abcArquivos Brasileiros de CardiologiaArq. Bras. Cardiol.0066-782X1678-4170Sociedade Brasileira de Cardiologia - SBCSão Paulo, SP, Brazil6VLwcDZXwqFdd9c6M7svKZC00013S0066-782X2005000300013S0066-782X(05)0840031310.1590/S0066-782X2005000300013Artigos OriginaisAnálise comparativa dos fluxos da artéria torácica interna esquerda dissecada na forma pediculada versus a forma esqueletizada em cirurgia de revascularização do miocárdioCastroGustavo PeressoniRio Grande do SulUniversidade Federal do Rio Grande do SulHospital de Clínicas Serviço de Cirurgia CardiovascularBrazil0320058432612661905200431032004This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
OBJETIVO: Comparar os fluxos livres, os calibres e os comprimentos da artéria torácica interna esquerda (ATIE) pediculada (P) e esqueletizada (E) no transoperatório antes e depois da aplicação do vasodilatador tópico (VT). MÉTODOS: Em ensaio clínico randomizado e cego foram estudados 50 pacientes submetidos a cirurgia de revascularização miocárdica eletivas quanto ao emprego da ATIE in situ nas formas P ou E. Dos 25 pacientes no grupo pediculada (GP), 16 eram do sexo masculino, apresentando angina classe II e III (NYHA) e fração de ejeção (FE) de 50,8 ± 9,2%. No grupo esqueletizada (GE), 19 pacientes eram do sexo masculino, possuindo angina classe II e FE de 46,8 ± 9,3%. As medidas foram realizadas pré-circulação extracorpórea e divididas em duas fases: fase 1 (antes) e fase 2 (após 15 min da aplicação da papaverina tópica a 2,5 mg/ml a 37ºC). Durante as aferições, eram monitoradas a pressão arterial média, pressão venosa central e freqüência cardíaca. RESULTADOS: O GP apresentou fluxo de 46±16 e 77±28 ml/min e calibre de 1,4±0,1 e 1,7±0,1 mm nas fases 1 e 2, e o GE, 57±27 e 97±35 ml/min de fluxo e 1,4±0,1 e 1,8±0,2 mm de calibre, respectivamente, não havendo diferenças significativas no desfecho comprimento. CONCLUSÃO: ATIE E demonstrou um aumento significativo no fluxo e calibre, após o uso de VT com p=0,03 e p=0,01 respectivamente, comparados com a ATIE P.
Análise comparativa dos fluxos da artéria torácica interna esquerda dissecada na forma pediculada versus a forma esqueletizada em cirurgia de revascularização do miocárdio
Gustavo Peressoni Castro
Porto Alegre, RS
Serviço de Cirurgia Cardiovascular do Hospital de Clínicas de Porto Alegre da Universidade Federal do RS
Endereço para correspondência
RESUMO
OBJETIVO: Comparar os fluxos livres, os calibres e os comprimentos da artéria torácica interna esquerda (ATIE) pediculada (P) e esqueletizada (E) no transoperatório antes e depois da aplicação do vasodilatador tópico (VT).
MÉTODOS: Em ensaio clínico randomizado e cego foram estudados 50 pacientes submetidos a cirurgia de revascularização miocárdica eletivas quanto ao emprego da ATIE in situ nas formas P ou E. Dos 25 pacientes no grupo pediculada (GP), 16 eram do sexo masculino, apresentando angina classe II e III (NYHA) e fração de ejeção (FE) de 50,8 ± 9,2%. No grupo esqueletizada (GE), 19 pacientes eram do sexo masculino, possuindo angina classe II e FE de 46,8 ± 9,3%. As medidas foram realizadas pré-circulação extracorpórea e divididas em duas fases: fase 1 (antes) e fase 2 (após 15 min da aplicação da papaverina tópica a 2,5 mg/ml a 37ºC). Durante as aferições, eram monitoradas a pressão arterial média, pressão venosa central e freqüência cardíaca.
RESULTADOS: O GP apresentou fluxo de 46±16 e 77±28 ml/min e calibre de 1,4±0,1 e 1,7±0,1 mm nas fases 1 e 2, e o GE, 57±27 e 97±35 ml/min de fluxo e 1,4±0,1 e 1,8±0,2 mm de calibre, respectivamente, não havendo diferenças significativas no desfecho comprimento.
CONCLUSÃO: ATIE E demonstrou um aumento significativo no fluxo e calibre, após o uso de VT com p=0,03 e p=0,01 respectivamente, comparados com a ATIE P.
A artéria torácica interna é o enxerto de preferência para a cirurgia de revascularização miocárdica1-4 e na posição in situ, é considerada o padrão ouro para revascularizar a artéria interventricular anterior5,6, devido à sua patência, pois, em 10 anos de seguimento, este enxerto encontra-se pérvio em 90% dos casos6-9, ao passo que o enxerto venoso permanece patente em 50% dos casos no mesmo período10-13.
A dissecção da artéria torácica interna na forma pediculada já está estabelecida e comprovada, entretanto, há dúvidas quanto ao papel da dissecção esqueletizada.
Existem trabalhos na literatura tentando sedimentar esta técnica de dissecar a artéria torácica interna, comparando-a com a forma pediculada quanto ao fluxo sanguíneo livre14-17, ao calibre15,17, ao comprimento14,15,18, número de anastomoses distais e seqüenciais18, a função respiratória14,19,20, a preservação da pleura14,19,20, ao aporte sanguíneo do esterno após dissecção da artéria torácica interna21,22, as complicações esternais23,24, seu uso uni e bilateral23,25-27, em idosos26, em diabéticos23,26-28, comparando desfechos, como sobrevida e sobrevida livre de eventos18,27,29 (angina, angioplastia, infarto do miocárdio, acidente vascular encefálico, entre outros).
Tudo isso porque houve uma mudança no perfil dos pacientes submetidos a cirurgia de revascularização do miocárdio, que, atualmente estão apresentando comprometimento ventricular de grau moderado a severo, idade avançada, associados a outras doenças, como diabetes mellitus (tipo I ou II), doença broncopulmonar obstrutiva crônica (DBPOC), com hipertensão arterial sistêmica, insuficiência renal crônica (IRC), dislipidemias, além da obesidade e história de tabagismo.
