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PubMed1985

Artificial heart and assist devices: directions, needs, costs, societal and ethical issues.

A Working Group appointed by the Director of the National Heart, Lung, and Blood Institute (NHBLI) has reviewed the current status of mechanical circulatory support systems (MCSS), and has examined the potential need for such devices, their cost, and certain societal and ethical issues related to their use. The media have reported the limited clinical investigative use of pneumatically energized total artificial hearts (which actually replace the patient's heart) and left ventricular assist devices (which support or replace the function of the left ventricle by pumping blood from the left heart to the aorta with the patient's heart in place). However, electrically energized systems, which will allow full implantation, permit relatively normal everyday activity, and involve battery exchange or recharge two or three times a day, are currently approaching long-term validation in animals prior to clinical testing. Such long-term left ventricular assist devices have been the primary goal of the NHLBI targeted artificial heart program. Although the ventricular assist device is regarded as an important step in the sequence of MCSS development, the Working Group believes that a fully implantable, long-term, total artificial heart will be a clinical necessity and recommends that the mission of the targeted program include the development of such systems. Past estimates of the potential usage of artificial hearts have been reviewed in the context of advances in medical care and in the prevention of cardiovascular disease. In addition, a retrospective analysis of needs was carried out within a defined population. The resulting projection of 17,000-35,000 cases annually, in patients below age 70, falls within the general range of earlier estimates, but is highly sensitive to many variables. In the absence of an actual base of data and experience with MCSS, projection of costs and prognoses was carried out using explicit sets of assumptions. The total cost of a left ventricular assist device, its implantation and maintenance for a projected average of 4 1/2 years of survival might be approximately $150,000 (in 1983 dollars). The gross annual cost to society could fall in the range of $2.5-$5 billion. Ethical issues associated with use of the artificial heart are not unique. For individual patients these relate primarily to risk-benefit, informed consent, patient selection, and privacy. However, for society as a whole, the larger concern relates to the distribution of national resources.(ABSTRACT TRUNCATED AT 400 WORDS)

Assisted Circulation↗
PubMed1987

Fatigue and hemocompatibility of polymer materials.

Hemocompatibility and sufficient fatigue life of biomaterials are critical in the development of artificial hearts and circulatory assist devices. In this study, three segmented polyurethanes (PUs) were compared with a fourth PU (Czech PU) and the organosilicone rubber RKM to determine the interrelationships between type of synthetic polymer, degree of structural change in cyclic loading, and hemocompatibility. Uniaxial and biaxial static strain tests were conducted. Accelerated fatigue tests were used to predict the behavior of the materials in vivo. Damage from fatigue was assessed by light transmission and light scattering methods, and the number of adhering platelets and degree of morphological change in the platelets were compared between initial and fatigued materials. The relative index of platelet adhesion and the relative form factor were also obtained. The elasticity characteristics of the PUs were shown to be substantially greater than those of RKM. RKM required reinforcement. Czech PU was shown to have good mechanical characteristics (with high elasticity and low creep). The morphology of the cells after cyclic load changed insignificantly, whereas the number of adherent platelets increased in all cases.

Assisted Circulation↗
PubMed1987

Paracorporeal assistance system for restoring cardiac activity.

Two series of experiments were conducted to assess the potential of artificial ventricular bypass in restoring cardiac activity. One series evaluated use of a paracorporeal left ventricle in 17 calves; the other evaluated biventricular bypass in 11 calves. Module pumps with a seamless blood chamber of polyurethane were used. Pump function and system parameters were controlled by a Sinus VK-2 control system. Assisted perfusion began with the induction of ventricular fibrillation. The experiments showed that left ventricular bypass was an effective method for long-term maintenance of the hemodynamics during fibrillation, leading to certain biochemical corrections and restored electrical activity and myocardial contractile function. The hemodynamic state was maintained at a higher level with biventricular bypass and was accompanied by a greater percentage of restored myocardial function. Uneven restoration of contractile activity in the left and right ventricles points to the need for adequate support of both ventricles.

Adenine Nucleotides↗
PubMed1990

The effect of left ventricular bypass on the right ventricular function: experimental analysis of the effects of ischemic injuries to the right ventricular free wall and interventricular septum.

