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

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Abstract

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.

Introduction

Cardiovascular magnetic resonance (CMR) is widely used for the assessment of patients after surgery for congenital heart defects. It can provide structural and functional information that includes the pulmonary artery and its branches, non-invasively and without ionising radiation [1], [2]. Right or left branch pulmonary arteries (PA) stenosis may be found, notably after surgical repairs for transposition of the great arteries and tetralogy of Fallot.

The diastolic prolongation of forward flow, or diastolic tail, is known as an indicator of the haemodynamic significance of aortic coarctation or recoarctation [3], [4]. While reviewing CMR velocity acquisitions, we have seen similarly prolonged curves of flow in patients with a unilateral PA branch stenosis (Movie 1 and corresponding patient in Fig. 1a). We are not aware that this has been described before. We aimed to improve understanding of the nature and possible clinical implications of this pathophysiological finding.

Section snippets

Patient selection and healthy controls

We began by identifying patients with diastolic prolongation of forward flow in a branch pulmonary artery. This was initiated by one of us (PK) collecting examples as he recognised and reported them and supplemented by running a search for the finding in all CMR reports checked by him over a 5-year period, which included over 600 patients with either transposition of the great arteries corrected by arterial switch (TGA-ASO) or repaired tetralogy of Fallot (rToF) whose CMR acquisition protocols

Patient and volunteer group characteristics

In all, 20 patients aged 22 [14–42] years, 13 males (65%), with at least moderate unilateral branch PA stenosis were identified and studied. Ten patients had near competent pulmonary valve (PV) function, i.e. no significant pulmonary regurgitation, regurgitation fraction of 2.3% [0–8%] (Table 1) and at least moderate unilateral branch PA stenosis (Table 2). Seven patients had TGA-ASO, and 3 rToF. There were also 10 patients in the second group, all with incompetent PVs, regurgitation fraction

Discussion

We report the diastolic prolongation of flow that is associated with unilateral branch PA stenosis in a limited number of cases. We are not aware that a description of this has been published before. Despite the associated limitation of flow during systole, the prolongation of forward flow or diastolic tail was found to deliver net flow through the affected branch PA similar to that through the non-stenosed side, although this only occurred when the pulmonary valve was competent and not if it

Limitations

Significant unilateral branch PA stenosis combined with competence of the pulmonary valve appears to be relatively uncommon in the age group of patients studied. For this reason, the numbers of patients in each group were small, but nevertheless sufficient for significant differences to be found. For the same reason, it would have been hard to devise a realistic alternative to the retrospective and cross-sectional nature of the study. All measurements were made with patients at rest in the

Conclusion

Beyond a competent pulmonary valve, flow through a unilateral PA stenosis, although limited in systole can continue into diastole, maintaining flow volume to the lung on that side. This appears not to be the case if unilateral PA stenosis is combined with incompetence of the pulmonary valve, presumably because diastolic regurgitant flow ‘steals’ blood that might otherwise be delivered through the stenosis by recoil of the pulmonary trunk and contralateral PA branch. The reported differences of

Acknowledgement

The study was supported by the British Heart Foundation (PG/08/122) and the National Institutes of Health Cardiovascular Biomedical Research Unit at the Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London UK.

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Cited by (0)

Support is acknowledged from: The British Heart Foundation (PG/08/122) and the National Institutes of Health Cardiovascular Biomedical Research Unit at the Royal Brompton and Harefield NHS Foundation Trust and Imperial College, London UK.

☆☆

Neither author has any conflict of interest.

1

Both authors take responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation.

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