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Department of Neurology Neurosciences Centre, and Clinical Epidemiology Unit, All India Institute of Medical Sciences, New Delhi Delhi, India
Abstract
A 55-year-old man presents to the emergency department with history of chest pain of 4-h duration. You are called to see the patient in the emergency room.
Clinical Scenario
A 55-year-old man presents to the emergency department with history of chest pain of 4-h duration. You are called to see the patient in the emergency room.
The patient was diagnosed to have hypertension (on routine examinations) 5 years ago. On evaluation (then and subsequently), he has been found to be free of other risk factors for atherosclerotic vascular disease. He was advised salt restriction and ramipril 5 mg OD, with which his BP recorded periodically has been around 135/85 mmHg. He has been well except occasional burning epigastrium, which responds to antacids.
Today in the evening after returning from work, he complained of vague pain over the left side of chest. He initially attributed this to hyperacidity and took two Tsfs. of antacid gel. The pain did not respond, rather it slightly increased over the last 1 h, and he decided to come to the emergency.
On direct questioning, there is no radiation of the pain to the left arm and no associated sweating, vomiting or palpitation. The pain has a burning quality, but he also feels a sense of heaviness over the left parasternal region.
On examination, his pulse rate is 80/min and regular, BP 145/90 mmHg, RR 20/min. and afebrile. Systemic examination is normal. 12-lead ECG is also normal. You admit him to your chest pain assessment unit. You order continuous 12-lead ECG ST segment monitoring and serial measurements of CK-MB mass.
Patient’s wife asks: ‘What is wrong with him, doctor? Has he got “heart attack”?’ You told her that the probability of ‘heart attack’ is low, but you want to observe him for 6 h before deciding whether to admit him to the hospital or send him home.
You wondered whether you can rule out acute MI after 6 h. You conducted a MEDLINE search and found a recent article: ‘Is it possible to exclude a diagnosis of myocardial damage within 6 h of admission to an emergency department?’ Diagnostic cohort study by Herren et al. You decided to read this paper.
Example of Answers to Critical Appraisal of a Diagnosis Paper
Reference: Herren KR, Mackway-Jones K, Richards CR, et al. Is it possible to exclude a diagnosis of myocardial damage within six hours of admission to an emergency department? Diagnostic cohort study. BMJ. 2001;323(7309):372.
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Guide
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Comments
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Are the results of the study valid?
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Did the clinicians face diagnostic uncertainty?
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Yes, the physicians at the chest pain assessment unit were uncertain about having ruled out MI. They wanted to know whether it is safe to discharge after a 6-h rule out protocol
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Was there blind comparison with an independent gold standard?
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About the ‘gold standard’: Yes, the gold standard for comparison was troponin T test at 48 h. One can ask whether this is an acceptable gold standard. Does it diagnose the condition(s) of concern with sufficient (ideally 100 %) accuracy? What is the condition of concern? In the emergency room, one is concerned about controlling pain and not missing a cardiac condition, which results in cardiac failure or cardiac arrhythmia. Some might argue that the authors should have taken clinically relevant cardiac arrhythmia/failure or sudden cardiac death as the gold standard. Others might consider it adequate because negative troponin test at 48 h. is widely accepted to rule out acute MI which is the major concern in emergency admission
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About the ‘blind comparison’: We don’t know. Authors do not mention whether the laboratory personnel reporting troponin T concentration were unaware of the protocol test results and of the patients’ admission/discharge status
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Did the results of the test being evaluated influence the decision to perform the gold standard?
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No, the decision to perform the gold standard was independent of the protocol test results. But 76 patients could not be subjected to the ‘gold standard test’. Authors could trace 61 of these patients 4 weeks or more after discharge. All were apparently free of MI, suggesting that the negative protocol test result was correct. To assure the readers that these patients were not systematically different (more prone to MI) from the analysed sample, authors state that they had the same risk profile for MI and the same sex ratio as the patients with a gold standard. In fact, they were more likely to be aged less than 40 years and hence less likely candidates for MI. Still, there is no information about 15 patients. Does the lack of data on gold standard on the 15 patients invalidate the results? We can test this by doing a sensitivity analysis. Assuming they were all protocol test negative but gold standard positive (worst-case scenario), we can recalculate the likelihood ratios (They turn out to be LR +11, LR −0.34)
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What are the results?
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What likelihood ratios are associated with the range of possible test results?
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LR for positive test result is 13.9, and LR for negative test result is 0.03. Presenting the results at three or more levels would have been more informative
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How can I apply the results to patient care?
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Will the reproducibility of the test result and its interpretation be satisfactory in my setting?
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Standard test kit for CPK-MB is available. Authors give description and source of the assay they used. The description and source of the monitor for ST segment monitoring is also given. Both sources appear reliable. It may be desirable to have a quality control programme for the laboratory. Calibration and consistency checks should be run for both the tests on periodic basis
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Are the results applicable to my patient?
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