BEAT-TO-BEAT REPOLARIZATION LABILITY IDENTIFIES PATIENTS AT RISK FOR SUDDEN CARDIAC DEATH

Introduction: Recent studies have implicated repolarization lability i n the genesis of malignant ventricular arrhythmias. However, few data exist on assessment of temporal QT interval variability and its relati on to arrhythmogenesis, We tested the ability of the QT variability in dex (QTVI), a measure of beat-to-beat QT interval fluctuations measure d on a single ECG lead, to identify patients presenting with malignant ventricular arrhythmias and predict their subsequent occurrences. Met hods and Results: We measured the QTVI in 95 patients presenting for e lectrophysiologic study (EPS). The ability of the QTVI to identify pat ients with sudden cardiac death (SCD) or sustained monomorphic ventric ular tachycardia (MVT) on presentation and during follow-up of 23.7 +/ - 14.3 months was compared with spatial QT dispersion, T wave alternan s ratio during atrial pacing, MVT inducibility at FPS, signal-averaged EGG, heart rate variability, and ejection fraction. The QTVI was high er in patients with heart disease than in controls (-0.7 +/- 0.7 vs -1 .1 +/- 0.5, P < 0.05), and higher in patients presenting with SCD than in other patients with heart disease (0.0 +/- 0.6 vs -0.8 +/- 0.5, P < 0.05). The QTVI was the only clinical variable that identified patie nts who presented with SCD (P = 0.004, odds ratio = 12.5) on stepwise, logistic multiple regression. Fourteen patients had arrhythmic events during follow-up. In a Kaplan-Meier analysis of arrhythmic events, QT VI greater than or equal to 0.1 was a discriminator for higher risk of arrhythmic events (P < 0.05). Conclusions: (1) This noninvasive measu re of temporal repolarization lability identified patients with SCD an d predicted arrhythmia-free survival. (2) Further studies are needed t o determine the mechanisms that mediate beat-to-beat QT interval varia bility.