Original research articlePrognostic significance of zero coronary calcium scores on cardiac computed tomography
Introduction
The principal cause of morbidity and mortality in all industrialized nations is coronary artery disease (CAD).1 In approximately half of the persons, the initial presentation of CAD is either myocardial infarction (MI) or death.2 Unfortunately, conventional risk factor assessment predicts only 60%–65% of cardiovascular risk, leaving many persons to have cardiovascular events in the absence of traditional risk factors for atherosclerosis.3 One study showed that only 25% of younger patients who had presented with a MI would have qualified for pharmacotherapy with a statin, based on their Framingham risk profile before the occurrence of MI.4 It is extremely disturbing to note that most cardiac events occur in the intermediate-risk population, and it is the same group in which aggressive risk-factor modification is most often applied haphazardly. Many physicians tend to overtreat patients in this intermediate-risk population, because of uncertainty about future cardiovascular risk. In the Anglo-Scandinavian Cardiac Outcomes Trial, in which hypertensive persons with 3 risk factors were randomly assigned to a statin or placebo, the number needed to treat was 93, indicating 93 persons had to be treated for 3.3 years to prevent one cardiac event.5 Treating all intermediate-risk persons will be highly cost-inefficient, and these patients tend to have poor long-term compliance with therapy.6, 7
The presence of calcium in coronary arteries is pathognomonic of atherosclerosis, as confirmed by prior histopathology and intravascular ultrasound studies. Coronary artery calcium (CAC) detected and quantified represents an anatomic measure of plaque burden. Available outcome data for CAC scoring in almost every study have shown CAC to be an independent and incremental predictor of future events and coronary heart disease (CHD) over conventional risk factors.8, 9 Coronary calcium score (CCS) was also shown to add incremental value to newer studied risk factors, including C-reactive protein.7 Because treatment in this intermediate-risk population is most uncertain, CAC can theoretically direct the treatment of a high score, suggesting intensive treatment, and a zero score, suggesting lifestyle changes with no or minimal drug therapy.10 We sought to evaluate whether the event rates in persons with negative calcium scores may be considered low risk for hard cardiovascular events, providing physicians with some comfort in not treating this portion of the population with aggressive lipid-lowering therapies.
Section snippets
Methods
We used established methods for systematic review. A broad search of the literature in all languages was performed, incorporating both electronic and manual components. The electronic search was performed using PubMed, which includes MEDLINE, OLDMEDLINE, OVID, and the Cochrane Library database. PubMed was searched from 1975 (before electron beam CT was developed) to February 2007. Search terms were as follows: spiral CT/spiral computed tomography matched with coronary artery, coronary artery
Results
Thirteen coronary calcium studies with cardiac outcomes reported as MI or cardiovascular death were included. These encompassed 35,765 asymptomatic subjects, with weighted mean follow-up of 4.7 years. Summary data showed that in a total follow-up of 35,765 persons, 16,106 (45%) had CCSs of zero. There were 48 hard events in this population, with an annual event rate of 0.027%, or an estimated 10-year event rate of 0.3% (Table 1). Pooled sensitivity for CAC to detect a cardiovascular event was
Discussion
Recent guidelines have suggested that the use of a CCS derived from noncontrast cardiac CT can refine the traditional risk factor stratification such as the Framingham risk score (FRS).13, 14 Specifically, low scores are associated with a low adverse event risk and high scores are associated with a worse event-free survival. Current data support the recommendation to measure atherosclerosis burden in clinically selected intermediate-risk patients with CAD (such as 10%–20% 10-year risk estimate
References (31)
- et al.
Sudden death: lessons from subsets in population studies
J Am Coll Cardiol
(1985) - et al.
Mild hypercholesterolemia and premature heart disease: do the national criteria underestimate disease risk?
J Am Coll Cardiol
(2000) - et al.
ASCOT Investigators: Prevention of coronary and stroke events with atorvastatin in hypertensive patients who have average or lower-than-average cholesterol concentrations, in the Anglo-Scandinavian Cardiac Outcomes Trial–Lipid Lowering Arm (ASCOT-LLA): a multicenter randomized controlled trial
Lancet
(2003) Prevalence of soft plaque detection with computed tomography
J Am Coll Cardiol
(2006)- et al.
Quantitation of coronary arterial narrowing at necropsy in sudden coronary death: analysis of 31 patients and comparison with 25 control subjects
Am J Cardiol
(1979) - et al.
Long-term prognosis associated with coronary calcification: observations from a registry of 25,253 patients
J Am Coll Cardiol
(2007) - et al.
34th Bethesda Conference: executive summary: can atherosclerosis imaging techniques improve the detection of patients at risk for ischemic heart disease?
J Am Coll Cardiol
(2003) - et al.
Relationship between stress-induced myocardial ischemia and atherosclerosis measured by coronary calcium tomography
J Am Coll Cardiol
(2004) - et al.
Use of electron beam tomography data to develop models for prediction of hard coronary events
Am Heart J
(2001) - et al.
Coronary calcium independently predicts incident premature coronary heart disease over measured cardiovascular risk factorsPACC Project
J Am Coll Cardiol
(2005)
Coronary calcification, coronary disease risk factors, C-reactive protein, and atherosclerotic cardiovascular disease events: the St. Francis Heart Study
J Am Coll Cardiol
Screening patients with chest pain in the emergency department using electron beam tomography: a follow-up study
J Am Coll Cardiol
Use of electron-beam computed tomography in the evaluation of chest pain patients in the emergency department
Ann Emerg Med
SHAPE Task Force: From vulnerable plaque to vulnerable patient--part III: executive summary of the Screening for Heart Attack Prevention and Education (SHAPE) Task Force Report
Am J Cardiol
Prediction of coronary events with electron beam computed tomography
J Am Coll Cardiol
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Conflict of interest: The authors report no conflict of interest.