Dyslipidemia, Coronary Artery Calcium, and Incident Atherosclerotic Cardiovascular Disease

Implications for Statin Therapy From the Multi-Ethnic Study of Atherosclerosis

SS Martin, MJ Blaha, R Blankstein, AS Agatston, JJ Rivera, SS Virani, P Ouyang, SR Jones, RS Blumenthal, MJ Budoff, K Nasir
Circulation 2013 Oct 20;[EPub Ahead of Print]

TAKE-HOME MESSAGE

• What is the relationship between coronary artery calcium (CAC) scores and dyslipidemia in relation to outcomes of cardiovascular disease?
• Over 5500 trial participants who were not on baseline medications for dyslipidemia were classified by baseline CAC score and lipid abnormalities and were assessed for incidence of myocardial infarction, angina resulting in revascularization, resuscitated cardiac arrest, stroke, and cardiovascular death. Follow-up was 7.6 years.
• The CAC score may be helpful in matching statin therapy to risk of cardiovascular disease.

Commentary By: Peter Lin, MD, CCFP

This study looked at coronary artery calcium (CAC) scores vs lipid abnormalities in > 5500 people to see which one is better correlated with cardiac events. After 7 years, there were 353 events, 194 of which occurred in patients with CAC > 100. The CAC score was better correlated with cardiac events than cholesterol levels. This makes sense because cholesterol increases your risk of damage, but calcium is an actual sign of damage in the artery. So, at first glance, it would seem like everybody should get a CAC done.

But let’s think about the numbers. In this study, 5500 people were scanned and only 1155 people had a CAC score > 100. And, of those people, only 194 had an event, which means that the majority (83%) of the patients with CAC > 100 did not have events over a 7-year period. This represents a significant financial cost, as well as a radiation cost to the patients. The radiation dose quoted in the article is 0.5 mSv, which is still one-sixth of our annual background dose of 3 mSv. That means that > 5300 patients had extra radiation without any clear benefit.

CAC is a useful test—but not for mass for screening. We should use our clinical skills and assess family history, Framingham risk scores, and metabolic syndrome features, and, in the majority of cases, we will know how to treat that patient. It is only in the select few patients for whom we are still confused as to what to do we can, perhaps, accept the cost and the radiation risk of obtaining a CAC score.

Abstract

Background—Worldwide clinical practice guidelines for dyslipidemia emphasize allocating statin therapy to those at the highest absolute atherosclerotic cardiovascular disease (CVD) risk.

Methods and Results—We examined 5,534 MESA participants who were not on baseline medications for dyslipidemia. Participants were classified by baseline CAC score (>0, >=100) and the common clinical scheme of counting lipid abnormalities (LA), including LDL-C >=3.36 mmol/L (130 mg/dL), HDL-C <1.03 mmol/L (40 mg/dL) for men or <1.29 mmol/L (50 mg/dL) for women, and triglycerides >=1.69 mmol/L (150 mg/dL). Our main outcome measure was incident CVD (myocardial infarction, angina resulting in revascularization, resuscitated cardiac arrest, stroke, cardiovascular death). Over a median follow-up of 7.6 years, more than half of events (55%) occurred in the 21% of participants with CAC>=100. Conversely, 65% of events occurred in participants with zero or one LA. In those with CAC>=100, CVD rates ranged from 22.2 to 29.2 per 1,000 person-years across LA categories. In contrast, with CAC=0, CVD rates ranged from 2.4 to 6.2 per 1,000 person-years across LA categories. Individuals with zero LA and CAC>=100 had a higher event rate compared to individuals with three LA but CAC=0 (22.2 vs 6.2 per 1,000 person-years). Similar results were obtained when classifying LA using dataset-quartiles of TC/HDL-C, LDL-C, non-HDL-C, or LDL particle concentration and guideline-categories of LDL-C or non-HDL-C.

Conclusions—CAC may have the potential to help match statin therapy to absolute CVD risk. Across the spectrum of dyslipidemia, event rates similar to secondary prevention populations were observed for patients with CAC>=100.

Full Story:  http://www.practiceupdate.com/journalscan/6489
Journal Abstract:  http://circ.ahajournals.org/content/early/2013/10/18/CIRCULATIONAHA.113.003625