Serial electrophysiologic studies of the effects of oral diltiazem on paroxysmal supraventricular tachycardia

Efficacy and safety of intravenous diltiazem for treatment of atrial fibrillation and atrial flutter. The Diltiazem-Atrial Fibrillation/Flutter Study Group

This study evaluates the effectiveness and safety of intravenous diltiazem for the treatment of atrial fibrillation and atrial flutter. A double-blind, parallel, randomized, placebo-controlled protocol was used, and 6 large, urban hospitals, both university-affiliated and private, participated. The study involved 113 patients with atrial fibrillation or flutter, a ventricular rate greater than or equal to 120 beats/min and systolic blood pressure greater than or equal to 90 mm Hg without severe heart failure. The dose of intravenous diltiazem (or identical placebo) was 0.25 mg/kg/2 minutes followed 15 minutes later by 0.35 mg/kg/2 minutes if the first dose was tolerated but ineffective. If a patient did not respond, the code was broken and the patient was allowed to receive open-label diltiazem if placebo had been given. Of 56 patients, 42 (75%) randomized to receive diltiazem responded to 0.25 mg/kg and 10 of 14 responded to 0.35 mg/kg, for a total response rate of 52 of 56 patients (93%), whereas 7 of 57 patients (12%) responded to placebo (p less than 0.001). After the double-blind protocol, 49 of the 57 patients who received placebo were then given diltiazem; 47 of 49 responded, for an overall response rate of 99 of 105 patients (94%) with diltiazem. The median time from the start of drug infusion to the maximal decrease in heart rate was 4.3 minutes. Side effects occurred in 14 patients, 7 of whom had asymptomatic hypotension not requiring intervention. Thus, intravenous diltiazem was rapidly effective for slowing the ventricular response in most patients with atrial fibrillation or atrial flutter. Blood pressure decreased slightly. Side effects were mild.

An interindividual variability in the sensitivity of atrioventricular node to diltiazem in patients with paroxysmal supraventricular tachycardia

To study the sensitivity of atrioventricular (AV) node to diltiazem in seven patients with paroxysmal supraventricular tachycardia (PSVT), we analyzed the plasma concentration-response relationship of this Ca-antagonist using AH interval as an index for assessing its Ca channel blocking effect on the AV node after an IV infusion (0.4 mg/kg). The postdose AH intervals were prolonged compared with the baseline, and their percentage changes correlated significantly (P less than 0.01) with log-diltiazem concentrations in all patients. However, drug concentrations associated with a 20% prolongation of AH interval differed considerably among the patients (range; 65 to 260 ng/ml), indicating a large interindividual variability in the sensitivity of AV node to diltiazem. These results suggest that the interindividual difference in the responsiveness of AV node to diltiazem-induced Ca channel blocking effect may be one of the possible explanations for the therapeutic failure of this Ca-antagonist for terminating PSVT or preventing its recurrences in certain patients.

Management of supraventricular tachyarrhythmias

Supraventricular tachyarrhythmias are common and treatment is based on the frequency and hemodynamic severity caused by these arrhythmias. Empiric therapy with currently available medications often satisfactorily controls symptomatic arrhythmias. Nonpharmocologic therapy with permanent antitachycardia pacemakers, percutaneous catheter ablation or surgery can be effective for selected patients with medically refractory supraventricular tachyarrhythmias after thorough electrophysiologic evaluation. In selected patients with life-threatening supraventricular tachyarrhythmias due to the WPW syndrome, surgical ablation is the therapy of choice.

The effects of slow channel blockers and beta blockers on atrioventricular nodal conduction

The PR interval on the electrocardiogram represents the time that it takes an impulse to travel through the atrium and atrioventricular (AV) conduction system to the ventricles. Normally, activation is slowest in the AV node, and variations in PR interval most commonly parallel changes in AV nodal activation time. The AV nodal conduction time and effective refractory period are rate dependent and, in adult humans, are usually prolonged with increasing atrial paced rates. In addition, alterations in autonomic tone effect AV nodal conduction as well as sinus rate. The effect is usually in the same direction but often to different degrees. In patients with normal AV nodal function, parasympathetic and sympathetic tone are balanced at rest, but in patients with abnormal AV conduction, the effect of the parasympathetic system is more marked. Drugs including the slow channel blockers and beta blockers, affect AV nodal function. Slow channel blockers inhibit the slow inward calcium current, which may prolong conduction and refractoriness in the AV node. However, whereas diltiazem and verapamil have been shown to prolong AV nodal conduction and refractoriness in humans, nifedipine, a potent vasodilator, cannot be used in doses large enough to affect the AV node. The increase in PR interval caused by verapamil is minimal, and at doses of less than 480 mg/d, AV block occurs infrequently. When AV block occurs, it is first degree block in most patients, and it is usually asymptomatic. The electrophysiologic effects of diltiazem are similar to those of verapamil. Beta blockers also have a negative dromotropic effect on the AV node. They prolong the AH interval and AV nodal refractory periods and may lengthen the PR interval. The prolonged PR interval rarely results in more than first degree AV block in patients receiving maintenance therapy. In selected patients, combination therapy with a slow channel blocker and a beta blocker rarely causes second-degree AV block.

Pharmacokinetics and pharmacodynamic effects of aqueous diltiazem in healthy humans

Aqueous diltiazem was given to ten healthy male volunteers in a single oral dose of 2.5 mg/kg body weight. Serum diltiazem levels were measured at various intervals up to 24 hours after administration of the drug as were blood pressure, heart rate, and PR interval. The pharmacokinetics followed a one-compartment model in six and two-compartment model in four subjects. The mean distribution half-life in the latter four subjects was 15.8 +/- 3.7 minutes (range, 10.4-18.8 min). In the ten subjects, the peak serum diltiazem level was attained in 20 to 45 minutes (mean, 32.5 +/- 9.5 min) and ranged from 136 to 701 ng/mL (mean, 332 +/- 180 ng/mL). The elimination half-life ranged from 2.8 to 4.8 hours (mean, 3.8 +/- 0.6 hr). The area under the concentration-time curve varied from 508 to 2,245 ng-hr/mL, indicating differing bioavailability. Slight but significant blood pressure reduction was seen only at one to three hours. Changes in heart rate were not significant at any measurement. Transient facial flushing, beginning at ten to 20 minutes after administration, was noted in nine subjects, reflecting the vasodilatory effect of the drug. Significant prolongation (greater than 10%) of PR intervals began at ten minutes in three, at 20 minutes in six, and at 30 minutes in one participant, and progressed to second-degree Wenckebach atrioventricular (AV) block in six subjects 20 to 60 minutes after administration and third-degree AV block in one person 45 minutes after dosing. These AV blocks resolved by the third hour without treatment, and PR prolongation resolved by the fifth to seventh hours.(ABSTRACT TRUNCATED AT 250 WORDS)