Maximal exercise testing for the selection of heart transplantation candidates -: Limitation of peak oxygen consumption

Background: Peak exercise oxygen consumption (peak V(over dot)o(2)), which is considered an indicator of prognosis in advanced heart failure, is currently being used as a major criterion in many centers for the selection of candidates for heart transplantation. Available studies suggest that patients with peak V(over dot)o(2) < 14 mL/min/kg have improved survival and significant functional benefit with transplantation. Since patients may terminate symptom-limited exercise tests for a variety of reasons, peak V(over dot)o(2) does not necessarily reflect maximal V(over dot)o(2), leading to the possibility of inappropriate selection for transplantation. Therefore, we investigated the proportion of transplant candidates referred for exercise testing considered to have achieved maximal results from studies. Methods: Fifty-five patients with heart failure, aged 51 +/- 9 pears, (mean +/- SD) underwent maximum symptom-limited exercise tests on a cycle ergometer utilizing a Jones stage 1 incremental protocol. Tests were considered maximal if subjects achieved peak heart rate (HR) > 85% predicted ("cardiocirculatory limitation") or peak minute ventilation (V(over dot)(E)) > 85% predicted ("ventilatory limitation"), and achieved an anaerobic threshold (AT) by noninvasive measures. Results: Seven tests were terminated because of chest pain, ST-segment abnormalities, or ventricular arrhythmias. Of the remaining 48 studies, the reasons for stopping exercise were leg fatigue in 52%, dyspnea in 16%, and both symptoms in 23%, Sixteen of the 48 patients (33%) had peak V(over dot)o(2) < 14 mL/min/kg. In 8 of these 16 patients, both peak HR and V(over dot)(E) were < 85% predicted. Of these eight without apparent HR or ventilatory limitation, none had oxygen desaturation below 90% or fall in BP, two were in atrial fibrillation, and only three had evidence that an AT was achieved. Conclusions: Among the patients with peak V(over dot)o(2) < 14 ml/min/kg, there were no objective signs of a cardiocirculatory or a respiratory limitation to exercise in half of them, and 31% did not achieve an AT either, thus not meeting any criteria to support evidence of maximal exercise. Exercise tests without objective evidence of cardiocirculatory or ventilatory limitation may not represent maximal performance. Consequently, peak V(over dot)o(2) may misclassify an appreciable proportion of candidates if the test results are submaximal. Clinical implications: Clinical exercise studies indicating low peak V(over dot)o(2) must be interpreted in the context of whether a defined objective exercise limitation is evident to avoid biasing the selection of heart transplant candidates.