Learning Ultrasound – 4 – The Subxyphoid Cardiac Scan

All of the posts of the series Learning Ultrasound are excerpts from the book Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”. I purchased the e book two years ago. The e book is only available on Apple devices. The e book is only about $15 and it is simply the best there is on learning  to perform point of care ultrasound (POCUS). You need to buy it now.

In this post you will watch a brief YouTube video on what you will see in a correctly performed subxiphoid cardiac ultrasound exam.

Then we will go over the often difficult technical points of conducting the exam from Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”.

The following YouTube video is a good introduction to what you will see with a well performed subxiphoid cardiac ultrasound scan.

The technical aspects of probe placement can be very difficult for the beginner. And as usual the best resource for learning to actually perform the scan is  Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”; “The clearest and most concise approach to emergency ultrasound.” There is an ebook available for Apple device users and it only costs $15. If you have an Apple device get it now.

I have posted these Learning Ultrasound series, temporarily, for a friend who does not currently have access to an Apple device.

What follows are excerpts from the above book:

Setting Up The Scan

Set the depth to maximum. You will use the curved array probe that you use for most abdominal scans. You can also use the phased array probe if you have one.

Step 1

The key acoustic window here is the liver. That is the window that allows you to peer from the abdoman into the chest. This means that the probe will need to be placed caudad to the liver.

It is therefore vital to start the scan very low on the abdoman, just a bit above the umbilicus (Figure 1 Below). In this manner you will be certain to start the scan below the liver [and the liver is your acoustic window to see the heart]. . . . As with all basic EDE scans done in the transverse plane, the indicator should be oriented to patient right.

In placing the probe on your starting point, you will note that the hand must be completely over the probe (Figure 2). [Otherwise you won’t be able to lay the probe flat on the patient’s abdomen. If the probe is not flat on the abdomen, you won’t be able to see the heart which is an anterior structure].

Before you start scanning put a lot of gel on the patient in the midline from the umbilicus to the xiphoid.

Step 2

While doing your slide, apply downward probe pressure toward the back [And be sure to keep the probe pointing in the midline as the heart is a midline structure].

If you hold the probe only lightly on the abdoman, the probe will not make sufficient contact with the skin and your image will appear dark. Sufficient pressure will cause the skin to envelop the probe and will cause the probe and create good contact. Do not be dismayed if the probe head farthest from the body does not touch the abdomen. So long as even a few millimeters of the probe are in contact with the skin from extreme left to extreme right, an acceptable image will be generated

Step 3

As you slide up the abdomen, the liver will appear on the screen in the near field. At this point, the heart should come into view.

In different patients, [the heart] will appear first at different points in your slide. Sometimes it will appear when you are still distant from the ribs, and sometimes it will only appear once the probe is abutted against the costal margins.

If you have not seen the heart at all to this point [meaning when the probe is abutted against the costal margins], perform an AP sweep ( i.e., [be sure the probe is lying] almost flat on the patient’s abdomen and then sweep slowly posteriorly). The natural reflex is to point the probe towards the patient’s back. Remember you are looking up at an anterior structure in the chest. You are much more likely to see it with the probe flat on the abdomen.

Once you see the heart, you will notice that it appears as a mostly black structure – because it is fluid filled within a bright white envelope (Figure 5)

Commonly, the heart will be too dark when it first appears; you will not see the white envelope well. [Don’t turn up the gain until you have tried everything else.]

First, do you have enough gel?

Next, are you applying sufficient pressure with the probe? Not only do you need probe pressure directed towards the back, but there should be some directed toward the heart.

If you are already pressing against the costal margins and the patient is uncomfortable, you may need to slide a bit caudad, away from the ribs and then re-apply pressure.

Lastly, consider having the patient take a deep breath.

[Once you have identified the heart, you’ll need to center it on the screen. Adjust the depth and/or move the heart image left or right (by sliding the probe or heeling it in the appropriate direction).]

Step 4

If you are searching for a pericardial effusion, the next step is to identify the pericardium (Figure 6).

There is no pericardium around the “top-right” corner of the heart ( which would be the far-field and screen-left corner on the screen) because that is where the great vessels enter and exit the heart.

Since the most dependent part of the supine patient’s heart is found in the infero-posterior area. PCEs will first be visible in the near field. Because the PCE may only be visible through part of the sweep, it is important to define minimum criteria for an acceptable scan. The white line between the ventricles is obviously the septum. If you can see the inferior pericardium all the way to the septum you have seen enough of the inferior pericardium to declare the scan negative for PCE (Figure 5)

Step 5

It is necessary to sweep completely through the heart, passing from anterior to posterior and back again, watchin the heart disappear at each extreme (Figure 7). This is called “sweeping through the “Area of Interest.”

