Intracellular recording of in situ ventricular cells during ventricular fibrillation.

Transmembrane action potentials (AP) from ventricular cells during ventricular fibrillation (VF) have not been systematically studied. We have recently developed a motion-compensated micropipette holder that holds a micropipette and moves in synchrony with heart motion. AP of subepicardial ventricular cells were recorded in 14 open-chest anesthetized dogs prior to occlusion (control) of left anterior descending artery (LAD) and during first 10 min of reperfusion-induced VF. During control, characteristics (means +/- SE) of AP are: excitation rate (R), 112 +/- 4 beats/min; resting potential (Vr), -79.3 +/- 1.0 mV; overshoot potential (Vov), 17.9 +/- 1.8 mV; 90% AP duration (APD), 251 +/- 8 ms. During VF, AP from the reperfused areas are: R, 173 +/- 27 beats/min; Vr, -60.6 +/- 2.2 mV; Vov, 3.4 +/- 2.9 mV; APD, 134 +/- 9 ms (significantly different from control at P less than 0.001, except R). During VF, cells from the reperfused areas are made inexcitable with verapamil, but not by tetrodotoxin. In conclusion, during VF accurate AP recording is possible from in situ heart, and subepicardial cells in reperfused areas seem to have AP of slow-channel type.