Quantitative assessment of coronary artery stenosis by intravascular Doppler catheter technique. Application of the continuity equation.

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Abstract
BACKGROUND: Quantitative assessment of coronary artery stenoses plays a central role in clinical decision making. According to the continuity equation, the ratio of the time-velocity integral of prestenotic to stenotic flow velocities represents the ratio of the cross-sectional area of the stenotic to prestenotic segments. However, no data exist regarding the application of this method to clinical assessment of human coronary artery diseases. Therefore, we attempted to determine the severity of coronary artery stenoses by applying the continuity equation to the coronary circulation. METHODS AND RESULTS: Nineteen patients with a stenosis of the proximal left anterior descending coronary artery (LAD) and one patient with a stenosis in an aortocoronary bypass graft to the LAD were studied. Coronary flow velocities at the prestenotic and stenotic segments were measured with an end-mounted Doppler catheter (3F, 20 MHz), and the time-velocity integral ratio was calculated. Percent area stenosis was calculated as (1-time-velocity integral ratio) x 100. In three patients with severe stenosis (greater than 90% in area stenosis), velocity at the stenosis could not be determined because of aliasing of Doppler signals, and in four, Doppler signals at the stenosis were not measurable because of technical difficulties. The stenotic flow velocity was successfully recorded in 13 patients (65%) with mild to moderate stenosis. The diastolic peak flow velocity at the stenosis was 90 +/- 36 cm/sec (mean +/- SD), and was significantly greater than the velocity at the prestenotic segment, 48 +/- 18 cm/sec (p less than 0.01). Percent area stenosis determined by Doppler continuity equation correlated closely with that by biplane coronary angiography (r = 0.83, y = 0.92x-0.45, p less than 0.01). CONCLUSIONS: Application of the continuity equation to Doppler catheter measurement of coronary flow velocity can be used to successfully compute the severity of coronary stenoses. This may be a useful alternative method to estimate functional severity of coronary artery disease, although further technical developments will be necessary to improve the sensitivity.

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