Prolongation of QT interval and antiarrhythmic action of bepridil

Bepridil is potent against SARS-CoV-2 in vitro

Guided by a computational docking analysis, about 30 Food and Drug Administration/European Medicines Agency (FDA/EMA)-approved small-molecule medicines were characterized on their inhibition of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) main protease (Mpro). Of these small molecules tested, six displayed a concentration that inhibits response by 50% (IC50) value below 100 μM in inhibiting Mpro, and, importantly, three, that is, pimozide, ebastine, and bepridil, are basic molecules that potentiate dual functions by both raising endosomal pH to interfere with SARS-CoV-2 entry into the human cell host and inhibiting Mpro in infected cells. A live virus-based modified microneutralization assay revealed that bepridil possesses significant anti-SARS-CoV-2 activity in both Vero E6 and A459/ACE2 cells in a dose-dependent manner with low micromolar effective concentration, 50% (EC50) values. Therefore, the current study urges serious considerations of using bepridil in COVID-19 clinical tests.

Block of Na+ channel by bepridil in isolated guinea-pig ventricular myocytes

The effects of bepridil, a potent antiarrhythmic agent, on the Na+ current (INa) of single guinea-pig ventricular myocytes were studied using the whole-cell patch-clamp technique. Bepridil inhibited INa in a dose-dependent manner without causing any change in the I-V. relationship for INa. Bepridil suppressed INa with Kd values of 342 and 40 microM when cells were clamped to holding potentials of -140 and -90 mV, respectively. 10 microM bepridil shifted the steady-state inactivation curve for INa toward more negative potentials by 7.7 mV (n = 6). Bepridil also produced marked use-dependent block with a rapid onset. Recovery of INa from inactivation was retarded (time constant 290 ms) at a holding potential of -140 mV in the presence of 10 microM bepridil. When the onset of INa block was studied in experiments using a double-pulse protocol, bepridil blocked INa by 11.5% after a 4-ms pre-pulse, but significantly blocked it after pre-pulses longer than 16 ms. These results suggest that: (1) bepridil has a higher affinity for the inactivated state than the resting state of Na+ channel; (2) the drug also produces an open channel block; and (3) the drug shows a lidocaine-like fast kinetic block of Na+ current.

Bepridil prolongs the action potential duration of guinea pig ventricular muscle only at rapid rates of stimulation

1. We examined the electromechanical effects of the calcium antagonist, bepridil (1-20 microM), on isolated guinea pig ventricular muscles, driven at various stimulus frequencies (0.1, 0.5, 1, 2 and 5 Hz) in Tyrode's solution containing various K+ concentrations (1.4-43.2 mM). 2. Conventional microelectrode and tension-recording techniques were used. 3. We found that bepridil decreased the maximum upstroke velocity (Vmax) of the action potential with no change in the resting membrane potential (RMP). 4. The former effect depended on both stimulus frequency and the drug concentration used. 5. Bepridil lengthened the duration of the action potential at the level of 25% repolarization (APD25) at the highest frequency (5 Hz), but shortened it at lower frequencies (< or = 2 Hz). 6. The drug also lengthened the APD90 at the highest frequency (5 Hz) but without significant effect at lower frequencies (< or = 2 Hz). 7. Bepridil depolarized the RMP at relatively low extracellular K+ concentrations (< or = 2.7 mM), accompanied by a prolongation of APD90. 8. There were no such effects at much higher K+ concentrations (> or = 5.4 mM), and the drug markedly depressed the Vmax and the action potential amplitude. 9. The drug eliminated the positive staircase phenomenon of twitch contraction, in a concentration-dependent manner. 10. All these findings taken together suggest that bepridil prolongs the action potential duration by inhibiting outward potassium currents (IK and IK1), at rapid rates of stimulation (approximately 300/min), which is comparable to the physiological heart rate of a guinea pig. 11. The prolongation of APD seemed to be secondary to the bepridil-induced reduction of intracellular Ca2+ concentration, [Ca2+]i.

