Can Diltiazem (calcium channel blocker) cause bradycardia (low heart rate)?

From the Guidelines

Diltiazem can cause bradycardia as a side effect, and patients taking this medication should be monitored for symptoms of low heart rate, such as dizziness, fatigue, weakness, or fainting. The most recent and highest quality study, 1, provides guidance on the management of adult patients with supraventricular tachycardia, including the use of diltiazem. According to this study, diltiazem can cause hypotension, worsening heart failure in patients with pre-existing ventricular dysfunction, bradycardia, abnormal liver function studies, and acute hepatic injury. Some key points to consider when using diltiazem include:

• The initial dose of diltiazem is 0.25-mg/kg IV bolus over 2 min, with a maintenance infusion at 5–10 mg/h, up to 15 mg/h.
• Diltiazem is contraindicated in patients with AV block greater than first degree or SA node dysfunction (in absence of pacemaker), WPW with AF/atrial flutter, hypotension, decompensated systolic HF/LV dysfunction, and drugs with SA and/or AV nodal–blocking properties.
• Patients with hepatic or renal dysfunction should be cautious when using diltiazem, as it is a substrate of CYP3A4 (major) and a moderate CYP3A4 inhibitor. The risk of bradycardia is higher in elderly patients, those with pre-existing heart conduction disorders, and when diltiazem is combined with other medications that slow heart rate like beta-blockers or digoxin, as noted in 1. Typical diltiazem dosing ranges from 120-360 mg daily for extended-release formulations, with lower doses recommended for patients at higher risk of bradycardia, as seen in 1. If bradycardia develops, dose reduction or medication discontinuation may be necessary under medical supervision.

From the FDA Drug Label

Diltiazem decreases sinoatrial and atrioventricular conduction in isolated tissues and has a negative inotropic effect in isolated preparations. Resting heart rate is usually slightly reduced by diltiazem. Diltiazem hydrochloride prolongs AV node refractory periods without significantly prolonging sinus node recovery time, except in patients with sick sinus syndrome. This effect may rarely result in abnormally slow heart rates (particularly in patients with sick sinus syndrome)

Diltiazem can cause low heart rate (bradycardia), as it decreases sinoatrial and atrioventricular conduction and has a negative inotropic effect.

• The drug can prolong AV node refractory periods, leading to abnormally slow heart rates, especially in patients with sick sinus syndrome.
• Resting heart rate is usually slightly reduced by diltiazem. 2 2

From the Research

Diltiazem and Bradycardia

• Diltiazem, a calcium channel blocker, can cause bradycardia (low heart rate) in some cases, particularly when combined with beta-blockers 3, 4.
• The risk of developing bradycardia or other cardiac conduction abnormalities may be increased in patients with pre-existing cardiac conditions, such as atrioventricular block or left ventricular dysfunction 3.
• Studies have shown that diltiazem can decrease heart rate in patients with hypertension or angina, but it may not have a significant effect on heart rate in patients with normal or low baseline heart rates 5.
• In some cases, diltiazem has been associated with severe bradycardia, cardiogenic shock, and even death, particularly when used in combination with beta-blockers 4.

Factors Influencing Bradycardia Risk

• The risk of bradycardia with diltiazem may be influenced by factors such as age, baseline heart rate, and the presence of underlying cardiac conditions 5, 6.
• Patients with reduced ejection fraction may be at increased risk of acute kidney injury when treated with intravenous diltiazem, but not necessarily at increased risk of hypotension or in-hospital mortality 7.

Clinical Implications

• Patients treated with diltiazem should be monitored closely for signs of bradycardia or other cardiac conduction abnormalities, particularly if they have pre-existing cardiac conditions or are taking beta-blockers 3, 4.
• The dosage of diltiazem or concomitant medications may need to be adjusted in patients who develop bradycardia or other adverse effects 3, 6.