The use of left ventricular epicardial surface velocity patterns as a marker of pacing site

Ectopic ventricular foci were simulated at selected endocardial sites in 15 closed-chest canines using ventricular pacing. During this pacing, a noninvasive x-ray backscatter imaging technique was used to measure epicardial LV displacements at 5-ms intervals during the cardiac cycle. These displacement measurements were used to calculate epicardial surface velocities in each study and were presented as a time sequence of color coded velocity maps. Characteristic patterns in the timing and spatial propagation of LV surface velocities were noted for each pacing site, particularly during the expansion of the LV during isovolumic contraction and the inward motion of the LV during ejection. Average surface velocity maps for the 15 canines were computed for each pacing site. These average maps were used as standards for comparison with individual pacing studies to determine the probable site of pacing. Comparisons were made using a computer algorithm, based upon auto- and cross-correlation techniques in the time domain. This algorithm correctly identified pacing sites with sensitivities of RA 74%, LV 76%, RV 79%, and RVOT 77% and specificities of RA 98%, LV 96%, RV 90%, and RVOT 93%. The results show that this noninvasive mapping procedure has potential for identifying the location of an ectopic ventricular focus.