Effects of intravenous diltiazem on sinus node function and atrioventricular conduction in patients

Interpretation and application of world-wide safety data on diltiazem

The safety of medicinal agents being introduced into the marketplace is of growing concern to consumers, health care providers, and regulatory agencies. Although there are ever increasing efforts to improve techniques for testing drugs, and for anticipating and confirming possible adverse effects, arrangements for monitoring and detecting adverse drug reactions are far from satisfactory. Some factors which need to be understood in order to appropriately interpret data include: maturation processes; pretesting affects, measuring instruments affects; selection bias; and the affects of differential experimental mortality. A safety profile has been presented for the calcium entry blocker diltiazem hydrochloride. Efforts were made to focus attention upon the source of safety information as it relates to the quality of the report. The data presented suggests that diltiazem hydrochloride has a low incidence of adverse experiences.

Effects of bepridil, diltiazem and verapamil on atrial refractoriness and heart rate in the conscious dog: comparison with quinidine

1. Bepridil at cumulative doses between 1.25 and 8.75 mg/kg and quinidine between 2.5 and 17.5 mg/kg given in conscious dogs with chronic atrioventricular block and implanted atrial pacing electrodes, dose-relatedly lengthened atrial effective refractory period (AERP), as reflected by the decrease in maximal atrial frequency determined by pacing. 2. Diltiazem shortened AERP at 0.25 mg/kg and lengthened it at 1.75 mg/kg, but both effects were very slight. 3. Verapamil between 0.06 and 0.435 mg/kg did not alter AERP at all. 4. Except for diltiazem at 0.75 and 1.75 mg/kg and bepridil at 8.75 mg/kg, each dose of each drug increased atrial rate. Each drug produced an increase in ventricular rate and a short-lasting lowering in mean blood pressure. 5. Thus, these results indicate that bepridil exhibits more marked antiarrhythmic potentialities than quinidine and that the atrial and ventricular tachycardic effects observed are mainly baroreceptor reflex effects.

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.

[Sinusal dysfunction secondary to the ingestion of diltiazem, cured by the administration of intravenous calcium]

An elderly patient, receiving long-term oral diltiazem at the usual dosage, presented a sudden attack of junctional bradycardia at 35 b X min-1; this was badly tolerated by the patient. The diltiazem blood level was normal. After recovery, nodal investigations were also normal. The treatment of this accident due to a calcium-blocker is stressed: the intravenous injection of a calcium salt only was sufficient, with a return to near-normal sinus function, so avoiding the necessity of pacing.

Hypotensive actions of diltiazem and nitroprusside compared during fentanyl anaesthesia for total hip arthroplasty

The potential for inducing hypotension during fentanyl anaesthesia by administering either diltiazem (n = 7) or sodium nitroprusside (n = 7) was investigated during total hip arthroplasty. Haemodynamic variables were obtained in the lateral position before, during and after administration of the hypotensive agent. Diltiazem 0.15 mg X kg-1 given as an IV bolus followed by a 12.5 +/- 3 micrograms X kg-1 X min-1 continuous infusion decreased mean arterial pressure (MAP) from 77 +/- 11 mmHg to 63 +/- 16 mmHg (p less than 0.05) while other haemodynamic parameters showed only minor and insignificant changes. Hypotension continued for at least 30 min after the cessation of diltiazem. With sodium nitroprusside MAP decreased immediately from 81 +/- 11 mmHg to 59 +/- 9 mmHg (p less than 0.01) and rapidly returned to its control value after cessation of the infusion. CI and Qs/Qt rose significantly (p less than 0.05) while the systemic vascular resistance index (SVRI) (p less than 0.01) and pulmonary vascular resistance index (PVRI) (p less than 0.05) fell significantly. The haemodynamic profile was significantly different between hypotensive agents for MAP (p less than 0.02), heart rate (HR) (p less than 0.01), SVRI (p less than 0.05), and PVRI (p less than 0.05). HR was lower with diltiazem than with nitroprusside. A bradycardia less than 50 beats/min was observed in five patients in the diltiazem group. MAP, SVRI and PVRI were lower with nitroprusside than with diltiazem. Diltiazem can induce and maintain moderate hypotension without tachycardia and decreased cardiac output in humans during fentanyl anaesthesia but the modulation of the level of arterial pressure and the depression of atrioventricular conduction are unpredictable.