The Positive Scan

There are two positive in the [subxiphoid cardiac ultrasoud]: cardiac standstill and pericardial effusion.

Clinical Applications

Cardiac Activity

The search for cardiac standstill will take place in any resuscitation situation where it can be used to guide, or terminate, the team’s efforts. Once you have determined whether cardiac activity is vigorous or absent, you go down one of two clear paths:

A. Heart Not Beating

Unless there is a defibrillatable rhythm on the monitor (e.g., ventricular fibrillation), this is cardiac standstill. This is almost certainly not survivable.

The one major exception to this would be the pediatric hypoxic arrest. Remember that kids are not dead until they are well-oxygenated and dead.

There are less common exceptions such as hypothermia and some toxidromes (e.g., a massive beta-blocker over dose). As always let your clinical judgment take precedence.

B. Heart Beating Vigorously

In the context of unexplained hypotension, this finding suggests that the cause is noncardiogenic and therefore potentially correctable. There are several readily reversible causes of this condition. First and foremost are hypovolemia, hypovolemia, and hypovolemia. Be aggressive with your fluid resuscitation. You should also search for heretofore unsuspected blood loss. Sepsis, anaphylaxis, tension pneumothorax, and other diagnoses should also be considered and pursued.

[There can occasionally be a third possibility. Sometimes the heart is beating but not in a normal way, not vigorously. In this case the scan is indeterminant and you proceed to manage the patient without using the scan in your decision-making]

Pericardial Effusion

[You should be performing] a cardiac ultrasound scan] on every patient who comes in with chest pain or shortness of breath, unless the etiology is absolutely clear. More than 99% of your scans will be negative, but your pickups will be life saving at an early juncture.

If you discover a pericardial effusion, you now have determine its cause. In trauma cases, the cause will be apparent, while in medical ones it may take a little digging.

Unless there are other competing diagnoses, it is reasonable [in trauma cases] to assume that the pericardial effusion is responsible for some, if not all, of the hypotension. This should lead you to perform an emergency pericardiocentesis.

[In medical cases, the pericardial effusion may have accumulated gradually and the pericardium can stretch to accomodate the fluid] and they will initially present with increasing shortness of breath on exertion and fatigue, rather than signs of shock. It is also possible that the PCE has nothing to do with the patient’s vital sign abnormalities. For example, in the presence of hypotension and a PCE, combined with a bradycardia and a temperature of 34.2 degrees, should suggest the diagnosis of myxedema.

[We will go over the echo diagnosis of cardiac tamponade in a later post]

Epicardial Fat

A source of false-positives that cannot be avoided is the presence of epicardial fat (figure 9 above). This strip of tissue is usually quite echogenic and can be remarkably thick. The giveaway is that it will appear anteriorly. Effusions appear posteriorly first (due to gravity) and never only anteriorly. It is worth mentioning that epicardial fat pads are quite common and can even be seen in rake-thin children. It should also be added that epicardial fat usually consists of some mild degree of echogenicity, often appearing as white strands, whereas PCEs are almost always completely black.

Final Tips

Respirations

If you are having trouble bringing the heart into view, there are a few things you can do to improve your image. First, you may be experiencing difficulty because the heart is too high in the chest. This is particularly true in the case of barrel-chested persons. In these situations it can be very helpful to ask the person in slowly and to hold their breath. This drops the diaphragm and, by extension, the heart, bring the target organ closer to the probe. This may not always be possible in with an emergency patient, but it can make all the difference in someone who can cooperate. When using this trick, it is necessary to sweep the probe posteriorly a few degrees as the patient inspires (Figure 10 below). If you do not do so, the heart will pass under the beam.

 

Slide To The Right

Some patients have a less-well developed left lobe of the liver (remember the liver is our accoustic window). In these cases, you may have to cheat over to to patient right to get a better window. This involves two distinct movements; sliding the probe to patient right, then heeling it to the left to re-center the heart, hopefully now with a better view (Figure 11 below). This maneuver also helps when gas in the stomach is obscuring too much of the heart to obtain a determinate view.

Resources:

Point-Of-Care Ultrasound for Emergency Physicians — “The EDE Book”; “The clearest and most concise approach to emergency ultrasound.” There is an inexpensive ebook available for Apple devices and I strongly recommend you purchase it right away.

 

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