Echocardiography basics

In short

Echocardiography uses pulsed high-frequency ultrasound (usually 2-7.5 MHz) to image the heart's chambers, walls, valves and great vessels in real time, and Doppler shift to measure the velocity and direction of blood flow. It is the first-line cardiac imaging test — non-ionising, portable, repeatable and inexpensive compared with CT, MRI or catheterisation — and the single most important skill a cardiac care technologist sells to an employer. A B.Sc Cardiac Care / Cardiovascular Technology student is examined on transducer physics, standard views, M-mode and 2D measurements, Doppler haemodynamics (gradients, valve areas, ejection fraction) and chamber quantification per ASE/EACVI recommendations. Jobs sit in echo labs of AIIMS, PGIMER, SCTIMST, CMC Vellore, Narayana Health, Apollo, Fortis, Medanta, Asian Heart and district cardiac units, plus device and service roles with GE, Philips, Siemens Healthineers, Mindray and Samsung Medison. Practice in India is regulated at the facility level by the Clinical Establishments (Registration and Regulation) Act, 2010 in adopting states and by the Atomic Energy Regulatory Board only for ionising modalities — ultrasound is not ionising, but the PC&PNDT Act, 1994 controls who may use any ultrasound machine capable of foetal sex determination.

Explained

Physics of ultrasound and the transducer

• Ultrasound is sound above 20 kHz; cardiac imaging uses 2-7.5 MHz (adults 2-3.5 MHz, paediatrics and TEE 5-7.5 MHz).
• Propagation speed in soft tissue is taken as 1,540 m/s; the machine converts echo return time to depth using distance = (c × t)/2 (the "2" because the pulse travels out and back).
• Wavelength λ = c/f. At 3 MHz, λ = 1540/3×10⁶ ≈ 0.51 mm — axial resolution is about one to two wavelengths, so higher frequency gives finer detail.
• Frequency trade-off: attenuation rises with frequency (roughly 0.5 dB/cm/MHz in soft tissue), so high frequency = good resolution, poor penetration. This is why an obese adult is scanned at 2 MHz and a neonate at 7 MHz.
• Piezoelectric effect: the crystal (lead zirconate titanate, PZT) converts electrical pulses to sound and returning sound to voltage — the basis of both transmit and receive.
• Resolution types: axial (along the beam, set by pulse length/frequency), lateral (across the beam, set by beam width and focusing), temporal (frame rate — narrow sector and shallow depth raise it).
• Transducer types: phased array (standard TTE — small footprint, electronic steering, fits between ribs), matrix array (3D/4D), micro-convex (paediatric), and the multiplane TEE probe swallowed into the oesophagus.
• Acoustic coupling gel excludes air, whose impedance mismatch with skin reflects almost all the beam.
• Harmonic imaging: the machine transmits at f and receives at 2f, cutting near-field artefact and clutter — now the default adult setting.

Modes of display

1. A-mode (amplitude vs depth) — historical, not used clinically in cardiology.
2. M-mode (motion mode): one scan line plotted against time; extremely high temporal resolution. Used for LV internal dimensions, aortic root and left atrium, mitral valve motion (the classic M, EF slope), septal/posterior wall thickness, and the "E-point septal separation".
3. 2D (B-mode) real-time imaging: the standard anatomical display — a sector sweep at 30-100 frames per second.
4. 3D / 4D echo: matrix array; used for mitral valve morphology, LV volumes without geometric assumption and pre-procedure planning (TAVI, device closure).
5. Doppler modes:
   • Pulsed-wave (PW): samples one small gate at a known depth — gives site-specific velocity but aliases above the Nyquist limit.
   • Continuous-wave (CW): transmits and receives continuously along a line — records very high velocities with no aliasing, but with range ambiguity (cannot say where along the line).
   • Colour flow Doppler: PW over a region, velocity mapped to colour. BART convention — Blue Away, Red Towards the transducer; turbulence shows as mosaic/green.
   • Tissue Doppler imaging (TDI): low-velocity, high-amplitude myocardial motion; gives s', e' and a' at the mitral annulus for diastolic function.
   • Strain / speckle tracking: global longitudinal strain (GLS), normal about −18% to −22% (more negative = better); detects subclinical dysfunction before EF falls, e.g. in chemotherapy monitoring.
6. Aliasing occurs when velocity exceeds the Nyquist limit (PRF/2); remedies are baseline shift, higher PRF/scale, lower frequency, or switching to CW.

