio. Tem sido observado que quanto maior o número de "ninhos de FA" mais freqüente e mais prolongada é a FA espontânea ou induzida. Pacientes que apresentam número muito reduzido de "ninhos de FA" são tipicamente resistentes à indução da arritmia pela estimulação atrial. Além disso, se induzida, a FA tende a ter duração curta e reversão espontânea. Neste estudo, observou-se que à medida que o número de "ninhos de FA" foi reduzido por meio de ablação com radiofreqüência, tornou-se mais difícil reinduzir a arritmia.
Taquicardia de background - Um fenômeno extremamente interessante observado durante a ablação espectral dos "ninhos de FA" foi a taquicardia de background"2. Trata-se de uma taquicardia atrial somente vista após a ablação dos "ninhos de FA" e obtida nas seguintes condições: durante FA, pela ablação progressiva de "ninhos de FA" ou durante ritmo sinusal, por meio de estimulação atrial programada e/ou progressiva (até 300 ppm), após a maioria dos "ninhos de FA" ter sido submetida a ablação.
Principais características da taquicardia de background:
1. Taquicardia atrial regular ou ligeiramente irregular.
2. Freqüência muito alta (256 ± 34 bpm).
3. Originada por reentrada (geralmente microrreentrada induzida por estimulação atrial rápida e/ou programada e revertida por overdrive).
4. Foco de origem altamente protegido (muito difícil de ser revertida por overdrive) (fig. 7).
5. Pode ser identificada por meio de subtração digital do QRS no ECG de superfície e análise espectral do traçado da FA pura (FFT), antes da ablação.
Relação entre taquicardia de background e fibrilação atrial - Neste estudo foi possível visualizar a taquicardia de background após a limpeza dos "ninhos de FA". Observou-se que a FA vai se organizando e se transforma em taquicardia de background com a progressiva eliminação dos "ninhos de FA". Esses dados sugerem ser essa taquicardia peça fundamental na fisiopatologia da FA. Trata-se de uma taquicardia regular (originada por reentrada), que, aparentemente, existe num segundo plano (background) durante a FA. Sua freqüência muito alta estimula os "ninhos de FA", promovendo sua desorganização, sua ressonância e sua realimentação. A presença de bloqueio de entrada protege o foco da taquicardia de background de forma que ela não é revertida pelos estímulos vindos da ativação dos "ninhos de FA". Quanto maior o bloqueio de entrada (mais difícil de reverter com estimulação atrial) mais prolongada a FA. A fusão da taquicardia de background com a freqüência muito alta e desorganizada dos "ninhos de FA" constitui a atividade elétrica aparentemente caótica que caracteriza a morfologia clássica das ondas f no ECG da FA franca. Muitas vezes, ocorre alternância periódica da ressonância dos "ninhos de FA", fazendo com que uma taquicardia de background pareça ciclicamente mais ou menos organizada, constituindo a condição freqüentemente conhecida como "fibrilo-flutter". Do ponto de vista elétrico, essa taquicardia é o oscilador mestre da FA2.
Ablação da taquicardia de background - Após a ablação dos "ninhos de FA", procurou-se localizar e realizar a ablação do foco da taquicardia de background induzida por estimulação atrial (fig. 8). Eventualmente, o foco dessa taquicardia pode ter sido eliminado de forma indireta durante a ablação dos "ninhos de FA". Neste estudo, a evolução dos pacientes que tiveram a taquicardia de background tratada ou daqueles nos quais foi impossível induzi-la comparativamente à do grupo no qual essa taquicardia não foi tratada foi muito diferente. No primeiro grupo, o sucesso foi de 88,9%; no segundo grupo, porém, a FA foi eliminada em apenas 73% (p = 0,008). Entretanto, em decorrência de mecanismos de proteção, muitas vezes a taquicardia de background pode não ser induzida. Adicionalmente, seu mapeamento é dificultado pela alta freqüência.
Fisiopatologia da fibrilação atrial baseada nos "ninhos de FA" - Este estudo sugere que a FA resulta da fusão de arritmias constituídas essencialmente por uma taquicardia atrial protegida (taquicardia de background), que excita os ninhos e os mantém em constante estado de respostas repetitivas (fig. 8). A observação desse grupo de pacientes, das respectivas ablações e da história clínica de cada caso permite estabelecer uma fisiopatologia específica para a FA baseada nos seguintes componentes:
1. Modulador: sistema nervoso autônomo (extensamente modificado pela ablação dos "ninhos de FA"20).
2. Deflagrador: extra-sístoles e taquicardias não-sustentadas das veias pulmonares9,22-24.
3. Substrato (elemento multiplicador): "ninhos de FA" que respondem com alta freqüência à estimulação atrial rápida, por causa das propriedades ressonantes (microrreentrada e/ou atividade deflagrada). A capacidade de multiplicar os estímulos é um dos fatores que sustentam a FA.
