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.
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 color flow Doppler 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.
APICAL WINDOW: 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. Before moving to the apical4, 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. Remember that the probe orientation for the apical4 view should be almost the same as for the PSAX view.
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 mitral and tricuspid valves visible. This does happen occasionally, as in the following example of a middle-aged tall, athletic man.
Unfortunately, this great view may not be 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 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 not be visible, the RV, RA, and tricuspid valve may be better seen and the interventricular septum may be more clear because it is more perpendicular to the ultrasound beam. 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 and caudad 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. Here is a good quality apical4 window being fanned to an apical5.
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 over the LV so move carefully. During the rotation the right side of the heart begins to disappear and the apical two chamber view (apical2) is seen after about 45 degrees of rotation. In this view the LV is on top with the LA below. Below is a clip of a normal apical2 view.
If the probe is rotated another 45 degrees 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 (same probe orientation as the PLAX), but now the view is from the apex (the PLAX view gets tipped up). Notice that the apical3 view is a 90-degree rotation from the apical4. 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 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 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 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 color flow. The IVS is usually perpendicular to the ultrasound waves with the subcostal view, creating a better view for IVS measurement than many apical4 views. The free, lateral wall of the RV is also perpendicular to the beam, making this the best view for measuring this wall. 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.
If a patient has suboptimal PSAX and apical2 views, but a reasonably good subcostal window, it is worth rotating the probe indicator about 90 degrees clockwise (indicator up or anterior) to obtain a view that is similar to a PSAX view. The probe needs to stay over the mid-ventricles to achieve this. Here is a clip of a normal subcostal short axis view with the right ventricle above the “doughnut” of the LV.
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 color flow over the inter-atrial septum in the subcostal view because this may better show an inter-atrial connection such as a PFO or an 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 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 color flow 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.