The right ventricular (RV) function during left heart bypass (LHB) was examined in open-chest anesthetized mongrel dogs (average weight, 11.8 kg). The LHB was carried out by a left ventricle (LV) to femoral artery bypass using a centrifugal pump for 90 min, and the bypass flow was kept maximum to obtain almost complete decompression of the LV. The RV function was evaluated by hemodynamic parameters and pressure-dimension (sonomicrometry) relationship at pre-LHB (control) and 30, 60, and 90 min after LHB (LHB-30, LHB-60, and LHB-90). The materials were divided into three groups after LHB-30: intact heart (group 1, n = 5), RV free wall ischemia (group 2, n = 5), and interventricular septum (IVS) ischemia group (group 3, n = 8). No significant changes in mean right atrial pressure (mRAP), RV end-diastolic pressure (RVEDP), RV maximum derivative pressure, or RV fractional shortening (RVFS) were found between pre-LHB and post-LHB in groups 1 and 2. On the contrary, group 3 showed significant increases in mRAP and RVEDP, and a decrease in RVFS at LHB-90 compared to both pre-LHB and LHB-30. The RV end-systolic dimension (percentage of pre-LHB) showed significant increases at LHB-90 compared to LHB-30 in groups 2 and 3. These results indicate that the LHB itself does not depress the RV function in the intact heart and in the RV free wall ischemic heart, while the impairment of the IVS during LHB appears to lead to RV dysfunction.

Animals↗
PubMed2004

Treatment of full-thickness skin defect with concomitant grafting of 6-fold extended mesh auto-skin and allogeneic cultured dermal substitute.

The aim of this clinical study was to evaluate an allogeneic cultured dermal substitute (CDS) as a biological dressing for highly extended mesh auto-skin grafting. The subjects were five patients with extensive deep burn wounds. Allogeneic CDS was prepared by seeding fibroblasts on a spongy matrix of hyaluronic acid and atelo-collagen. Six-fold extended auto-skin graft was applied to the debrided wound, on which allogeneic CDS was placed. A conventional ointment-gauze dressing was used to protect the CDS. The CDS was applied repeatedly at intervals of 5-7 days. In all cases, the wounds were closed by successful take of mesh auto-skin graft and prompt epithelization from the grafted skin. The skin on the grafted area had a cicatrix appearance, but was soft and thin, maintaining good quality. The application of 6-fold extended auto-skin graft in conjunction with allogeneic CDS is an effective method for treatment of extensive severe burn wounds.

Adult↗
PubMed2004

Under-utilization of mechanical circulatory support in Canada: why and what can be done?

In October of 2002, a workshop was held as part of the Canadian Cardiovascular Congress in Edmonton, Canada, entitled "Under-Utilization of Mechanical Circulatory Support in Canada. Why and What Can Be Done?" The workshop examined various issues related to the use of mechanical circulatory support devices in the Canadian context. Representatives from all Canadian centers with active mechanical circulatory support programs were invited to participate and participants included surgeons and cardiologists, as well as other affiliated health professionals. Opinions were solicited from the workshop participants and a series of recommendations were formulated.

Assisted Circulation↗
PubMed2007

Efficacy and mechanisms of biventricular and left/right direct cardiac compression in acute heart failure sheep.

Direct cardiac compression (DCC) with implanted heart patches has previously demonstrated efficacy of biventricular (BiV) support in acute heart failure (HF) sheep. We hypothesized that this was primarily due to a left ventricular (LV) effect. This study compared BiV, LV, and right ventricular (RV) assists in terms of hemodynamic and energetic response. Ten sheep underwent instrumentation and device implantation at least 1 week prior to study. HF (50% reduction in cardiac output) was maintained with intravenous esmolol infusion. BiV, LV, and RV assists were activated randomly with intervening stable HF periods. BiV assist was more effective than either LV or RV assist in restoring hemodynamic parameters; however, there was no difference in efficacy of LV and RV support. RV assist preserved left coronary flow patterns and chamber geometry compared to other assist conditions, but increased LV preload. These results suggest that LV and RV support each make a significant contribution to the efficacy of BiV assist, albeit through different mechanisms.

Animals↗
PubMed1986

Thermedics' approach to ventricular support systems.

