Indications and limitations of echocardiograms

Q: What is the principle behind echocardiography?

A: The techniques of echocardiography rely on ultrasound reflection off of cardiac structures, which then are used to generate images of the heart and great vessels.

Q: What information is typically gathered from an adult echocardiogram?

A: Echocardiograms are typically ordered to investigate for the presence of thrombi, valvular vegetations, anatomic abnormalities, and to evaluate the function of the heart itself.

Q: What role does the echocardiogram have in the diagnosis/treatment/monitoring of CHF?

A: An echocardiogram is warranted in any patient given a new clinical diagnosis of CHF. Echocardiograms are also warranted when there is a sudden worsening in the patient's condition, with the development of a new murmur or arrhythmia, and for the evaluation of therapy, either medical or surgical.

Q: What specific information about CHF does the echocardiogram provide?

A: The echocardiogram provides an estimation of left ventricular size and motion, ejection fraction, and information on valvular structure and function. Echocardiograms may therefore also suggest the underlying cause of the CHF, i.e., valvular insufficiency, dilated cardiomyopathy.

Q: Are there different types of echocardiography?

A: Yes, there is Doppler analysis, M-mode echocardiography, two-dimensional trans thoracic echocardiography (TTE), trans esophageal echocardiography (TEE), and 3-D echocardiography.

Q: What are the strengths of TTE? What are the weaknesses?

A: The TTE provides good images of the heart, the pericardium, and the great vessels. The procedure is by itself without risk and is associated with little discomfort. When stressing the heart with exercise or dobutamine, there is a small risk of arrhythmia, hypotension, and ischemia.

The study depends on good thoracic “windows” from the body surface to the interior of the heart. If a patient has significant lung disease or history of thoracic surgery, images can be compromised. Patients that cannot be laterally rotated such as ICU, ventilator dependent, or post-surgical patients provide additional challenges to the technician. Overweight patients also provide for technically challenged studies.

Q: What are the sensitivity and specificity of 2-D echocardiography for ventricular dysfunction consistent with heart failure?

A: As high as 80 and 100%, respectively

Q: What are the strengths of the TEE? What are the weaknesses?

A: The TEE, although more invasive than TTE, circumvents problems created by poor anatomical windows and patient position. It is usually indicated when the physician cannot reliably obtain a TTE. The transducer is fixed to a flexible endoscope and then slid into the esophagus and stomach.

The procedure is uncomfortable to the patient, carries a small risk of oral, pharyngeal, and esophageal trauma. There are also case reports of infective endocarditis associated with TEE.

Q: What is the role of Doppler echocardiography?

A: Doppler echocardiography is aimed at acquiring flow rates and for identifying the presence of obstruction, i.e., thrombus, to that flow. Doppler analysis in CHF patients is usually in conjunction with TTE, as flow velocity in the great vessels and across the valves can be assessed along with the function of the heart. Pressure gradients across the valves are also extrapolated from this information using a modified Bernoulli equation. Pressure change = 4 (velocity) 2

Q: What is M-mode echocardiography?

A: M-mode echocardiography is one dimensional echocardiography and can generate quantitative estimates of chamber size and function. Two-dimensional echocardiograms rely more on the qualitative descriptions of observers. M-mode echocardiography is dependent upon the patient having symmetrically contracting ventricles.

Note: 3-D echocardiography is growing in accessibility and utility and will likely play a greater role in the evaluation of cardiac function in the next 5-10 years. It promises exceptional images of the heart.

Q: What is stress echocardiography?

A: This usually entails the use of 2-D and Doppler echocardiography to confirm the suspicion of coronary artery disease, and if present, to determine its severity. Studies are performed at rest and after physical or pharmacological stress. These images are then compared side by side.

Q: What might be seen on a positive stress test?

A: A positive stress test usually entails evidence of ischemia. Ischemic myocardium performs differently than well-perfused myocardium. One might see regional wall abnormalities, an increase in end systolic volume, and a decrease in ejection fraction with an ischemic heart.

Q: What is the sensitivity and specificity of a dobutamine echocardiogram for detecting Coronary Heart Disease?

A: 78% and 88%, respectively.