Estudos para avaliar desfechos como fluxo, calibre e comprimento têm sido publicados14,16,17,30,31, na sua maioria estudo observacionais, poucos são ensaios clínicos randomizados, cegos ou duplo cegos; e, quando o são, utilizam em sua intervenção vasodilatadores com injeção intraluminal e ou dilatação hidrostática da artéria torácica interna com mensurações aferidas em circulação extracorpórea.
O presente estudo visa analisar comparativamente o comprimento, calibre e fluxo sanguíneo livre da artéria torácica interna esquerda na forma pediculada (convencional) versus a esqueletizada, antes e após o uso de vasodilatador tópico.
Métodos
O presente trabalho consiste em um ensaio clínico randomizado e cego. De janeiro a outubro de 2003, foram estudados 50 pacientes submetidos a cirurgia de revascularização do miocárdio eletivas e primárias, após randomização (fig. 1), foram divididos em dois grupos: grupo pediculado (GP), contendo 25 pacientes, com a artéria torácica interna esquerda dissecada na forma pediculada e grupo esqueletizado (GE), com 25 pacientes a artéria torácica interna esquerda na forma esqueletizada. Não participaram do estudo pacientes em choque cardiogênico, em assistência circulatória utilizando balão intra-órtico, cirurgia de revascularização do miocárdio associada a trocas valvares ou a outro procedimento, em fibrilação atrial, situações em que fosse contra-indicada a dissecção da artéria torácica interna, idade < 35 e > 80 anos, fração de ejeção < 30%; ainda, a pressão arterial média (PAM) < 70 e > 100mmHg e freqüência cardíaca (Fc) maior que 100 bpm durante as mensurações; e que discordassem em participar do estudo. Os casos incluídos no estudo, após esclarecidos e concordarem com o procedimento proposto, assinaram o termo de consentimento informado aprovado pela comissão científica e comissão de pesquisa e ética em saúde do Hospital de Clínicas de Porto Alegre onde foram realizadas as cirurgias.
Todos os pacientes receberam o mesmo regime anestésico e sem utilização de analgesia por cateter peridural. A medicação pré-anestésica (flunitrazepan, 2mg, VO) era administrada no dia anterior às 23:00h. Ao chegarem à sala cirúrgica, eram monitorizados quanto ao eletrocardiograma, pressão arterial invasiva (pela artéria radial), pressão venosa central (pela veia jugular interna ou veia subclávia), débito urinário (sondagem vesical), oximetria de pulso, temperatura retal e nasofaríngea. A indução anestésica era realizada, após pré-oxigenação, através de punções venosas periféricas (duas, em membro superior, com cateter nº 14 ou 16), utilizando midazolam (0,1mg/kg), fentanil (10mg/kg) e pancurônio (0,1mg/kg). A seguir, procedia-se a entubação orotraqueal e instalava-se a ventilação mecânica com uso de isoflurano na concentração de 1 a 2%. Para manutenção da anestesia eram empregadas as mesmas drogas da indução com suas doses reduzidas (midazolan 0,05mg/kg, fentanil 5mg/kg e pancurônio 0,03mg/kg).
Realizava-se a seguir a esternotomia mediana, a hemostasia necessária, a pericardiotomia e, na seqüência, a colocação do afastador para dissecção da artéria torácica interna esquerda (Quinelato-Dinkhhyiusen®).
O sorteio para dissecção pediculada ou esqueletizada era realizada pelo médico anestesista com moeda (cara ou coroa) antes de iniciar a incisão operatória, e os pacientes desconheciam a técnica de dissecção da artéria torácica interna esquerda a ser realizada.
Exposta a artéria torácica interna esquerda, iniciava-se a dissecção rebatendo a pleura do pulmão esquerdo, sempre com o intuito de mantê-la íntegra, um eletrocautério monopolar (Valleylab Force 2®) na potência de 25 watts foi usado na totalidade da dissecção (coagulação), e apenas quando havia ramos de calibre importantes era utilizado o aplicador (Ethicon®) de clipe (Ethicon®, tamanho LT 200). Foi utilizado como limite distal a bifurcação da artéria torácica interna em artéria músculo-frênica (AMF) e artéria epigástrica superior (AES), chegando até o bordo superior da primeira costela sendo o limite proximal (fig. 2). Nesta técnica, além da artéria torácica interna esquerda o pedículo era composto por veias, músculo, fáscia endotorácica e tecido adiposo, medindo aproximadamente 2cm de largura.
Nessa forma de dissecção foram utilizados os mesmos limites distal e proximal da técnica anterior, rebatendo a pleura do pulmão esquerdo, com o intuito de mantê-la íntegra, com eletrocautério monopolar (Valleylab Force 2®) na potência de 18 watts, abria-se a fáscia endotorácica desde a bifurcação da artéria torácica interna chegando até o bordo superior da primeira costela. A seguir, utilizando uma pinça delicada e a lâmina da caneta do cautério (sem usar corte ou coagulação nesta fase, apenas divulsão romba), fazia-se a dissecção esqueletizada da artéria torácica interna esuqerda, sem pinçá-la ou utilizando o cautério. Ao identificar seus ramos, estes eram isolados e ligados através de um aplicador (Vitalitec®) de clipe metálico (Vitalitec®, tamanho small), sempre fixando um proximal e outro distal, e seccionando-os com uma tesoura de Potts (fig. 3).
Após a heparinização sistêmica (4mg/kg), a artéria torácica interna esquerda era seccionada em nível de sua bifurcação e iniciavam-se as medidas do comprimento, calibre e fluxo sanguíneo livre.
Estas mensurações foram realizadas em duas fases: fase 1 (sem uso de vasodilatador) e 2 (com uso de vasodilatador tópico): fase 1-) foram realizadas as medidas do comprimento da artéria torácica interna esquerda através de uma régua metálica graduada (cm), tendo como limites: proximal, o bordo superior da primeira costela e limite distal, a bifurcação em AMF e AES. A seguir fazia-se a mensuração do calibre utilizando medidores metálicos de coronária que variavam de 1 a 2,5 mm de diâmetro. Por fim, a artéria torácica ine\terna esquerda em posição horizontal era deixada sangrar livremente, por 30s, em um recipiente plástico graduado. Este volume era multiplicado por 2, resultando no valor expresso em ml/min; fase 2-) finalizada a fase 1, a artéria torácica interna esquerda era ligada com um clipe metálico ao nível de sua bifurcação. Umedecida e envolvida por gazes embebidas pelo vasodilatador (papaverina na concentração de 2,5 mg/ml a temperatura de 37ºC). Após 15min reiniciavam-se as mensurações idênticas a fase 1, agora já com o efeito do vasodilatador tópico.
