Automated detection of myocardial ischaemia by epicardial miniature ultrasound transducers — a novel tool for patient monitoring during cardiac surgery☆

Abstract

Early detection of myocardial ischaemia in cardiac surgery is important. We have developed an ultrasonic system for continuous myocardial monitoring by use of miniature transducers. The aim of this study was to investigate the system's ability to detect ischaemia in patients undergoing off-pump coronary artery bypass grafting (CABG), and whether automated signal analysis could detect ischaemia. In 10 patients scheduled for CABG, ultrasound transducers were fixed to the epicardium in the area supplied by left anterior descending artery (LAD), and in a remote area for control. M-mode images with measurements of wall-thickening velocities were presented in real time and systolic (S') and post-systolic velocities (PSVs) were recorded. An automated algorithm for ischaemia detection was developed, using end-systolic wall thickening as a fraction of total wall thickening. Registrations were made at baseline and during LAD occlusion. Echocardiographic strain was used as reference. Nine of 10 patients developed ischaemia during LAD occlusion, with resulting decrease in systolic and increase in post-systolic wall-thickening velocities (P<0.001). In these nine patients, Vdiff shifted below zero with no overlap between baseline and LAD occlusion (P<0.001). The automated wall-thickening fraction was reduced from 0.93±0.05 to 0.57±0.15 (P=0.001). A cut-off value of 0.85 could completely separate normal from ischaemic myocardium in all patients. The ultrasonic system detected regional ischaemia during LAD occlusion. An automated analysis algorithm demonstrated excellent ability to detect ischaemia. This technology can develop into a useful tool to detect ischaemia in cardiac surgery.