4. Mantenedor: taquicardia de background que funciona como um marcapasso atrial assincrônico, com freqüência muito alta, capaz de acionar os "ninhos de FA", mantendo-os na faixa de respostas repetitivas. É o análogo do marcapasso artificial utilizado por Wijffels e cols.25 e Moreira e cols.26 para produzir FA, estimulando com freqüências muito altas.
Essa fisiopatologia explica os diversos quadros clínicos classicamente conhecidos (tab. 3).
Comparação com outros métodos de ablação de fibrilação atrial - A cura da FA é um grande desafio para todas as técnicas disponíveis27. Apesar de publicada em 20041, a ablação dos "ninhos de FA" foi desenvolvida no final da década de 1990, sem nenhum embasamento em técnicas anteriores. A proposta inicial dos autores deste estudo foi utilizar o mapeamento espectral para buscar o substrato da FA mesmo no coração aparentemente normal, inclusive em pacientes que ainda não tinham história de FA e, certamente, sem fibrose atrial. Os "ninhos de FA" são freqüentes no antro das veias pulmonares. Durante sua eliminação, pode ocorrer o isolamento elétrico dessas estruturas. Contudo, como o isolamento orientado pelo espectro busca as freqüências > 80 Hz, na maioria das vezes as veias pulmonares não são totalmente isoladas pela ablação dos "ninhos de FA", havendo condução elétrica de potenciais < 80 Hz. Isso diferencia essa técnica dos métodos desenvolvidos por Haissaguerre e cols.11, Natale e cols.28, Pappone e cols.19,29 e Oral e cols.30,31, entre outros, caracterizados pelo isolamento completo das veias pulmonares com a utilização de extensas ablações e grandes quantidades de energia. A eliminação exclusiva das altas freqüências do espectro permite preservar o miocárdio mais compacto da parede atrial, evitando lesões profundas e reduzindo o risco de perfuração, de fístulas atrioesofágicas29,32 e de estenose de veias pulmonares33,34, fato que também diferencia a técnica de outros métodos baseados em extensas e profundas linhas de bloqueio19.
Assim como as técnicas que eliminam diretamente os gânglios paracardíacos35,36, a ablação dos "ninhos de FA", de forma mais simplificada, promove importante denervação parassimpática pela eliminação direta dos neurônios intramurais e pela eliminação indireta dos gânglios paracardíacos. Dessa forma, além de atuar diretamente no sistema nervoso autônomo, elimina grande parte da interface neuromiocárdica, que tem propriedades ressonantes (decorrentes de sua microestrutura) e características espectrais específicas20 (interpolação de fibras). A eliminação do neurônio intramural e da fibrose da junção neuromiocárdica reduz sensivelmente a extensão da reinervação.
O método desenvolvido por Nademanee e cols.37, também publicado em 2004, descreve a ablação durante a FA orientada por potenciais complexos (complex fractionated electrograms – CFAEs), que são áreas de atividade elétrica altamente fracionada e identificadas diretamente pelo domínio do tempo. Sabe-se, entretanto, que durante a FA, pela grande quantidade de colisões entre frentes de ondas, formam-se muitas áreas virtuais de potenciais complexos, problema que não existe durante o ritmo sinusal e, portanto, na ablação dos "ninhos de FA". Provavelmente por causa desse fato, sabe-se que é difícil reverter uma FA persistente ou crônica com a ablação de CFAEs. Somente a FA paroxística pode ser revertida mais facilmente, e a reversão, nesse caso, pode ser ocasional e não necessariamente eletrofisiológica.
Na realidade, a maioria dos métodos tem evoluído no sentido de provocar lesões transmurais cada vez mais extensas na parede atrial. Obviamente, quanto maior a área destruída maior o número de "ninhos de FA" eliminados, o que poderá influenciar os resultados38, independentemente do método. Além disso, tem-se observado que a origem da taquicardia de background pode ser inadvertidamente eliminada nessas ablações extensas, favorecendo o resultado de longo prazo. Esse aspecto é altamente desejável; contudo, tomando como base o mapeamento espectral, entende-se que é preferível dirigir as ablações racionalmente para o substrato, eliminar somente as freqüências ressonantes (miocárdio fibrilar), preservando o músculo compacto, aplicar a menor quantidade de energia possível para prevenir complicações, e tentar induzir a taquicardia de background com subseqüente ablação de seu foco de origem.
