Heart Disease: Labs & Diagnostic Tests

This video clip is from episode #203 — AMA #34: What causes heart disease? — originally released on April 18, 2022.

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Show Notes

• There are Lp(a) particles
  • In Peter’s practice, apoB is the most important metric they look at to predict risk (though not the only marker)

Labs to identify biomarkers of ASCVD ]59:00]

•  The full lipid panel— he always wants to see the non-HDL cholesterol
•  Lp(a) (measured at least once)
  • If it’s elevated, he might look again, depending on certain interventions
•  apoB 
•   APOE (genotype) 
  • apoB and APOE  are largely unrelated for the purpose of this

These measures tell about the risk but not how much atherosclerosis is currently present

• There are not great biomarkers for assessing how much atherosclerosis is present
• The biomarkers for predicting risk are useful so we can lower risk by reducing them
• Additional measurements factor into how risk is managed:
  •  Homocysteine 
  •  Uric acid 
  •  Thyroid function 
  •  Iron 
  •  Ferritin 
• Realize these are biomarkers; he still looks at metabolic health with biomarkers and non-biomarkers
  • He’s aggressive in monitoring blood pressure 
    • Even slight elevations of blood pressure are important
    • A lot of this can be treated through changes in behavior

 

Diagnostic tests to determine the level of arterial damage present—CAC, CTA, CIMT, and more [1:00:30]

What diagnostics can capture the level of damage currently present in the arteries?

• The pathology slides discussed earlier show different levels of damage
• Biomarkers won’t differentiate this

The 2 most important things we can look at are: 

• 1 – Coronary artery calcium (CAC) score
• 2 – A CT angiogram (CTA)

 Calcium score (CAC) 

• This is done by doing a very quick CT scan of the heart without any intravenous contrast
• It looks at the amount of calcification in the coronary arteries
  • This is very late in the disease process
• Once you have calcium formation around coronary arteries you’re at the 2nd to last stage of atherosclerosis
  • It’s a late stage of healing
  • Calcium formation is a very advanced finding of disease but it doesn’t tell you much about what’s happening at the point of calcification 
• Just yesterday, Peter got a patient’s calcium score back and it was not a very high number, but it wasn’t 0
  • That’s already a big red flag 
  • It was at one part of their heart, but that doesn’t really tell much
  • The fact that they have a score of, say 15 at one part of their left anterior descending really means nothing about what’s happening there
  • But that becomes a real global alarm given that person’s age (early 40s)
  • Further, if they have a calcified point right there, they undoubtedly have atherosclerosis elsewhere

The CT angiogram (CTA) is a much better test

• But it comes at a higher cost and it comes with more radiation
  • At really good places, it should be in the ballpark of 2 millisieverts of radiation
    • That’s a very small dose of radiation, about 4% of your annual allotted radiation, according to the NRC
• A CT scan of the heart (this one is with contrast) captures the calcification
  • They typically run a dry scan first to look for calcium
  • But then once the contrast is in, you can see with great illumination the arteries
  • This gives a better sense of the luminal narrowing and the presence of soft plaque 

Really, the CAC and the CTA are a very important thing that we use also in risk prediction, especially if the patient is themselves on the fence about preventative measures