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Ann Thorac Surg 2005;79:S2228-S2231
© 2005 The Society of Thoracic Surgeons
Michael E. DeBakey Department of Surgery, The DeBakey Heart Center, Baylor College of Medicine, Houston, Texas
Accepted for publication March 7, 2005.
* Address reprint requests to Dr DeBakey, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 (E-mail: mdebakey{at}bcm.tmc.edu).
Presented at the 4th Annual Lillehei Heart Institute Symposium Celebrating the 50th Anniversary of Open-Heart Surgery by Cross Circulation, Minneapolis, MN, Oct 19–20, 2004.
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METHODS: A number of methods of mechanical devices to assist the failing heart are briefly assessed. Personal experimental and clinical studies of devices developed over several decades are presented.
RESULTS: Findings and data of devices used in assisting the failing heart, including those developed by the author, are analyzed.
CONCLUSIONS: On the basis of this review, the left ventricular assist device is believed to be the most effective. There is also reason to believe that the axial flow system has considerable advantages. This form of therapy has potentially great value for permanent use in some patients with intractable heart failure.
A little more than a half century ago, indeed on May 6, 1953, Dr John H. Gibbon, Jr, performed the first successful clinical surgical procedure with the use of the heart-lung machine, which he had developed in research laboratories during more than two decades. The procedure consisted in the suture closure of an atrial septal defect in an 18-year-old woman by open direct vision, while the heart-lung machine provided the function of the heart and lungs for 26 minutes [1].
This was a seminal event in medical history, for it demonstrated indubitably that the function of the heart and lungs could be replaced temporarily by mechanical means. This accomplishment "had a profound impact on the medical community, particularly on researchers who were interested in the cardiovascular field" [2]. It was well expressed in the citation of the Lasker Award Gibbon received for this scientific achievement in 1968: "The vast impact of Dr Gibbon’s discovery on medical sciences exemplifies the way in which new knowledge gained from a single research project can trigger a chain reaction of inquiries leading to additional knowledge and ultimately to the prevention and cure of human disease" [2].
In the medical zeitgeist of that period, this event was eagerly awaited. For some time before, medical investigators both in this country and abroad were actively engaged in studies concerned with the failing heart and mechanisms directed toward its correction. For example, on April 5, 1951, Clarence Dennis and his associates at the University of Minnesota reported the use of a pump-oxygenator apparatus to correct a huge interatrial defect under direct vision in a 6-year-old girl with dyspnea and some cyanosis on exertion. Although the patient did not survive the operation, they expressed encouragement "with the performance" of the apparatus [3]. The following year, on April 3, 1952, Helmsworth and associates [4] used a pump-oxygenator in a 45-year-old man with chronic cor pulmonale for 75 minutes, during which "striking relief of cyanosis, dyspnea, and orthopnea occurred," but he was subsequently discharged from the hospital in the "same state of cardiorespiratory dysfunction as prior to admission." He returned to the hospital 10 days later and died on the fourth hospital day. To permit visual control to correct congenital pulmonic stenosis, Varco, in 1951, temporarily occluded the cavae to obtain a dry field for 2 to 3 minutes [5].
The pioneering use of hypothermia and its potential role in cardiac surgery was being studied by Bigelow and his associates in the 1940s [6]. As a consequence of these studies, successful clinical use of hypothermia was reported by Dogliotti and Ciocotti [7] for relief of superior vena caval obstruction, and by Lewis and Taufic [8] and Swan and associates [9] for successful direct vision closure of atrial septal defect. Considerable impetus was given to direct vision intracardiac surgery in 1954, by the cross-circulation use of blood-compatible human donors for temporary support of the circulation in patients by Lillehei and his associates [10]. Moreover, research in the development of a heart-lung machine was underway in a number of experimental laboratories in departments of surgery here and abroad. Accordingly, the announcement of the first successful clinical application by Dr Gibbon was not entirely unexpected, as evidenced by its rapid clinical adoption and the numerous advances made in its mechanism, particularly in the oxygenator component of the machine.
Of particular significance were a number of consequential and instructive observations made during the early clinical use of the heart-lung machine. Among the most important was that after completion of the operation with use of the heart-lung machine, it was sometimes impossible to wean the patient off the heart-lung machine because of failure of the heart to resume adequate function. Sometimes, however, more prolonged support with the heart-lung machine allowed the patient to be weaned off the machine during a period of 1 to 2 hours [11]. The fact that not all such patients survived led to the obvious search for other methods of more prolonged support of the failing heart, for days or weeks, to give the heart more time to recover. This search culminated in the concept of assisted circulation and the ventricular assist device (VAD). The indications for the clinical use of this concept in reversible heart failure after surgical cardiotomy were expanded to failure after myocardial infarction, pulmonary embolism, and other causes [12].
In general, four methods of assisted circulation were investigated [13]: (1) total or partial cardiopulmonary bypass [14–16], (2) venoarterial shunting [17–19], (3) counterpulsation [20–24], and (4) left atrial-femoral bypass [11, 25, 26]. Early on, Salisbury and colleagues [26] expressed preference for left heart bypass in all types of heart failure except cor pulmonale. Extensive experimental and clinical investigations have since confirmed this preference.
