Point of Care Ultrasound for Paramedics and Nurses
POCUSSTUFF
Cardiac Ultrasound
Acquiring ultrasound images of the heart can be challenging, but with practice, these images can provide valuable information to guide patient care. When imaging the heart, we aim to answer questions such as whether there is cardiac activity, the presence of large pericardial effusions, and if the image quality permits, we can evaluate global Left Ventricular function and identify any Regional Wall Motion Abnormalities that may suggest a coronary occlusion.
One of things that makes understanding Cardiac Ultrasound images comes down to how we have been trained and educated how to imagine the heart. For the longest the time the model of the heart we have been provided is a static image typically with the right side of the heart colored blue and the left side of the heart colored red.
Using cardiac ultrasound, we obtain live images of the heart, capturing two-dimensional cross-sectional views that reveal its actual movement. By adjusting our mental model of the heart, we can enhance our understanding of its function.
The Cardiology Convention
In ultrasound there are two primary conventions, the Standard Ultrasound Convention and the Cardiology Ultrasound convention. These conventions affect where you will see Probe Orientation Marker placed on the on screen, but should not affect where you point the probe orientation marker on the probe to acquire the desired image.
The Standard Ultrasound Convention:
​
In this convention you will see the probe orientation marker (Blue Dot for BFIQ probes) on the LEFT side of the screen. This convention used for all ultrasound applications other than cardiac images, or using a phased array probe. You will find the probe orientation marker of left side of the screen, when doing abdominal images, vascular scans, lung ultrasound ect.
The Cardiology Ultrasound Convention:
​
In the cardiology convention, whenever you are using a probe in a Cardiac present or a Phased Array probe you will see the probe orientation marker on the RIGHT side of the screen. Why these two different conventions for the placement of the probe orientation marker? This a mystery of the universe that may never be solved.
These two conventions may complicate or confuse you when acquiring cardiac images is when you trying to get an image of the heart using a non-cardiac preset or something other than a phased array probe. It is still possible to get good images of the heart using these other probes or presets but the probe orientation marker will be on the left side of the screen.
In these cases the image will be "flipped" 180* from what you are expecting to see. This can confuse your interpretation of the image especially in situations when you are getting an Apical Four Chamber (A4C) view of the heart and trying to compare relative sizes of the Right and Left Ventricles.
This is an Apical Four Chamber view using a the Aorta preset that defaults to the Standard Ultrasound Convention placing the probe orientation marker on the left side of the screen. If we are not aware of this we can mistakenly identify the Left Ventricle as the Right Ventricle.
This is an Apical Four Chamber image taken in a cardiac preset with the probe orientation maker on the Right Side of the screen following the Cardiology Convention.
The Cardiac Cycle
This is a Parasteral Long Axis view of the heart. This is a view of the heart that is taken from the left sternal border at about the same location you would place V2 for a 12-lead EKG. In this view the top of the image would be the closest to the chest wall, the bottom of the image would be closer to the spine, the left side of the image would be towards the apex of the heart, and the right side of the image towards the base of the heart
RV = Right Ventricle
LV = Left Ventricle
MV = Mitral Valve
AV = Aortic Valve
S1 = Closure of the Mitral Valve,
beginning of Systole
S2 = Closure of the Aortic Valve,
beginning of Diastole
​
Cardiac Imaging Windows:
Parasternal Long Axis
(PLAX)
Probe/Preset:
Phased Array / Cardiac
​
Body Plane:
Relative to the heart
​
Probe Indicator:
Towards Patient’s Right Shoulder
​
Depth:
At least 15cm
​
Location:
Left Sternal border, 3rd to 5th Intercostal Space. Similar location to V2
​
Identify:
-
Left Ventricle
-
Right Ventricle
-
Intraventricular Septum
-
Mitral Valve
-
Aortic Valve
-
Descending Aorta
Notes:
Assess for cardiac motion and the presents of a large pericardial effusion. Multiple views should be acquired to confirm the presents of a pericardial effusion. Global Cardiac function can be visually assessed or measured using M-Mode by evaluating E-Point Septal Separation (EPSS).
​
_edited.jpg)
_edited.jpg)
_edited.jpg)
Parasternal Short Axis
(PSAX)
Probe/Preset:
Phased Array / Cardiac
​
​Body Plane:
Relative to heart
​Probe Indicator:
Towards Patient’s Left Shoulder
​Depth:
At least 15cm
​Location:
Left Sternal border, 3rd to 5th intercostal space. Similar location to V2
​Identify:
-
Left Ventricle
-
Right Ventricle
-
Mitral Valve
-
Papillary Muscles
​Notes:
From the optimal PLAX view rotate the probe 90* right, towards the left shoulder, to obtain the PSAX view. By fanning the probe right and left you are able to evaluate the heart through multiple levels. (ex: Mitral Valve, Mid-Ventricular, Basal Left Ventricular Segments)
_edited.jpg)
Apical Four Chamber
(A4C)
Probe/Preset:
Phased Array / Cardiac
​
Body Plane:
Relative to the heart
​
Probe Indicator:
Towards Patient’s left
Depth:
At least 20cm
Location:
Point of Maximal impulse, approximately the 5th intercostal Space, midclavicular line, with probe pointed face pointed towards the right scapula Similar location to V4 or V5
Identify:
-
Left Ventricle
-
Right Ventricle
-
Left Atria
-
Right Atria
-
Mitral Valve
-
Tricuspid Valve
​Notes:
For the optimal A4C view the intraventricular septum should be roughly vertical on the screen. This is a good view to evaluate relative chamber size. Ensure proper probe orientation during scan, otherwise right and left sides of the heart may be misidentified.
