Previous studies of animal and human experiments have shown excellent correlation between true or angiographic stenosis severity and stenosis severity calculated from intracoronary Doppler flow measurements and continuity equation method. However, there remains practical problems to be solved on its clinical application. To minimize these problems, the concept of modified continuity equation method, calculating the percent area stenosis by comparing the maximal in-stenosis flow velocity to the distal reference flow velocity, was introduced and compared with dipyridamole stress thallium-201 SPECT.

In this prospective study, 102 patients (mean age 57±10 years, 69 men, 33 women) with coronary artery stenoses ranging from 23-89% in percent diameter stenosis, who received coronary angiography, dipyridamole stress thallium-201 SPECT, and successful intracoronary flow velocity measurements were included. Modified continuity equation method and distal coronary flow velocity reserve were compared to the result of dipyridamole stress thallium-201 SPECT and quantitative coronary angiography.

Measurements of adequate intralesional and stenosis distal flow velocities were successful in 102 out of 106 stenoses (96%). Minimal luminal area and percent area stenosis calculated from modified continuity equation method showed significant correlations with those of quantitative coronary angiography. Modified continuity equation method significantly underestimated the severity of stenosis than quantitative coronary angiography did. The test accuracy in relation to the result of dipyridamole stress thallium-201 SPECT were 91% in modified continuity equation method, 80% in quantitative coronary angiography and 63% in distal coronary flow velocity reserve.

Application of intracoronary Doppler guide wire and modified continuity equation method appears to provide useful on-site implications for the anatomic and functional assessment of coronary artery stenosis. The modified continuity equation method would be one of the promising concepts for clinical decision making during coronary interventions.