Intra-Aortic Balloon Pump, Arterial Line, and EKG Waveforms
The intra-aortic balloon pump (IABP) is a form of mechanical circulatory support used in cardiogenic shock, facilitating separation from cardiopulmonary bypass, percutaneous coronary interventions, unstable angina, and in thrombolytic therapy following a myocardial infarction. The device is introduced from the femoral artery and guided into the aorta till its tip is just distal to the left subclavian artery takeoff from the aortic arch. Therefore, when properly positioned, the IABP occupies the entire descending thoracic aorta and much of the suprarenal abdominal aorta. Although fluoroscopy/echocardiography can help guide placement, they are not absolutely necessary in emergent situations.
The basic premise behind the IABP is to increase aortic diastolic pressure to improve coronary perfusion. The balloon inflates rapidly with helium (less dense gas creates less turbulent flow and faster inflation/deflation) during diastole and creates an “augmented diastolic pressure“ higher than the normal diastolic pressure. It is this diastolic pressure which is a primary determinant in coronary perfusion pressure. With the onset of systole, the balloon deflates dropping the afterload and improving cardiac output. Because of this constant mechanical agitation within the aorta, absolute contraindications include severe aortic insufficiency, aortic dissection, and severe peripheral vascular disease.
So how can the IABP tell when systole and diastole occur, and in turn, know when to deflate and inflate? We can trigger the IABP by syncing it with the patient’s EKG, the arterial waveform (the dicrotic notch represents aortic valve closure and the end of systole), and even pacing spikes. We can even set the IABP to augment every cardiac cycle (1:1), every other cycle (1:2), etc.
Here’s an illustration I sketched how the EKG, arterial line (A-line), and IABP waveforms line up vertically. The IABP will inflate at the end of systole (where the dicrotic notch would appear on the arterial waveform) and in the mid-T wave on EKG. It deflates on the R wave. Look at the tan line for an easy comparison.
It’s imperative to check that the IABP is firing appropriately relative to the cardiac cycle. Having the balloon inflated during systole will cause a significant impediment to forward flow, and having it deflated during diastole defeats the purpose.
These are just the basics of this useful counterpulsation device. Drop me a comment below with questions! 🙂