Electrocardiographic prediction of early ischemic arrhythmias (Phase 1A)

Early ischemic ventricular fibrillation (phase 1 A VF) frequently occurs before the first medical contact, which necessitates tools for arrhythmia prediction. This study aimed at establishing ECG predictors for phase 1 A VF.

Simultaneous recordings of limb‑lead ECGs and epicardial electrograms were performed in 24 anesthetized pigs before and during the first 10 min after coronary occlusion. In unipolar epicardial electrograms, local activation time (AT), end of repolarization time (RT), and rate-corrected activation-repolarization interval (ARIc) were determined. Maximal AT (ATmax), mean ARIc, maximal ARIc (ARIcmax), and maximal QRS and corrected QT intervals (QRSmax and QTcmax) were analyzed.

After occlusion onset, ATmax increased and mean ARIc shortened. QRSmax increased in animals with phase 1 A VF, whereas QTcmax remained stable in both groups. Compared with animals without phase 1 A VF, affected animals had longer mean ARIc from baseline through 2.5 min, longer ATmax and QRSmax from 2.5 min onward, and longer QTcmax at all assessed time points. In Cox regression and ROC analyses, QTcmax predicted phase 1 A VF at baseline, whereas QRSmax became predictive from 2.5 min onward. Kaplan-Meier analysis showed significantly different phase 1 A VF incidence between animals with baseline QTcmax >410 ms and those with QTcmax ≤410 ms.

Prolonged repolarization and delayed activation were associated with phase 1 A VF, with different temporal patterns. As ischemia progresses, the role of prolonged repolarization decreases, and that of delayed activation increases. Pre-ischemic QTcmax may serve as a marker of susceptibility to early ischemic VF.