Cardiac CT

Purpose: To obtain detailed 3D images of the heart and surrounding structures.
Cardiac CT vs. CT Coronary Arteries (CTCA):
- CTCA is used for symptomatic patients suspected of having Coronary Artery Disease (CAD).
- A good negative score on CTCA indicates a low risk for CAD.
CTCA Includes:
- Calcium Score
- Imaging of Valves & Heart Chambers
- Congenital Pathologies
- Pre/Post Surgery Assessment

Normal Cardiac Anatomy

RA – Right Atrium
RV – Right Ventricle
LA – Left Atrium
LV – Left Ventricle
Ao – Aorta/Aortic Root
N – Non-coronary Cusp
R – Right Coronary Cusp
L – Left Coronary Cusp
LM – Left Main
LAD – Left Anterior Descending
CX – Circumflex
RCA – Right Coronary Artery

Abnormal Cardiac Anatomy and Pathologies

Coronary Artery Disease (CAD):
- Damage or disease in the heart's major blood vessels.
- Buildup of fats and cholesterol on artery walls, leading to narrowing and reduced blood flow.
- Symptoms: Chest pain (Angina), Shortness of Breath (SOB), Fatigue.
Grading of Artery Stenosis:
- 90% stenosis means 10% of the artery is open.
- 10% stenosis means 90% of the artery is open.
Congenital Pathologies:
- Aortic Valve Stenosis: Narrowing of the aortic valve.
- Patent Ductus Arteriosus: Extra blood in the lungs, leading to increased right heart pressure.
- Septal Defects: Atrial or Ventricular, causing decreased or increased heart pressure.
- Tetralogy of Fallot: A combination of heart defects, leading to complications in growth and development, heart failure, and pulmonary hypertension.

Indications and Screening for CTCA

Indications:
- CTCA is primarily used for patients with suspected coronary artery disease who have a low or intermediate risk.
- Low-risk patients: Symptoms suggestive of coronary artery disease, normal ECG, normal cardiac enzyme tests, and no risk factors for coronary artery disease.
- Intermediate-risk patients: Similar symptoms, negative ECG and cardiac enzymes, but with risk factors for coronary artery disease.
- Examples of risk factors: Chest Pain on Exertion, SOB, Family History, High Cholesterol.
Pre-requisites for CTCA:
- Non-Acute Investigation of Chest Pain/Pathology: CTCA is usually not performed on acute patients who are more likely to undergo invasive coronary angiography.
  - No elevation of serum markers indicating cardiac damage (Troponin, Creatine Kinase-MB, Myoglobin, Lactase Dehydrogenase).
  - No ECG changes of acute cardiac ischemia (ST-Segment Elevation, T-Wave Changes, Reciprocal/Depression, Arrhythmias).
  - No Renal Failure: eGFR < 30mL/min indicates acute presentations.
  - No Pregnancy due to radiation and contrast exposure.
Screening Patient Pathway:
- Diagnostic algorithm for patients with possible ischemic heart disease:
  - Run tests:
    - Normal: No further action needed.
    - Indicative of heart disease: Referred to cardiologist.
    - Equivocal: Needs further investigation.
  - Further investigation:
    - Normal: No further action needed.
    - Indicative of heart disease: Referred to cardiologist.
    - Equivocal: CTCA is performed.

Patient Preparation for Cardiac CT

Heart Rate:
- High heart rates decrease diagnostic accuracy.
- Ideal HR: <60/65 bpm
- Elevated HR: 60/65-80 bpm
- High HR: >80 bpm
Medications to slow HR:
- No Stimulants for 12 hours prior (Caffeine, Alcohol, Tobacco, Exercise).
- β-Blockers: Necessary if HR on breath-hold is >65 bpm or irregular.
  - Oral Beta Blockers (Metoprolol or Ivabradine): Prescribed by requesting Doctor or Radiologist.
    - Radiologist Dose: 50mg tablet taken 1 hour prior to scan.
  - IV Beta Blockers: Independent or Supplementary to Oral β-B.
    - Administered on the table.
    - Dose: up to 15mg IV delivered in 2.5mg titration.
Vasodilators:
- Improve image quality and diagnostic accuracy by relaxing vessel walls and increasing vessel diameter.
- Increases the number of coronary segments able to be assessed by CTCA.
- Medications: GTN (Glyceryl Trinitrate) administered via 2 sprays sublingually.
- Contraindications:
  - Viagra/Cialis within 72 hours.
  - Patients with low blood pressure.
- Side Effects:
  - May result in increased HR.
  - Can cause blood pressure to decrease.
  - Light-headedness/headache.