Antiarrhythmic and electrophysiological effects of SD-3212, a novel Na+ and Ca++ channel blocker, in anaesthetized dogs with myocardial infarction in comparison with its stereoisomer (SD-3211) and bepridil

Antiarrhythmic and electrophysiological effects of SD-3212, a novel antiarrhythmic agent, which has both Na+ channel and Ca++ channel blocking activities, were compared with those of its (+)-stereoisomer, SD-3211, which has only a Ca++ channel blocking activity, and bepridil, a known Ca++ channel blocker with additional Na+ channel blocking activity, using the two-stage coronary ligation induced arrhythmia (24 h after the ligation of the left anterior descending coronary artery) and 7 day-old myocardial infarcted hearts in anaesthetized dogs. SD-3212 showed a dose-dependent antiarrhythmic effect on the two-stage coronary ligation induced arrhythmia. SD-3212 at a dose of 3 mg/kg reduced the arrhythmic ratio, i.e. ectopic beats per min divided by the sum of ectopic beats and sinus beats per min, significantly from 1 up to 12 min after the administration. Neither bepridil (1-6 mg/kg) nor SD-3211 (1 mg/kg) had an antiarrhythmic effect. SD-3212 (0.3-3 mg/kg) prolonged both the conduction time in the normal myocardium and the delayed potential in the infarcted myocardium in the 7 day-old myocardial infarcted hearts in anaesthetized dogs in a dose-dependent manner. This effect of SD-3212 was shown at coupling intervals of 150-1000 ms increasing with decreasing interval. In this respect, SD-3212 is similar to drugs which show fast recovery of Vmax from use-dependent block such as lidocaine. Bepidril (1-6 mg/kg) also prolonged these parameters in a dose-dependent manner, however, the prolongation induced by bedripil was limited to shorter coupling intervals as compared with that induced by SD-3212. SD-3212 (0.1-1 mg/kg) did not show this prolonging effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Bepridil hydrochloride compared with placebo in patients with stable angina pectoris

Bepridil is a calcium antagonist with a unique chemical composition and a long elimination half-life (42 hours). We evaluated the efficacy of bepridil 300 mg once/day in a crossover comparison with placebo in 45 patients with angina. Patients had an average of 7.6 anginal episodes/week during the placebo baseline phase of the trial. After 4 weeks of bepridil therapy, anginal frequency decreased to 2.9 episodes/week (p less than 0.05). Likewise, mean nitroglycerin consumption declined from 7.4 tablets/week during the placebo baseline phase to 4.0 tablets/week during bepridil therapy (p less than 0.05). Statistically significant increases over the previous period (placebo baseline or double-blind placebo) were seen in total exercise time, time to angina, and total work (p less than 0.05). During bepridil therapy, 13 of 45 patients (29%) no longer experienced angina as an exercise end point despite the increase in work and exercise time. Bepridil significantly prolonged both the QT and corrected QT (QTc) intervals; the mean increases were 10.0% and 5.6%, respectively. Side effects were reported with equal frequency in the placebo and bepridil arms of the trial, and no serious side effects were reported. In an intermediate fixed dose of 300 mg/day, bepridil relieved anginal symptoms with few side effects. Bepridil appears to be a safe and effective treatment for stable angina.

Bepridil therapy: guidelines for patient selection and monitoring of therapy

Bepridil is a calcium antagonist with a unique electrophysiologic profile, a long elimination half-life, and demonstrated efficacy as an antianginal agent in the setting of chronic stable angina. It is well tolerated, with relatively mild gastrointestinal and neurologic side effects. A major safety concern with bepridil is the occurrence of ventricular arrhythmias, especially torsades de pointes associated with QT interval prolongation, particularly in the context of hypokalemia with concomitant diuretic therapy. An appreciation of the electrophysiologic profile of this compound and the setting in which potentially serious proarrhythmic actions occur allows the identification of patients in whom the drug should be avoided. Among the exclusionary criteria are hypokalemia or risk of hypokalemia, baseline corrected QT interval greater than 0.44 sec, history of serious ventricular arrhythmias requiring treatment with major antiarrhythmic compounds, and concomitant use of other drugs that prolong the QT interval. Appropriate use of this effective antianginal agent requires a knowledge of its electrophysiology and adherence to patient selection and monitoring guidelines.

