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

Short PR Interval: Clinical Significance and Implications

A short PR interval on an electrocardiogram (ECG) primarily indicates ventricular pre-excitation, most commonly seen in Wolff-Parkinson-White (WPW) syndrome, which requires careful evaluation due to the risk of sudden cardiac death. 1

Definition and Diagnostic Criteria

• A short PR interval is typically defined as less than 120 ms and may be associated with ventricular pre-excitation syndromes 1
• In WPW syndrome, the classic ECG findings include a short PR interval, prolonged QRS duration, and initial slurring of the QRS complex (delta wave) 2
• The short PR interval occurs due to an accessory pathway that bypasses the AV node, allowing for early ventricular activation 1

Clinical Significance

• Short PR interval with a delta wave (widened QRS) indicates WPW syndrome, which carries a risk of sudden cardiac death due to rapid conduction of atrial fibrillation across the accessory pathway potentially leading to ventricular fibrillation 1
• An isolated short PR interval without delta wave or widened QRS may represent either a normal variant (particularly in athletes) or Lown-Ganong-Levine syndrome 1
• Short PR interval has been associated with an increased risk of atrial fibrillation, particularly in women (HR 1.32,95% CI 1.12-1.56) 3

Risk Stratification in WPW Syndrome

• The highest risk for sudden cardiac death in WPW is associated with:
  • Shortest pre-excited RR interval <250 ms during atrial fibrillation 1, 4
  • History of symptomatic tachycardia 1
  • Multiple accessory pathways 1, 5
  • Presence of Ebstein's anomaly 1
• In children with WPW who experienced cardiac arrest, a shortest pre-excited RR interval <220 ms was 100% sensitive for identifying those at risk for sudden death 4
• Adenosine administration during pre-excited atrial fibrillation can precipitate ventricular fibrillation, particularly in patients with accessory pathways having short refractory periods 6

Evaluation Approach

• For patients with short PR interval with delta wave (WPW pattern), further evaluation should include: 1

  • Assessment of symptoms (palpitations, syncope)
  • Family history of pre-excitation, cardiomyopathy, or sudden death
  • Echocardiography to rule out structural heart disease (Ebstein anomaly, hypertrophic cardiomyopathy, glycogen storage disease)
  • Risk stratification with exercise testing, where abrupt loss of pre-excitation at higher heart rates suggests a low-risk pathway
  • Electrophysiological study for definitive risk assessment if non-invasive testing is inconclusive

• For isolated short PR interval without delta wave: 1

  • Careful evaluation is still warranted as it may reflect either Lown-Ganong-Levine syndrome or underlying structural heart disease such as hypertrophic cardiomyopathy or Fabry's disease

Management Considerations

• For high-risk WPW (shortest pre-excited RR interval ≤250 ms during atrial fibrillation), catheter ablation is recommended 1
• Intermittent pre-excitation during sinus rhythm suggests a low-risk pathway 1
• Some physicians recommend electrophysiological studies for all competitive athletes involved in moderate or high-intensity sports regardless of non-invasive test results 1

Important Caveats

• Cardiac arrest is the first manifestation of WPW in approximately half of cases, emphasizing the importance of proper identification and risk stratification 1
• Non-invasive tests are considered inferior to invasive electrophysiological assessment for determining sudden cardiac death risk in WPW syndrome 1
• The loss of pre-excitation after administration of procainamide has been used to identify low-risk patients 1