Intra-aortic balloon counterpulsation

Principle

A 30–40mL balloon is placed in the descending aorta. The balloon is inflated with helium during diastole, increasing diastolic blood pressure above the balloon which thus improves coronary and cerebral perfusion. The balloon is deflated during systole, decreasing peripheral resistance and increasing stroke volume. No drug therapy exists which can increase coronary blood flow while reducing peripheral resistance. Intra-aortic balloon counterpulsation may improve cardiac performance in situations where drugs are ineffective (see figure 3.2).

Indications

It can be used to support the circulation where a structural cardiac defect is to be repaired surgically. It may also be used for acute circulatory failure where resolution of the cause of the cardiac dysfunction is expected. In acute MI, resolution of peri-infarct oedema may allow spontaneous improvement in myocardial function; the use of balloon counterpulsation may provide temporary circulatory support and promote healing by improving myocardial blood flow. Other indications include acute myocarditis and poisoning with myocardial depressants. It should not be used in aortic regurgitation as the rise in diastolic blood pressure would increase regurgitant flow.

Insertion of the balloon

The usual route is via a femoral artery. Percutaneous Seldinger catheterization (9 an introducer sheath) provides a rapid, safe technique with minimal arterial trauma and bleeding. Open surgical catheterisation may be needed in elderly patients with atheromatous disease. Check the balloon position on a chest X-ray to ensure that the radio-opaque tip is at the level of the 2^nd intercostal space.

Anticoagulation

The presence of a large foreign body in the aorta requires systemic anticoagulation to prevent thrombosis. The balloon should not be left deflated for longer than a minute while in situ, otherwise thrombosis may develop despite anticoagulation.

Control of balloon infl ation and defl ation

Helium is used to inflate the balloon, its low density facilitating rapid transfer from pump to balloon. Inflation is commonly timed to the ‘R’ wave of the ECG, although timing may be taken from an arterial pressure waveform. Minor adjustment may be made to the timing to ensure that inflation occurs immediately after closure of the aortic valve (after the dicrotic notch of the arterial pressure waveform) and deflation occurs at the end of diastole. The filling volume of the balloon can be varied up to the maximum balloon volume. The greater the filling volume, the greater the circulatory augmentation. The rate at which balloon inflation occurs may coincide with every cardiac beat or every 2^nd or 3^rd cardiac beat. Slower rates are necessary in tachyarrhythmias. Weaning of intra-aortic balloon counterpulsation may be achieved by reducing augmentation or the rate of inflation.

 Fig. 3.2 Arterial waveform with and without intra-aortic counterpulsation.