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Postoperative myocardial ischemia in patients undergoing coronary artery bypass graft surgery. S.P.I. Research Group
R C Smith1, J M Leung, D T Mangano
1Department of Anesthesia, University of California, San Francisco 94121.
Insights
Postoperative myocardial ischemia is common after coronary artery bypass graft surgery, often occurring silently and linked to adverse cardiac events. Early detection and management are crucial for improving patient outcomes.
Area of Science:
- Cardiology
- Cardiac Surgery
Background:
- Coronary artery bypass graft (CABG) surgery remains a significant procedure with associated risks of cardiac morbidity and mortality.
- Postoperative myocardial ischemia is a recognized complication, but its prevalence, characteristics, and prognostic implications require further elucidation.
Purpose of the Study:
- To investigate the prevalence, characteristics, and prognostic significance of perioperative myocardial ischemia in patients undergoing CABG surgery.
- To assess the relationship between ischemia, clinical presentation, and adverse cardiac outcomes.
Main Methods:
- Continuous two-lead electrocardiography (ECG) monitoring of 50 patients for 10 perioperative days.
- Defined ECG criteria for ischemia: reversible ST depression (≥1 mm) or elevation (≥2 mm) lasting ≥1 min.
- Independent blinded investigators verified all ischemic episodes using ECG printouts.
Main Results:
- 52% of patients experienced 207 episodes of perioperative ischemia (3,409 minutes).
- Postoperative ischemia occurred in 48% of patients, predominantly in the early period (PODs 0-2), peaking within 2 hours post-revascularization.
- Most postoperative ischemic episodes (98%) were asymptomatic and difficult to detect by clinical ECG monitoring. Early postoperative ischemia was associated with adverse cardiac outcomes, while late ischemia was not.
Conclusions:
- Myocardial ischemia is more prevalent postoperatively than preoperatively or intraoperatively before bypass.
- Early postoperative ischemia is often silent, challenging to detect, and linked to adverse cardiac outcomes.
- Late postoperative ischemia is less prevalent, asymptomatic, and not associated with in-hospital adverse events. Persistent tachycardia may be related to ischemia.
Abstract:
Cardiac morbidity and mortality after coronary artery bypass graft (CABG) surgery continue to be significant problems. To determine the prevalence, characteristics, and prognostic importance of postoperative myocardial ischemia after CABG surgery, the authors monitored 50 patients continuously for 10 perioperative days with the use of two-lead electrocardiography (ECG). ECG changes consistent with ischemia were defined as a reversible ST depression of 1 mm or greater or an elevation of 2 mm or greater from baseline, lasting at least 1 min. Baseline was adjusted for positional changes and temporal drift. All episodes were verified, with the use of the ECG monitor printout (ECG complexes), by two independent blinded investigators. Clinical care was not controlled by study protocol, and clinicians were unaware of the research data collected. Twenty-six of 50 patients (52%) had 207 episodes of perioperative ischemia (3,409 ischemic minutes). Postoperatively, ischemia developed in 48% of patients, compared with 12% preoperatively and 10% intraoperatively before bypass. Postoperative ischemia was most common in the early period (postoperative days [PODs] 0-2; 38% of patients), peaking during the first 2 h after revascularization, and less common during the late postoperative period (PODs 3-7; 24% of patients). Almost all (120 of 122; 98%) postoperative episodes (after tracheal extubation) were asymptomatic: only 9 of 70 (13%) early episodes were detected by clinical ECG monitoring. Postoperative ischemia did not appear to be related to acute changes in myocardial oxygen demand: only 39% of the postoperative episodes were preceded by a greater than 20% increase in heart rate. However, tachycardia persisted throughout the postoperative week (22-33% of all heart rates greater than 100 beats per min), and patients with postoperative ischemia (POD 0) more frequently had tachycardia (median 43% vs. 12% of the time; P less than 0.01). Five adverse cardiac outcomes occurred on the day of surgery; all five were preceded by postoperative ischemia, three by intraoperative ischemia before bypass, and none by preoperative ischemia. Patients with late postoperative ischemia did not have an adverse cardiac outcome. The authors conclude the following: 1) ischemia is more prevalent postoperatively than preoperatively or intraoperatively before bypass; 2) the incidence of postoperative ischemia peaks shortly after revascularization, during which time it is symptomatically silent, difficult to detect, and related to adverse cardiac outcome; 3) late postoperative ischemia also is silent, but it is less prevalent and not associated with in-hospital adverse cardiac outcome; and 4) a relationship between ischemia and persistently elevated postoperative heart rate may exist and warrants additional investigation.