Effects of simultaneous atrioventricular pacing on atrial refractoriness and atrial fibrillation inducibility: Role of atrial mechanoelectrical feedback

Atrial Mechanoelectrical Feedback. Introduction: The purpose of this study was to evaluate the effects of an acute increase In atrial pressure on refr actoriness (mechanoelectrical feedback) and the vulnerability to atrial fib rillation (AF) and to investigate the effects of autonomic blockade and ver apamil on mechanoelectrical feedback in humans. Methods and Results: Right atrial pressure and effective refractory period (ERP) at the right atrial appendage (RAA) and high right atrial septum were measured during sinus rhythm, and during atrial and simultaneous AV pacing at a cycle length of 300 msec, either in the absence (n = 25) or presence (n = 22) of pharmacologic autonomic blockade. In another 15 patients, the p rotocol was performed before and after infusion of verapamil 0.15 mg/kg, In the absence of autonomic blockade, AV pacing resulted in a higher mean rig ht atrial pressure (11.7 +/- 3.3 vs 4.3 +/- 3.0 mmHg, P < 0.001) and a shor ter atrial RAA ERP (144 +/- 23 msec vs 161 +/- 21 msec; P < 0.001) compared with atrial pacing; AF was induced more often during AV pacing (87%) than during atrial pacing (20%) and was related directly to the right atrial pre ssure (r = 0.39, P = 0.004) and indirectly to the RAA ERP (r = -0.42, P < 0 .001). The susceptibility to sustained AF was greatly enhanced by autonomic blockade. Verapamil markedly attenuated the shortening of ERP and the prop ensity for AF that occurred during simultaneous AV pacing. Conclusion: An acute increase in atrial pressure during tachycardia is asso ciated with shortening of atrial refractoriness and a propensity for AF, i. e., atrial mechanoelectrical feedback, which may be enhanced by autonomic b lockade and attenuated by calcium channel blockade.