SonoTips & Tricks: The FAST scan: The Cardiac views #FOAMed

Finishing the ultrasound QA sessions that we do every week at Stanford, I was reminded about how bedside ultrasound is a tool that helps when resources were limited. If you hadn’t heard, there was an Asiana Airlines plane crash at San Francisco International Airport with over 180 patients requiring medical care, 55+ of which came to Stanford. Luckily, we just added 4 new SonoSite EDGE ultrasound machines to our 4 MTurbos and 3 GE Vscan systems the week before – and they sure were used well! The FAST scan was used as a screening tool and to help prioritize those who would go to the CT scanner. Once, again, it is important to know how to do it and do it well.  Our latest insert in the ACEP Ultrasound Section newsletter is below – on the FAST scan – the Cardiac sections. The prior entry was on the FAST scan: The Upper Quadrants ( go here. ) – And Ultrasound Podcast recorded with Cliff Reid about it this week too!

I’ll start with what I’ve said before: “2013 is the YEAR OF ULTRASOUND – and for good reason – there are only a few tools that give us such immediate information that can save a life. The ACEP US Section is the go-to site for everything you want to know about starting an US program, credentialing in ultrasound, the policies and politics, and is the home of SonoGuide – an amazing educational resource for bedside ultrasound, and the EMSONO: Ultrasound Test. It is also where we add our entries for their newsletter that goes over tips and tricks, cases, and all things ultrasound in the news. We recently wrote an article for the ACEP Ultrasound Section Newsletter – which is available for all members of the ACEP US Section – and I highly recommend becoming a member – it’s totally worth it.”

It was a TRUE pleasure to record a podcast recently with Dr. Scott Weingart (aka, my hero) on EMCrit (twitter: EMCrit), and writing this article with our ultrasound fellow, Dr. Viveta Lobo, describes some of what was spoken about.

By Viveta Lobo, MD and Laleh Gharahbaghian, MD, FACEP

As discussed in our last entry, the FAST exam is undoubtedly the most widely used bedside ultrasound application used in emergency medicine. Its incorporation in the ATLS revised protocol, the RUSH exam, and several other published protocols, makes it an invaluable screening tool for intra abdominal injury causing hemoperitoneum, cardiac injury with pericardial effusion, and unexplained hypotension.

We will continue our discussion of the FAST scan by reviewing the cardiac views, and relay some tips and tricks for each. Refer to the previous newsletter for tips onscanning the right upper quadrant (RUQ) and left upper quadrant (LUQ).

The Cardiac Views:

The traditional cardiac view obtained as part of the FAST exam is the subxiphoid view. The main focus of this view in the FAST exam is to evaluate for evidence of cardiac injury by evaluating for pericardial effusion and/or cardiac tamponade. The phased array probe is placed in the subxiphoid space medially, applying pressure to go under the xiphoid process and flattening out the probe while aiming caudally.

Tips for the Subxiphoid View: 

1. Use your liver as an acoustic window. 
Sound waves will travel through liver to the heart, allowing you to visualize the heart. Often one can even place the probe slightly to the right of the xiphoid process, to allow for better liver visualization, and then adjust your depth to be able to look past the liver to the heart. Without the liver in view, gas scatter will affect your image acquisition.

2. Visualize both the inferior and superior pericardial borders, to completely evaluate for pericardial effusion or, rarely, loculated pericardial effusions. It is possible for one area to have pericardial effusion and not the other. Click Here for a Video.

3. Have the patient take a deep breath and hold it. When you notice that the heart is far from the probe, and you find yourself adjusting your depth to more than 20cm, having your patient take a deep breath will lower the heart closer to the probe, improving visualization. Click Here for a Video.

Despite the subxiphoid view being the traditional view for the FAST exam, the parasternal long view is becoming more of the ‘go-to’ window to evaluate for pericardial effusion. This may be due to several very relevant clinical factors: You simply cannot get a good subxiphoid view. An injury, foreign body, or abdominal pain does not allow for subxiphoid probe placement/pressure. Or you can differentiate pericardial fluid from pleural fluid in the parasternal long view. 

Tips for Parasternal Long View:
As far as patient positioning, if you’ve already evaluated the RUQ and LUQ (so as to not affect free fluid evaluation) and the patient is able to turn into a left lateral decubitus position, it will help bring the heart closer to the chest wall for visualization. This can be difficult, or impossible, in trauma patients, so the below tips may help:

1. Start high and start medial – Place your phased array probe just next to the sternum, starting just under the clavicle. If you don’t see the heart there, slide down a rib space, and fan through that space to find the heart. Continue sliding down rib spaces, until you find it.

2. Slowly change the angle of your probe (up and down) when you’re assessing each rib space as described above. ‘Slowly’ is the key word here. If you’re angling downward too much in a rib space and see the PSL heart, you may need to just slide down a rib space. If that makes the image worse, slide back up.