Conclusões
Os "ninhos de FA" foram facilmente encontrados em ritmo sinusal por meio do mapeamento espectral, permitindo que fossem tratados por ablação com radiofreqüência convencional, independentemente do isolamento das veias pulmonares. Durante a FA, esse tipo de miocárdio (fibrilar) apresenta padrão reativo-ressonante de alta freqüência, que realimenta a arritmia. Ao contrário, o miocárdio compacto responde de forma organizada e com baixa freqüência. Após a ablação dos "ninhos de FA", tornou-se progressivamente mais difícil a reindução da FA, demonstrando que estão diretamente relacionados com a fisiopatologia da arritmia. Além disso, a retirada dos "ninhos de FA" permitiu visualizar uma taquicardia residual com bloqueio de entrada e freqüência alta, a taquicardia de background. O tratamento dessa taquicardia foi acompanhado de melhora significativa dos resultados. Essas observações, além de contribuírem para o melhor entendimento da fisiopatologia da FA, permitem concluir que a ablação dos "ninhos de FA" seguida do tratamento da taquicardia de background é um método seguro, possível e altamente eficiente para curar ou para controlar clinicamente a FA.
Potencial Conflito de Interesses
Declaro não haver conflitos de interesses pertinentes.
Fontes de Financiamento
O presente estudo não teve fontes de financiamento externas.
Vinculação Acadêmica
Esse artigo é parte de tese de livre-docência de José Carlos Pachón Mateos, pela Universidade de São Paulo.
Referências
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Correspondência:
José Carlos Pachón Mateos
Av. Açocê, 515/31
04075-000
São Paulo, SP - Brasil
E-mail:
jcpachon@hotmail.com
Artigo recebido em 25/02/07; revisado recebido em 01/03/07; aceito em 07/03/07.
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Selective atrial vagal denervation guided by evoked vagal reflex to treat patients with paroxysmal atrial fibrillationCirculation2006876859114ScanavaccaMPisaniCFHachulDLaraSHardyCDarrieuxF37. Nademanee K, McKenzie J, Kosar E, Schwab M, Sunsaneewitayakul B, Vasavakul T, et al. A new approach for catheter ablation of atrial fibrillation: mapping of the electrophysiologic substrate. J Am Coll Cardiol. 2004; 43 (11): 2044-53.A new approach for catheter ablation of atrial fibrillation: mapping of the electrophysiologic substrateJ Am Coll Cardiol.20042044531143NademaneeKMcKenzieJKosarESchwabMSunsaneewitayakulBVasavakulTetal38. Arruda M, Natale A. The adjunctive role of nonpulmonary venous ablation in the cure of atrial fibrillation. J Cardiovasc Electrophysiol. 2006; 17 (Suppl 3): S37-S43.The adjunctive role of nonpulmonary venous ablation in the cure of atrial fibrillationJ Cardiovasc Electrophysiol.2004S37S4317ArrudaMNataleAOriginal ArticlesRadiofrequency catheter ablation of atrial fibrillation guided by spectral mapping of atrial fibrillation nests in sinus rhythm
BACKGROUND: Two types of myocardia can be observed through the endocardial spectral mapping (SM) in sinus rhythm: the compact type with a smooth spectrum and the fibrillar type with a segmented spectrum (atrial fibrillation nests). During the atrial fibrillation (AF), the compact type has an organized activation and low frequency (passive), whereas the fibrillar type has a rather disorganized activation and high frequency (active/resonant), with both being activated by high-frequency sustained tachycardia - the background tachycardia (BT). OBJECTIVE: To describe the treatment of AF by the ablation of the AF nests and BT. METHODS: 1) Catheter ablation of the AF nests with RF [4/8mm-60º/30-40J/30s] guided by SM in sinus rhythm, outside the pulmonary vein; 2) atrial stimulation -300ppm; 3) Additional ablation of the AF nests if AF is induced; 4) Focal ablation if BT and/or Flutter is induced; 5)Clinical follow-up+ ECG+ Holter. RESULTS: A total of 50±18 AF nests/patient were treated. After 11.3±8m, 81 patients (88%) did not present AF (28.3% with antiarrhythmic drugs). After the ablation of the AF nests, AF was not reinduced in 61 patients (71%) and BT was induced and treated in 24 patients (26%). There were two episodes of pericardial bleeding (1 treated clinically and 1 surgically), caused by sheaths that are no longer used CONCLUSION: The SM in sinus rhythm can be used in the ablation of AF nests. During the AF, the AF nests present a reactive-resonant pattern and the compact myocardium is passive, stimulated by the high frequency of the BT. After the ablation of the AF nests and the BT, it was not possible to reinduce the sustained AF. The Ablation of AF nests outside the pulmonary veins showed to be safe and highly effective in the cure and/or clinical control of the AF.
Radiofrequency catheter ablation of atrial fibrillation guided by spectral mapping of atrial fibrillation nests in sinus rhythm
José Carlos Pachón Mateos; Enrique I. Pachón Mateos; Tasso J. Lobo; Maria Zélia C. Pachón; Juán Carlos Pachón Mateos; Denilda Queiroz V. Pachón; Remy Nelson A. Vargas; Leopoldo S. Piegas; Adib D. Jatene
Hospital do Coração (HCor) and Instituto Dante Pazzanese de Cardiologia - São Paulo, SP - Brazil
Mailing address
SUMMARY
BACKGROUND: Two types of myocardia can be observed through the endocardial spectral mapping (SM) in sinus rhythm: the compact type with a smooth spectrum and the fibrillar type with a segmented spectrum (atrial fibrillation nests). During the atrial fibrillation (AF), the compact type has an organized activation and low frequency (passive), whereas the fibrillar type has a rather disorganized activation and high frequency (active/resonant), with both being activated by high-frequency sustained tachycardia - the background tachycardia (BT).