Among the early workers to support this concept and to devise a procedure for its clinical application was Clarence Dennis and his associates [25], who used a special cannula that could be passed from the right external jugular vein into the right atrium and, with fluoroscopic control, through the fossa ovalis into the left atrium. The normal oxygenated blood from the left atrium was allowed to flow by gravity into a reservoir and then returned by means of a roller pump into the femoral artery. After demonstrating its feasibility in animals in the experimental laboratory, they reported its use in 12 patients. Immediate results were good-to-improved in 3 of the patients pumped 4 to 17 hours, but none completely recovered.
Like other investigators in this field, we established our own experimental laboratory with a machine shop in the early 1950s (headed by an excellent machinist), supported by funds from our Department of Surgery, special grants from grateful patients, and the local American Heart Association [27]. The National Institutes of Health funding for this purpose was instituted later, after my testimony before Senator Hill’s committee in 1963, after which Congress appropriated $10 million for this purpose [28].
Our research program was directed toward the development of VADs and a total artificial heart. The first VAD developed in our laboratory consisted of a double-lumen silicon elastomer tube reinforced with polyethylene terephthalate fiber (Dacron), with a rigid outer and an inner compressible silicon elastomer tube, which is the blood chamber, that is collapsed by pressurized air entering the housing. Ball valves at either end provide unidirectional flow [29]. After experimental studies in 50 animals demonstrated its efficacy, it was first applied clinically in 1963 in a patient who had cardiac arrest on the day after aortic valve replacement. After being resuscitated by open chest technique, he experienced severe pulmonary edema unresponsive to standard therapy. On the basis that the source of the pulmonary edema was left ventricular failure, we implanted the VAD by attachment of the inlet tube to the left atrium and the outlet tube to the descending thoracic aorta. With pump flows of 1,800 to 2,500 mL/min, the pulmonary edema resolved completely during the next few days and remained so until this patient’s death on the fourth postoperative day, presumably owing to brain damage during the cardiac arrest [29].
Further experience in our laboratory led to the realization that this problem required a coordinated multidisciplinary approach. We established a collaborative venture with the Engineering Department of Rice University and received substantial support from the National Institutes of Health. Several different types of pumping mechanisms were developed by this collaborative effort [30]. Among the earliest was a sac-type device consisting of two layers of Dacron-reinforced silicon elastomer. An externally placed pump pulsed air between the two walls, causing the inner wall to collapse and expel the blood from its cavity; ball valves placed at each end gave the blood unidirectional flow. In animals, this device was successfully applied as a left ventricular bypass by attachment of the inlet tube to the left atrium and the outlet tube to the ascending or descending thoracic aorta, and as a right ventricular bypass by attachment of the inlet tube to the right atrium and the outlet tube to the pulmonary artery.
Another approach in experimental animals was the use of similar types of pumps as intraventricular pumping devices [31]. Still another experimental device, which simulated cardiac massage, consisted of a cup-like structure [31] with a diaphragm that could be placed around the heart. Alternating positive and negative pressure provided systolic and diastolic cardiac assistance.
The most satisfactory left ventricular bypass pump that emerged from the collaborative effort with the Rice University Department of Engineering was a gas-energized synchronized pump of hemispherical design made of Dacron-reinforced silicon elastomer, with a molded diaphragm separating the gas chamber from the blood chamber [11]. Pressurized carbon dioxide pulsed into the gas chamber collapses the central lumen or blood chamber and thereby empties it. The pump is extracorporeal, with the inlet tube, inserted through a right intercostal incision, attached to the left atrium and the outlet tube attached to the right axillary artery by end-to-side anastomosis. The lining of the interior surfaces of both the pumping chamber and the connecting tubes is made of Dacron velour to provide a more satisfactory blood interface and thereby to reduce the need for systemic anticoagulation during use of the pump. In this connection, the following statement made in one of my articles more than 30 years ago remains true today: "It has long been recognized that one of the most critical problems to be solved in the development of an artificial heart is the blood interface or contact surface of the blood" [32].
Our first clinical application of this pump was on August 8, 1966, in a white woman with heart failure caused by severe aortic insufficiency and mitral stenosis [11]. After replacement of both valves, it was impossible to wean the patient off the heart-lung machine despite prolonged support, and the bypass pump was then attached to the patient. With a pump flow of 1,200 mL/min, it was possible to wean the patient off the heart-lung machine. On the 10th postoperative day, it became possible to discontinue the use of the bypass pump as the heart maintained normal function. The patient recovered completely and returned home to resume normal activities. Unfortunately, she was killed in an automobile accident 6 years after operation.
In the meantime, we continued our laboratory research work on the total artificial heart, and in 1972 we reviewed and analyzed our experience with our orthotopic cardiac replacement in 29 calves, expressing our discouraging results in the conclusion of the article thus: "... as one reviews our 2 years’ observation of the fate of animals following implementation of an artificial heart device, it is, of course, disheartening that previously healthy animals are rendered moribund by one or another variation of a pneumatically powered orthotopic cardiac prosthesis, an experience shared by all investigators to date ..." [33].
