Pharmacological mapping of regional effects in the rabbit heart of some new antiarrhythmic drugs

Pharmacogenetic interactions between Angiotensin-converting enzyme insertion/deletion polymorphism and response to cibenzoline in patients with hypertrophic obstructive cardiomyopathy

Cibenzoline, a Class I antiarrhythmic agent, can attenuate the left ventricular pressure gradient (LVPG) in patients with hypertrophic obstructive cardiomyopathy (HOCM). An association between the insertion/deletion polymorphism of the angiotensin-converting enzyme (ACE) gene and the progression of left ventricular hypertrophy in patients with hypertrophic cardiomyopathy has been reported. The aim of this study was to investigate the pharmacogenetic interactions between the ACE insertion/deletion polymorphism and the response to cibenzoline in patients with HOCM. Twenty-four patients with HOCM participated in this study. The LVPG and left ventricular function were measured by echocardiography before and 2 hours after administration of a single oral dose of 200 mg cibenzoline. The ACE insertion/deletion polymorphism was genotyped. The frequencies of the genotypes D/D, D/I, and I/I were 16%, 42%, and 42%, respectively. Before administration of cibenzoline, the LVPG was higher in patients with the D allele than in those without it (105 +/- 47 mm Hg versus 64 +/- 24 mm Hg, P = 0.0195). After administration of cibenzoline, the LVPG significantly decreased to 41 +/- 27 mm Hg in those with the D allele (P = 0.0001) and to 33 +/- 24 mm Hg in those without it (P = 0.0003). The LVPG in patients with the D allele was significantly decreased by cibenzoline when compared with patients without the allele (64 +/- 45 mm Hg versus 31 +/- 17 mm Hg, P = 0.038). Patients with HOCM with the ACE D allele had a high LVPG. Cibenzoline was more effective in patients with HOCM with the ACE D allele.

Cibenzoline attenuates systolic anterior motion of the mitral valve after mitral valvoplasty

We report a patient in whom severe hemodynamic instability occurring after mitral valvoplasty (MVP) was successfully treated with cibenzoline. Left ventricular outflow tract obstruction (LVOTO) with mitral regurgitation (MR) resulting from the systolic anterior motion (SAM) of the mitral valve that occurs after MVP often leads to hemodynamic collapse. Patients who develop SAM after MVP have been managed with intravenous volume loading, reduction/discontinuation of inotropic drugs, and with increased afterload, but these strategies were often ineffective. Cibenzoline decreased myocardial contraction, attenuated SAM, and improved hemodynamics in our patient. We recommend that cibenzoline be administered before further surgical manipulation is considered for patients who develop SAM after MVP.

Effect of cibenzoline on regional left ventricular function in hypertrophic obstructive cardiomyopathy

BACKGROUND

Cibenzoline, a class Ia antiarrhythmic drug, can be used to relieve left ventricular (LV) outflow obstruction in hypertrophic obstructive cardiomyopathy (HOCM). However, the mechanism of this agent in HOCM has been controversial.

HYPOTHESIS

This study was designed to investigate the effect of cibenzoline on regional LV function and the acoustic properties in HOCM using ultrasonic integrated backscatter.

METHODS

Ten patients with HOCM and 16 healthy volunteers were examined. In patients with HOCM, wall thickening (%WT) and the magnitude of cyclic variation of integrated backscatter (mag-CVIBS) in the interventricular septum (IVS) and LV posterior wall were measured before and after oral administration of cibenzoline. To assess asynchrony of contractile elements, the phase difference between CVIBS and %WT were measured from the LV posterior wall. Pressure gradients at the LV outflow tract were estimated using continuous-wave Doppler echocardiography.

RESULTS

Although %WT decreased significantly in the LV posterior wall, %WT and mag-CVIBS remained unchanged in the IVS. The phase difference in the LV posterior wall was significantly greater in patients with HOCM than in healthy volunteers (HOCM:healthy volunteers, 1.57 +/- 0.23:1.00 +/- 0.03, p < 0.001) at baseline. After administration of cibenzoline, the phase difference shifted to normal value (from 1.57 +/- 0.23 to 1.28 +/- 0.27, p = 0.0382), and pressure gradients at the LV outflow tract decreased (from 109 +/- 55 to 58 +/- 48 mmHg, p = 0.0063). Changes in pressure gradients at the LV outflow tract and the phase difference were closely related.

