Hemolytic differences among artificial cardiac valves used in a ventricular assist pump.

Ventricular assist devices (VADs) required for cardiac support may produce clinically significant hemolysis. VAD valves differ in both mechanics and hemodynamics. Therefore, we examined a ball valve, a modified tilting disc (MTD) valve, a polyurethane trileaflet valve, and a Björk-Shiley monostrut valve to determine their degrees of hemolysis. The valves were tested in a Pierce-Donachy VAD which pumped fresh bovine blood through a mock loop. Blood samples were analyzed for hematocrit and plasma hemoglobin, from which the indices of hemolysis were calculated. A one-way analysis of variance indicated significant differences between certain valves. The MTD was the most hemolytic. No significant hemolytic difference was found between the trileaflet and monostrut valves despite their different designs. The monostrut valve and the MTD valve were hemolytically very different despite their similar design. This study suggests that the valve type significantly affects the hemolysis produced by the VAD.

An annular compliance chamber for the Pennsylvania State University electric total artificial heart.

To eliminate the need for a separate parapleural compliance chamber, we are currently investigating the feasibility of an annular compliance chamber. This chamber wraps around the energy converter and fits between the blood pumps of the Pennsylvania State University electric total artificial heart. For the 100 cc total artificial heart, the compliance chamber volume is 76 ml and the tissue contacting surface area is approximately 85 cm2. The chamber is made of Dacron velour covered segmented polyether polyurethane urea. The annular compliance chamber was evaluated in vitro by comparing pump balance control performance against that obtained with an open vent. In the CVP range of 5-12 mmHg, LAP was maintained within 1 mmHg of the values obtained with a vent. Studies continue to determine the range of volumes over which the chamber is effective, differences in rates of diffusion, and performance during changes in barometric pressure.

An electrically powered total artificial heart. Over 1 year survival in the calf.

An electric motor driven orthotopic artificial heart was implanted in a 110 kg female Holstein calf as part of a series of 12 such implants intended to demonstrate the in vivo durability and compatibility of the device. The device uses pusher plates set into motion by a reversing brushless DC motor and roller screw to alternately eject two cylindrical sac type blood pumps. The pumps use Bjork-Shiley Delrindisc convexo-concave or monostrut valves. The left pump provides an 88-90 ml dynamic stroke volume. Woven Dacron grafts and polyurethane coated Dacron/Lycra cuffs are used to attach the device to the major arteries and atria, respectively. A polyurethane conduit and anchoring skin button bring motor wires percutaneously to an extracorporeal controller. The controller provides balanced cardiac output sensitive to atrial or aortic pressures, without operator intervention. The system is hermetically sealed and uses a simple compliance sac to maintain thoracic pressure between the pumps. The calf recovered uneventfully from surgery and thrived thereafter. She was killed on the 388th post-operative day because of worsening cardiac insufficiency. The previous three operative survivors in this series lived 131, 134, and 204 days. These results indicate the device's good potential for durability and body compatibility.

An electric artificial heart for clinical use.

Advances in microelectronics, high-strength magnets, and control system design now make replacement of the heart using an implantable, electrically powered pump feasible. The device described herein is a compact, dual pusher plate unit with valved polyurethane sac-type ventricles positioned at either end. The power unit consists of a small, brushless direct current motor and a motion translator. A microprocessor control system is used to regulate heart beat rate and provide left-right output balance. Bench studies lasting for as long as 1 year have been performed. Heart replacement with the electric heart has been performed in 18 calves since 1984. The longest survivor lived for more than 7 months. Among the causes of termination were component failure, thromboembolic complications, and bleeding. No major problem has been identified that precludes prolonged use of the electric heart. In the future the patient with end-stage heart disease will have an electric artificial heart as one therapeutic option.

In vitro and in vivo evaluation of a right ventricular assist device.

A simple right ventricular assist device (RVAD) has been developed. This device will be useful in situations where biventricular failure has been partially treated by placement of a left ventricular assist device, or when right ventricular failure occurs in isolation. This pneumatically actuated, R-wave synchronized, sac type pump contains no valves, and is connected by a graft to the pulmonary artery. The RVAD was tested in a circulation simulator to verify its hemodynamic efficacy and then implanted in six calves for 2-4 weeks to evaluate its biocompatibility. In vitro testing of the RVAD demonstrated that it restored normal hemodynamics in the presence of severe simulated RVF. In six animal implantations, a small amount of thrombus was found in one pump. No anticoagulants were employed. Thrombus was present in the connecting graft in three animals; in two this was clearly related to technical implant errors. No evidence of significant hemolysis was found. This simple RVAD has been found to be hemodynamically effective, is simple to use, and is well tolerated. Refinements in the interconnection graft between the pulmonary artery and the device are necessary.