Comparative efficacy and safety of bepridil and diltiazem in chronic stable angina pectoris refractory to diltiazem. The Bepridil Collaborative Study Group

The efficacy and safety of bepridil hydrochloride (200 to 400 mg/day) were evaluated in patients with chronic stable angina refractory to maximal tolerated doses of diltiazem (median 360 mg/day) in a randomized, multicenter, double-blind, parallel study. Baseline diltiazem data were obtained during a 2-week period, after which 86 patients were randomized to bepridil (n = 46) or diltiazem (n = 40). Angina frequency, nitroglycerin consumption and ischemic manifestations induced by exercise treadmill testing were evaluated over 8 weeks. Bepridil significantly (p less than 0.05) increased time to angina onset, time to 1 and 2 mm of ST-segment depression, total exercise time and total work over baseline values. Changes in time to angina onset and time to 1 mm of ST-segment depression were significantly (p less than 0.05) greater for bepridil than for diltiazem. Angina frequency and nitroglycerin consumption did not differ significantly between groups. Compared with baseline, bepridil significantly (p less than 0.001) decreased heart rate (mean 4 beats/min) and prolonged QTc (mean 35 ms). The most frequent adverse effects in both groups were nausea, asthenia, dizziness, headache and diarrhea. Four patients taking bepridil and 1 taking diltiazem withdrew from the study because of adverse reactions. No sudden deaths, myocardial infarctions or instances of sustained ventricular tachycardia or torsades de pointes occurred in either group. The data indicate that bepridil provided safe and effective antianginal and antiischemic therapy in patients with chronic stable angina who exhibited less than optimal response to maximal tolerated doses of diltiazem.

Effects of bepridil and diltiazem on ventricular repolarization in angina pectoris

To examine the time-course and potential predictors of prolongation of ventricular repolarization with the calcium antagonist bepridil, the effects of bepridil (300 to 500 mg/day; n = 45) and diltiazem (180 to 300 mg/day; n = 42) on QT and QTc interval duration were analyzed in a randomized double-blind study in patients with angina pectoris. Electrocardiograms were recorded before and 14, 28, 70 and 112 days after treatment was begun. After 14 days, bepridil prolonged QT interval by 26 +/- 35 ms (range, -60 to 120 ms) and QTc (Bazett's formula) by 17 +/- 33 ms (range, -73 to 107 ms) compared to baseline (both p less than 0.05). QT or QTc did not significantly increase thereafter. However, among the 30 patients who had less than 40 ms QTc prolongation at day 14 compared with baseline, 13 (43%) exceeded this limit on at least 1 of the following visits. Diltiazem did not significantly alter QT or QTc intervals. The absolute change in QTc interval from baseline observed after 14 days of bepridil therapy was inversely proportional to the baseline QTc interval (r = -0.68; n = 42; p less than 0.001). The degree of bepridil-induced QTc prolongation on day 14 correlated with pretreatment RR interval (r = 0.36; n = 42; p less than 0.02). In conclusion, chronic administration of bepridil but not of diltiazem prolongs ventricular repolarization in patients with angina pectoris. The overall effects of bepridil therapy on QT and QTc intervals can be assessed by an electrocardiogram recorded after 14 days of treatment but subsequent measurements may be required in individual patients. A short baseline QTc interval and a slow initial heart rate may be potentially useful predictors of a greater QTc prolongation with bepridil.

