P286 Microcirculation of the human myocardium during ischemic preconditioning.
1K.Knobloch, 1A.Lichtenberg, 1N.Khaladj, 1H.Schacht, 2S.Ringes-Lichtenberg, 1M.Pichlmaier, 1H.Mertsching, 1A.Haverich
1Thorax-, Herz- & Gefäßchirurgie, Medizinische Hochschule, Hannover; 2Kardiologie & Angiologie, Medizinische Hochschule, Hannover.

The phenomenon of “ischemic preconditioning” has been described in experimental animals as well as in human. The mechanisms involved are activation of KATP-channels and modulation of several different adenosine receptor subtypes. In this study we sought to evaluate the human myocardial microcirculation during brief intermittent occlusions of the left anterior descending coronary artery (LAD) by a new laser Doppler flowmetry and remission spectroscopy system (Oxygen-To-See-“O2C”, LEA Medizintechnik, Giessen, Germany) during off-pump coronary artery bypass grafting (OPCAB).

Methods: 23 patients (16 males) scheduled for OPCAB procedure were enrolled in the study. Intraoperatively, the LAD was occluded for 3 min followed by a 3 min reperfusion interval. The procedure was repeated three times. The microcirculation in the left ventricular myocardial area 2 cm distal to the occlusion was continuously monitored using the “O2C” device. Myocardial oxygen saturation (SO2), postcapillary hemoglobin concentration (rHB), superficial (2mm) and deep (8mm) blood flow were measured and recorded (sampling rate 500 Hz).

Results: Left ventricular myocardial baseline SO2 was 88%. During ischemia, left ventricular myocardial SO2 increased from the first to the third occlusion from 75±6% to 85±4% (p<0.001). rHb as a marker of postcapillary venous hemoglobin concentration increased significantly (77±6 vs. 85±6, p=0.002). Superficial and deep myocardial blood flow decreased significantly (317±17 vs. 308±36, p <0.001; 402±56 vs. 350±50, p < 0.001; respectively).

Conclusions: Our study shows that brief intermittent periods of coronary ischemia increase myocardial tissue oxygen saturation. The tolerance of myocardium to ischemia may thus be increased by intermittent occlusions of the coronary vessels. The oxygen-to-see system is capable of detecting parameters of myocardial microcirculation in vivo real time.