OBJECTIVE: To describe the treatment of AF by the ablation of the AF nests and BT.
METHODS: 1) Catheter ablation of the AF nests with RF [4/8mm-60º/30-40J/30s] guided by SM in sinus rhythm, outside the pulmonary vein; 2) atrial stimulation -300ppm; 3)Additional ablation of the AF nests if AF is induced; 4) Focal ablation if BT and/or Flutter is induced; 5)Clinical follow-up+ ECG+ Holter.
RESULTS: A total of 50±18 AF nests/patient were treated. After 11.3±8m, 81 patients (88%) did not present AF (28.3% with antiarrhythmic drugs). After the ablation of the AF nests, AF was not reinduced in 61 patients (71%) and BT was induced and treated in 24 patients (26%). There were two episodes of pericardial bleeding (1 treated clinically and 1 surgically), caused by sheaths that are no longer used.
CONCLUSION: The SM in sinus rhythm can be used in the ablation of AF nests. During the AF, the AF nests present a reactive-resonant pattern and the compact myocardium is passive, stimulated by the high frequency of the BT. After the ablation of the AF nests and the BT, it was not possible to reinduce the sustained AF. The Ablation of AF nests outside the pulmonary veins showed to be safe and highly effective in the cure and/or clinical control of the AF.
The conventional electrophysiological study is based on the analysis of amplitude variations over time (time domain). However, the spectral analysis of a wave correlates amplitude and/or potency with the intrinsic signal frequencies (frequency domain), supplying a large amount of additional information. The heart rate is measured in beats per minute (extrinsic signal frequency), i.e., time domain, whereas the normal R wave peak, for instance, changes voltage abruptly due to the fact that it has high intrinsic spectral frequencies (frequency domain), measured in hertz (Hz, cycles per second). Therefore, the term frequency can be related to temporal or spectral values. Using real-time spectral analysis in sinus rhythm, it is observed that the atrial walls are constituted by two distinct types of myocardia, the compact and the fibrillar types (Fig. 1). The first type presents a continuous and organized spectrum, with most of the potency grouped to the left (low frequency). The second type presents a segmented spectrum, with a large amount of the segments shifted to the right (high frequencies, > 80 Hz)1. The fibrillar myocardium is usually grouped in small areas, which are more or less extensive. During the atrial fibrillation (AF), the compact myocardium presents an organized behavior and high-amplitude electrical activation, low frequency, slightly irregular, suggesting a passive behavior. On the other hand, the fibrillar myocardium presents low-amplitude electrical activity, which is highly disorganized and has high frequency, showing, from an electrical point of view, a resonant behavior.
Resonant is the system that presents resonance. The resonance - the state of a system that vibrates in its own frequency, generally with decremental amplitude, as the result of external stimuli - can be mechanical, such as that of a tuning fork; electrical, such as that of inducers, tuners and oscillators; electromagnetic, such as that of a microwave oven and magnetic resonance imaging, etc.
It has been observed that the elimination of the fibrillar myocardium makes it progressively more difficult to reinduce AF. Additionally, these areas present he highest frequencies during this type of arrhythmia. Therefore, the places with high density of fibrillar myocardium were called AF "nests"1,2. Moreover, after the elimination of the AF nests, it has been possible to induce very rapid atrial tachycardia that is highly protected from reversion. Some evidence has demonstrated that this tachycardia occurs secondarily during the AF (background tachycardia), being its maintenance element. The present study describes the mapping and the ablation of the AF nests, followed by the induction and ablation of the background tachycardia.
Hypothesis - The AF nests can be easily identified through spectral mapping during the sinus rhythm and eliminated with ablation by radiofrequency. This could weaken one of the mechanisms of AF maintenance, contributing to its ultimate treatment. Additionally, it would allow the visualization of background tachycardia2, permitting its mapping and respective ablation.
Objectives - To propose a new alternative for the treatment of AF based on a spectral mapping during sinus rhythm and describe new findings, aiming at a better understanding of the physiopathology of this arrhythmia.
