Slowing the heart saves lives: advantages of perioperative beta-blockade

Perioperative myocardial infarction—aetiology and prevention

Perioperative myocardial infarction (PMI) is one of the most important predictors of short- and long-term morbidity and mortality associated with non-cardiac surgery. Prevention of a PMI is thus a prerequisite for an improvement in overall postoperative outcome. The aetiology of PMI is multifactorial. The perioperative period induces large, unpredictable and unphysiological alterations in coronary plaque morphology, function and progression, and may trigger a mismatch of myocardial oxygen supply and demand. With many diverse factors involved, it is unlikely that one single intervention will successfully improve cardiac outcome following non-cardiac surgery. A multifactorial, step-wise approach is indicated. Based on increasing knowledge of the nature of atherosclerotic coronary artery disease, and in view of the poor positive predictive value of non-invasive cardiac stress tests, and the considerable risk of coronary angiography and coronary revascularization in high-risk patients, the paradigm is shifting from an emphasis on extensive non-invasive preoperative risk stratification to a combination of selective non-invasive testing and aggressive pharmacological perioperative therapy. Perioperative plaque stabilization by pharmacological means may be as important in the prevention of PMI as an increase in myocardial oxygen supply or a reduction in myocardial oxygen demand.

Beta-adrenergic blockade during severe ischemia

OBJECTIVE

To examine the effect of acebutolol, a beta-adrenergic-receptor blocker, on severe regional myocardial ischemia, specifically the effects on regional myocardial function and metabolism.

DESIGN

Randomized study.

SETTING

Animal laboratory of the Department of Anesthesiology and Critical Care, University of Stellenbosch Medical School.

PARTICIPANTS

Anesthetized open-chest pig model (n = 18).

INTERVENTIONS

Regional left ventricular function and metabolism were evaluated. Severe stenosis was applied to the left anterior descending coronary artery. After establishing regional myocardial ischemia, acebutolol was administered intravenously, and results were compared with controls who did not receive acebutolol. Animals were prospectively randomized to 1 of the groups.

MEASUREMENTS AND MAIN RESULTS

Regional myocardial function and metabolism were assessed by end-systolic pressure relationship, regional systolic shortening, postsystolic shortening, regional myocardial oxygen consumption, and lactate dynamics. Coronary blood flow was determined with a Doppler flow probe. Results indicated that acebutolol increased regional myocardial blood flow, and this resulted in less severe regional myocardial ischemia, improved function, and an increase in regional myocardial oxygen consumption.

CONCLUSION

The beta-Adrenergic-receptor antagonist was successful in reducing regional myocardial ischemia in this model. This reduction was achieved by an increase in coronary blood flow, which resulted in an improvement in regional mechanical function and an increase in oxygen consumption.

Prediction of cardiac risk before abdominal aortic reconstruction: comparison of a revised Goldman Cardiac Risk Index and radioisotope ejection fraction

BACKGROUND

A revised Goldman Cardiac Risk Index has been suggested to identify patients at higher risk for cardiac complications in patients who undergo major noncardiac surgery. The aim of this study was to test the usefulness of this model in an independent series of patients who underwent abdominal aortic surgery and to compare the index with the multiple gated acquisition (MUGA) scan in the prediction of cardiac complications.

METHODS

We studied 77 patients who underwent MUGA scan before elective abdominal aortic reconstruction. The revised index was calculated for each patient after recording the following five risk factors: history of ischemic heart disease, congestive heart failure, cerebrovascular disease, insulin-dependent diabetes, and creatinine level more than 2 mg/dL. Technetium-99m MUGA scan provided information about the resting left ventricular ejection fraction (LVEF) and the presence of regional wall motion abnormalities.

RESULTS

Fourteen patients (18%) had cardiac complications develop. The index proved to be a satisfactory predictor of postoperative cardiac events (P =.008), and an abnormal LVEF failed to do so (P =.1). The presence of wall abnormalities, with or without an abnormal LVEF, predicted cardiac complications (P =.004 and P =.006). Patients with a higher index score showed a tendency to have a lower LVEF (Spearman rank correlation, r = -0.43; P <.001). Wall abnormalities, with or without an abnormal LVEF, were more frequent in patients with higher scores (P =.03 and P =.009). Combining the index with the LVEF or the wall abnormalities or both could further stratify the cardiac risk (P =.004, P =.0003 and P =.0006, with chi(2) test for trend).

CONCLUSION

For those patients who undergo elective abdominal aortic surgery, the revised Goldman Cardiac Risk Index is a simple method of evaluating cardiac risk with minimum resource implications. MUGA scan can offer additional stratification in patients judged with the index to be at high risk.