Exercise capacity testing
Assessing functional and exercise capacity is an important part of the clinical assessment of patients with heart failure.
The NYHA classification is a widely used tool to grade the severity of a patient’s symptoms. However, reproducibility of NYHA class is low, with low validity and reproducibility.9,10 Objective measures such as the 6-minute walk test (6MWT) give more reliable information regarding a patients’ exercise capacity, although are susceptible to a ‘learning effect’.
The 6MWT measures the distance walked during six minutes on a hard, flat surface. The patient goes at their own pace and rests as needed. It is easy to perform in the corridor of a ward or outpatient clinic without the need for equipment: the recommended corridor length is 30 metres.11 In healthy adults, the normal 6MWT distance is between 400-700m.In patients with heart failure, 6MWT distance <300m is associated with worse cardiovascular outcomes.12
While the 6MWT is a test of aerobic endurance, incremental exercise tests such as the Bruce treadmill test or incremental shuttle walk test, are a better indicator of maximal aerobic performance. In patients without significant limitation, incremental exercise tests may be preferable to the 6MWT for assessing the exercise capacity of patients with heart failure.
Gas exchange analysis using the peak oxygen consumption (peak VO2)
An incremental protocol can be coupled to the measurement of metabolic gas exchange to derive objective measures of exercise capacity such as the anaerobic threshold, peak oxygen consumption and the ventilatory response to exercise. Such tests can be helpful in differentiating dyspnoea of cardiac or respiratory origin, and are often used as part of assessment for heart transplant.
Normal exercise capacity in a patient not receiving treatment effectively excludes the diagnosis of symptomatic heart failure. However, there is a poor correlation between exercise capacity and resting haemodynamic measures, including ejection fraction.
Haemodynamic assessments of patients with heart failure can give information on a patient’s fluid status. They are usually invasive, and continuous monitoring techniques in ambulatory patients are not routinely available.