September 16, 2013- By Ashish Shah, MD, Cardiac transplant surgeon, The Johns Hopkins Medical Center
Left ventricular assist devices (LVADs) arose from the ashes of the total artificial heart era. The idea of a permanent mechanical solution was abandoned in the 80’s after very public cases involving the Jarvik 7 total artificial heart. However, a few teams utilized the same technology to temporize critically ill patients until a donor heart was available. This effectively “bridged” them to heart transplant.
Throgh the 90’s, attention turned to univentricular support rather than total replacement. These LVADs serve to bridge the patient until they are well enough to be listed for heart transplant: bridge to transplant (BTT). After the publication of the REMATCH trial in 2001, a new class of LVAD patients were defined. Destination therapy (DT) represents the idea that a patient is actually not a candidate for transplant. The LVAD is the final therapy.
The BTT patients typically look like good heart transplant candidates but have run out of time or have reversible end organ dysfunction like renal insufficiency, malnutrition, or pulmonary hypertension that need the support period to improve their post transplant outcome. The DT patients on the other hand, may be older with a greater burden of extra cardiac organ dysfunction.
Over the last decade, however, the distinctions have become blurred and many candidates fall into a third category: A bridge to decision. Complicating matters further, continuous flow devices have now supported patients for 7 or more years and are far more durable than previous pulsatile pumps. Thus a DT patient may become a BTT patient. The improving technology has muddied the waters under the bridge.
The recent Center for Medicare and Medicaid coverage guidelines highlight some of the problems with current device utilization in the US. The coverage proposal continues to utilize the BTT versus DT categories. The only real difference from CMS standpoint is whether the patient is listed for transplant by a center. This may seem trivial, but now that there is a real competitor for Thoratec’s Heartmate 2 in the Heartware LVAS, so it matters. Both devices are now FDA approved for BTT, but only the HM2 is approved for DT. The market for DT or anyone who cannot be listed in good conscience is much larger than BTT.
The devices themselves are similar in that they are continuous flow devices and much smaller than older pumps. The Heartware LVAS requires even less room in the chest than Heartmate 2 and can potentially be utilized as a right ventricular assist device. Nonetheless only the Heartmate 2 can be utilized outside of the BTT population. The Heartware device is currently pursuing FDA approval for DT, but the current clinical climate makes the distinction even more artificial.
The Medicare NCD also has eliminated membership into INTERMACS as necessary. In current budgetary environments, this will likely be a significant threat to the survival of the registry since cheap in-house software can be used to track patients.
But the real question is why make this distinction in at all? BTT and DT patient are treated by the same multidisciplinary teams and the outcomes can be quite good. However, the third group of patients, bridge to decision, is uncharted ground. Many of these patients are potential transplant candidates but have uncertain psychosocial resources, compliance problems, and are frequently obese. As such BTD ends up as a bridge to nowhere.
I suspect this distinction will be eliminated in the future once the Heartware device (or any other) gets FDA approval. Teams will gain more experience with the different devices and will decide for themselves the advantages and disadvantages for individual patients. For example, a patient with tenuous right ventricular function may be better served with lifelong biventricular support, making Heartware the best choice.
For now, however, the distinction persists. LVAD teams will have to make very clear whether a patient is BTT or DT and reevaluate patients for possible transplant over the course of device support. Such a bridge for some, may be a bridge too far. Only time will tell.