Can Losartan (angiotensin II receptor antagonist) cause Atrioventricular (AV) block?

Losartan and Atrioventricular Block

Losartan is not known to cause atrioventricular (AV) block, unlike calcium channel blockers such as verapamil and diltiazem which are documented to potentially cause AV block. The available evidence does not support a causal relationship between losartan and AV block.

Cardiovascular Effects of Losartan

• Losartan is an angiotensin II receptor blocker (ARB) commonly used for hypertension, heart failure, and to reduce left ventricular hypertrophy 1.
• The typical dosage of losartan ranges from 50-100 mg daily for hypertension and can be titrated up to maximize benefits 1, 2.
• Unlike calcium channel blockers (verapamil, diltiazem) and beta-blockers, ARBs like losartan do not directly affect cardiac conduction 1.

Medications Known to Cause AV Block

• Calcium channel blockers (particularly non-dihydropyridines like verapamil and diltiazem) and beta-blockers are well-documented to potentially cause AV block by slowing conduction through the AV node 1.
• In patients with supraventricular tachycardia, verapamil and diltiazem are specifically used for their AV nodal blocking properties 1.
• Beta-blockers exert their effect by antagonizing sympathetic tone in nodal tissue, resulting in slowing of conduction, which can lead to AV block in susceptible individuals 1.

Evidence Regarding Losartan and Cardiac Conduction

• In the LIFE study (Losartan Intervention For Endpoint reduction in hypertension), losartan was actually associated with a reduced incidence of new-onset atrial fibrillation compared to atenolol, suggesting favorable effects on atrial electrophysiology 3, 4.
• A study examining losartan's effects in hypertensive men found that while it effectively reduced blood pressure and left ventricular hypertrophy, it did not alter arrhythmias, suggesting minimal direct effect on cardiac conduction 5.
• The European Heart Journal guidelines on heart failure mention ARBs like losartan as having fewer side effects than ACE inhibitors, with no mention of AV block as a potential adverse effect 1.

Risk Factors for AV Block

• Pre-existing conduction system disease (bifascicular block, bundle branch block) increases the risk of developing high-degree AV block 1.
• Prolonged HV interval on electrophysiology study is a predictor of progression to AV block 1.
• While medications are commonly associated with AV block, a study found that AV block is truly caused by drugs in only about 15% of patients taking beta-blockers, verapamil, or diltiazem 6.

Clinical Implications

• When evaluating a patient with AV block who is on losartan, clinicians should consider other more likely causes including:
  • Intrinsic conduction system disease 1
  • Other medications (beta-blockers, calcium channel blockers, digoxin) 1, 6
  • Structural heart disease 1
• If a patient develops AV block while on losartan, discontinuation of the drug is unlikely to resolve the conduction abnormality, as losartan is not established as a cause of AV block 6.

In conclusion, while many medications can be associated with AV block, the available evidence does not support losartan as a cause of AV block. When AV block occurs in a patient taking losartan, other etiologies should be investigated.