Effects of sustained intravenous diltiazem infusion in healthy persons

Intravenous diltiazem infusions for rapid atrial fibrillation or flutter in the emergency department: A retrospective, exploratory analysis

BACKGROUND

Emergency physicians commonly treat patients with atrial fibrillation (AF) or atrial flutter (AFL) with rapid ventricular response, and intravenous (IV) diltiazem is the most commonly used medication for rate control of such patients. We sought to compare rate control success and safety outcomes for emergency department (ED) patients with AF or AFL who, after a diltiazem bolus, received a diltiazem drip compared to those who did not receive a drip.

METHODS

We performed a retrospective cohort study comparing outcomes of ED patients from a single hospital system with AF and AFL and a heart rate (HR) > 100 beats/min who received a diltiazem drip after an IV diltiazem bolus to those who received no drip. The primary outcome was a HR < 100 beats/min at the time of ED disposition. Secondary outcomes were hospital length of stay and safety (hypotension, electrical cardioversion, vasopressor use, and death). We compared groups using propensity score matching.

RESULTS

Between January 1, 2020, and November 8, 2022, there were 746 AF or AFL patients eligible for analysis. Of those, 382 (51.2%) received a diltiazem drip and 364 (48.8%) did not. In the unadjusted analysis, the last recorded ED HR was <100 beats/min in 55.2% of patients in the drip group compared to 65.9% in the no-drip group (difference 10.7%, 95% confidence interval [CI] 3.7 to 17.7). After propensity matching, diltiazem drip use was associated with lower likelihood of rate control in the ED (OR 0.69, 95% CI 0.48-0.99) and 22.5 h (95% CI 12.2-36.8) longer hospital stay.

CONCLUSIONS

For patients with AF or AFL, the use of a diltiazem drip after an IV diltiazem bolus was associated with less rate control in the ED.

Usefulness of diltiazem in the acute management of supraventricular tachyarrhythmias in the elderly

Acute management of supraventricular tachyarrhythmias is often difficult in elderly patients. Diltiazem was given intravenously (loading dose of 0.25 mg/kg over 2 minutes followed by a 4 mg/kg/24 hr infusion) in 37 elderly patients (mean age 70 years, range 60-91). Fifteen out of the 37 patients (41%) had left ventricular cardiac disease, 12 (32%) had cor pulmonale, and 10 (27%) had no obvious cardiac disease. Hemodynamic tolerance of the supraventricular tachyarrhythmia was poor in 12 patients. A good result was defined as a return to sinus rhythm after bolus or infusion, or as a slowing of the ventricular rate (VR) to less than 100 beats/min. Of the 23 patients in atrial fibrillation, about half reverted to sinus rhythm after diltiazem, and in most of the others the ventricular rate decreased to less than 100 beats/min. Side effects occurred in 10 patients (bradycardia in 6, cutaneous rash in 2, hypotension in 2). They rapidly reversed after cessation of diltiazem. They were responsible for 2 out of the 5 poor results. Thus, diltiazem appeared effective and safe when used carefully in elderly patients with supraventricular tachyarrhythmia.

Contemporary management of atrial fibrillation

The incidence of atrial fibrillation approximately doubled for every 10-year increment in age in the Framingham Heart Study cohort; thus physicians will be faced with an increasing patient population with atrial fibrillation. Hypertension is observed to be the most common associated risk factor in both sexes. The management of patients with atrial fibrillation is evolving as a result of a number of published studies. Calcium channel blockers and beta-blockers are emerging as the preferred choices for rate control rather than digoxin. Low-dose anticoagulation therapy has shown beneficial effects not only in primary prevention, but also for secondary prevention of thromboembolism. Thus, patients who cannot be successfully cardioverted should be anticoagulated if there are no contraindications (Table 3) and if they do not fall into the low-risk group--defined as patients under the age of 65 without risk factors (hypertension, diabetes, previous stroke). Patients not eligible for anticoagulation should be on aspirin therapy. Patients with lone atrial fibrillation are not at higher risk for thromboembolism than the general population; therefore, they can be managed without anticoagulation or antiplatelet therapy. Antiarrhythmic treatment should be approached cautiously; amiodarone in low doses is the most effective and safe treatment, but this remains controversial.

Pharmacokinetics and pharmacodynamics of intravenous diltiazem in patients with atrial fibrillation or atrial flutter

BACKGROUND

Diltiazem, a calcium channel blocker, has been shown to be safe and effective in the treatment of patients in atrial fibrillation and/or atrial flutter. However, there have been no pharmacokinetic/pharmacodynamic studies of diltiazem in these patients.

