Objective To assess the clinical efficacy and accuracy of an emergency department based six hour rule-out protocol for myocardial damage. Design Diagnostic cohort study. Setting Emergency department of an inner city university hospital. Participants 383 consecutive patients aged over 25 years with chest pain of less than 12 hours' duration who were at low to moderate risk of acute myocardial infarction. Intervention Serial measurements of creatine kinase MB mass and continuous ST segment monitoring for six hours with 12 leads. Main outcome measure Performance of the diagnostic test against a gold standard consisting of either a 48 hour measurement of troponin T concentration or screening for myocardial infarction according to the World Health Organization's criteria. Results Outcome of the gold standard test was available for 292 patients. On the diagnostic test for the protocol, 53 patients had positive results and 239 patients had negative results. There were 18 false positive results and one false negative result. Sensitivity was 97.2% (95% confidence interval 95.0% to 99.0%), specificity 93.0% (90.0% to 96.0%), the negative predictive value 99.6%, and the positive predictive value 66.0%. The positive likelihood ratio was 13.9 and the negative likelihood ratio 0.03. Conclusions The six hour rule-out protocol for myocardial infarction is accurate and efficacious. It can be used in patients presenting to emergency departments with chest pain indicating a low to moderate risk of myocardial infarction.

Chest pain accounts for 2%-4% of all new attendances at emergency departments (ED) in the United Kingdom.1 2 Chest pain can be the presenting complaint in a myriad of disorders ranging from life threats such as acute myocardial infarction (AMI) to mild self limiting disorders such as muscle strain. Possible cardac chest pain can be viewed as a continuum, ranging from total global AMI to simple short lived angina. Within this spectrum lie the acute coronary syndromes with critical cardiac ischaemia and minimal myocardial damage.Nationally over 129 000 deaths a year are attributable to ischaemic heart disease.3 AMI case mortality is currently 45% with over 70% of these dying before they reach medical care. 4 One in eight patients with unstable angina will infarct within two weeks without appropriate treatment. In the UK around 30% of patients with chest pain are admitted and 70% discharged from the ED 1 while in the United States 60% are admitted and 40% discharged. 4 Despite such high admission rates 3%-4% of AMI are inadvertently discharged from US EDs. In the UK significantly fewer patients are admitted; while the number of missed AMIs is unknown, recent evidence suggests that some 6% of patients discharged from EDs may have prognostically significant myocardial damage.

A short cut review was carried out to establish whether there was any evidence to decide between oral or intravenous antidote in paracetamol (acetaminophen) poisoning. Altogether 330 papers were found using the reported search, of which two presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated. Clinical scenarioA 23 year old woman attends an emergency department having taken sixty 500 mg paracetamol tablets. Her four hour paracetamol levels are above the treatment line. She does not want to be treated with intravenous therapy. You wonder whether oral antidote is as effective. Search outcomeAltogether 330 papers were identified, of which two were directly relevant to the question (table 1). Comment(s)Perry's study used historical controls although the demographic characteristics of the two groups were remarkably similar. It was not included in Buckley's meta-analysis because the patients were not recruited sequentially and it was unclear whether the patients were treated solely at the study centre (possible variations in other treatment modalities could act as confounding factors).There have been no RCTs in this area. A meta-analysis of observational studies has failed to show a difference in efficacy between the oral and intravenous routes. However, these studies do not address other factors that may influence the choice of route, which include: activated charcoal adsorbs antidote and therefore precludes its use; the IV regimen is shorter than the oral (24 hours and 52 hours respectively); the IV route is safer with patients with altered levels of consciousness (for example due to coingestants) who may subsequently lose their airway protective reflexes.c CLINICAL BOTTOM LINE The IV route is the treatment of choice for paracetamol poisoning, but the oral route has a similar efficacy and is a suitable alternative if IV access is difficult (for example IV drug abusers) or refused by the patient. Best evidence topic reports (BETs) summarise the evidence pertaining to particular clinical questions. They are not systematic reviews, but rather contain the best (highest level) evidence that can be practically obtained by busy practising clinicians. The search strategies used to find the best evidence are reported in detail in order to allow clinicians to update searches whenever necessary. The BETs published below were first reported at the Critical Appraisal Journal Club at the Manchester Royal Infirmary. 1 Each BET has been constructed in the four stages that have been described elsewhere.2 The BETs shown here together with those published previously and those currently under construction can be seen at http://www.bestbets.org.3 Six BETs are included in this issue of the journal.

A short cut review was carried out to establish whether there was any evidence to decide between oral or intravenous antidote in paracetamol (acetaminophen) poisoning. Altogether 330 papers were found using the reported search, of which two presented the best evidence to answer the clinical question. The author, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of these best papers are tabulated. A clinical bottom line is stated. Clinical scenarioA 23 year old woman attends an emergency department having taken sixty 500 mg paracetamol tablets. Her four hour paracetamol levels are above the treatment line. She does not want to be treated with intravenous therapy. You wonder whether oral antidote is as effective. Search outcomeAltogether 330 papers were identified, of which two were directly relevant to the question (table 1). Comment(s)Perry's study used historical controls although the demographic characteristics of the two groups were remarkably similar. It was not included in Buckley's meta-analysis because the patients were not recruited sequentially and it was unclear whether the patients were treated solely at the study centre (possible variations in other treatment modalities could act as confounding factors).There have been no RCTs in this area. A meta-analysis of observational studies has failed to show a difference in efficacy between the oral and intravenous routes. However, these studies do not address other factors that may influence the choice of route, which include: activated charcoal adsorbs antidote and therefore precludes its use; the IV regimen is shorter than the oral (24 hours and 52 hours respectively); the IV route is safer with patients with altered levels of consciousness (for example due to coingestants) who may subsequently lose their airway protective reflexes.c CLINICAL BOTTOM LINE The IV route is the treatment of choice for paracetamol poisoning, but the oral route has a similar efficacy and is a suitable alternative if IV access is difficult (for example IV drug abusers) or refused by the patient. Best evidence topic reports (BETs) summarise the evidence pertaining to particular clinical questions. They are not systematic reviews, but rather contain the best (highest level) evidence that can be practically obtained by busy practising clinicians. The search strategies used to find the best evidence are reported in detail in order to allow clinicians to update searches whenever necessary. The BETs published below were first reported at the Critical Appraisal Journal Club at the Manchester Royal Infirmary. 1 Each BET has been constructed in the four stages that have been described elsewhere.2 The BETs shown here together with those published previously and those currently under construction can be seen at http://www.bestbets.org.3 Six BETs are included in this issue of the journal.

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