Temporary and permanent ventricular assist systems, developed by Thermedics, Inc., are described, including rationale, design, operation and surgical applications. Clinical data are presented for pneumatically driven temporary left ventricular assist devices (LVAD). Usefulness of this device rests on the assumption that tissue of a weakened heart can recover if relieved for a time by an LVAD. The surgical implantation of an LVAD is reported in a case where the patient later received a heart transplant. The concept and technology of the subsystems of a permanent ventricular assist system (VAS), now ready for preclinical trials, are discussed. Design of a low-speed, torque-motor driven blood pump is described. Details are presented on transcutaneous energy transmission by means of a transformer, one of whose coils is embedded under the skin. Though less efficient than percutaneous transmission, the method eliminates infection risk. Special types of polyurethanes are analyzed in respect to their biocompatibility. It is concluded that flocking of the polyurethane surface allows the growth of a biological lining which is highly antithrombogenic. Sintered metal powders are found to be most efficient for fabrication of rigid pump components. A lenticular pump design is proposed to solve the problem of pressure differentials in the sealed device. Cardiac endocrine functions are cited in support of using assist devices that leave the heart in place.

Assisted Circulation↗
PubMedDate not supplied

Systemic and local effects of heat dissipation in the thermally powered LVAS.

A thermally powered left ventricular assist system (LVAS) requires 20 W of heat dissipation either to the blood or to the surrounding tissues, such as the lung subcutaneous tissues. Postoperative systemic and local effects of heat dissipation were studied in 5 thermally powered LVASs and 2 heated blood pumps implanted in calves, and compared with 10 pneumatically powered left ventricular assist devices (LVADs). Postoperative mean temperatures of the heat dissipation group were as follows: 1. rectal (RT), 39.1 x 0.4 degrees C (NS versus control); 2. Lung interface, 41.6 +/- 0.6 degrees C (P less than 0.01 versus RT); 3. tissue interface, 40.2 +/- 1.2 degrees C (P less than 0.01 versus RT); and 4. blood, 39.2 +/- 0.8 degrees C (NS versus RT). There was no significant postoperative change in heart rate, respiratory rate, or rectal temperature between the two groups. No difference was shown between the two groups in hematologic parameters, plasma free hemoglobin, liver and renal function, fibrinogen levels, or coagulation processes at the same postoperative time. Heat dissipation to the pump-blood interface promoted a thinner neointima when compared with the nonheated surface. Angioneogenesis was observed in the tissue capsule adjacent to the heat dissipating surface. These results indicated that the thermal LVAS induced no deleterious local or systemic effects on recipient animals.

Air↗
PubMedDate not supplied

Results of mechanical circulatory assistance before heart transplantation.

Between February 1984 and December 1987, 63 patients were accepted as candidates for heart transplantation. Eighteen patients (29%) required some form of mechanical circulatory support before transplantation; eight patients received an intraaortic balloon pump, five patients had left ventricular assist devices, two patients received biventricular assist devices, and in three patients the total artificial heart was implanted. Fourteen of the 18 patients underwent transplantation with seven longterm survivors.

Assisted Circulation↗
PubMed1989

Prolonged ventricular support using a centrifugal pump.

The Biomedicus centrifugal pump was required to provide prolonged ventricular support to 13 patients with hemodynamic instability: 11 after cardiovascular surgical procedures, 1 after myocardial infarction and 1 after failure of a heart transplant. The duration of support ranged from 3.5 hours to 9 days (mean 72 hours). Complications included bleeding in six patients, renal insufficiency in three and central nervous system deficit in three. Six patients (46%) were successfully weaned from the pump. The patient with graft failure had hyperacute rejection of a second heart. Five patients were discharged from the hospital. There was one death 8 months postoperatively. Prolonged ventricular support with the centrifugal pump may allow recovery of potentially reversible ventricular dysfunction in selected patients after cardiac surgical procedures.

Adolescent↗
PubMed1988

Effect of perioperative myocardial infarction on survival of postcardiotomy patients supported with ventricular-assist devices.

