What does a short PR (P-R) interval syndrome mean?

Short PR Interval Syndrome: Clinical Significance and Evaluation

Definition and Significance

A short PR interval (<120 ms) without a widened QRS or delta wave in an asymptomatic individual is generally a benign finding that does not require further assessment. 1 However, when accompanied by specific features, it can indicate underlying cardiac conditions that require evaluation.

Associated Conditions

Short PR interval can be associated with several conditions:

1. Wolff-Parkinson-White (WPW) pattern/syndrome:

   • Characterized by PR interval <120 ms + delta wave + QRS duration >120 ms
   • Occurs in up to 1 in 250 athletes
   • Represents ventricular pre-excitation via an accessory pathway bypassing the AV node 2

2. Storage diseases:

   • Pre-excitation is common in Pompe disease, PRKAG2, and Danon disease
   • A short PR interval without pre-excitation is seen in Anderson-Fabry disease 2

3. Mitochondrial disorders:

   • MELAS (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes)
   • MERFF (Myoclonic Epilepsy with Ragged Red Fibers) 2

4. Lown-Ganong-Levine syndrome:

   • Short PR interval with normal QRS complex
   • Associated with paroxysmal atrial tachycardia 3

Pathophysiological Mechanisms

Short PR interval can result from:

• Accessory pathway conduction: Bypassing the normal delay in the AV node
• Enhanced AV nodal conduction: Faster than normal conduction through the AV node
• Sino-atrial conduction abnormalities: As proposed by Condorelli, a conduction defect in the sino-atrial pathways while sino-nodal conduction remains normal 4

Clinical Evaluation

For asymptomatic individuals with isolated short PR interval:

• If there is no widened QRS or delta wave, and no family history of sudden death, no further evaluation is typically needed 2, 1

For individuals with short PR interval plus delta wave (WPW pattern):

1. Initial assessment:

   • Echocardiogram to rule out structural heart disease
   • 24-hour ECG monitoring
   • Exercise stress test 1

2. Risk stratification:

   • Exercise testing: abrupt loss of pre-excitation at higher heart rates suggests a low-risk pathway
   • Intermittent pre-excitation during sinus rhythm also suggests low risk 2
   • High-risk features include shortest pre-excited RR interval ≤250 ms during atrial fibrillation 2

3. Electrophysiological study is recommended for:

   • Symptomatic patients
   • Patients with high-risk features
   • Athletes involved in moderate or high-intensity sports 2

Management

Management depends on the underlying cause and risk assessment:

• Asymptomatic short PR without delta wave: No specific treatment needed
• WPW pattern with high-risk features: Catheter ablation is recommended 2, 1
• Symptomatic patients: Treatment based on the specific arrhythmia

Special Considerations

• Pediatric patients may be at higher risk due to faster conduction through accessory pathways 1
• Avoid digoxin or verapamil in patients with suspected WPW as they can accelerate conduction through accessory pathways 1
• Athletes with WPW pattern may require more aggressive evaluation and management due to high catecholamine states during intense exercise 2

Common Pitfalls

• Misdiagnosis due to improper ECG calibration and technique
• Overlooking subtle delta waves that may indicate WPW pattern
• Underestimating risk in asymptomatic individuals with WPW pattern, as the first presentation can be sudden cardiac arrest 1
• Failure to recognize that short PR interval can be a marker of underlying metabolic or storage diseases, particularly in pediatric patients 2

In patients with short PR interval and symptoms such as palpitations or syncope, a thorough evaluation is essential to identify potential arrhythmic mechanisms and guide appropriate management.