262.1 🎓 醫學生版

262.1.0.1 📌 一頁重點

262.1.0.1.1 Cardiac CT

262.1.0.1.1.1 Coronary Artery Calcium (CAC) Score

• Non-contrast cardiac CT
• Quantifies coronary calcification (Agatston score)
• Risk stratification for primary prevention
• CAC 0: very low ASCVD risk → consider deferring statin
• CAC 100-300: intermediate → statin
• CAC > 300 or > 75th percentile: high risk → statin + aggressive prevention
• Especially useful in intermediate ASCVD risk (10-20%) for decision-making

262.1.0.1.1.2 Coronary CT Angiography (CCTA)

• Contrast-enhanced
• High sensitivity for CAD (95%+)
• High negative predictive value (rules out CAD)
• First-line for chest pain workup in low-intermediate pretest probability (ESC 2024)
• Detects:
  • Coronary stenosis
  • Plaque characterization (vulnerable plaque features)
  • Coronary anomalies
• Limitations: high heart rate, irregular rhythm, severe calcification (overestimation)

262.1.0.1.1.3 Other CT Indications

• CTA of aorta: aortic aneurysm + dissection (gold standard)
• CT pulmonary angiogram: PE
• Cardiac CT for structural assessment: pre-TAVR (annulus sizing), pre-MitraClip, left atrial appendage (Watchman)

262.1.0.1.2 Cardiac MRI (CMR)

262.1.0.1.2.1 Gold Standard for Tissue Characterization

• Late gadolinium enhancement (LGE): detects fibrosis, infarction, infiltration
• T1 + T2 mapping: tissue characterization (edema, fibrosis, iron, fat)
• Extracellular volume (ECV): amyloid quantification
• No radiation (vs CT, nuclear)

262.1.0.1.2.2 Indications

• Cardiomyopathy workup (DCM, HCM, RCM, ARVC, amyloid, sarcoid, Anderson-Fabry, hemochromatosis)
• Myocarditis (Lake Louise criteria — T1/T2/LGE)
• Viability assessment (LGE > 50% wall thickness = non-viable)
• Congenital heart disease evaluation
• Cardiac masses + tumors
• Pericardial disease
• Coarctation of aorta
• Aortic disease (aneurysm + dissection follow-up)

262.1.0.1.2.3 LGE Patterns

• Subendocardial: infarction (CAD distribution)
• Mid-wall: dilated cardiomyopathy, sarcoidosis
• Epicardial: myocarditis
• Diffuse / patchy: amyloidosis (subendocardial diffuse + atrial walls + RV)
• Septal: HCM, sarcoid

262.1.0.1.2.4 Newer Techniques

• Strain imaging (similar to echo strain)
• 4D flow MRI: complex hemodynamics
• MR fingerprinting
• AI-enhanced MRI for automated quantification

262.1.0.1.2.5 Limitations

• Cost + availability
• Claustrophobia
• Pacemakers + ICDs (now mostly MRI-conditional)
• Renal failure (gadolinium → NSF concern — older, now much rarer with macrocyclic agents)

262.1.0.1.3 Nuclear Cardiology

262.1.0.1.3.1 SPECT (Single-Photon Emission Computed Tomography)

• Myocardial perfusion imaging (MPI)
• Tracers: technetium-99m sestamibi, tetrofosmin
• Stress (exercise or pharmacologic) + rest: detects reversible (ischemic) vs fixed (infarct) defects
• Quantifies ischemia + LVEF (gated SPECT)
• Older standard but limited by attenuation artifacts

262.1.0.1.3.2 PET (Positron Emission Tomography)

• PET myocardial perfusion: rubidium-82, ammonia-N-13
• Higher resolution + better attenuation correction than SPECT
• Coronary flow reserve (CFR) — diagnostic + prognostic
• Hibernating myocardium assessment (mismatch — perfusion ↓ + viability ↑ on FDG)
• Cardiac sarcoidosis: FDG-PET (active inflammation)
• Amyloidosis (specific subtypes — ATTR): bone-tracer imaging (PYP, HMDP) — see below

