What are the implications of first-degree atrioventricular (AV) block and premature ventricular contractions (PVCs) in a patient taking Metoprolol (metoprolol)?

From the Guidelines

Metoprolol can be used to manage PVCs in patients with first-degree AV block, but it requires careful monitoring due to its potential to worsen AV conduction. For PVC treatment, typical starting doses are 25-50 mg twice daily of metoprolol tartrate or 50-100 mg once daily of metoprolol succinate, with gradual titration based on symptom control and heart rate response 1. Since metoprolol can worsen AV conduction, patients with first-degree AV block should have regular ECG monitoring to ensure the PR interval doesn't progressively lengthen beyond 300 ms or develop into higher-degree heart blocks. If the PR interval extends significantly or symptoms like dizziness, fatigue, or syncope develop, the dose may need reduction or the medication discontinued. Metoprolol works by blocking beta-1 adrenergic receptors, reducing sympathetic stimulation to the heart, which helps suppress PVCs by decreasing myocardial excitability and automaticity. This mechanism also explains why it can slow AV conduction. Some key points to consider when using metoprolol in this context include:

• Monitoring for signs of worsening AV conduction, such as an increasing PR interval or the development of higher-degree AV blocks 1
• Adjusting the dose based on symptom control and heart rate response, with typical starting doses ranging from 25-50 mg twice daily of metoprolol tartrate or 50-100 mg once daily of metoprolol succinate 1
• Considering alternative options, such as calcium channel blockers, if metoprolol exacerbates conduction issues or is not effective in managing PVCs 1 It's also important to note that the choice of beta blocker for an individual patient is based primarily on pharmacokinetic and side effect criteria, as well as on physician familiarity, and that beta blockers without intrinsic sympathomimetic activity are preferred 1. Additionally, patients with marked first-degree AV block (i.e., ECG PR interval greater than 0.24 s) should not receive beta blockers on an acute basis, unless they have a functioning implanted pacemaker 1.

From the FDA Drug Label

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. Myocardial Infarction Metoprolol is contraindicated in patients with a heart rate < 45 beats/min; second- and third-degree heart block; significant first-degree heart block (P-R interval ≥ 0.24 sec);

Metoprolol may be used with caution in patients with first-degree AV block. However, patients with significant first-degree heart block (P-R interval ≥ 0.24 sec) should not use metoprolol. Regarding PVCs (Premature Ventricular Contractions), there is no direct information in the provided drug labels that addresses the use of metoprolol in patients with PVCs. Key considerations:

• Monitor heart rate and rhythm in patients receiving metoprolol.
• If severe bradycardia develops, reduce or stop metoprolol 2.
• Metoprolol is contraindicated in patients with significant first-degree heart block (P-R interval ≥ 0.24 sec) 2.

From the Research

First Degree AV Block and PVC with Metoprolol

• First-degree atrioventricular (AV) block is a condition where the electrical signal from the atria to the ventricles is delayed, resulting in a prolonged PR interval 3.
• Marked first-degree AV block (PR ≥ 0.30 s) can produce symptoms similar to those of the pacemaker syndrome, and clinical evaluation may require a treadmill stress test to assess the patient's condition 3.
• Patients with first-degree AV block and normal left ventricular (LV) function may improve with conventional dual-chamber pacing, while those with LV systolic dysfunction and heart failure may benefit from a biventricular DDD device 3.
• The use of metoprolol, a beta-blocker, may affect the heart rate and PR interval, potentially exacerbating the symptoms of first-degree AV block 3.
• Premature ventricular contractions (PVCs) can occur in patients with first-degree AV block, and their frequency and severity may be influenced by the use of metoprolol and the underlying cardiac condition 3.
• The management of first-degree AV block and PVCs with metoprolol should be individualized, taking into account the patient's symptoms, cardiac function, and response to treatment 3.