Performance Prediction of a Percutaneous Ventricular Assist System Using Nonlinear Circuit Analysis Techniques

Abstract

A percutaneous ventricular assist device (pVAD) is an extracorporeal cardiac assist system that supports the failing ventricle in advanced stage heart failure by bypassing blood from the venous to the arterial circulation through a blood pump. The system can be implanted in a Cath lab using standard interventional techniques, and typically consists of a venous or atrial drainage cannula, the VAD (or blood pump), and an arterial perfusion cannula. Because the device allows clinicians the freedom of choosing the configuration and size of the cannulae based on the patient's body size and the size of the artery, it is extremely difficult but important to be able to predict the amount of blood flow that the device can provide before it is implanted to support the patient. In this paper, we develop a novel method that can be used to accurately predict the mean flow rate that the device can provide to the patient based on the size and configuration of the arterial cannula, the pump speed, and the patient's left atrial and mean arterial pressures. To do this, we first develop a nonlinear electric circuit model for the pVAD. This model includes a speed dependent voltage source and flow dependent resistors to simulate the pressure-flow relationship in the various cannulae in the device. We show that the flow rate through the device can be determined by solving a quadratic equation whose coefficients are scaled depending on the size and configuration of the arterial cannula. The model and prediction method were tested experimentally on a test loop supported by the TandemHeart pVAD (Cardiacassist, Inc., Pittsburgh, PA). A comparison of the predicted flow rates obtained from our method with experimental data shows that our method can predict the flow rates accurately with error indices less than 6% for all test conditions over the entire range of intended use of the device. Computer simulations of the pVAD model coupled to a cardiovascular model showed that the accuracy- of the method in estimating the mean flow rate is consistent over the normal range of operation of the device regardless of the pulsatility introduced by the cardiovascular system. This method can be used as an additional too to assist cardiologists in choosing a proper arterial cannulae configurations and sizes for pVAD patients. It can also be used as a tool to train clinical personnel to operate the device under different physiological conditions.

Inductive Transcutaneous Power Transfer Design for Cardiac Assist Devices by Use of Inhomogeneous Biocompatible Core Material

“…Due to the varying daily activities of the patient, the blood flow rate has to be adapted to the changing load conditions. This is achieved by increasing or decreasing the input power of the blood pump [1]- [4], [29]- [33].…”

“…Moreover, heart failure is among the main causes of human mortality worldwide. To support and treat an ailing heart during heart therapy, ventricular assist devices (VADs) have been developed [1], [2].…”

Applications of modeling and identification in ventricular assist device development

“…If more blood flow is needed for the patient, two arterial cannulae, of the same or of different sizes, can be arranged in a parallel configuration with the device through a Y-adaptor. This device can be inserted in a cathlab setting using standard interventional techniques [2]. When using the pump as an implantable VAD (AB-180 CSS), the pump receives blood from the left atrium and returns it to the ascending aorta [5].…”

“…The flow predictions obtained from solving the quadratic equation exhibited a very strong correlation with the flow rates measured experimentally. In the dual arterial cannulae configuration where a ratio parameter α is introduced into the flow prediction equation, it was shown that the four different ways of selecting this parameter did not produce any significant ifferences in terms of the accuracy of the method [2]. …”

“…More recently, two other roles for the LVAD have evolved. The first is a bridge to recovery where the patient eventually is able to have the device removed and return to a normal life style with his or her own natural heart, and the second is destination therapy, where the LVAD will remain implanted for the duration of the patient's life [2].…”