Echocardiogram: Ultrasound Imaging of the Heart

An echocardiogram is a diagnostic imaging study that uses high-frequency sound waves to produce real-time images and measurements of the heart's structure, function, and blood flow dynamics. It is among the most widely ordered cardiac tests in clinical practice, applicable across the full spectrum of cardiovascular conditions. The information on this page covers how echocardiographic imaging is performed, the major modalities in clinical use, the clinical scenarios that drive its use, and the decision boundaries that distinguish it from alternative imaging approaches such as cardiac MRI or nuclear studies.

Definition and scope

An echocardiogram generates images by emitting ultrasound pulses — typically in the range of 1 to 5 megahertz — that reflect off cardiac structures and return to a transducer, where a processor reconstructs them into moving images. Unlike radiographic imaging, no ionizing radiation is involved. The American College of Cardiology (ACC) and the American Heart Association (AHA) classify echocardiography as a Class I recommended imaging modality for the initial evaluation of a wide range of structural and functional cardiac abnormalities, a designation reflecting the highest level of evidence and agreement in their joint guideline framework (ACC/AHA Clinical Practice Guidelines).

The test produces data on four primary domains:

1. Chamber dimensions — measured in millimeters or centimeters, including left ventricular internal diameter and wall thickness
2. Systolic function — expressed primarily as left ventricular ejection fraction (LVEF), the percentage of blood ejected with each contraction
3. Diastolic function — assessed through mitral inflow velocities and tissue Doppler imaging of the mitral annulus
4. Valvular anatomy and hemodynamics — including pressure gradients across stenotic valves and regurgitant jet characteristics

The American Society of Echocardiography (ASE) publishes the primary reference standards for measurement methodology, normal reference ranges stratified by body surface area, and reporting conventions (ASE Guidelines and Standards).

Four major echocardiographic modalities exist in routine clinical practice:

• Transthoracic echocardiogram (TTE) — performed from the chest surface using an external transducer; the standard first-line modality
• Transesophageal echocardiogram (TEE) — a probe is passed into the esophagus to obtain higher-resolution images of posterior cardiac structures; requires sedation and formal procedural consent
• Stress echocardiogram — TTE images acquired at rest and during exercise or pharmacological stress to unmask ischemia or dynamic valvular changes; described further at Cardiac Stress Testing
• Three-dimensional (3D) echocardiography — volumetric image reconstruction that improves accuracy for LVEF quantification and surgical planning for valve repair

How it works

In a standard TTE, the patient lies in the left lateral decubitus position on a cardiac examination table. A sonographer or physician applies ultrasound gel to the chest and positions the transducer at standardized windows — parasternal, apical, subcostal, and suprasternal — each providing distinct anatomical views. The full examination typically takes 30 to 60 minutes.

Doppler technology is integrated into every modern echocardiographic system and operates in three modes:

1. Pulsed-wave Doppler — measures blood flow velocity at a specific depth; used for mitral and pulmonary venous inflow
2. Continuous-wave Doppler — samples velocity along an entire scan line without depth resolution; used to measure peak gradients across stenotic valves, such as the aortic valve in aortic stenosis
3. Color flow Doppler — superimposes a color-coded velocity map onto the 2D image, enabling rapid identification of regurgitant jets and septal defects

Speckle-tracking echocardiography (STE), a post-processing technique endorsed in ASE consensus statements, tracks myocardial motion frame-by-frame to quantify global longitudinal strain (GLS) — a marker of subclinical systolic dysfunction that can be abnormal even when LVEF remains above 50%.

For TEE, the esophageal probe sits 3 to 5 centimeters posterior to the left atrium, yielding superior resolution of structures such as the left atrial appendage, mitral valve leaflets, and prosthetic valve components. The Centers for Medicare and Medicaid Services (CMS) categorizes TEE as a separately reimbursable procedural service under specific CPT codes distinct from TTE, reflecting its greater complexity and procedural risk (CMS Physician Fee Schedule).

Common scenarios

Echocardiography is ordered across a broad range of clinical presentations. The most frequent indications, as reflected in ACC/AHA appropriate use criteria, include:

• Heart failure evaluation — LVEF below 40% defines reduced ejection fraction heart failure (HFrEF); values between 41% and 49% indicate mildly reduced ejection fraction (HFmrEF); 50% or above is classified as preserved ejection fraction (HFpEF)
• Valvular disease surveillance — serial TTE every 3 to 5 years for mild aortic stenosis, annually for severe asymptomatic disease per ACC/AHA valve guidelines
• Atrial fibrillation — initial TTE to exclude structural causes; TEE when cardioversion is planned within 48 hours of unknown onset, to rule out left atrial appendage thrombus
• Infective endocarditis — both TTE and TEE are employed, with TEE offering sensitivity exceeding 90% for prosthetic valve vegetations per Duke criteria standards
• Congenital heart disease in adults — patients with conditions such as congenital heart defects undergo echocardiographic surveillance throughout adulthood
• Pre- and post-procedural assessment — required before transcatheter aortic valve replacement (TAVR) and after interventions such as angioplasty and stenting

The regulatory and billing framework governing appropriate echocardiographic ordering is discussed in the regulatory context for cardiology, including the role of appropriate use criteria in Medicare audit processes.

Decision boundaries

Echocardiography and competing modalities serve overlapping but distinct purposes. The following framework reflects published guideline-based decision logic:

Echocardiogram preferred when:
- First-line assessment of chamber size, LVEF, and valvular pathology
- Rapid bedside evaluation is required (point-of-care ultrasound protocols)
- Serial monitoring of known conditions (heart failure, valvular disease)
- Radiation avoidance is a priority (pregnancy, repeated surveillance)

Cardiac MRI preferred when:
- Tissue characterization is required (myocarditis, cardiac sarcoidosis, amyloidosis)
- Acoustic windows are inadequate on TTE (obesity, chest wall deformity, post-surgical anatomy)
- Precise volumetric quantification of right ventricular function is needed

Nuclear cardiology preferred when:
- Viability assessment drives revascularization decisions in coronary artery disease
- Perfusion imaging is required and echocardiographic image quality is suboptimal

A key contrast between TTE and TEE: TTE carries no procedural risk beyond rare transducer-related discomfort, whereas TEE carries an esophageal perforation risk estimated at approximately 1 in 10,000 procedures (ASE/Society of Cardiovascular Anesthesiologists TEE Practice Guidelines). This risk differential directly governs the clinical threshold for TEE ordering.

The index of cardiology topics provides context for where echocardiography sits within the broader diagnostic pathway for cardiovascular disease evaluation.

References

• American College of Cardiology — Clinical Practice Guidelines
• American Heart Association — Clinical Statements and Guidelines
• American Society of Echocardiography — Guidelines and Standards
• Centers for Medicare and Medicaid Services — Physician Fee Schedule
• ACC/AHA Appropriate Use Criteria for Echocardiography (Journal of the American College of Cardiology)
• Duke Criteria for Infective Endocarditis — Referenced in AHA Scientific Statement on Endocarditis

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)