The use of mechanical support in acute left ventricular failure can provide temporary circulatory support and is most commonly utilized in the setting of acute myocardial infarction (MI) complicated by cardiogenic shock. The main purpose of a ventricular assist device (VAD) is to unload the failing heart and maintain circulation to vital organs. These devices were initially developed to serve as temporary support to allow the heart to recover or as a bridge to transplant. Currently there are 3 types of FDA-approved percutaneous VADs that can be categorized as follows:
INTRA-AORTIC BALLOON PUMP
The intra-aortic balloon pump (IABP) was developed in the 1960s as a relatively simple and quick system to provide left ventricular assistance (Figure 32-1). The IABP is a catheter-based system that can be placed at the bedside or in the catheterization laboratory. It consists of a polyethylene balloon mounted on a catheter that is placed in the descending aorta. It is typically inserted percutaneously from the femoral artery with the distal tip positioned 2 to 3 cm from the left subclavian artery. The balloon is inflated with helium and deflated in a 1:1 ratio with the cardiac cycle, though lower ratios (1:2, 1:3, 1:4) are frequently employed during weaning and prior to IABP removal. Inflation of the balloon can be triggered by the electrocardiogram (ECG), systolic upstroke, or a pacemaker spike. Because the timing of balloon inflation and deflation is dependent on the cardiac cycle, tachycardia and irregular rhythms such as atrial fibrillation can cause less than ideal augmentation.
Intra-aortic balloon and console. (Image courtesy of Teleflex Incorporated. © 2018 Teleflex Incorporated. All rights reserved.)
The balloon is inflated at the start of diastole, which augments diastolic pressure and improves coronary blood flow. The balloon deflates just prior to the onset of systole, reducing central aortic pressure and consequently early afterload on the left ventricle (Figure 32-2). The 4 main effects of the IABP are:
increase in aortic flow,
reduction of systolic left ventricular pressure due to phasic deflation of the balloon,
diastolic aortic pressure augmentation, and
increase in coronary flow due to inflation of the balloon.
IABP waveform demonstrating both native (unassisted) and assisted systolic pressures. Note the augmentation in diastolic pressure corresponding to balloon inflation as well as the decrease in the end-diastolic pressure.
The combined augmentation of diastolic coronary filling and reduction in ventricular afterload with IABP results in decreased ventricular end diastolic pressure, reduced systemic vascular resistance, and increased cardiac output in both ischemic and nonischemic heart failure (HF).1