Background. Ischemic preconditioning has been advocated as a method of card
ioprotection for minimally invasive direct coronary artery bypass. This stu
dy was performed to estimate the cardioprotective effect of ischemic precon
ditioning before ischemia by examining the changes in myocardial tissue oxy
genation and-also to examine whether adenosine triphosphate-sensitive potas
sium channel opener enhances the cardioprotective effect of ischemic precon
ditioning.
Methods. Myocardial ischemia was induced in three groups of 6 dogs by tempo
rary occlusion of the left anterior descending coronary artery. Group I dog
s received a 30-minute coronary occlusion and subsequent 3-hour reperfusion
. Groups 2 and 3 dogs underwent three periods of 5-minute coronary occlusio
n and Ei-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 now was measured by the colored mic
rosphere method.
Results. During ischemic preconditioning the myocardial tissue oxygen satur
ation decreased rapidly at coronary occlusion and increased at reperfusion.
It was increased stepwise at the second and third coronary occlusion. Myoc
ardial oxygen saturation during 30-minute sustained ischemia was significan
tly higher in groups 2 and 3 than in group 1 (p < 0.05). The myocardial tis
sue hemoglobin concentration showed similar changes to myocardial oxygen sa
turation. 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 s
howed no difference after 30 minutes of sustained ischemia among the three
groups. Troponin-T levels were significantly lower in groups 2 and 3 than i
n group 1 (p < 0.01).
Conclusions. Ischemic preconditioning had beneficial effects on myocardial
oxygenation during sustained ischemia, and the protected state of the myoca
rdium could be monitored with the use of near-infrared spectroscopy. Ischem
ic preconditioning coupled with nicorandil administration might provide pro
tection for minimally invasive direct coronary bypass. (C) 2000 by The Soci
ety of Thoracic Surgeons.