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Submitted by Dr. Yasser Mokhtar, MD. Dept. of internal medicine. School of medicine, University of South Dakota.

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TEE improves diagnostic information in various cardiovascular diseases compared to conventional echo.

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There are two approaches to a TEE study:

The first is to begin imaging from transgastric position (normally obtained when the transducer is at 40-45 cm from incisors) and then pull the probe back to examine various sections of the heart from apex to base and to view aorta by posterior rotation of transducer.

The second approach is to start at the base of the heart (25-30 cm from the incisors) and progress towards transgastric views and examination of aorta during withdrawal.

Biplane TEE imaging

This was described by Fisher et al. in 1991 and later by Khandheria et al. in 1994. Biplane probe gives additional longitudinal windows. Transducer position is detected by echocardiographic images on monitor and probe?s centimeter markings that measure the depth from the incisor teeth to transducer position within the esophagus (Fisher et al., 1991 and Khandheria et al., 1994).

I. Horizontal TEE imaging

With horizontal imaging, structures that are anterior anatomically are most distant from transducer and appear on the bottom of the screen and posterior structures appear at the top because they are more proximal to the probe.

Anteflexion and retroflexion are the maneuvers most commonly used to optimize anatomic delineation.

A. Basal short axis scans:    

Transducer is at 25-30 cm from incisor teeth where it is posterior to the left atrium. With mild anteflexion (tilting the tip superiorly) or slight withdrawal of the transducer sequential basal short axis scans are obtained. Traditional orientation is to place anterior structures at the bottom, posterior structures at the top, left sided structures to viewer?s right on video display.

  • Aortic valve view: Where aortic root, aortic valve cusps and atrial septum are seen.

  • Coronary artery view: The left coronary artery is seen more often and more clearly than the right coronary artery. TEE is used to detect left main coronary stenosis and anomalous coronary arteries and to assess coronary blood flow (Pearce et al., 1989, Yoshida et al., 1990, Salloum et al., 1991, Iliceto et al., 1991, Smolin et al., 1992 and Rubin et al., 1992).

  • Left atrial appendage view: Left atrial appendage is seen as a triangular extension of the left atrium (pectinate muscles are seen with high-resolution TEE transducers and should not be confused with thrombi). Also seen are the left upper pulmonary vein, the transverse sinus of pericardium, the transverse orifice of SVC, aortic and pulmonary valves, the right pulmonary veins and the right and left atria separated by the interatrial septum.

  • Pulmonary artery view: Main pulmonary artery and its bifurcation, proximal ascending aorta and superior vena cava are seen in this view. Clockwise rotation of the transducer allows the visualization of the proximal portion of the left pulmonary artery. The portion distal to its first bifurcation can be seen. Counterclockwise rotation enables the examiner to see the very proximal portion of the left pulmonary artery. Its distal portion can not be viewed as it is obscured by air in the left main bronchus.

B. Frontal four chamber scans:

TEE probe position is at the mid esophageal level (30-35 cm from the incisor teeth.

  • Left ventricle outflow view: Transducer tip anteflexed. Shows the left ventricle outflow tract, anterolateral papillary muscle, aortic valve, left atrium, mitral valve and its support structures.

  • Four-chamber view: Transducer tip retroflexed. Shows atrial septum with membrane of fossa ovalis, ventricular septum, septal leaflet of the tricuspid valve and septal attachment of the anterior mitral leaflet (mitral valve inserts higher than the tricuspid valve), anterolateral papillary muscle, coronary sinus, right atrium, right ventricle, right coronary artery and inferior vena cava.

  • Coronary sinus view: The coronary sinus courses in the atrioventricular groove and enters the right atrium at the lower margin of the atrial septum.

II. Longitudinal TEE imaging:

In the longitudinal plane, to optimize the anatomic delineation, axial rotation and lateral movement of the transducer are the maneuvers most commonly used.

A. Primary longitudinal views:

The images are in the sagittal plane of the thorax but are oblique to the heart. Transducer tip is at 25-30 cm from the incisor teeth. Axial rotation of the transducer from the left to right side yields the following views in the following sequence:

  • Left ventricle and left atrial two chambers view: is ideal for longitudinal examination of left atrial appendage, left pulmonary veins, anterior and inferior walls of the left ventricle and the mitral leaflets and its support apparatus.

  • Right ventricle outflow long axis view: allows visualization of the right ventricle outflow tract, pulmonary valve and main and proximal pulmonary arteries. It is helpful in assessment of the congenital anomalies of the right ventricle outflow tract and for detection of proximal pulmonary thromboembolism.

  • Ascending aorta and atrial septum view: Aortic dissection localized to the aortic root is best delineated in this imaging plane.

  • Caval, right atrial and atrial septal view: shows SVC in long axis, ascending aorta, left atrium, atrial septum, right atrium, right atrial appendage and IVC. This view is commonly used during contrast echocardiography for detection of patent foramen ovale. Atrial septal defects are best delineated in this view. It also facilitates evaluation of atrial masses and thrombi.

B. Secondary longitudinal views:

Longitudinal arrays can be reoriented from sagittal plane of the thorax to planes that are in the long or short axes of the heart.

  • Long axis view: results from leftward flexion of the transducer tip. Permits left ventricle outflow tract visualization in the long axis.

  • Short axis view: results from rightward flexion of the transducer tip. Comparable to conventional transthoracic short axis view. Visualizes aortic valve in short axis.

III. Transgastric views:

Transducer is advanced into fundus of stomach (35-40 cm from incisors). Images are oriented to show anterior structures at top and left sided structures to right of screen. Both views are similar to transthoracic parasternal long and short axes views.

  1. Long axis view: permits evaluation of the anterior and inferior left ventricle walls, both papillary muscles and the mitral valve.

  2. Short axis view: By anteflexing the transducer, the examiner can scan from the apices of the left and right ventricles to the level of the atrioventricular valves.

IV. Examination of the aorta:

TEE can image the entire aorta from the basal short axis views of the left ventricle. The transducer is rotated counterclockwise so that the descending aorta is visualized. The aortic root, the proximal supravalvular-ascending aorta, the transverse aortic arch and the descending aortic arch are examined. A 1-2 cm long region of ascending thoracic aorta just above the aortic root is obscured by the air filled trachea and is a blind spot for monoplane horizontal imaging but is more easily seen on biplane longitudinal imaging which enhances visualization of the descending aorta. Transthoracic and transesophageal imaging should be combined to facilitate complete evaluation of the entire aorta (Fisher et al., 1991).

Contrast echocardiography

Opacification of the right heart cavities with dense ultrasound reflectances during IV contrast injection was first applied clinically in 1968 (Gramiack et al., 1968).

The origin of the dense intracavitary echoes is the microbubbles within the injectate. Any agitated liquid injected intravenously causes this effect (Meltzer et al., 1980).

Since room air microbubbles with the diameter of pulmonary capillaries persist in the blood for less than one second before dissolving, agitated agents injected IV can not cross the lungs and enter the left heart chambers. Thus, the presence of echoic contrast entering the left heart chambers after IV injection of an agitated liquid indicates the presence of a right to left shunt (Kerber et al., 1974 and Valdes et al., 1984).

Contrast injection can be used to delineate right heart anatomy. Identification of intracardiac shunts, particularly patent foramen ovale in patients with unexplained cerebral ischemia remains the most frequent indication for contrast echocardiography. Simple agitated saline solution remains the most commonly used contrast agent for such studies (Lechat et al., 1988).

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