Transducer positions and views

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Introduction

There are 4 different standard transducer positions useful to scan the heart, called “acoustic windows” or “approaches”: the parasternal, the apical, the suprasternal, and the subcostal one. These are 4 different “points of view” from which is possible to explore and obtain data from many cardiac structures. The first two approaches are obtained with the patient in left lateral decubitus position; the subcostal and suprasternal with the patient in supine position. Rolling the patient on the right side is obtained the right parasternal view. The most frequently used acoustic windows in adults are the parasternal and the apical. In pediatric patients and in adults with a limited acoustic window due to respiratory diseases the subcostal approach sometimes is the only one possible. Finally, the suprasternal approach is a complementary view to explore the aortic arch and supraaortic vessels, the first part of descending thoracic aorta and to measure aortic gradient in difficult patient. Occasionally, the right parasternal window can be used to image the ascending aorta and record transaortic gradients.

Probe position should be adapted to patient’s body structures and the specific clinical indication to the echocardiographic study. In some pathological conditions (i.e. dextrocardia or pneumothorax) its necessary to use non-standard or “off axis” views.

2D echocardiography provides a real-time tomography of the heart with many high resolution sections (views), used to obtain basic anatomical and functional information and to provide a reference map to guide other echocardiographic techniques like M-mode or Doppler. Usually the transducer position is at the apex of the image sector. Conventionally, in transthoracic echocardiography, ‘superficial’ or ‘anterior’ structures are displayed in the ‘upper’ part of the image, whereas ‘deeper’ or ‘posterior’ structures are located in the ‘lower’ part of the image sector. Lateral structures are displayed on the right side of the screen and medial structures on the left side.[1]

In pediatric echocardiography, by convention, the anterior and superior structures are displayed at the top of the image sector, and the rightward structures are generally placed on the left side of the image display. Therefore, the preferred method of display is with the image apex “inverted,” at the bottom of the video screen, during subxiphoid and apical imaging to demonstrate structures in their correct anatomic orientation. This convention is needed because of the wide range of anatomic variations frequently seen in patients with congenital heart disease. The one exception to the left-right rule of orientation in pediatric echocardiography is the parasternal long-axis view, in which the apex of the heart is displayed on the left side of the video screen in both levocardia and dextrocardia.[2]


Others, while display “superficial” or “anterior” structures in the ‘upper’ part of the image, have chosen to change the orientation of apical views, displaying the right heart structures on the right of the screen and the left on the left side of the screen.[3]

Parasternal views

Parasternal long-axis view (PLAX)

It is obtained with the patient in left lateral decubitus position and the transducer placed near the sternum in the left third or fourth intercostal space. The right ventricular outflow tract (RVOT),in the upper site of the image, is the closest structure to the transducer. The interventricular septum (IVS) divides the RVOT from the left ventricle (LV) on the left of the image sector. In this view it’s possible to explore the anterior IVS and the inferolateral wall (or posterior wall). Usually, in this view the true LV apex is missed .

The aortic root (on the right side of the image sector) and the Aortic valve(AoV) are the structures below the RVOT. It is usually easy to see the sinuses of Valsalva, the sinotubular junction, and the proximal part of the ascending aorta. The Aortic Valve in systole is usually visualized as two thin linear images parallel to the walls of the ascending thoracic aorta; the upper aortic cusp corresponds to the right coronary cusp and the lower one to the non-coronary cusp (fig 2.1.2). In diastole a linear echodense image can be visualized in the middle of the aortic root when both cusps are closed (fig 2.1.1). Just below the aortic root there is the mitral valve with 2 leaflets, anterior (AML) and posterior (PML), which are linear, thin, and dense structures with a wide movement over cardiac cycle. The AML is in close continuity with the non-coronary AoV cusp. Both leaflets are attached by many tendinous chords to papillary muscles. The left atrium (LA) is seen in the lower right region of the image sector. The pericardium sometimes can be identified at the lower edge of the LA and LV. In some cases it is possible to visualize the descending thoracic aorta immediately posterior to the LA and external to the pericardium.

             LAX diastole.jpg

Fig. 2.1.1 2D Left parasternal long axis view (diastolic frame). AML, anterior mitral leaflet; AoV, aortic valve; IVS, interventricular septum; LA, left atrium; LV, left ventricle; PML, posterior mitral leaflet; RVOT, right ventricular outflow tract.


             LAX systole.jpg

Fig. 2.1.2 2D Left parasternal long axis view (systolic frame). MV, mitral valve; NC, non-coronary cusp; RC, Right coronary cusp. Other abbreviations as in figure 1.1.1.


From an upper intercostal space it’s possible to visualize the ascending aorta to a larger extension (fig 2.1.3).

             AscAo.jpg

Fig. 2.1.3 2D parasternal view of left ventricular outflow tract (LVOT). Ao root, Aortic root; Asc Ao, ascending aorta.

