Limitations of the zero crossing detector in the analysis of intracoronary doppler: A comparison with fast fourier transform analysis of basal, hyperemic, and transstenotic blood flow velocity measurements in patients with coronary artery disease

Abstract

The current clinical standard for the analysis of intracoronary Doppler signals is the application of a zero‐crossing (ZC) detector. However, the accuracy of the method is questionable, especially in areas of disturbed flow, as confirmed by in vitro studies, animal experiments, and intraoperative observations. The aim of this study is the comparison of a conventional ZC detector and a custom‐designed spectral analyzer (fast Fourier transform, FFT) in the analysis of intracoronary Doppler signals obtained in 19 patients undergoing coronary angioplasty. A 3F catheter with an end‐mounted Doppler ceramic crystal was placed over an 0.014″ guidewire in a normal or near‐normal segment proximal to the lesion to be dilated. The Doppler signal was recorded before and after intracoronary infusion of 12.5 mg of papaverine. In 9 patients high flow velocities could be recorded when the catheter was advanced across the stenosis. The blood flow velocity measurements obtained with ZC were significantly lower than the maximal FFT flow velocity measurements (16±12 cm/s vs. 29±18 cm/s, p < .001). In all the conditions of Doppler signal acquisition (baseline, hyperemia, stenosis) a large scattering of the signed differences between corresponding measurements was observed. The standard deviation of the difference ZC‐FFT was ±11 cm/s and ±5 cm/s for the maximal and mean FFT flow velocity, corresponding in both cases to ±37% of the mean of the ZC and FFT measurements. Large differences were also observed in the values of coronary flow reserve (CFR) calculated as the ratio between ZC and FFT flow velocity measurements 30 s after papaverine intracoronary and at baseline. The standard deviation of the difference ZC‐FFT based CFR was ±1.3 and ±1.2 for the values derived from the maximal and mean FFT flow velocities (percent difference ±32% and ±37%, respectively). In conclusion, the measurements obtained from the same intracoronary Doppler signal analyzed with a ZC detector and an FFT technique showed large differences in various conditions of flow and also in the assessment of relative flow velocity derived indices such as CFR. Spectral analysis should replace the current use of a ZC detector for the evaluation of coronary Doppler signals, even for the assessment of relative flow velocity changes.