_edited.jpg)
Subcostal Four Chamber
(S4C)
Probe/Preset:
Curvilinear, Phased Array / FAST, Cardiac
​
Body Plane:
Relative to the Heart
​
Probe Indicator:
Towards Patient’s Left
Depth:
At least 20cm
​
Location:
Patient Midline, in the epigastric to subxiphoid space. Approximate 15-20* angle of the probe relative to the patient's skin surface, with probe face angled towards the head
​
Identify:
-
Liver
-
Left Ventricle
-
Right Ventricle
-
Mitral Valve
-
Tricuspid Valve
Notes:
Good for pericardial effusions, and cardiac activity intra-arrest. This view maybe difficulty to obtain due to patient anatomy. Utilize the liver as an acoustic window to visualize the heart. Adjust gain and depth to optimize image.
_edited.jpg)
Ultrasound Assisted
Pulse Check
One of the most important assessments we can make on a patient is determining whether or not they have a pulse. Is the patient truly pulseless with no cardiac activity? Is the patient profoundly hypotensive and I cannot feel a pulse? The answer to this question will lead us down different treatment pathways.
Each of us can probably have a story managing an intra-arrest patient where we have multiple providers attempting to palpate for a pulse finding ourselves in the situation asking each other, "Do you feel a pulse? I don't feel a pulse. Does anybody feel a pulse?" There have been multiple studies conducted where the question has been asked how accurate are providers at detecting a carotid pulse in the hypotensive patient. The unfortunate answer to that question is we are not that good at it. We are only able to accurately answer that question about 50% of the time, and usually takes longer than the AHA recommendation of 5-10 seconds. [Eberle B, Dick WF, Schneider T, Wisser G, Doetsch S, Tzanova I. Checking the carotid pulse check: diagnostic accuracy of first responders in patients with and without a pulse. Resuscitation. 1996 Dec 1;33(2):107—16]
With Ultrasound we have a method to aide our physical assessment that provides an objective answer that everyone in view of the screen can come to a consensus on. Ultrasound pulse checks have been shown not to take more time than a manual pulse check, and is able to be completed by prehospital providers with minimal training. [Badra K, Coutin A, Simard R, Pinto R, Lee JS, Chenkin J. The POCUS pulse check: A randomized controlled crossover study comparing pulse detection by palpation versus by point-of-care ultrasound. Resuscitation. 2019;139:17—23]
The carotid and femoral artery are common locations to assess for a pulse manually and with ultrasound. When getting a short axis view of either the femoral artery or the carotid artery it will appear a anechoic (black) circular structure that is pulsatile when slight pressure is applied, where veins will have a irregular circular shape and will collapse when pressure is applied.
Power Doppler:
Detects flow without the ability to detect direction of flow. Ideal in low flow states.
To the left is an example of a pulsatile carotid artery when minimal pressure is applied when using standard B-Mode imaging. You can also use either Power or Color Doppler, but you need to ensure that the sampleing box is located over the artery in order to detect blood flow through the vessel.
Color Doppler:
Is able to detect the direction of flow using the convention Blue is flow away from the probe, and Red is flow towards the probe.
True Pulseless Electrical Activity
Vs
Pseudo-PEA
A collection of three different studies covering 341 found no survival in patients in True PEA where there is electrical activity, no pulse, and no cardiac activity. Conversely, a patent in pseudo-PEA, +Electrical Activity, -Pulse, +cardiac activity, are more likely to achieve ROSC. Your ability to reliability obtain a cardiac image and identify cardiac activity can impact your decision to either continue or terminate resusitative efforts.
-
Blaivas et al. Outcome in cardiac arrest patients found to have cardiac standstill on the bedside emergency department echocardiogram. Acad Emerg Med 2001
-
P. Salen et al. Can cardiac sonography and capnography be used independently and in combination to predict resuscitation outcomes? Acad Emerg Med 2001
-
P. Salen Does the presence or absence of sonographically identified cardiac activity predict resuscitation outcomes of cardiac arrest patients? Am J Emerg Med 2005
With the goal of not delaying time off the chest the Cardiac Arrest Sonographic Assessment (CASA) exam recommends having a provider prepositioned to obtain a subxiphoid image of the heart looking for cardiac activity. From the subxiphoid window, the imaging provider is able to begin getting a cardiac image, without impeding other providers doing ongoing chest compressions. One thing to keep in mind is to limit imaging time to less than 10 seconds, ideally less than 5 seconds to determine the presents or absents of cardiac activity.
