Synergistic electrophysiologic and antiarrhythmic effects of the combination of ranolazine and chronic amiodarone in canine atria

Abstract

Background: Amiodarone and ranolazine have been characterized as inactivated- and activated-state blockers of cardiac sodium channel current (I(Na)), respectively, and shown to cause atrial-selective depression of I(Na)-related parameters. This study tests the hypothesis that their combined actions synergistically depress I(Na)-dependent parameters in atria but not ventricles.

Methods and results: The effects of acute ranolazine (5 to 10 micromol/L) were studied in coronary-perfused right atrial and left ventricular wedge preparations and superfused left atrial pulmonary vein sleeves isolated from chronic amiodarone-treated (40 mg/kg daily for 6 weeks) and untreated dogs. Floating and standard microelectrode techniques were used to record transmembrane action potentials. When studied separately, acute ranolazine and chronic amiodarone caused atrial-predominant depression of I(Na)-dependent parameters. Ranolazine produced a much greater reduction in V(max) and much greater increase in diastolic threshold of excitation and effective refractory period in atrial preparations isolated from amiodarone-treated versus untreated dogs, leading to a marked increase in postrepolarization refractoriness. The drug combination effectively suppressed triggered activity in pulmonary vein sleeves but produced relatively small changes in I(Na)-dependent parameters in the ventricle. Acetylcholine (0.5 micromol/L) and burst pacing induced atrial fibrillation in 100% of control atria, 75% of ranolazine-treated (5 micromol/L) atria, 16% of atria from amiodarone-treated dogs, and in 0% of atria from amiodarone-treated dogs exposed to 5 micromol/L ranolazine.

Conclusions: The combination of chronic amiodarone and acute ranolazine produces a synergistic use-dependent depression of I(Na)-dependent parameters in isolated canine atria, leading to a potent effect of the drug combination to prevent the induction of atrial fibrillation.

Conflict of interest statement

Conflict of Interest Disclosures: Dr. Antzelevitch is a consultant to and received research support from CV Therapeutics (now Gilead Sciences, Inc). Dr. Luiz Belardinelli is an employee of Gilead Sciences, Inc., Palo Alto, CA.

Figures

Figure 1

Effects of acute ranolazine, chronic amiodarone, and its combination on action potential duration measured at 75 % and 90 % repolarization (APD75 and APD90) and effective refractory period (ERP) in coronary-perfused right atrial (A) and left ventricular wedge (B) preparations. Ranolazine significantly prolongs ERP but not APD in the atrium causing significant post repolarization refractoriness (PRR) in atrial, but not ventricular preparations isolated from chronic amiodarone-treated dogs. ERP-APD = PRR. n = 4–17. * p<0.01 vs respective APD75 controls: Chronic amiodarone + Ranolazine vs. Chronic amiodarone alone, Ranolazine (5 μM) vs. control, Chronic amiodarone vs. control. Atria: control n=17 dogs; ranolazine n=10 dogs; chronic amiodarone n =8 dogs; chronic amiodarone+ranolazine n=4 dogs. Ventricle: control n=5 dogs; ranolazine n=5 dogs; chronic amiodarone n =4 dogs; chronic amiodarone+ranolazine n=4 dogs.

Figure 2

Synergistic reduction of the maximum rate of rise of the action potential upstroke (Vmax) by combination of chronic amiodarone and acute ranolazine in canine coronary perfused right atrial preparations. Shown are Vmax values from individual experiments n=4–14. Control (n=14), Ran = Ranolazine (n=10); Amio = Chronic amiodarone (n=14), Ran + Amio (n=4). * p<0.0.5 vs control and Ran 5 μM. Control n=14 dogs; ranolazine n=10 dogs; chronic amiodarone n =14 dogs; chronic amiodarone+ranolazine n=4 dogs.

Figure 3

Synergistic effects of acute ranolazine and chronic amiodarone to significantly increase diastolic threshold of excitation (DTE) in coronary-perfused right atrial preparations. n=6–12. * p† p<0.01 vs chronic Amiodarone alone and vs ranolazine. Control n=9 recordings (8 PM and 1 CT) from 8 dogs; ranolazine n=9 recordings(8 PM and 1 CT) from 8 dogs; chronic amiodarone n =12 recordings (7 PM and 5 CT) from 8 dogs; chronic amiodarone+ranolazine n=6 recordings (4 PM and 2 CT) from 4 dogs.

Figure 4

Potent depression of excitability induced by a combination of chronic amiodarone and acute ranolazine (5 μM) leading to activation failure at rapid rates in coronary-perfused right atria. A: Failure of 1:1 activation at a pacing cycle length (CL) of 350 ms. B: Failure of 1:1 activation at a CL of 200 ms in the presence of acetylcholine (B). C: Increase in CL needed to maintain 1:1 activation (see Table 1 for actual numbers). Ran = Ranolazine (n=10); Amio = Chronic amiodarone (n=8). Ran + Amio (n=4). Ran n=10 dogs; Amio n =8 dogs; Amio+Ran n=4 dogs.

Figure 5

Rate-dependent effects of chronic amiodarone, alone and combined with acute ranolazine (5 and 10 uM), on maximum rate of rise of action potential upstroke (Vmax) and action potential characteristics in a pulmonary vein (PV) sleeve preparation. A–C: Action potentials (AP) recorded at different basic cycle lengths (BCLs) from a PV sleeve isolated from a chronic amiodarone-treated dog before (panel A) and after addition of ranolazine (5 and 10 μM) (panel B and C). In the absence of ranolazine, the chronic amiodarone-treated PV sleeve displayed 2:1 activation failure at BCL 300 ms. The addition of 5 μM ranolazine induced a marked decrease in Vmax and 4:3 and 4:1 activation failure at 1000 and 300 ms, respectively. The addition of 10 μM ranolazine rendered the preparation inexcitable.

Figure 6

Rate-dependence of action potential and conduction characteristics in LV wedge preparation isolated from chronic amiodarone-treated dog in the absence and presence of acute ranolazine (5 and 10 uM). Each panel shows a pseudo-ECG (top trace) and action potentials recorded from the M cell region. 1:1 activation persisted following a decrease in basic cycle length (BCL) from 2000 to 1000 and 300 ms.

Figure 7

Composite data of the effect of ranolazine (5 or 10 μM) on basic cycle length (BCL) at which 1:1 activation failure occurred in pulmonary vein (PV) sleeve (A, n=5) and left ventricular (LV) wedge (B, n=4) preparations isolated from untreated and chronic amiodarone-treated (Amio) dogs. In untreated dogs, ranolazine (10 μM) induced a significant increase of the BCL permitting 1:1 activation in PV but not LV wedge preparations. Chronic amiodarone treatment led to a significant increase in the basic cycle length (BCL) permitting 1:1 activation in both PV sleeve and LV, wedge, which was greatly accentuated in PV sleeves but not LV wedges following the addition of ranolazine (5 and 10 μM). *p† p<0.05 Amio+Ranolazine vs Amio alone. Ran = ranolazine; Amio = chronic amiodarone. PV sleeve: n=5 dogs for each condition; LV wedge: n =4 dogs for each condition.