CONCLUSIONS

Regional function and the acoustic properties of myocardium in HOCM were altered by cibenzoline in the LV posterior wall but remained unchanged in the IVS. The normalization of the phase difference in the LV posterior wall was closely related to the decrease in pressure gradients at the LV outflow tract. These findings suggest that negative inotropic action and the improvement of asynchrony in the LV posterior wall rather than in the IVS may contribute to the reduction of pressure gradients at the LV outflow tract in HOCM.

Cibenzoline attenuates upregulation of Kv1.5 channel gene expression by experimental paroxysmal atrial fibrillation

Antiarrhythmic drugs exert their effects by inhibiting the ion channels of cardiomyocytes. However, these effects could also modify the ionic environment around them, and thereby affect the expression of ion channels, leading to biochemical enhancement or attenuation of the antiarrhythmic effects. To test this hypothesis, the physiological and biochemical effects of cibenzoline were evaluated in a rapid atrial pacing model in rats. In rats with rapid atrial pacing, pretreatment with cibenzoline significantly inhibited the increases in Kv1.5 mRNA at 2 hours and immunoreactive protein at 4 hours by 35 +/- 15% and 30 +/- 10%, respectively. These effects were observed only in the rapid atrial pacing group, not in the sham-operated group. With cibenzoline pretreatment, 4-hour rapid atrial pacing resulted in significant prolongation of the atrial refractory period compared to the untreated group even after removal of cibenzoline. In contrast, the sham and rapid atrial pacing model with and without cibenzoline pretreatment showed similar acute physiological responses to cibenzoline. In conclusion, in addition to the acute physiological effects, pretreatment with cibenzoline exerted pleiotropic effects of inhibition of Kv1.5 channel upregulation by rapid pacing, implying differences in the cibenzoline effects when administered before and after onset of paroxysmal atrial fibrillation.

Cardiovascular effects of optical isomers of cibenzoline, assessed in the canine isolated, blood-perfused papillary muscle and sinoatrial node preparations

A clinically available racemic mixture of the optical isomers of cibenzoline possesses a potent sodium channel-blocking action in addition to the moderate calcium channel-blocking action. It has been reported that the S(-)-isomer inhibits sodium channels more potently than calcium channels, whereas the R(+)-isomer suppresses the sodium channels as well as calcium channels, and that the calcium channel-blocking potency of these isomers is similar. This study was designed to assess the effects of each optical isomer of cibenzoline on ventricular contraction, coronary blood flow, and sinus node automaticity by using the canine isolated, blood-perfused papillary muscle and sinoatrial node preparations. Each isomer showed negative inotropic and chronotropic effects as well as coronary vasodilator action in a dose-dependent manner. The negative inotropic effect of S(-)-cibenzoline was 1.8 times more potent than that of R(+)-cibenzoline, whereas there was no significant difference between the isomers in the negative chronotropic and coronary vasodilator effects. These results suggest that the difference of the inotropic effects between the optical isomers of cibenzoline is mainly derived from the extent of the sodium channel-blocking action, whereas the vasodilator and negative chronotropic effects may chiefly depend on the calcium channel inhibition.

Profiles of aprindine, cibenzoline, pilsicainide and pirmenol in the framework of the Sicilian Gambit. The Guideline Committee for Clinical Use of Antiarrhythmic Drugs in Japan (Working Group of Arrhythmias of the Japanese Society of Electrocardiology)

The Vaughan Williams classification has been used widely by clinicians, cardiologists and researchers engaged in antiarrhythmic drug development and testing in many countries throughout the world since its initial proposal in the early 1970s. However, a major criticism of the Vaughan Williams system arose from the extent to which the categorization of drugs into classes I-IV led to oversimplified views of both shared and divergent actions. The Sicilian Gambit proposed a two-dimensional tabular framework for display of drug actions to solve these problems. From April to December 1996, members of the Guideline Committee met to discuss pharmacologic profiles of 4 antiarrhythmic drugs (aprindine, cibenzoline, pilsicainide, and pirmenol) that were not included in the original spreadsheet but are used widely in clinical practice in Japan. The discussion aimed to fit the drug profiles into the Gambit framework based on all the important literature published to date regarding the actions of the 4 drugs. This report is a summary of that deliberation.

