Maximal blood flow velocity in severe coronary stenoses measured with a Doppler guidewire: Limitations for the application of the continuity equation in the assessment of stenosis severity

Abstract

In vitro and animal experiments have shown that the severity of coronary stenoses can be assessed using the continuity equation if the maximal blood flow velocity of the stenotic jet is measured. The large diameter and the low range of velocities measurable without frequency aliasing with the conventional intracoronary Doppler catheters precluded the clinical application of this method for hemodynamically significant coronary stenoses in humans. This article reports the results obtained using a 12 MHz steerable angioplasty guidewire in a consecutive series of 52 patients undergoing percutaneous coronary angioplasty (61 coronary stenoses). The ratio between coronary flow velocity in a reference segment and in the stenosis was used to estimate the percent cross-sectional area stenosis. A Doppler recording suitable for quantization was obtained in the stenotic segment in only 10 of 61 arteries (16%). The time-averaged peak velocity increased from 15 ± 5 to 115 ± 26 cm/sec from the reference normal segment to the stenosis. Volumetric coronary flow calculated from the product of mean flow velocity and cross-sectional area was similar in the stenosis and in the reference segment (33.2 ± 14.9 vs 33.5 ± 17.0 ml/ min, respectively, difference not significant). The percent cross-sectional area stenosis and minimal luminal cross-sectional area derived from the Doppler velocity measurements using the continuity equation and calculated with quantitative angiography were also similar (Doppler, 86.7 ±5.1% and 1.00 ± 0.48 mm 2; quantitative angiography, 85.9 ± 7.9% and 1.02 ± 0.50 mm 2). A significant correlation was observed between Doppler-derived and angiographic measurements (percent cross-sectional area: r = 0.64, p < 0.05; minimal cross-sectional area: r = 0.69, p < 0.05). Although the percent cross-sectional area stenosis and minimal cross-sectional area derived from the Doppler measurements based on the continuity equation were significantly correlated with the corresponding quantitative angiographic measurements, this determination could be achieved in a minority of cases (16%), limiting the practical application of this approach for the assessment of coronary stenosis severity.