METHODS AND RESULTS

The pharmacokinetics and pharmacodynamics of intravenous diltiazem were determined in 32 patients with atrial fibrillation or atrial flutter (mean +/- SD age, 66 +/- 7 years; mean baseline heart rate, 131 +/- 10 beats per minute) after 20 mg or 20 mg followed by 25-mg bolus doses and a 10 and 15 mg/hr infusion for 24 hours. After the 10 and 15 mg/hr infusions of diltiazem, mean +/- SD elimination half-life was 6.8 +/- 1.8 and 6.9 +/- 1.5 hours, volume of distribution was 411 +/- 151.8 and 299 +/- 70.8 I, and systemic clearance was 42 +/- 12.4 and 31 +/- 8.3 l/hr, respectively. Percentages of the plasma concentrations of the principal metabolites desacetyldiltiazem and N-desmethyldiltiazem to diltiazem were < 15% and < 10%, respectively. Thirty of 32 patients maintained response throughout the 24-hour infusion of diltiazem. Using a sigmoidal Emax pharmacodynamic model, a strong relation (mean +/- SD r2, 0.78 +/- 0.2) was observed between plasma diltiazem concentration and percent heart rate reduction. Mean +/- SD Emax (maximum percent reduction in heart rate from baseline) and EC50 (plasma diltiazem concentration that achieves half Emax) were 52 +/- 17% and 110 +/- 84 ng/ml, respectively. The model predicts that mean plasma diltiazem concentration of 79, 172, and 294 ng/ml are required to produce a 20%, 30%, and 40% reduction in heart rate, respectively. A relation between plasma diltiazem concentration and percent change in systolic blood pressure (SBP) or diastolic blood pressure (DBP) from baseline was not observed (mean +/- SD r2, SBP/DBP: 0.35 +/- 0.24/0.36 +/- 0.2). There were no untoward side effects observed.

CONCLUSIONS

First, the pharmacokinetics of diltiazem in patients with atrial fibrillation or atrial flutter is nonlinear with an apparent dose-dependent decrease in systemic clearance with increasing infusion rate. Second, using a sigmoidal Emax model, there is a strong relation between plasma diltiazem concentration and percent heart rate reduction. Third, the plasma concentrations of the principal metabolites desacetyldiltiazem and N-desmethyldiltiazem are low and are not expected to contribute significantly to the pharmacodynamics of intravenous diltiazem in these patients.

Use of intravenous diltiazem in patients with acute coronary artery disease

The use of calcium antagonists for the treatment of patients with unstable angina and acute myocardial infarction has been a promising area of both basic and clinical research. Despite consistently beneficial effects experimentally, the clinical extrapolation of these results has been less than ideal, especially in patients with evolving myocardial infarction. Calcium antagonists have in some instances failed to manifest benefit and at times have been shown to have negative effects. One reason for this could be the use of oral or sublingual preparations, which result in variable absorption, variable volumes of distribution, and variable clearance. For this reason, an intravenous preparation of one of the calcium antagonists, diltiazem, may be more beneficial. Such a preparation has been developed and its safety confirmed in patients without cardiovascular disease and in patients with acute infarction. Substantial benefit has been documented in patients with stable angina and during noncardiac surgery. Preliminary data in patients with unstable angina suggest that the drug is effective, although studies comparing intravenous diltiazem with other agents or with the oral preparation of diltiazem have not yet been reported. Experimental data in animals with acute infarction have demonstrated that administration of intravenous diltiazem after occlusion, but prior to reperfusion, elicits a marked increase in the degree of myocardial salvage induced by thrombolysis. This appears to be due to the inhibition of lipid peroxidation rather than alterations in coronary perfusion. Thus, it appears that the intravenous preparation may permit the more effective use of diltiazem in patients with acute coronary artery disease.

Role of calcium antagonists for heart rate control in atrial fibrillation

Atrial fibrillation is one of the most common symptomatic sustained arrhythmias seen in clinical practice. Many patients with atrial fibrillation and a ventricular response greater than 120 beats/min will experience cardiac symptoms. In the past, control of heart rate in these patients consisted of administration of intravenous digoxin, but this often proved to be ineffective or limited by toxicity. Recently, intravenous beta blockers such as esmolol have been used to slow the ventricular rate during atrial arrhythmias, but in some studies their use has been limited by hypotension. Alternatively, a bolus of an intravenous calcium antagonist, e.g., diltiazem or verapamil, may be administered to achieve acute slowing of the ventricular response. An intravenous bolus of diltiazem or verapamil may be effective, but use of either may be limited by its short duration of action and the inability to administer repeated boluses to tightly control or "fine tune" the heart rate. However, a new bolus plus maintenance infusion technique with diltiazem has shown promise in initial studies. It appears that in the future, continuous infusion techniques with intravenous calcium antagonists will be available that provide safe and effective sustained control of the ventricular response during atrial arrhythmias.

Efficacy, electrocardiographic and renal effects of intravenous diltiazem for essential hypertension

The acute systemic blood pressure, electrocardiographic and renal function responses to an intravenous bolus infusion of diltiazem (0.2 to 0.5 mg/kg) were evaluated in 18 subjects with mild to moderate essential hypertension. Although a significant blood pressure response occurred within 5 minutes, blood pressure returned to pretreatment levels within 1 to 3 hours. After drug infusion, a variety of rhythm and conduction disturbances were noted; the most important were transient prolongation of the PR Interval (first-degree atrioventricular block), a single episode of second-degree atrioventricular block (Mobitz I) associated with T-wave inversion and a transient episode of junctional escape rhythm and atrioventricular dissociation. Intravenous diltiazem had no consistent effect on glomerular filtration rate or effective renal plasma flow. Natriuresis and kaliuresis were observed only at the highest infusion dose. It is concluded that an alternative dosing regimen will be required if intravenous diltiazem is to be used safely and effectively to control blood pressure in patients with hypertensive disease.