Incremental prognostic value of the exercise electrocardiogram in the initial assessment of patients with suspected angina: cohort study
BMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a2240 (Published 14 November 2008) Cite this as: BMJ 2008;337:a2240All rapid responses
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Upton points out that patients with a positive exercise test might be
given different treatment to those with a negative test. Similarly, a
positive test result might lead to different lifestyle advice from health
care professionals and provide increased motivation for the patient to
make positive lifestlye changes. It is also more likely to lead to the
patient being included in general practice disease registers leading to 6-
12 monthly recall and review. Along with probable differences in
secondary preventative medication, these differences might serve to reduce
the ability of this study to detect additional predictive power of
exercise testing over and above the clinical history.
One other point. Why did a very large proportion of the study cohort not
have exercise testing? If this was simply due to an inability or
contraindication to perform the test we should not expect this to effect
the conclusions of the study. However, if there were other reasons e.g.
the clinician thought the risk of coronary disease so low exercise testing
was not warranted, the overall results might be affected.
Competing interests:
None declared
Competing interests: No competing interests
We are concerned that the authors of this large cohort have not
presented gender differences in the value exercise electrocardiogram in
the initial assessment of patients with suspected angina [1]. Even the
number of men and women is not specified. Currently exercise
electrocardiogram is thought to be of less value in women than in men
[2,3,4,5,6]. We suggest that the authors re-examine their data and present
gender specific information which would be of great clinical interest.
References
1. Sekhri N, Feder GS, Junghans C, Eldridge S, Umaipalan A, Madhu R,
Hemingway H, Timmis AD. Incremental prognostic value of the exercise electrocardiogram in the
initial assessment of patients with suspected angina: cohort study BMJ
2008; 337: a2240
2. Okin PM, Kligfield P. Gender-specific criteria and performance of the
exercise electrocardiogram. Circulation. 1995; 92: 1209-1216.
3.Miller TD, Roger VL, Milavetz JJ, Hopfenspirger MR, Milavetz DL, Hodge
DO, Gibbons RJ. Assessment of the exercise electrocardiogram in women
versus men using tomographic myocardial perfusion imaging as the reference
standard. Am J Cardiol 2001;87:868-73.
4. Al-Khalili F, Wamala SP. Orth-Gomér K, Schenck-Gustafsson K Prognostic
value of exercise testing in women after acute coronary syndromes. Am J
Cardiol 2000,:86:211-3
5. Al-Khalili F, Svane B, Wamala SP, Orth-Gomér K, Rydén L. Schenck-
Gustafsson K Clinical importance of riskfactors and exercise testing for
prediction of significant coronary artery stenosis in women recovering
from unstable
coronary artery disease:the Stockholm Female Coronary Risk Study, Am
Heart J 2000 June;139(6):971-8
6. Al-Khalili F, Janzsky I, Andersson A, Svane B, Schenck-Gustafsson K.
Physical activity and exercise performance predict long-term prognosis
in middle-aged women surviving acute coronary syndrome, J Intern Med.
2007;261:178-187.
Competing interests:
None declared
Competing interests: No competing interests
I read the Sekhri et al study with interest along with the responses
above.
The message from this work is very clear; the crucial part of a Rapid
Access Chest Pain Clinic (RACPC) consultation is taking a good history to
elicit the nature of the symptoms and the risk factors for coronary artery
disease. An exercise test is an adjuct to this, however the clinician
should have made up their mind about the diagnosis and subsequent
management in many cases prior to performing this test.
RACPC pose a major problem to many UK NHS Hospitals as there is a
government directive that all patients referred must be seen within 2
weeks of the referral being made or else the hospital risk a monitory
fine. The logistics of this can be complicated, particularly if the
service is run by junior doctors who have varying other commitments such
as study days and on call shifts.
As a result of these problems with junior doctors an increasing
number of hospitals are aiming to make RACPC completely nurse led. It
seems to be felt that teaching a nurse to interpret an exercise test is
very feasible and once they can do this, they should be able to run the
clinic.
The Sekri et al study shows the potential problems with this
attitude. The clinical part of the consultation is far more important than
the exercise test. Taking is a good history is a challenging skill that is
often not easy for junior doctors who are likely to have more training and
more experience in this regard than a Nurse Practitioner (NP).