Na+ channel blocking effects of cibenzoline on guinea-pig ventricular cells

The effects of cibenzoline on transmembrane action potentials were examined in right ventricular papillary muscles and in single ventricular myocytes isolated from guinea-pig hearts. In papillary muscles, cibenzoline > or = 3 microM caused a significant decrease in the maximum upstroke velocity (Vmax) of the action potential without affecting the action potential duration. The inhibition of Vmax was enhanced at higher stimulation frequencies. In the presence of cibenzoline, trains of stimuli at rates > or = 0.2 Hz led to a use-dependent inhibition of Vmax. The time constant for Vmax recovery (tauR) from the use-dependent block was 26.2 s. The use-dependent block of Vmax with cibenzoline was enhanced and tauR was shortened when the resting potential was depolarized by high (8, 10 mM) [K+]o. The curve relating membrane potential and Vmax in single myocytes was shifted by cibenzoline (10 microM) in a hyperpolarizing direction by 7.1 mV. In myocytes treated with cibenzoline (10 microM), a 10-ms conditioning clamp to 0 mV caused a significant decrease in Vmax of the subsequent test action potential; the Vmax inhibition was enhanced modestly in association with a prolongation of the 0 mV clamp pulse duration. In the presence of cibenzoline (3 microM), application of a train of depolarizing pulses (10 ms, 200 ms) to myocytes from the resting level (-80 mV) to 0 mV resulted in a progressive Vmax reduction in a pulse number-dependent manner. Unlike glibenclamide (30 microM), cibenzoline (10 microM) did not prevent the hypoxia-induced shortening of action potential duration in papillary muscles. These findings indicate that the onset and offset kinetics of use-dependent Na+ channel block by cibenzoline are slow. Given its state dependence, cibenzoline may be a blocker of activated Na+ channels. The inhibitory action of this compound on the ATP-sensitive K+ current (I(K), ATP) would be minimal or negligible at concentrations causing sufficient Na+ channel block.

Class Ia antiarrhythmic drug cibenzoline: a new approach to the medical treatment of hypertrophic obstructive cardiomyopathy

BACKGROUND

The class Ia antiarrhythmic drug disopyramide relieves the outflow tract obstruction of hypertrophic obstructive cardiomyopathy (HOCM). Disopyramide, however, has several adverse effects, such as dysuria and thirst, resulting from its anticholinergic activity. A new class Ia antiarrhythmic drug, cibenzoline, has little anticholinergic activity. The aim of this study is to elucidate whether cibenzoline attenuates left ventricular pressure gradient (LVPG) in patients with HOCM.

METHODS AND RESULTS

Ten patients with HOCM (mean age, 59+/-12 years) participated in this study. LVPG and left ventricular functions were measured before and 2 hours after administration of a single oral dose of 150 or 200 mg cibenzoline. LVPG decreased from 123+/-60 to 39+/-33 mm Hg (P=.0026). The E/A ratio in transmitral Doppler flow increased from 1.20+/-0.84 to 2.00+/-1.72 (P=.029). Isovolumic relaxation time increased from 73+/-16 to 101+/-23 ms (P=.0026). Left ventricular diastolic dimension remained unchanged, but left ventricular systolic dimension enlarged significantly, from 21.6+/-2.4 to 26.2+/-3.3 mm (P=.0004). Fractional shortening decreased from 47.6+/-6.1% to 34.6+/-8.8% (P=.0007). Left ventricular ejection time index decreased significantly, and preejection period index increased in all the patients. Decreased LVPG remained maintained even in the long-term treatment with cibenzoline. Conclusions These results indicate that cibenzoline can markedly attenuate LVPG in patients with HOCM. A decrease in myocardial contractility seems to be closely related to a marked decrease in LVPG.

Electrophysiologic effects of a class I antiarrhythmic agent, cibenzoline, on the refractoriness and conduction of the human atrium in vivo

