Is metoprolol contraindicated in first-degree atrioventricular (AV) block?

From the Guidelines

Metoprolol, a beta-blocker, is not absolutely contraindicated in patients with first-degree atrioventricular (AV) block, but its use requires caution.

Key Considerations

• In patients with first-degree AV block, metoprolol may be initiated at a low dose, such as 25-50mg daily, and titrated upwards as needed and tolerated, with close monitoring of heart rate and AV conduction 1.
• However, in patients with a PR interval greater than 0.24 seconds, alternative agents or closer monitoring may be considered to minimize the risk of worsening AV block 1.

Monitoring and Dosing

• Patients with significant chronic obstructive pulmonary disease who may have a component of reactive airway disease should be given beta blockers very cautiously; initially, low doses of a beta-1–selective agent should be used 1.
• If there are concerns about possible intolerance to beta blockers, initial selection should favor a short-acting beta-1–specific drug such as metoprolol or esmolol 1.
• Mild wheezing or a history of chronic obstructive pulmonary disease mandates a short-acting cardioselective agent at a reduced dose (e.g., 12.5 mg of metoprolol orally) rather than the complete avoidance of a beta blocker 1.

Clinical Context

• The rationale for beta-blocker use in all forms of CAD, including UA, is generally favorable, with the exception of initial HF 1.
• In the absence of contraindications, the new evidence appears sufficient to make beta blockers a routine part of care 1.
• A related group shown to benefit are high- or intermediate-risk patients who are scheduled to undergo cardiac or noncardiac surgery 1.

From the FDA Drug Label

CONTRAINDICATIONS ... significant first-degree heart block (P-R interval ≥ 0.24 sec); Bradycardia, including sinus pause, heart block, and cardiac arrest have occurred with the use of metoprolol. Patients with first-degree atrioventricular block, sinus node dysfunction, or conduction disorders may be at increased risk.

Metoprolol is contraindicated in patients with significant first-degree heart block (P-R interval ≥ 0.24 sec), but it is not contraindicated in all cases of first-degree atrioventricular (AV) block. Patients with first-degree AV block may be at increased risk of bradycardia and should be monitored. 2 2

From the Research

Metoprolol and First-Degree Atrioventricular (AV) Block

• Metoprolol is a beta-blocker that can affect atrioventricular (AV) nodal conduction, potentially prolonging the PR interval 3.
• In patients with normal AV nodal function, beta-blockers like metoprolol can prolong the AH interval and AV nodal refractory periods, which may lengthen the PR interval 3.
• However, the prolonged PR interval rarely results in more than first-degree AV block in patients receiving maintenance therapy with beta-blockers like metoprolol 3.

Contraindications of Beta-Blockers in AV Block

• Beta-blockers, including metoprolol, are generally contraindicated in patients with greater than first-degree atrioventricular (AV) block due to the possibility of further slowing of heart rate and/or the development of high-grade AV block 4.
• However, there is no clear evidence to suggest that metoprolol is contraindicated in first-degree AV block specifically.
• In fact, beta-blockers like metoprolol may be used in patients with first-degree AV block, but caution is advised, and the patient's condition should be closely monitored 4.

Clinical Considerations

• The decision to use metoprolol in patients with first-degree AV block should be based on individual patient factors, including the presence of concomitant disease and underlying left ventricular function 4.
• Patients with first-degree AV block who are treated with metoprolol should be closely monitored for signs of worsening AV block or other adverse effects 5.