What is Echocardiography: Its Structure and Function
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What is Echocardiography: Its Structure and Function

Echocardiography is a noninvasive modality that utilizes reflected sound waves to image the heart and define both its structure and function.

 

Description

• Echocardiography is a noninvasive modality that utilizes reflected sound waves to image the heart and define both its structure and function.

• Two-dimensional echocardiography is used to assess cardiac structure, left ventricular function, valvular integrity and function, and the pericardium. It also permits calculation of chamber dimensions, areas, and volumes.

• The Doppler principle, as it applies to echocardiography, states that the frequency of ultrasonic reflection increases as the reflecting object moves closer to the transducer and decreases as the reflecting object moves further away from the transducer. By applying this principle to echocardiographic analysis, the velocity of flow can be measured, which can then be utilized to calculate stroke volume, intracardiac pressure gradients, and crosssectional areas within the heart (i.e., valve areas). Color flow imaging is an adjunct to Doppler imaging that arbitrarily assigns different colors to blood that is moving toward the transducer (red) and away from the transduce (blue). It is used to detect abnormal flow such as valvular regurgitation, intraventricular shunts, and obstruction of flow within or between the cardiac chambers.

• Tissue Doppler interrogation measures the velocity and direction of the myocardium itself (especially the mitral annulus) and is used to assess diastolic function.

• Contrast echocardiography employs echo reflectors such as agitated saline or commercially developed perfluorocarbons to opacify various cardiac chambers. Agitated saline bubbles are too large to traverse the pulmonary capillary bed and thus only opacify the right-sided cardiac structures when injected intravenously. If they are visible in the left-sided chambers an intracardiac or extracardiac right to left shunt exists. The commercially based perfluorocarbon bubbles are much smaller in size and capable of crossing the pulmonary capillary bed. They are used to assess wall motion.

Indications

Echocardiography provides indispensable and comprehensive cardiac information noninvasively, and therefore is the most commonly ordered cardiac diagnostic test.

• Evaluation of murmurs and valvular heart disease:

- Any murmur associated with cardiorespiratory symptoms.

- Asymptomatic patients with a murmur suggestive of structural heart disease.

- Assessing the severity of established valvular heart disease and concomitant ventricular size and function.

- Evaluation of patients with established valvular heart disease and new or progressive cardiac symptoms. Also sometimes used in the serial evaluation of asymptomatic patients with moderate to severe valvular heart disease. Serial echocardiographic data can be used to determine optimal timing of medical and/or surgical interventions.

- Detection of vegetations, myocardial abscesses, or shunts in patients with known or suspected bacterial endocarditis. In addition, serial studies may prove useful in patients with a complex clinical course.

- Evaluation of prosthetic heart valves in patients with new or progressive cardiac symptoms (sometimes useful in asymptomatic patients).

• Chest pain and suspected ischemic heart disease:

- Evaluation of chest pain in patients with suspected MI, suspected aortic dissection, suspicion of valvular or pericardial disease, or in patients with hemodynamic instability.

- Measurement of baseline left ventricular function in the setting of an acute MI.

- Assessment for mechanical complications of an MI such as papillary muscle rupture or ventricular septal defect.

- Assessment of left ventricular function in patients with chronic ischemic heart disease.

• Left ventricular function, pericardial disease, and miscellaneous structural abnormalities:

- Excellent test to assess left ventricular function in patients with signs and symptoms of congestive heart failure (dyspnea or edema).

- Patients with suspected pericardial disease, a pericardial friction rub, or suspicion of bleeding into the pericardial space (i.e., trauma). The echocardiogram is also useful as a follow-up study to assess resolution of pericardial pathology.

- Used to identify cardiac masses, tumors, and thrombi as well as a tool to assess recurrence following excision of masses (particularly those at high risk for recurrence, i.e., myxoma).

• Pulmonary disease:

- To evaluate patients with suspected pulmonary hypertension_

- To follow pulmonary pressures in patients treated for pulmonary hypertension

• Hypertension:

- Assessment of LV function, hypertrophy, or remodeling in patients with longstanding hypertension or in patients with changing clinical status

• Neurologic or vascular events:

- To evaluate for a cardiac source of emboli in patients with abrupt occlusion of a major peripheral artery

- To evaluate for a cardiac source of embolus in patients younger than age 45 years with a stroke or in any patient with a stroke and no evidence of cerebrovascular disease

• Arrhythmias and palpitations:

- Evaluation of structural heart disease in patients with documented atrial or ventricular arrhythmias

- Evaluation of patients with a family history of a genetically transmitted cardiac disease that may predispose to arrhythmias such as hypertrophic obstructive cardiomyopathy or tuberous sclerosis

• Syncope:

- To evaluate syncope in patients with exertional syncope or in patients with suspected structural heart disease

- Evaluation of syncope in patients working in a high-risk setting (i.e., pilots)

• Routine screening:

- Patients with a family history of genetically transmitted heart disease

- In potential donors for cardiac transplantation

- To evaluate patients with phenotypic features of Marfan syndrome

- At baseline and then routine reevaluation of patients undergoing chemotherapy with cardiotoxic agents such as doxorubicin (Adriamycin)

• Critically ill or injured patients:

- Echocardiography is indicated in any patient who is hemodynamically unstable with no obvious explanation.

- To evaluate cardiac function in a patient with serious blunt or penetrating trauma, especially when the patient is hemodynamically unstable.

- Evaluation of suspected iatrogenic injury from venous catheters, guidewires, pacemaker leads, or pericardiocentesis needles regardless of tamponade symptoms.

• Adults with congenital heart disease:

- To evaluate patients with suspected congenital heart disease based on signs and symptoms such as a murmur, cyanosis, unexplained arterial desaturations, an abnormal ECG, or an abnormal chest x-ray.

- Follow-up examinations in patients with known congenital heart disease, especially when there has been a change in clinical course.

- Routine echocardiograms are indicated in patients with known congenital heart disease to follow ventricular function, valvular function, or pulmonary artery pressures.

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