Daniel Tamez

Controller algorithms are an important feature for assessment of ventricular assist device performance. Flow estimation is one algorithm implemented in the HeartWare continuous-flow ventricular assist device pump system. This parameter estimates flow passing through the pump and is calculated using speed, current, and hematocrit. In vitro and in vivo studies were conducted to assess the algorithm accuracy. During in vitro testing, three pumps were tested in four water–glycerol solutions at 37°C with viscosities equivalent to hematocrits of 20, 30, 40, and 50%. By using a linear regression model, a correlation coefficient of >0.94 was observed between measured and estimated flow for all conditions. In vivo studies (n = 9) were conducted in an ovine model where a reference flow probe was placed on the outflow graft and speed was adjusted from 1,800 to 4,000 revolutions per minute. During in vivo experiments, estimated pump flow (mean, minimum, and maximum) was compared with measured pump flow. The best-fit linear regression equation for the data is y = 0.96x + 0.54, r² = 0.92. In addition, waveform fidelity was high (r² > 0.96) in normal (i.e., nonsuction) cases where flow pulsatility was >2 L/min. The flow estimation algorithm demonstrated strong agreement with measured flow, both when analyzing average waveform magnitude and fidelity.

Continuous-flow ventricular assist devices (VADs) are a viable therapy for the treatment of end-stage heart failure, offering support for bridge-to-transplantation and destination therapy. As support duration for VADs continues to rise, patient management and device maintenance will play an increasingly crucial role. The HeartWare Ventricular Assist System¹ has currently been implanted in >4,000 patients worldwide. The HeartWare controller stores approximately 30 days of VAD data including pump rotational speed, power consumption, and estimated VAD flow. Routine assessment of controller log files can serve as a pump performance tool and clinical management aid, assisting the clinician to make accurate and timely diagnoses. Here, we discuss the controller’s data collection system as well as present the process for evaluation and reporting of controller log files to clinicians.

Implantable left ventricular assist devices provide circulatory support for patients at risk of death from refractory, end-stage heart failure. Rotary blood pumps have been designed for increased reliability and smaller size for use in a broader population of patients than the first-generation pulsatile devices. The design concepts and principle of operation of the HeartWare System are discussed. The HeartWare Ventricular Assist System (HVAD) is a small centrifugal flow pump with a displacement volume of 50 ml and an output capacity of 10 L/min. A unique wide-blade impeller is suspended by hybrid passive magnets and hydrodynamic forces. An integrated inflow cannula is inserted into the left ventricle and is held in position by an adjustable sewing ring; the pump is positioned in the pericardial space. The 10-mm outflow graft is anastomosed to the ascending aorta. External system components include the microprocessor-based controller, a monitor, lithium-ion battery packs, alternating current and direct current power adapters, and a battery charger. Physiologic control algorithms are incorporated for safe operation. Preclinical life cycle tests have shown the HVAD to be highly reliable. This system design offers reliability, portability, and ease of use for ambulatory patients.