BAPTA-AM and Repetitive Endocardial Focal Discharges. Introduction: In isolated rabbit hearts, repetitive endocardial focal discharges (REFDs) were consistently observed during ventricular fibrillation (VF) with prolonged (>5 minutes) global ischemia (GI). We hypothesized that BAPTA-AM, a calcium chelator, can suppress these REFDs. Methods and Results: Using a two-camera optical mapping system, we simultaneously mapped endocardial (left ventricle, LV) and epicardial (both ventricles) activations during ventricular arrhythmia with GI. In 5 hearts (protocol I), we infused Tyrode's solution (no BAPTA-AM) for ≥30 minutes before the onset of no-flow GI. In 7 additional hearts (protocol II), BAPTA-AM (20 μmol/L) was infused for ≥30 minutes before the initiation of GI. In protocol I, sustained VF (>30 seconds) was successfully induced in all 5 hearts with prolonged GI. REFDs were present in >85 % of recording time. In protocol II, however, ventricular arrhythmia was not inducible and REFDs were not observed after 5-minute GI in 5 hearts. Effects of BAPTA-AM on intracellular calcium (Ca i) at the LV endocardium were also evaluated in 5 hearts (protocol III) using dual Ca i/membrane potential mapping. GI, both without and with BAPTA-AM pretreatment, caused a decrease of Ca i amplitude during S 1 pacing. However, this effect was more pronounced in the hearts with BAPTA-AM pretreatment (P < 0.001). GI, without BAPTA-AM pretreatment, caused broadening of Ca i transient. In contrast, GI, with BAPTA-AM pretreatment, caused narrowing of Ca i transient. Conclusions: BAPTA-AM pretreatment attenuates Ca i transient, suppressing the genesis of REFDs and pacing-induced ventricular arrhythmia during GI. These findings support the notion that Ca i dynamics is important in the maintenance of REFDs.
- optical mapping
- ventricular fibrillation