Patients - A total of 92 patients, 76 males, whose mean age was 52.4 ± 11 yrs were included in the study. All patients had frequent AF that was refractory to at least two antiarrhythmic drugs and 51 (55.4%) reported at least one electrical cardioversion. In this group, all the antiarrhythmic drugs available in our country, as well as flecainamide, showed to be ineffective in one or more patients. Regarding the type of AF, 56 cases (61%) presented the paroxysmal type (3.6 ± 1.3, with 2 to 7 crises per year), 25 (27%) presented the persistent type (2.6 ± 1.2, with 1 to 6 crises per year) and 11 (12%) presented the permanent type. Very frequent episodes of non-sustained or incessant AF were observed in 9 patients. Most of the patients did not present any significant cardiopathy. The left atrium diameter was normal or moderately increased (41.9 ± 5 mm). The mean ejection fraction was 0.61 ± 0.8. The most relevant etiologies were: idiopathic, 42%; hypertension, 22%; congenital cardiopathy, 11%; rheumatic cardiopathy, 10%; coronaropathy, 9%; and others, 6%.
Methods
The patients using oral anticoagulants were admitted at the hospital 24 or 48 to have the International Normalized Ratio (INR) adjusted for < 1.4. All cases, especially those with a history of thromboembolism, were treated only after the confirmation of the absence of cardiac thrombi through transesophageal echocardiography3-5. The conventional monitoring with surface electrocardiography (ECG) radiotransparent defibrillation adhesive plaques, orotracheal intubation with mechanical ventilation and inhalation anesthesia was used, as well as the passing of a transesophageal echocardiography transducer. After asepsis, five venipunctures were performed (one subclavian and four femoral ones). A decapolar catheter was introduced through the subclavian vein to catheterize the coronary sinus. Two quadripolar catheters were introduced through the femoral vein into the right atrium and ventricle, an octapolar catheter was positioned at the His and a transeptal punction was performed (five patients had a patent foramen ovale). The following equipment were utilized: Cícero EM anesthesia equipment (Dräger); HP/Philips M1026A multiparametric monitor; HP/Philips echocardiography equipment model Sonos 2500; 32-channel TEB polygraph with modified software for real-time spectral post-analysis (TEB-Pachón); computerized spectrometer (Pachón®) for real-time spectral analysis (Fig. 2); Digital Siemens radioscopy; Biotronik Abcontrol MDS; radiofrequency generator; Philips Heartstart XL biphasic defibrillator with transcutaneous pacemaker; brain-activity spectrometer-BIS (in cases with higher thromboembolic risk). The ablations were carried out with a Blazer EPT 4-mm or 8-mm catheter or 4-mm or 8-mm Medtronic Conductor. All patients received information about the methods and potential complications and agreed with the procedures by signing the informed consent form.
Through a transeptal punction a spiral catheter (Supreme St. Jude or Biotronik Lexx) and the ablation catheter were introduced. Heparin was administered IV to maintain the activated coagulation time between 300 and 400 s. The atrial endocardia were scanned with real-time spectral analysis. All AF nests found were eliminated by applying radiofrequency (30-40 W/30 s/60ºC) until the fibrillar pattern disappeared (Fig. 3). No complete intentional isolation of the pulmonary veins or blockage lines was carried out, according to the existing conventional techniques6. The spiral catheter was used to safely identify the atrial limits and detect AF nests, which are less evident with an 8-mm catheter.
Post-ablation re-study - After the ablation of the AF nests, programmed (up to three extra-stimuli) as well as progressive (up to 300 ppm) atrial stimulation were performed. If AF were induced, new AF nests would be sought and treated. If residual tachycardia were induced (background tachycardia2), it would be mapped and treated at its focus of origin. The authors of the present study chose to use the term "background tachycardia", instead of secondary tachycardia, as the term "background" has been incorporated into the Brazilian Portuguese language, according to version 5.11 of Novo Dicionário Aurélio. In case of history or induction of flutter, the specific ablation was carried out. The criteria to finish the ablation were: 1. Impossibility to re-induce AF or tachycardias; 2. Induction only of non-sustained tachycardia/AF < 10 sec; and 3. Impossibility to eliminate residual tachycardia or prolonged procedure (more than five hrs); in these cases, the external thoracic cardioversion was carried out.
Post-ablation medication - Even being ineffective or little effective in the pre-ablation phase, the antiarrhythmic medication was used for two months to reduce the atrial excitability caused by the cicatricial process. Warfarin anticoagulants were administered for three months post-ablation, keeping the prothrombin time between 2 and 3 INR. After this period, several anti-aggregants were used in cases that presented thromboembolism risk (age, heart failure, mitral dysfunction, dilated left atrium, etc), including those patients with sustained or non-sustained AF recurrence and adequate pharmacological response. The antiarrhythmic medication was withdrawn, except in 23 cases in whom it was necessary to maintain the sinus rhythm.
Post-ablation follow-up - The follow-up consisted of clinical control and ECG (at hospital discharge, after one, three and six months and after one year) and Holter (one month, six months and one year) or whenever there were symptoms. Additionally, a continuous control was kept through telephone calls.