As aferições foram realizadas pré-circulação extracorpórea e, nos casos onde a freqüência cardíaca era < que 90 bat/min, adotava-se a estimulação cardíaca artificial temporária atrial na freqüência de 90 bpm, e monitoradas e registradas a pressão arterial media, pressão venosa central, freqüência cardíaca e se estavam sendo usadas drogas vasoconstritoras ou vasodilatadoras. Todas as artérias torácicas internas esquerdas foram anastomosadas na artéria interventricular anterior (fig. 4) e optou-se pelo enxerto venoso (veia safena) para completar o restante da revascularização miocárdica. Foi usada circulação extracorpórea com temperatura corpórea em média de 32ºC e utilizada proteção miocárdica anterógrada, hipotérmica e cristalóide, repetida de 25 em 25min.
Os dados estão apresentados em média e desvio padrão, e as variáveis quantitativas analisadas pelo teste t de Student para amostras independentes e as variáveis qualitativas pelo teste qui-quadrado. Adicionalmente, utilizou-se a análise de variância para os dados repetidos e regressão linear múltipla para avaliar as modificações dos valores nas variáveis de desfecho e os fatores que as influenciaram. Para análise estatística utilizou-se o programa Statistical Package for the Social Sciences (SPSS) versão 11.0. Diferenças com p< 0,05 foram consideradas estatisticamente significativas.
Resultados
Os dados pré-operatórios dos pacientes, como sexo, idade, superfície corpórea, classe funcional pela New York Heart Association, doenças associadas, história de tabagismo e a fração de ejeção mensurada pela ventriculografia estão na tabela I. Não sendo detectadas diferenças importantes entre os grupos. A tabela II apresenta as medicações com implicações cardíacas de uso prévio dos pacientes. Não foram evidenciadas diferenças importantes entre os grupos. Os resultados dos dados hemodinâmicos e operatórios (tab.III) apresentaram diferença estatística nas variáveis tempo de circulação extracorpórea e manutenção da pleura íntegra (4 no GP e 18 pleuras no GE) para o GE, com p=0,04 e p=0,0002 respectivamente. Não identificando diferenças significativas nas variáveis: número de anastomoses distais (2,96±0,8 versus 3,16±0,6 anastomoses, no GP e GE respectivamente); tempo de pinçamento aórtico (42,21±14,3 versus 51,68±21,8 min, no GP e GE respectivamente) e também nas PAMs, PVCs e Fcs quando comparados os grupos (P versus E) na fase 1 e 2 das mensurações (antes e após o uso de vasodilatador tópico). Houve 1 caso de infarto agudo do miocárdio perioperatório no grupo P e um caso de infecção superficial de esterno no grupo E. Na fase hospitalar, não ocorreram óbitos, deiscência de esterno, mediastinite e não houve diferença no tempo de internação hospitalar, sendo 9,1±1,69 versus 8,96±1,49 dias com p=0,65 para o GP e GE respectivamente. Os resultados dos desfechos secundários, calibre e comprimento estão na tabela IV, onde é evidenciado que não houve aumento significativo no desfecho comprimento, em ambas as fases e, também, na variável calibre na fase 1, após comparação dos grupos. Contudo, constatou-se um aumento significativo no calibre, após o uso do VT com p=0,01, para o GE. A figura 5 mostra o resultado do desfecho principal do estudo, o fluxo sanguíneo livre, onde verificou-se aumento no fluxo no GE, tanto na fase 1 (57 ± 27 ml/min) como na fase 2 (97,1±35 ml/min), significativo nesta última, ao se confrontar com o GP antes (46,2±16,7 ml/min) e depois do VT (77,2±28,8 ml/min), com p=0,09 e p=0,03 respectivamente.
Discussão
Uma das razões para se escolher a dissecção esqueletizada da artéria torácica interna o fato de proporcionar um maior comprimento14,25,29,32-34 e calibre17 em comparação com a técnica convencional (pediculada), assim podendo revascularizar coronárias com lesões distais e mantendo a artéria torácica interna na forma in situ, pois é conhecida a perda de 10 a 15% de sua patência quando esta artéria permanece como enxerto livre e é anastomosada na aorta ascendente5.
O comprimento da artéria torácica interna esquerda, neste estudo, não demonstrou diferença estatística entre os grupos, provavelmente, devido ao tipo de administração do vasodilatador na forma tópica ou ao método de aferição empregado; entretanto, evidenciou-se, na prática, uma mobilidade superior no enxerto esqueletizado.
Calafiore e cols., em um estudo observacional, envolvendo 1146 pacientes submetidos a cirurgia de revascularização do miocárdio, confrontaram a forma pediculada (n=304) com a esqueletizada (n=842); observando em um subgrupo com 28 pacientes, o comprimento da artéria torácica interna esquerda, sendo 14 no GP e 14 no GE, evidenciando um aumento no comprimento nos dois grupos com 16,1±1,4 para 16,4±1,7cm e de 17,6±1,4 para 20,1±1,6 cm respectivamente. Contudo, as mensurações foram realizadas antes e após 10min do uso de papaverina com injeção intraluminal 10ml (1mg/ml)18.
Deja e cols., em artigo envolvendo comparação do comprimento entre dissecção pediculada e esqueletizada mostraram aumento, mas não significativo com p=0,11 para o GE. Esse estudo foi realizado após a utilização da papaverina (0,2%) tópica e a mensuração ocorreu apenas antes de ser feita a anastomose da artéria torácica interna esquerda na artéria interventricular anterior, ou seja, houve um período de tempo maior para a ação do vasodilatador e também a influência da pressão arterial média (medidas em circulação extracorpórea com fluxo de 2,2 l/min/m²) onde, não ocorreu aferição do comprimento sem vasodilatador14.
