World Anaesthesia Issue 14

Issue 14 (2002) Article 4: Page 1 of 2		Go to page: 1 2
Anaesthesia for patients with cardiac disease undergoing non-cardiac surgery (cont'd)

AORTIC STENOSIS

With a narrowed aortic valve, left ventricular (LV) outflow obstruction occurs. LV hypertrophy develops in compensation. This leads to reduced compliance, which is a reduction in ventricular wall movement for a fixed end-diastolic pressure. The eventual result is a fixed low cardiac output and inability to cope with systemic vasodilation. Coronary blood flow is also compromised due to the raised LV end-diastolic pressure. In addition to hypertrophy LV dilatation may also result, further reducing cardiac output. Aortic stenosis may result from rheumatic fever, often in association with the mitral valve. It may also be congenital, presenting in middle age, or be degenerative due to calcification in the elderly.

Symptoms of aortic stenosis usually occur when the valve area falls below 1cm2 (normal 2-3cm2), including angina, syncope on exertion, and symptoms of heart failure (dyspnoea, orthopnoea and paroxysmal nocturnal dyspnoea). Symptoms suggestive of aortic stenosis are angina and syncope on exertion, and symptoms of LV failure (dyspnoea, orthopnoea and paroxysmal nocturnal dyspnoea). An ECG will show signs of LV hypertrophy and strain, and an echocardiogram will assess (a) the pressure gradient between the LV and the aortic root, and (b) the LV contractility.

Anaesthesia may precipitate myocardial ischaemia or arrhythmias in patients with aortic stenosis. LV failure may also result. In the absence of treatment, sudden death occurs in 15-20%.

Anaesthesia

The aim is to maintain haemodynamic stability, in particular perfusion of the coronary vessels which are dependent on aortic root diastolic blood pressure. It is important to avoid reducing the systemic vascular resistance by vasodilation, but also not to cause excessive vasoconstriction. Tachycardia, myocardial depression and non-sinus rhythm (with consequent loss of the atrial contribution to ventricular filling) are all adverse factors. Spinal and epidural anaesthesia causes falls in systemic vascular resistance, and is therefore relatively contraindicated.

Table 4. Prevention of endocarditis in patients with heart-valve lesion, septal defect, patent ductus, or prosthetic valve. Guidelines from the British National Formulary 2002.

Dental procedures under local or no anaesthesia,

patients who have not received more than a single dose of a penicillin in the previous month, including those with a prosthetic valve (but not those who have had endocarditis), oral amoxicillin 3 g 1 hour before procedure; CHILD under 5 years quarter adult dose; 5–10 years half adult dose
patients who are penicillin-allergic or have received more than a single dose of a penicillin in the previous month, oral clindamycin 600 mg 1 hour before procedure; CHILD under 5 years clindamycin 150 mg or azithromycin 200 mg; 5–10 years clindamycin 300 mg or azithromycin 300 mg
patients who have had endocarditis, amoxicillin + gentamicin, as under general anaesthesia

Dental procedures under general anaesthesia,

no special risk (including patients who have not received more than a single dose of a penicillin in the previous month),
- either i/v amoxicillin 1 g at induction, then oral amoxicillin 500 mg 6 hours later; CHILD under 5 years quarter adult dose; 5–10 years half adult dose
- or oral amoxicillin 3 g 4 hours before induction then oral amoxicillin 3 g as soon as possible after procedure; CHILD under 5 years quarter adult dose; 5–10 years half adult dose
special risk (patients with a prosthetic valve or who have had endocarditis), i/v amoxicillin 1 g + i/v gentamicin 120 mg at induction, then oral amoxicillin 500 mg 6 hours later; CHILD under 5 years amoxicillin quarter adult dose, gentamicin 2 mg/kg; 5–10 years amoxicillin half adult dose, gentamicin 2 mg/kg
patients who are penicillin-allergic or who have received more than a single dose of a penicillin in the previous month,
- either i/v vancomycin 1 g over at least 100 minutes then i/v gentamicin 120 mg at induction or 15 minutes before procedure; CHILD under 10 years vancomycin 20 mg/kg, gentamicin 2 mg/kg
- or i/v teicoplanin 400 mg + gentamicin 120 mg at induction or 15 minutes before procedure; CHILD under 14 years teicoplanin 6 mg/kg, gentamicin 2 mg/kg
- or i/v clindamycin 300 mg over at least 10 minutes at induction or 15 minutes before procedure then oral or i/ v clindamycin 150 mg 6 hours later; CHILD under 5 years quarter adult dose; 5–10 years half adult dose

Upper respiratory-tract procedures, as for dental procedures; post-operative dose may be given parenterally if swallowing is painful.

Genito-urinary procedures, as for special risk patients undergoing dental procedures under general anaesthesia except that clindamycin is not given, see above; if urine infected, prophylaxis should also cover infective organism.

