How silent is perioperative myocardial ischemia? A hemodynamic, electrocardiographic, and biochemical study in patients undergoing coronary artery bypass graft surgery.

OBJECTIVE

To analyze the relationship among Holter electrocardiogram (ECG) recordings, hemodynamic measurements indicative of global myocardial oxygen balance, and serum cardiac troponin I concentrations (cTnI) in the early postoperative period after coronary artery bypass graft (CABG) surgery.

DESIGN

Prospective observational study.

SETTING

University teaching hospital.

PARTICIPANTS

Thirty patients undergoing CABG surgery.

INTERVENTIONS

ECG measurements consisted of Holter and standard ECG recordings. Hemodynamic measurements included heart rate, systolic and diastolic blood pressure (SBP, DBP), pulmonary capillary wedge pressure, and cardiac index (CI). Derived indices included tension time index (TTI), rate-pressure product, pressure work index (PWI), and endocardial viability ratio (EVR). Serial measurements of cTnI concentrations were measured postoperatively; the area under the cTnI concentration time curve was calculated for each patient (AUC cTnI).

MEASUREMENTS AND MAIN RESULTS

Episodes of myocardial ischemia were associated with small but significant rises in SBP (p = 0.01), DBP (p = 0.001), and TTI (p = 0.005) compared with periods without ischemia in the same patients. Serum cTnI concentrations 24 hours after cardiopulmonary bypass (p = 0.03) and AUCcTnI (p = 0.01) values were greater in patients who developed ECG myocardial ischemia compared with patients who did not.

CONCLUSIONS

The small changes in hemodynamics seen, although statistically significant, are unlikely to be the primary cause of the ischemia. They more likely reflect an independent process that causes or occurs as a result of ischemic episodes. Ischemic episodes detected by the Holter monitor are associated with significant release of cardiac troponin from the myocardium.