Can sotalol prolong the PR (P-R) interval?

Sotalol's Effect on PR Interval

Yes, sotalol can prolong the PR interval due to its beta-blocking properties, which slow conduction through the atrioventricular (AV) node.

Mechanism of Action

Sotalol has a dual mechanism of action that affects cardiac conduction:

1. Beta-blocking activity (Class II):

   • Slows conduction through the AV node
   • Prolongs PR interval
   • Decreases heart rate

2. Potassium channel blocking (Class III):

   • Prolongs cardiac repolarization
   • Extends QT interval
   • Increases effective refractory period

Evidence for PR Interval Prolongation

The American Heart Association guidelines confirm that sotalol increases the PR interval by 4-6% (p<0.001) 1. This effect is primarily due to its beta-blocking properties, which slow conduction through the AV node.

Multiple studies have documented sotalol's effects on cardiac conduction intervals:

• Increases PR interval by approximately 6% 2
• Significantly lengthens AH interval (atrial to His bundle conduction time) 3
• Does not significantly affect HV interval (His bundle to ventricular conduction) 3

Clinical Implications

The PR interval prolongation with sotalol has several important clinical implications:

Monitoring Requirements

• ECG monitoring is necessary during initiation to assess PR interval, QRS duration, and QT interval 1
• Inpatient monitoring has traditionally been required for sotalol initiation, though recent evidence suggests home monitoring with remote ECG devices may be feasible in selected patients 4

Risk Factors for Excessive PR Prolongation

• Pre-existing conduction disease
• Concomitant use of other medications that affect AV conduction
• Electrolyte abnormalities (particularly hypokalemia)
• Renal dysfunction (sotalol is primarily renally cleared)

Contraindications

• Sotalol is contraindicated in patients with significant sinus or AV conduction disease without a pacemaker 5
• Should be used with caution in patients with first-degree AV block

Comparison to Other Antiarrhythmics

While sotalol prolongs the PR interval, its most concerning effect is QT interval prolongation, which can lead to torsades de pointes. The American College of Cardiology/American Heart Association guidelines note that when using class IA or class III drugs like sotalol, the corrected QT interval should be kept below 520 ms 1.

Practical Management

When initiating sotalol:

• Baseline ECG to assess PR interval and other intervals
• Start with lower doses in patients with borderline PR prolongation
• Monitor PR interval during dose titration
• Consider dose reduction if PR interval increases excessively
• Be vigilant for symptoms of bradycardia or higher-degree AV block

Conclusion

While sotalol's QT prolongation effect receives more attention due to the risk of torsades de pointes, its beta-blocking properties do cause PR interval prolongation that requires monitoring, especially in patients with pre-existing conduction abnormalities.