Machines versus medication for biventricular heart failure: focus on the total artificial heart.

The medical/surgical management of advanced heart failure has evolved rapidly over the last few decades. With better understanding of heart failure pathophysiology, new pharmacological agents have been introduced that have resulted in improvements in survival. For those patients that fail to improve, mechanical circulatory support with left ventricular assist devices and total artificial hearts (TAHs) have served as a beneficial bridge to transplantation. The TAH has continued to play a significant role as a bridge to transplantation in patients with biventricular failure and more selected indications that could not be completely helped with left ventricular assist devices. Improved survival with the TAH has resulted in more patients benefiting from this technology. Improvements will eventually lead to a totally implantable device that will permanently replace the failing human heart.

[The results of the artificial heart]. / Les résultats du coeur artificiel.

The artificial heart is no more a dream but a reality. Over the last 40 years, many circulatory assist devices have been developed. First were the pneumatic devices, external or implantable, providing uni- or biventricular support; next were the partially implantable electromecanical devices. We went from the first generation of devices with all components (pump, energy power, control system) outside of the body to the second generation of devices with the pump and the motor implanted inside the body. Recently, the third generation of artificial hearts appeared with all components implanted inside the body allowing better mobility and quality of life. Results depend on the indication and on the kind of artificial heart implanted: partial (native heart still in place) or total (native heart removed). Essentially developped as a bridge to transplant, the artificial heart is now allowed as destination therapy.

HeartQuest ventricular assist device magnetically levitated centrifugal blood pump.

Improvements in implantable ventricular assist device (VAD) performance will be required to obtain patient outcomes that are comparable with those of heart transplantation. The HeartQuest VAD (WorldHeart, Oakland, CA, U.S.A.) is an advanced device, with full magnetic suspension of the rotor, designed to address specific clinical shortcomings in existing devices and to maximize margins of safety and performance for an implantable assist device. The device dimensions are 35 x 75 mm, with a total weight of 440 g. The system was designed using extensive computer modeling of device function; a total of two iterations of device prototypes were built before building the clinical version. Animal study results have been very promising, with over 30 calf studies completed. Plasma-free hemoglobin levels returned to preoperative levels, and other hematology results were in the normal ranges. Highlights include clean surfaces seen in a 116-day experiment with no anticoagulation after day 43. Feasibility clinical trials are planned to start in 2006.

Temporary or permanent support and replacement of cardiac function.

Cardiac assist devices are classified into the traditional engineering categories of displacement and rotary pumps. Clinical use and indications of the various pump categories are outlined and a detailed description of the currently available systems is given. The first section deals with extracorporeal as well as implantable ventricular assist devices of the displacement type and is followed by a section on current developments in the field of total artificial hearts. The latter part of the article covers the rotary pump category from cardiopulmonary bypass applications to implantable systems, including specific design aspects of radial, diagonal and axial pumps.

Automatic detection and classification of abnormalities for artificial hearts using a hierarchical self-organizing map.

A hierarchical self-organizing map (SOM) has been developed for automatic detection and classification of abnormalities for artificial hearts. The hierarchical SOM has been applied to the monitoring and analysis of an aortic pressure (AoP) signal measured from an adult goat equipped with a total artificial heart. The architecture of the network actually consists of 2 different SOMs. The first SOM clusters the AoP beat patterns in an unsupervised way. Afterward, the outputs of the first SOM combined with the original time-domain features of beat-to-beat data are fed to the second SOM for final classification. Each input vector of the second SOM is associated with a class vector. This class vector is assigned to every node in the second map as an output weight and learned according to Kohonen's learning rule. Some experimental results revealed that a certain abnormality caused by breakage of sensors could be identified and detected correctly and that the change in the state of the circulatory system could be recognized and predicted to some extent.

Implantation of the undulation pump total artificial heart in the goat.

The undulation pump total artificial heart (UPTAH) was developed by using small-size continuous-flow displacement-type blood pumps (undulation pump). To clarify and improve the problems accompanied by the implantation in the chest, 14 animal experiments were performed on goats weighing 41.3-79.2 kg. The UPTAH could be implanted in the chest of all goats and was driven with a modulation pulsatile mode. The first problem was the atrial suction effect. This problem could be prevented to some extent by developing the soft disk and by improving atrial cuffs. An automatic detection and releasing of the atrial suction effect was also tried. The next problem was acute lung edema accompanied by the postural change of the animal. Development of the automatic control of left atrial pressure could prevent this problem. Small blood leakage from a pinpoint hole in the seal membrane was the next problem. Improvement of the manufacturing procedure of the membrane prevented this. With these improvements, a 10 day survival could be obtained with this unique implantable total artificial heart.