Effects of bepridil and CERM 4205 (ORG 30701) on the relation between cardiac cycle length and QT duration in healthy volunteers

Bepridil is a calcium antagonist that prolongs the duration of ventricular repolarization, whereas CERM 4205, another calcium antagonist, seems to be devoid of any effect on QT interval. The aim of this study was to compare the effects of bepridil and CERM 4205 on the QT-RR relation at different heart rates during rest and exercise and the results of pharmacologic tests designed to vary neurovegetative tone. Twelve healthy men (21 to 37 years) participated in a placebo-controlled, randomized, crossover, double-blind study and received either bepridil (200 mg/day twice daily) or CERM 4205 (200 mg/day twice daily), or matching placebo during three 14-day treatment periods at 2-week intervals. Bepridil, but not CERM 4205, caused a significant prolongation of resting QT interval. The RR-QT relation was monoexponential for all subjects during resting and exercising physiologic conditions and remained unchanged after 14 days with placebo or CERM 4205. Bepridil significantly shifted the relation upward, resulting in a rate-dependent QT prolongation that predominated during bradycardia. After isoprenaline, QT no longer adapted to changes in heart rate, whereas atropine resulted in a rate-dependent shortening in QT. These results suggest that bepridil and CERM 4205 exert different effects on ventricular repolarization, since only bepridil significantly prolonged QT duration. Bepridil-induced prolongation of QT increased at slow heart rates, which could explain the greater incidence of torsades de pointes in bradycardia.

Recent antiarrhythmic drugs

Clinical failure of antiarrhythmic drugs often occurs in practice. Therefore, there is a need for new, effective and long-acting drugs with a wide therapeutic range and a low level of toxicity. Most new class I compounds block the fast sodium ion inward current of myocardial cells. According to their effects on the recovery kinetics of the sodium ion channel, these drugs are classified into 3 groups: IA (intermediate--cibenzoline, pirmenol, hydroxy-3-S-dihydroquinidine, quinacainol); IB (fast--tocainide, moricizine); IC (slow--flecainide, encainide, propafenone, lorcainide, indecainide, recainam and penticainide). Class IC drugs greatly depress intracardiac conduction and are the most potent antiarrhythmic compounds able to suppress ventricular premature beats. However, it is doubtful that long-term suppression of ventricular arrhythmias will improve survival of the patients. Some new drugs have been developed belonging to other classes: class II, esmolol, a new ultrashort-acting beta blocker; class III, N-acetyl-procainamide and sotalol, which prolong duration of the action potential and increase ventricular refractoriness; class IV, the mixed sodium ion-calcium ion-potassium ion antagonist, bepridil. The pharmacologic properties and the clinical effects of these new antiarrhythmic drugs are reviewed. However, future therapeutic trends will depend on the results of large multicenter clinical secondary prevention trials such as the Cardiac Arrhythmia Suppression Trial. New antiarrhythmic drugs with original electrophysiologic profiles and minimal adverse effects must prove their ability not only to suppress arrhythmias but also to reduce sudden cardiac death rate.

Effects of the calcium entry blocker bepridil on repolarizing and pacemaker currents in sheep cardiac Purkinje fibres

(1) Effects of bepridil (0.3-100 mumol/l) on transmembrane currents which are active during the repolarization of the cardiac action potential were studied in sheep cardiac Purkinje fibres with the two-microelectrode voltage-clamp technique. Transmembrane currents were activated at a frequency of 0.03 Hz. (2) The initial inwardly rectifying current (iK1) was reduced by 1.8 mumol/l bepridil to 70% of the reference iK1-current in the absence of the drug. (3) An initial outward current, which is activated at positive membrane potentials (iinst) was depressed to 70% of reference by 14 mumol/l bepridil. (4) The time-dependent outward current (iK) was decreased by 1.8 mumol/l bepridil to 70% of its amplitude in the absence of bepridil. The biexponential time course of iK-current activation changed to be monoexponential with 100 mumol/l bepridil. The effect of bepridil on iK-current resulted in a shift of the activation curve of iK-current to more positive membrane potentials (10 mumol/l bepridil) and an additional decrease of driving force and/or conductance of the iK-channels with higher bepridil concentrations (100 mumol/l). (5) The transient outward current (ito) was completely blocked by 30 mumol/l bepridil. Inhibition to 70% of reference occurred with 1 mumol/l bepridil. The voltage-dependent inactivation of ito-current was affected by bepridil: the amplitude of the steady-state inactivation curve was reduced and ito-current was inactivated faster after application of bepridil. Bepridil caused no pronounced shift of the steady-state inactivation curve along the voltage axis.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bepridil on ventricular depolarization and repolarization of rabbit isolated hearts with particular reference to its possible proarrhythmic properties

