What is the diagnosis and treatment for first degree atrioventricular (AV) block?

From the Guidelines

First-degree AV block typically does not require specific treatment as it is generally benign and asymptomatic. This condition is characterized by a prolonged PR interval (greater than 200 milliseconds) on an electrocardiogram (ECG), indicating delayed conduction through the atrioventricular (AV) node 1. The causes of first-degree AV block are varied and include aging, medications (beta-blockers, calcium channel blockers, digoxin), increased vagal tone, ischemic heart disease, or inflammatory conditions affecting the heart.

Key Considerations

• First-degree AV block occurs when electrical impulses from the atria are slowed as they travel to the ventricles, but all impulses still successfully reach the ventricles.
• Common causes include:
  • Aging
  • Medications (beta-blockers, calcium channel blockers, digoxin)
  • Increased vagal tone
  • Ischemic heart disease
  • Inflammatory conditions affecting the heart
• While usually not concerning on its own, first-degree AV block may warrant monitoring if the PR interval is significantly prolonged (>300 ms) or if it occurs alongside other conduction abnormalities 1.

Management and Recommendations

• Patients should be aware that this condition may progress to higher-degree blocks in some cases, particularly with certain medications or underlying heart disease 1.
• Regular cardiac follow-up is recommended, especially if symptoms like dizziness, fatigue, or syncope develop, though these symptoms are rarely attributed to first-degree AV block alone.
• The 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay does not recommend permanent pacing for first-degree AV block unless there are accompanying conditions such as neuromuscular disease or a high risk of developing complete atrioventricular block 1.
• In certain conditions like Kearns-Sayre syndrome or Anderson Fabry disease, the risk of atrioventricular block and sudden cardiac death may be higher, necessitating closer monitoring and potentially different management strategies 1.

From the Research

First-Degree AV Block Overview

• First-degree AV block is a condition where the electrical signal from the atria to the ventricles is delayed, but not blocked 2.
• It was previously considered a benign condition, but recent studies have shown that it may be associated with an increased risk of heart failure, pacemaker implantation, and death 2.

Clinical Manifestations and Indications for Pacing

• Marked first-degree AV block (PR > 0.30 s) can produce a clinical condition similar to that of the pacemaker syndrome 3.
• Clinical evaluation often requires a treadmill stress test because patients are more likely to become symptomatic with mild or moderate exercise when the PR interval cannot adapt appropriately 3.
• Uncontrolled studies have shown that many symptomatic patients with normal left ventricular function improve with conventional dual-chamber pacing 3.

Pacemaker Management and Consequences

• Patients with first-degree AV block have a poorer outcome with cardiac resynchronization therapy (CRT) than patients with a normal PR interval 3.
• The long PR interval may be a marker of more advanced heart disease, and patients with first-degree AV block may experience more episodes of undetected "electrical desynchronization" 3.
• RV pacing with the optimal AV delay of 160 ms increased stroke volume in patients with pacemakers and first-degree AV block, but the risk of heart failure may be increased with RV pacing if the E/E' ratio is > 15 4.

Programming Patterns and Possible Consequences

• The optimal way of pacing in patients with an indication for pacing and concomitant first-degree AV block is not known, and firm guidelines on this topic are lacking 5.
• A retrospective chart review study found that the majority of patients had their pacemakers programmed to atrial pacing (AAI/DDD +/-R), whereas 32% and 2.7% of the pacemakers were programmed to AV-sequential pacing (DDD) and ventricular pacing (VVI), respectively 5.
• Patients with pacemakers programmed to AAI had a lower ventricular pacing percentage at follow-up, and the choice of pacing mode affects long-term pacing burden, which in turn has been shown to influence outcome 5.

Drug-Induced AV Block

• Beta-blockers, verapamil, and diltiazem are considered a cause of AV block for which pacemaker implantation is not indicated 6.
• However, it is not known if such patients can expect a benign course after discontinuation of the culprit medication, and drug discontinuation was followed by resolution of AV block in 41% of cases 6.
• Atrioventricular block that was "truly caused by drugs" was found in only 15% of patients who had II or III degree AV block during therapy with beta-blockers, verapamil, or diltiazem 6.