Cardiac surgery

Published on 11/04/2015 by admin

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Cardiac surgery

Introduction and cardiopulmonary bypass

Surgery of the heart has long fascinated surgeons but only a very limited range of cardiac procedures was possible until cardiopulmonary bypass was successfully employed in 1953. For the first time, the systemic circulation could be sustained artificially, with the heart and lungs bypassed. The heart could be manipulated and lung ventilation discontinued, giving optimal conditions for operating on the heart. Since then, cardiac surgery has developed and expanded swiftly.

In keeping with the move towards minimal access in other areas, coronary artery bypass grafting and various valvular procedures can now be performed ‘off-pump’ via small incisions on the beating heart without bypass. However, most cardiac surgery is still carried out on bypass, with a bloodless field created by clamping the ascending aorta just proximal to where the aortic cannula returns arterial blood from the bypass machine (see Fig. 44.1). Without coronary artery blood flow, myocardial ischaemic damage has to be mitigated by reducing metabolic demands by inducing diastolic arrest with a high-potassium cardioplegic solution (16 mmol/L KCl) (Table 44.1) and cooling (to between 4 and 12°C).

Table 44.1

Constituents of a typical infusate for cold cardioplegia (St Thomas’s solution)

Constituent Quantity
Sodium chloride 110.0 mmol/L
Potassium chloride 16.0 mmol/L
Magnesium chloride 16.0 mmol/L
Calcium chloride 1.2 mmol/L
Sodium bicarbonate 10.0 mmol/L
Procaine 16.0 mmol/L

Several problems may arise when blood is exposed to artificial surfaces in a cardiopulmonary bypass machine:

Assessing risk in cardiac surgery

The complexity of cardiac surgery makes it potentially risky. In the UK, all cardiac surgical units have to undertake prospective audit including risk assessment and submit data to a national registry. Results of all units are published online, allowing suitable standards to be developed and maintained. This process will shortly be introduced in general surgery in the UK.

Several scoring systems have been devised to take patient factors into account in order to predict the risk of morbidity and mortality for an individual undergoing a particular operation, a process called risk stratification. Systems generally take account of the surgical procedure, its urgency and pre-existing co-morbidities. Online calculators for STS score and for EuroSCORE II are the latest tools and are based on actual outcomes in large numbers of the patients recently operated upon.

Congenital cardiac disease

Types of congenital heart disease

Congenital heart disease occurs in about 2 per 1000 live births and falls into two main groups: those with and those without cyanosis.

Cyanotic heart disease

Cyanotic heart disease exists when there is mixing of systemic arterial and venous blood through a predominantly right-to-left cardiac shunt. The most common examples are:

• Tetralogy of Fallot—the four features are ventricular septal defect (VSD), pulmonary stenosis, right ventricular hypertrophy and an aorta which overrides the ventricular septum, receiving blood from both ventricles

• Transposition of the great arteries—the pulmonary artery arises from the left ventricle and the aorta from the right ventricle

• Tricuspid atresia—absence of a functional tricuspid valve

• Truncus arteriosus—the pulmonary artery and aorta fail to develop separately

• Total anomalous pulmonary venous drainage—pulmonary venous blood drains into the right side of the heart

• Eisenmenger’s syndrome—increased pulmonary blood flow caused by a pre-existing left-to-right shunt (see next section) causes severe pulmonary hypertension later in life, which result in spontaneous reversal of the shunt so flow reverses to become right-to-left

Management of congenital heart disease

In early cardiac surgery, palliation was often all that could be offered. Later, palliation was sometimes followed by a corrective operation when the child was larger. Nowadays, corrective procedures are usually offered at the outset, as operations have become more routine, myocardial protection is more predictable and operative risks are lower.

Acquired heart disease

The types of acquired heart disease are listed in Table 44.2.

Table 44.2

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