3. Slowly rotate your probe while keeping the angle described above (clockwise/counterclockwise depending on whether you use the right shoulder or the left hip to direct your probe marker). Rotate until you visualize the longitudinal view of the left side of the heart.

4. Slide your probe medially/laterally only if you need to in order to center the aortic and mitral valves on your screen.

5. Ensure adequate depth in order to distinguish a left sided pleural effusion from a pericardial effusion. This will allow visualization of the descending thoracic aorta seen in its transverse view just deep to the heart, which is your landmark in differentiating pleural effusion from pericardial effusion. Pleural effusion will travel posterior to the aorta while pericardial effusion will travel anterior to it (and possibly circumferentially around the heart).

Lastly, it can be very difficult in both subxiphoid and parasternal long views to differentiate epicardial fat pad from pericardial effusion. One tip: epicardial fat is seen anteriorly and has echogenicity within it, while pericardial effusion is seen posteriorly or inferiorly and is anechoic, but can travel anteriorly if large enough to become a circumferential pericardial fluid collection. Despite this tip, clinical correlation is needed.

Look out for Part 3 of the FAST Exam: The Pelvis, in the next newsletter. Until next time, happy scanning!

For a set of links to online education in bedside ultrasound, go here. Another post on Social Media in EM Ultrasound and the amazing tools out there to learn it for free, go here.”

References
1. Ma OJ, Mateer JR, Ogata M, et al. Prospective analysis of a rapid trauma ultrasound examination performed by emergency physicians. J Trauma. 1995; 38:879-85.
2. Wherrett LJ, Boulanger BR, McLellan BA, et al. Hypotension after blunt abdominal trauma: the role of emergent abdominal sonography in surgical triage. J Trauma. 1996;41:815-20.
3. Schiavone WA, Ghumrawi BK, Catalano DR, et al. The use of echocardiography in the emergency management of nonpenetraing traumatic cardiac rupture. Ann Emerg Med. 1991;20:1248-50.
4. Rozycki GS, Feliciano DV, Ochsner MG, et al. The role of ultrasound in patients with possible penetrating cardiac wounds: a prospective multicenter study. J Trauma. 1999;46:543-52.

 

 

 

SonoLectures: Free lecture on Ultrasound in the Critically Ill -by Dr. Cliff Rice (& other free lectures)

Got an email from ACEP and thought it was too good not to share: Hear Dr. Cliff Rice, an ultrasound extraordinaire and emergency physician speak about bedside ultrasound and its use in critical care medicine. At the end of this post are even more lectures that are free. As you will hear, he states “Think about how you would use it in some of our sickest patients that come to the emergency department….. where the differential diagnosis is quite broad, and the treatment for shock might be detrimental if we are wrong.”

As ACEP states in the email: “Practicing emergency physicians need to be able to utilize ultrasound effectively in the evaluation of the critically ill patient. In this free audio recording from the 2012 ACEP Scientific Assembly, Dr. Rice highlights the use of ultrasound to perform a FAST scan, to dynamically monitor and measure the IVC in the setting of hypovolemic shock, and to detect pericardial effusion and perform ultrasound guided pericardiocentesis [in 45 minutes]. This [lecture] explains where you should start scanning, narrows your differential and guides your resuscitation.”

Other free lectures for your viewing/hearing pleasure on bedside ultrasound:

Dr. Chris Fox’s comprehensive emergency ultrasound lectures in iTunes

Dr. Phil Perera comprehensive emergency ultrasound lectures on Sound-Bytes

AIUM UltrasoundFirst lecture series on various ultrasound topics

UltrasoundPodcast with a variety of lectures on bedside ultrasound

UltrasoundVIllage website on a variety of ultrasound topics

Vanderbilt’s excellent lectures library on bedside ultrasound

SonoStudy and Tutorial: EPSS vs fractional shortening for LV function – is EPSS good enough?

In a recent issue of the Journal of Ultrasound through AIUM, Weekes et al. (and Kendall et al in AM J EM) talk about a hot topic that emergency and critical care physicians hold dear to them – the EPSS , or E-point septal separation – the minimal distance between the anterior mitral valve leaflet and the interventricular septum in the parasternal long view of the cardiac echo during diastole using M-Mode. Now, EPSS is not a part of point of care echo right now (i know, phew!), but there are conversations about whether it should be. The reason is because it is thought that EPSS is a good tool for LV function delineation, possibly better than simple visualization, despite knowing the risks of underestimating ejection fraction due to endocardial output limitations (see below). …Yeah, I know, that’s a lot of words and it took me a year to really understand what the above meant. So, let’s talk about it…especially as it is included in the updated RUSH protocol by Seif, Perera, et al.

