Aortic Regurgitation Severity Classification by Pressure Half-Time
For chronic aortic regurgitation, pressure half-time (PHT) <200 ms indicates severe AR, PHT >500 ms indicates mild AR, and intermediate values (200-500 ms) suggest moderate AR 1.
Specific PHT Cutoff Values
The European Association of Cardiovascular Imaging provides the most widely accepted thresholds:
- Mild AR: PHT >500 ms
- Moderate AR: PHT 200-500 ms (intermediate range)
- Severe AR: PHT <200 ms
These values are derived from continuous wave Doppler assessment of the aortic regurgitant jet, typically obtained from the apical five-chamber view 1.
Critical Caveats and Limitations
PHT should only serve as a complementary parameter, not a standalone measure 1. Several important factors significantly influence PHT measurements:
Physiologic Factors That Shorten PHT (May Overestimate Severity):
- Increased LV diastolic pressure
- Vasodilator therapy
- Dilated, compliant aorta
- Tachycardia (particularly HR ≥85 bpm) 2
- Acute severe AR (PHT almost always short regardless of actual severity)
Factors That Lengthen PHT (May Underestimate Severity):
- Chronic AR with compensated LV
- Bradycardia
- Reduced aortic compliance
- Left ventricular hypertrophy 3
Technical Considerations:
- Requires excellent Doppler beam alignment with careful probe angulation 1
- Cannot be measured in 17-25% of patients due to faint or absent Doppler signal 3
- Chamber compliance and aorto-ventricular pressure gradient significantly affect measurements 1
Practical Application Algorithm
- Obtain PHT measurement from apical five-chamber view (or right parasternal for eccentric jets)
- Check heart rate: If HR ≥85 bpm, consider corrected PHT (PHT/√RR interval) with adjusted cutoff <300 ms for severe AR 2
- Assess LV hypertrophy:
- Without significant LVH: Use PHT <347 ms for severe AR
- With more than mild LVH: Use PHT <420 ms for severe AR 3
- Always integrate with other parameters: PHT alone is insufficient—must combine with vena contracta (≥6 mm for severe), EROA (≥30 mm² for severe), regurgitant volume (≥60 mL for severe), and holodiastolic flow reversal in descending aorta (end-diastolic velocity >20 cm/s for severe) 1
When PHT is Most Reliable
PHT <300 ms has high specificity (92%) and predictive value (90%) for significant AR 4. The method is most valuable for identifying patients with the most severe regurgitation who need early surgical intervention 5. However, PHT values between 300-500 ms show considerable overlap between severity grades and should not be used in isolation 5.
The 2020 ACC/AHA guidelines notably do not include PHT in their severity grading criteria, instead emphasizing vena contracta, regurgitant volume, regurgitant fraction, and ERO 6. This reflects the limitations and variability of PHT measurements in clinical practice.