Real-Time Assessment of Murine Cardiac Oxygenation Using Photoacoustic Imaging

Background Perioperative incidents such as hypoxic cardiac injury often have subtle or nonspecific clinical manifestations. Reduction in myocardial oxygenation precedes biochemical changes, as well as electrical and functional changes. Photoacoustic imaging (PAI) is a modality that uses laser irradiation of tissue to generate ultrasonic waves, enabling spatially resolved quantitative mapping of oxygenated and deoxygenated haemoglobin. We investigated the utility of PAI for real-time monitoring of myocardial and great vessel oxygenation. Methods Male CD-1 mice were anaesthetised, and photoacoustic and simultaneous B-mode images were acquired of the myocardium and right ventricular outflow tract (RVOT), the pulmonary artery, and aorta. PAI was performed at fractional inspired oxygen levels (FiO2) of 100%, 21%, and then 10%. Separate cohorts of mice were exposed to increasing intravenous doses of either combined phenylephrine and isoprenaline, or individual administration of vasoactive or adrenergic agents. Results PAI reliably distinguished changes in oxygenation in the RVOT cavity, pulmonary artery, aorta, and myocardium. PAI detected hypoxia-induced changes in oxygenation, revealing greater desaturation in the myocardium than in the RVOT (-9.85%, 95% CI -14.94 to -4.77, P<0.0001). Escalating doses of phenylephrine and isoprenaline caused a progressive desaturation of the myocardium and RVOT (mean [95% CI]; myocardium 16 mg/kg: -14.64% [-27.62 to -1.65], P=0.0038 and RVOT 32 mg/kg: -18.71% [-32.15 to -5.27], P=0.0003). Myocardial deoxygenation was detected before changes in systolic function or electrical abnormalities. Conclusions This work demonstrates that PAI can reliably monitor cardiac oxygen desaturation, potentially offering an earlier warning of cardiac dysfunction and injury compared to existing monitoring tools. Keywords: Echocardiography, hypoxaemia, hypoxia, myocardial injury, oxygenation, perioperative monitoring, photoacoustic imaging