Is sinus rhythm with first-degree atrioventricular (AV) block without symptoms a normal variant?

From the Guidelines

First-degree AV block without symptoms can indeed be a normal variant in some individuals. This condition, characterized by a prolonged PR interval on an ECG (greater than 200 milliseconds) with all atrial impulses still conducting to the ventricles, often requires no treatment when asymptomatic, as noted in the guidelines by the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society 1. In many cases, particularly in young adults, well-trained athletes, and during sleep, this finding represents a benign variation in cardiac conduction rather than pathology. The prolonged conduction time through the AV node may result from increased vagal tone, which is common in physically fit individuals.

Some key points to consider in the management of first-degree AV block without symptoms include:

• The presence of a significantly prolonged PR interval (>300 ms) may lead to symptoms even in the absence of higher degrees of AV block, as suggested by the 2012 ACCF/AHA/HRS focused update 1.
• First-degree AV block can sometimes be caused by medications (such as beta-blockers, calcium channel blockers, or digoxin), electrolyte abnormalities, or underlying heart disease.
• For asymptomatic individuals with isolated first-degree AV block and no other cardiac abnormalities, routine monitoring is typically sufficient without specific intervention, as there is little evidence to suggest that pacemakers improve survival in patients with isolated first-degree AV block 1.
• If other conduction abnormalities develop, closer follow-up may be warranted even in the absence of symptoms.

It's also important to note that AV block can sometimes be provoked by exercise, and if not secondary to myocardial ischemia, AV block in this circumstance usually is due to disease in the His-Purkinje system and is associated with a poor prognosis; thus, pacing is indicated 1. However, in the absence of symptoms, these abnormalities are reversible and do not require pacing. The decision regarding implantation of a pacemaker must be considered with respect to whether AV block will be permanent, and reversible causes of AV block, such as electrolyte abnormalities, should be corrected first 1.

From the Research

Sinus Rhythm First Degree AV Block Without Symptoms

• First-degree AV block is generally considered a benign condition, but recent studies have shown that it may be associated with an increased risk for heart failure, pacemaker implantation, and death 2, 3, 4.
• A study published in the Journal of Interventional Cardiac Electrophysiology found that 40.5% of patients with first-degree AV block received a pacemaker during follow-up, and in 93.3% of cases, the implant was needed to treat a more severe bradycardia or progression of the conduction disease 2.
• Another study published in the Annals of Noninvasive Electrocardiology noted that extreme forms of first-degree AV block can cause symptoms due to inadequate timing of atrial and ventricular contractions, similar to the pacemaker syndrome 5.
• The Mode Selection Trial found that patients with first-degree AV block were at greater risk of death, stroke, or heart failure hospitalization, and had a trend towards a higher incidence of atrial fibrillation 3.
• A study published in the Journal of Hypertension found that first-degree AV block is an independent risk factor for future development of advanced AV block, atrial fibrillation, and left ventricular dysfunction in patients with hypertension 4.

Clinical Implications

• First-degree AV block may not be entirely benign, and patients with this condition should be monitored for progression to higher grade block or bradycardia requiring pacemaker implantation 2, 3, 4.
• The presence of first-degree AV block may be a marker of more advanced heart disease, and patients with this condition may have a poorer outcome with cardiac resynchronization therapy 6.
• Patients with first-degree AV block and symptoms similar to those of pacemaker syndrome or with hemodynamic compromise may benefit from permanent pacemaker implantation 5.

Risk Factors

• Advanced age, male sex, and presence of comorbidities such as hypertension and heart failure may be associated with an increased risk of adverse outcomes in patients with first-degree AV block 3, 4.
• The presence of first-degree AV block may be a risk factor for future development of advanced AV block, atrial fibrillation, and left ventricular dysfunction in patients with hypertension 4.