| Popis: |
L-type Ca(2+) current (I(Ca,L)) has been shown to play a crucial role in initiation of early after depolarization (EAD) in cardiomyocytes. To study the possible role of EAD in spontaneous initiation of atrial fibrillation (AF), we tested the effects of L-type Ca(2+) channel blocker verapamil in canine models of cholinergic-dependent AF. In anesthetized open-chested dogs (n=13) spontaneous AF was induced by two methods: (1) perfusion with acetylcholine (ACh) in normal Tyrode solution at 9 ml/min into the sinus node artery (SNA) and (2) tonic stimulation of the right cervical vagus nerve (5 sec train). In the control, AF was induced in all dogs by perfusion with ACh (2.9+/-0.8 microM, mean+/-SEM) in 96+/-4% of attempts and by vagal stimulation (VS, 59+/-8 Hz) in 74+/-9% of attempts. Verapamil (0.2 mg/kg i.v.) did not alter the AF inducibility both during ACh perfusion and during VS (93+/-4% and 77+/-13%, NS, respectively) in dogs that retained sinus rhythm (n=8). However, verapamil significantly decreased AF inducibility to 50+/-4% and 21+/-13%, respectively, in dogs that passed to AV rhythm (n=5). Verapamil increased duration of both ACh- and vagally-mediated AF from 15+/-2 sec and 15+/-2 sec to 34+/-6 sec and 23+/-4 see (p0.05 vs. control), respectively. The activation mapping (112 unipolar electrodes) during the initiation of AF did not reveal a difference in epicardial activation patterns before and after verapamil treatment. Inhibiting the I(Ca,L) by verapamil resulted in significant (p0.05 vs. control) decrease in systolic and diastolic blood pressure, PQ interval prolongation and slowing down of the sinus rate. Verapamil did not affect atrial effective refractory period (AERP) and conduction velocity in the right atria. The reduction of AERP and the deceleration of heart rate by VS (8 Hz) remained unchangeable after verapamil treatment in comparison to control. Thus, the data suggest that the mechanism of spontaneous AF initiation during increased cholinergic activity is not related to EAD in atria. |
