Continuous assessment of cardiac function during rotary blood pump support: A contractility index derived from pump flow

BACKGROUND: The clinical application of rotary blood pumps (RBPs) for bridge-to-recovery and destination therapy has focused interest on the remaining contractile function of the heart and its course. This study reports a method to determine contractility that uses readily measured variables of the RBP. METHOD: The proposed index (IQ) is defined as the slope of a linear regression between the maximum derivative of the pump flow and its peak-to-peak value. IQ was compared with the maximal derivative of ventricular pressure (dP/dt(max)) vs end-diastolic volume (EDV) and the pre-load-rccruitable stroke work. All indices were. evaluated using computer simulations and animal experiments. For in vivo studies, a MicroMed-DeBakey ventricular assist device (VAD) was implanted in 7 healthy sheep. Ventricular contractility was examined under normal conditions and after pharmacologic intervention. For the computer simulation, variations of ventricular contractility, ventricular pre-load and after-load, and pump speeds were studied. RESULTS: In vivo and computer simulations showed the IQ index to be sensitive to changes of cardiac contractility, similar to other classic indices. For reduced cardiac contractility, it decreased to 9.3 +/- 3.9 (s(-1)) vs 15.3 +/- 4.0 (s(-1)) in the control condition (in vivo experiments). The IQ index was only marginally influenced by pre-load and after-load changes: a variation of 7.0% +/- 8.9% and 1.3% +/- 7.1%, respectively, was observed in computer simulations. CONCLUSIONS: The IQ index, which can be derived from pump data only, is a useful parameter for continuous monitoring of the cardiac contractility in patients with RBP support. J Heart Lung Transplant 2010;29:37-44 (C) 2010 International Society for Heart and Lung Transplantation. All rights reserved.