Electrophysiologic effects of bepridil in the anesthetized dog studied by endocardiac electrodes

Effects of bepridil versus E-4031 on transmural ventricular repolarization and inducibility of ventricular tachyarrhythmias in the dog

BACKGROUND

Bepridil (a multiple channel blocker) may markedly prolong the QT interval and induce polymorphic ventricular tachyarrhythmias (VTA). We compared the transmural ventricular repolarization characteristics and inducibility of polymorphic VTA after administration of bepridil versus the pure I(Kr) blocker, E-4031, each administered to five open-chest dogs.

METHODS

We used plunge needle electrode to record transmural left ventricular (LV) repolarization and activation-recovery interval (ARI) to estimate local repolarization. The correlation between paced cycle length and ARI was separately examined in the LV endocardium, mid-myocardium (Mid), and epicardium. Attempts to induce VTA were made during bradycardia and sympathetic stimulation.

RESULTS

Bepridil and E-4031 prolonged QT interval and ARI in all LV layers, though the magnitude of prolongation was greatest in Mid, increasing the transmural ARI dispersion, particularly during bradycardia. Compared with E-4031, bepridil caused mild, reverse use-dependent changes in ventricular repolarization, and less ARI dispersion than E-4031 during slow ventricular pacing. Both drugs increased ARI(max) and cycle length at 50% of ARI(max), though the changes were smaller after bepridil than after E-4031 administration. Bradycardia after the administration of each drug induced no VTA; however, sympathetic stimulation induced sustained polymorphic VTA in two of five dogs treated with E-4031 versus no dog treated with bepridil.

CONCLUSIONS

Unlike the pure I(kr) blocker, E-4031, bepridil exhibited weak properties of reverse use-dependency and protected against sympathetic stimulation-induced VTA. It may be an effective supplemental treatment for recipients of implantable cardioverter defibrillator.

Comparison of electropharmacological effects of bepridil and sotalol in halothane-anesthetized dogs

BACKGROUND

Bepridil is known to have a multiple ion channel-blocking property in the heart, which has been applied for the treatment of atrial fibrillation and drug-refractory ventricular tachyarrhythmias. In this study, the electro-pharmacological effects of bepridil were compared with those of dl-sotalol, a representative class III antiarrhythmic drug, using the halothane-anesthetized canine model.

METHODS AND RESULTS

Cardiovascular and electrophysiological variables were measured under the halothane anesthesia. Intravenous administration of bepridil (0.3 mg/kg, n=4) delayed the intraventricular conduction and prolonged the ventricular effective refractory period, whereas dl-sotalol (0.3 mg/kg, iv, n=4) inhibited atrioventricular conduction and prolonged the atrial and ventricular effective refractory period. The additional administration of 10 times the higher dose of bepridil or dl-sotalol (ie, 3 mg/kg, iv, n=4 for each group) decreased blood pressure, suppressed ventricular contraction and sinus automaticity, and prolonged the atrial and ventricular effective refractory period and monophasic action potential duration, in addition to the effects of the low dose.

CONCLUSIONS

The electropharmacological effects of bepridil and dl-sotalol were similar, although their potency for each cardiovascular variable varied significantly. These findings can be useful when selecting these drugs according to the pathophysiological condition of a patient.

Cardiac electrophysiologic interactions of bepridil, a new calcium antagonist, with enflurane, halothane, and isoflurane

