Misinterpretation of Stenosis Severity in the Presence of Serial Coronary Stenoses: An In-Vitro Study

In patients with multiple stenoses in the same coronary artery, the severity of one stenosis influences the diagnosis of the serial stenosis. Currently used diagnostic end-point, Fractional Flow Reserve, FFR (ratio of distal to proximal pressure of a stenotic region), has a cut-off point of 0.75. A value of FFR < 0.75 leads to a clinical intervention. However, FFR may fail to account for multiple stenoses interactions and might lead to clinical misinterpretation of one serial stenosis severity. In order to assess the effect of one stenosis on the other serial stenosis, we tested three combinations of serial stenoses: 80%–64%, 80%–80% and 80%–90% area stenosis (AS) respectively, using an in-vitro experimental setup. The hyperemic flow decreased from 136.4 ml/min to 126.4 ml/min and further to 90.7 ml/min as downstream stenosis severity increased from 64% AS to 80% AS and further to 90% AS, respectively. More importantly, the individual FFR values of the upstream stenosis (80% AS) increased from 0.76 to 0.79 and further to 0.88 as the downstream stenosis increased from 64% AS to 80% AS and further to 90% AS, respectively. On the contrary, the combined FFR across both the stenosis was below the threshold value of 0.75. These results indicate that the presence of a downstream stenosis might lead to a clinical misinterpretation of the upstream stenosis severity and also the combined stenosis severity.