Monitoring tissue oxygenation of the heart after myocardial revascularization.

A polarographic technique capable of simultaneous monitoring of myocardial tissue oxygen tension (MPO2) and intramyocardial electrograms by way of the same electrodes has been developed. Initially, the method was evaluated in dogs to verify the appropriateness of the directional changes of MPO2 in function of selected determinants of myocardial oxygen supply (regional coronary blood flow, arterial blood oxygen tension) and demand (heart rate, force of ventricular contraction). A combined reduction of MPO2 and elevation of the S-T segment in the corresponding electrograms was observed only when a 50 percent or greater reduction of blood flow to the sampled area was effected. Subsequently, in nine patients undergoing aortocoronary bypass surgery, MPO2 was measured from 48 areas for 2 weeks postoperatively. In 11 normal and 31 revascularized areas, MPO2 increased during the postoperative period. In four areas subsequently found to be supplied by occluded grafts MPO2 decreased from 12.7 +/- 3.1 (mean +/- standard error) to 10.1 +/- 3.3 mm Hg (P less than 0.05). In two areas, MPO2 decreased during the 3rd postoperative day from 16 to 3 and from 14 to 4.2 mm Hg, respectively. This reduction was attended by a significant rise in the S-T segment of the corresponding electrograms. This finding preceded by 24 hours standard electrocardiographic evidence of myocardial infarction. This technique appears to be sensitive and reliable, and thereby capable of enhancing the management of patients during the high risk early postoperative period after coronary bypass surgery.

Monitoring regional myocardial function after myocardial revascularization.

A system using only small platinum electrodes for monitoring intramyocardial polarographic oxygen tension (MP02), electrograms (ECG), and impedance-derived wall motion (WM) was experimentally tested and clinically implemented. In nine open-chest, anesthetized dogs. two platinum electrodes were inserted along the subepicardial direction of the muscle fibers. As verified by cinefluoroscopy, WM corresponded to changes in distance between the platinum electrodes (r = 0.91 +/- 0.02). The system responded to a 10 minute occlusion of the left anterior descending coronary artery (LAD) as follows: Dyskinetic WM appeared in 10 seconds (p less than 0.05); MP02 decreased (26.4 +/- 1.8 to 14.8 +/= 1.9 mm Hg, p less than 0.05) in 1 minute; ST segments increased (4.8 +/- 1.5 to 12.3 +/- 3.1 mV, p less than 0.05) in 3 minutes. On reperfusion, WM, ST segments, and MP02 normalized in 15 seconds, 30 seconds, and 1 minute, respectively. Hence, ischemia affects WM more acutely than either ECG or MP02. In five patients, ischemic changes before coronary bypass were reversed over 5 days: MP02 (17.4 +/-; 1.9 to 19.6 +/-1.7 mm Hg), ST segment (2.2 +/- 6 to 1.0 +/- 0.4 mV), and WM returned to normal. Thus a system has been designed which simultaneously monitors regional WM, MP02, and ECG. The method has proved to be a sensitive and practical approach for assessing perioperative myocardial function.