Pulmonary regurgitation in the late postoperative follow-up of tetralogy of Fallot. Volumetric quantitation by nuclear magnetic resonance velocity mapping.

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Abstract
BACKGROUND Pulmonary regurgitation frequently occurs after surgical correction of tetralogy of Fallot. To date, reliable quantitation of pulmonary regurgitation has not been possible, and therefore the clinical significance of pulmonary regurgitation is controversial. Nuclear magnetic resonance (NMR) velocity mapping allows accurate measurement of volumetric flow. The feasibility and accuracy of NMR velocity mapping to quantify pulmonary regurgitation volumes are studied in patients after Fallot repair. METHODS AND RESULTS In 18 patients (mean age, 16.5 +/- 6.5 years), late (12.6 +/- 5.2 years) after Fallot surgery, forward and regurgitant volume flow was measured in the main pulmonary artery with NMR velocity mapping. To validate the measurements of pulmonary forward flow, right ventricular stroke volume was used as an internal reference standard. Pulmonary regurgitation volumes were compared with the differences between the corresponding right and left ventricular stroke volumes. Ventricular volumes were measured with a multisection gradient echo NMR method. In addition, the relation between pulmonary regurgitation and right ventricular volumes was studied. Measurements of pulmonary regurgitation volume with NMR velocity mapping closely corresponded with the tomographically determined volumes (r = .93). Forward pulmonary volume flow was nearly identical to right ventricular stroke volume (r = .98). Pulmonary regurgitation volume was significantly correlated with end-diastolic volume (r = .82, P < .0005), end-systolic volume (r = .63, P < .01), and stroke volume (r = .89, P < .0005) of the right ventricular but not with right ventricular ejection fraction (r = .41, P = NS). CONCLUSIONS NMR velocity mapping is an accurate method for the noninvasive, volumetric quantification of pulmonary regurgitation after surgical correction of tetralogy of Fallot.

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