Parasternal Short Axis image with obvious cardiac activity.
Parasternal Short Axis image with no detectable cardiac activity.
Pericardial Effusion
A pericardial effusion is an abnormal collection of fluid located outside of the heart within the protective pericardial sac. Some causes would be pericarditis, Left ventricular rupture after Myocardial Infarction, cancer, and trauma to the chest. The difference between a pericardial effusion and cardiac tamponade is hemodynamic compromise being caused by the fluid. This hemodynamic compromise is caused when the increased amount of fluid puts pressure on the right ventricle decreasing its ability to fill with blood.
One thing to keep in mind is that the volume fluid is less important than the rate of accumulation. In situtations where a large amount of pericardial fluid is accumulated over a long period of time the heart has time to adapt and compensate for this increased fluid. Where in a pericardial effusion is caused be trauma, relatively small amounts of fluid developed rapidly can impact hemodynamics.
A pericardial effusion will appear as black anechoic segment surrounding the heart, it may also be able to see the heart "swinging" within that fluid collection.
​
In the PLAX image right we see the anechoic fluid above the heart and the heart swinging.
PLAX
PSAX
A4C
S4C
In circumstances where a Pericardial Effusion is suspected, it is good practice to evaluate the heart from multiple windows in order to confirm its presents.
Left Ventricular Function Assessment using
E-Point Septal Separation (EPSS)
Left Ventricular Ejection Fraction (LVEF) is the amount of blood that is ejected from the left ventricle during systole, and is expressed in percent (%) normal LVEF is 50-70%. The amount of blood that remains in the heart after systole represents the preload that will be available for the next cardiac cycle. An LVEF of 49-45% is described as Reduced LVEF, and less than 34% would be a severely reduced ejection fraction.
During a formal Echocardiogram, LVEF is typically measured by taking multiple views of the heart, taking measurements at peak systole and diastole and comparing the difference in LV chamber size to these two points.
Peak systole
End Diastole
It is possible to make a rapid assessment of LVEF by either taking a measurement using M-Mode or visually assessing the amount of separation between the Anterior Mitral Valve Leaflet and the Intraventricular Septum during peak diastole in a Parasternal Long Axis image of the heart. This measurement is called E-Point Septal Separation (EPSS). Among ED Physicians there been a strong correlation between the measurements taken at bedside and those later calculated during a formal echocardiogram.
Parasternal Long Axis view of the Heart (below), M-Mode scroll (above)
Intraventricular Septum (IVS) between blue lines
Anterior Mitral Valve Leaflet
Posterior Mitral Valve Leaflet
E-Wave: is the first deflection of the Anterior Mitral Valve leaflet during early diastole and should be the largest movement of the MV.
A-Wave: is the second deflection of the Anterior Mitral Valve Leaflet during diastole, and represents atrial kick caused by atrial contraction.
To obtain a E-Point Septal Separation measurement you first get a Parasternal Long Axis image of the heart, then activate the M-Mode function, and place the M-Mode spike through the distal portion of the anterior mitral valve leaflet. You will then use the calipers to get a measurement on the vertical axis (Y-axis) from the maximum deflection of the MV at the E-Wave, to the closest point to the Intraventricular Septum.
In the image left, measurement B in light blue represents a measurement of EPSS with a value of 0.15cm. Measurement A in yellow is Heart Rate, measured on the horizontal (x-axis) from two repeating points, and is 76bpm, in this case.
In order for the EPSS measurement to be reliable the Mitral valve must be healthy. This means in cases where the MV is stenotic, prolapsed, or if there is regurgitation, the EPSS measurement should not be reliabled upon.
EPSS Measurements with LVEF approximations:
-
0 - 0.6cm = Normal Function with LVEF >50%
-
0.7 - 1.2cm = Reduced Function LVEF 49-36%
-
>1.3cm = Severely Reduced LVEF <35%
With time and practice it is possible to make a visual, "Eyeball Call" on EPSS estimating LVEF. What you are looking for in patients with normal function is for the Anterior Mitral Valve leaflet to touch the Intraventricular Septum. In patients with generally poor function you are looking for a significant (>1.0cm) visual separation between the MV and the IVS. Below is a collection of PLAX images with normal function, and reduced function.
Normal Cardiac Function:
Pay close attention Anterior MV Leaflet touching or making a close approach to the Intraventricular Septum.
In this example we can see the MV touching the IVS, which would indicate normal function, but you may also appreciate a small LV chamber size. So depending on clinical circumstances, the function maybe consider Hyperdynamic, due to underfilling of the LV related to hypovolemia.
Poor Cardiac Function:
In the examples below, you will notice a large separation between the MV and the IVS.
An example of Poor function and bradycardia. This patient also has aortic stenosis, and you maybe able to notice an enlarged Left atria to the right of the MV.
In this example the patient has normal function, but is being bolsetered with an Infusion of Norepinephrine and Dobutamine
In this image you can note the poor function, but also pericardial fluid layered below the heart within the pericardial sac.