What Does PRP Finding in ECG Stand For?
PRP on an ECG stands for "PR Prolongation" or "P-R interval Prolongation," which refers to a PR interval exceeding 200 milliseconds, clinically defined as first-degree atrioventricular (AV) block. 1
Definition and Measurement
The PR interval represents the time from the onset of atrial depolarization (beginning of the P wave) to the onset of ventricular depolarization (beginning of the QRS complex). 2
Normal PR interval: 120-200 milliseconds 1, 2
PR prolongation (first-degree AV block): PR interval >200 milliseconds 1, 2
To measure accurately:
- Identify the earliest onset of the P wave across multiple leads 2
- Mark the earliest deflection of the QRS complex across all leads 2
- Count the small boxes between these points (each small box = 40 milliseconds) 2
Clinical Significance
The PR interval provides critical diagnostic information about atrial and AV nodal conduction. 1 When prolonged beyond 200 ms, it indicates delayed AV conduction, most commonly occurring at the level of the AV node. 1
Prognostic Implications
PR prolongation is not always benign despite traditional teaching:
- Increased risk of atrial fibrillation: 2-fold adjusted risk (HR 2.06) 3
- Increased risk of pacemaker requirement: 3-fold adjusted risk (HR 2.89) 3
- Increased all-cause mortality: 1.4-fold adjusted risk (HR 1.44) 3
- Each 20-millisecond increment in PR interval increases mortality risk by 8% (HR 1.08) 3
However, one large European study found no increased mortality in middle-aged populations, and noted that PR intervals normalized in 30% of affected individuals during long-term follow-up. 4 This discrepancy highlights the importance of considering patient age and comorbidities.
Degrees of PR Prolongation
Mild prolongation: 200-280 ms - typically represents AV nodal delay 5
Moderate prolongation: 280-400 ms - suggests more diffuse conduction system involvement 5
Marked prolongation: ≥400 ms - requires further evaluation even in athletes 6, 2
Special Consideration: Athletes
In highly trained athletes with increased vagal tone, PR intervals up to 400 ms may be physiological and normal. 6, 2 The key distinguishing feature is that the PR interval should normalize with mild aerobic activity (running in place, climbing stairs). 6, 2
When to Evaluate Further
Immediate evaluation is warranted for:
- PR interval ≥400 ms 6, 2
- Symptoms of presyncope or syncope 6
- PR interval that fails to normalize with exercise 6, 2
- Family history of cardiac disease or sudden death 6
- Associated bifascicular block with syncope 6
Evaluation should include:
- Exercise ECG testing to assess chronotropic response 6, 2
- Echocardiogram if structural disease suspected 6
- Ambulatory ECG monitoring if symptoms present 6
Common Pitfall
Do not assume all first-degree AV block is benign. 7 Extremely prolonged PR intervals (>0.48-0.56 seconds) can be associated with AV dissociation and pseudo-pacemaker syndrome, causing exercise intolerance and syncope despite being classified as "first-degree" block. 7 These cases require subspecialty evaluation and may need pacing despite the traditional teaching that first-degree AV block never requires intervention.