O calibre mostrou um aumento significativo no GE ao se comparar com o GP na fase 2 (1,7 ± 0,1 versus 1,85 ± 0,2 mm) com p= 0,01, sendo que, na fase 1, os calibres eram praticamente iguais (1,43 ± 0,13 versus 1,44 ± 0,19 mm). Choi & Lee observaram que após o uso de papaverina tópica (1,25mg/ml) em 23 pacientes com dissecção esqueletizada da artéria torácica interna esquerda, 21 ficaram com o calibre entre 1,5 a 2 mm e 2 com diâmetro > 2 mm. No GP dos 14 pacientes, 6 permaneceram com calibre < 1,5 mm, 7 entre 1,5 a 2 mm e 1 com espessura > 2 mm. Neste estudo não houve medidas pré-vasodilatador e as medidas foram realizadas em circulação extracorpórea, antes da anastomose com a artéria interventricular anterior e não ocorreu comparação estatística com o GP17.
Nesta variável a ação da técnica de dissecção esqueletizada resultou no aumento do diâmetro do calibre de forma significativa, assim proporcionando melhores condições para a realização das anastomoses e contribuindo para um maior fluxo sanguíneo livre.
A técnica esqueletizada da artéria torácica interna proporciona vantagens como a de preservar a circulação colateral do esterno e diminuindo assim as complicações esternais23-25,29,31-36 e reduzindo as complicações respiratórias através da preservação da pleura19,20 e; com um fluxo inicial maior de sangue atenua a ocorrência da síndrome de hipoperfusão16,17, levando em consideração o tempo superior (10 a 15 min) em dissecá-la16.
Diferentes grupos têm mostrado o positivo efeito da papaverina no fluxo da artéria torácica interna34,37-41. Mills e cols. e Degrelid e cols. publicaram trabalhos onde utilizaram a forma de injeção intraluminal com diluição da papaverina, resultando em fluxo superior comparada com a tópica. Entretanto, realizado estudo morfológico mostrou danos ao endotélio pela aplicação intraluminal e pelo pH ácido do vasodilatador37,38. Noera e cols. estudaram a artéria torácica interna esquerda na forma pediculada versus esqueletizada, comparando também, os subgrupos: injeção intraluminal da papaverina com dilatação hidrostática versus aplicação tópica do vasodilatador. Observando ao final da avaliação histológica que todos os subgrupos com injeção intraluminal e dilatação hidrostática mostraram lesões na camada íntima do endotélio, assim recomendando a utilização tópica da papaverina34. Trabalhos vêm demonstrando que a forma de administração tópica da papaverina é eficaz, como a injeção intraluminal34,38-41. Bilgen e cols. demonstraram que o uso tópico da papaverina a 37ºC tem melhores resultados do que a 20 a 22ºC40.
A manutenção da pleura íntegra, neste ensaio clínico, apresentou resultados semelhantes com a literatura 14,19,20.
O fluxo sanguíneo livre demonstrou superioridade no GE, após compararem-se os grupos nas duas fases das mensurações com 46,2±16,7 versus 57±27 ml/min e 77,2±28,8 versus 97,1±35 ml/min nos GP e GE respectivamente, sendo significativo na fase 2, com um p=0,03, devido à contribuição do aumento do calibre, após serem analisados os dados. Entretanto observando o ganho do fluxo, ou seja o fluxo 2 menos o fluxo 1 em ambos grupos e comparando-os evidenciou-se que houve um aumento no ganho do fluxo para o GE, mas não significativo. Neste modelo onde se utilizou a dissecção pediculada versus a esqueletizada com a papaverina na forma tópica e na concentração de 2,5 mg/ml a 37ºC, sendo as mensurações realizadas pré circulação extracorpórea, é difícil realizar uma comparação segura com outros modelos da literatura, pois esses utilizam o vasodilatador em temperaturas e concentrações diferentes, além do uso intraluminal16 e também estão em circulação extracorpórea14, quando fazem as aferições. Desta forma, as medidas da fase 2 em relação ao fluxo sanguíneo livre é semelhante com a literatura14,16, considerando as diferenças metodológicas. Wendler e cols. utilizaram como modelo a papaverina com injeção intraluminal, resultando em um fluxo maior após o vasodilatador, sendo 147±70,5ml/min para GP e 197±66,6ml/min para o GE. Entretanto, o fluxo inicial da forma pediculada era maior do que a esqueletizada com 68±54 versus 51±39ml/min, respectivamente; mas sem diferença estatística16.
Este estudo tem a limitação de medir somente fluxo livre dos enxertos, o que não é uma avaliação completa do assunto porque a resistência do runoff distal deve provavelmente exercer uma função importante na distribuição do fluxo após o implante da artéria torácica interna esquerda na artéria intraventricular anterior, sendo esta a sua condição definitiva. É claro, de que o fluxo livre representa o fluxo máximo dos enxertos em condições naturais e não é difícil concordar que as medidas dos fluxos obtidas nas artérias dos pacientes devam ser adequadas para revascularizar a região do miocárdio correspondente.
Calafiore e cols.29 relataram que a patência da forma esqueletizada e pediculada sejam semelhantes. Entretanto, os pacientes tinham um seguimento de aproximadamente 9 anos, enquanto a forma pediculada possui avaliações da patência com 15,17 e 20 anos3,42. Neste estudo, a angiografia foi limitada a 1/3 dos pacientes com média de seguimento de 17,5 meses e com amplo desvio padrão (± 18,4 meses)43.
Estudos com vistas a avaliar a permeabilidade a longo prazo da artéria torácica interna esqueletizada são necessários para esclarecer o papel definitivo da dissecção esqueletizada na cirurgia de revascularização miocárdica.
Neste ensaio clínico, que comparou medidas de comprimento, calibre e fluxo, é possível concluir que: a artéria torácica interna esquerda esqueletizada na variável comprimento não evidenciou diferença estatística; entretanto, o calibre e o fluxo sanguíneo livre apresentaram um aumento significativo na fase 2 do experimento com p=0,01 e p=0,03 respectivamente, comparados com a artéria torácica interna esquerda pediculada.
Endereço para correspondência
Gustavo Peressoni Castro
São Manoel, 808/504
Cep 90620110 - Porto Alegre - RS
E-mail:
castrogp@hotmail.com
Recebido em 31/03/2004 - Aceito em 19/05/2004
Co-Autores: Luiz Henrique Dussin, Orlando B. Wender, Gilberto V. Barbosa e Eduardo K. Saadi.
O arquivo disponível sofreu correções conforme ERRATA publicada no Volume 85 Número 2 da revista.