Results
On average, 50 ± 18 AF nests were treated per patient. After the ablation, it was not possible to induce sustained AF in 65 (71%) cases. In 27 cases (29%), it was possible to induce a non-sustained episode of atrial tachycardia or AF (< 10 s). In 24 patients (26%), it was possible to induce atrial tachycardia with special characteristics (induced by programmed or progressive high-frequency atrial stimulation, highly protected by inflow blockage, difficult to induce and very difficult reversion through atrial stimulation), which was called "background tachycardia"2. Eighteen patients (19%) presented a history of common flutter or it was induced, being treated with the bidirectional blockage of the cavotricuspid isthmus. After a mean follow-up of 11.3 ± 8 months, 81 patients (88%) were in sinus rhythm, 23 cases (28%) using previously ineffective antiarrhythmic drugs at reduced doses (amiodarone, 100 mg/day to 300 mg/day; sotalol, 60 mg/day to 160 mg/day; propafenone, 150 mg/day to 600 mg/day; quinidina, 200 mg/day to 400 mg/day). Nine patients (9.8%) underwent re-ablation due to the difficulty in the clinical control of AF or atrial tachycardia in the late phase post-ablation (more than six months of evolution).
At the initial phase of this method, two episodes of pericardial bleeding occurred (one that resolved clinically and another that had to be surgically drained), probably related to the simultaneous manipulation of multiple sheaths inside the left atrium, as the tip of the involved electrodes (EPT 4 mm large), differently from the sheaths, is very malleable, being unlikely that it would have caused the lesion. Additionally, this complication did not occur after the sheaths started to be removed from the left atrium during the ablation, even when more rigid 8-mm electrodes were used. No other complication was observed.
The most common locations of "AF nests" are shown in Table 1.
In 11 patients (46%) of the 24 cases in whom background tachycardia was induced, the focus was well defined by mapping, with tachycardia reversion following the use of radiofrequency at the place of better mapping (Table 2). In the other 13 cases (54%), the external thoracic cardioversion (10) or reversion by overdrive (3) was carried out due to inconsistent mappings, very high tachycardia frequency, more than one focus or prolonged procedures.
The mean procedure and radioscopy duration were, respectively: 4.3 ± 1.2 hrs and 53.8 ± 19 minutes.
Discussion
This study demonstrates the use of real-time spectral mapping, in sinus rhythm, in the identification and ablation of AF nests. It was possible to observe that the more extensive the ablation of the AF nests, the lower the possibility of inducing this arrhythmia through stimulation. Additionally, a large number of these patients (88%) remained without AF or had controlled AF during follow-up, despite the 39% of cases with persistent and permanent AF, types that are normally associated to poorer outcomes7. These data suggest that, apparently, the lower the number of AF nests, more stable the atrial walls become, from an electrical point of view. Additionally, their elimination allowed the identification of tachycardia with very specific characteristics, likely constituting an essential connection in the physiopathology of AF.
AF substrate - Large contributions have been made in the identification of AF triggers8-10 as well as in the treatment of this arrhythmia by the ablation or isolation of these triggers11,12. However, the identification of the substrate has advanced very little. It is relatively easy to understand an arrhythmia such as the AF in a dilated atrium with significant fibrosis and degeneration; however, how does one explain this arrhythmia in apparently normal hearts? The initial observations of the present study indicate the AF nests and the background tachycardias. When comparing normal patients with and without paroxysmal AF, it was observed that the number of AF nests is significantly higher in cases with spontaneous or laboratory-induced AF1,13.
Fibrillar myocardium and AF nests: The different spectrums of compact and fibrillar myocardia suggest that the great difference between the two types lies in the degree of connection among the cells, which gives those very distinct electrical resonance frequencies. The compact myocardium is very well connected and functions as a "large cell", whereas the fibrillar type behaves as a set of bundles with varied velocities of conduction and refractoriness. From the spectral point of view, the fibrillar and compact myocardia have high and low resonance frequencies, respectively. Therefore, when the atrial walls are stimulated with progressive frequencies, it is observed that the fibrillar myocardium presents autolimited repetitive responses at a much lower frequency than the compact myocardium (234 ± 28 x > 300 ppm; p = 0.018), i.e., the compact myocardium is much more resistant to rapid atrial stimulation. Due to this property, during the AF the fibrillar myocardium constantly maintains a very high, irregular and disorganized frequency (multiplying element), justifying the name "AF nests", whereas the compact myocardium maintains an organized depolarization, much lower frequency and no repetitive responses (passive element) (Fig. 4).
Resonance of the AF nests - During the AF, the AF nests frequently alternate periods of low amplitude and disorganized high frequency with high amplitude and organized low frequency (Fig. 4). This happens due to a periodical electrical instability that promotes the alternateness of high and low frequencies. In this case, AF nests that are close and at different phases can feed again, favoring the maintenance of AF (Fig. 5). This periodicity of electrical organization/disorganization is called electrical resonance (a known biological property observed in some cells of the mammalian and amphibian nervous system), as its behavior is comparable to that of an electronic resonator14, capable of multiplying the initial stimulation. The microreentry and/or reflection between close cell bundles, as well as periods of autolimited triggered activity due to a transitory calcium phenomenon, can explain this property of AF nests15,16.
