SIGNIFICANT DIFFERENCES BETWEEN SIDE-MOUNTED AND END-MOUNTED INTRACORONARY DOPPLER FLOW PROBES FOR THE MEASUREMENT OF BLOOD-FLOW VELOCITY

Use of the intracoronary Doppler flow probe is an established method f or the assessment of coronary blood flow velocity. The aim of this stu dy was to perform an in vitro comparison of two commonly used Doppler probes, which differ in the location of the piezo-electric crystal (en d-mounted vs side-mounted). Blood flow velocity was measured over a wi de range of flow rates in a flow simulator using heparinized whole blo od. Measurements were made with both Doppler probes assessed in two po sitions (supported and unsupported) within the tubing. The results wer e compared with estimated true velocities. Further measurements were m ade with six side-mounted probes, correcting for the assumed crystal m ounting angle and for the angle calculated from magnified images of th e individual crystals. Mean velocities for end- and side-mounted probe s correlated highly with predicted Velocities (all r greater than or e qual to 0.99), but the side-mounted probes significantly overestimated velocity by > 100%. Estimation of the true crystal mounting angle of the side-mounted probe revealed considerable variability (range 30-42 degrees) and was lower than the recommended angle correction factor of 60 degrees. Velocities corrected for the individual crystal mounting angles agreed more closely with predicted mean velocities. Although bo th probes are adequate for the assessment of relative changes in flow, the side-mounted probe considerably overestimates mean velocity, whic h is partly explained by the variable mounting angle of the crystal. T he demonstrated limitations of the side-mounted Doppler flow probe in vitro should be considered in undertaking measurement of intracoronary blood flow velocity.