The intraaortic balloon pump (IABP) is the single most effective and widely used device for temporary mechanical assistance of the failing heart. Although the principles underlying IABP function are simple, various biologic factors often determine its performance in a particularly complicated way. We briefly describe the basic disciplines of counterpulsation by IABP and the induced hemodynamic changes while clarifying the biologic mechanisms that play a crucial role in the modification of IABP acute hemodynamic performance.

Basic principles of the intraaortic balloon pump and mechanisms affecting its performance.

Infectious complications during support with a ventricular assist system (VAS) can cause severe morbidity and mortality, affecting nearly one-half of all VAS recipients. Because of the lack of a uniform definition of infection, the incidence of this complication is hard to determine accurately. It is approximately 50% for patients being supported by an implantable VAS as a bridge to heart transplantation and 28% for patients supported by an external, short-term VAS. Infections can be classified according to the involvement or noninvolvement of the implanted device and according to the severity of the infection. Severe infections involving the implanted device may preclude heart transplantation for some patients, but numerous patients with milder infections have undergone successful transplantation. Numerous factors predispose VAS patients to infection. Postoperative bleeding necessitating re-operation is an important contributing factor. Endotracheal tubes, intravascular catheters, and other indwelling tubes necessary for the care of postsurgical patients are also common routes of contamination. Control of infection may be improved with new VAS designs, antibiotic impregnated drivelines, and innovative therapies such as antibiotic beads. The next generation of VASs should be inherently less susceptible to infection because of their smaller size, reduced thrombogenicity, and better flow characteristics. In addition to more effective antibiotics, improved VAS designs that incorporate transcutaneous energy transmission systems may reduce infectious complications and allow safe, long-term VAS support.

Infectious complications associated with ventricular assist systems.

Clinical temporary ventricular assist. Pathologic findings and their implications in a multi-institutional study of 41 patients.

Synthesis and antithrombogenicity of heparinized polyurethanes with intervening spacer chains of various kinds.

The development and clinical use of continuous-flow left ventricular assist devices (LVADs) stimulated our interest in developing a total heart replacement with continuous-flow rotary blood pumps. We constructed a continuous-flow total artificial heart (CFTAH) from 2 HeartMate II axial-flow LVADs and used this CFTAH to replace the native heart of a calf. The purpose of this experiment was to study the effects of total continuous flow on physiologic parameters at rest and during exercise after the animal recovered from surgery.

We monitored pulmonary and systemic pump performance, and we assessed arterial blood gases, hemodynamic and biochemical variables, and neurohormone levels during the 7 weeks of CFTAH support. At day 36 after CFTAH implantation, the calf was exercised on a treadmill at increasing speeds for 40 minutes; total oxygen consumption, pump flow, blood pressure, and respiratory rate were monitored.

Baseline hematologic levels were altered postoperatively but returned to normal by 2 weeks. We saw no signs of hemolysis or thrombosis during CFTAH support. The calf had a normal physiologic response to treadmill exercise. The animal gained weight and appeared to function normally during the study. The CFTAH operated within design specifications throughout the study.

Homeostasis, end-organ and vasomotor function, and the ability to exercise are not adversely affected by 7 weeks of totally pulseless circulation in a calf.

Continuous-Flow Total Artificial Heart Supports Long-Term Survival of a Calf

An electrohydraulic total artificial heart (EHTAH) has been developed and evaluated by long-term in vivo studies. The EHTAH is composed of blood pumps with an interatrial shunt (IAS), an energy converter, and electronics. The EHTAH with external electronics was implanted in four calves weighing from 81-90 kg. Two animals died on the 1st and 5th post operative days, the third animal survived for 32 days, and the fourth for 159 days. The IAS was free of thrombus at autopsy in all animals. The longest surviving animal increased in size from a pre operative weight of 81 kg to 134 kg on day 144. Cardiac output ranged from 9.3 to 10.5 L/min, whereas right and left atrial pressures increased with the calf's growth from 4-10 to 16-20 mmHg and from 8-14 to 18-22 mmHg, respectively. The animal favorably tolerated up to 3.4 km/hr of treadmill exercise, both hemodynamically and metabolically. The elevation of atrial pressures during treadmill exercise was significantly alleviated by employing an automatic control mode. It is concluded that the device has the potential to be a totally implantable system for permanent use.

In vivo long-term evaluation of the Utah electrohydraulic total artificial heart

Evaluation of treadmill exercise on total artificial heart recipients.

Experience with a valveless, implantable abdominal aortic counterpulsating device.

Diagnosis of mechanical failures of total artificial hearts.

In a retrospective study of 330 animals with total artificial hearts (TAH), 103 (31%) had microbially infected thrombi (MIT). The incidence of MIT approximated 75% in the animals surviving more than 100 days. The most common pathogen isolated from animals with MIT was Pseudomonas. Most thrombi appeared to have originated from valve junctions and connectors. Methods to prevent MIT should be aimed at eliminating thrombus formation by improved design and materials and controlling the route of bacterial colonization. These findings suggest that bacterial interaction with the thrombus, device-related bacterial colonization, host immunomodulation, and gut barrier function after TAH implantation need further study.

Microbially infected thrombus in animals with total artificial hearts.

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