Fernanda Aburesi Salvadori et al. Eduardo Martelli Moreira Murilo Bacchini Dias Amaro Nunes Duarte-Neto Edison Ferreira de Paiva
Discussion
Long QT syndrome (LQTS) can be congenital or acquired. The causes of acquired LQTS include hypocalcemia, due to prolongation of the phase 2 of the action potential (AP), medications (amiodarone, antidepressants and neuroleptics), hypokalemia, hypomagnesemia and severe bradycardia. – LQTS is associated with a specific polymorphic ventricular tachycardia (VT), named as torsades de pointes (TdP), because of the characteristic shift in the QRS axis that gives the impression of a “torsion”.
The QT interval is a marker of the AP duration. In LQTS patients, the AP is prolonged unevenly across the myocardium, so as to cause high dispersion of repolarization. The AP prolongation favors the formation of early afterdepolarization (EAD), which are deformities in the plateau and rapid repolarization phases (2 and 3) capable of inducing ventricular extrasystoles. EADs in the unevenly repolarized myocardium are the cause of TdP. Tachycardia is sustained due to focal electric activity and/or a reentrant mechanism. It may either cease spontaneously or degenerate into ventricular fibrillation and cardiac arrest , .
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