Total artificial heart: from bridge to transplantation to permanent use.

BACKGROUND: Pneumatic artificial hearts have played an important role in supporting the circulation in patients before cardiac transplantation. Pneumatic hearts have also been used for permanent cardiac replacement, but most agree they have serious limitations. METHODS: Several groups are now developing electric artificial hearts in which electrical energy crosses the skin using a wireless technique. The electrical energy powers a small direct-current motor, which actuates the blood pump. RESULTS: Important progress in these devices has resulted in animal survival with electric hearts of more than 1 year. CONCLUSIONS: Extensive bench testing and animal testing will be performed before the initial clinical use of these devices will be initiated. One of the early scientific achievements of the 21st century will be the initial use of the electric artificial heart in humans.

Left ventricular mechanoenergetics during asynchronous left atrial-to-aortic bypass. Effects of pumping rate on cardiac workload and myocardial oxygen consumption.

The purpose of this study was to analyze left ventricular energetics during asynchronous, pulsatile left atrial to aortic bypass in the failing heart with the use of the pressure-volume relationship. In 12 anesthetized Holstein calves (body weight 94 +/- 7 kg), 10 microns microspheres (3.3 x 10(7) +/- 1.1 x 10(7)/100 gm left ventricular weight) were injected into the left main coronary artery to induce heart failure. Baseline left ventricular end-systolic elastance significantly decreased from 7.9 +/- 0.7 to 5.5 +/- 0.4 mm Hg/ml 100 gm left ventricular weight. Left ventricular pressure was measured with a micromanometer, and ultrasonic dimension transducers measured left ventricular orthogonal diameters. Ellipsoidal geometry was used to calculate simultaneous left ventricular volume. End-systolic elastance, pressure-volume area, external work, potential energy, and myocardial oxygen consumption were analyzed during steady-state contractions. After pre-pulsatile left atrial to aortic bypass measurements were taken, the measurements were repeated during asynchronous pulsatile left atrial to aortic bypass at the maximal pumping rate (69 +/- 13 beats/min) termed 100%, and then 80%, 60%, and 40% of the maximal pumping rate in the full to empty mode. With increases in pumping rate, pressure-volume area and external work proportionally decreased, whereas potential energy remained unchanged except for 100% of maximal pumping rate. Pressure-volume area correlated linearly with myocardial oxygen consumption during asynchronous pulsatile left atrial to aortic bypass (r = 0.971). As a result, pumping rate correlated linearly with conservation of myocardial oxygen consumption (r = 0.998). In conclusion, decreased pressure-volume area accounts for the reduction in myocardial oxygen consumption during asynchronous pulsatile left atrial to aortic bypass. Conservation of myocardial oxygen consumption is mainly attributed to the reduction of external work.

Long-term left ventricular assist device use before transplantation.

Between September 1992 and April 1995, 19 patients at the authors' institution received pneumatic, pulsatile left ventricular assist devices (LVADs) for bridging to cardiac transplantation. The mean (+/- SD) age of the patients was 51 +/- 14 years (range, 19-64 years). Nine (47%) patients had end-stage idiopathic cardiomyopathy, five (26%) had ischemic cardiomyopathy, and five (26%) other recipients were in cardiogenic shock caused by acute myocardial infarction (AMI). Fifteen (79%) patients were supported with an intraaortic balloon pump or centrifugal LVAD at the time of LVAD insertion (duration, 5.5 +/- 4.1 days). Aprotinin was given to limit bleeding; heparin, followed by warfarin sodium, was used for anticoagulation. A vigorous exercise and nutrition protocol was followed. Cardiac index averaged 2.94 +/- 0.87 L/min/m2 immediately after the implantation procedure. No patient required placement of a right VAD. Average duration of LVAD support was 45 +/- 39 days (range, 3-153 days). Major complications included bleeding requiring reoperation (three patients); cerebrovascular accident (three patients); and severe dysrhythmias requiring direct current cardioversion (four patients). Fourteen (74%) patients underwent transplantation, with one patient still being mechanically supported. All of the patients receiving transplants were discharged from the hospital. Of the individuals who died while supported with the LVAD, 75% were patients with AMI. Timely application of LVADs as part of the interdisciplinary management of end-stage heart disease has generated excellent results for transplant candidates. Right ventricular dysfunction has not necessitated right VAD placement in the authors' experience. Patients with AMI have a higher risk of death while being supported with the device than do more chronically ill recipients.

Linear end-systolic pressure-volume relationship during pulsatile left ventricular bypass represents native heart function.