262.1.0.1.3.3 PYP / HMDP Bone Tracer (Amyloid)

• TC-99m PYP or HMDP uptake — sensitive for ATTR amyloidosis (cardiac)
• Differentiates from AL amyloidosis (no uptake or minimal)
• • Free light chains negative → non-invasive ATTR diagnosis without biopsy

262.1.0.1.3.4 Cardiac Sarcoidosis Imaging

• FDG-PET for active inflammation
• Late gadolinium enhancement on MRI for fibrosis
• Combined assessment

262.1.0.1.4 Multimodality Approach

• Often complementary (echo + CT + MRI + nuclear)
• Stress imaging selection:
  • Exercise treadmill ECG (low-intermediate risk; can exercise)
  • Stress echo (moderate-high; exercise or pharmacologic)
  • Stress nuclear (moderate-high; can’t exercise; specific clinical questions)
  • Stress MRI (specific scenarios; gadolinium contrast)
• 2024 ESC chest pain guidelines: CCTA first-line for ruling out obstructive CAD; stress imaging for known CAD or higher pretest probability

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262.1.0.2 1️⃣ Coronary Artery Calcium (CAC) Score

262.1.0.2.1 Indications

• Primary prevention risk assessment
• Intermediate ASCVD risk (10-20%) by calculator — decision support for statin therapy
• Asymptomatic patients

262.1.0.2.2 Not Indicated

• Symptomatic patients (use CCTA or stress test)
• Already on statin
• Known CAD
• Very low risk (CAC won’t change management)
• Very high risk

262.1.0.2.3 Interpretation

• CAC 0: very low 10-year ASCVD risk → consider deferring statin (50% reduction in CV events)
• CAC 1-99: low-intermediate; statin discussion
• CAC 100-300: intermediate; statin recommended
• CAC > 300 or > 75th percentile: high risk; aggressive statin + lifestyle + monitor
• CAC > 1000: very high risk; consider further imaging + intensive prevention

262.1.0.2.4 Patient Counseling

• “Tell me my number” approach increasingly used
• Empowers shared decision-making
• Helps overcome hesitancy about lifelong statin

262.1.0.2.5 Limitations

• No detection of soft (non-calcified) plaque
• May not reflect acute plaque rupture risk
• Older patients have CAC by default
• Not for diabetics (CAC < 100 in diabetic still high risk)

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262.1.0.3 2️⃣ Coronary CT Angiography (CCTA)

262.1.0.3.1 Procedure

• IV contrast
• ECG-gated (low heart rate ideal; β-blocker often)
• Breath-hold
• Modern scanners: 256-slice or 320-slice → low radiation
• Visualizes coronary lumen + plaque + wall

262.1.0.3.2 Strengths

• High sensitivity (95%+) for obstructive CAD
• Very high negative predictive value (rules out CAD)
• Plaque characterization (vulnerable features: positive remodeling, low attenuation, napkin-ring sign, spotty calcification)
• Coronary anomaly detection
• Bypass graft assessment

262.1.0.3.3 Limitations

• Severe calcification: overestimates stenosis
• High heart rate: motion artifact (β-blocker recommended)
• Irregular rhythm: AF → motion artifact
• Pacemaker / ICD artifacts
• Contrast nephropathy risk

262.1.0.3.4 Indications (ACC/AHA/ESC 2024)

• Acute chest pain low-intermediate risk (PROMISE, PROMISE-2 trials)
• Chronic stable chest pain low-intermediate pretest probability
• Pre-operative cardiac risk assessment
• Coronary anomaly workup
• Bypass graft patency

262.1.0.3.5 Output

• Stenosis severity (CAD-RADS classification 0-5)
• Plaque burden + characteristics
• Vulnerable plaque features

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262.1.0.4 3️⃣ Cardiac MRI (CMR)