Ventricular-assist devices (VAD) have increased survival in patients with postcardiotomy shock, but the predictors of success need to be elucidated. We evaluated 45 patients treated with centrifugal (n = 18) or pulsatile (n = 27) VAD for postcardiotomy cardiogenic shock to determine the effect of perioperative myocardial infarction (PMI) on survival. The patients ranged in age from 15 to 72 years (mean age, 55.1 years). VAD support was left ventricular in 29, right ventricular in seven, and biventricular in nine, and the flow-rate range was 1.6-5.2 l/min (mean rate, 3.97 l/min) for 0.2-22 days (mean time, 4.1 days). PMI was determined by analysis of postoperative electrocardiogram (EKG), enzyme levels, or at necropsy. PMI was considered "possible" if there were either EKG or enzyme level changes, and "definite" if there were EKG and enzyme level changes or necropsy evidence. Of the 45 patients, 19 were successfully weaned from ventricular assistance; 12 were discharged (Group 1), and seven died (Group 2); the remaining 26 patients could not be weaned from VAD support (Group 3). In Group 1, one patient had a definite PMI, and three had a possible PMI. Among the 33 nonsurvivors (Groups 2 and 3), 24 patients had PMI by necropsy examination. Definite PMI was much more common in nonsurvivors (72.7%) than in survivors (8.3%) (p less than 0.05). However, Group 2 nonsurvivors were weaned despite PMI in 100% of cases. These data suggest that, although PMI is a strong negative determinant of survival in postcardiotomy patients, it cannot be considered a contraindication because it does not preclude myocardial recovery.

Adolescent↗
PubMedDate not supplied

In vitro and in vivo testing of a totally implantable left ventricular assist system.

The totally implantable Novacor LVAS is being tested under NIH auspices to demonstrate safety and efficacy before clinical trials. Twelve complete systems (submerged in saline at 37 degrees C) are being tested, with an NIH goal of demonstrating 80% reliability for 2 year operation with a 60% confidence level. The systems, which are continuously monitored, are diurnally cycled between two output levels by automatically varying preload and afterload. Currently, 14.3 years of failure-free operation have been accumulated, with a mean duration of 14 months. Using an exponential failure distribution model, the mean time to failure (MTTF) is greater than 8.8 years, corresponding to a demonstrated reliability (for a 2 year mission time) of 80% (80% confidence level). Recent ovine experiments with VAS subsystems include a 767 day volume compensator implant, a 279 day pump/drive unit implant and a 1,448 day BST implant. The last 12 chronic pump/drive unit experiments had a mean duration of 153 days (excluding early postoperative complications). This compares favorably with the NIH goals for complete systems (5 month mean duration). Complete system experiments are currently underway.

Animals↗
PubMed1986

Strategy for treatment of acute evolving myocardial infarction with pulsatile left heart assist device. Can this modality increase survival and enhance myocardial salvage?

This article describes the technique of left heart bypass in the treatment of both experimental and clinical acute myocardial infarction. A new technique of closed-chest percutaneous left heart bypass that can be used in patients with acute evolving myocardial infarction and cardiogenic shock is also described.

Acute Disease↗
PubMed1985

Two-dimensional echocardiographic evaluation of right ventricular function during left heart bypass.

Right ventricular (RV) function in terms of hemodynamics and RV wall motion was studied in 14 mongrel dogs during left heart bypass (LHB) using a centrifugal blood pump. The wall motion was analyzed by two-dimensional echocardiography (2D-echo). Incremental changes in LHB flow ratios of 0% (controls), 25%, 50%, 75% and a maximum 85-100% were accompanied by decrements of segmental shortening of the interventricular septum (IVS) by 54 +/- 12%, 43 +/- 5%, 42 +/- 2%, 35 +/- 0% and 0%, respectively. In addition to akinesis of the IVS during maximum flow, a specific part of the RV free wall adjacent to the IVS also had marked depression of contractions and overall RV contraction was nearly dependent on the RV free wall opposite to the IVS. Maximum LHB flow induced complete depression of the left ventricular cavity, a marked increase in RV volume, and depression of the RV ejection fraction on 2D-echo. Excessive or prolonged LHB reduces the RV wall motion capability and may lead to right heart failure. Our results suggest that an LHB ratio of about 75% is optimum to maintain normal cardiac function, particularly that of the right heart.

Animals↗