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Clinical Investigations: CARDIOLOGY |

Maximal Exercise Testing for the Selection of Heart Transplantation Candidates*: Limitation of Peak Oxygen Consumption

David Ramos-Barbón, MD; David Fitchett, MD; William J. Gibbons, MD; David A. Latter, MD; Robert D. Levy, MD, FCCP
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*From the Respiratory and Cardiology Divisions, Department of Medicine, the Division of Cardiovascular and Thoracic Surgery, Royal Victoria Hospital, and Meakins-Christie Laboratories, McGill University, Montreal, Quebec, Canada.



Chest. 1999;115(2):410-417. doi:10.1378/chest.115.2.410
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Background: Peak exercise oxygen consumption (peak V̇o2), 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 V̇o2 < 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 V̇o2 does not necessarily reflect maximal V̇o2, 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 years, (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 (V̇e) > 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 V̇o2 < 14 mL/min/kg. In 8 of these 16 patients, both peak HR and V̇e 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 V̇o2 < 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 V̇o2 may misclassify an appreciable proportion of candidates if the test results are submaximal.

Clinical implications: Clinical exercise studies indicating low peak V̇o2 must be interpreted in the context of whether a defined objective exercise limitation is evident to avoid biasing the selection of heart transplant candidates.

Abbreviations: AT = anaerobic threshold; BMI = body mass index; HR = heart rate; LVEF = left ventricular ejection fraction; MVV = maximum voluntary ventilation; RER = respiratory exchange ratio; SaO2 = arterial oxygen saturation; V̇e = minute ventilation; V̇o2 = oxygen consumption; V̇o2max = maximum oxygen consumption

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