An intracorporeal (abdominal) left ventricular assist device. Initial clinical trials

Mechanical Support After Cardiac Surgery

Mechanical circulatory support for low cardiac output after cariac surgery was first attempted in 1962. Since then, many ventricular assist devices have been developed and employed. The following is a discussion of the history, demographics, inications, and devices used for mechanical circulatory suport in this setting. lntra-aortic balloon pulsation, pulsatile verus non-pulsatile flow, volume bypass, roller and centrifugal pumps, extracorporeal membrane oxygenation, and imlantable devices are reviewed. Early postoperative care, reovery and weaning from mechanical circulatory support, and the special issues that relate to biventricular failure and control of right-sided ventricular function, as well as anticoagulation, and sepsis are addressed.

Simulation study of the Hemopump as a cardiac assist device

A dynamic model was developed for a Hemopump that withdraws blood from the left ventricle and discharges it to the aorta through a miniature axial-flow pump. Incorporation of the Hemopump model in a previously established model for the canine circulatory system enabled the effects of the Hemopump on various haemodynamic variables of the circulatory system to be studied, and the benefit of the Hemopump to the failing heart was investigated. In addition, the influence of the physiological status of the right ventricle on the Hemopump performances was examined, and the synchronous and non-synchronous operations of the Hemopump were compared. Results verified that the Hemopump assists the failing heart by increasing the oxygen supply, while reducing the oxygen consumption of the heart through a reduction in the workload of the left ventricle. These beneficial effects were enhanced when the pump's rotation speed was increased. When pump speed was increased from 17,000 to 23,000 revolutions min-1, the oxygen supply increased 101%, and the oxygen consumption decreased 60%. However, when the pump rotation speed was too high, the inflow to the pump could be impaired and the pump performance could be negatively affected. Predications from the model were in good agreement with the results previously obtained in animal experiments and in vitro measurements.

Mechanical cardiac assistance: historical perspectives

Cardiac transplantation remains the therapeutic option of choice for treating patients with chronic, progressive, end-stage heart failure. However, over the past 40 years, a number of mechanical assist systems have been developed with the goal of treating and rehabilitating patients with severe circulatory compromise. Today, a wide array of devices is available to provide increasing levels of circulatory support. When used as bridges to heart transplantation, long-term circulatory support systems are a reliable means of keeping heart-failure patients alive as they await suitable donor hearts. Initially, transplant candidates who were receiving this type of support were unable to leave the hospital; today, however, because of advances in mechanical support technology and the portability of the current systems, these patients may return to their homes and even to their jobs while awaiting transplantation. Although heart transplantation may now be considered a routine procedure, the demand for donor hearts will always outweigh the supply, creating a definite need for long-term mechanical circulatory support. Already, clinical trials are underway to test the effectiveness of left ventricular assist devices as long-term support. As smaller, more effective cardiac assist devices become available, they should benefit even more the number of patients who may need permanent circulatory support. The fact that myocardial function can improve enough with chronic ventricular unloading to allow removal of the device may further broaden the use of this technology.

First human use of the Hemopump, a catheter-mounted ventricular assist device

The Hemopump, a catheter-mounted, temporary ventricular assist device, consists of an external electromechanical drive console and a disposable, intraarterial axial-flow pump (21F). Power is transmitted percutaneously to the pump by a flexible drive shaft within the catheter. The device is positioned in the left ventricle by way of the femoral artery approach or through the ascending aorta. Blood is drawn from the left ventricle through the transvalvular inlet cannula and pumped into the aorta. As of December 1988, the Hemopump had successfully supported the circulation of 7 patients (5 men, 2 women) ranging in age from 44 to 72 years (mean age, 59 years) and suffering from cardiogenic shock (cardiac index less than 2.0 L/min/m2). Indications for use included failure to be weaned from cardiopulmonary bypass in 4 patients, acute myocardial infarction in 1, severe cardiac allograft rejection in 1, and donor heart failure in 1. Duration of support ranged from 26 to 113 hours (mean, 66 hours). Although 5 patients demonstrated transient hemolysis, none experienced infection, thrombosis, or vascular injury. Hemodynamic variables improved in all patients during support by the device. As of December 1988, 5 of the 7 patients were alive more than 30 days after support had been discontinued, and 3 of these patients were discharged from the hospital. On the basis of our initial clinical results, the Hemopump, which does not require a major surgical procedure for insertion, provides effective, temporary circulatory support in patients with potentially reversible cardiac failure.