1. Effects of bepridil on ventricular depolarization and repolarization sequences were examined in rabbit Langendorff-perfused hearts. 2. In distant bipolar electrograms (DBEs), bepridil, 10(-6) M, caused a significant prolongation of QT intervals. At 10(-5) M, the QT prolongation was further enhanced, and a significant prolongation of QRS duration was also observed. Polymorphous ventricular tachycardia was frequently induced by a single premature stimulus at the higher concentration. 3. In epicardial electrograms recorded through modified bipolar electrodes, bepridil, 10(-6) M, prolonged the interval from the peak negative deflection of the QRS complex to the apex of the T wave (Q-aT), which corresponded to the intracellular action potential duration at 90% repolarization (APD90). The Q-aT prolongation was larger in the base than in the apex, resulting in a marked distortion and dispersion of repolarization. The epicardial activation sequence was unaffected. 4. At 10(-5) M bepridil, the dispersion of repolarization was much more enhanced by activation delay in the epicardial surface. 5. These findings suggest that bepridil causes regionally different lengthening of APD in ventricular muscle leading to an increase in temporal dispersion of repolarization, and that this dispersion may be inducive for re-entrant arrhythmias when accompanied by slow conduction at toxic doses.

The antiarrhythmic effects of d-sotalol

The antiarrhythmic properties of d-sotalol were studied in 38 patients undergoing electrophysiologic studies. Programmed electrical stimulation studies were performed in 28 men and in 10 women with a mean age of 67 years and a mean ejection fraction of 37 +/- 3%. All patients had inducible ventricular tachycardia while they were off all antiarrhythmic therapy. D-sotalol was given as a 2 mg/kg infusion over 15 minutes and did not significantly change the PR, QRS, or QTc intervals from baseline values in the group as a whole. In the group protected by d-sotalol, the percent change in the QTc interval as well as the percent change in refractoriness was significantly increased as compared to the group not protected. D-sotalol also significantly decreased heart rate. D-sotalol prevented the induction of ventricular tachycardia in 18 of the 38 patients, while significantly slowing the rate of the ventricular tachycardia in the group that could still have tachycardia provoked. Seventeen patients were tested on procainamide and only four were protected, while d-sotalol prevented the induction of ventricular tachycardia in 7 of these 17. Eleven patients were discharged on oral d-sotalol doses ranging from 100 to 400 mg twice daily. One patient died 1 month post discharge due to an acute myocardial infarction, and one patient had a cardiac arrest while on d-sotalol and survived and was switched to amiodarone therapy. The remaining nine patients are alive and well at 14 +/- 3 months. D-sotalol appears to be an effective antiarrhythmic drugs and appears to be well tolerated.

Bepridil: a new long-acting calcium channel blocking agent

Bepridil is an investigational calcium channel blocking agent with antianginal activity that has a distinct and complex pharmacologic profile. Bepridil produces significant coronary vasodilation and modest peripheral effects, in addition to negative inotropic and chronotropic effects. Bepridil favorably modifies both myocardial oxygen demand and supply, supporting its use as an antianginal drug. Electrophysiologically, bepridil exhibits classes I, III, and IV antiarrhythmic activity. Five U.S. trials evaluating the short-term antianginal efficacy of bepridil collectively reported that bepridil causes significant improvement in both subjective and objective parameters of efficacy without depressing left ventricular function. In addition, one U.S. trial reported continued antianginal effects of bepridil after long-term use. There are limited data comparing and/or combining bepridil with other antianginal drugs, but the available information is promising. Limited information also exists on the use of bepridil in acute myocardial infarction and arrhythmias. Tolerance to bepridil therapy has been excellent, with the most common adverse effects being diarrhea and dizziness. It is unclear whether bepridil will be used as a first-line agent in the treatment of chronic stable angina pectoris; however, its long half-life, which makes once daily dosing possible, is certainly a significant advantage.