EPSS by echo has even been compared to cardiac MRI for LV function recently. And, Dr. Mike Stone and friends did a study last year with regard to EPSS compared to qualitative LV function, stating: “Dyspneic patients with acute decompensated heart failure (ADHF) often present to the emergency department (ED), and emergency physicians (EPs) must act quickly and accurately to evaluate and diagnose patients with ADHF. Traditionally, key components of the patient’s history, physical examination, electrocardiography, and chest radiography are used to diagnose ADHF. However, no single test is highly accurate, and even with the incorporation of B-type natriuretic peptide levels, the diagnosis of ADHF in a dyspneic patient in the ED can be a challenge. Additional modalities that allow prompt and accurate diagnosis of ADHF would be of clinical utility, and estimation of left ventricle ejection fraction (LVEF) using point-of-care ultrasound has been the focus of prior research” showing that EPSS is a good tool compared to qualitative LVEF visualization. EM News folks also highlighted EPSS in a recent entry.

Now, lets talk a bit about the anatomy and physiology about this before we talk about the study. The mitral valve has an anterior leaflet and a posterior leaflet. You can see the mitral valve open and close in the parasternal long view of the heart. the below picture indicates the anterior leaflet:

Using the Cardiovscular Institute’s diagrams, we can see the functioning of the mitral valve during systole and diastole in relation to the EKG, with every movement /peaks delineated with a letter  ….one of them being “e” (where E of EPSS comes from):

…and in relation to the EKG on M-mode on the PSL view (aka motion mode – basically visualizing the motion of objects in time).

EPSS of >7mm is thought to be an indication of poor LV function. Some use 1cm as the mark to increase their sensitivity for low ejection fraction. So, you can see that it should be a good indicator of LV function.

Fractional shortening (FS), however, is….(LVEDd-LVESd) / LVEDd expressed as a percentage. Placing the M-mode cursor across the LV just beyond the mitral valve leaflets, a tracing is shown whose measurements of the LV chamber diameter in both systole and diastole can illustrate FS, or LV contractility (not ejection fraction as it is not a volume measurement). Normal FS being 30-45%. For a complete description of these terms go here – a great overview by ICU Sonography –  and here – a simpler way to understand the measurements through the Stanford ICU website. The updated RUSH protocol, also explains this well, with images from their most recent publication below:

Hyperdynamic/hypercontractile: FS >45%

Abnormal: hypocontractile LV: FS<30%

So, the study was a prospective study, thankfully, and seemed to really want EPSS to be good for LV function, but it looks like it’s not as good as we think:

Abstract: “Objectives Rapid bedside assessment of left ventricular (LV) function can aid in the evaluation of the critically ill patient and guide clinical management. Our primary hypothesis was that mitral valve E-point septal separation measurements would correlate with contemporaneous fractional shortening measurements of LV systolic function when performed by emergency physicians. Our secondary hypothesis was that E-point septal separation as a continuous variable would predict fractional shortening using a linear regression model.

Methods We studied a prospective convenience sample of patients undergoing a sequence of LV systolic function measurements during a 3-month period at a suburban academic emergency department with a census of 114,000 patients. The sample included adult emergency department patients who were determined by the treating emergency physician to have 1 or more clinical indications for bedside LV systolic function assessment. Investigators performed bedside M-mode cardiac sonographic measurements of fractional shortening and E-point septal separation using the parasternal long-axis window. The sequence of LV systolic function measurements was randomized.

Results A total of 103 patients were enrolled. The Pearson correlation coefficient for E-point septal separation and fractional shortening measurements was –0.59 (P< .0001). Linear regression analysis performed for E-point septal separation with fractional shortening as the dependent variable yielded an R2 value of 0.35.

Conclusions E-point septal separation and fractional shortening measurements had a moderate negative correlation. E-point septal separation, when used as a continuous variable in a linear regression model, did not reliably predict fractional shortening.”

The limitations of EPSS as discussed in Stone’s paper:

Valvular diseases that restrict anterior mitral leaflet motion ( mitral stenosis, aortic insufficiency) – will exaggerate EPSS.

Asymmetric septal hypertrophy,

Severe left ventricular hypertrophy,

Discrete proximal septal thickening (sigmoid septum) can lead to small
estimates of EPSS.

Failure to obtain a true parasternal long-axis view may result in falsely elevated
EPSS measurements due to a tangential measurement from mitral valve leaflet to septal wall.

….At the end of the day, my opinion -> just visualizing the LV contractility, as long as you have a good PSL and PSS long view, and you’ve seen enough to know normal versus abnormal, is good enough for me!

SonoApp: IVC ultrasound – aka “the gift that keeps on giving.”

The IVC is a beautiful thing; it returns blood to the heart from all over the body, and without that, we would die – truly is the gift that keeps on giving. It gives so much information about a patient as it gets affected by so many disease processes:

IVC dilation (hypervolemic)- tamponade, PE, CHF exacerbation, severe mitral regurgitation or aortic stenosis, significant renal failure, severe COPD/Cor Pulmonale

IVC collapsed (hypovolemic) – septic shock, hypovolemic shock, dehydration

Now lets talk technique: