6. CARDIOVASCULAR DISEASE

ISCHAEMIC HEART DISEASE

Assessing patients with coronary artery disease who are having non-cardiac surgery is difficult.

The purpose of the preoperative evaluation is:

to identify patients who would benefit from further cardiac testing,

to decide if the risk can be reduced and

to decide if the non-cardiac surgery is so urgent that it should be carried out rapidly despite the risk.

In hospitals that have assess to all investigations and all medical and surgical treatments, preoperative management would depend on clinical assessment and preoperative testing (for example: exercise electrocardiogram, dipyridamole-thallium scan, left ventricular ejection fraction, dobutamine stress echocardiogram, transthoracic echocardiogram and coronary angiogram). The patient may then proceed to further treatment including coronary artery surgery, angioplasty or maximal medical treatment of the ischaemic heart disease.

In hospitals that do not have access to all investigations and treatment, patients may still be effectively managed by clinical assessment alone. History and examination of the patient are key elements of preoperative risk assessment. The anaesthetist must determine the patient’s risk factors, the surgical risk factors and the overall fitness (functional capacity) of the patient.

Patient Risk Factors

Patient risk factors should be subdivided into major, intermediate and minor.

Major patient risk factors are markers of unstable coronary artery disease and include myocardial infarction within 6 weeks, unstable or severe angina, ongoing chest pain after myocardial infarction, clinical ischaemia and uncontrolled congestive heart failure, clinical ischaemia and arrhythmias (high grade AV block or SVT with uncontrolled ventricular rate) or coronary artery bypass operation within 6 weeks. These patients should not have elective operations until they are investigated and treated. Only emergency procedures should be considered.

Intermediate patient risk factors are markers of stable coronary artery disease and include myocardial infarction longer than 6 weeks ago but less than 3 months ago, stable angina, diabetes and controlled congestive cardiac failure.

Minor patient risk factors are markers of coronary artery disease but not of increased perioperative risk. They include a family history of coronary artery disease, uncontrolled hypertension, hypercholesterolaemia, electrocardiogram abnormalities (arrhythmia, left ventricular hypertrophy, bundle branch block) and patients who have had a previous myocardial infarction more than 3 months ago and are asymptomatic without treatment.

Functional Capacity

The patient’s general health (exercise tolerance or functional capacity) will provide the anaesthetist with a good estimate of perioperative risk. Patients with vascular disease who can exercise to 85% of their estimated maximal heart rate (220 minus age) have a low risk of perioperative cardiac complications. Climbing stairs is a simple test of perioperative cardiac risk. Patients who cannot climb one flight of stairs are at increased risk of cardiovascular complications.

Surgical Risk Factors

Surgery can also be considered as low, intermediate or high risk.

Low risk surgery includes endoscopic, breast, skin, limb, eye and plastic surgery.

Intermediate risk surgery includes minor vascular, minor abdominal and thoracic, neurosurgery, ENT and orthopaedic surgery.

High-risk surgery includes emergency intermediate risk surgery, aortic and major vascular, thoracic and prolonged surgery.

Management

The anaesthetist must take a history and perform an examination and assess the patient risk factors, surgical risk and the patient’s functional capacity. With this knowledge the anaesthetist can estimate the patient’s risk of perioperative cardiac complications.

If the patient is at high risk and the operation is elective, the patient should not have the surgery.

If the surgery is urgent and the patient is at an increased risk then the anaesthetist must ensure that the patient has the best available care. High risk patients with high risk surgery and poor exercise tolerance may need coronary angiography and coronary artery bypass operation before the non-cardiac surgery.

It is very important that the anaesthetist always avoids events that will increase the risk of perioperative cardiac complications such as hypothermia, extreme anaemia, hypotension, tachycardia and postoperative pain. This can easily be achieved. Perioperative beta-blockade may also be of benefit.

VALVULAR HEART DISEASE

Patients with valvular heart disease will have abnormal cardiac function. They must have a full preoperative assessment. As with ischaemic heart disease, the patient’s exercise tolerance is a good indicator of the severity of the heart disease.

