Objectives: This study was designed to investigate the value of noninvasive imaging modalities for the detection of obstruction in extracardiac ventriculopulmonary conduits.
Background: the diagnosis of obstruction in a conduit by noninvasive methods can be difficult. Obstruction may be silent and its progression unnoticed. Nuclear magnetic resonance imaging (NMR) with velocity mapping is a new noninvasive technique that can provide high resolution images and has been shown to be a reliable method of measuring blood flow velocity.
Methods: Two-dimensional echocardiography, pulsed wave Doppler echocardiography and NMR spin echo imaging were used in 52 patients with an extracardiac ventriculopulmonary conduit. Continuous wave Doppler echocardiography was used in 30 of these, Doppler color flow mapping in 26 and NMR velocity mapping in 12. Cardiac catheterization data were available in 27 patients and operative or autopsy findings in 11.
Results: The conduit could be assessed by two-dimensional and pulsed wave Doppler echocardiography in only 17% of patients. Doppler color flow and continuous wave echocardiography provided technically satisfactory data in 19% and 83%, respectively. The anatomy of the conduit was adequately displayed by NMR imaging in 90%. A minimal diameter less than 18 mm indicated conduit obstruction, although failure to detect calcification resulted in obstruction being missed in some patients. Calculated gradients in obstructed conduits derived from NMR velocity mapping correlated well with results of continuous wave Doppler echocardiography and gave an accurate localization of the site of obstruction as well as a measure of its severity.
Conclusion: NMR imaging with velocity mapping is the most effective noninvasive method of assessing obstruction in ventriculopulmonary conduits and can obviate the need for invasive investigation before an interventional procedure is performed.