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Bilateral internal mammary artery grafting: midterm results of pedicled versus skeletonized conduitsAnn Thorac Surg199916374267CalafioreAMVitollaGIacoAL19. Matsumoto M, Konish Y, Miwa S, Minakata K. Effect of different methods of internal thoracic artery harvest on pulmonary function. Ann Thorac Surg 1997; 63: 653-5. Effect of different methods of internal thoracic artery harvest on pulmonary functionAnn Thorac Surg1997653563MatsumotoMKonishYMiwaSMinakataK20. Bonacchi M, Prifti E, Giunti G et al. Respiratory dysfunction after coronary artery bypass grafting employing bilateral internal mammary arteries: the influence of intact pleura. Eur J Cardio-Thorac Surg 2001; 19: 827-33. Respiratory dysfunction after coronary artery bypass grafting employing bilateral internal mammary arteries: the influence of intact pleuraEur J Cardio-Thorac Surg20018273319BonacchiMPriftiEGiuntiG21. Cohen AJ, Lockman J, Lorberboym M et al. 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Bilateral internal thoracic artery grafting: long-term clinical and angiographic results of in situ versus Y grafts. J Thorac Cardiovasc Surg 2000; 120: 990-8. Bilateral internal thoracic artery grafting: long-term clinical and angiographic results of in situ versus Y graftsJ Thorac Cardiovasc Surg20009908120ColafioreAMContiniMVitollaG30. Takami Y, Ina H. Effects of skeletonization on intraoperative flow and anastomosis diameter of internal thoracic arteries in coronary artery bypass grafting. Ann Thorac Surg 2002; 73: 1441-5. Effects of skeletonization on intraoperative flow and anastomosis diameter of internal thoracic arteries in coronary artery bypass graftingAnn Thorac Surg20021441573TakamiYInaH31. Higami T, Yamashita T, Nohara H et al. Early results of coronary grafting using ultrasonically skeletonized internal thoracic arteries. Ann Thorac Surg 2001; 71: 1224-8. Early results of coronary grafting using ultrasonically skeletonized internal thoracic arteriesAnn Thorac Surg20011224871HigamiTYamashitaTNoharaH32. Parish MA, Asai T, Grossi EA et al. The effects of different techniques of internal mammary harvesting on sternal blood flow. J Thorac Cardiovasc Surg 1992; 1104: 1303-7. The effects of different techniques of internal mammary harvesting on sternal blood flowJ Thorac Cardiovasc Surg1992130371104ParishMAAsaiTGrossiEA33. De Jesus RA, Acland RD. Anatomic study of the collateral supply of the sternum. Ann Thorac Surg 1995; 59: 163-8. Anatomic study of the collateral supply of the sternumAnn Thorac Surg1995163859DeJesus RAAclandRD34. Noera G, Pensa P, Lodi R et al. Influence of different harvesting techniques on the arterial wall the internal mammary artery graft: microscopic analysis. Thorac Cardiovasc Surgeons 1993; 41: 16-20. Influence of different harvesting techniques on the arterial wall the internal mammary artery graft: microscopic analysisThorac Cardiovasc Surgeons1993162041NoeraGPensaPLodiR35. Wender O, Hennen B, Demertzis S et al. Complete arterial revascularization in multivessel coronary artery disease with 2 conduits (skeletonized grafts and T grafts). Circulation 2000;102(suppl III): 79-83. Complete arterial revascularization in multivessel coronary artery disease with 2 conduits (skeletonized grafts and T grafts)Circulation20007983suppl III102WenderOHennenBDemertzisS36. Bical O, Braunberg E, Fischer M et al. Bilateral skeletonized mammary artery grafting: experience with 560 consecutive patients. Eur J Cardio-Thorac Surg 1996; 10: 971-6. Bilateral skeletonized mammary artery grafting: experience with 560 consecutive patientsEur J Cardio-Thorac Surg1996971610BicalOBraunbergEFischerM37. Mills NL, Bringaze WL. Preparation of the internal mammary artery graft. Wich is the best method? J Thorac Cardiovasc Surg 1989; 98: 73-9. Preparation of the internal mammary artery graftWich is the best method? J Thorac Cardiovasc Surg198973998MillsNLBringazeWL38. Dregelid E, Heldal K, Resch F et al. Dilation of the internal mammary artery by external and intraluminal papaverine application. J Thorac Cardiovasc Surg 1995; 110: 697-703. Dilation of the internal mammary artery by external and intraluminal papaverine applicationJ Thorac Cardiovasc Surg1995697703110DregelidEHeldalKReschF39. Villareal RP, Mathur VS. The string phenomenon: an important cause of internal mammary artery graft failure. Tex Heart Inst J 2000; 27: 346-9. The string phenomenon: an important cause of internal mammary artery graft failureTex Heart Inst J2000346927VillarealRPMathurVS40. Bilgen F, Yapici MF, Serbetgioglu A et al. Effect of normothermic papaverine to relieve intraoperative spasm of the internal thoracic artery. Ann Thorac Surg 1996; 62: 769-71. 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Tex Heart Inst J 2003; 30: 170-5.Pedicled or skeletonizedTex Heart Inst J2003170530DelCampoOriginal ArticlesComparative analysis of the flows of left internal thoracic artery grafts dissected in the pedicled versus skeletonized manner for myocardial revascularization surgery
OBJECTIVE: To compare the free blood flow, caliber, and length of the left internal thoracic artery (LITA), dissected in the pedicled (P) and skeletonized (S) manners, during surgery before and after topical vasodilator (TV) application. METHODS: A randomized, blind, clinical trial was carried out with 50 patients undergoing elective myocardial revascularization to assess the use of the LITA in situ in its pedicled or skeletonized form. The 25 patients in the pedicled group (GP) had NYHA class II or III angina, ejection fraction (EF) of 50.8±9.2%, and 16 were of the male sex. The patients in the skeletonized group (SG) had NYHA class II angina, EF of 46.8±9.3%, and 19 were of the male sex. The measurements were performed before extracorporeal circulation and divided into 2 phases: phase 1 (before topical papaverine application) and phase 2 (15 min after topical application of papaverine, 2.5 mg/mL, at 37ºC). During the measurements, mean blood pressure, central venous pressure, and heart rate were monitored. RESULTS: The phase 1 and 2 results are as follows: 1) PG: blood flow, 46±16 and 77±28 mL/min; caliber, 1.4±0.1 and 1.7±0.1 mm, respectively; 2) SG: blood flow, 57±27 and 97±35 mL/min; and caliber, 1.4±0.1 and 1.8±0.2 mm, respectively. No significant differences were observed in length. CONCLUSION: The LITA in SG had a significant increase in blood flow and caliber after the use of TV compared with blood flow and caliber in PG (P=0.03 and P=0.01, respectively).