Standard transthoracic examination and views

• Patient preparation: left lateral decubitus, left arm raised, ECG electrodes attached for timing, chest exposed, gel applied; scanning is done from the patient's left side in most Indian labs, with the room darkened.
• Four acoustic windows and the main views:
  • Parasternal long axis (PLAX) — left 3rd/4th intercostal space: LV, LA, mitral and aortic valves, aortic root, IVS and posterior wall; the plane for M-mode measurements and for RV outflow/RVOT.
  • Parasternal short axis (PSAX) — rotate ~90° clockwise: levels at aortic valve ("Mercedes-Benz" cusps, with RVOT, PV, TV and the inter-atrial septum), mitral valve ("fish-mouth"), and papillary muscle/apex level for regional wall motion.
  • Apical — apex: 4-chamber (all four chambers, both AV valves, septa), 5-chamber (adds LVOT/aortic valve — the window for CW across the aortic valve), 2-chamber (anterior and inferior walls), 3-chamber / apical long axis.
  • Subcostal — below xiphisternum: IVC with respiratory collapse, atrial septum, pericardial effusion, good in ventilated or emphysematous patients.
  • Suprasternal notch — aortic arch, coarctation, patent ductus flow.
• Transducer manoeuvres: sliding, angulation (tilting), rocking, rotation; the index mark convention places the screen marker on the right of the image.
• Image optimisation: depth, gain, time-gain compensation, focus, sector width, and Doppler alignment — keep the intercept angle below 20°, because measured velocity = true velocity × cos θ.

What echo reports: structure and function

• Chamber quantification (ASE/EACVI 2015 and later updates): LV internal diameter, wall thickness, LV mass, LA volume indexed to body surface area, RV basal diameter. Values are indexed and reported against age- and sex-specific normals; Indian normal ranges run slightly smaller than Western ones because of body size, so indexed values matter.
• Systolic function: ejection fraction (LVEF) by biplane Simpson's method of discs (the recommended 2D method), fractional shortening from M-mode, Teichholz volumes (now discouraged), 3D EF (most accurate), dP/dt, and MAPSE. Visual "eyeball EF" is used in practice but must be stated as estimated.
• EF grading commonly used: ≥52% (men) / ≥54% (women) normal; mild 41-51%; moderate 30-40%; severe <30%. HFrEF is defined at EF ≤40%, HFmrEF 41-49%, HFpEF ≥50% — ranges differ slightly between guideline versions, so quote the lab's reference.
• Diastolic function: mitral E and A velocities and E/A ratio, E deceleration time, e' by TDI, E/e' ratio (average >14 suggests raised filling pressure), LA volume index, tricuspid regurgitation velocity. Grades: I impaired relaxation (E/A <0.8), II pseudonormal, III restrictive (E/A >2).
• RV function: TAPSE (normal ≥17 mm), RV s' by TDI (≥9.5 cm/s), RV fractional area change, RIMP.
• Valves: morphology (thickening, calcification, prolapse, vegetation, rheumatic commissural fusion), gradients by CW Doppler, valve area by planimetry, continuity equation or pressure half-time; regurgitation graded by jet area, vena contracta width, PISA-derived effective regurgitant orifice area and regurgitant volume.
• Pericardium: effusion size and distribution, tamponade signs (RA/RV diastolic collapse, IVC plethora, >25% respiratory variation in mitral inflow, swinging heart).
• Others: intracardiac masses and thrombus, vegetations, congenital shunts (ASD, VSD, PDA) with colour and agitated-saline bubble study, aortic dimensions and dissection flap, IVC diameter for volume status.
• In rheumatic heart disease — still a major Indian workload — echo shows mitral commissural fusion, doming, the "hockey stick" anterior leaflet, and the Wilkins score that decides suitability for balloon mitral valvotomy.

Specialised and advanced echo

• Transoesophageal echo (TEE/TOE): probe in the oesophagus, 5-7 MHz, far better resolution of LA appendage thrombus, prosthetic valves, endocarditis vegetations, aortic dissection and atrial septum. Needs fasting ≥4-6 hours, topical/sedative anaesthesia, consent, pulse oximetry, bite guard and probe disinfection (high-level, e.g. glutaraldehyde or OPA/automated reprocessor). Contraindicated in oesophageal stricture, varices, perforation.
• Stress echo: images at rest and at peak exercise (treadmill/bicycle) or with pharmacological stress (dobutamine, dipyridamole) to detect inducible ischaemia as new wall-motion abnormality; also used to grade valve lesions and viability (low-dose dobutamine).
• Contrast echo: agitated saline for right-to-left shunt; microbubble contrast agents for LV opacification and perfusion.
• Point-of-care / focused echo (FoCUS): ICU, emergency and peri-arrest use — effusion, gross LV function, RV strain, volume status.
• Fetal and paediatric echo, intracardiac and intraoperative echo are sub-specialities; a technologist in a paediatric cardiac unit will be expected to handle segmental analysis of congenital heart disease.

