Antiarrhythmic effects of simvastatin in canine pulmonary vein sleeve preparations

Abstract

Objectives: The purpose of this study was to determine the electrophysiologic effects of simvastatin in canine pulmonary vein (PV) sleeve preparations.

Background: Ectopic activity arising from the PV plays a prominent role in the development of atrial fibrillation.

Methods: Transmembrane action potentials were recorded from canine superfused left superior or inferior PV sleeves using standard microelectrode techniques. Acetylcholine (1 μM), isoproterenol (1 μM), high calcium ([Ca(2+)](o) = 5.4 mM), or a combination was used to induce early afterdepolarizations or delayed afterdepolarizations and triggered activity. Voltage clamp experiments were performed in the left atrium measuring fast and late sodium currents.

Results: Under steady-state conditions, simvastatin (10 nM, n = 9) induced a small increase in action potential duration measured at 85% repolarization and a significant decrease in action potential amplitude, take-off potential, and maximum rate of rise of action potential upstroke at the fastest rates. The V(max) decreased from 175.1 ± 34 V/s to 151.7 ± 28 V/s and from 142 ± 47 V/s to 97.4 ± 39 V/s at basic cycle lengths of 300 and 200 ms, respectively. Simvastatin (10 to 20 nM) eliminated delayed afterdepolarizations and delayed afterdepolarization-induced triggered activity in 7 of 7 PV sleeve preparations and eliminated or reduced late-phase 3 early afterdepolarizations in 6 of 6 PV sleeve preparations. Simvastatin (20 nM) did not affect late or fast sodium currents measured using voltage clamp techniques.

Conclusions: Our data suggest that in addition to its upstream actions to reduce atrial structural remodeling, simvastatin exerts a direct antiarrhythmic effect by suppressing triggers responsible for the genesis of atrial fibrillation.

Figure 1

Effect of simvastatin in a pulmonary vein (PV) sleeve preparation. A. Control action potentials recorded at basic cycle lengths (BCLs) of 2000, 500, and 300 ms. B. Effect of simvastatin (10 nM). Simvastatin accentuated the depolarization and reduction of take-off potential observed in the PV sleeve at fast rates.

Figure 2

Rate-dependent effects of simvastatin on V_max in PV sleeve preparations. A. Control recording of V_max recorded at basic cycle lengths (BCLs) of 2000, 1000, 500, 300, and 200 ms in a PV sleeve preparation. B. Effect of simvastatin (10 nM). C. Composite data (n=9) of effects on V_max expressed in absolute values. D. Effects on V_max expressed as values normalized to a BCL of 2000 ms. Acceleration from a BCL of 2000 to 300 ms led to a 16.8% decrease of V_max under control conditions and a 27.5% decrease following addition of simvastatin (p<0.05). A change in BCL from 2000 to 200 ms produced a 33.1% decrease under control conditions and a 54 % decrease upon addition of simvastatin (p<0.05).

Figure 3

Effect of simvastatin to suppress isoproterenol-induced delayed afterdepolarizations (DADs) and triggered activity. A. Induction of DAD and triggered response following a train of 20 beats at basic cycle lengths (BCLs) of 120 and 110 ms, respectively, in the presence of isoproterenol. B. Simvastatin (10 nM) eliminates the triggered beat and reduces DAD amplitude. C. Simvastatin (20 nM) eliminates the triggered beat as well as DAD activity. D. Washout of simvastatin restores triggered activity.

Figure 4

Simvastatin eliminates late-phase 3 early afterdepolarizations (EADs) and triggered activity. A. Effect of acetylcholine (ACh, 1 uM) and high calcium (5.4 mM) to induce late-phase 3 EADs and triggered activity following a train of 20 beats at a basic cycle length (BCL) of 200ms. B. Simvastatin (10 nM) suppresses EADs and triggered activity. C. Washout of simvastatin restores triggered activity.

Figure 5

Effect of simvastatin to suppress late phase 3 early afterdepolarizations (EADs) elicited at rapid stimulation rates (BCL= 150 ms). A. Acetylcholine (ACh, 1 uM) and high calcium (5.4 mM) induce late phase 3 EADs in alternate beats. B. Simvastatin (10 nM) eliminates late phase 3 EADs.

Figure 6

Late I_Na unaffected by simvastatin. A. Currents recorded during a train of 15 pulses in control solution (left) and in 5 uM simvastatin (right) at a diastolic interval of 200 ms. B. In the presence of 5 uM simvastatin, rate dependence of drug was investigated by shortening the diastolic interval to 160 ms.

Figure 7

Early and late I_Na in the presence of 20 nM simvastatin. Currents were normalized to the corresponding current recorded in control solution. A. Normalized fast I_Na as a function of pulse number recorded from a holding potential of -90 mV (panel A, n=11 atrial cells, p>0.05) or -120 mV (panel B, n=11 atrial cells, p>0.05). C. Late I_Na in the presence of 20 nM simvastatin as a function of pulse number (n=11 atrial cells, p>0.05). Late I_Na was measured as the area delimited by the dotted lines.