Cardiac Ultrasound (Echocardiography)
Cardiac Ultrasound tests a structured, quantitative approach: chamber size, systolic and diastolic function, valve severity, and pericardial disease. The exam expects you to know which measurement is valid in which window and how errors propagate.
Core rules
- Left ventricular ejection fraction is measured by Simpson's biplane method of disks, tracing end-diastole and end-systole in apical four- and two-chamber views.
- LVOT diameter is measured inner edge to inner edge at the hinge points in mid-systole, zoomed in the parasternal long axis.
- Aortic stenosis severity: peak velocity ≥4 m/s, mean gradient ≥40 mmHg, or valve area <1.0 cm²; very severe is <0.6 cm².
- The continuity equation: AVA = (LVOT area × LVOT VTI) ÷ aortic valve VTI.
- Diastolic function uses E/A, septal e′ <7 cm/s, lateral e′ <10 cm/s, E/e′ >14, TR velocity >2.8 m/s and left atrial volume index >34 mL/m².
- Pericardial effusion anterior to the descending aorta is pericardial; posterior to it is pleural.
Worked example
LVOT diameter 2.0 cm, LVOT VTI 20 cm, aortic valve VTI 100 cm. LVOT area = π × 1.0² = 3.14 cm². AVA = (3.14 × 20) ÷ 100 = 0.63 cm². With peak velocity 4.3 m/s (peak gradient 4V² = 74 mmHg) and mean gradient 45 mmHg, this is severe aortic stenosis at normal flow. Show the formula and units; a 2 mm LVOT error changes the area by roughly 20%.
Traps that cost marks
Over-sizing the LVOT; using peak rather than mean gradient for severity; ignoring pressure recovery in small aortas; and diagnosing tamponade from effusion size alone rather than chamber collapse and Doppler findings.