Coronary CT Angiography


Coronary CT Angiography, CT Coronary Angiogram, CT Angiography of Coronary Vessels, Coronary CT Angiogram, CCTA, Computed Tomographic Angiography of Coronary Arteries, CT Angiography of Coronary Arteries

  • Definition
  1. Coronary Artery CT Imaging for atherosclerosis
  • Indications
  1. See advantages and disadvantages below
  2. Low Risk Acute Coronary Syndrome Management risk stratification
    1. TIMI Score 0 to 2 AND
    2. Negative cardiac biomarkers (e.g. Troponin) AND
    3. No acute Electrocardiogram changes
  3. Other uses
    1. Consider in patients with known perfusion defects on prior imaging
  • Contraindications
  1. Absolute contraindications
    1. Anaphylaxis to IV Contrast Dye
  2. Relative contraindications
    1. Pregnancy
    2. Renal Insufficiency
  • Precautions
  1. Coronary CT Angiography (CCTA) is best used in Low Risk Chest Pain
    1. As with stress testing, avoid in patients at too low of risk (False Positives)
    2. Avoid in moderate to high risk patients who would more likely benefit from Coronary Angiography
    3. Avoid in patients over 65 years old due to higher risk of CAD
  2. However, in Low Risk Chest Pain, there is high risk of False Positive tests and unnecessary cardiac catheterization
    1. Risk of serious short-term adverse coronary event in Low Risk Chest Pain is roughly 0.2-0.3% (2-3 per 1000)
    2. CCTA has a Test Specificity at best of 90%, or 100 patients in 1000 tested with a False Positive result
    3. CCTA could subject 100 Low Risk Chest Pain patients to invasive catheterization to find 2-3 true positives
    4. Morgenstern (2020) EM:Rap 20(1): 11-2
  • Preparation
  1. Heart Rate control
    1. Goal Heart Rate <60 bpm
    2. Administer Beta Blocker if Heart Rate >65 bpm
      1. Metoprolol 50 to 100 mg orally at 45 to 60 minutes prior to scan
      2. Lopressor 5 mg IV dosed as needed immediately prior to imaging if Heart Rate still >65 bpm
  2. Other preparatory measures
    1. Nitroglycerin prior to imaging improves vessel definition
  • Advantages
  1. Non-invasive, accurate Coronary Angiography
  2. May be performed as part of "Triple Screen" chest Pain Evaluation
    1. Assesses for Aortic Dissection, Pulmonary Embolism and coronary disease
    2. However, requires increased radiation and contrast load compared with CT angiography alone
  3. Chest Pain risk stratification with a negative test allowing safe discharge from Emergency Department
    1. Most useful at ruling-out Acute Coronary Syndrome in Low Risk Chest Pain (see NPV below)
    2. Low Risk Chest Pain and a negative CCTA is associated with a <1% miss rate for significant CAD
    3. Litt (2012) N Engl J Med 366(15): 1393-403 [PubMed]
  4. Obviates the need for Stress Imaging within 72 hours and offers better reassurance if negative
    1. Normal CCTA in Low Risk Chest Pain is definitive
      1. Normal studies need no further evaluation for CAD with <0.1% risk of adverse cardiac events in 2 years
      2. CCTA with 25-50% stenosis may benefit from further evaluation and cardiology follow-up
    2. Contrast with standard Stress Imaging which is not definitive
      1. Despite normal stress test results, may require re-hospitalization for recurrent symptoms
      2. Miller (2011) Soc Acad Emerg Med 18(5): 458-67 [PubMed]
  5. May reduce overall costs of care
    1. Decreased emergency department length of stay
    2. Decreased hospitalization rates
    3. Decreased re-hospitalization rates (CCTA more definitive than stress testing in its Negative Predictive Value)
  6. Stable Chest Pain and intermediate Cardiac Risk patients had similar outcomes with CCTA compared with early PTCA at 3 years
    1. Considerably fewer patients in the CCTA group required revascularization procedures (but did require more functional testing)
    2. Maurovich (2022) N Engl J Med 386(17): 1591-602 [PubMed]
  • Disadvantages
  1. High radiation exposure
    1. See CT-associated Radiation Exposure
    2. CT Calcium Score (performed prior to each CCTA): 3 to 4 mSv
    3. CCTA-64 slice with Retrospective Gating of diastole: 16 mSv in men and 23 mSv in women
    4. CCTA-64 slice with Prospective Gating of diastole: 10 mSv in men and 14 mSv in women
    5. CCTA-64 slice with Dual Source of diastole: 2 to 4 mSv
    6. However, Stress Imaging (outside of Stress Echo) also exposes to radiation with lower NPV
      1. Stress Myocardial Perfusion Imaging radiation exposure: 7 mSv (dual isotope 21 mSv)
  2. IV Contrast Material exposure
    1. See Intravenous Contrast Related Acute Renal Failure
  3. Requires Heart Rate be suppressed to 60 bpm or less
  4. Low sensitivity for small vessels
  5. Unlike standard angiography, CT is diagnostic only (no ability to stent)
  6. Positive results vary based on the reading clinician and the cut-off
    1. Arbitrary positive cutoff of 50% stenosis was used in the Litt Study
    2. ROMICAT II study had 76% accuracy with an equal number of False Positives and False Negatives
  7. May not add significant value to acute risk stratification beyond two negative serial Troponins
    1. Negative TIMI Risk Score and biomarkers reduces missed-MI risk without CTA to 0.1%
    2. Litt (2012) N Engl J Med 366(15): 1393-403 [PubMed]
  8. Increased longterm costs due to a 6-fold increase in later testing at 150% of the cost and no survival benefit
    1. Shreibati (2011) JAMA 306(19):2128-36 [PubMed]
  9. Associated with greater intervention rate for PCI and CABG (due to False Positives) without decreased MI
    1. In a low risk population, CCTA has a high False Positive Rate
    2. Morris (2016) Acad Emerg Med 23(9): 1022-30 +PMID:27155236 [PubMed]
  10. No Functional Evaluation
    1. Test is done at rest (contrast with stress testing)
  • Efficacy
  1. Coronary CT Angiography (CCTA) Image quality compared with Angiography
    1. Standard angiography (gold standard)
      1. Temporal resolution: 20 msec
        1. Reflects the time to acquire a high quality image (within diastole)
      2. Spatial resolution: 0.2 mm
        1. Smallest slice width to distinguish between small structures
    2. Coronary CT Angiography (CCTA) 64-Slice
      1. Temporal resolution: 165 msec
      2. Spatial resolution: 0.4 mm
    3. Coronary CT Angiography (CCTA) dual-source
      1. Temporal resolution: 83 msec
      2. Spatial resolution: 0.4 mm
  2. Coronary CT Angiography (CCTA) accuracy in diagnosing >50% stenosis (64-slice CT)
    1. Most useful at ruling-out Acute Coronary Syndrome in Low Risk Chest Pain (see NPV below)
    2. Test Sensitivity: 93 to 95%
    3. Test Specificity: 85 to 90%
    4. Positive Predictive Value (PPV): 48-94%
    5. Negative Predictive Value (NPV): 99%
  • Resources
  1. Jacobs (2006) How to perform coronary CTA: A to Z, Appl Radiol Supp p. 10-17
    1. http://www.ctisus.com/resources/images/features/64-Slice-MDCT-of-the-Heart/AR_12_06_CTA_Jacobs.pdf
  • References