SynCardia Total Artificial Heart

The SynCardia temporary Total Artificial Heart (TAH-t) (SynCardia Systems, Inc.; Tucson, Ariz) has now been implanted in more than 1,100 patients in approximately 100 centers in North America, Western Europe, Russia, Turkey, Israel, and Australia; this includes 125 implants in 2012. It is a pneumatic, biventricular, orthotopic, pulsatile device that weighs 160 g and displaces 400 mL. Blood flow through this device follows a path that is nearly identical to the path through the normal heart. Flow rates in SynCardia patients are normally 7 to 9 L/min, and there is very little turbulence within the device. The pneumatically activated diaphragm system automatically balances blood output between the left and right sides and also automatically responds to increased venous return with increased outputs (Starling-like response). There is no suction.

To date, the longest duration of support has been 3.75 years, in a man who has since survived after transplantation. More than 47 patients have survived for longer than 1 year of support, and 72% of those underwent transplantation. In the bridge-to-transplantation application, 70% to 80% of patients have survived to transplantation, even though they have been selected primarily from Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) status 1 (sickest patients). The survival rate for 1 year post-transplantation has been 80% to 86%. Most of the strokes associated with this device are immediately post-implantation (4%). Anticoagulation has included aspirin and warfarin in most centers. The stroke rate after the first 2 post-implant days in patients free of endo-device infection (98% are free) is 8 events per 100 patient-years. Fatal infections associated with the device have been observed in 2% of patients, and spontaneous hemorrhage from arteriovenous malformations has not been observed.¹

Table I lists selection criteria for SynCardia TAH-t implantation that were used in the multi-institutional U.S. Food and Drug Administration (FDA) study.² Using these criteria, the survival rate to transplantation was 79%. When we classified the patients in that study by INTERMACS status, 94% were status 1 (“crash and burn,” days to live). A small group of patients, sicker than those described in Table I, were implanted during that study as “out-of-protocol compassionate use” patients, with nearly a 100% mortality rate.

TABLE I. Selection Criteria

Patient-selection patterns that have focused on bridge-to-transplantation in adults may soon change. A destination-therapy application has been approved by the FDA, and a smaller 50-mL pump is scheduled for use in smaller adults and children down to a weight of about 40 kg. A second-generation <13-lb portable driver and an improved 55-lb in-hospital console are ready for widespread use. Dissemination of the SynCardia TAH-t has been hampered by lack of portable drivers, and there have been only 36 “Big Blue” in-hospital drivers to support the entire world market. Hundreds of portable drivers are now available, and by 2014 the availability of small “in-hospital” drivers and portable drivers will no longer be restrictive.

Other trends have been noticed in the past year. 1) Nearly 20% of implants are for left ventricular assist device (LVAD) failure. 2) Increasing use has been noted for graft failure in cardiac transplant recipients. Graft failure is the major cause of death after cardiac transplantation. 3) Several centers once considered strongholds of an “LVAD-only” philosophy have become or applied to become implanting centers. 4) There is increasing use of the 70-mL device in pediatric cardiac surgical centers for congenital heart lesions.