Near-infrared monitoring of myocardial oxygenation during ischemic preconditioning.
BACKGROUND
Ischemic preconditioning has been advocated as a method of cardioprotection for minimally invasive direct coronary artery bypass. This study was performed to estimate the cardioprotective effect of ischemic preconditioning before ischemia by examining the changes in myocardial tissue oxygenation and also to examine whether adenosine triphosphate-sensitive potassium channel opener enhances the cardioprotective effect of ischemic preconditioning.


METHODS
Myocardial ischemia was induced in three groups of 6 dogs by temporary occlusion of the left anterior descending coronary artery. Group 1 dogs received a 30-minute coronary occlusion and subsequent 3-hour reperfusion. Groups 2 and 3 dogs underwent three periods of 5-minute coronary occlusion and 5-minute reperfusion and then received 30-minute sustained ischemia and 3-hour reperfusion. In group 3, nicorandil was administered during the procedure. Myocardial oxygenation was measured using three-wavelength near-infrared spectroscopy. Myocardial blood flow was measured by the colored microsphere method.


RESULTS
During ischemic preconditioning the myocardial tissue oxygen saturation decreased rapidly at coronary occlusion and increased at reperfusion. It was increased stepwise at the second and third coronary occlusion. Myocardial oxygen saturation during 30-minute sustained ischemia was significantly higher in groups 2 and 3 than in group 1 (p < 0.05). The myocardial tissue hemoglobin concentration showed similar changes to myocardial oxygen saturation. During 30-minute sustained ischemia, it was significantly higher in group 2 than in group 1 (p < 0.001), and it was significantly higher in group 3 than in groups 1 and 2 (p < 0.05). Regional myocardial blood flow showed no difference after 30 minutes of sustained ischemia among the three groups. Troponin-T levels were significantly lower in groups 2 and 3 than in group 1 (p < 0.01).


CONCLUSIONS
Ischemic preconditioning had beneficial effects on myocardial oxygenation during sustained ischemia, and the protected state of the myocardium could be monitored with the use of near-infrared spectroscopy. Ischemic preconditioning coupled with nicorandil administration might provide protection for minimally invasive direct coronary bypass.
Kawasuji
M
M
Department of Surgery (I), Kanazawa University School of Medicine, Japan. kawasuji@med.kanazawa-u.ac.jp
Ikeda
M
M
Sakakibara
N
N
Fujii
S
S
Tomita
S
S
Watanabe
Y
Y
D000818:Animals; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology; D004285:Dogs; D019157:Ischemic Preconditioning, Myocardial; D016343:Monitoring, Intraoperative; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology; D009206:Myocardium / Q000378:metabolism*; D020108:Nicorandil / Q000494:pharmacology; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology*; D019265:Spectroscopy, Near-Infrared; D014665:Vasodilator Agents / Q000494:pharmacology; D016277:Ventricular Function, Left / Q000187:drug effects / Q000502:physiology
D014665:Vasodilator Agents; D020108:Nicorandil