RESUMO
AIMS: "Cardiac memory" refers to abnormal T waves (TW) appearing after transient periods of altered ventricular depolarization. The aim of the study was to test the hypothesis that in the presence of abnormal TW, short periods of tailored ventricular pacing (VP) can be followed by normalization of ventricular repolarization. METHODS: Ten patients with normal TW (control group) and 18 patients with abnormal TW (study group) underwent 15 min of VP at a cycle length of 500 ms. In the control group, VP was performed from the right ventricular apex, and in the study group from right or left ventricular sites that resulted in paced QRS complexes of opposite polarity to that of the abnormal TW. Before and after VP, atrial pacing was maintained at a stable cycle length. Simultaneous 12-lead electrocardiography (ECG) was recorded before, during, and following VP to assess changes in TW polarity, amplitude, electrical axis, QTc interval, and QTc interval dispersion. RESULTS: As expected, VP was followed by memory-induced changes in TW in eight of ten patients in the control group. Mean T wave axis shifted from +60 degrees + or - 21.2 degrees to +23.5 degrees + or - 50.7 degrees (p = 0.01) in the frontal plane. In the study group, complete or partial normalization of TW occurred in 17 of 18 patients. Mean T wave axis shifted from -23.7 degrees + or - 22.9 degrees to +19.7 degrees + or - 34.7 degrees (p < 0.0002) in the frontal plane when paced from right ventricular outflow tract. The QTc interval shortened after VP both in the control group (424 + or - 25 vs. 399 + or - 27 ms; p = 0.007) and in the study group (446 + or - 26 vs. 421 + or - 22 ms; p < 0.0002). No significant changes were found in QTc interval dispersion. CONCLUSIONS: Transient changes in the sequence of ventricular activation may either induce or normalize abnormal TW. The background of preceding ventricular depolarization needs to be taken into account before determining the clinical significance of a given pattern of ventricular repolarization.
Assuntos
Estimulação Cardíaca Artificial , Eletrocardiografia , Sistema de Condução Cardíaco/fisiopatologia , Taquicardia Ventricular/diagnóstico , Taquicardia Ventricular/terapia , Potenciais de Ação , Adolescente , Adulto , Idoso , Mapeamento Potencial de Superfície Corporal/métodos , Estudos de Casos e Controles , Feminino , Seguimentos , Ventrículos do Coração/fisiopatologia , Humanos , Masculino , Pessoa de Meia-Idade , Valores de Referência , Medição de Risco , Estatísticas não Paramétricas , Disfunção Ventricular Esquerda/fisiopatologia , Adulto JovemRESUMO
La electroestimulación cardíaca permanente ha modificado el pronóstico de los pacientes con trastornos del automatismo y de la conducción sintomßticos. Sin embargo, aún existe un número considerable de complicaciones cuya incidencia fue puesta en perspectiva recientemente en los estudios multicéntricos realizados para comparar la morbimortalidad con distintas modalidades de estimulación. La fibrilación auricular, la insuficiencia cardíaca y el accidente cerebrovascular son las causas mßs frecuentes de las complicaciones clínicas del marcapasos
Assuntos
Arritmias Cardíacas , Bradicardia , Cardioversão Elétrica , EmergênciasRESUMO
La electroestimulación cardíaca permanente ha modificado el pronóstico de los pacientes con trastornos del automatismo y de la conducción sintomßticos. Sin embargo, aún existe un número considerable de complicaciones cuya incidencia fue puesta en perspectiva recientemente en los estudios multicéntricos realizados para comparar la morbimortalidad con distintas modalidades de estimulación. La fibrilación auricular, la insuficiencia cardíaca y el accidente cerebrovascular son las causas mßs frecuentes de las complicaciones clínicas del marcapasos (AU)