Differential Branch Pulmonary Artery Regurgitant Fraction Is a Function of Differential Pulmonary Arterial Anatomy and Pulmonary Vascular Resistance

Objectives We sought to investigate whether differential branch pulmonary artery (BPA) regurgitation correlates with differences in BPA anatomy and physiology. Background Patients with repaired conotruncal anomalies such as Tetralogy of Fallot frequently have residual BPA stenosis or BPA size differences. Previous reports have demonstrated an increased left pulmonary artery (LPA) regurgitant fraction (RF) in these patients. Methods We retrospectively reviewed 76 consecutive cardiac magnetic resonance (CMR) studies for BPA size and phase-contrast magnetic resonance data, including 13 consecutive patients who underwent both CMR and catheterization. Results Thirty of the 76 patients had either BPA stenosis or significant size discrepancy. Whereas previous studies had shown an increased RF in the LPA, patients with BPA stenosis or size discrepancy showed no significant difference between right and left BPA RF (30% vs. 30%, p = 0.985). However, there was a significantly increased RF of the larger versus smaller BPA (39% vs. 21%, p < 0.001), resulting in an insignificant deviation from normal fractional flow distribution (RPA 63% vs. LPA 37%; normal net fractional flow distribution RPA 55% vs. LPA 45%). Retrospective review of patients who underwent both CMR and catheterization provides support for the preceding findings and validates differential BPA RF as strongly correlating with differential pulmonary vascular resistance (PVR) (r = 0.8364, p < 0.001). Conclusions BPA RF is a function of the relative PVR and the presence of BPA stenosis or size discrepancy. Contrary to prior reports, the LPA RF is only elevated in patients with relatively equal sized BPAs. In the setting of BPA stenosis or size discrepancy the larger BPA has a relatively increased RF and PVR. Therefore, the differential RF is an important tool for screening patients with unilateral stenosis for contralateral increases in PVR that cannot be identified with net flows alone. This can affect the indication and timing for BPA intervention.