Hemodynamic effects of a new right ventricular assist device.

A right ventricular assist device (VAD) based on the principle of counterpulsation has been developed at our institution. The device is a valveless, pneumatically actuated, 40 cc, sac-type pump, with a single inlet-outlet port. For right ventricular support, the "Uniport" pump is anastamosed end-to-side to the pulmonary artery. In previous experimental trials, the device has been shown to impart minimal trauma to blood components. In this study, biventricular failure was induced in eight Holstein calves by normothermic ischemia during cardiopulmonary bypass. A Pierce-Donachy left VAD (LVAD) was used for left ventricular support following the ischemic insult. Hemodynamic measurements were obtained throughout the study, and each animal served as its own control. A significant increase in post injury cardiac output (33.5 +/- 11.4%) was obtained with use of the Uniport and LVAD, as compared to use of the LVAD alone (p less than or equal to 0.005). Other hemodynamic parameters of right heart failure, including right atrial pressure (RAP), pulmonary artery pressure (PAP), and left atrial pressure (LAP) were not significantly affected. These data suggest that the Uniport right ventricular assist device significantly improves cardiac output in this model of moderate right ventricular failure. Additional studies are required, however, to optimize pump stroke volume, and to further define the performance envelope of the device.

In vivo determinants of energy consumption in electric motor driven artificial hearts.

To identify factors responsible for energy consumption, a retrospective investigation of the in-vivo performance of the 100 ml electric motor-driven left ventricular assist device (ELVAD), and the e-motor 100 ml total artificial heart, was undertaken. Multivariate regression analysis of the device parameters demonstrated that device flow, and estimated outlet pressure, were the most significant independent variables for predicting changes in motor power. Weighted least-square curvefit, using the product of these two variables, showed that changes in energy consumption can be well predicted for the ventricular assist device (r2 = 0.732). However, by applying the same model to the total artificial heart (ETAH), less favorable results were achieved (r2 = 0.422). In this model, device flow seemed to be more important in predicting energy consumption for the ETAH compared to the ELVAD. Therefore, changing the model by using flow to the third order significantly improved the fit (r2 = 0.6706) for the ETAH, and could compensate in part for the greater variability of the values and increased number of outliers in this group.

Postoperative cardiac support with a pulsatile assist pump: techniques and results.

Since 1980 this group has employed a pulsatile assist pump(s) in 23 patients. Postoperative survival was 39% (9/23). In this group, 16 patients have required left ventricular support; 9 have been weaned from the pump, and 7 have survived (44%). Three patients required right ventricular support, and two have survived (66%). Four patients required biventricular assistance, but none survived. There have been four late deaths in this group. Of the five patients alive and well, all are New York Heart Association Class I or II. Important conclusions include the following: The pulsatile pump can adequately support the pulmonary or systemic circulation for a period of days; dramatic improvement in ventricular function is frequently observed in patients with univentricular failure; adequate right ventricular function is a major determinant of survival in a patient with pulsatile left ventricular support; preoperative cardiogenic shock and/or a prolonged time on cardiopulmonary bypass (CPB) predispose the patient to diffuse intravascular coagulation and a poor result; considerable information remains to be learned regarding the selection of assist pump candidates, optimal CPB techniques, and intraoperative identification of biventricular failure, which will further improve these results.

A segmented polyurethane composite prosthetic anterior cruciate ligament in vivo study.

A segmented polyurethane prosthetic anterior cruciate ligament prototype has been developed and its in vivo integrity assessed in canine subjects. Prosthetic ligaments surgically implanted for 3, 4, 6, 8, 12, and 16 months were assessed clinically in living subjects, at time of autopsy, and microscopically postautopsy. It was found that the ligaments were adequate in strength to provide stability and last for periods up to 16 months. Notching of the ligaments was observed at two designated friction points.

The compliance problem: a major obstacle in the development of implantable blood pumps.

The compliance problem represents a major obstacle in the development of implantable blood pumps. The motor-driven pumps are enclosed in an airtight casing with gas in the motor space. The trapped gas in the motor space either increases the load on the motor during systole or impedes blood sac filling. Potential solutions to the compliance problem include the use of a conventional blood pump with a compliance chamber, a blood pump with an isolated blood sac and accumulator, or a volume-compensated blood pump. Most experimental studies designed to investigate this problem have been performed with compliance chambers. An ideal compliance chamber should accept 100 ml gas with less than a 15-mm Hg increase in pressure and should automatically compensate for changes in atmospheric pressure. To date, two designs have been shown to be effective in laboratory and animal studies: a collapsible rectangular sac design developed by our group, and a lenticular chamber developed by Nosé and associates. Compliance chambers of the former design have now been employed to provide the required compliance for motor-driven assist pumps in long-term calf studies.

