Effects of procainamide on electrical activity in thoracic veins and atria in canine model of sustained atrial fibrillation

Abstract

Focal discharges (FDs) are present in thoracic veins during atrial fibrillation (AF). We hypothesize that procainamide exerts its anti-AF action by suppressing FDs in the thoracic veins. We studied six mongrel dogs (22-27 kg) with sustained (>6 h) AF induced by 47 +/- 20 days of chronic rapid LA appendage (LAA) or pulmonary vein (PV) pacing. Procainamide was infused intravenously until AF was terminated or a cumulative dose of 20 mg/kg was reached. High-resolution mapping during AF showed FDs in the vein of Marshall, PVs, and the LAA. Procainamide significantly (P < 0.05) reduced the frequency of these FDs and suppressed the interactions of wave fronts between PVs and LA. The cumulative dose of PA needed to terminate AF correlated negatively (r =-0.9, P < 0.05) with the baseline effective refractory period (ERP) of PV and positively (r = 0.8, P < 0.05) with the baseline maximum dominant frequency (DF) of AF. In four of five dogs, AF converted to atrial tachycardia originating from the PVs before termination. Attempts to reinduce sustained AF were unsuccessful in these five dogs. AF was resistant to procainamide in the sixth dog. In conclusion, procainamide reduced the rate of FDs in the thoracic veins and the LA and suppressed the interaction between PVs and LA. Second, FDs in the PV are more resistant to procainamide's action than FDs in the atria. Third, inherent PV ERP is important in determining the antifibrillatory efficacy of procainamide.

An Acute Experimental Model Demonstrating 2 Different Forms of Sustained Atrial Tachyarrhythmias

“…Thus, the administration of the same propafenone dose caused a significantly greater slowing of conduction than that seen before GP ablation with rapid termination of ATa/AF (2Ϯ1 minute). An apparently contradictory finding was reported by Chou et al, 25 who found that a similar class I agent, procainamide, also reduced the rate of focal discharge in a long-term pacing model of sustained AF. However, 5 of 6 instances of focal discharge-based AF were terminated.…”

Intracellular Calcium Dynamics and Anisotropic Reentry in Isolated Canine Pulmonary Veins and Left Atrium

“…We 20,21 previously documented that wavefronts from the LA propagated to the PV and that pharmacological interruption of this PV-LA communication played an important role in chemoconversion AF in dogs. These PV-LA interactions increase the activation rates of PV, which might facilitate Ca i accumulation and the development of focal discharge from the PV.…”

Effects of Na+ and K+ channel blockade on vulnerability to and termination of fibrillation in simulated normal cardiac tissue

“…Largescale clinical trials (3,55) and experimental studies (11,47,62) have convincingly demonstrated that Na ϩ and K ϩ channel blockers are sufficiently proarrhythmic after myocardial infarction to preclude their use as a primary strategy for preventing VF. Yet antiarrhythmic drugs can terminate VF (1,28,29,52) and are fairly effective at terminating atrial fibrillation (AF) (9,19,21,22,31,32,51,57,58). To some extent, their antifibrillatory actions have been rationalized according to Garrey's "critical mass hypothesis" (16) and Moe's "multiple wavelet hypothesis" (30).…”