262.1.0.4.1 Tissue Characterization (Unique Strength)

262.1.0.4.1.1 Late Gadolinium Enhancement (LGE)

• IV gadolinium → 10-20 min delayed imaging
• Detects:
  • Infarction (subendocardial pattern, CAD distribution)
  • Fibrosis (mid-wall — DCM)
  • Edema (myocarditis)
  • Infiltration (amyloid — diffuse + atrial)
  • Inflammation (sarcoid, myocarditis)

262.1.0.4.1.2 Specific LGE Patterns

Pattern	Disease
Subendocardial / transmural CAD distribution	Infarction / ischemia
Mid-wall septal / lateral wall	Dilated cardiomyopathy
Patchy mid-wall	Sarcoidosis
Epicardial / subepicardial	Myocarditis
Subendocardial circumferential + atrial + RV	Amyloidosis (especially AL)
Septal junction sites	Hypertrophic cardiomyopathy
Sub-tricuspid (free wall)	ARVC

262.1.0.4.1.3 T1 + T2 Mapping

• T1: pre-contrast + post-contrast values
• T2: edema detection
• ECV (extracellular volume): quantifies myocardial fibrosis
• Native T1 elevated: edema (acute), amyloid, fibrosis
• Native T1 decreased: lipid (Fabry, fat), iron overload

262.1.0.4.2 Strain Imaging

• Similar to echo strain
• Less artifact in obese / lung disease

262.1.0.4.3 4D Flow MRI

• Complex congenital heart disease
• Valvular regurgitation quantification

262.1.0.4.4 Indications

262.1.0.4.4.1 Cardiomyopathy

• Dilated cardiomyopathy: mid-wall septal LGE present in some; predicts arrhythmia + mortality
• Hypertrophic cardiomyopathy: septal LGE; predicts ventricular arrhythmia + SCD
• Restrictive: amyloid pattern; iron overload; Fabry
• ARVC: RV free wall + fat infiltration (best on MRI vs other imaging)
• Sarcoidosis: patchy LGE; combined with PET-FDG for active inflammation
• Amyloidosis: diffuse / circumferential LGE; ECV elevated; T1 elevated
• Anderson-Fabry: decreased T1 (lipid); LGE inferolateral mid-wall
• Hemochromatosis: decreased T1 (iron)

262.1.0.4.4.2 Myocarditis

• Lake Louise Criteria:
  • T1 / T2 mapping abnormal
  • LGE (epicardial / patchy)
  • Pericardial effusion
• Increasingly preferred over biopsy

262.1.0.4.4.3 Viability Assessment

• LGE > 50% wall thickness = non-viable (won’t recover after revascularization)
• LGE 25-50%: variable response
• LGE < 25%: likely viable + improves with revascularization

262.1.0.4.4.4 Congenital Heart Disease

• Adult congenital cardiology imaging
• Tetralogy of Fallot follow-up
• ASD / VSD
• Coarctation

262.1.0.4.4.5 Cardiac Tumors

• Differentiate thrombus, benign tumor (myxoma, lipoma), malignant tumor
• Cardiac MRI gold standard

262.1.0.4.4.6 Pericardial Disease

• Pericardial thickening (constrictive)
• Effusion
• Pericardial masses

262.1.0.4.5 Limitations

• Cost + availability
• Time (45-60 min)
• Claustrophobia
• Pacemakers / ICDs (MRI-conditional usage)
• Renal failure (gadolinium NSF rare with macrocyclic agents)
• Breath-hold required

262.1.0.4.6 AI in Cardiac MRI

• Automated segmentation
• Quantitative analysis
• Strain analysis automation
• Faster workflows

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262.1.0.5 4️⃣ Nuclear Cardiology

262.1.0.5.1 SPECT Myocardial Perfusion Imaging (MPI)

262.1.0.5.1.1 Procedure

• IV radiotracer (Tc-99m sestamibi or tetrofosmin)
• Stress (exercise or pharmacologic — adenosine, dipyridamole, regadenoson) + rest images
• Compare perfusion at stress vs rest

