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 more advanced views. The heart and lungs move with changes in body position. The left lateral decubitus position improves parasternal views in many patients but some patients have shoulder or mobility problems that make this position difficult. The supine position must then be used for all views. The apical views may be better in between the supine and left lateral decubitus positions. If the subcostal window is important for a patient, but suboptimal in the left lateral or supine positions, the standing position may improve the view.
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. aorta and aortic valve) while others are better in a lower interspace (papillary muscles and distal LV). Thus, it is optimal to spread gel along the left sternal border from the 2nd to the 5th interspace.
The default depth for the heart with Venue at COC is deliberately set several centimeters greater than needed for the average heart to facilitate detection of pleural and pericardial fluid in the PLAX. After this fluid assessment, the depth must be brought up to just below the pericardium. Then, move the probe to a higher interspace, hoping to get a good view of the more distal ascending aorta as discussed in a subsequent chapter. Next, briefly evaluate each lower interspace before settling on the best window for the standard PLAX and PSAX. Moving interspaces is 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 because you don’t know what the apical window will be like. To do this, look in between the aortic valve and mitral valve and angle a little towards the patient’s right shoulder. Activate Color for the tricuspid valve if even part of it is seen. Here is the tricuspid valve in a PSAX. This view is only partly parallel to flow through the valve.
The short axis descending aorta is usually seen below the left atrium in the PLAX. However, there may be another nearby vascular structure, the coronary sinus, which can be seen in the PLAX 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 subclavian vein. A normal coronary sinus is < 1 cm in diameter. Here is an enlarged coronary sinus (just below the posterior mitral valve annulus) in the PLAX.
While you are performing the PSAX, notice whether the probe orientation is atypical because the hand/probe position for the apical4 will be analogous to the PSAX. The most important error with apical4 is 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.
The standard apical4 seeks to have the septum vertical on the screen with the atria and ventricles full size with two leaflets of the mitral and tricuspid valves visible. This does happen occasionally, as in the following apical4.
Unfortunately, this full view may not be possible, and the probe is then sequentially adjusted to allow observation of different parts of the heart. One adjustment is the RV enhanced view. In this view, the probe is moved out lateral and cephalad around the apex so the septum on the screen leans toward the RV. While part of the lateral side of the LV may disappear, the lateral RV may be better seen and the interventricular septum may be more defined because it is more perpendicular to the ultrasound beam. This clip shows an RV-enhanced apical4.
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 and the LV lateral wall is better seen. Here is an LV-enhanced apical4.
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 cephalad/anterior 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. Here is an apical5.
The other modified apical4 view is called the apical coronary sinus view. Slowly fan the probe caudad/posterior 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. Here is a normal apical coronary sinus.
Next is 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 important to stay over the LV so rotate carefully, usually with two hands. During the rotation the right side of the heart should disappear and the apical two chamber (apical2) is seen after about 45 degrees of rotation. In this view the LV is on top with the LA below. Here is a normal apical2.
If the probe is rotated another 45 degrees counterclockwise from the apical2, the apical 3 chamber (apical3) will appear. This is also called the apical long axis because it is the same cut through the heart as the PLAX (same probe orientation as the PLAX), but now the view is from the apex (the PLAX gets tipped up). Notice that the apical3 is a 90-degree rotation from the apical4 just as the PLAX is 90 degrees away from the PSAX. The aortic and mitral valves are viewed more parallel to flow with the apical3 than with the PLAX view. Here is a normal apical3.
SUBCOSTAL (SUBXIPHOID) WINDOW
The subcostal (SC) view is important in many patients. It is optimal to obtain this while the patient remains in the left lateral position, which increases the chance that the liver will be down below the costal margin, giving a sonic window, and the antrum of the stomach will be decompressed. 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 standard SC is a SC4 and it looks like an apical4 turned sideways.
The SC4 is particularly good for seeing pericardial effusions. The SC4 can also be excellent to measure chamber sizes and wall thickness because the ultrasound beam is more perpendicular to the walls. Many things about a SC4 may be improved if the patient stands. Here is a normal SC4 periodically showing what would be a SC5.
If a patient has suboptimal parasternal and apical views, but a reasonably good SC window, it is worth rotating the probe indicator about 90 degrees counterclockwise (indicator down or posterior) to obtain a SC short axis view (SCSAX) that resembles a PSAX. Here is a normal SCSAX.
Always put Color over the inter-ventricular and inter-atrial septum in the SC4 because this may best show shunts such as VSD, PFO, and ASD because the ultrasound beam is more parallel to flow. 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. 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 enters 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. If the IVC view is important, but poor in the SC window, the probe can be placed just to the patient’s right in a medial intercostal space and angled back towards the IVC.
Rotate the probe indicator cephalad to get the standard IMBUS longitudinal IVC view. 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 Color on a possibly dilated longitudinal IVC and look for flow coming back down the IVC and into hepatic veins. This can substantiate severe TR. Here is such a case.