Echocardiography Study Guide

📖 Core Concepts Echocardiography – ultrasound imaging of the heart; can be plain B‑mode or combined with Doppler to assess blood flow velocity. Doppler modes – pulsed‑wave (samples at a single depth) and continuous‑wave (samples along the whole beam) for measuring flow speed. Ejection Fraction (EF) – % of left‑ventricular (LV) blood pumped out each systole; $$\text{EF} = \frac{\text{EDV} - \text{ESV}}{\text{EDV}} \times 100\%$$ where EDV = end‑diastolic volume, ESV = end‑systolic volume. Valvular severity – graded (mild‑moderate‑severe) using Doppler‑derived gradients, pressure half‑time, vena contracta, and jet area. Stress Echo – compares resting wall‑motion to peak‑exercise (≈ 85 % of age‑predicted HR = 220 − age) to uncover ischemia. Imaging windows – parasternal long/short, apical 2‑/3‑/4‑chamber, subcostal; each yields 2‑D, M‑mode, and (if available) 3‑D data. Indexing – dimensions are often normalized to body surface area (BSA) (e.g., LV mass index). 📌 Must Remember EF thresholds – Normal ≥ 55 %; reduced EF < 40 % guides heart‑failure therapy & ICD eligibility. Pressure half‑time (PHT) – Used for aortic stenosis; severe if PHT < 100 ms, mild if > 200 ms. Vena contracta width – ≥ 0.7 cm = severe mitral regurgitation. E/A ratio – E/A < 0.8 (impaired relaxation), 0.8‑1.5 (normal), > 2 (restrictive filling). Deceleration time (DT) – Short DT (< 150 ms) suggests high filling pressures. Isovolumic relaxation time (IVRT) – Prolonged > 100 ms indicates diastolic dysfunction. Right ventricular systolic pressure (RVSP) – estimate pulmonary pressure: $$\text{RVSP} = 4(v{\text{TR}})^2 + \text{RA pressure}$$ where $v{\text{TR}}$ = tricuspid regurgitant velocity (m/s). 🔄 Key Processes Performing a TTE Position transducer → obtain standard windows. Acquire 2‑D loops → measure LV dimensions (end‑diastolic & end‑systolic diameters). Switch to M‑mode for precise wall thickness & fractional shortening. Add Doppler: a. Pulsed‑wave at mitral inflow → record E & A velocities → calculate E/A ratio & DT. b. Continuous‑wave across valve → measure peak gradient → apply Bernoulli $$\Delta P = 4v^2$$ to grade stenosis. If image quality poor → consider contrast‑enhanced study or TEE. Stress Echo Workflow Baseline images at rest. Apply exercise/pharmacologic stress → achieve target HR (≈ 85 % of 220 − age). Capture images at peak stress → compare wall‑motion to rest; new hypokinesis = positive for CAD. Quantifying Regurgitation Locate jet → measure vena contracta width. Use proximal isovelocity surface area (PISA) if needed: $$\text{Regurgitant flow} = 2\pi r^2 \times V{\text{alias}}$$ where $r$ = PISA radius, $V{\text{alias}}$ = aliasing velocity. 🔍 Key Comparisons Pulsed‑wave vs Continuous‑wave Doppler PW: depth‑specific, limited to ≤ 2 m/s (aliasing). CW: captures all velocities along beam, no aliasing, but no depth discrimination. TTE vs TEE TTE: non‑invasive, limited by chest wall; first‑line. TEE: invasive probe in esophagus; superior for posterior structures, prosthetic valves, and when TTE windows are poor. M‑Mode vs B‑Mode M‑Mode: single‑line, ultra‑high temporal resolution (≤ 1 ms) → precise timing & dimensions. B‑Mode: 2‑D cross‑sectional view → anatomy, wall motion, volume. ⚠️ Common Misunderstandings “EF = stroke volume” – EF is fraction of EDV ejected; stroke volume = EDV − ESV. “All regurgitant jets look the same” – Jet area alone overestimates severity; vena contracta and PISA are more reliable. “A normal EF rules out heart failure” – Diastolic dysfunction can cause HFpEF with preserved EF; look at E/A, DT, LA volume. “Contrast only for LV function” – Also improves endocardial border definition for valvular assessment and detects LV thrombus. 🧠 Mental Models / Intuition “Velocity → Gradient” – Remember Bernoulli’s simple rule: every 1 m/s increase in velocity ≈ 4 mmHg pressure rise. “Window → View → Verdict” – Each standard window offers a specific “look angle”; memorize which valve/structure is best seen where (e.g., parasternal long‑axis for aortic valve, apical 4‑chamber for mitral valve). “Stress = Unmask” – Ischemic myocardium is silent at rest; stress forces it to show wall‑motion deficits—think of a hidden crack that only appears under load. 🚩 Exceptions & Edge Cases Atrial fibrillation – Irregular RR intervals → average several beats for Doppler measurements; EF may be misleading. Severe mitral stenosis with low flow – Mean gradient may underestimate severity; use valve area (planimetry) instead. Obesity or COPD – Poor acoustic windows → early move to TEE or contrast‑enhanced TTE. Prosthetic valves – Acoustic shadowing limits Doppler; rely on continuity equation or CT for gradients. 📍 When to Use Which TTE – First‑line for any new cardiac evaluation, routine follow‑up, and valvular grading when windows are adequate. TEE – Indicated when TTE is nondiagnostic (e.g., endocarditis, prosthetic valve assessment, atrial thrombus). Stress Echo – Preferred functional test for CAD when radiation or contrast CT is undesirable; also for viability assessment. Contrast‑enhanced echo – Use if endocardial border is fuzzy, LV thrombus suspected, or to improve EF accuracy. 👀 Patterns to Recognize “High velocity + narrow jet” → stenosis (e.g., aortic stenosis). “Low velocity + broad jet” → regurgitation (e.g., mitral regurg). “Delayed relaxation (prolonged IVRT) + reduced E/A → impaired relaxation diastolic pattern. “RVSP > 35 mmHg + TR jet > 2.8 m/s → pulmonary hypertension. 🗂️ Exam Traps Mistaking peak velocity for mean gradient – Remember to convert: mean gradient ≈ ½ × peak gradient for aortic stenosis. Using EF alone to grade severity of aortic stenosis – Severity is based on valve area & gradients, not EF. Assuming a jet area > 50 % of LA = severe MR – Overestimates; always check vena contracta or PISA. Confusing deceleration time with E‑wave velocity – DT measures the slope after the E‑wave; a short DT indicates high left‑atrial pressure, not high flow. Choosing TEE for routine follow‑up of mild valve disease – Over‑use; guidelines advise against routine echo in asymptomatic mild disease.