Effectiveness of intra-aortic balloon counterpulsation on systolic unloading

The therapeutic benefit of intra-aortic balloon pumping (IABP) is believed to result from the combined action of reducing myocardial demand (systolic unloading) while improving myocardial supply (diastolic augmentation). However, the relative importance of these aspects has not been fully understood. Accordingly, the systolic unloading responses to IABP were studied in 13 dogs on total coronary bypass. By perfusing the coronary circulation from an extracorporeal source at a controlled pressure the authors were able to analyse the systolic unloading responses without diastolic augmentation directly altering coronary flow. The results suggest that IABP is effective only in reducing myocardial demand at normotensive levels; IABP during hypotensive states did not assist the failing heart mechanically by systolic unloading. Therefore the therapeutic action of IABP must result from increases in coronary blood flow by diastolic augmentation.