Artefacts, limitations and the technologist's role

• Common artefacts: reverberation, mirror image, acoustic shadowing (by calcium, prosthesis or rib), side lobes, near-field clutter, lateral drop-out of thin structures (atrial septum) mimicking a defect, and "pseudo-dissection" of the ascending aorta.
• Limitations: operator-dependent, needs an acoustic window (fails in obesity, emphysema, chest deformity, post-sternotomy patients), geometric assumptions in 2D volume methods, foreshortened apical views under-reading volume, and angle dependence of Doppler.
• No ionising radiation, no known biological risk at diagnostic cardiac intensities; ALARA and the mechanical/thermal index still apply, and thermal index matters in fetal scanning.
• The technologist's duties: machine QA and probe care, patient identity and consent, acquiring a complete protocol-driven study, correct measurement and tabulation, archiving to PACS/DICOM, reporting technical findings to the cardiologist (interpretation and diagnosis are the physician's responsibility), infection control and probe disinfection.
• Indian regulatory points: any ultrasound machine capable of foetal imaging is covered by the PC&PNDT Act, 1994 and its Rules — registration of the facility, Form F for obstetric scans, the mandatory declaration that sex determination is not done, and heavy penalties; cardiac echo labs that own such machines must still display the notice and keep the machine registered. Hospital registration falls under the Clinical Establishments Act, 2010 where the state has adopted it, and biomedical waste (gel wipes, probe covers, TEE accessories) under the Bio-Medical Waste Management Rules, 2016 as amended. Equipment itself is a notified medical device under the Medical Devices Rules, 2017 administered by CDSCO. Certification and scope of practice for technologists vary by state council and institution; there is no single nationwide licence, so verify local requirements.

Key points

• Echocardiography - pulsed ultrasound imaging plus Doppler flow measurement of the heart; first-line cardiac imaging.
• 1,540 m/s - assumed speed of sound in soft tissue; all depth calculation rests on it.
• λ = c/f - higher frequency means shorter wavelength, better axial resolution, less penetration.
• Piezoelectric crystal (PZT) - converts electrical energy to ultrasound and back.
• M-mode - single line vs time, highest temporal resolution; used for LV dimensions and fractional shortening.
• PW Doppler - depth-specific velocity, aliases above the Nyquist limit (PRF/2).
• CW Doppler - any high velocity recorded without aliasing, but no range resolution; used across stenotic valves.
• Colour Doppler BART - Blue Away, Red Towards; mosaic indicates turbulence.
• Doppler angle - velocity underestimated by cos θ; keep intercept angle under 20°.
• Four windows - parasternal, apical, subcostal, suprasternal; PLAX, PSAX, A4C, A5C, A2C are the core views.
• Biplane Simpson's method - recommended 2D EF method; traces endocardium in A4C and A2C at end-diastole and end-systole.
• Normal LVEF - about ≥52% men, ≥54% women; HFrEF is EF ≤40%.
• TAPSE ≥17 mm - simple M-mode index of RV systolic function.
• E/A and E/e' - diastolic function; E/e' above ~14 suggests raised LV filling pressure.
• Simplified Bernoulli ΔP = 4v² - converts peak Doppler velocity (m/s) into pressure gradient (mmHg).
• Continuity equation - conservation of flow gives aortic valve area from LVOT area and velocity ratios.
• Pressure half-time 220/PHT - gives mitral valve area in mitral stenosis.
• PC&PNDT Act, 1994 - governs possession and use of any ultrasound machine capable of foetal sex determination in India.

Formulas and examples

Example 1 — Wavelength, resolution and penetration. A 3.5 MHz adult probe is swapped for a 7 MHz paediatric probe.

• λ at 3.5 MHz = 1540 / 3.5×10⁶ = 4.4 × 10⁻⁴ m = 0.44 mm.
• λ at 7 MHz = 1540 / 7×10⁶ = 2.2 × 10⁻⁴ m = 0.22 mm — axial resolution roughly halves (improves).
• Attenuation at 0.5 dB/cm/MHz over a 15 cm path (one way): 0.5 × 15 × 3.5 = 26.3 dB at 3.5 MHz versus 0.5 × 15 × 7 = 52.5 dB at 7 MHz — hence poor penetration at 7 MHz in an adult.

Example 2 — Fractional shortening and ejection fraction from M-mode. PLAX M-mode gives LVIDd = 5.4 cm, LVIDs = 4.0 cm.