Sequential radionuclide imaging during paracorporeal left ventricular support

A paracorporeal left ventricular to ascending aorta assist device (LVAD) was utilized in four patients with refractory cardiogenic shock following cardiac surgery. Hemodynamic stabilization was achieved in all four patients, two of whom were subsequently discharged from the hospital and continue to do well one year later. A technique is described for obtaining radionuclide ejection fractions (EFs) during temporary LVAD interruption. The EFs appeared to be predictive of eventual unassisted ventricular function and possibly of patient survival.

A prosthetic myocardium for repair of localized defects of the left ventricle: Concept and hemodynamic feasibility

As an approach to the treatment of patients with large but circumscribed akinetic or dyskinetic regions in the left ventricular myocardium as sequelae of acute myocardial infarction, excision of the defect and implantation of a mechanical functional equivalent of myocardium is suggested. Experimental investigation of this technique is described.

Hemodynamic data from a series of dog experiments indicate that activation of the prosthetic myocardium after excision of the left ventricle is followed by improvement in various hemodynamic parametres of interest Although substantial experimental work must be completed and difficult bioengineering problems solved, preliminary results have encouraged us to continue our investigations of the prosthetic myocardium.

An imposing array of treatment methods is now available to the clinician who must deal with the sequelae of acute myocardial infarction. Selecting from pharmacologic, electrophysiologic, and surgical approaches the physician can in many instances design a treatment plan precisely tailored to the clinical problem.

Large left ventricular aneurysms and their functional equivalents of ventricular dyskinesis or hypokinesis continue, however, to represent a class of problems in which established techniques have been less then satisfactory. Surgical excision with closure of the defect is regarded as effective for small aneurysms, but such procedures may so compromise cardiac output in patients with large ones as to be unacceptable. Unfortunately, it is just the latter group in which medical palliation is least likely to be effective in managing congestive failure, angina, and other pathophysiologic manifestations.

A relatively unsual approach derived from in-series techniques of mechanical assistance to the failing circulation (1) offers the theoretical possibility of a treatment tailored to the problem of a large ventricular aneurysm. Experimental investigation of this technique in the Surgical Research Laboratory at the Sinai Hospital of Detroit has progressed to the point that a report of our experiences to date may be of interest.

Partial artificial heart (ALVAD) use with subsequent cardiac and renal allografting in a patient with stone heart syndrome

The abdominal left ventricular assist device (ALVAD) is an order of magnitude more effective than conventional intra-aortic balloon pumping (IABP) in unloading and providing circulatory support to the failing left ventricle. This is a report of a unique case which demonstrates that in the absence of pulmonary vascular obstruction or constriction, the ALVAD can substitute for both left and right heart function. A 21-year-old patient with a congenital bicuspid aortic valve developed acute valvular endocarditis which rapidly progressed to congestive heart failure. An operation was undertaken, the mitral and aortic valves were excised and replaced by porcine heterografts, and a fistula from the right sinus of Valsalva to the right ventricle was closed. When coronary circulation was restored, irreversible ischemic contracture of the left ventricle, or "stone heart" syndrome, developed and emergency ALVAD or partial artificial heart implantation was effected. This device functioned as a total artificial heart for nearly six days, while a donor heart was sought. The patient then underwent removal of the ALVAD and cardiac and renal allografting. The transplanted heart functioned well, but the patient expired fifteen days later from gram-negative sepsis.

