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 curre ntly being used as a major criterion in many centers for the selection of c andidates for heart transplantation. Available studies suggest that patient s with peak V(over dot)o(2) < 14 mL/min/kg have improved survival and signi ficant functional benefit with transplantation. Since patients may terminat e 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 p ossibility of inappropriate selection for transplantation. Therefore, we in vestigated the proportion of transplant candidates referred for exercise te sting 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 ergome ter utilizing a Jones stage 1 incremental protocol. Tests were considered m aximal if subjects achieved peak heart rate (HR) > 85% predicted ("cardioci rculatory limitation") or peak minute ventilation (V(over dot)(E)) > 85% pr edicted ("ventilatory limitation"), and achieved an anaerobic threshold (AT ) by noninvasive measures. Results: Seven tests were terminated because of chest pain, ST-segment abno rmalities, or ventricular arrhythmias. Of the remaining 48 studies, the rea sons for stopping exercise were leg fatigue in 52%, dyspnea in 16%, and bot h 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 l imitation, none had oxygen desaturation below 90% or fall in BP, two were i n 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, t here were no objective signs of a cardiocirculatory or a respiratory limita tion to exercise in half of them, and 31% did not achieve an AT either, thu s not meeting any criteria to support evidence of maximal exercise. Exercis e tests without objective evidence of cardiocirculatory or ventilatory limi tation may not represent maximal performance. Consequently, peak V(over dot )o(2) may misclassify an appreciable proportion of candidates if the test r esults 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 tra nsplant candidates.