Protocol May ID Low-Risk Chest Pain

ACEP News
May 2011

Protocol May ID Low-Risk Chest Pain 

COMMENTARY 'Acceptable Miss Rate' a Vexing Question for Emergency Physicians The authors of this paper report the use of an accelerated diagnostic protocol (ADP) in the ED evaluation of patients with chest pain. They suggest that their version of an ADP can identify patients at low risk of a major adverse cardiac event (MACE).

As always when considering such an approach, we want to know about sensitivity and specificity. The reported specificity tells us that about 1 in 10 patients thus evaluated would be identified as safe for discharge from the ED after 2 hours. The sensitivity (with attention to the lower limit of the 95% confidence interval), however, suggests a 2% "miss rate." So the salient question appears to be whether it is worth it to discharge 10% of these patients identified as being at very low risk for MACE when 2% of the discharged patients have been so identified incorrectly. The question of acceptable miss rate is one that has vexed emergency physicians in so many clinical contexts for so long, and we are probably not getting any closer to a definitive answer. Tort reform, anyone?

Then there is the trouble we discover when we take even a cursory look at the methods. For example: just how reliable is telephone follow-up for identifying patients with MACE? Yes, that is a rhetorical question.

Finally, while we must not dismiss this study out of hand just because the authors had highly relevant industry ties, their assertion that the sponsors had no role in the study or the report is sure to raise the skeptic's eyebrow. More disturbing, however, is that The Lancet was apparently unable to find someone without highly relevant industry ties to write an editorial comment.

 

DR. ROBERT C. SOLOMON is medical editor of ACEP News.

BY JENNIE SMITH 

Elsevier Global Medical News

 

A new, faster screening protocol can identify patients at a very low risk of cardiovascular events when they present to the emergency department with chest pain, allowing them to be safely discharged in 2 hours instead of the usual 6 or more, a New Zealand-based team of researchers has found.

The "accelerated diagnostic protocol," or ADP, evaluated in the study consists of three widely available measures: a patient's thrombolysis in myocardial infarction, or TIMI, score; an electrocardiograph; and a biomarker panel of troponin, creatine kinase MB, and myoglobin. The current standard of care consists of serial sampling of cardiac troponin over 6 hours from the onset of symptoms.

The researchers, led by Dr. Martin Than of Christchurch Hospital, studied the protocol in the Asia-Pacific Evaluation of Chest Pain Trial (ASPECT), which included 3,582 consecutive patients who presented with chest pain suggestive of acute coronary syndromes at hospitals in nine countries in the Asia-Pacific region. All patients were followed for a month. Participants were mostly older, men, and either white or Chinese, the investigators wrote (Lancet 2011 March 23 [doi:10.1016/ S01406736(11)603103]).

Just under a tenth (352) of subjects qualified for early discharge under the protocol. This meant that they had a TIMI risk score of 0 (out of 7), no ischemic ECG changes, and normal point of care triplemarker panels at presentation and 2 hours later.

The study's primary end point was a major adverse cardiac event within the 30 days of follow-up, including death that was not clearly noncardiac, MI, cardiogenic shock, and arrhythmia or atrioventricular block requiring intervention. A major adverse cardiac event occurred in three (0.9%) of the ADP-screened patients, Dr. Than and colleagues reported, giving the protocol a sensitivity of 99.3% (95% confidence interval, 97.9%-99.8%) and a specificity of 11%.

"The near 10% possible reduction in patients needing prolonged assessment in this large patient group could reduce overcrowding in hospitals and emergency departments and provide earlier reassurance and greater convenience for patients," Dr. Than and colleagues wrote.

They acknowledged as among the trial's weaknesses its observational design and the protocol's low specificity, which they described as commensurate with that of other diagnostic instruments to exclude acute coronary syndromes.

They also pointed out that "patients without chest pain but who presented with atypical symptoms (fatigue, nausea, vomiting, diaphoresis, faintness, and back pain) were not included in this trial," and that the researchers could not tell how many presented with those symptoms. "Thus," they wrote, "the applicability of the ADP is limited to the selected cohort of patients with chest pain (or discomfort) suggestive of acute coronary syndromes for whom the attending physician planned to investigate for these syndromes."

In an editorial comment (Lancet 2011 March 23 [doi:10.1016/S01406736(11)603929]) accompanying Dr. Than and colleagues' article, Dr. Richard Body of the Cardiovascular Research Group at the University of Manchester (England), noted that "the need for an effective rapid ruleout strategy to facilitate early discharge from the emergency department has been appreciated for over 20 years," and yet none has been widely adopted.

Dr. Body praised Dr. Than and colleagues' study as "well designed to achieve its objectives," and showing "that it is possible to achieve an acceptably high sensitivity when triplemarker testing is used in the appropriate population."

However, he cautioned, the triple-marker testing alone had a sensitivity of only 82.9%. The overall sensitivity of the protocol "increased to an acceptable level because of the application of Bayesian principles, with biomarker testing only in patients with a low pretest probability of disease."

Dr. Than and several coauthors disclosed receiving grants, supplies, speaking honoraria, and/or travel expenses from Alere Medical, a maker of diagnostic tests and equipment and the major funding source of the study. Investigators in some countries received country-specific funding from other companies. The sponsors had no role in the study or the report, the authors declared. Dr. Body disclosed past donations of supplies from diagnostics firms owned by Roche, Siemens, and Alere, and travel reimbursements from Roche and Randox.

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