Making Waves - All About Ultrasound BloG
Scanning those tortuous Carotid vessels can sometimes be tricky! So here we'll go through 5 quick scanning tips to help you get great carotid images and accurate velocities.
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Diastology can often be confusing, as there have many updates to the standards and guidelines regarding how to assess and grade left ventricular diastology in the past few years. So let's dig in to how to assess this and the echocardiographer's role in evaluating diastology based on the updated
2016 ASE Guidelines.
So as cardiac sonographers, we should all know the basics... E/A reversal = Diastolic Dysfunction, but there is a little more to it than that. If you're not fully evaluating diastology with additional measures, you're probably missing some positive cases. Also the Intersocietal Accreditation Commission now includes reporting of left ventricular diastolic function as a requirement for echocardiography accreditation.
What exactly is diastolic dysfunction? This is a decrease in left ventricular compliance during diastole. While the ejection fraction and left ventricular systolic function are needless to say, pretty important, the diastolic function of the heart is important too. If the heart does not rest properly during diastole, then it cannot fill with the right amount of blood volume needed and eventually this can lead to heart failure and significant clinical implications. So it's important to know the left atrial pressures and end diastolic left ventricular pressures in order to determine the level of severity of the diastolic dysfunction. The updated guidelines break it down like this:
Grade 0 = Normal
Grade 1 = Impaired Relaxation/Diastolic Dysfunction
Grade 2 = Pseudonormalization
Grade 3 = Restrictive Pathophysiology
So how do we get to the diagnosis? Based on the updated standards from the ASE, determination of normal vs diastolic dysfunction is evaluated initially, based on the patient's EF.
If a patient has a normal ejection fraction then the algorithm looks at four components to determine whether or not the patient has a degree of diastolic dysfunction:
1. Average E/e’ > 14
2. e' velocity
-Septal e’ velocity < 7 cm/s
-Lateral e’ velocity <10 cm/s
3.TR velocity > 2.8 m/s
4. LA volume index >34ml/m2
If <50% are positive, the patient is considered normal. If >50% are positive, the patient has a degree of diastolic dysfunction. If only 50% are positive, then we are unable to determine whether the patient has diastolic dysfunction.
If the patient has a compromised ejection fraction, then we can assume that there is a degree of diastolic dysfunction and can grade it based on the E/A ratio.
When the mitral inflow pattern shows an E/A ratio <0.8 along with a peak E velocity of <50cm/sec, then the mean LAP is either normal or low and this is considered a Grade 1.
When the mitral inflow pattern shows an E/A ratio of >2, the mean LAP is elevated, consistent with Grade 3 diastolic dysfunction. Keep in mind patients with young or athletic patients may show this ratio in the setting of normal diastolic function. Also, patients in atrial fibrillation may exhibit a reduced or loss of the mitral A wave and may also produce similar findings.
For patients with reduced EF's that do not meet one of those parameters and the mitral inflow shows an E/A Ratio >0.8 AND the peak E velocity is >50 cm/sec OR E/A Ratio >8 but <2, then other parameters are required for determination of diastolic dysfunction.
1. Average E/e’ Ratio - average E/e’ ratio >14
2. TR Velocity - peak jet velocity >2.8 m/sec
3. LA Volume Index - >34 mL/m2
If 2 of 3 are negative, the patient is considered to have Grade 1 diastolic dysfunction, where if 2 of 3 are positive, then this is considered Grade 2.
So, are you confused yet? Let's look at the grading parameters a little closer.
GRADE 0 - NORMAL DIASTOLOGY
This means that left atrial pressures (LAP) are normal and the diastolic function is not impaired. The left ventricle relaxes normally throughout diastole and allows for complete diastolic filling. The E/A ratio in a normal setting, is between 1 and 2. This gradually reduces with age and E/A ratio >0.75 may be considered normal above 75 years.
GRADE 1 - IMPAIRED RELAXATION/DIASTOLIC DYSFUNCTION
Patients that do not have a NORMAL EF, will have a degree of diastolic dysfunction and are evaluated based on filling pressures of the left atrium. Left atrial pressures can be somewhat normal in a patient with Grade 1 diastolic dysfunction, but will increased as this progresses. Patients with Grade 1 diastolic dysfunction will have reduced e' velocities and prolonged deceleration time.
GRADE 2 - PSEUDONORMALIZATION
One of the biggest factors that our role as sonographers requires, is knowing your patient history. This will often help you know whether or not you're dealing with a normal waveform or pseudonormalization. Granted there are some other key factors but the most obvious is whether or not the patient has previously been diagnosed with diastolic dysfunction. If they have previously had reversal of the E/A waveform and now have a normal waveform pattern, this is a pretty good indicator that the patient is in pseudonormalization. Also, keep in mind some of the other factors associated with increased left atrial pressures, such as blunting or changes to the pulmonary venous waveform, as well as reduced e' velocities. When pseudonormalization is present, the valsalva maneuver can assist to "unload" the ventricle and to reduce filling pressures, causing the E/A reversal to be unmasked.
