Ischaemic heart disease

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Major clinical predictors of perioperative cardiac complications are patients with recent (within 6 months) myocardial infarction, severe or unstable angina, and significant arrhythmias. However, many patients have

Table 10.1 Risk of major perioperative cardiac event according to type of surgery

Low risk (< 1%)

Intermediate risk (1-5%)

High risk (> 5%)

Endoscopic

Carotid endarterectomy

Emergency major surgery

procedures

Superficial

Head & neck

Aortic/major

procedures

vascular surgery

Cataract

Intraperitoneal

Peripheral vascular

Breast

Intrathoracic

Prolonged procedure

with large fluid

shifts/blood loss

Orthopaedic

Prostate

Table 10.2 Risk of major perioperative cardiac event according to type of patient

Minor

Intermediate

Major

Advanced age

Mild angina

Unstable coronary syndromes

(class 1-2)

• recent MI (< one month)

• unstable/severe angina

Abnormal ECG

Previous myocardial

Decompensated heart

infarction (history

failure

or ECG)

Rhythm other

Compensated or

Significant arrhythmias

than sinus

previous heart

failure

Low functional

Diabetes

Severe valve disease

capacity

History of stroke

Uncontrolled

hypertension

controlled ischaemic heart disease and, although there are a number of tests available to assess this group, they are not necessarily helpful. History, examination, and resting ECG can readily categorise risk (Table 10.2).

Additional scoring systems have been developed (for example, the Goldman cardiac risk index) that can help quantify risk and these are based on observational studies. Probably the most useful measure with regard to ischaemic heart disease is the patient's functional ability. Risk is increased in patients who cannot reach 4 METS (metabolic equivalents) workload; 1 MET is equivalent to the oxygen consumption of a resting 40-year-old 70 kg man. Climbing a flight of stairs, briskly walking on the flat, mowing the lawn, swimming, or playing a round of golf is at least 4 METS.

Surgery may proceed without further evaluation in patients with minor risk factors and good function who are undergoing low or intermediate risk surgery. Patients with intermediate risk factors and poor functional capacity may need further evaluation and optimisation before surgery. Exercise ECG testing is widely available but impractical for many high risk surgical patients.

Dobutamine stress echocardiography is the best test to predict perioperative events, according to most studies. It has a 100% negative predictive value and patients with extensive ischaemia experience 10 times more perioperative cardiac events than those with limited ischaemia. Coronary angiography is indicated in appropriate high risk patients or intermediate risk patients after screening.

Overall, less than 10% surgery is associated with a perioperative cardiac event. However, vascular surgery poses particular risks because many of the risk factors for peripheral vascular disease are the same for coronary artery disease (diabetes, smoking, and hyperlipidaemia). In one study, 1000 consecutive patients with peripheral vascular disease but no clinical evidence of ischaemic heart disease underwent coronary angiography; 37% had at least one coronary artery stenosis of > 70%. The incidence is higher in vascular patients with clinical evidence of ischaemic heart disease - approximately 60%. Cardiac symptoms may be masked in some of these patients because their mobility is limited. Major vascular surgery is also associated with fluctuations in intravascular volume and blood pressure, which stress the heart.

Several randomised trials have looked at medical therapy to reduce perioperative risk (P blockers, nitrates and calcium channel blockers). There is evidence to suggest that perioperative P blockers reduce cardiac complications (ischaemic episodes, myocardial infarction, and mortality). One randomised trial used prophylactic atenolol immediately before and up to 7 days after non-cardiac surgery. This reduced the cardiovascular mortality rate at 6, 12, and 24 months. In both vascular and general surgery, atenolol reduces perioperative cardiac mortality and ischaemic complications. In a study on vascular patients, cardiac mortality and morbidity was reduced by bisoprolol from 34% to 3 4%. P blockers are therefore recommended for high risk patients and patients with hypertension, ischaemic heart disease, or risk factors for ischaemic heart disease. If preoperative administration is not possible, intravenous P blocker given at induction of anaesthesia followed by postoperative treatment is also effective. The intraoperative use of nitroglycerine in high risk patients does not affect outcome despite reduced ischaemia on the ECG.

The diagnosis of myocardial infarction in the perioperative period can be difficult. One half of patients do not have typical chest pain. They may present with arrhythmias, pulmonary oedema, hypotension, or confusion. ECG changes are common postoperatively and do not necessarily indicate myocardial infarction. Up to 20% postoperative patients have new ECG abnormalities - usually T wave changes. Creatinine kinase rises non-specifically with surgery and troponin measurements are more appropriate.

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