Po-topic I-01: Detection of ischemic areas in the in vivo pig hearts by near-infrared spectroscopic imaging

Abstract

We hypothesize that near-infrared (NIR) imaging can visualize ischemic areas in the beating heart, highlighting areas of increased deoxy-hemoglobin and -myoglobin (deoxy-(Hb+Mb)) concentrations and reduced flow. Open-chest pigs (n = 6) under general anesthesia were provided with lidocaine (20 μg/min/kg) and glucose (in saline) intravenous infusion over the experimental protocol. The protocol consisted of baseline, occlusion of the left anterior descending artery (LAD) between 2nd and 3rd branches for 90 minutes, and reflow for 120 minutes. ECG-gated NIR images of the heart were obtained using a CCD-array camera with a liquid crystal tunable filter, which acquired absorption spectra in the range of 650–1,050 nm for each of 256 × 256 pixels (< 1 mm2 resolution, 5 minutes acquisition time). Deoxy-, oxy- and total-(Hb+Mb) concentrations were mapped using a spectral fitting algorithm based on their absorption spectra between 650–890 nm. To visualize flow distribution of a bolus of intravascular tracer, indocyanine green (ICG, 12.5 mg/5 mL) was injected intravenously at each step of the protocol and images gated to cardiac cycle were acquired at 800 nm every second over a 3-minute period. Following LAD occlusion deoxy-(Hb+Mb) levels increased and oxy-(Hb+Mb) decreased in the area at risk, determined by the lack of Evans Blue staining (17.3±3.9% of the total ventricular mass). ICG images showed rapid distribution of the dye through the large vessels (LAD and its branches) and capillaries and no dye in the area at risk, indicating severe flow reduction. The areas that remained unstained with ICG coincided with those of increased deoxy-(Hb+Mb) levels. Time courses of ICG absorbance in the normally perfused areas showed rapid absorbance rise (2–5 seconds) with subsequent decrease and equilibration within 1 minute. Reflow restored oxygenation levels at the area at risk and made it accessible to ICG. We conclude that NIR imaging is well suited for visualizing cardiac ischemia in vivo.