left internal thoracic arterycoronary artery bypass graftingskeletonized
ORIGINAL ARTICLE
Comparative analysis of the flows of left internal thoracic artery grafts dissected in the pedicled Versus skeletonized manner for myocardial revascularization surgery
Gustavo Peressoni Castro
Porto Alegre, RS - Brazil
Hospital de Clínicas de Porto Alegre da Universidade Federal do RS
Correspondence
ABSTRACT
OBJECTIVE: To compare the free blood flow, caliber, and length of the left internal thoracic artery (LITA), dissected in the pedicled (P) and skeletonized (S) manners, during surgery before and after topical vasodilator (TV) application.
METHODS: A randomized, blind, clinical trial was carried out with 50 patients undergoing elective myocardial revascularization to assess the use of the LITA in situ in its pedicled or skeletonized form. The 25 patients in the pedicled group (GP) had NYHA class II or III angina, ejection fraction (EF) of 50.8±9.2%, and 16 were of the male sex. The patients in the skeletonized group (SG) had NYHA class II angina, EF of 46.8±9.3%, and 19 were of the male sex. The measurements were performed before extracorporeal circulation and divided into 2 phases: phase 1 (before topical papaverine application) and phase 2 (15 min after topical application of papaverine, 2.5 mg/mL, at 37ºC). During the measurements, mean blood pressure, central venous pressure, and heart rate were monitored.
RESULTS: The phase 1 and 2 results are as follows: 1) PG: blood flow, 46±16 and 77±28 mL/min; caliber, 1.4±0.1 and 1.7±0.1 mm, respectively; 2) SG: blood flow, 57±27 and 97±35 mL/min; and caliber, 1.4±0.1 and 1.8±0.2 mm, respectively. No significant differences were observed in length.
CONCLUSION: The LITA in SG had a significant increase in blood flow and caliber after the use of TV compared with blood flow and caliber in PG (P=0.03 and P=0.01, respectively).
The internal thoracic artery is the preferred graft for coronary artery bypass grafting1-4, and, in the in situ position, it is considered the gold standard for revascularizing the anterior interventricular artery5,6 due to its patency. On a 10-year follow-up, that graft remains patent in 90% of the patients6-9, while the venous graft remains patent in 50% of patients in the same period10-13.
Dissection of the internal thoracic artery in the pedicled form has already been well established; the skeletonized dissection technique, however, bears some uncertainties.
Reports have been published about the technique of skeletonization for internal thoracic artery dissection, comparing it with the pedicled dissection in regard to the following characteristics: free blood flow14-17; caliber15,17; length14,15,18; number of distal and sequential anastomoses18; respiratory function14,19,20; preservation of the integrity of the pleura14,19,20; blood supply to the sternum after internal thoracic artery dissection21,22; sternal complications23,24; uni- and bilateral use of the artery23,25-27; use in the elderly26; and use in diabetic patients23,26-28. Outcomes, such as survival and event-free survival (angina, angioplasty, myocardial infarction, stroke)18,27,29, have been compared.
A change has been observed in the profile of the patients undergoing coronary artery bypass grafting. They currently have ventricular impairment of a moderate to severe degree, advanced age, and other associated diseases, such as diabetes mellitus (type I or II), chronic obstructive bronchopulmonary disease (COBPD), systemic arterial hypertension, chronic renal failure (CRF), dyslipidemias, obesity, and a history of tobacco use.
Studies assessing outcomes, such as blood flow and the caliber and length of the graft, have been published14,16,17,30,31, most of which are observational studies, only a few being blind or double-blind randomized clinical trials. In the latter, intraluminal injection of vasodilators or hydrostatic dilation of the internal thoracic artery has usually been used, and the measurements have been taken during extracorporeal circulation.
The present study aimed at comparing length, caliber, and free blood flow of the left internal thoracic artery graft in its pedicled (conventional) versus skeletonized form before and after the topical application of a vasodilator.
Methods
This randomized, blind, clinical trial assessed, from January to October 2003, 50 patients undergoing elective and primary coronary artery bypass grafting. After randomization (fig. 1), the patients were divided into 2 groups as follows: pedicled group (PG), comprising 25 patients with the left internal thoracic artery dissected in the pedicled manner; and skeletonized group (SG), comprising 25 patients with the left internal thoracic artery dissected in the skeletonized manner. Patients with the following characteristics were excluded from the study: cardiogenic shock; need for circulatory support with intra-aortic balloon; coronary artery bypass grafting associated with valvular replacements or any other procedure; atrial fibrillation; situations in which internal thoracic artery dissection was contraindicated; age < 35 and > 80 years; ejection fraction < 30%; mean blood pressure (MBP) < 70 and > 100 mm Hg and heart rate (HR) greater than 100 bpm during the measurements; and those who did not agree to participate in the study. The patients taking part in the study were informed about the research and, after agreeing with the proposed procedure, they signed the written informed consent approved by the scientific committee and the committee on ethics and research on health of the Hospital de Clínicas de Porto Alegre, where the surgeries were performed.
All patients received the same anesthetic regimen without analgesia through a peridural catheter. The preanesthetic medication (oral flunitrazepam, 2 mg) was administered on the preceding day at 11 pm. After arriving at the operating room, the patients were monitored by electrocardiography, invasive arterial blood pressure (through the radial artery), central venous pressure (through the internal jugular vein or subclavian vein), urinary output (vesical catheter), pulse oximetry, and rectal and nasopharyngeal temperatures. Anesthetic induction was performed after preoxygenation through peripheral venous punctures (2 in the upper limb with a 14 or 16 catheter) using midazolam (0.1 mg/kg), fentanyl (10 mg/kg), and pancuronium (0.1 mg/kg). Then, orotracheal intubation was performed and mechanical ventilation was installed with isoflurane at a concentration of 1 to 2%. For anesthesia maintenance, the same drugs used during induction were used at reduced doses (midazolam, 0.05 mg/kg; fentanyl, 5 mg/kg; and pancuronium, 0.03 mg/kg).
