gms | German Medical Science

Question: The sequence of epicardial repolarization in fish and amphibians is unknown. Furthermore, a contribution of local durations of repolarization to the epicardial sequence of recovery remains largely unclear. The present study aimed at investigation of responses of repolarization durations in different ventricular zones to the ectopic excitation in fish and amphibian hearts.

Methods used: Epicardial mapping was done in frogs (n=9) and pikes (n=8). Electrical bipolar pacing was performed at the atrium (supraventricular rhythm) and the ventricular apex and base (ectopic excitation). The activation time, the recovery time and activation-recovery interval (ARI) – as an index of local duration of repolarization, were determined in each of 24 epicardial leads.

Results: In pikes, under supraventricular rhythm, the apical ventricular region was the first to recover whereas the basal area was the latest to be repolarized. In frogs, similarly, the repolarization times and ARIs progressively increased from the apex to the base (P<0.05). Under ectopic ventricular excitation ARIs decreased in most pacing protocols. At apical pacing in frogs, ARIs shortened in all leads (P<0.01) with the most prominent shortening being at the apex as compared with other regions (P<0.05). In frogs, basal pacing resulted in ARI shortening at the basal and middle areas (P<0.001), whereas at the apex ARI changes were insignificant. Under apical pacing in pikes the earliest repolarization was located near the pacing lead. Apical pacing produced the greater ARI shortening throughout the overall ventricular epicardium as compared to basal pacing (P<0.001).

Conclusion: Ectopic ventricular excitation in pikes and frogs resulted in the decrease of local repolarization durations. Apical pacing produced the greatest repolarization shortening as compared to the basal pacing. At the same pacing protocol (either apical or basal) the shortest ARIs and recovery times were associated with the area of pacing.