Intra-Aortic Balloon Pump (IABP): This is a specialist procedure and should only be performed by trained specialists. It is presented to aid understanding of when it should be employed in general medical practice.
Indications of Intra-Aortic Balloon Pump (IABP)
• Cardiogenic shock post-MI.
• Acute severe mitral regurgitation.
• Acute ventricular septal defect.
• Preoperative (ostial left coronary stenosis).
• Weaning from cardiopulmonary bypass.
• Treatment of ventricular arrhythmias post-MI.
• Unstable angina (e.g. as a bridge to CABG).
Contraindications of Intra-Aortic Balloon Pump (IABP)
• Aortic regurgitation.
• Dilated cardiomyopathy (if patient not a candidate for transplantation).
• Aortic dissection.
• Severe aorto-iliac atheroma.
• Bleeding diathesis.
Complications of Intra-Aortic Balloon Pump (IABP)
• Aortic dissection.
• Arterial perforation.
• Peripheral embolism.
• Limb ischaemia.
• Balloon rupture.
Mechanism of action of Intra-Aortic Balloon Pump (IABP)
The device consists of a catheter with a balloon (40 mL in size) at its tip which is positioned in the descending thoracic aorta. The balloon inflation/deflation is synchronized to the ECG. The balloon should inflate just after the dicrotic notch (in diastole), thereby increasing pressure in the aortic root and increasing coronary perfusion. The balloon deflates just before ventricular systole, thereby decreasing afterload and improving left ventricular performance. Arterial balloon counterpulsation has a number of beneficial effects on the circulation.
• Increased coronary perfusion in diastole.
• Reduced left ventricular end-diastolic pressure.
• Reduced myocardial oxygen consumption.
• Increased cerebral and peripheral blood flow.
The IAB cannot assist the patient in asystole or ventricular fibrillation. It requires a minimum cardiac index of 1.2–1.4 L/min/m2 and may require additional inotropes.
Technique Balloon insertion
Previous experience is essential. Formerly, a cut-down to the femoral artery was required, but newer balloons come equipped with a sheath which may be introduced percutaneously. Under fluoroscopic control, the balloon is positioned in the descending thoracic aorta, with the tip just below the origin of the left subclavian artery. The patient must be fully anticoagulated with intravenous heparin. Some units routinely give intravenous antibiotics (e.g. flucloxacillin) to cover against staphylococcal infections.
Triggering and timing
The balloon pump may be triggered either from the patient’s ECG (R wave) or from the arterial pressure waveform. Slide switches on the pump allow precise timing of inflation and deflation during the cardiac cycle. Set the pump to 1:2 to allow you to see the effects of augmentation on alternate beats.
• Seek help from an expert! There is usually an on-call cardiac technician, senior cardiac physician, or surgeon.
• Counterpulsation is inefficient with heart rates over 130/min. Consider antiarrhythmics or 1:2 augmentation instead.
• Triggering and timing. When using ECG triggering, select a lead with the most pronounced R wave. Ensure that the pump is set to trigger from the ECG and not the pressure. Permanent pacemakers may interfere with triggering. Select a lead with negative and smallest pacing artefact. Alternatively, set the pump to be triggered from the external pacing device. A good arterial waveform is required for pressure triggering. The timing will vary slightly, depending on the location of the arterial line (slightly earlier for radial artery line, compared with a femoral artery line). Be guided by the haemodynamic effects of balloon inflation and deflation, rather than the precise value of delay.
• Limb ischaemia is exacerbated by poor cardiac output, adrenaline, noradrenaline, and peripheral vascular disease. Wean off, and remove the balloon (as described in the next section).
• Thrombocytopenia is common. It does not require transfusion, unless there is overt bleeding, and returns to normal once the balloon is removed. Consider prostacyclin infusion if platelet counts fall below 100 x 109/L.
Removal of the intra-aortic balloon
The patient may be progressively weaned by gradually reducing the counterpulsation ratio (1:2, 1:4, 1:8, etc.) and/or reducing the balloon volume and checking that the patient remains haemodynamically stable. Stop the heparin infusion, and wait for the ACT (activated clotting time) to fall <150 s (APTT <1.5 normal). Using a 50 mL syringe, have an assistant apply negative pressure to the balloon. Pull the balloon down until it abuts the sheath; do not attempt to pull the balloon into the sheath. Withdraw both balloon and sheath, and apply firm pressure on the femoral puncture site for at least 30 minutes or until the bleeding is controlled