title: Understanding the mechanism for branch pulmonary artery stenosis after the arterial switch operation for transposition of the great arteries.
abstract: OBJECTIVE
  The pathophysiology of branch pulmonary artery (PA) stenosis after the arterial switch operation, most commonly on the left, is incompletely understood. This study examines factors associated with left PA (LPA) obstruction.
  
  
  RESULTS
  Cardiac magnetic resonance (CMR) imaging studies performed in patients after arterial switch operation (ASO) were retrospectively analysed. Blood flow was measured in both branch PAs and neo-pulmonary root position in relation to the aorta was expressed as an angle, relative to a line connecting the sternum and the spine. Sixty-six patients were included for analysis. Seventy per cent (n = 46) had balanced pulmonary blood flow, 28% (n = 18) had decreased flow to the left, and 2% (n = 2) had decreased flow to the right lung. LPA area indexed to body surface area (BSA) was smaller than RPA area (62 ± 37 vs. 120 ± 64 mm2/m2, P < 0.0001). Patients with reduced LPA flow were more likely to have required pulmonary arterioplasty at the time of ASO (17 vs. 2%, P = 0.04) and had a larger aortic root diameter (25 ± 7 vs. 22 ± 5 mm2/m2, P = 0.01). Greater rightward orientation of the neo-pulmonary root correlated inversely with LPA cross-sectional area (r = -0.39, P = 0.001) but not with LPA flow. Aortic root diameter correlated inversely with LPA flow (r = -0.43, P = 0.0004) but not with LPA cross-sectional area (P = 0.32). Patients with a rightward neo-pulmonary root and/or a dilated aortic root in the upper quartile range had a smaller LPA area (53 vs. 73 mm2/m2, P = 0.04) and less pulmonary blood flow (41 vs. 46%, P = 0.02) compared with patients without those risk factors.
  
  
  CONCLUSIONS
  Neo-pulmonary to neo-aortic geometry as well as post-operative compression of the LPA by an enlarged aorta impact LPA size and perfusion of the left lung.
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8.
authors.forename: Conall Thomas
authors.initials: CT
authors.lastname: Morgan
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8.
authors.forename: Luc
authors.initials: L
authors.lastname: Mertens
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8.
authors.forename: Heynric
authors.initials: H
authors.lastname: Grotenhuis
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8.|Department of Diagnostic Imaging, The Hospital for Sick Children, University of Toronto, Toronto, Canada.
authors.forename: Shi-Joon
authors.initials: SJ
authors.lastname: Yoo
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8.|Department of Diagnostic Imaging, The Hospital for Sick Children, University of Toronto, Toronto, Canada.
authors.forename: Mike
authors.initials: M
authors.lastname: Seed
authors.affiliation: Labatt Family Heart Centre, The Hospital for Sick Children, Department of Pediatrics, University of Toronto, 555 University Avenue, Toronto, ON, Canada M5G 1X8 lars.grosse-wortmann@sickkids.ca.|Department of Diagnostic Imaging, The Hospital for Sick Children, University of Toronto, Toronto, Canada.
authors.forename: Lars
authors.initials: L
authors.lastname: Grosse-Wortmann
mesh_terms: D000069278:Arterial Switch Operation / Q000009:adverse effects* / Q000379:methods; D001783:Blood Flow Velocity; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D019918:Heart Valve Prosthesis Implantation / Q000379:methods; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D019028:Magnetic Resonance Imaging, Cine / Q000379:methods*; D008297:Male; D011652:Pulmonary Circulation / Q000502:physiology*; D011666:Pulmonary Valve Stenosis / Q000000981:diagnostic imaging* / Q000209:etiology / Q000401:mortality / Q000601:surgery; D012189:Retrospective Studies; D018570:Risk Assessment; D015996:Survival Rate; D013997:Time Factors; D014188:Transposition of Great Vessels / Q000000981:diagnostic imaging / Q000401:mortality / Q000601:surgery*; D016896:Treatment Outcome; D014654:Vascular Patency / Q000502:physiology
keywords: Arterial switch; Branch pulmonary artery stenosis; Complications; Magnetic resonance imaging; Transposition of the great arteries