Coronary CT angiography (protocol)

Last revised by Andrew Murphy on 23 Mar 2023

The coronary CT angiography or cardiac CT angiogram protocol is the most common dedicated cardiac CT examination and is a non-invasive tool for the evaluation of the coronary arteries.

Note: This article is intended to outline some general principles. Protocol specifics especially medications, contrast doses and decisions versus other cardiac acquisitions will vary subject to institutional protocols and patient factors as well as CT hardware and software.

The medication and contrast doses apply to cardiac CT examinations in adults.

Classical indications for a coronary CT angiography are the following 1:

The main purpose is a diagnostic acquisition of a coronary angiogram at a radiation dose as reasonably low as possible.

Contraindications include the following 1:

  • acute ST-elevation myocardial infarction (time delay for PCI)
  • screening of asymptomatic patients with low risk of CAD
  • factors leading to potentially non-diagnostic scans
    • inability to cooperate (e.g. breath-hold instructions, arm elevation etc.)
    • site maximum for reliable diagnostic scans after beta-blockers
    • markedly irregular rhythm (e.g. atrial fibrillation)
    • body mass index >39 kg/m2
  • contraindications against iodinated contrast media
  • pregnancy or uncertain pregnancy status in premenopausal women

Contraindications to ß-blockers include:

  • 2nd or 3rd-degree atrioventricular block
  • systolic blood pressure ≤90 mmHg
  • active bronchoconstriction, asthma or bronchospastic disease with regular inhaler use

Contraindications to nitrates include:

Some acquisition methods have specific technical requirements. Minimal technical requirements for a coronary CT angiogram are the following 2:

  • 64-slice scanner
  • detector element width ≤0.625 mm
  • option of cardiac CT and ECG-gated triggering

Checking indications, contraindications, explanation of the examination and obtaining informed consent is obvious as in other CT examinations.

Beyond that patient preparation for cardiac CTA includes the following 2:

  • checking contraindications for nitrates and ß-blocker
  • patients should take their cardiac medications as usual
  • no food 3-4 hours before the scan
  • no caffeine for 12 hours
  • instruction on how to breathe
  • an electrocardiogram signal needs to be acquired
  • heart rate control

Premedication comprises the following 2:

  • check heart rate and blood pressure before administration of medications
  • administration of nitrates (400-800 µg of sublingual nitroglycerin e.g. 1-2 sprays)
  • administration of ß-blocker (to target pulse of ≤60 bpm)
    • e.g. metoprolol 50-100 mg one hour before the exam
    • e.g. metoprolol 5mg iv followed by monitoring for 5 min repeatedly up to 15-20 mg
  • patient position
    • supine with both arms above their head (as comfortably as possible)
    • ECG placement
  • acquisition
  • tube potential
    • ​100 kVp if patient’s weight ≤100kg or BMI <30kg/m2
  • tube current
    • ​ use automated current adjustment mode
  • scout
    • pulmonary apices to below the heart
  • scan extent
    • ideally to be determined by calcium scoring
    • just below tracheal bifurcation to below the heart
  • scan direction
    • craniocaudal 
  • ECG considerations
    • check scan can occur in the agreed-upon portion of the R-R interval within the patient's current heart rate
    • typically in mid-diastole in lower heart rates <70 bpm
    • mid-diastole to end-systole at higher heart rates of 70-80 bpm
      • a more reliable way to ensure end-systole is setting the timing to ms rather than percentage i.e. 350ms 
  • contrast injection considerations
    • contrast agents with high iodine concentrations (270-400 mg iodine/mL)
    • contrast timing
      • monitoring: ascending aorta
      • test bolus (test volume 10-20 mL at the same flow as the cardiac scan e.g. 5.0-6.0 mL/s)
      • bolus tracking
    • contrast volume
      • triphasic injection (for longer bolus) 
        • 50-70 mL contrast media at 5-7 mL/s
        • 10-20 mL contrast media with 30-40 mL saline at 5-7 mL/s
        • 30-40 mL saline chaser at 3-5 mL/s
      • biphasic injection (standard contrast injection) 
        • 50-80 mL contrast media at 5-7 mL/s
        • 40-50 mL saline chaser at 5-7 mL/s
  • respiration phase
    • inspiration
    • for breath-hold consistency, a medium-sized breath is easier to reproduce throughout the examination compared to sharp deep breaths
  • a high-pitch acquisition can be considered in patients with stable sinus rhythm and a heart rate of less than 60 bpm and a body weight ≤100 kg (very low radiation dose)
  • a prospective ECG-gated acquisition should be performed in most situations with a regular rhythm, where high-pitch or high-volume scans are not available or contraindicated
  • retrospective ECG-gated acquisition should be considered in patients with an irregular rhythm or high heart rate
  • calculating scan delay for a test bolus
    • as the time-enhancement curve will only begin recording after the scan delay.
    • the widely accepted formula for calculating the scan delay is 4: peak contrast enhancement (time-enhancement curve) + scanner's diagnostic scan delay

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