Position control of intravascular Doppler guidewire: concept of a tracking indicator and its clinical implications

Intracoronary Doppler ultrasound guidewires (DGW) utilize a wide ultrasound beam combined with a measurement of the spectral peak velocity to estimate the spatial peak velocity within a blood vessel. However, the spectral peak velocity may underestimate the true spatial peak velocity if the DGW is not properly positioned. The purpose of this study was to find a Doppler-derived parameter that would aid in the optimal positioning of the DGW within the vessel lumen. We studied the relationship between the time-averaged, spectral-peak velocity (APV) and the normalized first Doppler moment (M1/M0) to develop a DGW position indicator and demonstrate its clinical utility. In vitro, heparinized, human whole blood with a hematocrit of 45% was directed from a reservoir via a roller pump into four serially connected straight silicone tubes of known diameter (2.5, 3.0, 3.5, 4.0 mm). A DGW was inserted into the tubes where simultaneous APV and M1/M0 measurements were obtained for flow rates ranging from 49 to 316 ml/min. Optimal positioning of the DGW was identified at the position where maximum APV and M1/M0 were obtained. With optimal positioning the correlation between APV and M1/M0 was good (APV = 1.62 M1/M0 + 5.0; R2 = 0.98). Importantly, this correlation showed no dependence on the tube diameter. In vivo, in four patients APV and M1/M0 measurements were obtained in 16 coronary artery segments in one left anterior descending, two circumflex, and two right coronary arteries. In 10 vessel segments, there was no discrepancy between the measured and expected M1/M0 after positioning the DGW with help of the Doppler signal quality only. In six vessel segments, repeat DGW positioning using M1/M0 was necessary, yielding an average increase of APV of 20% (7-38%). We conclude that DGW positioning can be optimized using the correlation between APV and M1/M0 as a reference. For any given APV value, there is a corresponding expected value for M1/M0 under the condition of optimal positioning. Any discrepancy between the measured and expected values for M1/M0 then indicates suboptimal positioning.