In vivo detection of myocardial ischemia in pigs using visible light spectroscopy

BACKGROUND:: Monitoring tissue oxygenation (StO2) by visible light spectroscopy (VLS) can identify tissue ischemia, but its feasibility for detecting myocardial ischemia is not known. We hypothesized that VLS can reliably detect changes in myocardial StO2 in pigs subjected to acute regional or global myocardial ischemia. METHODS:: In 11 pigs, regional myocardial ischemia was created by ligation of left anterior descending artery (LAD). Myocardial StO2 was determined from the ischemic and nonischemic left ventricular (LV) regions and compared to coronary venous saturations. Myocardial function was assessed by echocardiography. In six pigs, LV-StO2 was measured during cardiopulmonary bypass (CPB), after cardioplegic cardiac arrest, and during CPB with inadequate myocardial protection. Additionally, right ventricular (RV)- and LV-StO2 were assessed during acute RV pressure overload from pulmonary artery (PA) banding. RESULTS:: StO2 baselines in pigs undergoing LAD occlusion were similar in the ischemic and nonischemic myocardium (70% ± 8% vs 74% ± 5%). After LAD ligation, StO2 rapidly declined (30 s: 59% ± 8%; 1 min:50 ± 9; 5 min:42% ± 4%; P < 0.05) in the ischemic myocardium. Decreases in StO2 correlated with coronary venous saturations (r = 0.88) and were associated with myocardial dysfunction. In pigs undergoing CPB, LV-StO2 remained unchanged with initiation of CPB or after cardioplegic cardiac arrest, but LV ischemia was detected by StO2 after aortic cross-clamp without adequate myocardial protection. Similarly, PA banding resulted in a profound decrease of RV-StO2 from 69% ± 6% to 52% ± 7% (P < 0.05) with recovery after PA release. CONCLUSIONS:: VLS is a reliable method of detecting alterations in myocardial StO2 and can be a useful monitor for rapid identification of myocardial ischemia.