Insights into catheter Doppler discrepancies in congenital aortic stenosis

Despite inherent discrepancies between Doppler and catheter gradients in ao rtic stenosis, the simplified Bernoulli equation is still the accepted noni nvasive technique to quantitate severity. The Reynolds number is a dimensio nless parameter that characterizes the nature of flow as being viscous, tur bulent, or transitional. Recently, in vivo and animal studies have successf ully used a Reynolds number-based approach to reconcile Doppler-estimated a nd catheter-measured discrepancies. At the midrange of Reynolds number, pre ssure recovery effects are most evident, resulting in "overestimation" of c atheter gradients by Doppler, At the lower range of the Reynolds number vis cous effects are important, whereas at a higher range, turbulent factors ar e dominant; both result in a tendency toward agreement. We recorded 18 peak instantaneous gradients from dual left ventricular catheters (15 to 95 mm Hg), while simultaneously recording Doppler velocities before and after int ervention in 11 pediatric patients (ages 0.5 to 16 years, mean 4.5), Dopple r correlated but overestimated catheter-measured peak instantaneous gradien ts (y = 0.84x + 18.4, r = 0.8, SEE +/- 15.2 mm Hg, mean percent difference 29.9 +/- 36) over the range of catheter gradients measured. Accounting for the Reynolds number successfully collapsed delta onto a single curve. Our s tudy confirms in a clinical setting the importance of applying fluid dynami c principles such as the Reynolds number to explain apparent discrepancies between catheter and Doppler gradients. These principles provide a foundati on for developing clinically appropriate correction factors. (C) 1999 by Ex cerpta Medico, Inc.