Unilateral pulmonary artery branch stenosis: diastolic prolongation of forward flow appears to maintain flow to the affected lung if the pulmonary valve is competent.

BACKGROUND: We sought to improve understanding of the diastolic prolongation of forward flow seen through a unilateral branch pulmonary artery (PA) stenosis.

METHODS AND RESULTS: Of patients studied by cardiovascular magnetic resonance (CMR) for congenital heart disease, we reviewed right and left PA flow to find 10 cases with a diastolic prolongation of flow in a stenosed branch PA. They were aged 20 years (median, range = 14-40 years, 7 males). Seven had transposition of the great arteries corrected by arterial switch (TGA-AS) and 3 had repaired tetralogy of Fallot (rToF). All had at least moderate unilateral stenosis and competent pulmonary valves. For comparison, we identified 10 patients with unilateral stenosis and at least moderate pulmonary regurgitation, 9 rTOF and 1 TGA-AS, aged 23.5 years (range = 14-42 years, 6 males). Flow in each PA was measured, and in 10 healthy volunteers aged 27 years (range = 20-42 years, 5 males). The curves of flow through stenosed and non-stenosed arteries were averaged for each patient group and compared with those from controls. In competent pulmonary valve patients, the minimum diameters of the stenosed versus non-stenosed branches were as follows (median [range]): 4 [3-8] mm versus 13.5 [10-28] mm, p<0.001, although their flows differed a little: 2.5 [1.5-6.8] L/min versus 3.2 [1.2-8.8] L/min, p=0.6. No diastolic tail was identifiable in the patients with unilateral PA stenosis and pulmonary regurgitation, where stenosed versus non-stenosed diameters were 7 [4-12] mm versus 20.5 [13-33] mm, p<0.001, and flows differed: 1.3 [0.4-2.9] L/min versus 3.8 [3.0-5.0] L/min, p<0.001. No controls showed stenosis or diastolic tail.

CONCLUSIONS: Beyond a competent pulmonary valve, flow through a unilateral PA stenosis, although limited in systole, can continue into diastole, maintaining flow to the lung.