I just transferred from interventional radiology to the cath lab. We used the intra-aortic balloon pump (IABP) last week, and I just don’t understand how a balloon inflation in the aorta can have any value.
– Cath lab staff member, rural Alabama, via Facebook

   The use of the intra-aortic balloon pump (IABP) can certainly be counterintuitive. Understanding the differences in coronary artery physiology and the concepts of IABP usage can help. Granted, a full IABP lesson could take many hours, or several articles, to properly address. You should take advantage of your IABP clinical representative to get a full tutorial. I will only address the information specific to your question in this article.

   Most people know that in systole, blood flows forward through our body to provide oxygenation and nutrients to our body. In the heart, that concept is altered. Think of it this way, during systole, the ventricles are contracted in order to push the blood around the body. During this time, there would be no way to get blood to the myocardium because of that contraction of the muscle, and subsequently, the endocardial arteries that supply blood to that muscle (Figure 1).

   During the relaxation phase, diastole, the blood is then ‘sucked in’, if you will, to the coronary arteries to provide blood flow to the cardiac muscle. The important part to remember is that coronary artery perfusion occurs in diastole (Figure 2).

   You can see examples of diastole filling at: http://www.rcisreview.com/ AskTheInstructorJuly2010.htm
That now brings us to why the IABP helps when it inflates and deflates (Figures 3-5).

   When the IABP is inflated, it is inflated in diastole (after the aortic valve closes) to provide a forward ‘push’ of the blood to the coronary arteries. Since you now know that the bulk of coronary artery blood flow occurs in diastole, you can appreciate that this forward ‘push’ can only help with coronary artery perfusion. This also directly increases the myocardial oxygen supply in a heart that has had an injury or infarct and has a demand for more oxygen.

   It should also be mentioned that not only does the balloon inflate to provide support to the heart, but the deflation of the balloon also has benefits. The deflation of the balloon just before systole decreases the AFTERLOAD of the heart, or the amount of resistance that the heart has to push against. It does this by “sucking” some of the blood around the arch and down the body. This, in turn, decreases the work requirement of the heart, and will increase cardiac output slightly because it is assisting the heart.

    Understanding that coronary artery blood flow is at its peak during diastole, and that the IABP catheter inflates during diastole, will help conceptualize why the inflation of the balloon will help with the hemodynamics of the patient with a stressed heart.

Submit your question to Todd at tginapp@rcisreview.com, or via Facebook at www.facebook.com/RCISReview.

Note: Shortly after the RCIS exam article was published in the June 2010 issue, I received emails concerning the comments about use of intracardiac echo (ICE) in the cath lab. Many of these comments were about ICE being used for patent formen ovale (PFO)/atrial septal defect (ASD) closures, transeptal heart caths and pediatric cases. I agree that many facilities utilize ICE during these cases, and not just during EP cases as came out in the article. I apologize for the oversight.
It does bring up an interesting question concerning the types of skills and procedures upon which individuals will be tested. As an example, while many facilities utilize ICE, a larger percentage of smaller facilities will never perform those procedures. The challenge for those educating others, or preparing individuals for the RCIS exam, is how to expose these smaller facilities’ staff to the procedure, and come up with a way for them to retain the information, in order to be able to correctly answer these questions on the exam. Thanks again for everyone’s feedback.