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TECHNOLOGY, COMPUTING, AND SIMULATION

In Vivo Detection of Myocardial Ischemia in Pigs Using Visible Light Spectroscopy

Jonathan K. Ho, MD^*, Oliver J. Liakopoulos, MD, Ryan Crowley, MD^*, Aaron B. Yezbick, MD^*, Elizabeth Sanchez, BS^*, Kalyanam Shivkumar, MD, PhD, and Aman Mahajan, MD, PhD^*

From the Departments of *Anesthesiology, Cardiothoracic Surgery, David Geffen School of Medicine, University of California, Los Angeles, California; Department of Cardiothoracic Surgery, University of Cologne, Germany; and Division of Cardiology, David Geffen School of Medicine, University of California Los Angeles, California.

Address correspondence and reprint requests to Aman Mahajan, MD, PhD, Department of Anesthesiology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095. Address e-mail to amahajan{at}mednet.ucla.edu.

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.

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