Perioperative Ischemia Reduction Study (PROSE) Pilot

Perioperative myocardial ischemia has been studied in the pre-, intra-, and postoperative periods. The intraoperative incidence is similar to the preoperative period but the postoperative incidence is doubled that of the preoperative period. These results have two implications: postoperative myocardial ischemia cannot be predicted by preoperative ambulatory ECG monitoring since only half of those are seen preoperatively; the postoperative period is when significant myocardial ischemia occurs.

The role of myocardial ischemia, especially prolonged ischemia, in perioperative myocardial infarction (PMI) has been recognized by a number of investigators. In the presence of postoperative myocardial ischemia, the relative risk of a postoperative cardiac event was 16 in one study and the odds ratio for an ischemic cardiac event was 9.2 in another. Using 12-lead continuous monitoring, one study found that all PMI were preceded by myocardial ischemia.

Ambulatory ECG in the postoperative period has been well reported in the past. Recently, Landesberg reported the sensitivity and specificity of lead placements to detect myocardial ischemia in the postoperative period. Lead combinations were compared with continuous 12-lead ECG in 185 consecutive patients. Combining two precordial leads, the sensitivity for detecting ischemia was 97.4% for V3 + V5; 92.1% for V4 + V5; and for infarction was 100% for V3 + V5 or V4 + V5.

We believe that the pathogenesis of PMI is multifactorial. Apart from the coronary anatomy and the vulnerable plaque, stress hormones and catecholamine surges in the perioperative period are well reported. Stress increases systolic BP, which is a major determinant of LV wall tension, and hence, myocardial oxygen demand. The oxygen cost of "pressure work" is greater than "volume work", with the area-under-the-curve for LV pressure closely correlating with myocardial oxygen demand. Hypercoagulable state has also been implicated in PMI.

With so many possible pathogenesis, it is our belief therefore that postoperative myocardial ischemia may be one of the final pathways just before postoperative ischemic cardiac complications. This is especially so when all PMI were preceded by myocardial ischemia in one study. With potentially multiple pathogenesis, it is unknown if postoperative myocardial ischemia is amenable to treatment. It is, however, our belief that postoperative myocardial ischemia can be aborted using existing treatment modalities. The implication is that the reduction of postoperative myocardial ischemia may reduce the incidence of postoperative ischemic cardiac complications, including PMI.