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CLINICAL STUDIES

Use of the continuity equation for transesophageal Doppler assessment of severity of proximal left coronary artery stenosis: a quantitative coronary angiography validation study

^a Division of Cardiology, Hôpital Nord, University Jean Monnet, Saint Etienne, France

Manuscript received October 20, 1997; revised manuscript received March 2, 1998, accepted March 16, 1998.

Address for correspondence: Dr. Karl Isaaz, Service de Cardiologie, Hôpital Nord, Centre Hospitalier Universitaire de Saint-Etienne, 42055 Saint-Etienne Cedex 2, France
KIsaaz{at}aol.com

Objectives. We tested the value of transesophageal Doppler echocardiography (TEDE) for quantitating proximal left coronary artery (LCA) stenosis by using the continuity equation.

Background. The continuity equation applied to a stenosis states that the ratio of the time–velocity integral (TVI) of prestenotic to stenotic flow velocities is equal to the ratio of stenotic to prestenotic cross-sectional areas. TEDE allows the measurement of coronary blood flow velocities within the proximal part of the LCA.

Methods. Forty-one patients with a stenosis of the proximal or mid left anterior descending coronary artery or with a nonostial stenosis of the left main coronary artery were studied. Coronary flow velocities were recorded by TEDE guided by color flow imaging. Prestenotic velocities were recorded by pulsed Doppler echocardiography and transstenotic velocities were recorded by pulsed or high pulse repetition frequency or continuous wave Doppler echocardiography. The prestenotic and transstenotic diastolic TVIs were calculated and the TEDE-derived percent area stenosis was calculated as (1 – TVI ratio) x 100. Quantitative angiography lesion analysis was performed using a computer-assisted automated edge-detection system.

Results. TEDE recordings were successful in 35 of the 41 patients. A good linear correlation was found between TEDE and quantitative angiographically derived percent area stenosis (r = 0.89, p = 0.0001, SEE 5.7). However, TEDE measurements underestimated the actual percent area stenosis (slope of regression 0.54). A better agreement (slope 1.08) was obtained after dividing prestenotic velocity by 2 in the continuity equation, based on the assumption of a parabolic cross-sectional velocity profile in the prestenotic segment.

Conclusions. TEDE may be used for quantitating stenosis of the proximal part of the LCA with the use of a modified continuity equation that takes into account the parabolic velocity profile in the normal prestenotic segment.

Abbreviations and Acronyms   CSA = cross-sectional area   DS = diameter stenosis   LAD = left anterior descending coronary artery   LCA = left coronary artery   LMCA = left main coronary artery   MLD = minimal lumen diameter   TEDE = transesophageal Doppler echocardiography   TVI = time–velocity integral

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