Coronary artery calcium score (CACS) is a simple, non-invasive measure for identifying coronary artery diseases (CAD). A recent prospective observational cohort study reports that zero CACS in patients presenting to the emergency department (ED) with chest pain, may be sent home safely without any additional cardiac testing. The findings of the study are published in the recent issue of the Annals of Emergency Medicine.

In order to assess the prognostic value of zero CACS, Faisal Nabi, Cardiologist, Methodist DeBakey Heart & Vascular Center, The Methodist Hospital in Houston, and colleagues, examined stable patients at the ED with complaints of chest pain of uncertain cardiac etiology. Stress myocardial perfusion single-photon emission computed tomography (SPECT) imaging and CACS were performed within 24 hours of admission in patients with nonischemic ECG, normal initial troponin values, and no coronary artery disease history. Any acute coronary syndrome at the index hospitalization or during follow up was considered an adverse cardiac event. The SPECT findings and cardiac events were used to assess CACS values.

The team observed that 1,031 patients (mean ± SD; 54±13 years) who participated in the study demonstrated a median CACS of zero (61%). The incidence of an abnormal SPECT finding ranged between 0.8% for zero CACS and 17% for CACS>400. Cardiac events were noted in 32 patients at the time of:
• index visit (n=28)
• 7.4±3.3 months following hospital discharge (n=4)

The study reported only two cardiovascular events (0.3%; 95% CI=0.04-1.1%) in 625 patients having a zero CACS. Two (6%; 95% CI=0.8-21%) out of 32 cardiac-event patients had zero CACS. The two patients had elevated troponin levels during their index hospital stay, and later demonstrated normal SPECT findings and serial ECG, without experiencing any adverse cardiac events during their 6-month follow-up. Based on the study findings, the researchers recommended that it may be safe to discharge patients with zero CACS, which successfully determines superior short-term outcome and a normal SPECT.

Earlier, Methodist Hospital researchers (Journal of the American College of Cardiology, 2009) explored the correlation between CACS and SPECT values in identifying patients with short- and long-term cardiac risks. The investigators followed up 1,126 asymptomatic individuals without any history of cardiovascular diseases for 6.9 median years. CACS and stress SPECT imaging were conducted within a close time period (median=56 days), and primary end points of composite cardiac events and all-cause death, or myocardial infarction were noted.

It was observed that an increase in the CACS from <1% (CACS ≤10) to 29% (CACS >400) was associated with an increase in the abnormal SPECT result. An increase in the rate of primary end points was also noted with abnormal SPECT scans and increasing CACS. The study results suggested that the CACS and SPECT tests provide independent and complementary prediction of cardiac events, both short and long term. Because a very high CACS can predict cardiac risk, despite a normal SPECT, the study substantiates the importance of conducting CACS in subjects at intermediate or high CAD risk, in order to identify all those with high long-term risk for developing major cardiac events.

Another study conducted by Cademartiri et al (European Radiology, 2009) reported that, relying on CACS was inadequate for the recognition of non-obstructive/obstructive CAD in asymptomatic high-risk population, when compared to computed tomography coronary angiography (CTCA). The study involved the assessment of 213 consecutive asymptomatic individuals demonstrating unfeasible or inconclusive stress test results, having over one risk factor, who were subjected to outpatient CACS and CTCA. CTCA was able to diagnose 65% prevalence of all CAD, while CACS could reveal only about 37%. Furthermore, the researchers found that CTCA provided a high diagnostic accuracy in detecting CAD.

According to the Centers for Disease Control and Prevention (CDC), coronary artery diseases constitute the most common form of heart diseases in the United States. It is estimated that an American will experience a coronary event roughly at every 25 seconds, with the death of one person at least every minute.

There exists increasing prognostic evidence to support the use of CACS measurement in CAD risk stratification of asymptomatic subjects. The current findings, emphasizing the clinical significance of zero CACS as a screening test, require broader evaluation to confirm its usefulness in medical decision making for the management of cardiovascular risk factors.

References

1. Nabi F, Chang SM, Pratt CM, et al. Coronary Artery Calcium Scoring in the Emergency Department: Identifying Which Patients With Chest Pain Can Be Safely Discharged Home. Ann Emerg Med. 2010 Feb 5. [Epub ahead of print]

2. Chang SM, Nabi F, Xu J, et al. The coronary artery calcium score and stress myocardial perfusion imaging provide independent and complementary prediction of cardiac risk. J Am Coll Cardiol. 2009 Nov 10;54(20):1872-82.

3. Cademartiri F, Maffei E, Palumbo A, et al. Coronary calcium score and computed tomography coronary angiography in high-risk asymptomatic subjects: assessment of diagnostic accuracy and prevalence of non-obstructive coronary artery disease. Eur Radiol. 2009 Sep 16. [Epub ahead of print]

4. Lloyd-Jones D, Adams R, Carnethon M, et al. Heart disease and stroke statistics–2009 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation. 2009 Jan 27;119(3):480-6.