Early Onset of Retrograde Flow in the Main Pulmonary Artery is a Characteristic of Pulmonary Arterial Hypertension

Purpose: To evaluate if early onset of retrograde flow in the main pulmonary artery is a characteristic of pulmonary arterial hypertension (PAH). Materials and Methods: Fifty-five patients with suspected pulmonary hypertension (PH) underwent rightsided heart catheterization and retrospectively ECG-gated MR phase-contrast velocity quantification in the main pulmonary artery. Pulmonary hypertension was defined by a mean pulmonary artery pressure being larger than 25 mmHg. The onset time of the retrograde flow relative to the cardiac cycle duration (Relative Onset Time ROT) was compared with mean pulmonary artery pressure. Results: By the catheterization, 38 patients were identified as having PAH. The ROT for these PAH patients was significantly different from those found in the 17 non-PH subjects (0.14 +/- 0.06 versus 0.37 +/- 0.06, P < 0.001). The mean pulmonary artery pressure was related to the ROT (r(2) = 0.62, P < 0.001) and could be estimated from the ROT with a standard deviation of 11.7 mmHg. With a cutoff value of 0.25, the ROT distinguished PAH patients from non-PH subjects. Conclusion: Early onset of retrograde flow in the main pulmonary artery is a characteristic of pulmonary arterial hypertension and is visible by standard MR phase-contrast velocity quantification.