• FS = (5.4 − 4.0)/5.4 × 100 = 1.4/5.4 × 100 = 25.9% (normal 25-45%, so borderline low).
• Teichholz volumes: V = 7D³/(2.4 + D).
  • EDV = 7 × 5.4³ / (2.4 + 5.4) = 7 × 157.46 / 7.8 = 1102.2 / 7.8 = 141.3 mL.
  • ESV = 7 × 4.0³ / (2.4 + 4.0) = 7 × 64 / 6.4 = 448 / 6.4 = 70.0 mL.
  • EF = (141.3 − 70.0)/141.3 × 100 = 71.3/141.3 × 100 = 50.5% — mildly reduced; report biplane Simpson's instead, because a single diameter cannot represent a regionally abnormal ventricle.

Example 3 — Stroke volume, cardiac output and aortic valve area (continuity equation). LVOT diameter 2.0 cm, LVOT VTI 22 cm, LVOT peak velocity 1.0 m/s; CW across the aortic valve gives peak velocity 4.0 m/s and VTI 95 cm. Heart rate 72/min, BSA 1.6 m².

• LVOT CSA = π/4 × 2.0² = 0.7854 × 4 = 3.14 cm².
• SV = 3.14 × 22 = 69.1 mL.
• CO = 69.1 × 72 = 4,975 mL/min = 4.98 L/min; CI = 4.98/1.6 = 3.11 L/min/m² (normal).
• Peak gradient = 4 × 4.0² = 64 mmHg.
• AVA = (3.14 × 22)/95 = 69.1/95 = 0.73 cm²; indexed = 0.73/1.6 = 0.45 cm²/m².
• Dimensionless index = 1.0/4.0 = 0.25.
• Interpretation: AVA <1.0 cm², indexed <0.6, DI ≤0.25 and peak velocity 4.0 m/s (peak gradient 64 mmHg) — severe aortic stenosis with preserved flow.

Example 4 — Mitral stenosis and pulmonary pressure. Rheumatic mitral stenosis: pressure half-time 220 ms, mean mitral gradient 12 mmHg, TR peak velocity 3.5 m/s, estimated RA pressure 10 mmHg.

• MVA = 220/220 = 1.0 cm² → severe mitral stenosis (severe <1.5 cm², very severe <1.0).
• RVSP = 4 × 3.5² + 10 = 4 × 12.25 + 10 = 49 + 10 = 59 mmHg → severe pulmonary hypertension by echo estimate.
• Together with a mean gradient of 12 mmHg this is a classic Indian echo lab finding referred for balloon mitral valvotomy if the Wilkins score is favourable and there is no LA thrombus (confirm on TEE).

Example 5 — Aliasing and the Nyquist limit. PW Doppler at 2.5 MHz with PRF 6 kHz, θ = 0°.

• Nyquist limit = 6,000/2 = 3,000 Hz Doppler shift.
• Maximum unaliased velocity v = (Δf × c)/(2 f₀ cos θ) = (3,000 × 1,540)/(2 × 2.5×10⁶ × 1) = 4,620,000/5,000,000 = 0.92 m/s.
• A mitral stenosis jet of 2 m/s will therefore wrap around; switch to CW Doppler (no Nyquist limit) to record it.

(Prices are indicative private-sector ranges and vary widely by city and scheme — CGHS and Ayushman Bharat PM-JAY rates are lower and are revised periodically.)

Where it is used

• Hospital echo labs and cath-lab support: non-invasive cardiology departments at AIIMS, PGIMER Chandigarh, SCTIMST Thiruvananthapuram, CMC Vellore, Narayana Health, Apollo, Fortis, Medanta, Asian Heart Institute — technologists run routine TTE lists, assist TEE and stress echo, and archive studies.
• Critical care, emergency and OT: FoCUS in ICUs and casualty for tamponade, RV strain in pulmonary embolism, volume status; intraoperative TEE in cardiac surgery and peri-operative monitoring.
• Rheumatic heart disease and congenital programmes: screening camps, school screening, Wilkins scoring before balloon mitral valvotomy, pre- and post-device-closure studies for ASD/VSD/PDA — a very large Indian caseload.
• Industry roles: application specialist, clinical demonstrator and service engineer with GE HealthCare, Philips, Siemens Healthineers, Mindray, Samsung Medison, Esaote; pre-sales demos and customer training on Vivid/EPIQ/ACUSON platforms.
• Research, clinical trials and cardio-oncology: core-lab reading and GLS-based monitoring for cardiotoxicity in patients on anthracyclines or trastuzumab; echo endpoints in CRO and academic trials.
• Teleradiology, insurance and preventive health: reporting support, corporate master health checks, fitness-for-work and insurance medicals, and overseas roles in the Gulf and the UK where Indian B.Sc cardiac technologists are widely recruited (subject to local registration such as DOH Abu Dhabi/DHA/MOH licensing exams).