Bepridil is an investigational calcium antagonist that also has fast sodium channel blocking and antidysrhythmic properties. In the present study, the potential interactions of bepridil with volatile anesthetics on cardiac electrophysiologic parameters were evaluated in open-chest dogs. Twenty-four dogs anesthetized with enflurane (n=6), halothane (n=6), isoflurane (n=6), or chloralose (n=6) received 2.5 mg/kg of bepridil intravenously (IV). Twenty-five additional dogs anesthetized with enflurane (n=7), halothane (n=6), isoflurane (n=6), or chloralose (n=6), received bepridil, 5.0 mg/kg, IV. Dogs anesthetized with cloralose served as controls. Cardiac electrophysiologic parameters were measured after the dogs were anesthetized and were repeated 5, 15, 30, 45, and 60 minutes after bepridil infusion. Plasma bepridil concentrations were also determined at the above time points. Synergy between bepridil and enflurane was demonstrated in the following cardiac electrophysiologic parameters: depression of sinus node function as evidenced by severe depression of sinus node automaticity and conduction; depression of atrioventricular function as evidenced by prolongation of the atrial-His bundle interval and the Wenckebach R-R interval; and, prolongation of the atrial effective refractory period. No synergy was demonstrated between bepridil and halothane or isoflurane when compared to bepridil's effects during chloralose anesthesia. It is concluded that significant synergistic cardiac electrophysiologic effects exist between bepridil and enflurane in dogs. It is recommended that caution be used when anesthetizing patients receiving bepridil with enflurane until human data on the use of this combination of pharmacologic agents is available.

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.

[Do beta adrenergic receptor blockaders increase bupivacaine cardiotoxicity?]

Bupivacaine is known to impair the electrophysiology of the heart as well as haemodynamic parameters. Administration of calcium channel blockers prior to bupivacaine enhances its cardiotoxicity. This study assessed the effects of bupivacaine at toxic dose in dogs with previous beta-adrenergic receptor blockade. It included 12 dogs anaesthetized with thiopentone, allocated in a control group (n = 6) receiving a bolus of bupivacaine (4 mg.kg-1) and a study group (n = 6) treated with the sequence propranolol (0.2 mg.kg-1) and bupivacaine (4 mg.kg-1), 15 min later. Infranodal conduction (HV conduction times and QRS durations) was worsened in both groups. Previous propranolol administration had no potentiating effects on these parameters. Conversely the latter was responsible of a greater decrease in heart rate, and increase in atrio-ventricular conduction time (77.9% vs 18.7%, p less than 0.05), as well as a more severe hypotension. Moreover, 3 out of the 6 animals in the study group suffered a cardiac arrest between the 5th and the 10th min. It is concluded that in anaesthetized dogs the cardiac and circulatory effects of a toxic dose of bupivacaine are increased in case of preexisting blockade of beta adrenergic receptors.

Electrophysiological effects of bepridil and its quaternary derivative CERM 11888 in closed chest anaesthetized dogs: a comparison with verapamil and diltiazem

1. The electrophysiological effects of bepridil, its quaternary derivative, CERM 11888 (methylpyrrolidinium bromide) (both 2.5 mg kg-1 i.v.) and those of verapamil and diltiazem (0.2 mg kg-1 i.v.) were studied in closed chest anaesthetized dogs at doses used in clinical studies. 2. The four drugs caused a bradycardia with the following order of potency: bepridil greater than CERM 11888 greater than diltiazem greater than verapamil. 3. All the compounds slowed conduction in the AV node, increased the refractory period (RP) and decreased Wenckebach rates with the following order: verapamil much greater than diltiazem greater than bepridil greater than CERM 11888. 4. Verapamil and diltiazem did not affect conduction or the RP in atria while bepridil weakly slowed the former and markedly increased the latter. CERM 11888 caused a lengthening of RP but this was a delayed effect. 5. In the ventricle, bepridil and CERM 11888 caused a small increase in the QRS and a more pronounced increase in the RP. Both compounds increased QTc but did not modify HV. Verapamil and diltiazem had no significant effects at the ventricular level. 6. Our results confirm that the main sites of action of calcium antagonists are the SA and AV nodes. Bepridil has a broader spectrum of activity and also acts at the atrial and ventricular levels. A comparison of the effects of bepridil with those of its quaternary derivative suggests the involvement of an intracellular action in the electrophysiological effects of bepridil.

