Abstract 10254: Continuous Monitoring of Regional Function by a Miniaturized Ultrasound Sensor Allows Early Quantification of Low Grade Myocardial Ischemia
Ischemia is a leading cause of decreased ventricular function during and after heart surgery. Continuous, sensitive methods for early detection are therefore crucial. We hypothesized that low grade ischemia could be detected quantitatively by a miniaturized epicardial ultrasound probe allowing continuous registrations. Myocardial lactate was used as reference method in a model of graded coronary flow reduction. In a porcine model (n=7) miniaturized epicardial ultrasonic transducers (Ø 5mm) were positioned in the LAD- and Cx-area. Left ventricular pressure (LVP) was obtained by a micromanometer. The left anterior mammary artery (LIMA) was grafted to the LAD, which was occluded proximal to the anastomosis. Coronary flow was regulated by intermittently reducing LIMA-flow from baseline to 75%, 50% and 25% for 18 min each. Subendocardial tissue velocity was displayed continuously. Peak systolic velocity (Vmax) was measured and a displacement trace was calculated by time integration. Regional work was assessed as pressure-displacement (LVP-D) loops. Tissue lactate from intramyocardial microdialysis was used to quantify ischemia. All steps of coronary flow reduction demonstrated myocardial ischemia by elevated tissue lactate concentrations. Vmax and LVP-D loops area were significantly reduced from baseline (p<0.05) during each intervention (Fig. 1A and B). The decreases in Vmax and LVP-D loop area were closely related to the degree of ischemia, and there were significant inverse correlations between tissue lactate and Vmax (r=-0.86, p<0.001) and regional work (r=-0.78, p<0.001) (Fig. 1C). No significant effects were seen in the Cx-area. In conclusion increasing loss of regional function and myocardial work, due to enhancing regional myocardial ischemia was quantified by a miniaturized epicardial ultrasound probe. This method is promising for sensitive and continuous real-time monitoring of myocardium at risk during and after cardiac surgery.
- © 2011 by American Heart Association, Inc.