Coronary Artery Calcium (CAC)

• Uses non-contrast CT with a fixed threshold of 130 Hounsfield units (HUs) for calcium detection
• With modern scanners and protocols, the radiation dose required for acquisition of a CT calcium score is approximately 1 mSV.
• Weighting
  • A weight of 1 is given for attenuation of 130 to 199
  • 2 for 200 to 299
  • 3 for 300 to 399
  • 4 for attenuation ≥400
  • The weighting factor is multiplied by the area of each lesion, with the sum of values for all lesions used to determine the total Agatston score

If patient with Familial Hyperlipidemia, don't even bother with CAC

CAC Scan Acquisition

• Slice thickness: 3mm
• Prospectively triggered scan
• Target exposure depends on heart rate (40-75%)
  • Diastasis is at ~75% of R-R interval (used when HR is nice and slow)
  • Isovolumic relaxation is at ~40% of R-R interval (used when HR is high)
    • The 🫀 can’t move (at least on the Left) because the AV and MV are closed during IVR
• Tube potential is fixed at 120 kV, tube current variable
• Non-contrast study

Advantages of obtaining a CAC scan prior to CCTA

• Minimizes Scan range
• Provides estimate of plaque burden - useful for prognosis
• Establishes pre-test probability for obstructive CAD (not actually true)
• CAC >600 should make you pause as it can ↓ sensitivity and specificity in looking for obstructive CAD
  • 🤔 Is this still the case in the era of photon-counting CT, I wonder
• 📄 Arbab-Zadeh A, Miller JM, Rochitte CE, Dewey M, Niinuma H, Gottlieb I, Paul N, Clouse ME, Shapiro EP, Hoe J, Lardo AC, Bush DE, de Roos A, Cox C, Brinker J, Lima JA. Diagnostic accuracy of computed tomography coronary angiography according to pre-test probability of coronary artery disease and severity of coronary arterial calcification. The CORE-64 (Coronary Artery Evaluation Using 64-Row Multidetector Computed Tomography Angiography) International Multicenter Study. J Am Coll Cardiol. 2012 Jan 24;59(4):379-87. doi: 10.1016/j.jacc.2011.06.079. PMID: 22261160; PMCID: PMC3348589.

Percentile Scoring

• cac-tools.com can be used for patients 30-45 years old
• MESA 10-Year CHD Risk with Coronary Artery Calcification works for 45-85 years of age

Coronary Age Calculation

• TODO

LDL Goals

CAC Score	Recommendation	LDL Goal
0	Consider no statin	-
1-99	Favors statin (esp if age >55 yo)	<100
100+ (or ≥75th percentile)	Statin	<70 (add Ezetimibe if needed)
1000+	Statin	<70 (add Ezetimibe + PCSK9i if needed)

![[Coronary Artery Calcium CAC-1744895073637.webp|531x908]] Figure source: ¹

National Lipid Association CAC-based management ² ![[Coronary Artery Calcium CAC-1744895219335.webp]]

Power of Zero (CAC of 0)

• If CAC 0, no need for statin unless Diabetes, smoker
• What does a zero coronary artery calcium score tell us?
  • Intermediate Risk w/ dyspnea or classic angina
    • 16% incidence inducible ischemia on PET
  • High Risk Symptomatic Patients in ED w/ ACS
    • 70% prevalence of obstructive CAD by CCTA
• 🌟 Negative CAC is helpful in Low and Intermediate Risk population (but not high-risk populations)

Warranty of CAC = 0?

• Blaha recommends 3-5 years ³
  • ![[Coronary Artery Calcium CAC-1744894912396.webp]]

Footnotes

1. Lloyd-Jones DM, Morris PB, Ballantyne CM, et al. 2022 ACC Expert Consensus Decision Pathway on the Role of Nonstatin Therapies for LDL-Cholesterol Lowering in the Management of Atherosclerotic Cardiovascular Disease Risk. Journal of the American College of Cardiology. 2022;80(14):1366-1418. doi:10.1016/j.jacc.2022.07.006 ↩

2. Orringer, Carl E., et al. “The National Lipid Association scientific statement on coronary artery calcium scoring to guide preventive strategies for ASCVD risk reduction.” Journal of clinical lipidology 15.1 (2021): 33-60. ↩

3. Dzaye O, Dardari ZA, Cainzos-Achirica M, et al. Warranty Period of a Calcium Score of Zero. JACC: Cardiovascular Imaging. 2021;14(5):990-1002. doi:10.1016/j.jcmg.2020.06.048 ↩