GRADE 3 - RESTRICTIVE FILLING PATTERN
Grade 3 diastolic dysfunction involves increased left atrial pressures and increased end diastolic left ventricular pressure. This may result in reversal of the pulmonary venous waveform and is often seen with the presence of left atrial enlargement and left ventricular hypertrophy.
ECHO DIASTOLOGY GRADING ANALYSIS TOOLS!
The newly updated algorithm for determining diastology and left atrial pressures can be a little overwhelming and difficult to follow, but we make it easy with our Echocardiography Analysis Tools which include our exclusive LV Diastology Assessment Tool! Quickly and easily determine and grade the diastology based on the updated ASE guidelines. Also there are many other parameters that affect diastology and the application of the diagnostic criteria, such as age, athletic hearts and other factors. Learn and review these additional factors and an in depth study of diastolic dysfunction in our MASTERING LV DIASTOLOGY CME COURSE!
REFERENCE: ASE/EACVI GUIDELINES AND STANDARDS Recommendations for the Evaluation of Left Ventricular Diastolic Function by Echocardiography: An Update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging; Nagueh et al
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Mastering Echocardiography can be tough, especially when it comes to complex processes like Constrictive Pericarditis. Patients with Constrictive Pericarditis do not present for typical pericarditis symptoms. Instead, they present with symptoms of heart failure and so this can often be a challenge for even very skilled sonographers to identify the subtle differences between Restrictive Cardiomyopathy and Constrictive Pericarditis. These two disease processes can appear very similar on echocardiography. However, there are a few things that clue us into the correct diagnosis.
Constrictive Pericarditis is seen with a fibrotic, thickened pericardium, which insulates the ventricle and constricts the ventricle from fully relaxing during diastole. Whereas, Restrictive Cardiomyopathy results in a thickened myocardium, which inhibits the ability of the ventricle to relax and also results in abnormal diastolic function. However, that's where the similarities end.
First of all, we need to evaluate for interdependence of the ventricles. But what does that mean? Ventricular interdependence is when there is a respiratory ventricular septal shift. This then leads to an increase in the volume of one ventricle associated with a decreased volume in the opposite ventricle. This can be tricky to diagnose, so it takes a pretty detailed echo exam and a keen eye of the sonographer and physician.
Secondly, when evaluating for constriction, we will need to look at respiratory changes to the Doppler waveform patterns. The respiratory changes in the Mitral inflow pattern will show a variation of greater than 15% when constriction is present. Whereas, with restriction, this waveform pattern will show a restrictive filling pattern with an E/A ratio >2.0 and deceleration time <160ms.
Another key factor in determining constriction vs. restriction is the E/e' ratio and diastolic function. Remember that both disease processes will have a degree of diastolic dysfunction. Normal left ventricular function will typically show a lateral e’ greater than septal/medial e' velocities, because the septal wall is somewhat restricted and the lateral wall is more free to move. However, with constriction the pericardium is insulating the ventricular movements and does not allow for full relaxation and movement of the lateral wall. This results in mitral annulus reversus, which is a decreased lateral e' velocity and compensatory increase in tissue velocities in the septal/medial annulus. Restrictive patterns in tissue velocities will show an overall decrease in both the lateral and septal e' velocities.
Additionally, with constriction, this will result in expiratory hepatic vein reversal. But why does this occur? Remember that air moves from areas of high pressure to low pressure, which allows for air flow into the lungs. During expiration, the volume of air (and the pressure) of the thoracic cavity decreases, causing the intrapulmonary pressure to rise above the atmospheric pressure. However, with constriction, the pericardium is insulating the intracardiac chambers and this keeps them from tracking normally with intrapulmonary pressures. Remember the pulmonary artery and aorta are OUTSIDE of the pericardium.
So with constriction the thorax pressure and the pulmonary venous pressure will drop, but there are phasic filling differences within the heart, because the gradient to fill the left side of the heart is decreased. The heart is no longer able to push outward against the pericardium, so the pressure is forced inward into the cardiac chambers. So during expiration, the pressure in the right atrium causes flow reversal in the hepatic veins. Whereas, with chronic late stages of restriction, there is an inspiratory reversal during diastole, because there is no shifting of septum and the right heart cannot accommodate increased flow which results from chronic diastolic dysfunction and this causes hepatic vein reversal.
While diagnosing Constrictive Pericarditis on echocardiography can certainly be a challenge, it can be done with confidence. Paying close attention to the details and recognizing when your patient with heart failure symptoms might actually be more than meets the eye, can help to make the correct diagnosis and ensure adequate treatment for your patient.
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Studying for that ARDMS or CCI ultrasound registry exam can be brutal!
So we've covered this topic a few times before, but it is always helpful to revisit some of these study tips. Passing your ARDMS or CCI Ultrasound Registry exam is easier than you think.... There's no need to worry!
Don't stress over it... just study. Mastering ultrasound physics or any other ultrasound specialty can be so overwhelming and often it can you make you want to give up. Don't give up! You've got this! Keep on studying and use these simple tips to study and PASS your ultrasound registry!