Clinical effectiveness of mechanical ventricular bypass in treating postoperative heart failure.

Our group has designed an air-powered, sac-type ventricular assist pump (VAP) that has a smooth polyurethane surface and Bjork-Shiley-type valves. This VAP has undergone extensive testing in calves and has been available for clinical use during the last 5 years. When properly employed, the circulatory support permitted immediate separation of the patient from bypass. Definite hemodynamic evidence of improved ventricular function has been observed during the period of unloading of the deranged ventricle by the VAP. However, during the first 3 years of our experience, the VAP was used in 11 patients with 1 survivor. During the last 2 years, specific attention has been directed to use of right, left, or biventricular assistance as indicated, to prompt application of the VAP when required, and to use of atrial rather than ventricular cannulation for VAP inflow. Accordingly, the survival rate over this 2-year period has increased to 50% (four of eight patients). The short-term assist pump is an important adjuvant for the surgeon who operates on seriously ill cardiac patients.

Approaches to the artificial heart. Invited speaker.

Over the last two decades, the implantable artificial heart has evolved from an idea to a device capable of completely supporting the circulation for periods now exceeding 5 months. Although initial animal studies were limited by thromboembolism and device breakage, the usual causes of death in experimental animals are now infection, atrioventricular valve obstruction, elastomer bladder calcification, or inadequate cardiac output because of the relatively rapid growth of the young calves. As a result of the bulky nature of the energy converter and the substantial risk of infection with large diameter percutaneous tubes, clinical use of their air-powered artificial hearts will be limited to patients who are awaiting or being prepared for heart transplantation. Artificial hearts with implanted energy converters are being developed for permanent heart replacement. These devices require well-designed, durable mechanical components and sophisticated control systems. Although initial designs centered around thermal engines powered by a completely implantable nuclear energy source, the excessive cost and potential dangers have shifted the focus away from the nuclear system. Several electrically driven artificial hearts, based on samarium-cobalt magnet brushless direct-current motors, are now undergoing bench testing and will be ready for long-term animal studies within 2 years. This research will culminate with the availability of an "off-the-shelf" electrically powered artificial heart for use in patients with a wide range of nonrepairable forms of end-stage heart disease.

Calcification inside artificial hearts: inhibition by warfarin-sodium.

Intracavitary calcium phosphate deposits were observed in smooth, elastomeric blood pump sacs implanted in male calves for periods of 115 to 166 days. These deposits occurred predominantly on the flexing surface of the sacs. In contrast, similar pump sacs remained generally free of mineral deposits for up to 150 days in calves treated with the anticoagulant warfarin-sodium. These results implicate a vitamin K-dependent process in calcium phosphate deposition on elastomeric sacs.

Mechanical circulatory assistance for postoperative cardiogenic shock: a three year experience.

Retrospective analysis of 14 patients undergoing circulatory support for postcardiotomy cardiogenic shock during the past 3 yrs has demonstrated the ability of the profoundly depressed myocardium to recover. Four patients were totally weaned from circulatory support and 2 are long-term survivors. Our results suggest that improved survival is dependent on the absence of certain peri-operative complications. To improve future clinical results we suggest that prompt application of assist pumping is necessary to eliminate prolonged cardiopulmonary bypass times and subsequent massive bleeding; those circulatory support systems requiring systemic anticoagulation are of no value in the treatment of postcardiotomy cardiogenic shock; the use of atrial cannulation may be advantageous in certain patients to eliminate critical inflow obstruction, further prolongation of cardiopulmonary bypass, and additional myocardial damage; and that the high incidence of right ventricular failure that is refractory to medical therapy makes the ability to support both ventricles mandatory.

A two and one half year clinical experience with a mechanical left ventricular assist pump in the treatment of profound postoperative heart failure.

A sac-type paracorporeal left ventricular assist pump was implanted in 9 patients suffering from profound left ventricular failure following open heart surgery. Two patients had good recovery of left ventricular function and were weaned from assist. One survived 14 months postoperatively. Primary causes of death among the remaining patients were (1) primary right ventricular failure, (2) assist pump inlet cannula obstruction and (3) excessive bleeding. The strategies developed or proposed to deal with these problems include, respectively: (1) biventricular assist for patients with concomitant right ventricular failure; (2) cannulation of the left atrium to avoid inlet cannula obstruction by the left ventricular wall and intraventricular septum; (3) more rapid selection of left assist candidates and more rapid implantation techniques to reduce the coagulopathy associated with prolonged cardiopulmonary bypass, and an effective autotransfusion system to augment blood replacement.