Prognosis and Peak VO2 in Heart Failure
Prognosis and Peak VO2 in Heart Failure
Background: Accurately establishing prognosis in severe heart failure has become increasingly important in assessing the efficacy of treatment modalities and in appropriately allocating scarce resources for transplantation. Peak exercise oxygen uptake appears to have an important role in risk stratification of patients with heart failure, but the optimal cutpoint value to separate survivors from nonsurvivors is not clear.
Methods: Six hundred forty-four patients referred for heart failure evaluation over a 10-year period participated in the study. After pharmacologic stabilization at entrance into the study, all participants underwent cardiopulmonary exercise testing. Survival analysis was performed with death as the end point. Transplantation was considered a censored event. Four-year survival was determined for patients who achieved peak oxygen uptake values greater than and less than 10, 11, 12, 13, 14, 15, 16, and 17 mL/kg/min.
Results: Follow-up information was complete for 98.3% of the cohort. During a mean follow-up period of 4 years, 187 patients (29%) died and 101 underwent transplantation. Actuarial 1- and 5-year survival rates were 90.5% and 73.4%, respectively. Peak ventilatory oxygen uptake (VO2) was an independent predictor of survival and was a stronger predictor than work rate achieved and other exercise and clinical variables. A difference in survival of approximately 20% was achieved by dichotomizing patients above versus below each peak VO2 value ranging between 10 and 17 mL/kg/min. Survival rate was significantly higher among patients achieving a peak VO2 above than among those achieving a peak VO2 below each of these values (P < .01), but each cutpoint was similar in its ability to separate survivors from nonsurvivors.
Conclusion: Peak VO2 is an important measurement in predicting survival from heart failure, but whether an optimal cutpoint exists is not clear. Peak VO2 may be more appropriately used as a continuous variable in multivariate models to predict prognosis in severe chronic heart failure.
Prognosis remains a major concern for patients with chronic heart failure. Despite advances in therapeutic options for this condition, the risk for death among patients with severe chronic heart failure remains 30% to 60% annually. Transplantation has been demonstrated to improve prognosis considerably. The 1-year survival rate is 85% to 90% and the 5-year survival rate 70% to 75%. Successful transplantation combined with rehabilitation is associated with improvements in exercise capacity. However, there remains a paucity of available donor hearts relative to demand. United Network for Organ Sharing data suggest that among approximately 400 new patients placed on the heart transplant waiting list each month, only 150 to 200 patients are able to undergo transplantation, resulting in a net increase of 200 or more patients to the waiting list per month.
To direct the limited number of donor hearts to patients who need them the most, a great deal of effort has been directed toward stratifying risk among patients with severe chronic heart failure through the use of clinical, hemodynamic, and exercise test data. In recent years, exercise capacity has been demonstrated to be an important component of the risk profile among persons with chronic heart failure. In particular, directly measured peak oxygen uptake in some studies has outperformed clinical, hemodynamic, and other exercise test data in predicting 1 to 2 year mortality. Several investigators have reported that patients who achieve a peak VO2 of 14 mL/kg/min appear to have a prog- nosis similar to that among patients who receive transplants (approximately 90% at 1 year). This finding implies that transplantation can be safely deferred among these patients. This cutpoint has emerged as a prominent prognostic marker in chronic heart failure and is listed as a relative indication for transplantation in both the recent Bethesda Task Force recommendations on recipient priority and the American Heart Association Scientific Statement on Cardiac Transplantation. Previous studies have generally made dichotomous comparisons, such as above versus below 14 or 15 mL/kg/min, above and below 10 mL/kg/min, and above 14 versus below 10 mL/kg/min. To our knowledge, there have been no direct comparisons between different values for peak VO2 within the relevant range in this population. To determine the optimal peak VO2 criteria for stratifying risk among patients with severe heart failure, we performed this study.
Background: Accurately establishing prognosis in severe heart failure has become increasingly important in assessing the efficacy of treatment modalities and in appropriately allocating scarce resources for transplantation. Peak exercise oxygen uptake appears to have an important role in risk stratification of patients with heart failure, but the optimal cutpoint value to separate survivors from nonsurvivors is not clear.
Methods: Six hundred forty-four patients referred for heart failure evaluation over a 10-year period participated in the study. After pharmacologic stabilization at entrance into the study, all participants underwent cardiopulmonary exercise testing. Survival analysis was performed with death as the end point. Transplantation was considered a censored event. Four-year survival was determined for patients who achieved peak oxygen uptake values greater than and less than 10, 11, 12, 13, 14, 15, 16, and 17 mL/kg/min.
Results: Follow-up information was complete for 98.3% of the cohort. During a mean follow-up period of 4 years, 187 patients (29%) died and 101 underwent transplantation. Actuarial 1- and 5-year survival rates were 90.5% and 73.4%, respectively. Peak ventilatory oxygen uptake (VO2) was an independent predictor of survival and was a stronger predictor than work rate achieved and other exercise and clinical variables. A difference in survival of approximately 20% was achieved by dichotomizing patients above versus below each peak VO2 value ranging between 10 and 17 mL/kg/min. Survival rate was significantly higher among patients achieving a peak VO2 above than among those achieving a peak VO2 below each of these values (P < .01), but each cutpoint was similar in its ability to separate survivors from nonsurvivors.
Conclusion: Peak VO2 is an important measurement in predicting survival from heart failure, but whether an optimal cutpoint exists is not clear. Peak VO2 may be more appropriately used as a continuous variable in multivariate models to predict prognosis in severe chronic heart failure.
Prognosis remains a major concern for patients with chronic heart failure. Despite advances in therapeutic options for this condition, the risk for death among patients with severe chronic heart failure remains 30% to 60% annually. Transplantation has been demonstrated to improve prognosis considerably. The 1-year survival rate is 85% to 90% and the 5-year survival rate 70% to 75%. Successful transplantation combined with rehabilitation is associated with improvements in exercise capacity. However, there remains a paucity of available donor hearts relative to demand. United Network for Organ Sharing data suggest that among approximately 400 new patients placed on the heart transplant waiting list each month, only 150 to 200 patients are able to undergo transplantation, resulting in a net increase of 200 or more patients to the waiting list per month.
To direct the limited number of donor hearts to patients who need them the most, a great deal of effort has been directed toward stratifying risk among patients with severe chronic heart failure through the use of clinical, hemodynamic, and exercise test data. In recent years, exercise capacity has been demonstrated to be an important component of the risk profile among persons with chronic heart failure. In particular, directly measured peak oxygen uptake in some studies has outperformed clinical, hemodynamic, and other exercise test data in predicting 1 to 2 year mortality. Several investigators have reported that patients who achieve a peak VO2 of 14 mL/kg/min appear to have a prog- nosis similar to that among patients who receive transplants (approximately 90% at 1 year). This finding implies that transplantation can be safely deferred among these patients. This cutpoint has emerged as a prominent prognostic marker in chronic heart failure and is listed as a relative indication for transplantation in both the recent Bethesda Task Force recommendations on recipient priority and the American Heart Association Scientific Statement on Cardiac Transplantation. Previous studies have generally made dichotomous comparisons, such as above versus below 14 or 15 mL/kg/min, above and below 10 mL/kg/min, and above 14 versus below 10 mL/kg/min. To our knowledge, there have been no direct comparisons between different values for peak VO2 within the relevant range in this population. To determine the optimal peak VO2 criteria for stratifying risk among patients with severe heart failure, we performed this study.