Probable focus of the AF nests - In the group of patients assessed in the present study, it was possible to associate the AF nests with the following conditions:
6. Pathological: degeneration, ischemia, inflammation or infiltrative disease com remodeling and reduction of conexins.
Recently it was observed that the elimination of the AF nests makes the response to atropine negative in patients who presented a previously normal response, showing a close association between AF nests and vagal innervation20 (Fig. 6).
Treating atrial fibrillation in sinus rhythm through ablation with radiofrequency of AF nests - The advantage of the concept of AF nests was to allow the ablation by catheter during sinus rhythm1 (Fig. 4) without performing the classical blockage lines. It has been observed that the higher the number of AF nests, more frequent and prolonged is the AF, whether spontaneous or induced. Patients that present a very reduced number of AF nests are typically resistant to arrhythmia induction by atrial stimulation. Additionally, when induced, the AF tends to be short and present spontaneous reversion. In the present study, we observed that as the number of AF nests was reduced through ablation with radiofrequency, it became more difficult to re-induce arrhythmia.
Background Tachycardia - An extremely interesting phenomenon observed during the spectral ablation of AF nests was the background tachycardia2. The latter is an atrial tachycardia observed only after the ablation of AF nests and attained at the following conditions: during AF, by progressive ablation of AF nests or during sinus rhythm, through programmed and/or progressive atrial stimulation (up to 300 ppm) after most of the AF nests have been submitted to ablation.
Main characteristics of background tachycardia:
1. Regular or slightly irregular atrial tachycardia.
2. Very high frequency (256 ± 34 bpm).
3. Originated by reentry (generally microreentry induced by rapid and/or programmed atrial stimulation and reversed by overdrive).
4. Highly protected focus (very difficult to be reversed by overdrive) (Fig. 7).
5. It can be identified by the digital subtraction of the QRS at the surface ECG and spectral analysis of the tracing of the fast Fourier transform (FFT), before the ablation.
Association between background tachycardia and atrial fibrillation - In the present study it was possible to visualize the background tachycardia after the ablation of the AF nests. It was observed that the AF starts to organize and becomes background tachycardia with the progressive elimination of the AF nests. These data suggest that this tachycardia is a key element in the physiopathology of AF. It is a regular tachycardia (originated by reentry), which, apparently exists at a second plane (background) during the AF. Its very high frequency stimulates the AF nests, promoting its disorganization, its resonance and refeeding. The presence of an entry blockage protects the background tachycardia focus, so that it is not reversed by the stimuli that originate from the activation of the AF nests. The larger the entry blockage is (more difficult to reverse with atrial stimulation), the more prolonged the AF. The combination of background tachycardia with very high and disorganized frequency of AF nests constitutes the apparently chaotic electrical activity that characterizes the classical morphology of f waves at the ECG of frank AF. Many times there is a periodical alternateness of resonance of the AF nests, making the background tachycardia to appear more or less cyclically organized. This constitutes a condition that is frequently known as "fibrillo-flutter". From an electrical point of view, this tachycardia is the main oscillator of the AF2.
Ablation of the background tachycardia - After the ablation of the AF nests, the focus of the background tachycardia induced by atrial stimulation was sought and its ablation was attempted (Fig. 8). Eventually, the focus of this tachycardia might have been eliminated indirectly during the ablation of the AF nests. In this study, the evolution of the patients who had the background tachycardia treated or those in whom it was impossible to induce it when compared to the group who remained untreated was very different. In the first group, the success rate was 88.9%; in the second group, however, the AF was eliminated in only 73% (p=0.008). Nevertheless, due to mechanisms of protection, many times the background tachycardia could not be induced. Additionally, its mapping is hindered by the high frequency.
Physiopathology of atrial fibrillation based on AF nests - This study suggests that the AF results from the fusion of arrhythmias constituted essentially by a protected atrial tachycardia (background tachycardia), which stimulates the nests and maintain them under a constant state of repetitive responses (Fig. 8). The observation of this group of patients, of the respective ablations and the clinical history of each case allows us to establish a specific physiopathology for AF based on the following components:
1. Modulator: autonomic nervous system (extensively modified by the ablation of the "AF nests"20).
2. Trigger: extra-systoles and non-sustained tachycardias of the pulmonary veins9,19,22-24.
3. Substrate (multiplier element): AF nests that respond with high frequency to the rapid atrial stimulation, due to the resonant properties (microreentry and/or triggered activity). The capacity to multiply the stimuli is one of the factors that sustain the AF.