Effects on hemodynamics and left ventricular ejection fraction of intravenous bepridil for impaired left ventricular function secondary to coronary artery disease

To define the hemodynamic effects of bepridil in patients with depressed left ventricular (LV) function, 22 patients with an LV ejection fraction (EF) of 0.45 or less were studied before and after 2 mg/kg (n = 11) and 4 mg/kg (n = 11) of intravenous bepridil. Maximal hemodynamic effects were evident between 15 and 30 minutes after drug infusion. After 2 mg/kg, heart rate decreased 9% (p less than 0.01), cardiac index 17% (p less than 0.01), LV dP/dt max 16% (p less than 0.01), stroke work index 14% (p less than 0.01) and mean aortic pressure 8% (difference not significant). Right atrial pressure increased 8% (not significant), pulmonary arterial wedge pressure 24% (p less than 0.01) and systemic vascular resistance 17% (p less than 0.01). After administering 4 mg/kg of bepridil the changes in heart rate, cardiac index, right atrial pressure, LV dP/dt max, mean aortic pressure and systemic vascular resistance were almost identical to those after the smaller dose. The larger dose produced a 40% (p less than 0.01) increase in pulmonary arterial wedge pressure and a 22% decrease in stroke work index (p less than 0.01), but only the change in wedge pressure was significantly greater (p less than 0.01) than that produced by the lower dose. Radionuclide-determined LVEF decreased 6% (p less than 0.05), from 0.33 +/- 0.14 after 2 mg/kg and 11% (p less than 0.05) from 0.27 +/- 0.11 after 4 mg/kg of bepridil. The data indicate that bepridil exerts significant negative inotropic and chronotropic effects in patients with impaired LV function.

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)

Effects of bepridil on force development and transmembrane electrical activity of adult canine Purkinje strands: comparison with nisoldipine and lidocaine

Superfusion of a bepridil containing normal Tyrode solution produced a concentration-dependent decrease in force development and shortening of action potential duration in isolated Purkinje strands. At a concentration close to the 50% inhibitory concentration for effects on force development and action potential duration, bepridil blocked 'slow' action potentials in potassium depolarized, isoproterenol-restored Purkinje strands. When the concentration-response relations for decreasing force development and shortening action potential duration were compared to those of nisoldipine and other calcium entry inhibitors, bepridil was the least potent. Bepridil also showed a concentration-dependent effect on the maximum rate of rise of the Purkinje fiber action potential upstroke similar to, though less potent than that of lidocaine. In addition, like lidocaine, bepridil shifted the membrane responsiveness curve of the Purkinje strands to the left. These findings indicate that bepridil produced effects that are consistent with its classification as a calcium entry inhibitor (class IV antiarrhythmic), as well as effects that are 'lidocaine-like' (class I antiarrhythmic).

Electrophysiologic and antiarrhythmic actions of bepridil. Comparison with verapamil and ajmaline for atrioventricular reentrant tachycardia

Bepridil (2 mg/kg intravenously) was given to 20 patients with atrioventricular (AV) reentrant tachycardia and its effects were compared with those of verapamil (0.15 mg/kg intravenously) in 8 patients and ajmaline (0.75 mg/kg intravenously) in 12. After baseline electrophysiologic measurements, the drugs were given during sustained AV reentrant tachycardia (8 patients had dual AV nodal pathways and 12 had an accessory AV pathway). Verapamil terminated AV reentrant tachycardia in 7 patients and bepridil terminated it in 6. In 8 of the patients who received ajmaline, AV reentrant tachycardia was terminated and in 6 of this group bepridil did so. Bepridil was more successful in terminating AV reentrant tachycardia in those with dual AV nodal pathways than in those with an accessory AV pathway. Bepridil slowed sinus rate by 10% (p less than 0.0001), whereas verapamil did not change it significantly. Both verapamil and bepridil administration prolonged AV nodal conduction (39% and 44%, respectively), lengthened AV nodal effective refractory period (18% and 17% respectively) and increased the Wenckebach cycle length of the AV node (24% and 25%, respectively) to a significant degree (p less than 0.05). Bepridil also lengthened atrial and ventricular effective refractory periods (p less than 0.01) and QT interval (p less than 0.0001) in the group as a whole; in those receiving ajmaline and bepridil only atrial refractoriness was significantly altered (p less than 0.05). After treatment for 3 to 5 days with oral bepridil, 19 patients underwent repeat study.(ABSTRACT TRUNCATED AT 250 WORDS)