Then, a median sternotomy was performed, followed by the required hemostasia, pericardiotomy, and, in the sequence, placement of a retractor for dissecting the left internal thoracic artery (Quinelato-Dinkhhyiusen).
Pedicled or skeletonized dissection was decided on by the anesthetist who tossed a coin (heads or tails) before beginning the surgical incision. The patients ignored the technique of left internal thoracic artery dissection they would undergo.
Once the left internal thoracic artery was exposed, dissection was initiated by pushing aside the left lung pleura, aiming always at maintaining it intact. A monopolar electrocautery (Valleylab Force 2) at the potency of 25 watts was used for the entire dissection (coagulation); a clip (Ethicon, LT 200 size) applicator (Ethicon) was used only for the important caliber branches. The distal limit was the bifurcation of the internal thoracic artery into the musculophrenic artery (MFA) and the superior epigastric artery (SEA), and the proximal limit was the superior margin of the first rib (fig. 2). In this technique, the pedicle comprised veins, muscle, endothoracic fascia, and adipose tissue, in addition to the left internal thoracic artery, and had an approximate width of 2 cm.
In the skeletonized dissection, the same distal and proximal limits of the previous technique were applied, and the left lung pleura was pushed aside and kept intact. By use of the monopolar electrocautery (Valleylab Force 2) at the potency of 18 watts, the endothoracic fascia was opened from the bifurcation of the internal thoracic artery until the superior margin of the first rib. Then, using a delicate tweezers and the blade of the cautery (using neither cut nor coagulation at this phase, but only blunt divulsion), skeletonized dissection of the left internal thoracic artery was performed, without tweezing the artery or using the cautery. After identification, the branches of the LITA were isolated and ligated by using the metallic clip (Vitalitec, small size) applicator (Vitalitec), always fixating one proximal and another distal clip, and sectioning with the Potts scissors (fig. 3).
After systemic heparinization (4 mg/kg), the LITA was sectioned at the level of its bifurcation, and the measurements of length, caliber, and free blood flow were taken.
Those measurements were taken in 2 phases: phase 1 (with no vasodilator), and phase 2 (with a topical vasodilator). In phase 1, the measurements of the length of the LITA were taken by using a graded metallic ruler (cm), and the limits were as follows: the proximal limit was the superior margin of the first rib, and the distal limit was the bifurcation into MFA and SEA. Then the caliber was measured by using metallic coronary measurers, whose diameters ranged from 1 to 2.5 mm. Then, the LITA was left in the horizontal position to drain freely for 30 seconds into a graded plastic receptacle. That volume was multiplied by 2, and the result was expressed in mL/min. In phase 2, the LITA was ligated with a metallic clip at its bifurcation. It was humidified and wrapped in gauze soaked with the vasodilator (papaverine at the concentration of 2.5 mg/mL at the temperature of 37ºC). After 15 minutes, the same measurements of phase 1 were taken again, now being affected by the topical vasodilator.
The measurements were performed before extracorporeal circulation, and in the cases in which the heart rate was < 90 bpm, artificial temporary atrial stimulation was adopted at a frequency of 90 bpm, and mean blood pressure, central venous pressure, and heart rate were monitored and recorded, as was the use of vasoconstrictive or vasodilating drugs. All left internal thoracic arteries were anastomosed in the anterior interventricular artery (fig. 4) and the venous graft (saphenous vein) was chosen to complete the rest of the myocardial revascularization. Extracorporeal circulation with a mean body temperature of 32ºC was used, as was anterograde, hypothermic, and crystalloid myocardial protection, which was repeated every 25 minutes.
The data are shown as mean and standard deviation. The quantitative variables were analyzed by using the Student t test for independent samples, and the qualitative variables were analyzed by using the chi-square test. In addition, analysis of variance was used for the repeated data, and multiple linear regression was used for assessing the changes in the values of the outcome variables and the factors that influenced them. The Statistical Package for the Social Sciences (SPSS), version 11.0, was used for statistical analysis. Differences with P < 0.05 were considered statistically significant.
Results
The preoperative data of the patients, such as sex, age, body surface, New York Heart Association functional class, associated diseases, history of tobacco use, and the ejection fraction measured on ventriculography are shown in table I. No significant differences were observed in the groups. Table II shows the medications with cardiovascular effects used by the patients in the preoperative period. No significant differences were observed between the groups. The results of the hemodynamic and surgical data (tab. III) showed statistical differences in the variables time of extracorporeal circulation and maintenance of pleural integrity (4 pleuras in the PG and 18 pleuras in the SG) for the SG (P=0.04 and P=0.0002, respectively). When the measurements in phases 1 and 2 (before and after the topical use of the vasodilator) in groups P and S were compared, no significant differences were identified in the following variables: number of distal anastomoses (2.96± 0.8 versus 3.16± 0.6 anastomoses, in PG and SG, respectively); time of aortic clamping (42.21±14.3 versus 51.68±21.8 min, in PG and SG, respectively); MBP; CVP; and HR. One PG patient had perioperative acute myocardial infarction, and an SG patient had a superficial sternal infection. In the in-hospital phase, the following findings were not observed: death, sternal dehiscence, mediastinitis, and difference in the hospital length of stay (9.1±1.69 versus 8.96±1.49 days for PG and SG, respectively, P=0.65). The results of the secondary outcomes (caliber and length of the vessel) are shown in table IV, in which one can see that a significant increase occurred neither in length in phases 1 and 2, nor in the variable caliber in phase 1, when comparing the groups. However, the caliber significantly increased after the use of TV (P=0.01) in SG. Figure 5 shows the result of the major outcome of the study, free blood flow, with an increase in blood flow in SG, both in phase 1 (57±27 mL/min) and phase 2 (97.1±35 mL/min), significant in the latter, when compared with that in PG before (46.2±16.7 mL/min) and after TV (77.2±28.8 mL/min) (P=0.09 and P=0.03, respectively).
Discussion
One of the reasons for choosing the skeletonized dissection of the internal thoracic artery is that it provides greater length14,25,29,32-34 and caliber17 compared with those provided by the conventional technique (pedicled), and, therefore, may revascularize coronaries with distal lesions. In addition, it maintains the internal thoracic artery in its in situ form, which is advantageous, because a 10 to 15% loss in the patency of that vessel is known to occur when it remains as a free graft, being anastomosed in the ascending aorta5.