We investigated the effects of a class I antiarrhythmic drug, cibenzoline, on human atrial muscle in vivo. Electrophysiologic measurements were performed in 44 patients (mean age 49 +/- 15 years), before and after an intravenous infusion of cibenzoline 1.4 mg/kg in 5 min. Extrastimuli at a basic cycle length (BCL) of 500 ms were delivered from the right atrial appendage. The effective refractory period of the right atrium (ERP-A), the conduction time from the high right atrium to the coronary sinus, maximum conduction delay (Max. CD), repetitive atrial firing zone (RAFZ), fragmented atrial activity zone (FAAZ), and conduction delay zone (CDZ) were measured. Patients were divided into two groups according to whether repetitive atrial firing (RAF) was induced (group A, n = 18) or not (group B, n = 26). Cibenzoline increased ERP-A from 198 +/- 25 to 214 +/- 26 ms (p < 0.05) and decreased Max. CD from 55 +/- 23 to 43 +/- 19 ms (p < 0.05). There were significant decreases in the RAFZ (10 +/- 17 to 4 +/- 10 ms, p < 0.05), the FAAZ (20 +/- 25 to 12 +/- 18, ms p < 0.05), and the CDZ (41 +/- 21 to 32 +/- 19 ms, p < 0.05). Cibenzoline significantly increased ERP.A (186 +/- 25 to 212 +/- 26 ms, p < 0.05) in group A, but not in group B. There were significant decreases in the RAFZ [25 +/- 19 to 9 +/- 15 ms (p < 0.05) and FAAZ 22 +/- 29 to 11 +/- 21 ms, (p < 0.05)] in group A, but not in group B. The results suggest that cibenzoline can suppress paroxysmal atrial fibrillation by prolongation of ERP-A and may also have preferential effects on the substrate of atrial fibrillation and RAF.

Comparison of the cromakalim antagonism and bradycardic actions of a series of novel alinidine analogues in the rat

Alinidine, and eight derivatives, were synthesized and tested for their ability to antagonise the actions of the K+ channel opener cromakalim in rat thoracic aorta, and for their ability to induce bradycardia in rat isolated spontaneously beating right atria. Ring segments of rat thoracic aorta were suspended in organ baths to record isometric tension. Tissues were precontracted with K+ (20 mM), and full concentration-relaxation curves constructed to cromakalim (0.01-30 microM) in the absence and presence of increasing concentrations of alinidine/derivative. The majority of the compounds tested caused rightward shifts in the cromakalim concentration-effect curves. Rat spontaneously beating right atria were suspended in organ baths to record rate of contraction. Addition of alinidine/derivative caused a concentration-dependent negative chronotropic response. In terms of structure-activity relationships, increasing the length of the N-allyl side-chain on the alinidine molecule (from 3 carbon (3C), to 5C) resulted in a significant increase in the activity of the compounds as both bradycardic agents and cromakalim antagonists. The most potent compounds in both cases (bradycardic agent and cromakalim antagonist) had no double bond in the side chain. The results suggest that the carbon side-chain influences the activity of alinidine-related compounds both as cromakalim antagonists and as bradycardic agents. However, while similar structure-activity relationships appear to apply for both effects in some instances, there was no significant correlation between the two actions of the alinidine analogues. The results suggest that the ability of alinidine-derivatives to induce bradycardia or to block K+ channels opened by cromakalim can be differentiated on the basis of structure.

Effects of hypoxia on the use-dependent inhibition of conduction velocity induced by cibenzoline in guinea pig ventricular myocardium

The use-dependent effects of cibenzoline, a new anti-arrhythmic drug, on the maximal rate of rise (Vmax) of the action potential and on conduction velocity, and their corresponding recovery kinetics were studied in isolated papillary muscles of guinea pigs under normal and hypoxic conditions. Standard microelectrode techniques were applied to monitor the action potential of the muscles and their conduction. Under control conditions, the amount of use-dependent block of Vmax, conduction velocity, and square of conduction velocity, induced by 10 mumol/L cibenzoline were 26.5 +/- 3.9, 13.8 +/- 1.4, and 25.6 +/- 2.4%, respectively; under hypoxic conditions, these values increased to 32.3 +/- 4.8, 19.7 +/- 1.2, and 35.5 +/- 2.0%, respectively. In the presence of 10 mumol/L cibenzoline, the mean values of time constants for the onset of the use-dependent inhibition of Vmax, conduction velocity, and the square of conduction velocity, during a 2-Hz stimulation, were 3.65 +/- 0.27, 2.77 +/- 0.33, and 2.56 +/- 0.26 seconds, respectively. Under hypoxic conditions, these values changed to 5.10 +/- 0.96, 3.05 +/- 0.44, and 2.84 +/- 0.39 seconds, respectively. The recovery time constants averaged 14.72 +/- 4.08 seconds (for Vmax), 22.23 +/- 3.78 seconds (for conduction velocity), and 23.17 +/- 13.38 seconds (for the square of conduction velocity) in the presence of 10 mumol/L cibenzoline, and 17.19 +/- 8.59 seconds (for Vmax), 15.77 +/- 2.37 seconds (for conduction velocity), and 16.82 +/- 2.61 seconds (for the square of conduction velocity) under hypoxic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Cibenzoline. A review of its pharmacological properties and therapeutic potential in arrhythmias

