Acute electrophysiologic effects of pirmenol in normal subjects and in patients with Wolff-Parkinson-White syndrome

Clinical effects and pharmacokinetics of a single oral dose of pirmenol hydrochloride

To establish the clinical efficacy of a single oral dose of pirmenol, we evaluated electrophysiologic and hemodynamic effects simultaneously after drug administration, performing electrophysiologic testing in 20 patients with ECG-documented paroxysmal supraventricular tachycardia (PSVT) before and after a single oral 200-mg dose of pirmenol. Hemodynamic measurements were made with a Swan-Ganz catheter in the first 10 consecutive patients. In a different series of patients, we administered a single 200-mg oral dose of pirmenol to evaluate its acute termination effect in 7 patients with PSVT and 9 with paroxysmal atrial fibrillation. Pirmenol prolonged the refractory period of the retrograde conduction system in patients with or without an accessory pathway, and supraventricular tachycardia was no longer inducible at 60 min in 11 patients [8 of 11 with atrioventricular (AV) reentrant tachycardia and 3 of 5 with AV nodal reentrant tachycardia]. Pirmenol increased the heart rate (p < 0.01) and total systemic resistance (p < 0.05), and reduced the stroke volume index (p < 0.01), all significantly. The plasma concentration of pirmenol at 1 h after administration was 0.75 +/- 0.48 microgram/ml. A single oral dose of pirmenol during tachyarrhythmia successfully restored sinus rhythm in 4 of 7 (57%) patients with PSVT and 4 of 9 (44%) patients with paroxysmal atrial fibrillation. A single oral dose of pirmenol was well tolerated as episodic treatment in patients with supraventricular tachyarrhythmias.

Regulation of beta-adrenoceptors in the guinea-pig sinoatrial node

This study examined the changes of beta-adrenoceptors in the guinea-pig sinoatrial nodal region following 7 day (-)-isoprenaline (400 micrograms/kg/h s.c.) infusion and the relationship between beta-adrenoceptor desensitization and receptor down-regulation. Changes in beta 1- and beta 2-adrenoceptor density were measured using quantitative autoradiography and function in organ bath studies. (-)-Isoprenaline treatment produced a marked decrease in total (from 57.5 to 33.9 fmol/mg protein), beta 1- (from 49.4 to 32.8 fmol/mg protein), and beta 2-adrenoceptor density (from 8.1 to 1.05 fmol/mg protein) in the sinoatrial node. In adjacent right atrium, treatment produced no change in total (39.5 and 36.7 fmol/mg protein) or beta 1-adrenoceptors (35.9 and 36.4 fmol/mg protein) but did decrease beta 2-adrenoceptors (from 3.7 to 0.3 fmol/mg protein). Chronotropic effects were measured in spontaneously beating right atrium. Procaterol, a selective beta 2-adrenoceptor agonist, caused a biphasic chronotropic response in control right atria, the first part of which was abolished in the tissue from treated animals. The maximum increase in right atrial rate to RO363, a beta 1-adrenoceptor selective partial agonist, was reduced from 114 bpm in control to 43 bpm in treated animals. In electrically driven right atrium with the sinoatrial node removed procaterol failed to produce a positive inotropic response via beta 2-adrenoceptors, but the maximum response to RO363 was reduced from 0.75 g in the control tissue to 0.12 g in the treated tissue. This study showed that changes in beta 2-adrenoceptor density following 7 day (-)-isoprenaline infusion are compatible with reduced functional responsiveness in the SA node. The reduction of beta 1-adrenoceptor number in the SA node was also compatible with the reduced chronotropic response in this tissue. However the lack of effect on beta 1-adrenoceptor density in the right atrium was not consistent with the decrease in beta 1-adrenoceptor mediated inotropic response in this tissue. This suggests that beta-adrenoceptor desensitization is not always associated with receptor down-regulation but depends also on the changes in the cell signalling system beyond the level of the receptor which differ according to the cardiac location.

Newer antiarrhythmic drugs

The effective management of cardiac arrhythmias remains a major challenge in cardiovascular therapeutics. The management of arrhythmias encompasses a wide spectrum of supraventricular and ventricular tachyarrhythmias occurring in patients with various cardiac diagnoses and different degrees of myocardial dysfunction. A number of the newer antiarrhythmic drugs that have either recently been released or appear promising are reviewed in this article. Drugs are described with respect to their basic pharmacology, electrophysiologic actions, pharmacokinetics and metabolism, hemodynamics, antiarrhythmic effects, side effects, interactions, indications, and dosage.