From the Guidelines
A prolonged PR interval signifies a delay in electrical conduction between the atria and ventricles of the heart, indicating first-degree atrioventricular block, which may be associated with underlying heart conditions, and requires identification of the underlying cause and consideration of treatment based on symptoms and degree of prolongation.
Causes and Clinical Significance
The causes of a prolonged PR interval include medications (beta-blockers, calcium channel blockers, digoxin, amiodarone), increased vagal tone, electrolyte abnormalities (particularly hyperkalemia), ischemic heart disease, or degenerative conduction system disease, as outlined in the 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay 1.
Diagnosis and Treatment
The clinical significance of a prolonged PR interval depends on the patient's symptoms, the degree of prolongation, and associated cardiac conditions, with profound first-degree atrioventricular block potentially leading to symptoms of fatigue or exertional intolerance if the PR interval is long enough to allow for loss of atrioventricular synchrony 1.
Key Considerations
It is essential to carefully evaluate the ECG to diagnose atrioventricular block, considering the 1:1 relationship between P waves and QRS complexes, and to identify the underlying cause of the prolonged PR interval, as treatment may involve dosage adjustment of medications or addressing underlying heart conditions, with the goal of improving morbidity, mortality, and quality of life.
- Common symptoms associated with atrioventricular block include fatigue, exertional intolerance, dizziness, and syncope, particularly in patients with underlying heart disease or conduction abnormalities.
- The 2018 ACC/AHA/HRS guideline provides a comprehensive framework for the evaluation and management of patients with bradycardia and cardiac conduction delay, emphasizing the importance of careful ECG evaluation and consideration of underlying causes and associated cardiac conditions 1.
From the Research
Prolonged PR Interval Significance
A prolonged PR interval can signify several conditions, including:
- Pseudo-pacemaker syndrome (PPMS), a rare complication of first-degree atrio-ventricular (AV) block, which can cause AV dyssynchrony and symptoms of hemodynamic instability 2
- First-degree AV block, which can produce a clinical condition similar to pacemaker syndrome, especially with marked first-degree AV block (PR ≥ 0.30 s) 3
- Adverse cardiovascular outcomes, including increased risk of mortality, heart failure, and atrial fibrillation 4
Clinical Implications
The clinical implications of a prolonged PR interval include:
- Symptomatic patients with normal left ventricular function may improve with conventional dual-chamber pacing 3
- Patients with marked first-degree AV block and left ventricular systolic dysfunction may benefit from biventricular pacing 3
- Prolonged PR interval may be a marker of more advanced heart disease and may predispose to loss of ventricular resynchronization during cardiac resynchronization therapy (CRT) 3
Associated Risks
A prolonged PR interval has been associated with several risks, including: