Influence of coronary pulsation on volumetric intravascular ultrasound measurements performed without ECG-gating. Validation in vessel segments with minimal disease

Abstract

Volumetric analysis of coronary arteries can be performed using intravascular ultrasound (IVUS) images selected at 1 mm intervals without ECG gating. However, there are few data regarding the influence of coronary pulsation on this volumetric analysis. We developed two models of consecutive area measurements consisting of duplicated area measurements from short coronary segments and virtual measurements based on a sine function. These models allowed the re-calculation of volumes using different sets of frames from the same simulated segments. The variability of the volume determinations was evaluated by its percent standard deviation [%SD = (SD/the mean value) x 100]. The relation of the variability to the extent of external elastic membrane (EEM) area change during the cardiac cycle (amplitude) and heart rates (frequency) were examined. In 58 short coronary segments of 15 patients, consecutive IVUS images were measured [%EEM area change: 12.3 +/- 7.7%, heart rate 78 +/- 21 beats/min (bpm)]. In both models, %SD of the volume calculations was directly proportional to the %EEM area change and showed two peaks at heart rates of 60 +/- 2 and 90 +/- 2 bpm. In the model based on actual coronary measurements, the %SD of volume calculations of a segment with 10% EEM area change was 0.7% except for heart rates of 60 +/- 2 and 90 +/- 2 bpm. The variability of a volumetric analysis based upon measuring IVUS images at constant intervals without ECG gating is affected by coronary pulsation, extent of cross-sectional area changes, and heart rate. Despite these limitations, this method is feasible and provides reproducible volume measurements.