From the Guidelines
Cardizem (diltiazem) decreases heart rate by blocking calcium channels in the heart, primarily affecting the atrioventricular (AV) node, and is commonly used to treat conditions like atrial fibrillation, atrial flutter, and supraventricular tachycardias. According to the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1, diltiazem is a reasonable option for treating supraventricular tachycardias that do not respond to adenosine or vagal maneuvers. The guidelines recommend administering diltiazem as a 15 mg to 20 mg (0.25 mg/kg) IV dose over 2 minutes, with an additional dose of 20 mg to 25 mg (0.35 mg/kg) if needed, and a maintenance infusion dose of 5 mg/hour to 15 mg/hour, titrated to heart rate 1.
Key points to consider when using Cardizem to decrease heart rate include:
- The medication should be used with caution in patients with impaired ventricular function or heart failure, as it can worsen these conditions 1
- Cardizem can cause side effects such as bradycardias, AV conduction delays, and hypotension, and should be used with caution in patients with obstructive pulmonary disease or congestive heart failure 1
- The combination of Cardizem with other AV nodal blocking agents, such as beta-blockers, should be avoided to prevent profound bradycardia 1
- Regular monitoring of heart rate and blood pressure is important while taking Cardizem to minimize the risk of adverse effects 1.
Overall, Cardizem is an effective medication for decreasing heart rate in patients with supraventricular tachycardias, but its use requires careful consideration of the patient's underlying medical conditions and potential interactions with other medications.
From the FDA Drug Label
Diltiazem prevents spontaneous and ergonovine-provoked coronary artery spasm It causes a decrease in peripheral vascular resistance and a modest fall in blood pressure, and in exercise tolerance studies in patients with ischemic heart disease, reduces the heart rate-blood pressure product for any given workload Resting heart rate is usually unchanged or slightly reduced by diltiazem Diltiazem hydrochloride has been shown to produce increases in exercise tolerance, probably due to its ability to reduce myocardial oxygen demand. This is accomplished via reductions in heart rate and systemic blood pressure at submaximal and maximal exercise workloads
Cardizem (diltiazem) effect on heart rate:
- Diltiazem can cause a reduction in heart rate due to its ability to reduce myocardial oxygen demand.
- Resting heart rate is usually unchanged or slightly reduced by diltiazem.
- In patients with sick sinus syndrome, diltiazem can significantly prolong sinus cycle length (up to 50% in some cases) 2.
- Concomitant use of diltiazem with beta-blockers may result in additive effects on cardiac conduction, including effects on heart rate 2.
From the Research
Cardizem Effect on Heart Rate
- Cardizem, also known as diltiazem, is a calcium-channel blocker that can affect heart rate 3, 4, 5.
- Studies have shown that diltiazem can slow the heart rate, with an increasing effect at higher initial rates 5.
- The heart rate-lowering effect of diltiazem is more pronounced in patients with elevated baseline heart rates, with a significant difference seen in patients with baseline heart rates of 74-84 beats/min and > or = 85 beats/min 5.
- Diltiazem has a regulating effect on heart rate, reducing tachycardia without inducing excessive bradycardia 5.
Comparison with Other Medications
- Diltiazem is different from dihydropyridine calcium antagonists, which tend to increase heart rate and have been associated with an adverse outcome in acute cardiovascular conditions 5.
- The combination of diltiazem and beta blockers can induce symptomatic bradycardia, particularly in elderly patients or those with left ventricular dysfunction or antecedent sinoatrial or atrioventricular conduction abnormality 6.
Clinical Implications
- Diltiazem can be used to control heart rate in patients with atrial fibrillation with rapid ventricular rate, with a dose of ≥ 0.13 mg/kg associated with significantly improved times to achieve heart rate control 3.
- The use of diltiazem should be cautious, especially in patients with abnormal cardiac substrate, electrolyte abnormalities, and during drug initiation, as it can provoke arrhythmias 7.