Clinical application of the ellipsoid left heart assist device

The ellipsoid left heart assist device (E-LVAD) was implanted in eight patients suffering from intraoperative heart failure. It was not possible to remove these patients from extracorporeal circulation following an intracardiac procedure; therefore, implantation of the E-LVAD was performed during extracorporeal circulation. The inflow connector was pushed forward from a purse-string suture on the right superior pulmonary vein, across the mitral valve and into the left ventricle. The outflow connector was joined to the ascending aorta. In two patients, the artificial heart chamber was removed after complete recovery of the circulation; these patients, however, later died. In six other patients, untreatable right heart failure developed and these patients died with the pump in place. It is concluded, therefore, that the right heart must also be mechanically supported during postoperative heart failure.

Intra-aortic balloon pumping: theory and practice. Experience with 325 patients

Intra-aortic balloon pumping to support the failing circulation is now an accepted therapeutic modality. The device is simple. Insertion can be accomplished rapidly and efficiently in emergency rooms, coronary care units, cardiac catheterization suites and operating rooms, preoperatively, intraoperatively and postoperatively. The hemodynamic effects are immediate and predictable, and the accruing clinical results show increasing survival and hospital discharge rates. In these institutions, mechanical support of the circulation by this and more advanced methods has been formalized within the responsibility of a Circulatory Support Service. The purpose of this report is to summarize some observations and analyses which have been made during care of 325 consecutive postcardiotomy and/or postinfarction cardiogenic shock patients. Historical, theoretical, basic, and applied aspects and current results are included. Foremost are the straightforward concepts of considering the heart as a pump, the failing heart as a failing pump and intra-aortic balloon pumping as a temporary intravascular, auxiliary pump, capable of stabilizing or reversing that failure if utilized early in its evolution.

Total support of the circulation of a patient with post-cardiotomy stone-heart syndrome by a partial artificial heart (ALVAD) for 5 days followed by heart and kidney transplantation

A patient with acute bacterial endocarditis in whom ischaemic contracture of the left ventricle (stone-heart syndrome) developed during aortic and mitral valve replacement had an emergency implantation of an intracorporeal partial artificial heart (an abdominal left-ventricular assist device of ALVAD). This device functioned as a total artificial heart for nearly 6 days, while a donor heart for transplantation was sought. The ALVAD was then removed, and the patient received allografts of a heart and a kidney. The transplanted heart functioned well, but the patient died 15 days later from gram-negative sepsis. There was no evidence of cardiac or renal allograft rejection.

Molecular, microscopic, microstructural and mechanical methods of analyzing pseudoneointimal linings within partial artificial hearts in man and the calf

Ex vivo molecular, microscopic (cellular), microstructural and mechanical methods have been utilized to evaluate biologic, blood-interfacing linings (pseudoneointimal) formed on textured, fibril-flocked pumping surfaces within abdominal left ventricular assist devices (ALVADs) on partial artificial hearts. Thus far, seventeen human and twenty bovine pseudoneointimal linings (1--28 day pumping durations) have been evaluated by these methods. The results indicate that pseudoneointima begins developing within 24 hours after contact of the pumping surface with blood and is well developed at five days. The linings exhibit surface immunofluorescent fibrinogen activity, viable surface macrophages and histiocytes and scattered erythrocytes at ALVAD removal. Structurally similar linings (20 micrometer to 500 micrometer in thickness) develop in calves and in man. Mechanically, pseudoneointima is a stable, adherent, highly compliant, isotropic structural material. It is linearly elastic and strain-rate independent, with small viscous energy losses under physiologic strains. The methods employed for the evaluation of pseudoneointima provide useful information to determine the suitability of textured or rough surfaces for blood interfacing. The cumulative results indicate that the textured surface approach is useful for intermediate-term clinical ALVAD utilization.