Cardiac imaging modalities

Echocardiography - Heart's Ultrasound Selfie

• Non-invasive ultrasound to visualize heart structure, function, and hemodynamics. Two primary modes:
  • Transthoracic (TTE): Standard, non-invasive view through the chest wall. Quick, safe, and widely available.
  • Transesophageal (TEE): Invasive probe in the esophagus. Provides clearer images, especially of posterior structures (e.g., left atrium, mitral valve, aorta). Used for endocarditis, aortic dissection, and guiding procedures.
• Key Assessments:
  • Structure: Chamber size, wall thickness, valvular morphology, pericardial effusion.
  • Function: Ejection Fraction (EF), wall motion abnormalities (ischemia), diastolic function.
  • Doppler: Measures blood flow velocity and direction to assess valvular stenosis/regurgitation and shunts.
• Stress Echocardiography: TTE at rest and after exercise/dobutamine to detect inducible ischemia.

⭐ TEE is superior to TTE for detecting small valvular vegetations (<5 mm) in suspected infective endocarditis.

Cardiac CT & MRI - Slicing the Ticker

• Cardiac CT (CCT): Best for coronary anatomy & calcification.
  • • Coronary Artery Calcium (CAC) Score: Risk-stratifies asymptomatic patients. A score >100 indicates moderate plaque burden.
  • • Coronary CT Angiography (CCTA): High negative predictive value to rule out CAD in low-intermediate risk patients. Involves radiation & iodinated contrast.
• Cardiac MRI (CMR): Gold standard for function, mass, and tissue characterization. No radiation.
  • • Assesses viability (scar), inflammation, and infiltrative disease.
  • • Key for differentiating ischemic vs. non-ischemic cardiomyopathies.

⭐ Late Gadolinium Enhancement (LGE) on CMR is the gold standard for assessing myocardial viability. The pattern of enhancement (e.g., subendocardial) helps determine ischemic etiology.

Nuclear Cardiology - Glowing Hearts Club

• Principle: Uses radiotracers (e.g., Thallium-201, Technetium-99m sestamibi) to assess myocardial perfusion and viability, primarily via SPECT or PET scans.
• Stress Methods:
  • Exercise: Treadmill (preferred).
  • Pharmacologic: Vasodilators (adenosine, regadenoson) or inotropes (dobutamine).
• Key Findings:
  • Reversible Defect: Ischemia (impaired perfusion on stress, normal at rest).
  • Fixed Defect: Infarction (impaired perfusion on both stress and rest).

⭐ PET is the gold standard for assessing myocardial viability, distinguishing stunned or hibernating myocardium (viable) from scar tissue. Hibernating tissue shows a perfusion-metabolism mismatch.

Coronary Angiography - Dyeing to See Arteries

• Gold standard for diagnosing Coronary Artery Disease (CAD).
• Procedure: Involves percutaneous femoral or radial artery access. A catheter is guided to the coronary ostia, followed by injection of iodinated contrast.
• Visualization: Provides real-time X-ray imaging (fluoroscopy) of coronary arteries, revealing:
  • Stenosis (% narrowing)
  • Thrombosis (clots)
  • Anomalous origins
• Risks: Bleeding/hematoma at access site, vessel dissection, arrhythmias, stroke, and contrast-induced nephropathy (CIN).

⭐ Clinical Significance: A stenosis of >70% is generally considered hemodynamically significant and often warrants intervention (e.g., stenting). For the left main coronary artery, >50% stenosis is critical.

High‑Yield Points - ⚡ Biggest Takeaways

• Echocardiography (TTE) is the initial test for most cardiac pathology, assessing valvular function and ejection fraction.
• Transesophageal Echo (TEE) provides superior views of posterior structures (e.g., left atrial appendage, mitral valve), crucial for endocarditis and thrombus.
• Stress testing with imaging (Echo or Nuclear) is key to diagnosing myocardial ischemia in stable coronary artery disease.
• Cardiac MRI (CMR) is the gold standard for assessing myocardial viability, infiltrative cardiomyopathies, and right ventricular analysis.
• Cardiac CT Angiography (CCTA) excels at ruling out CAD in low-to-intermediate risk patients.