Test Identifies Patients With Chest Pain Who Can Be Safely Discharged From ED

Fran Lowry

February 12, 2010

February 12, 2010 — A coronary artery calcium score (CACS) of 0 can identify patients with chest pain who can be safely discharged from the emergency department (ED) without the need for further cardiac testing, according to a prospective observational cohort study published online February 8 in the Annals of Emergency Medicine.

"The optimal strategy for evaluating chest pain in the [ED] remains a dilemma," write Faisal Nabi, MD, from the Methodist DeBakey Heart and Vascular Center, Methodist Hospital, Houston, Texas, and colleagues. "With more than 5 million annual hospital admissions, and at a cost of more than $10 billion, most patients (>60%) are found to have noncardiac chest pain."

CACS is a simple and readily available test for identifying coronary artery disease. The authors write that a CACS of 0 is rarely observed in patients with abnormal stress myocardial perfusion imaging (SPECT) or significant coronary artery disease or acute myocardial infarction.

The aim of this study was to determine whether a CACS of 0 would accurately identify low-risk patients among those with chest pain of unknown cause who could be sent home safely from the ED without needing further cardiac testing.

The study enrolled 1031 of 5066 patients who presented to the ED between September 2005 and February 2008. The enrolled patients all had a normal initial troponin level, nonischemic electrocardiogram, and no history of coronary artery disease. They underwent SPECT and CACS within 24 hours of admission to the ED.

The patients' mean age was 54 years (range, 41 - 67 years).

The investigators report that 61% of the patients in the study had a CACS of 0. The frequency of an abnormal SPECT ranged from 0.8% in patients with a CACS of 0 to 17% in patients with a CACS greater than 400.

Acute coronary syndrome events occurred in 28 patients during the index hospitalization and in 4 patients a mean of 7.4 months (range, 4.1 - 10.7 months) after hospital discharge.

Only 2 events occurred in 625 patients with a CACS of 0 (0.3%; 95% confidence interval [CI], 0.04% - 1.1%). In comparison, 30 events occurred in 406 patients with a CACS greater than 0 (7.4%; 95% CI, 5.0% - 10.4%).

The 2 patients with a CACS of 0 and a cardiac event both had abnormal troponin levels on their index admission (peak, 1.52 and 2.34 ng/dL, respectively), but had normal serial electrocardiogram and SPECT results. One patient, a 32-year-old man, had acute gastritis on upper endoscopy as a possible cause for his chest pain; the other, a 52-year-old woman, had chest pain that resolved spontaneously. Both were discharged and reported no cardiac events at 6-month follow-up, the study authors report.

In noting their study's limitations, the authors remind readers that it is a single-center study and that the results may not be applicable to the general population; in addition, the study population was at relatively low risk for acute coronary syndrome, which resulted in a very high negative predictive value for both a normal CACS and SPECT.

The authors also noted that a strict definition of acute coronary syndrome based on angiographic evidence of coronary artery disease was used in patients who did not meet criteria for myocardial infarction, but because all patients did not receive angiography, this could have biased the results. So could the fact that physicians were not blinded to the CACS results.

A final concern is that a CACS of 0 will miss noncalcified plaque that could result in acute coronary syndrome, the authors point out.

"There is a clear national mandate to improve health care utilization and reduce soaring costs," they write in their discussion and suggest that use of this simple, inexpensive test could save the healthcare system a considerable amount of money.

"A majority of patients with acute chest pain of uncertain cardiac cause have a CACS of 0, which predicts both a normal stress SPECT result and an excellent short-term outcome," the authors conclude. "If such a simple and straightforward testing strategy were widely adopted, it would streamline ED patient evaluation and might significantly reduce health care costs."

This is "a well-done study that makes an important observation," William Follansbee, MD, the master clinician professor of cardiovascular medicine and director of nuclear cardiology at the University of Pittsburgh Medical Center, Pennsylvania, commented to Medscape Emergency Medicine.

But a caveat is that a CACS of 0 implies that there is no significant atherosclerosis, but some patients in this category do have acute myocardial infarction when a minor plaque ruptures and sets off a cascade of events that result in a blocked artery. "A calcium score of zero does identify a population at very low risk, but not zero risk," he said.

The study excluded the higher-risk patients and ended up enrolling only about 20% of the patients who came to their ED, Dr. Follansbee pointed out. "Eighty percent of the patients who came in did not fit the criteria for the study. It is important when people apply these data to realize that you're applying it to that 20%, low-risk group, and not to everybody who comes in with chest pain. These results should not be generalized to all the patients who come in with chest pain."

He agrees with the study authors' assertions about the high cost of chest pain care and that the CACS might be of value in this setting.

"The point about the cost of chest pain care is quite legitimate, so even if you take 10% of the people who come in to the [ED] and do a simple test up front, you can identify them as low risk and send them home, and that still has some value and would then translate into some savings in healthcare dollars," Dr. Follansbee said. "But a lot of patients with chest pain do have some calcium in their arteries, and then the CACS is not going to be a useful marker."

The study was supported in part by a grant from the Methodist Hospital Foundation. The study authors have reported no other relevant financial relationships. Dr. Follansbee has reported no relevant financial relationships.

Ann Emerg Med. Published online February 8, 2010.

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