Download How do you measure exercise capacity in chronic heart failure?

European Heart Journal (2001) 22, 627–628
doi:10.1053/euhj.2000.2457, available online at http://www.idealibrary.com on
How do you measure exercise capacity in chronic heart
failure?
See page 684 for the article to which this Editorial
refers
In older editions of textbooks of cardiology, chronic
heart failure is described as a condition best treated
by rest, and even as a relative contraindication to
exercise testing. In common with much else we have
been taught about heart failure, such as the adverse
consequences of beta adrenoceptor blockade, these
injunctions turn out to be false. A series of papers has
testified to the potential symptomatic gains to be had
from a programme of exercise training[1]. Exercise
testing, particularly with metabolic gas exchange
measurements, is now part of the routine assessment
of heart failure patients, and has become an important tool for risk stratification and selection of patients
for cardiac transplantation.
Whilst there is now general agreement on the
benefits of exercise for heart failure, there is considerable difference of opinion over which is the most
appropriate exercise test to use. The standard method
is an incremental test with expiratory gas analysis
to derive maximal oxygen consumption, V
~ O2 max,
which represents a rather artificial physiological construct. It should be measured as a plateau of oxygen
consumption, such that an additional load imposed
does not result in a further increase in V
~ O2. In
practice, such a plateau is rarely seen in heart failure
patients, who are unable to sustain this sort of
exercise, and the term peak V
~ O2 is preferred. It is, of
course, a highly artificial kind of test, wholly unrepresentative of daily activities. Different exercise
test protocols elicit different results: cycle exercise
elicits a lower peak V
~ O2 than treadmill[2], as do
rapidly incremental protocols relative to slower.
Despite these weaknesses peak V
~ O2 remains a potent
predictor of outcome[4,5].
Tests more representative of ‘real life’ have become
more widespread. These can take the form of distance
covered in a fixed time, such as the 6 min walk test, or
time at a fixed workload. More indirect tests have
used pedometers to measure activity in the home in
heart failure[6].
Larsen et al.[7] have addressed the issue of the best
way of trying to measure the effects of training on
exercise capacity by comparing the effects of an
exercise training programme on end-points derived
from different exercise tests. Previous investigators
have concentrated on peak V
~ O2 as the main exercise
end-point for assessing the training response, and
most studies have reported an improvement of
around 20%. Larsen et al. used an intensive training
protocol with no strength training component and
found only a modest (and non-significant) increase in
peak V
~ O2. This is slightly unexpected as work performed during the maximal exercise test increased as
a result of training, which should necessitate an
increase in V
~ O2. By contrast, distance covered during
a 6 min walk increased. Interestingly, the total lactate
output during matched endurance exercise tests fell
following training. This finding is consistent with the
idea that a major impact of training is on skeletal
muscle. As muscle function improves, so there is less
reliance on anaerobic metabolism to perform work.
Which is the most appropriate exercise test will
depend upon the context of testing (Table 1). A
protocol used for assessing symptoms need not be the
same as one used for measuring the impact of a new
drug on exercise capacity. Exercise testing in heart
failure has a number of uses: (1) diagnosis; (2) risk
stratification; (3) pathophysiological investigation; (4)
measuring treatment response. Maximal incremental
tests will continue to be used, because of the important information they contain about prognosis, and
because of the additional information they may contain about the presence of ischaemia or arrhythmia.
For pathophysiological investigation, tests need to be
designed for individual studies.
Table 1 Relative value of different forms of exercise testing depending upon the
reason for testing
Maximal tests
Endurance tests
Diagnosis
Prognostication
Pathophysiology
Treatment
response
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2001 The European Society of Cardiology
628
Editorials
These kinds of tests may well be inappropriate for
assessing treatment effect. The work of Larsen et al.
emphasizes the importance of designing exercise
studies targeted at appropriate end-points. From the
perspective of the patients’ symptoms, changes in peak
V
~ O2 are not important, but changes in lactate production may well be; submaximal exercise testing appears
to be a more sensitive indicator of a training effect.
A. L. CLARK
J. G. F. CLELAND
Castle Hill Hospital,
Cottingham, Hull, U.K.
References
[1] Coats AJS, Adamopoulos S, Radaelli A et al. Controlled trial
of physical training in chronic heart failure: exercise performance, hemodynamics, ventilation, and autonomic function.
Circulation 1992; 85: 2119–31.
Eur Heart J, Vol. 22, issue 8, April 2001
[2] Buchfuhrer MJ, Hansen JE, Robinson TE, Sue DY,
Wasserman K, Whipp BJ. Optimizing the exercise protocol
for cardiopulmonary assessment. J Appl Physiol 1983; 55:
1558–64.
[3] Lipkin DP, Canepa-Anson R, Stephens MR, Poole-Wilson PA.
Factors determining symptoms in heart failure: comparison of
fast and slow exercise tests. Br Heart J 1986; 55: 439–45.
[4] Parameshwar J, Keegan J, Sparrow J, Sutton GC, PooleWilson PA. Predictors of prognosis in severe chronic heart
failure. Am Heart J 1992; 123: 421–6.
[5] Cohn JN, Johnson GR, Shabetai R et al. Ejection fraction,
peak exercise consumption, cardiothoracic ratio, ventricular
arrhythmias, and plasma norepinephrine as determinants of
prognosis in heart failure. Circulation 1993; 87 (Suppl VI):
5–16.
[6] Walsh JT, Charlesworth A, Andrews R, Hawkins M, Cowley
AJ. Relation of daily activity levels in patients with chronic
heart failure to long-term prognosis. Am J Cardiol 1997; 79:
1364–9.
[7] Larsen AI, Aarsland T, Kristiansen PT, Haugland A, Dickstein
K. Assessing the effect of exercise training in men with heart
failure; comparison of maximal, submaximal and endurance
exercise protocols. Eur Heart J 2001; 22: 684–92.