PERIOPERATIVE MYOCARDIAL-ISCHEMIA AND INFARCTION IN NONCARDIAC SURGICAL PATIENTS

Cardiovascular morbidity and mortality associated with non-cardiac surgery increase with the probability and severity of coronary artery disease in the surgical population. In the absence of coronary artery disease, the risk of a perioperative cardiac event is negligible. Preoperative evaluation of patients should always include a thorough history and clinical examination but specific investigations should be individualized as false-positive results are common when the incidence of coronary artery disease is low. Recent myocardial infarction, symptoms suggestive of unstable angina and the presence of heart failure are powerful predictors of perioperative cardiovascular morbidity. A routine 12-lead electrocardiogram should be obtained for all men over 40 years and for all women over 55 years as well as for all patients with a history suggestive of heart disease. Stress testing, with or without thallium, is useful for patients with peripheral vascular disease, and dipyridamole-thallium imaging may be of value in risk stratification for those patients in whom adequate exercise levels cannot be achieved. The risk of a cardiovascular event during surgery can be stratified using a 'risk index'. Coronary angiography allows precise definition of the coronary anatomy and accurate assessment of left ventricular function but this is usually reserved for patients with severe symptoms or for those found to be at high risk as a result of provocative testing, where it is felt that revascularization of the myocardium may be indicated before the proposed surgery. Every effort should be made to treat any reversible risk factors that arepresent (unstable angina, heart failure, etc.) before surgery, with the aim of decreasing perioperative morbidity and mortality. In general, all cardiac medications should be continued throughout the perioperative period unless specific complications occur necessitating their withdrawal. Throughout the stress of the perioperative period myocardial oxygen delivery must be maintained while myocardial oxygen consumption should be kept at a low level. Myocardial ischaemia is common in patients with coronary artery disease during anaesthetic inducation and perioperative infarction occurs largely in those patients who develop significant tachycardia, hypotension or hypertension during surgery, the risk of infarction being increased three-fold when perioperative ischaemia occurs. Monitoring of the cardiac rhythm, arterial pressure, ST segment changes and, in high-risk patients, more sophisticated parameters of cardiac function, will allow for the early diagnosis of myocardial ischaemia and allow therapy to be monitored. Anaesthetic risk cannot be eliminated but can be minimized. The anaestheticagents and technique can be tailored to a patient's cardiovascular status but much will also depend on the anaesthetist's experience and expertise. Even with the best management there will be circumstances when myocardial ischaemia and infarction will occur and successful management will depend upon recognition and treatment. Careful monitoring can help diagnose myocardial ischaemia but infarction may be difficult to diagnose unless there is a high index of suspicion. It is often not possible to obtain a history and the standard investigations such as the 12-lead electrocardiogram and cardiac enzymes can be difficult to interpret. Radionuclide techniques and echocardiography can be helpful. The initial treatment of myocardial ischaemia and infarction in the perioperative period is identical, with nitrates, β-blocking drugs, aspirin and calcium antagonists being used. Thrombolytic therapy is contraindicated during and immediately after surgery. A combination of improved anaesthetic agents and techniques, togetherwith advances in the treatment of coronary artery disease, appear to be making surgery safer for patients with heart disease. © 1990 Baillière Tindall. All rights reserved.