Present and Future Perspectives on Total Artificial Hearts
Present and Future Perspectives on Total Artificial Hearts
Between June 23, 2006, and December 31, 2013, 10,542 patients who received an FDA approved durable MCS device were entered in the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) database. The rate of implants per year has increased from 338 devices implanted a year in 2007 (first full year of data collection) to 2506 in 2013.
The dominance of continuous-flow left ventricular assist device (LVAD) technology has emerged since the approval of the HeartMate II device (Thoratec, Pleasanton, California, USA) in 2008 for BTT therapy and for long-term DT in 2010. In 2013, more than 42% of implants had been designated as DT. In contrast, the implant rate of the only FDA approved TAH, the Syncardia CardioWest, has moved from 22 devices implanted a year in 2007 to 66 a year in 2013 according to the INTERMACS registry. One might conclude that even in the context of biventricular failure, the improvement in flow through the systemic circulation achieved by use of an LVAD is sufficient to achieve a renal improvement in hemodynamic performance and organ function for many patients. However, INTERMACS reported that right heart failure is the primary cause of death in 4.7% of patients, while 2.8% of patients die of intractable arrhythmias and 3.4% of congestive heart failure during MCS, identifying a group of patients that might benefit from biventricular support. Moreover, besides overt biventricular failure, other cardiac pathologies that might contraindicate LVAD implantation include infiltrative cardiomyopathies (amyloid), restrictive cardiomyopathies, cardiac malignancies, post infarction VSD and the presence of heart valve mechanical prostheses. If the patient's condition does not allow concomitant heart surgery at the time of LVAD implantation to correct aortic regurgitation, cardiac aneurysm, or congenital heart malfunction, TAH implantation might be preferred. Finally, according to the International Society of Heart Lung Transplantation, cardiac graft failure is the major cause of death among heart-transplant patients, accounting for 44% of transplant deaths within five years. Despite this, only 2% of patients with a failed transplant can get a new heart transplant, largely due to the shortage of donor hearts. The TAH may be a superior therapy for such patients. Moreover, the fourth INTERMACS report showed improved survival at three and six months among patients with biventricular dysfunction supported with a TAH versus a BiVAD. The recent report from Groupe de Relexion sur l'Assistance Mecanique (GRAM) registry showed that Syncardia recipients experienced significantly fewer neurologic events compared to BiVAD recipients. There are likely design elements of the Syncardia which may be responsible for reduced thromboembolic events. These data supports the adoption of TAH over BiVAD for biventricular support patients with INTERMACS class I and II.
Syncardia INC has reported an increase in support time for patients worldwide. This can be attributed to the paucity of organ donors and the increasing expertise achieved in managing patients with a TAH. More than 92 patients have been supported with a CardioWest TAH for more than one year (Table 1). Interestingly, considering the growing adoption of LVAD as DT underlined by INTERMACS registry VI, the use of TAH as long-term support has been recently investigated in 47 patients supported for more than one year with a CardioWest TAH. The rate of successful transplantation in this cohort of patients was greater than 70%. Only two patients of 27 died due to device related problems (membrane rupture), and infections still represent the major limit of this bulky device. The long-term support record is held by an Italian patient, who was supported for 1,373 days with a CardioWest TAH before a successful transplant.
Considering the therapeutic need for TAHs, there really is a necessity for this device. The scarce adoption of TAHs for clinical use depends mostly on the technology limitations inherent to the TAHs currently available.
The Present: Do we Really Need TAHs?
Between June 23, 2006, and December 31, 2013, 10,542 patients who received an FDA approved durable MCS device were entered in the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) database. The rate of implants per year has increased from 338 devices implanted a year in 2007 (first full year of data collection) to 2506 in 2013.
The dominance of continuous-flow left ventricular assist device (LVAD) technology has emerged since the approval of the HeartMate II device (Thoratec, Pleasanton, California, USA) in 2008 for BTT therapy and for long-term DT in 2010. In 2013, more than 42% of implants had been designated as DT. In contrast, the implant rate of the only FDA approved TAH, the Syncardia CardioWest, has moved from 22 devices implanted a year in 2007 to 66 a year in 2013 according to the INTERMACS registry. One might conclude that even in the context of biventricular failure, the improvement in flow through the systemic circulation achieved by use of an LVAD is sufficient to achieve a renal improvement in hemodynamic performance and organ function for many patients. However, INTERMACS reported that right heart failure is the primary cause of death in 4.7% of patients, while 2.8% of patients die of intractable arrhythmias and 3.4% of congestive heart failure during MCS, identifying a group of patients that might benefit from biventricular support. Moreover, besides overt biventricular failure, other cardiac pathologies that might contraindicate LVAD implantation include infiltrative cardiomyopathies (amyloid), restrictive cardiomyopathies, cardiac malignancies, post infarction VSD and the presence of heart valve mechanical prostheses. If the patient's condition does not allow concomitant heart surgery at the time of LVAD implantation to correct aortic regurgitation, cardiac aneurysm, or congenital heart malfunction, TAH implantation might be preferred. Finally, according to the International Society of Heart Lung Transplantation, cardiac graft failure is the major cause of death among heart-transplant patients, accounting for 44% of transplant deaths within five years. Despite this, only 2% of patients with a failed transplant can get a new heart transplant, largely due to the shortage of donor hearts. The TAH may be a superior therapy for such patients. Moreover, the fourth INTERMACS report showed improved survival at three and six months among patients with biventricular dysfunction supported with a TAH versus a BiVAD. The recent report from Groupe de Relexion sur l'Assistance Mecanique (GRAM) registry showed that Syncardia recipients experienced significantly fewer neurologic events compared to BiVAD recipients. There are likely design elements of the Syncardia which may be responsible for reduced thromboembolic events. These data supports the adoption of TAH over BiVAD for biventricular support patients with INTERMACS class I and II.
Syncardia INC has reported an increase in support time for patients worldwide. This can be attributed to the paucity of organ donors and the increasing expertise achieved in managing patients with a TAH. More than 92 patients have been supported with a CardioWest TAH for more than one year (Table 1). Interestingly, considering the growing adoption of LVAD as DT underlined by INTERMACS registry VI, the use of TAH as long-term support has been recently investigated in 47 patients supported for more than one year with a CardioWest TAH. The rate of successful transplantation in this cohort of patients was greater than 70%. Only two patients of 27 died due to device related problems (membrane rupture), and infections still represent the major limit of this bulky device. The long-term support record is held by an Italian patient, who was supported for 1,373 days with a CardioWest TAH before a successful transplant.
Considering the therapeutic need for TAHs, there really is a necessity for this device. The scarce adoption of TAHs for clinical use depends mostly on the technology limitations inherent to the TAHs currently available.
