Can diltiazem (calcium channel blocker) cause complete heart block?

Diltiazem Can Cause Complete Heart Block

Yes, diltiazem can cause complete heart block, especially in susceptible individuals or when combined with other medications that affect cardiac conduction. 1, 2

Mechanism and Risk Factors

Diltiazem, a non-dihydropyridine calcium channel blocker, affects cardiac conduction in several ways:

• Prolongs AV node refractory periods, which can result in abnormally slow heart rates or second- or third-degree AV block (occurs in approximately 0.48% of patients) 1
• Has significant direct effects on atrioventricular conduction and heart rate 2
• Can induce atrioventricular block, particularly with the phenylalkylamine subclass of calcium channel blockers 2

Risk factors that increase the likelihood of diltiazem-induced heart block include:

• Pre-existing sick sinus syndrome 1
• Concomitant use with beta-blockers or digitalis (additive effects on cardiac conduction) 1, 3
• Advanced age 4
• Impaired renal function 4
• Pre-existing AV block greater than first degree 5
• Significantly impaired left ventricular function 2

Clinical Presentation and Management

Heart block from diltiazem may present as:

• Bradycardia 5
• Second-degree AV block 1
• Complete (third-degree) AV block 4
• In rare cases, asystole (2-5 seconds) has been reported even after a single 60 mg dose 1

Management of diltiazem-induced heart block includes:

• Immediate discontinuation of the drug 2
• For bradycardia: Administer atropine (0.60 to 1.0 mg); if no response, consider isoproterenol cautiously 1
• For high-degree AV block: Treat as for bradycardia; fixed high-degree AV block should be treated with cardiac pacing 1
• Intravenous calcium administration may help reverse the pharmacological effects of diltiazem, though effectiveness has been inconsistent 1
• Supportive measures including fluids and vasopressors to maintain blood pressure 1

Special Considerations

Combination Therapy Risks

• Concomitant use of diltiazem with beta-blockers significantly increases the risk of conduction abnormalities 3
• When diltiazem is used with beta-blockers, blood pressure, heart rate, and AV conduction should be carefully monitored 3
• The combination should be avoided in patients with AV block grade I, bradycardia, or hypotension 3

Paradoxical Use in Specific Conditions

Interestingly, while diltiazem can cause AV block, it can also be used to treat certain types of heart block:

• In cases of coronary artery spasm-induced complete AV block, diltiazem has been reported to be effective in restoring sinus rhythm 6
• This paradoxical effect occurs because the drug treats the underlying cause (coronary spasm) rather than directly affecting the conduction system 6

Prevention and Monitoring

To minimize the risk of diltiazem-induced heart block:

• Avoid use in patients with pre-existing AV block greater than first degree 5
• Use with caution in patients with impaired ventricular function 1
• Monitor ECG when initiating therapy, particularly in high-risk patients 3
• Consider dose adjustment in patients with renal impairment 3
• Have resuscitation equipment available when administering IV diltiazem 5

Conclusion

Diltiazem can indeed cause complete heart block, particularly in susceptible individuals or when combined with other medications affecting cardiac conduction. Healthcare providers should be aware of this potential adverse effect and monitor patients appropriately, especially those with risk factors for conduction abnormalities.