Echocardiography

in brief

Even with advances in other cardiovascular imaging modalities, such as cardiac magnetic resonance imaging (CMR) and computed tomography (CT), echocardiography remains the most frequently used and usually the initial imaging test to evaluate all cardiovascular diseases related to a structural, functional, or hemodynamic abnormality of the heart or great vessels. Echocardiography uses ultrasound beams reflected by cardiovascular structures to produce characteristic lines or shapes caused by normal or altered cardiac anatomy in one, two, or three dimensions by M (motion)–mode, two-dimensional, or three-dimensional echocardiography, respectively. Doppler examination and color flow imaging provide reliable assessment of cardiac hemodynamics and blood flow.

Echocardiography is a type of ultrasound test that uses high-pitched sound waves to produce an image of the heart.

M-Mode, Two-Dimensional, and Three-Dimensional Transthoracic Echo

An echocardiographic examination currently begins with real-time two-dimensional echocardiography, which produces high-resolution tomographic images of cardiac structures and their movements. These images are usually obtained from four standard transducer locations—parasternal, apical, subcostal, and suprasternal by manual rotation and angulation of the transducer. Qualitative and quantitative measurements of cardiac dimensions, area, and volume are derived from two-dimensional images or M-mode recordings derived from two-dimensional images. Also, two-dimensional echocardiography provides the framework for Doppler examination and color flow imaging. Newer matrix transducers with more than 3000 elements allow three-dimensional or multidimensional images of the heart. Customized as well as preformatted images (equivalent to two-dimensional views) can be obtained or derived from a full-volume three-dimensional echocardiographic image.

Parasternal long axis= PLAX

PLAX view is usually the first view obtained during echocardiography. It is obtained by keeping the transducer in the left parasternal region, with the subject in the left lateral position. The beam cuts the heart in its base to apex axis (long axis). Aortic root (Ao) and valves, left ventricle (LV), left atrium (LA), mitral valve, chordae tendinae, papillary muscles, interventricular septum (IVS) and part of the right ventricle are imaged in this view. Cross section of the descending aorta (Desc Ao) is seen posterior to the left atrium. The coronary sinus can be imaged if it is dilated and will be visible in the atrioventricular groove. A dilated coronary sinus would suggest a persistent left superior vena cava draining into the coronary sinus. In this still image, the mitral leaflets are closed and aortic leaflets are in the open position.

M-Mode

M-Mode examination was the initial mode of echocardiography to begin with and has been largely superseded by other modes of echocardiocardiography. It is still being used for taking measurements of the left ventricle (LV) to calculate the ejection fraction. The M-Mode cut is taken at the chordal level for this purpose. The interventricular septum (IVS) moves downwards in systole, towards the left ventricular cavity. The left ventricular posterior wall (LVPW) moves anteriorly towards the left ventricular cavity in systole. The systolic and diastolic measurements are taken using computerised callipers in the echocardiograph and the software package calculates the dimensions and ejection fraction. The fact that the interface between two different media produces the best echoes is demostrated in the pattern of the inter ventricular septum – both upper and lower margins are echo dense while the intervening tissue is less echo dense. Vertical axis is the depth and horizontal axis is the time.

Parasternal short axis= PSAX

Parasternal short axis view is naturally the next view to be obtained after parasternal long axis view as it can be obtained by rotating the transducer without moving from the previous location. Upward direction of the beam images the cross section of aortic root with pulmonary artery curving around it (circle and sausage appearance). This pattern is changed in transposition of great arteries where we get two circles instead. Pulmonary artery is identified by its bifurcation into left and right pulmonay arteries . Colour flow mapping (colour Doppler) shows a blue flow directed away from the transducer. A tiny reverse flow of pulmonary regurgitation can be seen in most normal individuals. It appears like a tiny flame directed upwards from the pulmonary valve in the closed position (seen well in the video at the end of this post). Perimembranous and subpulmonic ventricular septal defects can be imaged in this view and the gradient across if any quantitated.

Short axis

 

Short axis imaging at the ventricular level can be obtained by directing the beam downwards from the previous positon. It is used to assess the cross section of the mitral valve in mitral stenosis to quantify the mitral valve area. The left ventricular wall motion abnormalities can be visualised well in this view. A portion of the right ventricle is also visible beyond the interventricular septum. Left ventricle has a circular shape in this view and the right ventricle is semi-lunar with the septum convex to the right ventricle.

Apical four chamber= AP4CH

Apical four chamber view is obtained from the apex of the heart as the name implies. It gives a good image of all four chambers as well as the mitral and tricuspic valves. The inter atrial and interventricular septa are seen in this veiw. The tricuspid valve is attached more distally to the septum than the mitral valve and the region in between is called the atrioventricular septum, which separates the left ventricle from the right atrium. A defect in this location is called a Gerbode ventricular septal defect. Drop outs in the inter atrial septum are common in this view as in this case, whithout any atrial septal defect. This is because the ultra sound beam is parallel to the inter atrial septum in this view and the thin region at the fossa ovalis is often seen as an echo drop out. A subcostal view should be obtained to image the inter atrial septum before concluding that the drop out is an atrial septal defect. A good left to right flow demonstrated by colour Doppler in this view can also be used to confirm the presence of an atrial septal defect in this view, especially if the sub costal view is suboptimal, especially in adults. A slight tilt of fom the apical four chamber view opens up the aortic root and it is called the apical five chamber view. Apical five chamber view is used to measure aortic flow and the gradient in aortic stenosis.

Supra sternal view

Supra sternal view is often the last view obtained during echocardiography. The subcostal view has not been demonstrated in this series as the images were not of good quality as is sometimes the case in lean indiviuals with a narrow costal angle. The supra sternal view images the aortic arch and its branches and the proximal descending aorta. This view is used to detect coarctation of aorta and measure gradients across the coarctation. Ascending aorta can also be imaged with a tilt and ascending aortic flow is measured in aortic stenosis to get the gradient across the aortic valve. This is sometimes useful when the gradient is not picked up well in the apical five chamber view.

Echocardiography provides a substantial amount of structural and functional information about the heart.

Still frames provide anatomical detail. Dynamic images tell us about physiological function.