IMPROVED MEASUREMENT OF PRESSURE-GRADIENTS IN AORTIC COARCTATION BY MAGNETIC-RESONANCE-IMAGING

Objectives. This study evaluated whether magnetic resonance imaging (M RI) and magnetic resonance (MR) phase velocity mapping could provide a ccurate estimates of stenosis severity and pressure gradients in aorti c coarctation. Background. Clinical management of aortic coarctation r e quires determination of lesion location and severity and quantificat ion of the pressure gradient across the constricted area, Methods. Usi ng a series of anatomically accurate models of aortic coarctation, the laboratory portion of this study found that the loss coefficient (K), commonly taken to be 4.0 in the simplified Bernoulli equation Delta P = KV2, was a function of stenosis severity. The values of the loss co efficient ranged from 2.8 for a 50% stenosis to 4.9 for a 90% stenosis , Magnetic resonance imaging and MR phase velocity mapping were then u sed to determine coarctation severity and pressure gradient in 32 pati ents. Results. Application of the new severity-dependent loss coeffici ents found that pressure gradients deviated from 1 to 17 mm Hg compare d with calculations made with the commonly used value of 4.0, Comparis on of MR estimates of pressure gradient with Doppler ultrasound estima tes (in 22 of 32 patients) and with catheter pressure measurements (in 6 of 32 patients) supports the conclusion that the severity based los s coefficient provides improved estimates of pressure gradients. Concl usions. This study suggests that MRI could he used as a complete diagn ostic toot for accurate evaluation of aortic coarctation, by determini ng stenosis location and severity and by accurately estimating pressur e gradients. (C) 1996 by the American College of Cardiology