Continuous monitoring of regional function by a miniaturized ultrasound transducer allows early quantification of low-grade myocardial ischemia.
BACKGROUND
Sensitive methods for the early detection of myocardial dysfunction are still needed, as ischemia is a leading cause of decreased ventricular function during and after heart surgery. The aim of this study was to test the hypothesis that low-grade ischemia could be detected quantitatively by a miniaturized epicardial ultrasound transducer (Ø = 3 mm), allowing continuous monitoring.


METHODS
In 10 pigs, transducers were positioned in the left anterior descending and circumflex coronary artery areas. Left ventricular pressure was obtained by a micromanometer. The left internal mammary artery was grafted to the left anterior descending coronary artery, which was occluded proximal to the anastomosis. Left internal mammary artery flow was stepwise reduced by 25%, 50%, and 75% for 18 min each. From the transducers, M-mode traces were obtained, allowing continuous tissue velocity traces and displacement measurements. Regional work was assessed as left ventricular pressure-displacement loop area. Tissue lactate measured from intramyocardial microdialysis was used as reference method to detect ischemia.


RESULTS
All steps of coronary flow reduction demonstrated reduced peak systolic velocity (P < .05) and regional work (P < .01).The decreases in peak systolic velocity and regional work were closely related to the degree of ischemia, demonstrated by their correlations with lactate (R = -0.74, P < .01, and R = -0.64, P < .01, respectively). The circumflex coronary artery area was not affected by any of the interventions.


CONCLUSIONS
The epicardially attached miniaturized ultrasound transducer allowed the precise detection of different levels of coronary flow reduction. The results also showed a quantitative and linear relationship among coronary flow, ischemia, and myocardial function. Thus, the ultrasound transducer has the potential to improve the monitoring of myocardial ischemia and to detect graft failure during and after heart surgery.
['Hyler|Stefan|S|', 'Pischke|Søren E|SE|', 'Halvorsen|Per Steinar|PS|', 'Espinoza|Andreas|A|', 'Bergsland|Jacob|J|', 'Tønnessen|Tor Inge|TI|', 'Fosse|Erik|E|', 'Skulstad|Helge|H|']
D000818:Animals D042241:Early Diagnosis D004452:Echocardiography D004867:Equipment Design D019544:Equipment Failure Analysis D005260:Female D008297:Male D008904:Miniaturization D017202:Myocardial Ischemia D015203:Reproducibility of Results D012680:Sensitivity and Specificity D013318:Stroke Volume D013552:Swine D014159:Transducers D018487:Ventricular Dysfunction, Left
Ultrasound Ischemia Regional work Myocardial function Postsystolic contraction