Hemodynamic effects of n-acetylprocainamide compared with procainamide in conscious dogs

Comparison of Acute Hemodynamic Effects of Lidocaine and Procainamide for Postoperative Ventricular Arrhythmias in Dogs

Heart rate and systolic, diastolic, and mean pressures were measured in two groups of dogs during treatment of postoperative ventricular arrhythmias either with intravenous (IV) 2% lidocaine hydrochloride or procainamide hydrochloride. Hemodynamic parameters were not significantly changed after IV administration of either drug. Additionally, changes in hemodynamic parameters for dogs treated with 2% lidocaine were not significantly different from those of dogs treated with procainamide. When dosed appropriately in the clinical setting, one bolus of IV procainamide was safe for the treatment of postoperative ventricular arrhythmias.

Cardiac anticholinergic effects of procainamide and its N-acetylated metabolite: experimental pharmacological and radioligand binding studies

1. The cardiac anticholinergic effects of procainamide (1 mg kg(-1) min(-1)) and its N-acetylated metabolite (NAPA) at equimolar dose (1.16 mg kg(-1) min(-1)) were studied using in vivo experimental pharmacological and in vitro radioligand binding studies. 2. Procainamide and NAPA progressively reduced vagal stimulation-induced bradycardia in chloralose-anaesthetized dogs. As indicated by the ED50, the vagolytic activity of NAPA is 1.5-2.0 times weaker than that of procainamide. Both drugs increased heart rate, with lowering of mean blood pressure during the second part of procainamide infusion, but not during NAPA infusion. 3. Binding studies on rat heart membranes yielded Ki values that were 1.5 times higher for NAPA than for procainamide. 4. These results show that NAPA exerts a weaker cardiac vagolytic action than procainamide, which is probably linked to a lower ability to bind to cardiac muscarinic receptors.

Antiarrhythmic drugs. Treatment of cardiac arrhythmias

This article focuses on drugs that have been specifically developed for the treatment of cardiac arrhythmias. A brief overview of the principal mechanisms responsible for the development of cardiac arrhythmias is also included, because it has been the goal of pharmacologists and clinical cardiologists to develop drugs and prescribe specific antiarrhythmic therapy based on a knowledge of these mechanisms with the assumption that specific antiarrhythmic therapy will be the most efficacious in restoring and maintaining normal sinus rhythm.

Effects of intravenous N-acetylprocainamide on hemodynamics and left ventricular function in man

N-acetylprocainamide (NAPA) is the active metabolite of procainamide currently undergoing evaluation for its antiarrhythmic properties. Its effects on hemodynamic variables and on ventricular function in man are poorly defined. The effects of intravenously administered NAPA (18 mg/kg over 30 minutes; mean plasma level 40.2 +/- 6.2 micrograms/ml) on hemodynamics and left ventricular ejection fraction (LVEF) assessed by radionuclide ventriculography were therefore determined in 14 patients undergoing diagnostic cardiac catheterization. The peak effects of the drug with respect to most measured variables were seen at 30 minutes and were still apparent at 60 minutes. NAPA increased heart rate (3% at 10 minutes; p less than 0.01), decreased mean pulmonary arterial pressure (14%; p less than 0.05) and capillary wedge pressure (27%; p less than 0.01), decreased mean arterial pressure (12%; p less than 0.01), cardiac index (8%; p less than 0.01), LV dp/dtmax (9%; p less than 0.05), and stroke work index (17%; p less than 0.01). The LVEF increased 5% (p less than 0.05). There was a trend for the systemic vascular resistance to decrease, but this did not reach statistical significance. The data show that NAPA exerts relatively weak peripheral arteriolar and venodilator effects associated with a mild reduction in contractility and cardiac output but an increase in LVEF in patients with preserved ventricular function.

Procainamide in the dog: antiarrhythmic plasma concentrations after intravenous administration

Procainamide hydrochloride was administered to ouabain-intoxicated dogs to determine an antiarrhythmic plasma concentration of procainamide. Ventricular arrhythmias were produced in dogs following intravenous injections of ouabain. After a sustained ventricular tachycardia was achieved, procainamide was administered and plasma samples collected for assay. Plasma procainamide was assayed by fluorescence polarization immunoassay. Procainamide was administered at increasingly higher constant rate infusions in order to achieve intermittent, steady-state plasma concentrations. Infusion rates were calculated on the basis of previous pharmacokinetic information. All six dogs that received procainamide converted to a normal sinus cardiac rhythm after attaining a mean plasma concentration of 33.8 micrograms/ml with a range of 48.5 micrograms/ml-25.0 micrograms/ml. It was observed that the computer-generated prediction of plasma concentrations based upon previous pharmacokinetic data produced an underestimate of the actual plasma concentrations. These data may suggest that plasma concentrations of procainamide for controlling some cardiac arrhythmias in dogs may be higher than plasma concentrations cited for human patients.

The Inotropic Actions of N-Acetylprocainamide: Blockade and Reversal by Propranolol

The inotropic actions of N-acetylprocainamide (NAPA) were studied in chloralose-urethane anesthetized dogs. Myocardial contractile force was measured with a Walton-Brodie strain gauge sutured to the right ventricle. A low-dose NAPA infusion (12 mg/kg i.v.) increased myocardial force by a maximum of 11.6±2.4% (mean±SEM), whereas a high dose of NAPA (60 mg/kg i.v.) increased myocardial force by 33.3±2.6% at the peak of the effect. The high-dose NAPA infusion also caused significant reductions in heart rate and blood pressure, while the low-dose NAPA infusion lacked significant chronotropic or hypotensive actions. Pretreatment with propranolol (0.5 mg/kg i.v. loading, followed by a 10 μg/kg/min infusion) did not block the positive inotropic actions of NAPA 12 mg/kg, but these actions were blocked in dogs pretreated with both propranolol and atropine (1 mg/kg). On the other hand, pretreatment with propranolol blocked and reversed the inotropic actions of NAPA 60 mg/kg, and potentiated its negative chronotropic effects. Thus, the positive inotropic actions of NAPA are indirect and more than one mechanism is involved; a component due to direct action related to the lengthening of cardiac repolarization is not discounted. At low doses, the increase in myocardial force seems related to NAPA's vagolytic properties, whereas at high doses the positive inotropic actions appear to be catecholamine-mediated. Furthermore, a negative inotropic action of high-dose NAPA is apparent after beta-adrenergic receptor blockade.

Effect of procainamide on myocardial contractile function and digoxin inotropy

The effect of procainamide and digoxin, singly and together, on peak active force and rate of force development of isolated right ventricular papillary muscles from adult cats was examined. Procainamide (1.5 X 10(-5) M) increased force and rate of force development in each muscle with further increments in performance up to 2.4 X 10(-4) M in most muscles. The maximal increases in force (+/- SEM) averaged 75 +/- 13% above control values. Essentially no response to procainamide was observed when basal levels of contractile state were increased by increasing stimulus frequency or calcium concentrations of the bathing solution. Propranolol (10(-6) M) markedly reduced and verapamil (10(-7) M) abolished the inotropic effect of procainamide. Exposing muscles to procainamide (1.5 or 3 X 10(-5) M) before or after the administration of digoxin (2 or 4 X 10(-7) M) did not alter the inotropic action of either drug. Thus, procainamide in concentrations that are in the therapeutic range in human patients has potent positive inotropic effects that may be masked at high levels of contractile state. This action of procainamide appears to be due to an effect on calcium channels, which in part may be due to beta-adrenergic receptor stimulation. These concentrations of procainamide do not alter the inotropic response to digoxin.