What is the significance of a short PR interval on a 12‑lead electrocardiogram and how should it be evaluated and managed?

Short PR Interval: Clinical Significance and Management

Definition and Initial Assessment

A short PR interval (<120 ms) in isolation without a delta wave or widened QRS is typically a benign finding in asymptomatic individuals—particularly athletes—and does not require further evaluation. 1

However, the presence of a delta wave (slurred initial QRS upstroke) combined with a short PR interval and QRS duration >120 ms defines Wolff-Parkinson-White (WPW) pattern, which carries a risk of sudden cardiac death and mandates comprehensive evaluation. 1

Critical Distinction: WPW Pattern vs. Isolated Short PR

WPW Pattern (High-Risk Finding)

• Diagnostic criteria: PR interval <120 ms + delta wave + QRS duration >120 ms 1
• Occurs in approximately 1 in 250 athletes 1
• Sudden death can be the first manifestation due to rapid conduction of atrial fibrillation across the accessory pathway leading to ventricular fibrillation 1

Isolated Short PR (Usually Benign)

• PR <120 ms without delta wave or QRS widening 1
• Represents either enhanced AV nodal conduction or Lown-Ganong-Levine syndrome 2
• In asymptomatic athletes with normal echocardiogram, no further assessment is needed 1

Evaluation Algorithm

Step 1: Examine QRS Morphology

• Look for delta wave (slurred initial QRS upstroke) in all 12 leads 1, 3
• Measure QRS duration 1
• Assess for absence of septal R wave in lead aVR (suggests pre-excitation) 3
• Calculate PR dispersion (difference between maximum and minimum PR intervals across all leads); ≥20 ms suggests pre-excitation 3

Step 2: If WPW Pattern Confirmed

Mandatory workup includes: 1, 2

• Detailed symptom history: Specifically ask about palpitations, syncope, near-syncope, chest discomfort with palpitations, and episodes lasting >30 minutes 2
• Family history: Pre-excitation syndromes, cardiomyopathy, sudden cardiac death in young relatives 2
• Echocardiography: Rule out Ebstein's anomaly, hypertrophic cardiomyopathy, and glycogen storage cardiomyopathy (PRKAG2-related familial WPW) 1, 2

Step 3: Risk Stratification for WPW

Exercise stress testing (first-line non-invasive test): 1, 2

• Abrupt, complete loss of pre-excitation at higher heart rates = low-risk pathway 1
• This finding suggests a long anterograde refractory period and lower sudden death risk 1, 2
• May permit continued athletic participation in low-risk cases 1

24-hour Holter monitoring: 2

• Detects paroxysmal tachyarrhythmias 2
• Intermittent pre-excitation during sinus rhythm on resting ECG or Holter = low-risk pathway and may obviate need for exercise testing 1

Electrophysiological study (if non-invasive testing inconclusive): 1

• Determines shortest pre-excited RR interval during atrial fibrillation 1
• Shortest pre-excited RR interval ≤250 ms (≥240 bpm) = high-risk pathway requiring catheter ablation 1
• Some physicians advocate EP study for all competitive athletes in moderate/high-intensity sports regardless of exercise test results, given that high catecholamine levels during intense exercise may modify accessory pathway refractory period in ways not reproducible in laboratory testing 1

Step 4: If Isolated Short PR (No Delta Wave)

Assess for symptoms and structural disease: 2

• If asymptomatic with normal echocardiogram and no high-risk findings on exercise testing or Holter: likely benign variant, periodic surveillance with repeat ECG and clinical review 2
• If symptomatic (palpitations, syncope): Consider echocardiography to exclude hypertrophic cardiomyopathy, Fabry disease, or Pompe disease 2

Consider alternative diagnoses: 2

• Fabry disease: X-linked lysosomal storage disorder with short PR, sinus bradycardia, and left ventricular hypertrophy; consider especially with multisystem symptoms 2
• Pompe disease: Rare genetic disorder with short PR, extremely tall QRS complexes, and cardiomegaly 2
• Lown-Ganong-Levine syndrome: Short PR without delta wave, may predispose to supraventricular tachycardia 2

Management Recommendations

For Confirmed WPW Pattern

Catheter ablation is the definitive treatment for WPW pattern given sudden death risk, with >95% acute success rate, <5% recurrence, and <1% risk of complete heart block 2

High-risk features mandating ablation: 1

• Shortest pre-excited RR interval ≤250 ms during atrial fibrillation 1
• Symptomatic tachycardia 1
• Competitive athletes in moderate/high-intensity sports (many electrophysiologists recommend EP study and potential ablation regardless of stress test results) 1

For Isolated Short PR

Asymptomatic with normal echocardiogram: No further evaluation required; periodic clinical surveillance 1, 2

Symptomatic with arrhythmias: Beta-blockers or calcium channel blockers for supraventricular tachycardia control 2

Critical Pitfalls to Avoid

• Never dismiss WPW pattern as benign, even in asymptomatic patients—sudden death can occur without warning 1, 2
• Do not attribute short PR to "athletic heart" without carefully excluding delta wave 2
• Avoid AV-nodal blocking drugs (beta-blockers, calcium channel blockers, digoxin, adenosine) in WPW with atrial fibrillation—these can enhance conduction through the accessory pathway and precipitate hemodynamic collapse or ventricular fibrillation 2
• Ensure proper ECG calibration, especially with high QRS voltage (Pompe disease) 2
• Use age-appropriate PR interval norms, particularly in pediatric populations 2
• Consider Fabry disease before attributing short PR + LVH to hypertension or athletic heart 2