Antiarrhythmic drug effects on premature beats are partly determined by prior cardiac activation frequency in perfused guinea‐pig heart

Abstract

Antiarrhythmic drugs used to treat atrial fibrillation can occasionally induce ventricular tachyarrhythmia, which is typically precipitated by a premature ectopic beat through a mechanism related, in part, to the shortening of the excitation wavelength (EW). The arrhythmia is likely to occur when a drug induces a reduction, rather than an increase, in the EW of ectopic beats. In this study, I examined whether the arrhythmic drug profile is shaped by the increased cardiac activation rate before ectopic excitation. Ventricular monophasic action potential durations, conduction times and EW values were assessed during programmed stimulations applied at long (S 1 -S 1 [basic drive cycle length] = 550 ms) and short (S 1 -S 1 = 200 ms) cycle lengths in perfused guinea-pig hearts. The premature activations were induced with extrastimulus application immediately upon termination of the refractory period. With dofetilide, a class III antiarrhythmic agent, a prolongation in action potential duration and the resulting increase in the EW obtained at S 1 -S 1 = 550 ms were significantly attenuated at S 1 -S 1 = 200 ms, in both the regular (S 1 ) and the premature (S 2 ) beats. With class I antiarrhythmic agents (quinidine, procainamide and flecainide), fast S 1 -S 1 pacing was found to attenuate the drug-induced increase in action potential duration, while amplifying drug-induced conduction slowing, in both S 1 and S 2 beats. As a result, although the EW was increased (quinidine and procainamide) or not changed (flecainide) at the long S 1 -S 1 intervals, it was invariably reduced by these agents at the short S 1 -S 1 intervals. These findings indicate that the increased heart rate before ectopic activation shapes the arrhythmic profiles by facilitating drug-induced EW reduction. K E Y W O R D Santiarrhythmic agents, excitation wavelength, premature beats How to cite this article: Osadchii OE. Antiarrhythmic drug effects on premature beats are partly determined by prior cardiac activation frequency in perfused guinea-pig heart.

Electrocardiographic marker of the cardiac action potential triangulation induced by antiarrhythmic drugs in perfused guinea‐pig heart

“…In the present study, a prolongation of the phase 3 repolarization by antiarrhythmic drugs was significantly attenuated at the short pacing intervals, consistent with the reverse rate dependent mode of action of I Kr blockers (Jurkiewicz & Sanguinetti, 1993; Osadchii, 2012a, 2020). These effects are thought to be attributable to incomplete deactivation of I Ks , the slow component of the delayed rectifier, at the short PCL (Jurkiewicz & Sanguinetti, 1993).…”

“…In the present study, a prolongation of the phase 3 repolarization by antiarrhythmic drugs was significantly attenuated at the short pacing intervals, consistent with the reverse rate dependent mode of action of I Kr blockers (Jurkiewicz & Sanguinetti, 1993;Osadchii, 2012aOsadchii, , 2020.…”

“…The aortic perfusion pressure was measured with a ISOTEC pressure transducer and the coronary flow rate was determined using an ultrasonic flowmeter probe (Transonic Systems Inc., Ithaca, NY, USA) placed just above the aortic cannula. The electrical activity of the heart preparations was assessed from the volume-conducted ECG as well as monophasic action potential recordings, as described previously (Osadchii, 2018(Osadchii, , 2020. Throughout the experiments, the heart preparations were kept immersed in the temperaturecontrolled, perfusate-filled chamber to minimize thermal loss.…”