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 (I_Q) is defined as the slope of a linear regression between the maximum derivative of the pump flow and its peak-to-peak value. I_Q was compared with the maximal derivative of ventricular pressure (dP/dt_max) vs end-diastolic volume (EDV) and the pre-load-recruitable 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 I_Q 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 I_Q 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 I_Q 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.