After the early establishment of the concept of ventricular assistance in the 1950s and 1960s, considerable progress has been made in the development of circulatory assist devices. This research received great impetus from the successful application of VADs as a bridge-to-transplantation after the resurgence of heart transplants in the 1980s, owing to the introduction of cyclosporine and improved methods for control of rejection. Accordingly, VADs were used to support a failing heart in a patient awaiting a donor for heart transplantation who might otherwise not survive until a donor became available [34–44]. This experience has also demonstrated that such ventricular assistance can restore virtually normal resting hemodynamics and exercise tolerance and can normalize hepatic, renal, and neurohumoral function. Indeed, in some patients with cardiomyopathy, pump support for as long as 2 years has restored normal cardiac function, permitted removal of the assist device, and allowed the patient’s return to normal activity [45, 46].
The number and types of assist devices have also varied considerably in recent decades. These include pulsatile and nonpulsatile systems. Among the former, the more commonly used are Heartmate, Novacor, Thoratec, Abiomed, and Cardiowest. More recently, interest has intensified in some nonpulsatile devices such as the centrifugal pumps exemplified by the BioMedicus, Sarns, and Nikkiso pumps and the axial flow types of pump as described later.
The disheartening experimental results in our laboratory research on the total orthotopic artificial heart and the encouraging experimental and early clinical experiences with left VADs, reinforced by the impressive results with its use as a bridge-to-life transplant, focused our interest and limited resources on this area of endeavor.
Fortuitously in this connection, we performed a heart transplantation on a National Aeronautics and Space Administration engineer working at the Johnson Space Center. His interest in our laboratory work on artificial heart devices led to a collaborative effort with a small group of NASA engineers [47]. The design strategy of this combined effort, to develop a miniature blood pump that would meet the essential requirements for supplementing cardiac output, led to development of an axial flow pump that is 86 mm long and 25 mm wide, and weighs 95 g. The only moving part within the flow tube is an inducer-impeller. Rare earth magnets, which are embedded in the blades of the impeller, act as the rotor of the brushless motor, causing it to spin in a magnetic field. The pump can produce flows of 5 to 6 L/min against a 100 mm Hg pressure at about 10,000 rpm and requires less than 10 W of power. It is of historic interest that the axial flow concept was originated by Archimedes in the 3rd century BC, when he developed the "screw pump" for raising water for purposes of irrigation [48].
The performance characteristics of the MicroMed DeBakey VAD, in terms of hydraulic pressure and hemolysis, have proved satisfactory in extensive in vitro and in vivo experiments. Implantation of the pump in calves, with the inlet cannula inserted into the left ventricle and the outlet cannula, consisting of albumin-coated Dacron graft, attached to the descending thoracic aorta by end-to-side anastomosis, provided excellent results. Clinical trials were thus begun in Europe in 1998, and the satisfactory results earned the CE Mark, permitting regular clinical use in Europe. At the time of this writing, the clinical trials in the United States are still under US Food and Drug Administration guidelines as bridge-to-transplantation, but we hope it will soon be approved. Clinical experience with this left VAD in more than 200 patients has been satisfactory, with successful transplantation after periods ranging from a few months to well over 1 year, and with patients on the pump physically active [49].
Clinical experience with this pump has demonstrated its efficacy in unloading the ventricle and supplementing the circulation of the failed heart to provide adequate blood flow to permit resumption of reasonably normal physical activity. With its miniaturization and its facile surgical implantation, it can be used in a wide segment of the patient population, including women and children. Moreover, its potential clinical application has widespread indications, both for temporary use for patients with transient but recoverable cardiac failure resulting from myocardial infarction or cardiac operation, for patients awaiting heart transplantation, and for permanent implantation in patients with chronic irreversible heart failure [50].
In light of the recent Rematch Study [51] demonstrating conclusively the benefit of a left VAD over medical treatment for patients with irreversible heart failure, this type of pump may have potentially greater clinical significance in a much larger group of patients with chronic irreversible heart failure. The pump’s capability of supplementing an additional 3,000 to 5,000 ml/min to patients with significantly decreased cardiac output could permit them to resume reasonably normal lives. More than 5 million patients suffer from chronic heart failure, and the incidence is steadily rising in this country, with more than 500,000 new cases annually. Even if only a small proportion of these patients were candidates for this form of therapy, this pump would have great potential value.
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This article has been cited by other articles:
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  S. Aggarwal, F. Cheema, M. C. Oz, and Y. Naka Long-Term Mechanical Circulatory Support Card. Surg. Adult, January 1, 2008; 3(2008): 1609 - 1628. [Full Text]
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 M. Markl, C. Benk, D. Klausmann, A. F. Stalder, A. Frydrychowicz, J. Hennig, and F. Beyersdorf Three-dimensional magnetic resonance flow analysis in a ventricular assist device. J. Thorac. Cardiovasc. Surg., December 1, 2007; 134(6): 1471 - 1476. [Abstract] [Full Text] [PDF]
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