Flow visualization analysis for evaluation of shear and recirculation in a new closed-type, monopivot centrifugal blood pump.

Flow visualization has great potential in analyzing flow patterns of centrifugal blood pumps to locate possible hemolysis and thrombus formation sites. This study focused on the said phenomena thought to correlate with areas of high shear velocity and stagnation and analyzed a new closed-type centrifugal blood pump. As a result of analyzing the flow of inlet and front gap of the impeller, flow in the front gap was approximately 30% of the external flow. Visualization in the back gap showed sufficient exchange also. Analysis in the volute area and around the washout holes revealed high shear locations and quantified the highest shear velocity. Maximum shear on the volute wall was found to be 9,000-19,000 s-1 and was located in the 0.2-mm vicinity of the wall. Based on these results, previous hemolysis tests, and small pump size, one concludes that the analyzed closed-type centrifugal pump has a relatively smooth flow suitable for a totally implantable artificial heart.

System analysis of the flow/pressure response of rotodynamic blood pumps.

Design of a rotodynamic blood pumping system to have a suitable, controllable output is a key configuration issue. This study evaluates the benefits of selecting the impeller running specific speed, motor speed-torque line, and pump operating logic to jointly combine into a suitable characteristic. In this study, a "constant" flow for a given choice of control parameter value was the selected objective. The operating condition selected for analysis was chosen to be typical of an implanted, chronic support pump. Open-loop operation, fixed torque, fixed power, and fixed power/rpm2 ratio were combined with choices of impeller diameter and speed and motor speed-torque line. It was found that setting the running specific speed at a higher value than that associated with the best efficiency point resulted in a much more controllable pump. Overall efficiency was only slightly penalized for the model impeller chosen. Power/rpm2 control followed by torque control were most effective. With these control modes, motor characteristics were not critical.

Design and development strategy for the rotary blood pump.

Development of an antitraumatic antithrombogenic and durable blood pump is a very difficult task. Based upon this author's experience of over 35 years in the development of various types of cardiac prostheses, development strategies for a rotary blood pump are described. A step-by-step development strategy is thus proposed. Initially, the development of a 2 day antitraumatic pump (Phase 1) would be made. Then, conversion of this pump to a 2 week antithrombogenic pump (Phase 2) should be attempted. After the successful development of the Phase 2 pump, the conversion of this device to a durable, implantable, and long-term blood pump (Phase 3) should be established. Based upon this development strategy, 2 rotary blood pumps, namely, the axial flow blood pump and the centrifugal blood pump, have been developed in less than 6 years with modest development costs.

Constructional and functional characteristics of recent total artificial heart models TNS Brno VII, VIII, and IX.

Twelve total artificial heart (TAH) models have been developed at the Brno Research Center. Devices VII, VIII, and IX were constructed on the principle of asymmetry. Three main objectives had to be fulfilled by this construction. First, contact of the flap inflow valve with the diaphragm during the pumping cycle had to be avoided. Second, the evacuation regimen of the blood chamber needed to be improved. Third, the danger of thrombi formation due to the lesser incidence of the dead corners had to be decreased or eliminated. The type VII heart has a roof-shaped polyurethane valve in the outflow tract whereas the type VIII heart has a flap valve. The decrease of thrombi incidence around the outflow valve was thus secured, and the driving pressure was decreased as well. In the type IX heart, the small additional flap valve is attached to the outflow valve. In one Brno VII device, Imachi's jellyfish valve has been mounted. Altogether, 62 long-term experiments with survival times of 30-314 days have been performed. To this number, 4 comparative experiments using the Rostock artificial heart were added.

Evaluating the flow characteristics of artificial pumping devices using nuclear scintigraphy.

The design and development of artificial blood pumps require qualitative and quantitative data relative to pump filling, ejection, and wall motion in order to optimize the design and maximize the pattern of blood flow through the pump. To assist in the development of an artificial heart, we utilized radionuclide scintigraphy and a high-resolution gamma camera to evaluate the flow patterns through the pump. We performed a comparative analysis of the flow patterns in a pneumatically driven ventricular assist device (Sarns/3M VAD) and the electrically driven Milwaukee Heart. These analyses disclose some significant differences between the two devices with regard to the blood sac compression patterns and ejection as well as valvular regurgitation. On the basis of these findings, nuclear scintigraphy for analyzing fluid shear stress and flow dynamics seems a useful technique for evaluating blood flow through artificial blood pumps. Because the procedure does not require a translucent casing or direct contact with the device being studied, it would be especially useful in evaluating artificial blood pumps implanted in patients with heart failure.