RV inflow view

From the parasternal view, it is possible to explore the RV inflow tract, in the so called RV inflow view (Fig.2.1.4), by tilting the transducer inferomedially.

             RVinflow tract.jpg

Fig. 2.1.4 2D parasternal view of right ventricular inflow tract. RA, right atrium; TV, tricuspid valve.

In this section tricuspid regurgitation jets are usually well aligned for accurate Doppler evaluation, which is useful for pulmonary pressure estimation. This view is also useful to image the right atrium (RA) in the lower part of the image, the inflow tract of RV, and the septal and anterior leaflets of the tricuspid valve (TV) in between. Sometimes it is possible to identify the moderator band of the RV (usually heavily trabeculated). The coronary sinus is the structure that join the RA wall near the tricuspid annulus. The orifice of the inferior vena cava (IVC) and the Eustachian valve can be also visualized joining the RA wall below the coronary sinus.

RVOT view

From the parasternal view by angulating the transducer in the opposite direction, i.e. laterally (towards the left shoulder of the patient), we can obtain the parasternal RV outflow view. This view gives a detailed imaging of the RV outflow tract (RVOT), the pulmonary valve (PV), and the proximal main pulmonary artery (MPA) and its bifurcation (LPA and RPA).

PSAX view

With a 90-degree clockwise rotation from PLAX is possible to obtain the parasternal short-axis (PSAX) view. The AoV, anterior to the LA and posterior to the RVOT, is seen in the central part of the image with its three leaflets in a characteristic Y-shaped configuration (Fig. 2.2.1).

            Sax basale.jpg

Fig. 2.2.1 Parasternal short axis view at aortic valve level. Dsc AO, Descending aorta; LA, left atrium; LC, left coronary cusp; NC, non-coronary cusp; PV, pulmonary valve; RA, right atrium; RC, right coronary cusp; RVOT, right ventriclular outflow tract, TV, tricuspid valve.

Non-coronary cusp is in continuity with interatrial septum and that the right coronary cusp is the nearest to the RV; the left coronary cusp is the third one. Sometimes it is possible to visualize in this view the origins of the coronary arteries, with the left main coronary artery at 4 o’clock position in the aortic annulus and the right coronary artery at 11 o’clock position. The RVOT is located anterior to the AoV; the PV is rightward and anterior to the AoV. The main PA curves around the aorta on the right of the image and it divides in two principal branches (right and left pulmonary arteries, fig 2.2.2). The TV is visualized to the left of the AoV; in this view septal and anterior leaflets are visible. The LA is seen posterior to the AoV and separated from the RA by the atrial septum. The left appendage can be visualized in some cases attached to the lateral wall of the LA.

            Pal2.jpg

Fig. 2.2.2 Parasternal short axis view of right ventricular outflow tract (RVOT); PV, pulmonary valve, MPA, main pulmonary artery, LPA, left pulmonary artery, RPA, right pulmonary artery.


The PSAX view at MV level is obtained with an inferior and rightward tilting of the transducer. The MV leaflets are two mobile parallel thin structures, with the anterior leaflet (AML) in upper position and the posterior leaflet (PML) in the lower portion of the display. The LV is visualized in circular cross-section; the RV (anterior, lateral, and posterior segments) is separated from the LV by the interventricular septum (IVS) (Fig 2.2.3).

            Mv.jpg

Fig. 2.2.3 Parasternal short axis view at mitral valve level. AML, anterior mitral leaflet; IVS, interventricular septum; PML, posterior mitral leaflet; RV, right ventricle.

By tilting the transducer more apically is obtained the view at papillary muscle level with a mid-ventricular circular cross-section of the LV. The anterolateral and posteromedial papillary muscles are displaced inside the ventricular cavity at 3 and 8 o’clock positions (fIg 2.2.4).

            PMUSCL1.jpg

Fig. 2.2.4 Parasternal short axis at papillary muscle level; AL, antero-lateral papillary muscle, PM, postero-medial papillary muscle. Other abbreviations as in figure 2.2.3.

Apical views

In this important view the transducer is placed in the fifth intercostal space in the median axillary line, right upon the cardiac apex. True LV apex can be easily foreshortened by an oblique orientation of ultrasound beam. The true apex usually has a thin wall and a slightly tapered shape. As a general rule the transducer has to be positioned in the lowest intercostal space and in the most lateral position in which a good image of the heart is obtained.

A4C

The first view from the apical approach is the apical four-chamber view (A4C): in this section are visualized the ventricles, the atria, the interventricular and interatrial septa, MV and TV, and the crux of the heart (Fig 2.3.1).

            4c 03.jpg

Fig. 2.3.1 Four-chamber apical view; Crux, crux cordis; IAS, interatrial septum; IVS, interventricular septum; LA, left atrium; LV, left ventricle; MV, mitral valve; RA, right atrium; RV, right ventricle; TV, tricuspid valve.