Calcium Score vs. CT Coronary Angiograms

CT CALCIUM SCORING:
- Quantitative assessment of coronary artery lesions.
- Detects hard plaques only (no soft plaques).
- Determines total plaque burden, indicating the risk of a cardiac event.
- Performed independently or with CTCA.
- Risk stratification for women (35-70yrs) and men (40-60yrs). Generally accepted that 40yrs is the minimum.
- Matched against similar age, sex, population (MESA).
- Who is it for? Low risk and intermediate risk patients.
Patient Prep for Calcium Scoring:
- Prior to Arrival:
  - No caffeine, alcohol, cigarettes, exercise 12 hours prior.
  - No fasting required.
  - No withholding of medications.
- Prior to Scan:
  - Clothing above the waist removed.
  - Gown open at the front.
- On Table:
  - ECG Leads on patient.
  - Non-contrast.
  - Medium breath hold (excessive breath hold increases HR).
  - Agatston method
Technique for Calcium Scoring:
- AP Topogram
- Scan range to cover coronary vessels (carina → coronary arteries).
- 120kVp
- Tube current per patient.
- 3mm contiguous slices.
Post Processing for Calcium Scoring:
- Auto/Manual ‘tagging’ of hard plaques (Synago, Vitrea).
- Calculations, based on:
  - Individual lesions (area of calcification multiplied by weighted density score given to the highest attenuation value (HU) in the lesion; higher density = greater weighting factor).
  - Total score (sum of all lesions).
RESULTS of Calcium Scoring:
- CA score 1-100 → low risk → <10% chance of having MI/stroke in the next 10 years.
- CA score >400 → high risk → >20% chance of MI/stroke in the next 10 years.
- Can be used to guide treatment options (e.g. individualised statin/lifestyle regime).

Post Processing Techniques

Auto/manual ‘tagging’ of hard plaques:
- Syngo (via SIEMENS)
- Vitrea (via Cannon)

Non-Coronary Artery Procedures

Bypass Grafts:
- Monitoring post bypass graft surgery (Post Coronary Artery Bypass Grafts - CABG).
- Patient preparation is identical to CTCA.
- No calcium score required.
- Extended range:
  - Dependent on graft types (Common for LIMA (Left Internal Mammory Artery) + SVG (Scalable Vector Graphics)).
  - Subclavian to below heart
- Larger bolus: 70-80ml contrast/50ml saline.
- Test bolus & Scan Delay: Additional delay to allow for grafts to fill
- Prospective gating
  - High Pitch Spiral
- Consider higher kVp
  - Excessive plaque burden
  - Large BMI
Transcatheter Aortic Valve Implantation (TAVI):
- Pre-Surgery Planning + Post Surgery Eval.
- Patient Preparation Similar to CTCA:
  - No GTN and No β-B given.
- AP and Lateral Full Length Topograms
- Contrast Bolus:
  - No test bolus
  - Bolus tracking in Asc. Aorta @ $100 HU$
  - $90ml$ contrast/ $50ml$ saline @ $6ml/s$
- Imaging:
  - Ca Score of Aortic Valve
  - Retrospective gated Spiral/Helical Scan of Aortic Valve
  - Lower 1/3 of heart to carina
  - High Pitch helical Aorta
  - Mid carotids to below pubic symph.
Left Atrium:
- Indications:
  - Pulmonary Vein Isolation (PVI)
  - Left Atrial Appendage (LAA) Closure
- Patient Preparation Similar to CTCA
  - No GTN and No β-B given.
- AP Topogram
- Contrast Bolus:
  - Test Bolus (in left atrium)
    - $10ml$ contrast/ $30ml$ saline @ $6ml/s$
  - Scan
    - $60ml$ contrast/ $50ml$ saline @ $6 ml/s$
    - Consider $70ml$ @ $7ml/s$ for large patient
- Imaging:
  - Prospective
  - Arterial
    - Above Carina to Lower 1/3 of heart
    - Entire left atrium and Pulmonary Veins
  - Delayed Arterial
    - Top of heart/Pulmonary artery trunk to inferior to atrial appendage/mid heart
    - To cover left atrial appendage only
Shunting/Congenital
- Indications
  - Patent Foramen Ovale (PFO)
- Patient Preparation Similar to CTCA
  - No GTN and No β-B given.
- AP Topogram
- Contrast Bolus:
  - Test Bolus or bolus tracking
  - Scan
    - $70ml$ contrast/ $50ml$ saline @ $6 ml/s$
    - Consider $80ml$ @ $7ml/s$ for large patient
- Imaging:
  - Prospective Gating
  - Non-Contrast as required
  - Arterial
    - Whole heart or Region of Interest
  - Delayed Arterial as required
    - Region of interest

Routine Protocols in CT Cardiac Examinations

Pre-Exam Observations:
- Resting HR, BP, medication Hx
Patient Cannulated
Patient Changed:
- Clothing above waist removed
- Patient gown open at front (ECG leads placed on chest)
Patient Supine Feet-first
ECG Leads Connected
HR stabilised and optimal for scan
GTN Given
AP Topogram
+/- Calcium Score
Contrast Test bolus
- $10ml$ contrast/ $50ml$ saline @ $6ml/s$
Scan Technique selected based on HR
- <60/65 bpm = Prospective Gating
  - High pitch helical/Large Volume
- 60/65-80bpm = Prospective Gating
  - Sequential
- >80bpm = Retrospective Gating
  - Spiral/Helical (multiple cardiac cycles)
kVp
- Low for normal vessels
- Increase for excessive hard plaques or large BMI
mA
- Dose modulation to improve patient dose
Scan Range
- Above coronary arteries to below heart