Bepridil hydrochloride for treatment of benign or potentially lethal ventricular arrhythmias

To define the efficacy and safety of a new once-a-day calcium antagonist, bepridil, 21 patients with frequent ventricular premature complexes (VPCs) underwent a 14-day inpatient monitored trial. After Holter monitoring during placebo administration, patients underwent 2 days of a loading dose of bepridil followed by 12 days of bepridil, 400 mg/day. Holter monitoring during therapy showed that 10 patients (48%) had more than a 70% reduction in VPC frequency and 8 of 16 patients (50%) at least a 95% reduction in frequency of nonsustained ventricular tachycardia. Gastrointestinal and central nervous system side effects considered to be mild occurred in 13 patients (62%). One patient had an asymptomatic increase in VPC frequency and another had sustained ventricular tachycardia associated with a loading dose of 900 mg of bepridil. Thus, bepridil has moderate antiarrhythmic efficacy in patients with ventricular arrhythmias, but further definition of its potential for causing proarrhythmia must be determined.

Comparison of verapamil and bepridil, two slow channel inhibitors, in protection against calcium-induced arrhythmias

Verapamil and bepridil share the common property of antagonizing the slow inward calcium-mediated current, but bepridil has some additional antiarrhythmic properties. The efficacy of these two compounds against CaCl2-induced arrhythmias has been compared in rats. CaCl2 was administered i.v. by continuous infusion until death (25 mg X kg-1 X min-1 or 40 mg X kg-1 X min-1) or by bolus injection (160 mg X kg-1). Bepridil (5, 10 mg X kg-1) or verapamil (2.5, 5 mg X kg-1) were injected 10 min before CaCl2. Bepridil (10 mg X kg-1) or verapamil (5 mg X kg-1) prolong the survival time during CaCl2 infusion. After pretreatment, the injection of 160 mg X kg-1 CaCl2 is less toxic: 25% of animals are protected by bepridil (5 mg X kg-1), 41% by bepridil (10 mg X kg-1) or verapamil (5 mg X kg-1). At death the myocardial Ca2+ level is not different in controls and pretreated animals, thus, the ratio myocardial Ca2+/total injected Ca2+ is significantly lowered by bepridil (10 mg X kg-1) or verapamil (5 mg X kg-1). The efficacy of the two drugs on this model appears related solely to inhibition of slow inward current despite the additional antiarrhythmic profile of bepridil.

Bepridil abolishes exercise-induced regional contractile dysfunction in dogs

The effects of bepridil, a calcium antagonist, on hemodynamic parameters and regional contractile function were investigated in six dogs trained to submit to five treadmill exercise cycles consisting of 4 min of running and 11 min of recovery. The animals were chronically instrumented with a microtip manometer in the left ventricle, two pairs of piezoelectric crystals for sonomicrometry and a hydraulic occluder around the circumflex branch of the left coronary artery and arterial and venous catheters. Experiments were started 1 week after surgery. After a warming-up exercise the vessel was partly stenosed by external filling of the hydraulic occluder. Stenosis was considered adequate and maintained when hemodynamic and functional parameters were virtually unchanged at rest, but episodes of comparable regional contractile dysfunction of the area perfused by the stenosed artery occurred in response to exercise in five subsequent runs; the same degree of stenosis was used for the experiments with bepridil. After two runs with comparable regional contractile dysfunction bepridil was infused intravenously at a dosage of 2 mg/kg per 5 min. The exercise-induced dysfunction was minimally improved in the 1st post-drug run but completely abolished during the 2nd and 3rd post-drug runs. This marked improvement may be partly attributable to the hemodynamic effects of this drug, namely a diminished increase in heart rate and left ventricular end-diastolic pressure and even a reduction in end-diastolic segment length during exercise. These results support the findings of initial clinical trials and suggest a beneficial effect of bepridil in the treatment of exercise-induced angina pectoris in man.

