General guidelines for obtaining the basic cardiac windows
This chapter assumes basic skill in acquiring the four standard views of the heart and will cover a few special aspects of these standard views, as well as the utility of several non-standard views. Some realistic images and clips will be used as examples, rather than only outstanding views.
The optimal parasternal window is not reliably in any particular interspace. In addition, some structures may be better seen in a higher interspace (e.g. PLAX aorta and PSAX aortic valve) while others are better in a lower interspace (PSAX papillary muscles and distal LV).Thus, it is optimal to spread gel along the left sternal border from the 2nd to the 5th interspace and always begin the PLAX viewing at the highest interspace, hoping to get a good view of the more distal ascending aorta.
Briefly evaluate each lower interspace before settling on the best window for the PLAX and PSAX. The aortic valve may be better seen in the PSAX by moving up one interspace from the standard window and the more distal LV may be better seen down an interspace. Moving interspaces may be superior to just fanning the probe if a patient has a wide enough parasternal window.
Always try to image the tricuspid valve in the PSAX view because it may be the best (or only) view. To do this, fan up a little above the mitral valve level and then angle a little towards the patient’s right shoulder. Always activate CD for the tricuspid valve if even part of it is seen. Here is tricuspid regurgitation seen in a modified PSAX of a patient who had very poor apical views.
The descending aorta is usually seen in some fashion below the left atrium in the PLAX view. There may be another vascular structure, the coronary sinus, which can be seen in the PLAX view right underneath the posterior mitral valve. This is the vein that collects the venous blood from the myocardium and returns it to the RA. It runs on the posterior heart in between the atria and the ventricles. It enlarges when RA pressure is increased or in a congenital abnormality of the left part of the subclavian vein. A normal coronary sinus is usually < 1 cm in diameter. Here is an enlarged coronary sinus (just below the posterior mitral valve annulus) in the PLAX view.
Although the apical 4 chamber view (apical4) is standard, the most important error with this view is the failure to get lateral and caudal enough on the chest. This results in the probe being superior to the apex of the heart and the LV becomes more rounded in appearance instead of looking like a “bullet”. Always go out fully lateral and caudal until lung is seen and then gradually move medial and cephalad until the window comes into view. Notice the orientation of the probe in the parasternal views to get a clue to how horizontal or vertical the heart will lie in the apical window.
The standard apical4 view seeks to have the septum vertical on the screen with the atria and ventricles full size with both leaflets of the AV valves visible. It does happen if a patient is large enough and not too thin or too fat, as in the following example of a middle-aged tall, athletic man.
Unfortunately, this great view is often not possible and the probe is then adjusted to allow observation of different parts of the heart. A first common adjustment is the RV enhanced view. In this view, the probe is moved out lateral around the apex so the septum on the screen leans toward the RV. While part of the lateral side of the LV may not be visible, the RV, RA, and tricuspid valve may be better seen and the septum may be more clear because it is more perpendicular to the probe. This clip shows a good apical4 view being changed into an RV enhanced view.
To obtain the LV enhanced view the probe is moved medial around the apex angling toward the lateral wall of the LV. The septum tilts toward the LV on the screen. The next clip is an apical4 view that was changed to an LV enhanced view. LV width, wall motion, and even the mitral valve might be better seen in this view. The LV is a little too rounded in this particular example, but there wasn’t a window an interspace lower where the true apex of the LV would have been.
Two additional views are subtle modifications of the apical4. An important one is the apical 5 chamber (apical5) that brings the aortic valve and LV outflow tract into view. This view requires a slight, slow fanning of the probe so the cord goes down. This is usually the most important view for measuring the severity of aortic stenosis, as will be discussed in the Aortic Valve chapter. Particularly when assessing AS, we need the outflow track and aortic valve to be mostly vertical. Here is a good quality apical4 window being fanned to an apical5; the valve and outflow track are nicely vertical at the end.
The other modified apical4 view is called the apical coronary sinus view. Slowly fan the probe so the cord moves up until the atria start to disappear and then the horizontal coronary sinus entering the upper medial right atrium is seen. This first clip is of a normal heart in an RV enhanced and apical coronary sinus view. At the upper medial RA is the small coronary sinus.
Next is an apical coronary sinus view with an enlarged coronary sinus in a patient with chronic RA pressure and volume overload.
There are two other important apical views achieved from the apical4 with a slow rotation of the probe so the indicator moves down towards the bed (counter clockwise). It is also important to stay in the LV side of the window so move carefully. During the rotation the right side of the heart begins to disappear and the apical two chamber view (apical2) is seen. In this view the LV is on top with the LA below. Below is a still image of an apical2 view (from 123sonography,com) that shows a dilated coronary sinus just lateral to the posterior mitral valve.
There are several important features of the apical2. First, this is the only view in which the true inferior (on the left) and anterior (on the right) walls of the LV can be well seen (unless the PSAX view is unusually good). Second, the mitral valve is seen in a different plane so eccentric MR jets or mitral valve apparatus abnormalities may be better seen.
If the probe is rotated further counter-clockwise from the apical2 view, the apical 3 chamber view (apical3) will appear. This is often called the apical long axis view because it is the same cut through the heart as the PLAX view, but now the view is from the apex (the PLAX view gets tipped up). Here is an apical3 view (fair quality) in an aortic stenosis patient that showed the aortic valve and ascending aorta better than it had been seen in the parasternal window. The main utility of the apical3 is the possible better views of the aortic valve, ascending aorta, and mitral valve. The aortic and mitral valves are viewed more parallel to flow than with the PLAX view.
SUBCOSTAL (SUBXIPHOID) WINDOW
The subcostal view is important in many patients. It is optimal to first try this while the patient remains in the left lateral position; don’t roll the patient back supine. The left lateral position increases the chance that the liver will be down below the costal margin, giving a sonic window. If no liver is seen at the top of the screen, have the patient take in a deep breath and hold it to bring the liver down. The patient’s body habitus determines whether the heart will appear mostly transverse (more obese) or is tipped (thinner patients). The subcostal window is particularly good for seeing pericardial effusions, but it can also be used to measure chamber sizes and wall thickness and to evaluate valves with CD. Here is an image of a subcostal view that best measured the increased free wall thickness of the RV in a patient with pulmonary hypertension.
Sometimes an eccentric jet (MR, TR, or AR) can be best seen in the subcostal view. Here is a TR jet that was best seen in the subcostal view.
Always put CD over the inter-atrial septum in the subcostal view (even if this was done in the apical4 view) because this may show an inter-atrial connection such as a large PFO or an ASD. Here is a PFO with a small jet moving from the left to the right atrium during expiration, when LA pressure was relatively increased compared to the RA.
The final task with the subcostal window is to image the IVC, which will be additionally covered in several later chapters. Angle the probe towards the patient’s right shoulder to better bring in the RA. Then slowly elevate the probe towards vertical. This will bring in the IVC in cross section as it exits the RA. This view is often better than the longitudinal view for evaluating size, shape, and collapsibility of the IVC because it isn’t subject to some of the side-to-side movement that affects the longitudinal IVC view. Rotate the probe indicator towards the head to get the longitudinal view if needed. Remember that large IVCs can be seen in some normal people. Probably the only reliable IVC finding is a truly small IVC that collapses completely with inspiration. This almost always means that a patient should be volume responsive. Below is a transverse view of a round and dilated IVC (to the left of the vertebrae) that shows no respiratory variation at all.
Place CD on a possibly dilated IVC and look for flow coming back down the IVC. This can substantiate severe TR. Here is a longitudinal view of the IVC with CD showing some flow back into the IVC and even up into a hepatic vein.