262.1.0.5.1.2 Findings

• Reversible defect (perfusion abnormality only at stress) = ischemia
• Fixed defect (perfusion abnormality at stress + rest) = infarction / scar
• Severity quantified
• Gated SPECT: also measures LVEF + wall motion

262.1.0.5.1.3 Limitations

• Attenuation artifacts (breast attenuation in women, diaphragm in obese)
• Radiation exposure
• Limited spatial resolution

262.1.0.5.2 PET Myocardial Perfusion

262.1.0.5.2.1 Tracers

• Rubidium-82 (generator-produced)
• Ammonia-N-13

262.1.0.5.2.2 Advantages

• Higher resolution + better attenuation correction
• Quantifies coronary flow reserve (CFR)
• Better for obese patients
• Shorter protocol

262.1.0.5.2.3 Indications

• Similar to SPECT but preferred for:
  • Obese patients
  • Suboptimal SPECT
  • Quantitative perfusion needed

262.1.0.5.3 PET-FDG for Sarcoid + Inflammation

• FDG-PET detects active myocardial inflammation
• Cardiac sarcoidosis: active disease assessment
• Patchy uptake pattern
• Combined with MRI for fibrosis + inflammation

262.1.0.5.4 PYP / HMDP Bone Tracer (Amyloid)

• TC-99m PYP uptake = ATTR amyloidosis (sensitive)
• Heart-to-contralateral ratio
• • Negative free light chains → ATTR diagnosis without biopsy
• AL amyloid → no / minimal uptake

262.1.0.5.5 Viability with FDG-PET

• Mismatch = perfusion ↓ + FDG uptake ↑ = hibernating myocardium (viable, will recover with revascularization)
• Match = both ↓ = non-viable / scar

262.1.0.5.6 Radiation Exposure

• SPECT: ~ 9-10 mSv (similar to coronary CT)
• PET: ~ 3-5 mSv (lower)
• Higher in repeated imaging

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262.1.0.6 5️⃣ Multimodality Approach + Decision Algorithms

262.1.0.6.1 Chest Pain Workup (2024 ESC + ACC/AHA)

262.1.0.6.1.1 Acute Chest Pain (Low-Intermediate Risk)

1. ECG + troponin
2. CCTA (rules out obstructive CAD, low pretest probability)
3. If positive CCTA or higher risk: further evaluation / stress test
4. Cardiac catheterization for confirmed CAD or high-risk features

262.1.0.6.1.2 Chronic Stable Angina

1. Risk stratification
2. Low-intermediate pretest probability: CCTA (rules out CAD)
3. Higher pretest probability: stress imaging (echo, MPI, PET, MRI)
4. Coronary angiography if confirmed significant ischemia or refractory

262.1.0.6.2 Cardiomyopathy Workup

1. Echo + ECG + clinical assessment
2. Cardiac MRI for tissue characterization (HCM, DCM, RCM, ARVC, amyloid, sarcoid, infiltrative)
3. PET-FDG for sarcoid
4. PYP for amyloid
5. Genetic testing for familial

262.1.0.6.3 Heart Failure Etiology

1. Echo (functional + structural)
2. Coronary angiography or CCTA (ischemic vs non-ischemic)
3. Cardiac MRI (tissue characterization if non-ischemic)
4. PET for specific (sarcoid, amyloid)
5. Endomyocardial biopsy (rare)

262.1.0.6.4 Pre-Operative Cardiac Risk

1. Functional capacity (METs)
2. Calculator (RCRI, ACS-NSQIP)
3. Stress imaging for intermediate-risk
4. CT for vascular evaluation

262.1.0.6.5 Pulmonary Embolism

• CT Pulmonary Angiogram (CTPA): gold standard
• VQ scan for contrast-allergic / pregnancy
• Echo for hemodynamic assessment

262.1.0.6.6 Aortic Disease

• CTA for aortic aneurysm + dissection (often gold standard)
• MRI for follow-up (no radiation)
• TEE for proximal aortic dissection (rapid bedside)

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