Surface texturing and coating of biomaterial implants: effects on tissue integration and fibrosis.

To determine whether texturing and coating have additive effects in promoting tissue integration and inhibiting fibrosis, we evaluated smooth silicone rubber (SSR), textured silicone rubber (TSR), porous silicone rubber (PSR), expanded polytetrafluoroethylene (ePTFE), and porous polyurethane (PPU) subcutaneous implants in eight minipigs. Some of the implants were coated with type IV collagen (Col) and/or fibronectin (Fn). At 6 months, we removed the implants and examined them microscopically. Texturing was more important than Col and Fn in reducing fibrosis and inflammation. The PSR yielded the best response, including reduced fibrosis and inflammation, satisfactory adherence, and no dystrophic mineralization.

Separation of the natural atria in experimental implantation of total artificial heart.

Atrial connections in a single-unit total artificial heart (TAH) may be difficult to make because of the rigidity of the device and the fixed position of the atrial inlets. We developed a technique to separate the natural atrial borders in an experimental implantation of a unitary TAH. In this technique, the interatrial groove was dissected to separate the posterior wall of the right atrium from the roof of the left atrium before cardiopulmonary bypass (CPB) was initiated. After initiation of CPB and cardiectomy, the atrial septum was separated completely, and the right atrial wall was reconstructed with glutaraldehyde-treated autopericardium. We believe that this simple adjunctive technique provides increased mobility of the atrial cuffs and allows for an easier connection of the unitary TAH.

Frequency and significance of infections in patients receiving prolonged LVAD support.

Infections in patients undergoing mechanical circulatory support as a bridge to transplant are associated with significant mortality and morbidity. To determine the frequency and effects of infection during such procedures, a retrospective analysis was done of 14 patients who received prolonged (greater than 14 days) support with the Heartmate left ventricular assist device (LVAD) (Thermo Cardiosystems, Inc., Woburn, MA). All patients were men (mean age, 44.3 years), and duration of LVAD support ranged from 19 to 233 days (mean, 98.1 days). During LVAD support, five patients had no infections, and, in the remaining nine patients, infections were most common in the respiratory tract, catheter tips, and urine. Four device related infections occurred in three patients, all of which were resolved with antibiotic therapy. All 14 patients underwent transplantations, and none of the operations was delayed because of infection. Eleven of the patients are long-term survivors (range of time after transplant, 7.5-37 months). Infections were not associated with mortality or significant morbidity in this group of patients.

Extended support with a left ventricular assist device as a bridge to heart transplantation.

The Heartmate-1000IP, an intracorporeal, pneumatically activated, pulsatile left ventricular assist device (LVAD) with textured blood-contacting surfaces, is undergoing clinical evaluation as a bridge to heart transplantation (HTx). During a 3 year period (January 1988 to April 1991), the authors evaluated 12 patients who required extended LVAD support (greater than 30 days) while awaiting HTx. Duration of support ranged from 31 to 233 days (mean, 117 days). LVAD performance was excellent, with average pump flow indices of 2.5-3.5 L/min/m2. Long-term antithrombotic therapy consisted of dipyridamole and aspirin in all except one patient who received only low-molecular-weight dextran. After the initial recovery period, prothrombin and partial thromboplastin times returned to baseline levels. Plasma-free hemoglobin levels averaged less than 10 mg/dl. One patient is currently receiving support (91+ days); the 11 other patients underwent successful HTx, with follow-up ranging from 7 to 36 months. The authors' cumulative experience with this LVAD totals more than 1,506 days of support (greater than 4 years) without evidence of any thromboembolic episodes. These results suggest that this LVAD provides an effective bridge to HTx for extended periods.

Extended clinical support with an implantable left ventricular assist device.

Clinical evaluations are under way of an intracorporeal (abdominally positioned) pulsatile left ventricular assist device (LVAD) that is capable of providing support for extended periods (greater than 30 days) in patients awaiting heart transplantation. The LVAD, developed by Thermo Cardiosystems Inc. (Woburn, MA), has uniquely textured blood contacting surfaces and requires only minimal antithrombotic therapy. It has been used at the Texas Heart Institute as a bridge to transplantation in 11 patients, including 2 who are currently receiving support. Four patients required extended LVAD support (35-132 days); of those, three are doing well at 1.5, 8.5, and 13 months, respectively, after transplantation, and one died of liver failure 49 days after transplantation. The LVAD was operated in a fixed-rate mode to maintain pump flows at 4-8 L/min, resulting in stabilization of hemodynamic and secondary organ function in all patients. Blood chemistry and hematologic values returned to normal during LVAD support in three of four patients. Postoperative anticoagulation was gradually reduced over the course of the trials. The two most recent patients (35 and 132 days) received only oral dipyridamole (75 mg X 3/day) and aspirin (80 mg/day) after the early recovery period (four-six days), resulting in normal prothrombin and partial thromboplastin times. Plasma hemoglobin levels remained within acceptable limits, and there was no evidence of thromboembolism. Blood contacting surfaces were coated with a thin, adherent, biologically derived lining. The initial results indicate that the intracorporeal LVAD, with textured blood contacting surfaces, can effectively support the failing heart for extended periods (greater than 30 days) with minimal antithrombotic therapy.

Anatomic considerations for abdominally placed permanent left ventricular assist devices.

