Normal Main Pulmonary Artery Size on Echocardiography
The normal main pulmonary artery (MPA) diameter on transthoracic echocardiography is ≤25 mm, with values >25 mm considered abnormal and suggestive of pulmonary hypertension. 1, 2, 3
Guideline-Based Reference Values
The most recent and authoritative guidelines establish clear cutoffs:
- MPA diameter ≤25 mm is normal 1, 2, 3
- MPA diameter >25 mm is abnormal and represents one of the echocardiographic signs suggesting pulmonary hypertension 1, 2, 3
This threshold is part of the standardized criteria used by both the 2022 ACR Appropriateness Criteria and the 2015 ESC/ERS Guidelines for assessing pulmonary hypertension probability 1, 2, 3.
Body Size and Age Considerations
While the 25 mm cutoff is the established guideline standard, recent research suggests that indexing to height may provide more accurate reference limits:
- The 95th percentile for height-indexed MPA diameter is 15 mm/m in diastole and 19 mm/m in systole 4
- Age has only a weak effect on MPA size (explaining only 8-10% of variance) 4
However, these indexed values are from a 2024 research study and have not yet been incorporated into clinical guidelines. For clinical decision-making, use the guideline-established 25 mm cutoff.
Cardiac Phase Matters
Measurements should be made at end-diastole for consistency, as the MPA diameter varies with the cardiac cycle 4, 5. Systolic measurements are consistently larger than diastolic measurements 5.
Clinical Context
The MPA diameter is used as part of a comprehensive echocardiographic assessment for pulmonary hypertension, which includes:
- Category A (Ventricular): RV/LV basal diameter ratio >1.0, septal flattening
- Category B (Pulmonary Artery): PA diameter >25 mm, RV outflow acceleration time <105 ms, early diastolic PR velocity >2.2 m/s
- Category C (IVC/RA): IVC diameter >21 mm with decreased collapse, RA area >18 cm² 1, 2, 3
At least two categories must be positive to support an intermediate or high probability of pulmonary hypertension 1, 2, 3.
Important Caveats
- MPA diameter alone should not be used to diagnose pulmonary hypertension - it must be combined with other echocardiographic parameters and clinical context 1, 2, 3
- The MPA/ascending aorta ratio >1.0 is highly specific (96% positive predictive value) for pulmonary hypertension 6
- Right heart catheterization remains the gold standard for confirming pulmonary hypertension before initiating therapy 1, 6