ATLANTA — It is possible to preoperatively identify a small subgroup of candidates for left ventricular assist device implantation as destination therapy, that is, as a permanent alternative to heart transplantation because their poor outcomes would render a transplant futile, said Dr. Katherine Lietz at the annual meeting of the American College of Cardiology.
The long-term outcomes for such a subgroup are remarkably good, she said.
Dr. Lietz presented an analysis of the largest population of LVAD recipients as destination therapy ever described: 311 patients who received the Thoratec HeartMate XVE at 65 hospitals in the United States and who were enrolled in the Food and Drug Administration-mandated Thoratec Destination Therapy Registry, through which they have been followed for a median of 15 months.
The overall group had a 1-month survival of 86%, a 1-year survival of 57%, and a 2-year survival of 38%. But those figures mask a wide range of outcomes. For example, 26% of patients died before they were able to leave the hospital after surgery, with the causes of death being sepsis, multiorgan failure, and right heart failure. The fact that none died of LVAD failure in the first year suggests that patient selection plays a key role in early postoperative outcomes, said Dr. Lietz of the University of Minnesota Medical Center, Minneapolis.
She and her coworkers therefore sought to develop a prospective tool for preoperative risk stratification. They evaluated 65 variables for potential inclusion.
In a multivariate analysis, the significant predictors of poor outcome included malnutrition as reflected by a serum albumin below 3.3 g/dL, low pulmonary artery pressures, a need for ventilatory support, severe renal dysfunction with a creatinine clearance below 30 mL/min, anemia, coagulopathies, any degree of hepatic dysfunction, and an elevated WBC count and other signs and symptoms of infection. Patients who were not on an inotropic agent, a β-blocker, or an ACE inhibitor just before implantation were also at higher risk for early in-hospital mortality.
The investigators assigned each risk factor a weighted relative value and summed them to obtain a cumulative risk score for each patient. On the basis of those scores, they divided the registry cohort into risk categories for in-hospital mortality. The rate of survival to hospital discharge was 100% in the low-risk group, 95% in those at medium risk, 68% in the high-risk group, and 25% in the very-high-risk population.
Overall, 1-year survival was 94%, 73%, and 53% in the low-, medium-, and high-risk groups, respectively, compared with 6% in the very-high-risk subgroup.
This very-high-risk subgroup was composed of just 12% of the total population. By excluding patients in this group, 1-year survival in the remaining 88% of patients in the combined low-, medium-, and high-risk groups was 70%, with a 2-year survival of 50%.
Dr. Lietz stressed that she does not believe that candidates with a very-high-risk score should necessarily be denied destination therapy with an LVAD. After all, many of the risk factors are modifiable—for example, nutritional status and coagulopathies—and could be addressed before surgery to move the patient out of the least-favorable category.
Dr. Marvin A. Konstam, professor of medicine at Tufts University, Boston, and chief of cardiology at New England Medical Center, noted that the decision to resort to destination therapy is driven only in part by the likelihood of device therapy's long-term success. Another key factor in the equation is the patient's prognosis on medical therapy.
“If we can identify a subgroup in which the risk with medical therapy is highest and yet survival with an LVAD is adequate, those might be the ideal destination therapy candidates,” he said.
LVADs are most often implanted as a temporary bridge to heart transplantation in patients awaiting a donor organ. But in November 2002, the FDA approved the use of the Thoratec HeartMate XVE as destination therapy in response to the positive results of the Randomized Evaluation of Mechanical Assistance for the Treatment of Congestive Heart Failure (REMATCH) trial.
Medicare covers the therapy in patients with class IV, end-stage heart failure who otherwise have a life expectancy of less than 2 years and are not candidates for transplantation because of advanced age or comorbidities.