Cibenzoline is a class I antiarrhythmic drug with limited class III and IV activity which can be administered orally or intravenously. An elimination half-life of about 8 to 12 hours permits twice daily administration, although age and renal function must be considered when determining dosage. Cibenzoline has some activity in ventricular and supraventricular arrhythmias, including drug-refractory ventricular tachycardia or ventricular arrhythmias following recent acute myocardial infarction, although results in patients with sustained ventricular tachycardia are less promising. In comparative trials, cibenzoline has demonstrated efficacy similar to or better than that of a variety of other class I antiarrhythmic drugs and was at least as well tolerated, with a more convenient dosage schedule. However, further studies to clarify the proarrhythmic effects of cibenzoline and its use in patients with impaired left ventricular function are required, and the use of cibenzoline (and other class I antiarrhythmic agents) in patients with other than potentially lethal ventricular arrhythmias should be avoided following the results of the CAST studies. Thus, cibenzoline is an effective antiarrhythmic agent with a favourable pharmacokinetic profile that may be considered with other class I drugs in patients requiring therapy for high risk arrhythmias.

Anesthetized rabbit as a model for ischemia- and reperfusion-induced arrhythmias: effects of quinidine and bretylium

Experiments were performed to assess the feasibility of using anesthetized rabbits for the study of ischemia- and reperfusion-induced arrhythmias. Initial studies indicated that occlusion of the left anterior descending coronary artery produced ectopic activity in only one out of eight rabbits. All rabbits subject to occlusion of the left circumflex artery below where it emerges from under the left atrial appendage had ECG changes (ST-segment elevation, Lead II), 80% had arrhythmias, and 50% died in ventricular fibrillation during the first 20 min of coronary artery occlusion. Subsequent reperfusion in the survivors produced further arrhythmias in the majority of rabbits, and one fibrillated. Although a high incidence of ectopic activity was also observed in rabbits subject to occlusion of the left circumflex artery close to its origin, or both the left anterior descending and circumflex arteries, this was accompanied by marked reductions in arterial blood pressure. Thus, occlusion of the left circumflex artery at the lower site was chosen for all further studies. Quinidine hydrochloride 10 mg kg-1 (n = 10) or bretylium tosylate 20 mg kg-1 (n = 10) administered 15 min prior to coronary artery occlusion reduced the incidence of ischemia-induced ventricular fibrillation to 10% compared with 60% in controls (n = 15). Although bretylium reduced arterial blood pressure and heart rate, neither drug altered the hemodynamic consequences of coronary artery occlusion (e.g., increased left ventricular end diastolic pressure). Bretylium at doses of 5 and 20 mg kg-1, but not quinidine, reduced the ST-segment elevation that developed during the ischemic period. The ability to detect the antifibrillatory activity of quinidine and bretylium suggests that the anesthetized rabbit may provide a useful alternative or additional model for the study of arrhythmias induced by acute myocardial ischemia.

Effects of short-term ketanserin treatment on the QT interval and vagal function in healthy subjects

1. The serotonergic type-2 (5HT2) antagonist ketanserin was given in a dose of 40 mg twice daily for 3 days to eight healthy subjects in a double-blind placebo controlled randomized crossover study. 2. The QTc interval was prolonged slightly but significantly (P less than 0.01) by a mean of 29 +/- 7 milliseconds after ketanserin compared to placebo. 3. Ketanserin reduced both mean arterial pressure and heart rate (P less than 0.05), by 5.7 +/- 1.8 mmHg and 3.5 +/- 1.5 beats minute-1 respectively, when compared to placebo. 4. There was a tendency (not statistically significant) for cardiac vagal outflow to be reduced after ketanserin (assessed by the heart rate responses to standing, deep breathing and the Valsalva manoeuvre). 5. In healthy man, ketanserin causes prolongation of the QTc interval and a reduction in heart rate. These changes do not appear to be due to enhanced cardiac parasympathetic activity.