Effects of bepridil on the electrophysiologic properties of isolated canine and rabbit myocardial fibers

Bepridil hydrochloride is a relatively new calcium antagonist which appears to have a complex pharmacologic profile, but its concentration-response characteristics with respect to its electrophysiologic properties of varying concentrations (0.1 to 10.0 micrograms/ml) of the drug were therefore determined in rabbit and canine myocardial fiber preparations in vitro by standard microelectrode techniques. The following were measured: sinus cycle length (SCL), action potential amplitude (APA), maximum diastolic potential (MDP), threshold potential (TP), slope of phase 4 depolarization, action potential duration (APD), and dV/dtmax of phase O depolarization (Vmax) in rabbit sinoatrial (SA) node. Also measured were APA, membrane resting potential (MRP), Vmax, APD at 50% and 90% repolarization (APD50 and APD90), and effective refractory period (ERP) in rabbit atria and canine Purkinje fibers and ventricular muscle. At the lowest concentrations bepridil selectively prolonged SCL by reducing the slope of phase 4 and decreased APA and MDP in a concentration-dependent manner in the sinus node. At higher concentrations, bepridil exerted additional effects in producing concentration-dependent decreases in APA and Vmax in rabbit atria and in canine Purkinje fibers and ventricular muscle. During superfusion with 1.0 micrograms/ml bepridil, Vmax fell by 22.2% (p less than 0.05) in Purkinje fibers and by 11.8% (NS) in ventricular muscle; at 10.0 micrograms/ml, Vmax fell by 46.5% (p less than 0.01), respectively. The depression of Vmax was frequency dependent. There was a differential effect of bepridil on repolarization in Purkinje fibers as compared to that in ventricular muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic evaluation of the antiarrhythmic effects of N-acetylprocainamide for ventricular tachycardia secondary to coronary artery disease

Antiarrhythmic properties of N-acetylprocainamide (NAPA), an active metabolite of procainamide, were studied in 12 patients with coronary artery disease who presented with cardiac arrest or documented sustained ventricular tachycardia (VT). Programmed electrical stimulation (PES) studies were performed in 10 men and 2 women, aged 52 to 80 years (mean 63), who had a left ventricular ejection fraction of 16 to 69% (mean 33). All patients tested had inducible VT provoked by PES without antiarrhythmic therapy. Patients were then tested with procainamide, 1,000 mg administered intravenously. VT could be provoked after procainamide treatment in 8 of 10 patients. Twenty-four to 36 hours later NAPA was administered, 18 mg/kg body weight intravenously, and PES was performed after 20 minutes. NAPA did not significantly change heart rate, mean arterial blood pressure, electrocardiographic intervals and AH or HV conduction times. The QT interval lengthened, but not significantly. The mean serum NAPA levels were 15.7 +/- 4 micrograms/ml in the group protected by NAPA and 16.2 +/- 4 micrograms/ml in the group not protected by NAPA. Five patients were discharged with NAPA therapy, 1.5 g orally every 8 hours. Two patients have been maintained with chronic NAPA therapy (10 +/- 3 months), and 2 patients had breakthrough VT on follow-up Holter monitoring and alternative therapy was given. One patient died while taking oral therapy. NAPA demonstrates antiarrhythmic efficacy in preventing induction of VT by PES in a high-risk group of patients. During chronic oral therapy in some patients, NAPA appears to be well tolerated, with antiarrhythmic efficacy that may be enhanced with further upward dose titration.