Estimation of severity of stenosis with a Doppler guide wire in the experimental models

Application of the continuity equation to Doppler catheter measurement of quantitative coronary flow velocity has been reported recently to be one of the accurate methods to evaluate mild to moderate coronary stenosis. This method, however, has not been validated in moderate to severe coronary stenosis. Furthermore, the ratio of prestenotic velocity/stenotic velocity may be influenced by side branches proximal to moderate to severe stenosis. Therefore we designed this study to evaluate the accuracy of the continuity equation method in the assessment of moderate to severe stenosis by an 0.018-inch (0.46 mm) Doppler guide wire (12 MHz) and the influence of a side branch on estimation of stenotic severity. Doppler spectra were recorded in the straight rigid tubes (4 mm diameter) with different severities of stenosis (50%, 62.5%, and 75% diameter stenosis) without a side branch with a Doppler guide wire. By the continuity equation, percent diameter stenosis was calculated from the proximal/stenotic and distal/stenotic velocity ratios in each model at different flow rates. In the model of 75% diameter stenosis with a side branch (1 mm diameter) proximal to the stenosis and the model of 75% diameter stenosis with a side branch (1 mm diameter) distal to the stenosis, percent diameter stenosis was calculated by the same method. Percent diameter stenosis derived from the proximal/stenotic velocity ratio in each model was in agreement with the true severity of stenosis in each model without a side branch (48% +/- 1%, 62% +/- 1%, and 75% +/- 1%, respectively). Percent diameter stenosis from the distal/stenotic velocity ratio was also in agreement with the true severity of stenosis in each model without a side branch (48% +/- 3%, 61% +/- 1%, and 75% +/- 1% respectively). In the model of 75% diameter stenosis with a side branch proximal to the stenotic site, however, percent diameter stenosis derived from the proximal/stenotic velocity ratio was underestimated compared with the real stenosis and significantly smaller than that derived from the distal/stenotic velocity ratio (65% +/- 1% versus 74% +/- 1%; p < 0.001). On the other hand, in the model of 75% diameter stenosis with a side branch distal to the stenotic site, the percent diameter stenosis derived from both the proximal/stenotic and distal/stenotic velocity ratios was in agreement with that derived from the distal/stenotic velocity ratio (75% +/- 2% and 77% +/- 1%). In the experimental models the estimation of stenotic severity by a Doppler guide wire is accurate even in moderate to severe stenosis unless a side branch exists just proximal to the stenosis. However, the distal/stenotic velocity ratio is applicable even if a side branch exists. This suggests that severity of stenosis derived from the distal/stenotic velocity ratio may be more useful than that from the proximal stenotic velocity ratio in human coronary stenosis with side branches.