Rapid Responses to:
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Rapid Responses: Rapid Responses published:
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The sensitivity and specificity of exercise ECG for significant CAD
- Kevin Barraclough (16 November 2008)
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Re: The sensitivity and specificity of exercise ECG for significant CAD
- GH Hall (18 November 2008)
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Typo?
- Mayer Brezis (28 November 2008)
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Exercise ECGs - any silver linings?
- Mark N Upton (29 November 2008)
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angina and excercise teseting
- Henk de Vries, Neha Sekhri (29 November 2008)
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Who Should Run Rapid Access Chest Pain Clinics?
- Daniel M Sado (5 December 2008)
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Gender analysis required for prognostic value of the exercise electrocardiogram in the initial assessment of patients with suspected angina
- Margaret CP Rees, Karin Schenck-Gustafsson, Professor of Cardiology, Centre of Gender Related Medicine, Karolinska Institute, SE-171 77 Stockholm, Sweden. (5 December 2008)
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Changes following an exercise test
- G J Forbes (9 December 2008)
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Diagnosis and prognosis
- fabrizio Turrini (23 December 2008)
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Kevin Barraclough, general practitioner Painswick GL6 6TY
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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 |
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GH Hall, Retired physician EX1 2HW
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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 |
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Mayer Brezis, Professor of Medicine Hadassah University Hospital
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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 |
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Mark N Upton, General Practitioner Woodlands Family Medical Centre, 106 Yarm Lane, Stockton, TS18 1YE
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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 |
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Henk de Vries, locum gp HU10 7DS, Neha Sekhri
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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 |
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Daniel M Sado, SpR in Cardiology Dorset County Hospital, DT1 2JY
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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 |
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Margaret CP Rees, Reader in Reproductive Medicine, University of Oxford Nuffield Dept Obstet Gynaecol, John Radcliffe Hospital, Oxford OX3 9DU, Karin Schenck-Gustafsson, Professor of Cardiology, Centre of Gender Related Medicine, Karolinska Institute, SE-171 77 Stockholm, Sweden.
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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 |
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G J Forbes, GP Leadagte Surgery, Leadgate, Consett, Co Durham, DH8 6DP
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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 |
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fabrizio Turrini, Hospitalist MEDICINA CARDIOVASCOLARE - NUOVO OSPEDALE DI BAGGIOVARA (MODENA) 41100 Modena (ITALY)
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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:
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 |
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