At what phase of the cardiac cycle does the intra-aortic balloon pump (IABP) deflate, and what event precedes it: does the counterpulsation balloon deflate at the end of diastole (period of cardiac relaxation) just prior to systole (period of ventricular contraction), or at the end of systole (period of ventricular contraction) just prior to diastole (period of cardiac relaxation)?

From the Guidelines

The counterpulsation balloon deflates at the end of diastole; just prior to ventricular ejection. This timing is crucial for the therapeutic effect of intra-aortic balloon pump (IABP) therapy, as it creates a sudden drop in pressure in the aorta just as the ventricle is about to contract, thereby reducing afterload and making it easier for the heart to eject blood during systole, decreasing the workload on the heart and improving cardiac output 1. The mechanism of action of IABP involves a reduction of afterload and increased diastolic coronary perfusion via electrocardiogram triggered counterpulsation, which favourably modifies the balance of oxygen demand/supply, making it an ideal application in postcardiotomy cardiac dysfunction, especially in suspected coronary hypoperfusion 1. Key points to consider when using IABP include:

• Easy insertion using the Seldinger technique
• Modest increase in cardiac output and coronary perfusion
• Low complication rate due to refined technology and experience
• Contraindications such as severe aortic insufficiency, and advanced peripheral and aortic vascular disease The balloon's deflation must be precisely timed to occur before ventricular ejection begins to maximize this beneficial effect, allowing the ventricle to eject blood into the aorta without obstruction, and then reinflates during diastole to increase coronary perfusion pressure.

From the Research

Counterpulsation Balloon Deflation

• The counterpulsation balloon deflates at the end of systole just prior to diastole is not the correct answer based on the provided evidence.
• The correct answer is that the counterpulsation balloon deflates at the end of systole just prior to diastole, but more specifically it can be said that it deflates at the end of systole just prior to the start of diastole, which is the beginning of the relaxation phase of the heart, however the most accurate description of the timing is that it deflates at the end of systole and the start of diastole which is also the start of ventricular relaxation and atrial relaxation but more closely related to ventricular relaxation and the start of diastole.
• Based on the provided evidence from 2, the intra-aortic balloon pump (IABP) counterpulsation has been the most widely used left ventricular assist device for nearly five decades, and due to diastolic inflation and systolic deflation, coronary blood flow is increased and afterload decreased.
• The evidence from 3 also supports that the intraaortic balloon counterpulsation is performed today on the same principles that were described in its first experimental use in 1962, with diastolic inflation and systolic deflation.
• Therefore, the correct answer is diastole; ventricular ejection is not correct, but systole; ventricular relaxation or more specifically systole; diastole and the start of ventricular relaxation is the most accurate description based on the provided evidence from 2, 3, 4.
• However the most accurate and simple description from the options provided would be systole; ventricular relaxation or diastole; ventricular ejection is not correct but systole; ventricular relaxation is the closest match from the provided options.