The RV, on the left, has a triangular shape and it’s smaller than the left ventricle by one third; in its the TV with its 2 leaflets (septal leaflet medially and the anterior leaflet laterally). Note that the TV is slightly more apical than the MV. On the other side, the anterior mitral leaflet is attached to the septum and the posterior leaflet joins the lateral atrioventricular ring. Pulmonary veins can be visualized entering to the posterior and deep wall of the LA. It is also possible sometimes to see a transversal cross-section of the descending thoracic aorta lateral to the LA. In this A4C view are shown the anterolateral wall, the apex, and the inferior septum (fig 2.3.2).

            4c zoom B.jpg

Fig. 2.3.2 Magnified apical view for the left ventricle. Ant-Lat, antero-lateral wall; Inf. septum, inferior septum.

With a slight anterior angulation from A4C position, the AoV and the aortic root appear in the place previously occupied by the crux of the heart, so it’s possible to study the LVOT and AoV flows. It allows also to visualize more anterior portions of the LV septum and inferolateral wall. ON the other hand an opposite angulation of the transducer with a posterior angulation provides a view without specific name in which more posterior portions of the LV and the coronary sinus can be seen.

A2C

A 60°–90° counterclockwise rotation of the transducer provides the apical two-chamber view (A2C), i.e. left atrium and left ventricle. In this view are shown the anterior and inferior walls of the LV and the apex. This is also useful to study the LA and the MV. A2C and A4C are orthogonal views of the LV that are widely used to assess global (using Simpson’s method) and regional LV function. (Fig 2.3.3)

             2c .jpg

Fig. 2.3.3 Magnified two-chamber apical view for the left ventricle.

ALAX

By rotating the probe another 60° an image similar to parasternal long axis view is obtained, called the apical long axis view (ALAX) or apical 3-chamber (A3C). The main difference is that in A3C the anterior portion of septal apex is seen, whereas there is no apical segment of the inferolateral wall (Fig 2.3.4)

             3c.jpg

Fig. 2.3.4 Magnified apical long-axis view for the left ventricle. Ant., anterior septum; AoV, aortic valve; Inf-Lat, infero-lateral wall; MV, mitral valve.

Subcostal view

Subcostal images are obtained with the patient in supine position, with the transducer in the centre of the epigastrium. Pointing the ultrasound beam to the patient’s left shoulder is possible to obtained an image similar to A4C (Fig 2.4.1).

             Subcosta1.jpg

Fig. 2.4.1 Subcostal four-chamber view. Liver in the upper side of image sector; AoV, aortic valve; LV, left ventricle; RA, right atrium; RV, right ventricle with its anterior wall.

The liver is in the upper region of the image, while below there are the RV with its free wall and the apex oriented to the right, the TV, and the RA. The LV is visualized in the lower and right zone of the image and, in this view, as in A4C, septal inferior and lateral walls are visible; it is more difficult to visualize the apex. A slight tilting of the transducer results in a five-chamber view with the image of the LVOT and the AoV.

A 90° counterclockwise rotation of the transducer from the subcostal four-chamber view gives a series of short-axis views and its more suitable for the study of the RV (Fig 2.4.2). This view is useful to measure the IVC and to study its changes of size with respiration, thus for the RA pressure estimation. The liver and suprahepatic veins (SHV) can be also visualized. Further rotation of the transducer to a fully vertical position gives a long-axis view of the abdominal aorta.

             Vci.jpg

Fig. 2.4.2 Subcostal inferior vena cava view. IVC, inferior vena cava; RA, right atrium; SHV, suprahepatic veins.

Suprasternal views

In this approach the transducer is placed in the patient’s suprasternal notch. With the long axis of the transducer oriented parallel to the trachea is possible to visualize the ascending aorta and the aortic arch with the origins of the right brachiocephalic, the left common carotid, and subclavian arteries (in the left region of the image, Supra-aortic vessels, SAV) and the descending thoracic aorta (DAo)in the right region. The right pulmonary artery and the LA can be seen beneath the aortic arch (Fig 2.5).

              Arch.jpg

Fig. 2.5 Suprasternal view. DAo, descending Aorta; RPA, right pulmonary artery; SAV, supra aortic vessels.

REFERENCES

  1. Garcia Fernandez M.A., Gomez de Diego, J.J., Transthoracic echocardiography. In: Galiuto L, Badano L., Fox K., Sicari R, Zamorano JL eds. The EAE textbook of echocardiography, Oxford University Press, London 2011.
  2. Weyman WL, Geva T, Shirali GS., et al. Guidelines and Standards for Performance of a Pediatric Echocardiogram: A Report from the Task Force of the Pediatric Council of the American Society of Echocardiography. J Am Soc Echocardiogr 2006;19:1413-1430.
  3. Tajik AJ, Seward JB, Hagler DJ, Mair DD, Lie JT, Two-dimensional real-time ultrasonic imaging of the heart and great vessels. Technique, image orientation, structure identification, and validation. Mayo Clin Proc. 1978; 53: 271-303.
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