Independent Prognostic Value of Peak Oxygen Consumption in ICD and Non-ICD Patients

Guidelines recommend the use of peak oxygen consumption (VO2) to assess prognosis in advanced heart failure (HF) patients. Many HF patients are currently treated with internal cardiac defibrillator (ICD) therapy. There is no robust evidence evaluating the prognostic value of peak VO2 in ICD patients. Our objective was to study the independent association between peak VO2 and mortality in ICD patients and whether this association differed from non-ICD patients. In a retrospective cohort study, we included 839 consecutive ambulatory advanced HF patients and reduced left ventricular ejection fraction (LVEF<40%) who had a cardiopulmonary test between 2001 and 2013 at our institution. We evaluated the association between peak VO2 and mortality using multivariable Cox proportional hazards model and evaluated if this association was significantly different from non-ICD patients using subgroup analysis. We included 477 ICD patients and 362 non-ICD patients. ICD patients were older (54 ± 12 years vs. 51 ± 13 years in non-ICD), had higher creatinine (1.27 ± 0.5 mg/dL vs. 1.1 ± 0.07 in non-ICD) and BNP, lower LVEF, wider QRS with higher prevalence of ischemic cardiomyopathy (41% vs. 25% in non-ICD) more frequently treated with digoxin (48% vs. 34% in non-ICD) and spironolactone (56% vs. 45% in non-ICD). During a median follow up of 2.4 years (inter-quartile 4 years), 153 patients died. A 1ml/kg/min higher peak VO2 was associated with a 10% risk reduction (HR 0.90 per 1-ml/kg/min-increase, 95%CI 0.84-0.96) after adjusting for co-morbidities, hemodynamic parameters, laboratory values, QRS and medical therapies. Mortality risk effect was not significantly different between ICD and non-ICD patients (p for interaction = 0.46). Adjusted survival was similar in ICD and non-ICD patients with peak VO2 >14 ml/kg/min and <10ml/kg/min but it was significantly higher in ICD patients with peak VO2 between 10-14 ml/kg/min (p=0.02) (Figure). Peak VO2 remains an important predictor of mortality in patients with HF, irrespective of the presence of an ICD. The absolute mortality risk is greater for those patients without an ICD in the setting of an intermediate peak VO2 (10-14 ml/kg/min). This may inform decision making around the timing of advanced therapies for patients with and without an ICD.