Interview questions

• Q: Why is 1,540 m/s used for all soft tissue in echo? A: It is the average propagation speed of ultrasound through soft tissue; the scanner uses it with the echo return time to compute depth, which is why structures behind fat or a prosthesis can be mis-positioned slightly.
• Q: When would you choose PW Doppler over CW Doppler? A: When you need velocity at a known depth — LVOT, mitral inflow, pulmonary vein — and the velocity is below the Nyquist limit; for high-velocity stenotic or regurgitant jets use CW.
• Q: What is the simplified Bernoulli equation and when does it fail? A: ΔP = 4v², converting peak velocity in m/s to a gradient in mmHg; it fails when the proximal (LVOT) velocity exceeds about 1.5 m/s, in serial stenoses, in long tunnel-like obstructions and when the beam is badly aligned.
• Q: Why is biplane Simpson's method preferred to M-mode or Teichholz for EF? A: It sums actual traced disc volumes from two orthogonal apical views, so it does not assume a symmetrical ellipsoid and handles regional wall-motion abnormalities, which a single diameter cannot.
• Q: How do you estimate pulmonary artery systolic pressure on echo? A: Measure the peak tricuspid regurgitation velocity by CW, apply 4v² for the RV-RA gradient and add estimated RA pressure from IVC size and collapse; this equals PASP when there is no pulmonary stenosis or RVOT obstruction.
• Q: A patient's apical four-chamber EF looks much better than the visual impression. What would you check? A: Foreshortening of the apex, which shortens the long axis and under-reads volumes; also endocardial tracing including papillary muscles, incorrect end-systolic frame, and poor lateral wall definition.
• Q: What does TAPSE measure and what is normal? A: Longitudinal systolic excursion of the lateral tricuspid annulus by M-mode; normal is 17 mm or more, below which RV systolic dysfunction is suggested.
• Q: What are the preparation and safety steps before a TEE? A: Informed consent, 4-6 hours fasting, IV access, topical pharyngeal anaesthesia with or without sedation, bite guard, pulse oximetry and monitoring, exclusion of oesophageal disease, and high-level probe disinfection before and after.
• Q: How does colour Doppler decide red and blue? A: By direction relative to the transducer, not by oxygenation — red towards, blue away (BART); mosaic colour indicates high-velocity turbulence or aliasing.
• Q: Does echo use radiation, and what Indian law applies to the machine? A: No ionising radiation, so AERB licensing does not apply; however any ultrasound machine capable of foetal imaging falls under the PC&PNDT Act, 1994, and the equipment is a notified medical device under CDSCO's Medical Devices Rules, 2017.
• Q: Why does an aortic stenosis patient with low EF show a low gradient despite a small valve area? A: Low stroke volume produces a low transvalvular flow rate and therefore a low gradient — "low-flow, low-gradient" severe AS; the dimensionless index, indexed valve area and dobutamine stress echo help resolve it.
• Q: Name three echo artefacts you must not call pathology. A: Lateral drop-out of the atrial septum mimicking an ASD, reverberation or mirror artefact in the aorta mimicking dissection, and near-field clutter or side lobes mimicking apical thrombus — all confirmed by imaging from a second window.

Common mistakes

• Using the simplified ΔP = 4v² when LVOT velocity is high, or applying it to the mean instead of the peak velocity without saying so.
• Ignoring the Doppler intercept angle: at 60° the recorded velocity is only half the true value, and the gradient only a quarter.
• Measuring the LVOT diameter sloppily — it is squared in the CSA, so a 10% diameter error becomes a 21% error in stroke volume and valve area.
• Confusing colour Doppler red with arterial/oxygenated blood instead of direction towards the transducer.
• Taking M-mode or Teichholz EF as definitive in a dilated or regionally abnormal LV.
• Reporting PW Doppler velocities that have aliased, instead of switching to CW or shifting the baseline.
• Writing an interpretive diagnosis as a technologist, or releasing a study without patient identity verification, protocol completeness and probe disinfection.

Related topics

Electrocardiography (ECG): recording and interpretation · Cardiac stress testing and Holter monitoring · Cardiac catheterisation lab: angiography and angioplasty · Pacemakers and implantable cardiac devices · Cardiac anatomy and physiology · Haemodynamic monitoring and cardiac output measurement