A 75-year-old patient was admitted to ICU for management of cardiogenic shock after percutaneous coronary artery intervention (PCI). An intra-aortic balloon pump was inserted post procedure. An hour into the ICU admission the nurse alerts you that the diastolic augmentation alarm, set at 100 mmHg, is triggering.
a) List the causes of ineffective diastolic augmentation. (40% marks)
b) Explain the timing of diastolic augmentation in the following 1:2 IABP graphs (Scenarios 1 to 3 shown below). Outline the physiological consequences of the IABP traces.
Scenario 1: (20% marks)
Scenario 2: (20% marks)
Scenario 3: (20% marks)
Diastolic augmentation is the beneficial increase in aortic pressure which occurs when the balloon inflates in diastole, just as the aortic valve closes. This has a couple of benefits, the chief of which being improved coronary perfusion (but also some extra blood is pushed down into the systemic circulation). This is the effect of diastolic augmentation; which means that ineffective diastolic augmentation could actually mean a whole host of possible problems that result in insufficient diastolic coronary and systemic blood flow. The unready candidate would have had a hard time. To classify these, one method might be to separate them into patient problems, technique problems and machine problems:
Now, to these traces:
This is early balloon inflation. It results in:
This is late balloon deflation. It also results in increased LV oxygen demand due to increased afterload, but this time the situation is worse, as it mainly affects isovolumetric contraction, and this is where 90% of myocardial oxygen is usually spent.
This is late balloon inflation. It decreases diastolic augmentation, which results in decreased coronary perfusion. The balloon seems to be deflating correctly, so afterload does not seem to be affected.
Freedman, R. J. "The intra-aortic balloon pump system: current roles and future directions." Journal of applied cardiology 6.5 (1991): 313-318.
Hanlon-Pena, Patricia M., and Susan J. Quaal. "Intra-aortic balloon pump timing: review of evidence supporting current practice." American Journal of Critical Care 20.4 (2011): 323-334.