How should you evaluate a new 1st degree Atrioventricular (AV) block in an asymptomatic patient?

From the Guidelines

For an asymptomatic patient with a newly discovered first-degree AV block, no specific treatment is typically required, but a thorough evaluation should be performed to identify any underlying causes. Begin with a comprehensive history and physical examination, focusing on medication use (particularly beta-blockers, calcium channel blockers, digoxin, or antiarrhythmics) that could prolong AV conduction, as recommended by the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1. Order baseline laboratory tests including electrolytes, particularly potassium and magnesium levels, as abnormalities can affect cardiac conduction. A 12-lead ECG should be obtained to confirm the diagnosis (PR interval >200 ms) and assess for other cardiac abnormalities. Consider ambulatory ECG monitoring if there's concern about intermittent higher-degree AV blocks. An echocardiogram may be warranted to evaluate for structural heart disease, as suggested by the 2015 eligibility and disqualification recommendations for competitive athletes with cardiovascular abnormalities 1. If the patient participates in athletics, exercise stress testing might be appropriate to assess AV conduction during exertion. First-degree AV block is often benign in asymptomatic patients, representing delayed conduction through the AV node without missed beats, but it's essential to monitor periodically as it can occasionally progress to higher-degree blocks, particularly in patients with underlying cardiac disease, as noted in the 2005 indications and recommendations for pacemaker therapy 1. Given the most recent and highest quality study available, the 2019 guideline 1 provides the most relevant recommendations for evaluating and managing first-degree AV block in asymptomatic patients. Key points to consider in the evaluation include:

• Comprehensive history and physical examination
• Baseline laboratory tests, including electrolytes
• 12-lead ECG to confirm the diagnosis and assess for other cardiac abnormalities
• Ambulatory ECG monitoring if concern about intermittent higher-degree AV blocks
• Echocardiogram to evaluate for structural heart disease
• Exercise stress testing if the patient participates in athletics.

From the Research

Evaluation of New 1st Degree AV Block in Asymptomatic Patient

• The evaluation of a new 1st degree AV block in an asymptomatic patient should consider the potential risks and consequences of the condition, as it may not be entirely benign 2, 3.
• Studies have shown that 1st degree AV block can be associated with an increased risk of heart failure, pacemaker implantation, and death 2.
• The use of insertable cardiac monitors (ICMs) can help reveal progression of 1st degree AV block to higher grade block or bradycardia requiring pacemaker implantation 2.
• Clinical evaluation may require a treadmill stress test to assess symptoms and PR interval adaptation 4.
• Patients with marked 1st degree AV block (PR > 0.30 s) may experience symptoms similar to pacemaker syndrome and may benefit from pacing 4.

Considerations for Pacing and Management

• Permanent pacemaker implantation is reasonable for 1st degree AV block with symptoms similar to pacemaker syndrome or with hemodynamic compromise 3, 4.
• Conventional dual-chamber pacing may improve symptoms in patients with normal left ventricular function, but biventricular pacing may be considered in patients with left ventricular systolic dysfunction and heart failure 4.
• Patients with 1st degree AV block may experience loss of ventricular resynchronization during biventricular pacing, leading to a poorer outcome with cardiac resynchronization therapy (CRT) 4.

Pharmacological Considerations

• Slow channel blockers and beta blockers can affect AV nodal conduction and may prolong the PR interval, but rarely cause more than 1st degree AV block 5.
• Combination therapy with a slow channel blocker and a beta blocker may rarely cause 2nd degree AV block 5.
• Beta blockers and calcium channel blockers are first-line agents for the treatment of stable coronary ischemic disease and can reduce oxygen demand, but their use should be considered in the context of 1st degree AV block 6.