The effects of the 5 HT2 antagonist ritanserin on blood pressure and serotonin-induced platelet aggregation in patients with untreated essential hypertension

We have given the selective 5 HT2 antagonist ritanserin in a dose of 10 mg twice daily for 4 weeks in a double-blind, randomized, placebo-controlled, parallel group study of 18 patients with untreated essential hypertension. The fall in single platelet count due to 5 HT-induced platelet aggregation was significantly reduced by ritanserin compared with placebo (p less than 0.05). There were no significant changes in supine or erect blood pressure or heart rate after ritanserin compared to placebo. Forearm blood flow, measured by mercury-in-strain gauge venous occlusion plethysmography, was not significantly altered by ritanserin. Ritanserin caused prolongation of the QTc interval by 41 (SEM 11) ms (p less than 0.05 compared to placebo) but had no detectable effect on QRS duration, features suggestive of Class III antiarrhythmic activity. These findings do not support an independent role of the 5 HT2 receptor in maintaining raised arterial pressure in essential hypertension.

Evaluation of dosing interval and optimum dose of cibenzoline

Fifteen patients with ventricular premature complexes (VPCs) were included in this open study designed to assess the relative efficacy of bid (two times daily) and tid (three times daily) dosing regimens for cibenzoline as compared with qid (four times daily) administration. Patients started therapy with qid administration; this was followed in sequence by tid and bid administration at the maximum effective total daily dose determined during the qid administration. Of the nine patients evaluated for efficacy for suppression of VPCs, eight demonstrated a 75% or greater suppression of VPCs with cibenzoline administered qid (total daily dose of 130-325 mg). This effectiveness was maintained in four patients with a bid regimen and in three with a tid regimen. All four patients who had ventricular tachycardia (VT) had a decrease in the number of VT episodes while receiving cibenzoline (only one of these patients had satisfactory suppression of VPCs at the same dosage regimen). Twelve patients continued to receive extended therapy with cibenzoline for up to two years, as this was considered to be the optimum antiarrhythmic treatment for these patients. Two patients had to be removed from the study and two had the dosage lowered because of adverse reactions (dry mouth, blurred vision, dizziness, congestive heart failure) although in one instance, the congestive heart failure was subsequently considered to be unrelated to cibenzoline. One patient was able to complete the short-term phase of the trial, but was not given extended treatment because of persistent dry mouth. Two patients had treatment discontinued during the extended therapy phase because of adverse reactions (fever, nausea, vomiting, asthenia).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of cibenzoline, a class I antiarrhythmic drug, on action potential in canine ventricular muscle

Effect of cibenzoline, a class I (local anesthetic-type) antiarrhythmic drug, was investigated upon canine ventricular muscle using a conventional micro-electrode method. In the presence of cibenzoline at the concentration of 3 X 10(-6) M or higher, the maximum rate of rise of the action potential was inhibited and the action potential duration was lengthened significantly in a concentration-dependent manner. The effective refractory period was also prolonged. From its effect on the action potential duration, cibenzoline should belong to Ia, according to the Vaughan Williams classification of antiarrhythmic agents. On the other hand, cibenzoline inhibition of the maximum rate of depolarization was greater with an increase in stimulation frequency (a use-dependent block). In the presence of cibenzoline concentrations of 3 X 10(-6) M and 8 X 10(-6) M, which blocked the maximum rate of depolarization by 36% and 67% at 180 beats/min, the rates of onset of inhibition of the maximum rate of depolarization were 0.109 +/- 0.027 and 0.146 +/- 0.070 AP-1 (mean +/- S.D.), respectively. From the kinetics of inhibition of the maximum rate of depolarization, these results suggest that cibenzoline should be classified as an intermediate drug with the prolongation of the action potential duration.