The length of the left internal thoracic artery in this study was not statistically different between the groups, probably due to the topical administration of the vasodilator or the assessment method used; nevertheless, in practice, a greater mobility of the skeletonized graft was observed.
Calafiore et al 18, in an observational study comprising 1146 patients undergoing coronary artery bypass surgery, compared the pedicled (n=304) with the skeletonized (n=842) dissection of the left internal thoracic artery. They studied a subgroup of 28 patients (14 patients in the PG and 14 patients in the SG) and observed that the length of the left internal thoracic artery increased in both groups from 16.1±1.4 to 16.4±1.7 cm and from 17.6±1.4 to 20.1±1.6 cm, respectively. However, the measurements were performed before and 10 minutes after the intraluminal injection of 10 mL of papaverine (1 mg/mL).
Deja et al 14, in a study comparing the length of the vessel dissected in the pedicled and skeletonized manner, reported an increase, although not significant (P=0.11 for SG). This study was performed after the use of topical papaverine (0.2%), and measurement was taken only before performing the anastomosis of the left internal thoracic artery in the anterior interventricular artery, ie, the vasodilator had a longer time to act, and the influence of the mean blood pressure could be exerted longer (measured during extracorporeal circulation with a flow of 2.2 L/min/m2); no measurement of length was made without the vasodilator effect.
In our study, the caliber of the vessel increased significantly in the SG when compared with that in the PG in phase 2 (1.7±0.1 versus 1.85±0.2 mm; P=0.01), and, in phase 1, the calibers were almost the same (1.43±0.13 versus 1.44±0.19 mm). Choi and Lee 17 reported that, after topical use of papaverine (1.25 mg/mL), of 23 patients undergoing skeletonized dissection of the left internal thoracic artery, 21 had calibers between 1.5 and 2 mm, and 2 patients had diameters > 2 mm. Of 14 patients undergoing the pedicled dissection, in 6 the caliber was < 1.5 mm, in 7 between 1.5 and 2 mm, and in 1 it was > 2 mm. In their study, no measurement was performed before the use of the vasodilator, and the measurements were taken during extracorporeal circulation, before the anastomosis with the anterior interventricular artery, and no statistical comparison was performed with the pedicled group.
The technique of skeletonized dissection resulted in a significant increase in the caliber, therefore providing better conditions for performing the anastomoses, and contributing to a greater free blood flow.
The skeletonized dissection of the internal thoracic artery provides advantages, such as the preservation of the collateral circulation of the sternum, which reduces sternal complications23-25,29,31-36 and respiratory complications, due to pleural preservation19,20. In addition, the greater initial flow decreases the occurrence of hypoperfusion syndrome16,17, considering the longer time of dissection (10 to 15 min)16.
Different authors have shown the positive effect of papaverine on internal thoracic artery flow 34,37-41. Mills et al 37 and Degrelid et al 38 have studied the intraluminal injection of diluted papaverine and reported a greater flow compared with that resulting from the topical use of papaverine. However, a morphological study showed damage to the endothelium associated with the intraluminal injection of the vasodilator and its acid pH. Noera et al 34 studied the left internal thoracic artery in the pedicled versus skeletonized forms, and also compared the subgroups: intraluminal injection of papaverine with hydrostatic dilation versus topical application of the vasodilator. They reported that, at the end of the histological assessment, all subgroups with intraluminal injection and hydrostatic dilation had lesions in the intimal layer of the endothelium, and, therefore, recommended the topical application of papaverine. Some studies have shown that the topical administration of papaverine, such as intraluminal injection, is effective34,38-41. Bilgen et al40 have reported that the topical use of papaverine at 37ºC has better results than that at 20 to 22ºC.
In our study, maintenance of pleural integrity had results similar to those reported in the literature14,19,20.
Free blood flow was greater in SG when comparing the groups in the 2 phases of measurements (46.2±16.7 versus 57±27 mL/min and 77.2±28.8 versus 97.1±35 mL/min in PG and SG, respectively), being significant in phase 2 (P=0.03), due to the increase in caliber. However, considering flow gain, ie, flow in phase 2 minus flow in phase 1, and comparing it in both groups, an increase in flow gain was observed in SG, although not significant. In our study, the pedicled versus skeletonized dissection with topic papaverine at a concentration of 2.5 mg/mL at 37ºC was used, and the measurements were taken before extracorporeal circulation. Other studies in the literature, however, have used different temperatures and concentrations of the vasodilator, in addition to its intraluminal use16 and also the measurement being taken during extracorporeal circulation14. Therefore, a safe comparison is difficult. Considering the methodological differences, the measurements of free blood flow in phase 2 are similar to those reported in the literature14,16. Wendler et al16 used the model of intraluminal injection of papaverine, and reported a greater blood flow after using the vasodilator (147±70.5 mL/min in the PG, and 197±66.6 mL/min in the SG). However, the initial flow in the pedicled form was greater than that in the skeletonized form (68±54 versus 51±39 mL/min, respectively), but the difference was not statistically significant.
This study has the limitation of only measuring the free blood flow of the grafts, which is not a complete evaluation of the subject, because the resistance of the distal runoff may play an important role in blood flow distribution after implantation of the left internal thoracic artery in the anterior intraventricular artery, and that is its definitive condition. It is clear that free flow represents the maximum flow of the grafts in natural conditions, and it is not difficult to agree that the measurements of the flows obtained in the arteries of the patients should be adequate to revascularize the corresponding myocardial region.
Calafiore et al29 have reported that patency of the skeletonized and pedicled grafts is similar. However, the patients had a follow-up of approximately 9 years, while those with the pedicled form had patency assessment throughout 15.17 and 20 years3,42. In that study, angiography was limited to 1/3 of the patients with a mean follow-up of 17.5 months and wide standard deviation (± 18.4 months)43.
Studies aiming at assessing long-term patency of the skeletonized internal thoracic artery are required to clarify the definitive role of the skeletonized dissection in coronary artery bypass surgery.
To conclude this clinical trial comparing measurements of length, caliber, and flow: in regard to the variable length, the skeletonized left internal thoracic artery showed no statistical difference; however, in regard to caliber and free blood flow, it showed a significant increase in phase 2 (P=0.01 and P=0.03, respectively) when compared with those of the pedicled left internal thoracic artery.