To determine anatomic parameters for a permanent, electrically actuated left ventricular assist device (LVAD), the effects of abdominal placement of pneumatic LVADs used as temporary support for patients awaiting heart transplantation was studied. Understanding the anatomic constraints imposed by the abdominal viscera in LVAD placement is crucial, because improper placement can result in compression or obstruction of adjacent structures. Anatomic compatibility was assessed in four men (age 22-48 years) who were supported by the LVAD for over 1 month (range 35-132 days). The pump was intraperitoneally placed in the left upper quadrant. Radiographic techniques were employed, including CT scanning (with patients supine) and contrast imaging (patients in anatomical position), and the pump and conduits appeared to be properly positioned, with minimal compression of the body of the stomach, and no obstruction of adjacent organs. Three patients returned to a solid food diet and exercised daily by stationary cycling and walking. No signs of migration or erosion of the pump were present at the time of LVAD removal and cardiac transplantation. Successful clinical experience with short-term use of the LVAD suggests that the electrically actuated device can be well tolerated in patients requiring permanent left ventricular assistance.

Event-related brain potentials differentiate normal and disabled readers.

Auditory event-related potentials (AERPs) recorded to irrelevant tone pairs while subjects performed visual, reading-related cognitive tasks differed significantly between normal and disabled readers. Disabled readers as compared with normal readers showed significantly lower amplitude right hemisphere AERP responses during tasks that involved visual-phonemic transfer of information and simple pattern recognition. Disabled readers as compared with normal readers also showed significantly higher amplitude left hemisphere responses during the visual-phonemic task. In both experimental conditions the reading-disabled subjects showed significantly lower amplitude right than left hemisphere AERP responses. Task-related strategies did not differ between groups. The pattern of AERP amplitude asymmetry found for disabled readers, which was opposite to that found for normal readers, suggests that the same reading-related tasks activated different cerebral processes in the two groups studied.

Development and evaluation of a long-term, implantable, electrically actuated left ventricular assist system: THI/Gould LVAS.

A long-term, implantable, electrically actuated left ventricular assist system (THI/Gould LVAS) is being developed and characterized in vitro and in vivo for utilization in patients with end-stage heart disease. This system consists of five major components: a long-term, implantable blood pump (THI E-type ALVAD); an electrical-mechanical energy converter (Gould Model V); a control unit with batteries; a volume compensation system; and an external power supply and monitoring unit. Two of these components (blood pump and electrical-mechanical energy converter) have been integrated, and are undergoing chronic in vivo evaluations in calves. Thus far, 44 pneumatically and electrically actuated THI/Gould LVAS evaluations have been performed. This experience has resulted in greater than 6.5 years of actuation in vivo, with durations exceeding 1 year. System in vivo performance in terms of durability, mechanical reliability, hemodynamic effectiveness, and biocompatibility has been satisfactory. Demonstration of long-term (2-year) effectiveness in supporting the circulation is the ultimate goal.

Chronic in vivo evaluations of a long-term, implantable left ventricular assist system.

Total THI/Gould LVAS experience includes 59 pneumatically and electrically-actuated blood pump evaluations (in calves, goats and sheep), including 23 studies with the Gould Model V energy converter. This experience has resulted in greater than 8 cumulative years of actuation, in vivo, including electrically-actuated LVAS durations up to 6 mos.

Calcification in chronically-implanted blood pumps: experimental results and review of the literature.

Blood compatibility is a major objective in the development of long-term, implantable circulatory assist (left ventricular assist devices) and replacement (total artificial heart) devices. An important problem in experimental studies in animals has been the propensity for calcification to occur at the blood/material interface. Presented is a summary of our experience (27 studies) with blood pump calcification and a review of the current literature regarding this complication.

Development and evaluation of electrically actuated abdominal left ventricular assist systems for long-term use.

A long-term, totally implantable, electrically actuated, abdominally positioned left ventricular assist system (ALVAS) is being developed, characterized in vitro, and evaluated in vivo for utilization in patients with end-stage cardiac failure refractory to conventional therapeutic techniques. The first two major subsystems of the ALVAS (the pusher-plate blood pump and electrical-mechanical energy converters) have been integrated and are undergoing in vitro characterization and long-term in vivo evaluations in calves. Duration of these studies has exceeded 6 months. System performance in terms of hemodynamic effectiveness, mechanical reliability, and biocompatibility has been excellent and no untoward effects have been observed. Long-term effectiveness of the ALVAS remains to be established in continuing experiments, with a 2 year period of clinical use as an ultimate goal.

Intraaortic balloon pumping women: effects of balloon size on survival.

Between 1972 and 1978, 429 patients underwent intraaortic balloon pump (IABP) counterpulsation in our institution. Ninety-six were women (22.4). The overall mortality was 52.9% for men and 69.8% for women. During 1978, however, the mortality for women decreased to 57.1%, even though they comprised a larger percentage of patients (28.2%) than before. The major indication for IABP support in these women was ischemic myocardial dysfunction resulting in failure to wean from cardiopulmonary bypass (THI hemodynamic Classification C) despite volume expansion and pharmacologic support. Improved results were obtained with the use of larger intraaortic balloons and direct ascending aortic IABP insertion (which allowed use of larger, more effective 30 or 40 ml balloons), combined with delayed sternal closure.