Postoperative measurements of ventricular function in man using an implantable ultrasonic sensor

To monitor regional ventricular function in man following cardiac surgery we have developed an implantable ultrasonic sensor which is attached to the epicardial surface during surgery to measure wall thickening. During the last 18 months we have implanted sensors in 33 patients for up to 2 days postoperatively. Good quality signals were obtained from 25 of the sensors, and all were extracted sucessfully in the intensive care unit. Thickening fraction (TF) was highly variable among patients, dropped transiently after surgery, but remained relatively stable in most patients during the recovery period. Four patients developed sustained systolic thinning suggestive of ischemia or infarction during the recovery period. However, none of these patients were symptomatic or had ECG changes or other positive tests for ischemia. We conclude that the method is a safe, reliable, and accurate technique to monitor the recovery of ventricular function following surgery and that it provides quantitative information not obtainable by other methods.