Absolute beat-to-beat variability and instability parameters of ECG intervals predict ischemia-induced ventricular fibrillation

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Background: ECG interval measurement is possible during arrhythmias. Beat-to-beat variability and instability (BVI) of ECG intervals measured irrespective of rhythm (absolute BVI) predict drug-induced torsades de pointes (TdP) more accurately than the same variables derived exclusively during sinus rhythm (sinus BVI) in rabbits. We have tested whether this approach predicts another stochastic arrhythmia event, ventricular fibrillation (VF), in a different pathophysiological setting. Methods and Results: Langendorff perfused rat hearts were subjected to regional ischemia for 15 min. Absolute BVI parameters were derived from ECG intervals measured in 40 consecutive ventricular complexes (irrespective of the rhythm) immediately preceding VF onset and compared with values in time-matched ECGs in hearts that did not express VF. Increased frequency of non-sinus beats and ‘R on T’ arrhythmic beats, shortened mean RR and electrical diastolic intervals, and increased BVI of cycle length and repolarization were associated with VF occurrence. Absolute BVI parameters that quantify variability of repolarization (e.g. ‘short-term variability’ of QT interval) had the best predictive power with very high sensitivity and specificity. In contrast, VF was not predicted by any BVI parameter derived exclusively from sinus rhythm. Conclusions: The novel absolute BVI parameters that predicted TdP liability in rabbits also predict VF liability during regional ischemia in rat hearts, indicating a diagnostic and mechanistic congruence. Repolarization inhomogeneity appears to play a pivotal role in ischemic VF induction since absolute BVI parameters that quantify repolarization variability had outstanding predictive power.

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