Clinical electrophysiology, efficacy and safety of chronic oral cibenzoline therapy in refractory ventricular tachycardia

The electrocardiographic (ECG) and electrophysiologic (EP) effects, clinical efficacy and safety of oral cibenzoline therapy were evaluated using a twice-daily dosing regimen in patients with refractory ventricular tachycardia (VT). Twenty patients underwent EP studies in the control (drug-free) state and after cibenzoline therapy using an incremental dose-titration protocol. Oral cibenzoline (2.4 to 5.8 mg/kg/day) was administered in doses of 130, 160 or 190 mg at 12-hour intervals. ECG and EP variables, 24-hour ambulatory ECG monitoring and programmed electrical stimulation studies were obtained in the control state and after 11 +/- 4 days of cibenzoline therapy. Cibenzoline therapy prolonged the mean PR interval (from 179 +/- 29 to 201 +/- 36 ms, p less than 0.001), the mean QRS duration (from 107 +/- 21 to 130 +/- 25 ms, p less than 0.001), and the mean QTc interval (from 422 +/- 25 to 460 +/- 42 ms, p less than 0.001). It increased the mean HV interval (from 50 +/- 17 to 65 +/- 20 ms, p less than 0.01) and mean right ventricular effective refractory period (from 245 +/- 24 to 266 +/- 27 ms, p less than 0.01). After cibenzoline therapy, 5 patients (25%) had suppression of inducible sustained VT during programmed electrical stimulation. High-degree atrioventricular block occurred in 2 patients. Chronic cibenzoline therapy (mean follow-up 24 +/- 3 months) remained effective in long-term suppression of VT in 4 patients. Two patients had to discontinue therapy because of gastrointestinal intolerance. Cibenzoline is effective in suppression of refractory VT in selected patients using a twice-daily dosing schedule.

Inhibition of the myocardial Ca2+ inward current by the class 1 antiarrhythmic agent, cibenzoline

Cibenzoline, a class 1 (local anaesthetic-type) antiarrhythmic drug, was investigated for possible effects upon the myocardial Ca2+ inward current. In voltage-clamp experiments with isolated cardiac myocytes of guinea-pig, cibenzoline caused a concentration-dependent inhibition of the Ca2+ current, with an IC50 of 14 microM. Inhibition of the Ca2+ current by cibenzoline (2 microM) was dependent upon stimulation frequency, with a greater block occurring at 2 Hz (approximately 50%) than at 0.2 Hz (approximately 15%). The magnitude of Ca2+ current block was also potential-dependent. A markedly greater inhibition by cibenzoline (20 microM) was recorded when myocytes were depolarized (to +20 mV) from a holding potential of -35 mV than of -80 mV. At the less negative potential, cibenzoline also caused a reduction in the level of the holding current, which suggests a decrease in the inwardly rectifying K+ current. Cibenzoline also caused a concentration-dependent inhibition of KCl-induced contractures of isolated aortic strips of the rat (IC50 = 55 microM) and a reduction in contractile force of isolated, electrically-stimulated papillary muscles of the guinea-pig (IC50 = 35 microM). Thus, cibenzoline possesses Ca2+ channel blocking (class 4) properties in addition to its local anaesthetic actions.

Effects on rabbit cardiac potentials of aprindine and indecainide, a new antiarrhythmic agent, in normoxia and hypoxia

Intracellular potentials were recorded from rabbit atria, cardiac Purkinje cells and papillary muscles before and after exposure to various concentrations of indecainide. The effects of aprindine also were studied in the atrial preparations. Both drugs depressed the maximum rate of depolarization (MRD) in a dose-related manner, indecainide being approximately ten times more potent than aprindine. Aprindine caused a dose-related bradycardia, but indecainide had no significant effect on sinus node frequency. Indecainide had a dose-related negatively inotropic effect in normal, half-normal and twice-normal extracellular calcium concentrations. Indecainide shortened action potential duration (APD) in atrium and Purkinje cells but prolonged APD to 50% repolarization in ventricular muscle. The actions of indecainide were extremely persistent. No significant recovery of MRD was observed after pauses in stimulation of up to 16 s. Indecainide had no effect on effective refractory period (ERP) measured by interpolated premature stimuli. Indecainide is therefore categorized as a Class 1c antiarrhythmic agent. The effects of both aprindine and indecainide on MRD were increased in hypoxic atria. Conduction velocity in hypoxic atria exposed to indecainide was greater than in controls, however, suggesting the possibility of improved cell-to-cell coupling.

