Chloroquine Terminates Stretch-Induced Atrial Fibrillation More Effectively Than Flecainide in the Sheep Heart

Abstract

Blockade of inward-rectifier K+ channels by chloroquine terminates reentry in cholinergic atrial fibrillation (AF). However, it is unknown whether inward-rectifier K+ channels and reentry are also important in maintaining stretch-induced AF (SAF). We surmised that reentry underlies SAF, and that abolishing reentry with chloroquine terminates SAF more effectively than traditional Na+-channel blockade by flecainide. Thirty Langendorff-perfused sheep hearts were exposed to acute and continuous atrial stretch, and mapped optically and electrically. AF dynamics were studied under control and during perfusion of either chloroquine (4 µmol/L, n=7) or flecainide (2-4 µmol/L, n=5). Chloroquine increased rotor core size and decreased reentry frequency from 10.6±0.7 Hz in control to 6.3±0.7 Hz (P<0.005) just before restoring sinus rhythm (7/7). Flecainide had lesser effects on core size and reentry frequency than chloroquine and did not restore sinus rhythm (0/5). Specific IKr blockade by E-4031 (n=7) did not terminate AF when frequency values were >8 Hz. During pacing (n=11), flecainide reversibly reduced conduction velocity (≈30% at cycle length 300, 250, and 200 ms; P<0.05) to a larger extent than chloroquine (11% to 19%; cycle length, 300, 250, and 200 ms; P<0.05). Significant action potential duration prolongation was demonstrable only for chloroquine at cycle length 300 (12%) and cycle length 250 ms (9%) (P<0.05). Chloroquine is more effective than flecainide in terminating SAF in isolated sheep hearts by significantly increasing core size and decreasing reentry frequency. Chloroquine's effectiveness may be explained by its inward-rectifier K+ channel blockade profile and suggest that reentry is important to maintain acute SAF.