4. Maintainer: background tachycardia, which works as an asynchronic atrial pacemaker with a very high frequency, capable of activating the AF nests, maintaining them within the range of repetitive responses. It is the analogue of the artificial pacemaker used by Wijffels et al25 and Moreira et al26 to produce AF, stimulating with very high frequencies.
This physiopathology explains the several classically known clinical pictures (Table 3).
Comparison with other ablation methods of atrial fibrillation - The cure of AF is a great challenge for all the available technique27. Although it was published in 20041, the ablation of AF nests was developed in the end of the 90’s, without being based on previous techniques. The initial proposal of the authors of the present study was to use spectral mapping to search for the AF substrate even in an apparently normal heart, and including patients who had presented a history of AF and, certainly, without atrial fibrosis. The AF nests are frequent in the antrum of pulmonary veins. During their elimination, the electrical isolation of these structures can occur. However, as the spectrum-oriented isolation searches for the frequencies > 80 Hz, most of the times the pulmonary veins are not completely isolated by the ablation of the AF nests, resulting in the electrical conduction of potentials < 80 Hz. This fact differentiates this technique from the methods developed by Haissaguerre et al11, Natale et al28, Pappone et al19,29 and Oral et al30,31, among others, which are characterized by the complete isolation of the pulmonary veins with the use of extensive ablations and large amounts of energy. The exclusive elimination of the high frequencies of the spectrum allows the preservation of the more compact myocardium of the atrial wall, preventing deep lesions and reducing the risk of perforation, of atrioesophageal fistulas29,32 and of stenosis of the pulmonary veins33,34, a fact that also differentiates the technique from other methods based on extensive and deep lines of blockage19.
As well as in the techniques that directly eliminate the paracardiac ganglia35,36, the ablation of the AF nests, in a simplified form, promotes a significant parasympathetic denervation through the direct elimination of intramural neurons and the indirect elimination of the paracardiac ganglia. Therefore, in addition to acting directly on the autonomous nervous system, it eliminates a large part of the neuromyocardial interface, which has resonant properties (due to its microstructure) and specific spectral characteristics20 (interpolation of fibers). The elimination of the intramural neuron and the fibrosis of the neuromyocardial junction significantly reduces the extension of the reinnervation.
The method developed by Nademanee et al37, also published in 2004, describes the ablation during the AF oriented by complex fractionated electrograms (CFAEs), which are areas of highly fractioned electrical activity and directly identified by the time domain. It is known, however, that during the AF, due to the large number of wavefront collisions, many virtual areas of complex potentials are formed, a problem that does not exist during the sinus rhythm and, therefore, during the ablation of AF nests.
Likely due to this fact, it is well-known the difficulty to reverse a persistent or chronic AF with the ablation of CFAES. Only the paroxysmal AF can be reversed more easily and the reversion, in this case, can be occasional and not necessarily electrophysiological.
In fact, most of the methods have developed in the sense of causing progressively more extensive intramural lesions on the atrial wall. Clearly, the larger the area destroyed, the larger the number of eliminated AF nests, which can influence the results38, regardless of the method. Additionally, it has been observed that the origin of the background tachycardia can inadvertently eliminated during these extensive ablations, favoring the long-term outcome. This aspect is highly desirable; however, considering the spectral mapping as the basis, it is understood that it is preferable to direct the ablations rationally into the substrate, eliminate only the resonant frequencies (fibrillar myocardium), preserve the compact muscle, apply the least amount of energy possible to prevent complications and try to induce the background tachycardia with the subsequent ablation of its focus of origin.
Conclusions
The AF nests were easily found in sinus rhythm through the spectral mapping, allowing them to be treated by ablation with conventional radiofrequency, regardless of the isolation of the pulmonary veins. During the AF, this type of myocardium (fibrillar type) presents a reactive-resonant high-frequency pattern, which refeeds the arrhythmia. Differently, the compact myocardium responds in an organized form and with low frequency. After the ablation of the AF nests, it became progressively more difficult the reinduction of the AF, showing that they are directly associated with the physiopathology of arrhythmia. Additionally, the removal of the AF nests allowed the visualization of a residual tachycardia with entry blockage and high frequency, the background tachycardia. The treatment of this condition was followed by significant outcome improvement. These observations, in addition to contributing to the better understanding of the AF physiopathology, allow us to conclude that the ablation of the AF nests followed by the treatment of the background tachycardia is a safe, feasible and highly efficient method to cure or clinically control the AF.
Potential Conflict of Interest
No potential conflict of interest relevant to this article was reported.
Sources of Funding
There were no external funding sources for this study.
Study Association
This article is part of the thesis associate professor submitted by José Carlos Pachón Mateos, from Universidade de São Paulo.
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Mailing address:
José Carlos Pachón Mateos
Av. Açocê, 515/31
04075-000
São Paulo, SP - Brazil
E-mail:
jcpachon@hotmail.com
Manuscript received February 25, 2007; revised manuscript received March 1, 2007; accepted March 7, 2007.