Obstetric, gynaecological and gastro-intestinal procedures (prophylaxis required for patients with prosthetic valves or those who have had endocarditis only), as for genito-urinary procedures.

AORTIC REGURGITATION

An incompetent aortic valve leads to retrograde flow of blood from the aorta to the LV during diastole. This results in LV dilatation and hypertrophy. Initially, there is an increase in stroke volume, but eventually aortic regurgitation results in LV failure and a low cardiac output state. Causes include ischaemic heart disease, degeneration, infection (rheumatic fever, syphilis, endocarditis), ankylosing spondylitis, aortic dissection, or it may be congenital. Symptoms of aortic regurgitation are the symptoms of LV failure. Angina may occur at a late stage. An ECG may show LV hypertrophy, with a large left ventricle on chest X-ray.

Anaesthesia

It is important to avoid bradycardia as this increases the time for regurgitation and reduces forward flow and hence cardiac output. Peripheral vasoconstriction and increased diastolic pressure also increase the regurgitant flow. Conversely, vasodilation encourages forward flow of blood.

MITRAL STENOSIS

Patients become symptomatic when the mitral valve area falls from the normal of 4-6cm² to 1-3cm². The obstruction leads to left atrial (LA) hypertrophy and dilation. LV filling is also reduced, hence reducing cardiac output. Within the pulmonary circulation, pulmonary vascular resistance increases due to pulmonary congestion, reducing lung compliance. Pulmonary hypertension results. Atrial fibrillation occurs in 50% of patients with mitral stenosis due to the LA enlargement. Causes of mitral stenosis are rheumatic fever, infection, inflammatory conditions and it may be congenital. Arrhythmias, pulmonary oedema and myocardial ischaemia can occur during anaesthesia.

Symptoms include those of LV failure, in particular dyspnoea and haemoptysis. ECG changes are those of LA (P mitrale) and perhaps RV hypertrophy. A chest X-ray may show LA enlargement and pulmonary oedema, and an echocardiogram can demonstrate the presence of left atrial thrombus. Patients with mitral stenosis may be on digoxin and warfarin, so a clotting screen should show appropriate values for the proposed surgery, and hypokalaemia should be avoided since it can cause digoxin toxicity.

Anaesthesia

The anaesthetic goals are to prevent tachycardia, which allows less time for diastolic flow through the stenosed valve, and to try to preserve sinus rhythm. In addition, it is important to maintain cardiac output and avoid hypovolaemia and vasodilation, which cause reduced atrial and ventricular filling. Raised pulmonary vascular resistance can inadvertently be further increased by hypercarbia and hypothermia, which should be avoided.

Examples of causes of perioperative myocardial ischaemia
Preoperative	Intraoperative	Postoperative
Anxiety Pain Hypovolaemia Inadequate drug treatment	Tachycardia Extremes of blood pressure Anaesthetic agents Surgical stresses	Pain Hypoxia Hypothermia Anaemia Hypercoagulability

MITRAL REGURGITATION

The incompetent mitral valve allows retrograde flow of blood from the LV to the LA, resulting in LA dilation. Pulmonary oedema then develops. Atrial fibrillation occurs in severe cases. Rheumatic fever accounts for 50% of cases, with other causes including myocardial infarction (secondary to papillary muscle rupture), degenerative changes, bacterial endocarditis, ruptured chordae tendinae, and cardiomyopathies. The main symptom is dyspnoea. ECG changes are similar to those seen in mitral stenosis, and achest X-ray may show cardiac enlargement and pulmonary oedema.

Mitral valve prolapse is the most common valvular abnormality, occurring in 3-8% of the population, in which one of the mitral valve leaflets prolapses into the left atrium. Mitral regurgitation and autonomic dysfunction may be associated with this condition, but otherwise there are no significant anaesthetic implications.

Anaesthesia

The aim is to maintain cardiac output and reduce the regurgitant flow. Therefore, myocardial depression and hypovolaemia should be avoided. Bradycardias and systemic vasoconstriction will increase regurgitant flow.

Summary

Patients with cardiac disease present for anaesthesia every day. Since their perioperative courses are associated with greater morbidity and mortality, it is important to provide a haemodynamically stable anaesthetic. This requires knowledge of the pathophysiology of the disease, and of the drugs and procedures and their effects on the patient.

References

1. Lee TH et al. Derivation and Prospective Validation of a Simple Index for Prediction of Cardiac Risk of Major Noncardiac Surgery. Circulation 1999; 100: 1043-1049
2. Eagle KA et al. Guidelines for Perioperative Cardiovascular Evaluation for Noncardiac Surgery. Circulation 1996; 93: 1278- 1317
3. Mangano D, Layug E, Wallace A, Tateo I. Effect of Atenolol on Mortality and Cardiovascular Morbidity after Noncardiac Surgery. New England Journal of Medicine 1996; 335(23): 1713-1720