Cardiac monitoring using transducers attached directly to the heart

Cardiac ultrasound systems deliver excellent information about the heart, but are constructed for intermittent imaging and interpretation by a skilled operator. This paper presents a dedicated ultrasound system to monitor cardiac function continuously during and after cardiac surgery. The system uses miniature 10 MHz transducers sutured directly to the heart surface. M-mode images give a visual interpretation of the contraction pattern, while tissue velocity curves give detailed quantitative information. The ultrasound measurements are supported by synchronous ECG and pressure recordings. The system has been tested on pigs, demonstrating M-mode and tissue velocity measurements of good quality. When occluding the LAD coronary artery, the system detected changes in contraction pattern that correspond with known markers of ischemia. The system uses dedicated analog electronics and a PC with digitizers and LabVIEW software, and may also be useful in other experimental ultrasound applications.