Basic Echocardiography: A Primer of the Common Echo Images for the Cath Lab

Many patients who come to the cath lab have an echocardiographic study as part of their routine work-up. The ‘echo’ often contributes significantly to clinical decision-making before and during the cath procedure. Echocardiographic images are rich with information on left ventricular (LV) and valvular function, LV wall motion, pericardial fluid, atrial and ventricular chamber dimensions, evidence of prior myocardial infarction, and thickness of heart muscle due to hypertrophy or infiltrative diseases. Sometimes an urgent echo in the emergency room can add to the electrocardiogram (ECG) and change a ST-elevation myocardial infarction (STEMI) patient to a non-cardiac diagnosis.

In most circumstances, the physicians and residents review the echo images prior to the cath procedure to identify important findings, and confirm questions about heart and valve function. Many times, the cath lab team has the echocardiographers come to the cath lab to help with structural heart procedures, pericardiocentesis, and some complications of interventions. Other times, a basic bedside ultrasound machine (i.e. Sonosite) from the operating physician may suffice. In the post procedure period, echocardiograms may be ordered to establish a baseline image to follow over the ensuing months as the interventional treatments act to improve the patient’s heart health.  

For those not formally studying echocardiographic imaging and its particular contributions to cardiology, the most confusing part of interpreting echo images is understanding how the image is acquired and what is shown. The purpose of this editor’s corner is to give the cath lab team unfamiliar with echo a framework through which to understand the basics and appreciate what can be seen from the 3 most common echocardiographic views. This brief discussion is not intended to be extensive nor exhaustive on the subject of echo. Echocardiography is a subdiscipline within the specialty of cardiovascular disease that requires a complete course of study over several years. However, one has to start someplace.

The 3 echocardiographic views

The 3 most commonly used echocardiographic views are the apical 4-chamber (A4), parasternal long axis (PSL) and parasternal short axis (SA) views (Figure 1).  

Before discussing what each plane shows, it is helpful to visualize how the planes of the heart are cut by the echo beam. The echo transducer is composed of an array of multiple vibrating crystals that create the ultrasound beam and receive the ultrasound reflections. The beam is controlled electronically to produce a triangular-shaped plane of imaging, with the tip of the triangle at the transducer opening to a wide base of the plane away from the transducer (Figure 2). To simplify how the beam is positioned on the patient, I use a piece of folded paper. This paper plane can then be moved to easily see how the beam cuts through the heart (Figure 3). To help remember how the imaging planes are used, a line drawing of the heart shows the 3 views (Figure 3, top right) in relationship to each other.

The apical 4-chamber view (A4)

Placing the echo probe at the apex impulse on the chest (near the tip of the left ventricle) in the 6th or 7th intercostal space approximately on the mid clavicular line, angling the beam upward toward the sternal notch, the heart is cut to reveal the 4 chambers (2 atrial and 2 ventricles, Figure 4a). The A4 view is shown in Figure 4b and displays the apex of the heart closest to the beam (top of the echo image) and the atria furthest away from the transducer, at the base or widest part of the triangular beam. The heart is displayed as if you are looking up from underneath, so that the right-sided structures are on the left side of the screen, similar to how we view x-ray images.

In addition to seeing the size and relative shapes of the 4 chambers, we can also appreciate the interventricular septum and part the atrial septum, although this is not as easily interpreted as normal. Normally, the right ventricle is smaller than the left ventricle, and the atria are smaller than the ventricles and about the same size relative to one another. The mitral and tricuspid valves are easily seen in this view, with color Doppler identifying significant abnormalities in flow. The other common use of the A4 view is to assess LV and septal contraction, and the presence of pericardial effusion. For alcohol septal ablation procedures, one can easily see the entire septum from the base to the apex and the location of the obstructing septal muscle in this view.

The parasternal long axis view (PSL)

The probe is now moved up to the 3rd or 4th intercostal spaces adjacent to the left side of the sternum. The beam is directed on the long axis of the heart, aiming at the right shoulder (Figure 5a). The parasternal long axis displays the heart cut from the sternum through to the inferior wall with the apex at the left side of the image (Figure 5b). At the top of the beam is the sternum, then the right ventricle overlying part of the LV and aorta. The cut through the long axis of the aorta shows the aortic valve that is connected to and contiguous with the anterior leaflet of the mitral valve. The LA is behind the aortic root. The interventricular septum can be easily measured. The apex of the LV is often cut off in this view.    

The PSL view is used to see the size of the right ventricle (RV), posterior wall of the LV, mitral and aortic valve leaflet function and motion, left atrial size, aortic valve leaflet thickness and motion, and size of the ascending aortic root at the aortic valve.  

The short axis view (SA)

With the probe remaining at the same location as the PSL view, the probe is rotated 90 degrees (Figure 6a), cutting the long axis perpendicularly like a sliced bread loaf, producing short axis slices along the PSL (Figure 6b). The SA view shows the right ventricle closest to the echo beam as in the PSL, but cut perpendicularly. The interventricular septum can be easily seen dividing the RV and LV. The LV is normally circular, and varies in size and thickness as the cuts of the SA move from the base to apex of the heart. Figures 6c and 6d show SA cuts through the mitral valve and then deeper into the LV to show the cut at the level of the papillary muscles.  

The SA views are excellent to assess regional LV contraction, LV thickness, motion of the septum, size of the RV, and motion of the mitral valve. The SA view is often used to measure the opening area of the mitral valve.  

I use this method to introduce echocardiography to the residents in the coronary care unit. I hope this brief demonstration will help you understand the basic echo images, and what they can show us as our patients enter the cath lab for our coronary and structural heart disease interventions.