Short PR Interval Criteria
A short PR interval is defined as less than 120 milliseconds on the surface ECG. 1, 2, 3
Core Diagnostic Criteria
The fundamental measurement is straightforward:
- PR interval <120 ms constitutes a short PR interval by international consensus 1, 2, 3
- This measurement represents the time from the onset of the P wave to the beginning of the QRS complex 1
Critical Distinction: Two Completely Different Clinical Entities
The presence or absence of additional ECG features determines whether this represents a benign finding or a potentially lethal condition:
Isolated Short PR (Benign Variant)
- Short PR interval (<120 ms) without delta wave 1, 2
- Normal QRS duration (<120 ms) 1, 2
- No further evaluation needed in asymptomatic individuals 1, 2
- Represents either normal variant (especially in athletes) or Lown-Ganong-Levine syndrome 2, 4
Wolff-Parkinson-White Pattern (Requires Comprehensive Evaluation)
The WPW pattern requires all three of the following criteria:
- PR interval <120 ms 1, 2, 3
- Presence of delta wave (slurred upstroke of the QRS complex) 1, 2, 3
- QRS duration >120 ms (widened QRS from fusion of two wavefronts) 1, 2, 3
Pathophysiology Underlying the Short PR
The mechanism differs between the two entities:
- WPW pattern: An accessory pathway bypasses the AV node entirely, allowing premature ventricular activation through abnormal tissue 1, 2, 3
- Isolated short PR: May reflect enhanced AV nodal conduction, shortened His-Purkinje conduction time, or dual AV nodal pathways 5, 6
Age-Specific Considerations
Use age-appropriate normative values, particularly in pediatric populations:
- Infants and children have naturally shorter PR intervals that must be adjusted for gestational age and chronological age 2
- In infantile Pompe disease, short PR interval appears in 75% of cases alongside extremely tall QRS complexes 2
Common Pitfalls to Avoid
Never dismiss WPW pattern as benign, even in completely asymptomatic patients—sudden cardiac death can be the first manifestation in approximately 50% of cases 2, 4
Do not confuse isolated short PR with WPW pattern—the presence of a delta wave and QRS widening completely changes management from no evaluation to mandatory comprehensive risk stratification 2
Ensure proper ECG calibration, especially when QRS voltage is extremely high (as in Pompe disease), as operators may decrease gain and miss the short PR interval 2
Measure PR interval in multiple leads—variation of >30 ms between leads on the same ECG may indicate minimal pre-excitation even when classic WPW criteria are not fully met 7