Furthermore, NP training in clinical examination is very limited in that
they are taught and tested on going through the motions of doing this, but
are not examined to know how to identify pathology. In the case of RACPC,
the issue here would be in identifying patients with significant valvular
disease, who may be unsafe to perform an exercise tolerance test on.
Lastly, decision making in RACPC is often not easy and hence asking
an NP, who may have little experience in complicated out patient
management decisions may not be appropriate. Some NPs I have worked with
in RACPC have also not done their nurse prescribing course which also
leads to problems. How can they decide what medication is appropriate for
the patient in such a scenario? Furthermore, it seems ridiculous to assess
a patient so quickly, but not be able to provide them with treatment on
the same day.
In summary, RACPC are complicated to run. I find this clinic far more
challenging than any other out patient work that I am involved with.
Asking NPs to do this task is likely to be inappropriate in many cases and
hence may result in sub optimal care being provided.
Competing interests:
None declared
Competing interests: No competing interests
Angina is and remains a clinical diagnosis and this article obviously
confirms this. It is quite possible to do a PTCA and a CABG prodecure on
somebody with angiographically demonstrated laesions. That does not mean
that these symptoms necessarily relate to the angiographic findings and to
a improved result and I have seen patients who clearly have not benfitted
from the procedure for that reason. We should bear in mind that PTCA or
CABG are in essence palliative procedures after failed medical treatment.
We do find co-incidently patients with proximal disease and they
retrospectively have an improved survival prognosis. However we do not
routinely screen for this. The message therefore remains: angina is a
clinical diagnosis based on history and physical examination with
sometimes help from an excercise stress test and ECG. The treatment we
offer is palliative in all cases with prognostic survival benefits in a
subgroup, we can only identify retrospectively.
Competing interests:
None declared
Competing interests: No competing interests
I congratulate Neha Sekhri and colleagues on their well argued
manuscript about the paucity of incremental prognostic value of an
exercise ECG. It’s also good to see such a fine contribution from two
medical student co-authors so early in their careers. What depressing
reading! If we look for silver linings, one is the affirmation of the
importance of careful history taking in the assessment of patients who
have chest pain. I doubt that there are many others, however, please would
the authors address the following concerns:
1. An exercise test results in a decision being made about treatment.
The authors censored follow-up at revascularisation for those undergoing
CABG or PTCA because these procedures may affect prognosis. What about the
effect of newly added medication on prognosis? Following an exercise test,
we might expect that differential prescribing of medication will to some
extent flatten prognostic differences between low, medium and high risk
groups. Might this result in a conservative estimate of incremental
prognostic value?
2. Whatever the statistical advantages of a global assessment of
prognostic value using a comparison of C statistics, one is left with a
nagging doubt that this is not completely relevant to decision making in
the clinic. To some extent the authors addressed this concern by also
comparing C statistics in the sub-group of patients at intermediate risk.
The authors then used data in table 5 to argue that the 5 to 6% difference
in C statistic had trivial clinical implications. However table 5 reflects
a global assessment. To convince us of the lack of clinical utility in
those at intermediate risk, please could the authors estimate the
cumulative probability of events in those at intermediate risk who went on
to have negative and positive exercise test results.
3. Finally, might exercise testing have a different clinical utility
in (a) patients with and without diabetes (b) patients with and without a
typical angina history? Formally, was there any evidence of statistical
interaction in the Cox model?
Competing interests:
None declared
Competing interests: No competing interests
I gave this interesting and timely article as a reading exercise to
my medical students in a introductory course to EBM. They asked about
Figure 2, lower left inset: "how come the average AUC is 0.71, if the
95%CI is 0.72 to 076"?
Thank you in advance for helping me answer them.
Competing interests:
None declared
Competing interests: No competing interests
Behind all this is the problem of the "Gold Standard."
Angiographically demonstrated coronary artery disease is common and we
don't know which of the "positives" will develop or die of it. Are there
any long term follow ups- with a decent control group, of course!