All patients with valvular heart disease need antibiotic treatment to prevent bacterial endocarditis.

Mitral Stenosis

Mitral stenosis is usually due to rheumatic fever. Mitral stenosis prevents left ventricular filling, which results in decreased cardiac output. Left atrial emptying is decreased, which results in left atrial enlargement and increased pulmonary artery pressures to maintain cardiac output. These patients may develop pulmonary oedema, cardiac failure and atrial fibrillation. The main symptom of mitral stenosis is dyspnoea. Patients with atrial fibrillation, dyspnoea at rest and who wake at night short of breath (paroxysmal nocturnal dyspnoea) are at increased risk. The anaesthetist should avoid myocardial depressants, tachycardia (which reduces ventricular filling time), hypovolaemia and hypotension and increased pulmonary vascular resistance (e.g. due to hypoxia, pain or hypercarbia). The anaesthetist should aim for a slow sinus rhythm, normal intravascular volume, normal cardiac contractility and normal systemic vascular resistance.

If regional anaesthesia is used, epidural anaesthesia maybe safer than spinal anaesthesia. The anaesthetist must avoid hypotension.

Mitral Regurgitation

50% of mitral regurgitation is due to rheumatic fever. As the left ventricle contracts some of the blood flows backwards into the left atrium. The regurgitant flow will increase with increased systemic vascular resistance and bradycardia. Most patients with chonic mitral regurgitation are well for many years without evidence of heart failure. Dyspnoea and pulmonary oedema are signs of severe mitral regurgitation. The anaesthetist should avoid myocardial depressants, hypovolaemia, bradycardia and increased systemic vascular resistance. They should aim for a normal or increased heart rate, decreased systemic vascular resistance and normal cardiac contractility and intravascular volume.

Regional anaesthesia is well tolerated.

Aortic Stenosis

Aortic stenosis may be congenital or acquired. It is a chonic condition with symptoms only occurring when the stenosis is severe. The main symptoms of aortic stenosis are dyspnoea, angina and syncope. Once symptoms develop, the patient’s life expectancy may be less than 5 years and these patients should not have elective surgery. The anaesthetist must maintain sinus rhythm. Atrial contraction is vital to maintaining adequate ventricular filling. The heart rate should be normal. Tachycardia and bradycardia will both reduce coronary blood flow. The systemic vascular resistance should be kept normal. An increase in systemic vascular resistance will further reduce cardiac output and a reduction in systemic vascular resistance may reduce coronary blood flow. Myocardial depressants must be avoided.

Regional anaesthesia can cause dangerous changes in systemic vascular resistance and heart rate. However, epidural anaesthesia may be tolerated if performed slowly with careful monitoring and treatment of blood pressure and heart rate.

Aortic Regurgitation

Patients with aortic regurgitation may not have symptoms for many years. They may develop signs and symptoms of left ventricular failure. The anaesthetist should avoid bradycardia as this increases the time for backwards flow. They should also avoid increased peripheral resistance and myocardial depressants. They should aim to maintain an increased heart rate, adequate intravascular volume and decreased systemic vascular resistance.

Regional anaesthesia is well tolerated in patients with chonic aortic regurgitation.

HYPERTENSION

It is important that all antihypertensive medication is continued and that the patient is fully assessed for signs and symptoms of the complications of chonic hypertension. Organ damage from hypertension presents a greater risk than hypertension itself.

The management of patients with hypertension has changed over the last decades. Hypertension is defined by the World Health Organisation as a diastolic blood pressure greater than 95 mmHg and a systolic pressure greater than 160 mmHg. Chonic hypertension may cause renal failure, cardiac failure, stroke and myocardial infarction. Ideally all patients with hypertension should be treated before surgery. However, there is little evidence for an association between systolic pressures of less than 180 mmHg or diastolic pressures less than 110 mmHg and perioperative complications though the anaesthetist must be aware that the patient may have large swings in blood pressure.

Intra-operative arterial pressure should be maintained within 20% of the preoperative arterial pressure.