Modulation of the Sinus Rate during Ventricular Fibrillation

Background: During supraventricular and ventricular tachycardia, the arterial baroreflex predominates with minimal contribution from the cardiopulmonary reflex. To our knowledge, the role of the arterial baroreflex gain (BRG) during and immediately following termination of ventricular fibrillation (VF) has not been characterized. Objective: We hypothesized that (1) arterial BRG correlated with sinus node cycle length (SNCL) changes during VF, and that (2) the greater the arterial BRG, the greater the blood pressure (BP) recovery following successful defibrillation. Methods: Arterial BRG was assessed in 18 patients referred for the implantation of a defibrillator incorporating an atrial lead. The average SNCL was measured during the 5 seconds prior to VF induction and the last 5 seconds during VF before defibrillation. Percent SNCL change (%ΔSNCL) was determined. Arterial BP recovery was calculated as the difference in mean BP following defibrillation compared to during VF. Results: Arterial BRG ranged between –3 and 18 ms/mmHg. During VF, SNCL shortened in 11 patients (group A, mean %ΔSNCL =–15%), and surprisingly lengthened in seven patients (group B, mean %ΔSNCL = 5%). There was no correlation between %ΔSNCL and arterial BRG. In fact, arterial BRG in group A was lower when compared with group B (P = 0.075). Similarly, there was no correlation between arterial BRG and BP recovery. Conclusions: We found no correlation between arterial BRG and %ΔSNCL during VF, or BP recovery following defibrillation. Our findings of SNCL lengthening in 7 of 18 patients suggest that in some patients, arterial BRG plays a minor role during VF with a greater contribution from the cardiopulmonary BRG.