From the Guidelines
A prolonged PR interval can indicate first-degree atrioventricular block, which may lead to symptoms such as fatigue, exertional intolerance, or dizziness, particularly if the PR interval is greater than 300 ms, as stated in the 2019 ACC/AHA/HRS guideline 1.
Key Points to Consider
- Prolonged PR interval is defined as a PR interval greater than 200 milliseconds.
- First-degree atrioventricular block can be asymptomatic, but it may also cause symptoms such as fatigue, exertional intolerance, or dizziness, especially if the PR interval is significantly prolonged.
- The 2019 ACC/AHA/HRS guideline suggests that a PR interval greater than 300 ms can lead to loss of atrioventricular synchrony, resulting in decreased cardiac output and increased pulmonary capillary wedge pressure, also known as "pseudo pacemaker syndrome" 1.
- Underlying causes of prolonged PR interval include aging, medications, electrolyte abnormalities, increased vagal tone, myocarditis, coronary artery disease, or infiltrative heart diseases.
- In asymptomatic patients without other cardiac issues, no specific treatment is typically needed, but for symptomatic patients or those with concerning underlying conditions, further cardiac evaluation is recommended.
Clinical Implications
- The PR interval represents the time needed for the electrical impulse to travel from the sinoatrial node through the atria and AV node to the ventricles, and prolongation occurs when conduction through these pathways is slowed.
- A prolonged PR interval can be a sign of underlying cardiac conditions, and its presence should prompt further evaluation to determine the underlying cause and guide treatment.
- The 2013 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 guidelines for device-based therapy of cardiac rhythm abnormalities provides additional guidance on the management of patients with bifascicular block and prolonged PR interval 2.
Management and Treatment
- In patients with symptomatic first-degree atrioventricular block, treatment may involve addressing the underlying cause, such as adjusting medications or treating underlying cardiac conditions.
- For patients with concerning underlying conditions or symptoms, further cardiac evaluation, including electrophysiological studies, may be necessary to guide treatment and prevent complications such as syncope or sudden death.
From the Research
Prolonged PR Interval Indications
A prolonged PR interval can indicate several conditions, including:
- Delayed conduction through the AV node 3
- Delayed electrical impulse propagation through any part of the conduction system 3
- First-degree atrioventricular block, which is defined as a PR interval exceeding 200 milliseconds 4
- Increased risk of atrial arrhythmias, heart failure, and mortality 3, 4
- AV dyssynchrony and subsequent symptoms of hemodynamic instability in the absence of an implanted pacemaker, also known as pseudo-pacemaker syndrome (PPMS) 5
Associated Risks and Outcomes
Studies have shown that a prolonged PR interval is associated with:
- Increased risk of atrial fibrillation (AF) 4
- Increased risk of pacemaker implantation 4
- Increased risk of all-cause mortality 4
- Increased rates of heart failure hospitalization or death among cardiac resynchronization therapy (CRT) patients 6
- A 2-fold adjusted risk of AF, 3-fold adjusted risk of pacemaker implantation, and 1.4-fold adjusted risk of all-cause mortality in individuals with first-degree atrioventricular block 4
Clinical Significance and Treatment
The clinical significance of PR prolongation can vary depending on the underlying cause and individual patient characteristics. Treatment should be patient-tailored and based on the specific etiology once identified 5. However, the treatment of PPMS due to dual AV nodal physiology (DAVNP) without AVNRT presentation is yet to be clarified 5.