Antiarrhythmic effects of cibenzoline

Thirty-three patients with ventricular tachyarrhythmias were referred for evaluation of their arrhythmias using programmed electrical stimulation to guide antiarrhythmic therapy. Cibenzoline succinate, a new antiarrhythmic agent, was compared to procainamide in patients with ventricular tachycardia. Cibenzoline was given intravenously, initially 1.0 mg/kg, then in 1 mg/kg increments to a maximum of 3.0 mg/kg, during electrophysiologic testing. The results were compared to procainamide, which was also administered intravenously to 1000 and then to 1500 mg. Cibenzoline provided protection against ventricular tachycardia induction in 16 of 33 patients. The PR interval increased 13%, QRS duration widened 26%, and QTc interval was prolonged by 7%. There was a 9% fall in mean arterial blood pressure. Procainamide prevented ventricular tachycardia induction in 21 out of 31 patients tested. The PR interval increased 11%, QRS duration widened 27%, and QTc interval prolonged by 8%. Cibenzoline was given orally to 13 patients for chronic treatment. Chronic oral cibenzoline therapy after a mean follow-up of 8.8 months caused a reduction of ventricular ectopy from 666 to 190 beats/hr. Ventricular tachycardia events decreased per Holter monitor recording from 6 to 0.6. Cibenzoline therapy was discontinued in 5 of 13 patients due to break-through arrhythmias (nonsustained ventricular tachycardia on Holter monitor and recurrence of symptoms). Cibenzoline may be an effective antiarrhythmic agent in selected patients.

Indoramin-prolongation of repolarization time, a mechanism of bradycardia in man?

The effect of indoramin, a selective alpha 1-adrenoceptor antagonist, on ECG time intervals in normal man was studied. Significant prolongation of QTc was observed after indoramin 100 mg, with no change in QRS duration. In addition, the slope of the RR/QT relationship was changed by indoramin 100 mg. These results suggest that indoramin may have Class III antiarrhythmic activity. If such activity were to affect the SA node, it may explain at least in part the observed lack of reflex tachycardia after indoramin administration.

The efficacy of cibenzoline in preventing PES induction of ventricular tachycardia in the dog

The electrophysiologic effects of cibenzoline were studied using programmed electrical stimulation (PES) techniques and were compared to those of quinidine. Cibenzoline, like the conventional class 1 agent quinidine, was effective in preventing arrhythmia induction. Twelve dogs were given 0.02 mg/kg digoxin intravenously for seven days to achieve a steady-state digoxin level. On the eighth day, cibenzoline was administered in incremental doses (0.5 to 10.5 mg/kg) and PES was performed at 30-minute intervals. A mean dose of 2.6 +/- 0.8 mg/kg cibenzoline prevented ventricular tachycardia induction. At this dose, cibenzoline had no significant effect on mean arterial blood pressure, but PR interval increased by 17 +/- 9 per cent, QRS duration by 27 +/- 14 per cent, and the ventricular refractory period (ERP) for the first extra stimulus increased by 35 +/- 9 per cent. A gradual decrease in heart rate and an increase in PR interval and QRS duration was caused by incremental doses of cibenzoline. In six additional animals, quinidine was administered in incremental doses (1 to 30 mg/kg) and PES performed at 30-minute intervals. A mean of 15 +/- 5 mg/kg prevented induction of ventricular tachycardia in five animals. No significant change in heart rate, PR, QRS, and ERP was found at the effective dose.

An investigation into the characteristics of reperfusion-induced arrhythmias in the anaesthetized rat and their susceptibility to antiarrhythmic agents

Reperfusion-induced arrhythmias were elicited in the pentobarbitone-anaesthetized rat by occlusion of the left main coronary artery and subsequent release. These arrhythmias were rapid in onset, occurring within 20 s after release of the ligature, and were of short duration (1-2 min). Their severity was dependent upon the duration of the preceding occlusion. A 5 or 15 min occlusion period produced the most severe arrhythmias on release, the incidence of ventricular fibrillation being 56 and 50% respectively. Evidence that reperfusion had occurred was provided by fluorescein dye distribution and intramyocardial temperature studies. The severity of reperfusion arrhythmias and mortality was unaffected by bilateral vagotomy, beta-adrenoceptor blockade by atenolol (2 mg kg-1 i.v.) or a combination of the two. The incidence of reperfusion-induced ventricular fibrillation was significantly reduced by Org 6001 (which blocks the fast inward sodium current), melperone (which acutely prolongs the cardiac action potential duration) and bepridil (which blocks both fast and slow inward currents). It was unaffected by nitroglycerine and the calcium antagonists verapamil, prenylamine and nifedipine. We have shown that reperfusion-induced cardiac arrhythmias can be consistently elicited in the anaesthetized rat and that they are particularly susceptible to drugs that can block the fast inward sodium current.