Introduction: Amiodarone is an effective antiarrhythmic drug, but it has serious side effects and conducted trials did not support its prophylactic use in survivors of acute myocardial infarction. It is possible that the prophylactic use of the drug has not been tested effectively. To optimize therapy outcome, markers of drug efficacy might be developed to identify patients who, although at arrhythmic risk, would not benefit from amiodarone treatment. We investigated descriptors of QT/RR relationship for their potential value in predicting inefficient amiodarone treatment.
Methods and results: The study used 866 Holter recordings (462 amiodarone, 404 placebo) obtained 1 month after randomization in the European Myocardial Infarct Amiodarone Trial (EMIAT). A commercial Holter system was used to measure RR and QT intervals. Subject-specific descriptors of QT/RR relationship were calculated. Comparison was performed in amiodarone- and placebo-treated patients, distinguishing patients who did and did not suffer from arrhythmic death. QT/RR relationship and individually corrected QTc interval differed significantly, not only between amiodarone- and placebo-treated postmyocardial infarction patients but also between patients with and without arrhythmic death on amiodarone (QTc with vs without arrhythmic death 426.30 +/- 33.93 ms vs 444.23 +/- 36.65 ms, P = 6.5 x 10(-3)). In a multivariate analysis, reduced optimum regression residuum (14.33 +/- 7.08 vs 20.11 +/- 9.39, P = 4.4 x 10(-3)) and flatter slope (0.44 +/- 0.19 vs 0.55 +/- 0.24, P = 4.0 x 10(-2)) of the QT/RR relationship independently predicted arrhythmic death during follow-up.
Conclusion: Chronic amiodarone treatment markedly affects the QT/RR relationship. The lack of treatment-related QT/RR changes predicts arrhythmic death. Descriptors of complexity of QT/RR relation seem to be potent markers of treatment efficiency.