Competing interests:
None declared
Competing interests: No competing interests
This large cohort study suggests that, in a cohort of patients
considered (and proven) to be at high risk of angina, the exercise ECG
only had a sensitivity of 53% for identifying those who would have an
acute coronary event in the next 2.5 years. At first sight this seems
quite low.
The American Heart Association guidelines on exercise ECG testing quote
sensitivity and specificity levels of 68% and 77% for detecting
significant coronary disease at angiography. This figure is based on a
meta-analysis of 24,000 patients. However, the problem with the meta-
analysis figures is that, in most of the studies, not all the patients had
angiography. Far more patients with positive exercise ECG results have
angiography than those with negative results. This artificially elevates
the sensitivity and depresses the specificity.
When the gold standard is significant coronary disease at angiography it
is clearly necessary for all patients to have both exercise ECG and
angiography. When Froelicher et al did this for 814 patients they found
that the exercise ECG had a lower sensitity than previously found (only
45%) but a higher specificity (85%). This is more consistent with the
findings of the authors in this study.
The message seems to be that the exercise ECG is less sensitive than we
normally think but is more specific. A positive exercise ECG in a
symptomatic patient is unlikely to be a false positive but the exercise
ECG can be negative in nearly half of patients with significant disease.
Froelicher VF, Lehmann KG, Thomas R, Goldman S, Morrison D, Edson R
et al. The Electrocardiographic Exercise Test in a Population with Reduced
Workup Bias: Diagnostic Performance, Computerized Interpretation, and
Multivariable Prediction. Ann Intern Med 1998;128:965-74.
Competing interests:
None declared
Competing interests: No competing interests
Diagnosis and prognosis
In this interesting study by Sekhry et al. prognosis capability of
exercise testing is explored and not its diagnostic power, which is not
excellent. The final result is that most of the prognostic informations
are provided by simple clinical parameters.
The statistical analysis is applied to the whole cohort population with
“suspected angina”.
In my opinion this seems quite challenging because clinical and
instrumental evaluation, splits this population into two groups of
patients: those with a diagnosis of angina and those without.
This should imply a different prognosis by itself!
Authors ask a prognostic estimation from a test that can modify treatment
and …prognosis.
Patients with a diagnosis of angina receive treatments (medications and
revascularizations procedures) that modify prognosis. Patients undergoing
percutaneous procedures and by pass surgery were censored, but they were
only 6 % of the whole cohort (versus 29% of patients with angina
diagnosis). Medical therapy should modify prognosis (i). Statistical
analysis do not take in account the impact of medical therapy (most of
patient with angina should receive aspirin, statin, beta blocker...) on
prognosis(i).
In the light of poor diagnostic power of exercise testing, I think that
two important questions raising from daily practice should be:
1)What is the prognosis of patients without a diagnosis of angina? Is
there anyone of them that necessitate of deeper investigations? (ii)
2)What is the prognosis of patients on medical therapy? Is there anyone of
them that may have benefit from different treatment or attention?
Estimating prognosis should provide accurate answer to patient’s questions
regarding the probable outcome of their illness (if any) and should
identify those patients in whom interventions might improve outcome (iii).
I think that this brilliant study should include a statistical analysis
applied to those subgroups of patients (sample size should be adequate…).
I agree also that gender analysis is due.
i) T . Fraker Jr , S . Fihn. 2007 Chronic Angina Focused Update of
the ACC/AHA 2002 Guidelines for the Management of Patients With Chronic
Stable AnginaA Report of the American College of Cardiology/American Heart
Association Task Force on Practice Guidelines Writing Group to Develop the
Focused Update of the 2002 Guidelines for the Management of Patients With
Chronic Stable Angina . Journal of the American College of Cardiology
, Volume 50 , Issue 23 , Pages 2264 – 2274
ii) J Sanchis, V Bodí, Á Llácer, J Núñez, L Consuegra, M J Bosch, V
Bertomeu, V Ruiz, and F J Chorro. Risk stratification of patients with
acute chest pain and normal troponin concentrations Heart, Aug 2005; 91:
1013 – 1018
iii) F Froelicher, JN Myers. Manual of exercise testing. Mosby
Elsevier 2007; page 175
Competing interests:
None declared
Competing interests: No competing interests