What Is an Echocardiogram?
Echocardiography is a non-invasive way to visualize the heart. It uses ultrasound waves at frequencies of 1-20 MHz, i.e., 1-20 million hertz–cycles per second. (The normal range of frequencies that can be heard by the ear is 5 to 20 thousand hertz).
Ultrasound waves reflect back at levels consistent with the different tissue densities encountered and these reflections are computed into a visible image that can be used for measurements of cardiac anatomy, physiology, and function. There are no known adverse effects from clinical ultrasound.
- M-mode ultrasound: The original ultrasound technology that is now used infrequently to capture details of rapidly moving structures such as valve leaflets.
- 2D Ultrasound: Ultrasound waves are used to provide tomographic (“thin slice”) imaging which is then computed into a visual signal.
- 3D Ultrasound: A three-dimensional presentation of cardiac anatomy which integrates 2D and M-mode echocardiographic information.
- TDE: Tissue Doppler Echocardiography assess myocardial motion with color assignment to show frequency shifts of myocardial velocity, useful in documenting ventricular function and abnormalities such as regurgitation.
Types of Echocardiogram and Their Uses:
- Transthoracic Echo (TTE): Via a transducer on the outside of the chest. This is the standard diagnostic cardiac ultrasound.
- Transesophageal Echo (TEE): Via a transducer placed internally into the esophagus with a tube. This ultrasound complements the TTE by providing excellent vies of the posterior and medial portions of the heart without obstruction from lung or bone: potential cardiac sources of emboli, valves to rule out endocarditis, and to rule out thrombosis associated with atrial fibrillation.
Diagnosis of an Echocardiogram
2D echocardiography, consisting of thinly sliced multiple views, is useful to diagnose
- Vegetation (intracardiac pathology)
- Valvular heart disease
- Aortic wall thickening from inflammation
- Aortic abscess
- Presence or absence of atherosclerotic calcifications
- Aortic dissection
2D echocardiography is limited by its resolution limitations.
3D echocardiography can evaluate
- Cardiac chamber volumes of the left ventricle and right ventricle
- Ejection fraction measurements of the left and right ventricles
- Atrial volumes
- Myocardial function
- Views of the mitral, tricuspid, and aortic valves and valvular heart disease
- Intracardiac masses
- Myocardial strain
3D technology can render a frame-by-frame view of the endocardial surface. New technology allows for 3D printing for pre-surgical planning.
Doppler Flow Echocardiography (Tissue Doppler Echocardiography–TDE)
Doppler flow echocardiography can measure
- Velocities of flow through the heart valves, useful in measuring the severity of stenosis.
- Left ventricular function at rest and during stress testing.
- Myocardial strain and strain rate.
Cardiac Magnetic Resonance (CMR) Imaging
Although cardiac magnetic resonance does not involve reflected sound waves but other technology, it is part of the continuum of diagnostics that begin with electrocardiography (ECG) and echocardiographic techniques. CMR is useful to assess:
- Aortic disease (aneurysms, dissection, abscesses, and coarctation).
- Atherosclerotic plaques in the aorta
- Mitral valve regurgitation and its severity
- Mitral valve stenosis
- Pericardial and myocardial disease
- Ejection fractions
- Acute coronary syndrome
- Acute and chronic MI location and extent via contrast enhancement
- 3D rendering of the aorta and its branches for preoperative strategies
Echocardiography can compare and contrast cardiac function both at rest and under stress (pharmacologic or exercise-related). Pharmacologic agents such as the adrenergic agonist, dobutamine, or dynamic exercise, such as with a treadmill, can be used in conjunction with cardiac imaging and electrocardiography (ECG) in assessing the relationship between stressing the myocardium and any resulting myocardial strain. It is useful in evaluating patients with
- Dyspnea of cardiac origin
- Pulmonary hypertension
- Mitral valve disease
- Aortic stenosis
Management of Cardiac Disease
Management of cardiac disease (including acute coronary syndrome, endo-, myo-, and pericarditis, myocardial ischemia and infarction, heart failure, and valvular disease) is based on information gleaned from electrocardiography (ECG), echocardiography (2D, 3D, TDE), and when indicated, cardiac magnetic resonance.
3D modeling is extremely useful in planning surgical investigations and therapeutic protocols. The severity of cardiac conditions can be quantitated such that these assessments can drive further diagnostics and therapeutic decisions.
Structural abnormalities of the heart, aorta, and other aspects of the cardiovascular system can determine or rule out cardiovascular disease that involves the cardiac structure and anatomy, and stress echocardiography can determine or rule out cardiovascular disease impacting the physiology of the heart. Genetic cardiovascular anomalies are also identifiable anatomically and physiologically using ultrasound.
What Can Be Prevented with an Echocardiogram?
The final goal in any echocardiographic explorations into the anatomy and physiology of the heart is prevention of sudden cardiac death. Often this is only after a first cardiac incident which serves as the sentinel event to prompt a thorough cardiac evaluation via echocardiographic modalities.
Preoperative Risk Assessment
In patients undergoing surgery, either with or without heart disease, cardiac assessment is a foundation of preoperative anesthesiology preparation. For those without cardiac disease, initial screening for a risk stratification can be made via a 12-Lead ECG–based on age, BMI (obesity), lipid status, drug use, family history, and undiagnosed, suspicious events, such as syncope.
A normal preoperative ECG often can be misleading, but it is helpful in that it provides a baseline against which to compare peri-operative or postoperative ECGs that become abnormal.
In patients with heart disease, resting echocardiography, stress echocardiography, and 24-hour ambulatory monitoring are used to prevent progression of previously documented heart disease and prevent sudden cardiac events or death.