Michael Vollkron

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.

Coronary Hemodynamics and Myocardial Oxygen Consumption During Support With Rotary Blood Pumps

Mechanical support offered by rotary pumps is increasingly used to assist the failing heart, although several questions concerning physiology remain. In this study, we sought to evaluate the effect of left-ventricular assist device (VAD) therapy on coronary hemodynamics, myocardial oxygen consumption, and pulmonary blood flow in sheep. We performed an acute experiment in 10 sheep to obtain invasively measured coronary perfusion data, as well as pressure and flow conditions under cardiovascular assistance. A DeBakey VAD (MicroMed Cardiovascular, Inc., Houston, TX, USA) was implanted, and systemic and coronary hemodynamic measurements were performed at defined baseline conditions and at five levels of assistance. Data were measured when the pump was clamped, as well as under minimum, maximum, and moderate levels of assistance, and in a pump-off condition where backflow occurs. Coronary flow at the different levels of support showed no significant impact of pump activity. The change from baseline ranged from -10.8% to +4.6% (not significant [n.s.]). In the pulmonary artery, we observed a consistent increase in flow up to +4.5% (n.s.) and a decrease in the pulmonary artery pressure down to -14.4% (P = 0.004). Myocardial oxygen consumption fell with increasing pump support down to -34.6% (P = 0.008). Left-ventricular pressure fell about 52.2% (P = 0.016) as support was increased. These results show that blood flow in the coronary arteries is not affected by flow changes imposed by rotary blood pumps. An undiminished coronary perfusion at falling oxygen consumption might contribute to cardiac recovery.

Estimation of cardiac contractility during rotary blood pump support using an index derived from left ventricular pressure

Introduction In the clinical use of cardiac assist devices, the diagnostics of the remaining heart contractility is essential for the evaluation of therapeutical measures. In this study a contractility index based on the left ventricular pressure (LVP) was evaluated during rotary blood pump support, by comparison with two other indexes.

Clinical Evaluation of an Automatic Physiologically Responsive Control System for Rotary Blood Pumps

Rotary blood pumps have become an important tool for the therapy of end stage cardiac failure. However, at the moment most of these pumps are still operated at constant speed and adjusted by the physician. Adaptation to physiological demand is therefore provided only by the remaining functionality of the left ventricle. A physiologically responsive control would not only be important for minimization of suction events and subsequent arrhythmic episodes, but also for better adaptation to exercise and eventually ventricular recovery. Therefore, an automatic control with integrated suction detection was developed and evaluated in a clinical study. Here, not only the results of this study but also the potential to optimize the pump efficiency with this strategy is presented.

Cardiac Contractility Assessment in Rotary Blood Pump Recipients Derived from Pump Flow

A new cardiac contractility index derived from pump flow (IQ) has been developed for rotary blood pumps (RBPs) recipients, to determine preservation and eventual recovery of the remaining cardiac function. Pulse flow indices were used for comparison with IQ during pump speed changes.