This study assessed whether the end-systolic pressure-volume relationship obtained without any interventions during pulsatile left ventricular bypass adequately represents native heart function. In 11 anesthetized Holstein calves, left ventricular pressure was measured with a micromanometer while left ventricular volume was simultaneously calculated from orthogonal left ventricular diameters measured with ultrasonic dimension transducers. End-systolic pressure and volume data were subjected to linear regression analysis to achieve an end-systolic pressure-volume relationship. Data from both caval occlusions and aortic occlusion were used for the control end-systolic pressure-volume relationship (median r = 0.941, slope = 7.4 +/- 0.8 mm Hg per milliliter per 100 gm left ventricular weight; mean +/- standard error of the mean). During left atrial-aortic bypass with a Pierce-Donachy pneumatic assist pump in the asynchronous mode, the end-systolic pressure-volume relationships were obtained without interventions to change ventricular loading conditions. During maximal ventricular unloading during full to empty pumping, termed 100%, the resulting narrow range of pressure and volume data did not yield highly linear end-systolic pressure-volume relationships (median r = 0.669, slope = 4.9 +/- 0.9 mm Hg per milliliter per 100 gm left ventricular weight). However, at reduced rates off pumping, the end-systolic pressure-volume relationships were considerably linear (80%, median r = 0.819; 60%, median r = 0.868; 40%, median r = 0.899). Slopes did not significantly differ from control values (80%, 6.9 +/- 1.1; 60%, 8.2 +/- 1.1; 40%, 7.8 +/- 1.1). The end-systolic pressure-volume relationship obtained without exogenous load changes during asynchronous, pulsatile left ventricular bypass represents native left ventricular systolic function.

Left ventricular mechanics during synchronous left atrial-aortic bypass.

The purpose of this study was to analyze left ventricular mechanics during asynchronous, pulsatile left atrial-aortic bypass before and after microsphere injection with the pressure-volume relationship. In 14 anesthetized Holstein calves, left ventricular pressure was measured with a micromanometer and ultrasonic dimension transducers measured left ventricular orthogonal diameters. Ellipsoidal geometry was used to calculate simultaneous left ventricular volume. Contractility index, pressure-volume area, external work, and potential energy were calculated during steady-state contractions. These measurements were repeated during pulsatile left atrial-aortic bypass. To induce heart failure, we injected microspheres into the left main coronary artery, and the protocol for baseline and pulsatile left atrial-aortic bypass was repeated. Despite the significant differences in the baseline contractility index (7.4 +/- 0.7 mm Hg/ml versus 4.7 +/- 0.5 mm Hg/ml), contractility index remained the same during pulsatile left atrial-aortic bypass in control and heart failure modes, respectively. Pulsatile left atrial-aortic bypass significantly decreased end-diastolic volume (22% and 17%), pressure-volume area (58% and 48%) and external work (74% and 69%, all p < 0.05) during control and heart failure measurements, respectively. However, it did not change end-systolic volume or potential energy. In conclusion, asynchronous pulsatile left atrial-aortic bypass did not affect left ventricular contractile state in either the normal or failing heart. Although decreased pressure-volume area accounts for the reduction in myocardial oxygen consumption, unchanged potential energy suggested a limited unloading of the ventricle.

In vivo testing of a completely implanted total artificial heart system.

The authors performed 14 implants of a completely implanted total artificial heart (TAH) system in calves. The system consisted of a dual pusher plate rollerscrew energy converter, two sac type blood pumps, an implanted electronic control and battery package, and a transcutaneous energy transmission system. Ten of the implants included a percutaneous lead for monitoring of the implant; the remainder made use of wireless two way telemetry between the implant and the outside. Three animals survived the perioperative period. These calves survived for 98 to 118 days, and one was still alive at 150 days. Causes for termination of the 98 and 118 day cases were abdominal pocket sepsis originating at a monitoring line, and systemic sepsis acquired perioperatively. Death or termination in the shorter cases was mainly due to respiratory complications or bleeding. The TAH system proved capable of providing adequate cardiac outputs at modest atrial pressures. Wireless monitoring and wireless intervention for weaning from cardiopulmonary bypass were readily achieved. All organ systems functioned normally in the presence of the device. Once recovery from implantation in these very young animals was achieved, the system proved its ability to reliably support these animals until body mass exceeded its cardiac output capabilities.

A completely implanted left ventricular assist device. Chronic in vivo testing.

A completely implantable left ventricular assist device (LVAD) designed for permanent circulatory support has recently been tested in animals without the use of percutaneous leads, using transcutaneous energy transmission and wireless telemetry. The LVAD consists of a brushless DC motor and rollerscrew energy converter, a pusher plate actuated blood pump with a seamless segmented polyurethane blood sac, Bjork-Shiley Delrin disk monostrut valves, an implanted compliance chamber, an implanted electronic controller and battery, and a transcutaneous energy transmission system. The blood pump/energy converter assembly weighs 565 g and displaces 295 cc. The dynamic stroke volume is 60 ml, and the maximum output is 9 L/min. Pump output is automatically controlled to maintain full stroke volume as preload varies. Hall effect sensors for detecting rotary position of the motor are the only sensors used. Six bovine implants were performed, with durations of 84, 208, 244, 130, 70 (ongoing), and 15 (ongoing) days. Four animals used two-way telemetry, whereas the remaining two used one-way (outgoing) telemetry. These first chronic in vivo tests with the Penn State completely implanted LVAD system have demonstrated that it is a feasible solution to long-term ventricular support.