Near-infrared monitoring of myocardial oxygenation during intermittent warm blood cardioplegia

OBJECTIVE: This study was performed to examine the ability of near-infrared spectroscopy to monitor tissue oxygenation in the cardioplegically arrested heart and to assess myocardial oxygen metabolism during intermittent warm blood cardioplegia. METHODS: Using a three-wavelength near-infrared spectroscopy, we continuously measured myocardial tissue oxygen saturation and the tissue hemoglobin concentration during intermittent warm blood cardioplegia. Under normothermic cardiopulmonary bypass, 20 dogs received three 5-min periods of antegrade warm blood cardioplegia, interrupted by three 10- min episodes of ischemia in group 1 (n = 7), three 15-min episodes of ischemia in group 2 (n = 6), or three 20-min episodes of ischemia in group 3 (n = 7). RESULTS: Myocardial oxygen saturation during beating and ventricular fibrillation was 80 ± 1 and 59± 1%, respectively. Myocardial oxygen saturation rapidly increased to 82± 1% at blood cardioplegic infusion and decreased to 58 ± 1% 3 min after cardioplegic interruption. The time required to reach the peak oxygen saturation level decreased significantly at the second and third infusions compared to the first infusion in group 1, whereas the time increasedsignificantly at the third infusion in groups 2 and 3. The slower rate ofincrease in oxygen saturation suggested reduced coronary vasodilator reserve due to microvascular abnormalities. Reperfusion ventricular fibrillation occurred in none of group 1, one of group 2 and three of group 3. CONCLUSIONS: Near-infrared spectroscopy is a useful method of continuously monitoring myocardial oxygenation and ischemia during warm heart surgery. Episodes of ischemia longer than 10 min during warm blood cardioplegia resulted in less-than-optimal myocardial preservation and should be avoided.