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It is so easy to get caught up with our patients who need our immediate attention for things that aren't even ultrasound related and even seasoned sonographers can ignore physics altogether, but when we take it back to the basics, this is where image optimization begins. So, let's take a step back and look at the basics again..... Doppler principles and hemodynamics... I know, I know, for some just saying the words brings tears to their eyes as they recall sleepless nights studying for the Ultrasound Physics registry! But no need to fear! Doppler is simple when you break it down. So the Doppler Effect is quite simply either a positive shift which is a compression in the wavelength (a higher frequency) or a negative shift, which results in an elongated wavelength, (a lower frequency) and this is of course all relative to the observer.
So what does this have to do with Doppler ultrasound? I'm glad you asked.
Doppler frequency shifts come from moving red blood cells and give us the spectral display that we see in Continuous Wave and Pulse Wave Doppler. The velocities obtained from these frequency shifts can also be displayed in Color Doppler, superimposed on top of the 2D ultrasound image. This is a method of displaying the mean or average velocity, while the spectral Doppler display can quantify specific velocities, like the peak systolic and end diastolic velocities, at a point in time.
Because the Doppler frequency shift is relative to the position of the observer, this is important when placing the Doppler sample and angle of insonation. The Doppler sample volume is the "observer" and the frequency shift created by the moving red blood cell is what we are evaluating on the spectral display. But what happens if the observer changes position? The velocity observed will be different. This is extremely important for Doppler Angle. The Society for Vascular Ultrasound recommends that scanning angle be maintained between 45-60 degrees. While we know that the closer to 0 degrees, the more accurate the velocity result because of the math and the cosine of the angle, try getting that on a your average carotid Doppler. It is often not attainable and so for reporting and to maintain consistency in the lab, it is best to stay within the range of what can be easily obtained on most exams.
So as you can see from the image, as the angle of insonation is moved, the velocity result is SIGNIFICANTLY impacted. This can be a very big factor in following up serial ultrasound studies if the same Doppler angle is not used for follow up exams. This is why it is so important to look at the previous study images, especially if there is disease. So when you're scanning don't forget these very basic settings and factors that can have a large impact on your patient's results.
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Mesenteric Abdominal Duplex – it sounds complicated right? In reality though, as long as your patient is prepped, there’s not much to it. I say that with caution though – we’ve all had those patients that just really need another modality of testing. Let's be real... we all know that our ultrasound transducer is NOT a magic wand!
First and foremost - Patient Prep! Your patient prep is one of the most important factors when performing Mesenteric Duplex Ultrasound. Your patient needs to be NPO for at least 6-8 hours before scanning. A test done without the right prep, might as well have not been done at all. This is for a number of reasons:
1. You can't see squat with air and gas in the way!
2. The mesenteric arterial system should be scanned both pre and post prandial for evaluation of stenosis and arterial ischemic response.
So where to begin and what protocol? I've got that covered for you! A mesenteric duplex protocol should include, at a minimum... Transverse and Longitudinal approach with 2D, Longitudinal approach with Color and PW Doppler (Record PSV and EDV) at each of the following locations:
•Branching of Common Hepatic Artery and Splenic Artery from the Celiac Artery
•SMA origin, proximal, mid, distal
•IMA origin, proximal and as distal as possible
A few things can help you improve your imaging and will also help you evaluate patient pathology.
Okay, so now that we have the basics out of the way... you're probably wondering, what should the waveforms look like and what is normal/abnormal? So here's a quick guide:
Remember that the Celiac Artery supplies the liver, spleen and stomach, which are low resistance vascular beds. Normal Doppler waveforms will show increased diastolic flow because of the organs supplied. Flow may also increase with inspiration.
Don't forget to evaluate the branches! This is best done in a transverse plane.
≥70% Celiac Artery Stenosis will show a peak systolic velocity of ≥200 cm/s.
Superior Mesenteric Artery
Remember that the SMA supplies the jejunum, ileum, and both the right and transverse colon. Because of this, waveform characteristics will vary based on state (ie. NPO, post-prandial). Diastolic flow will increase as needed for digestion, post-prandially.
In the normal vessel, post-prandial evaluation should show increased peak systolic flow velocities. If PSV flow does not increase, this is suggestive of a hemodynamically significant stenosis. Also keep in mind that inspiration will show an increase in peak systolic velocities.
≥70% SMA stenosis will show a peak systolic velocity of ≥275cm/s or absence of color flow in the SMA. End diastolic flow velocities of ≥45cm/s are also an indication of ≥70% SMA stenosis.
Also keep in mind that you can find pathology based on the angle of the SMA takeoff from the aorta. If the angle is markedly increased, it may indicate the presence of adenopathy. The SMA should course parallel to the aorta.
Inferior Mesenteric Artery
The IMA supplies the distal 1/3 of the transverse colon, splenic flexure, descending colon, sigmoid colon and rectum. It's waveform characteristics are similar to the SMA and will vary based on state (ie. NPO, post-prandial). Diastolic flow will increase as needed for digestion, post-prandially.
≥70% IMA stenosis will show a peak systolic velocity of ≥275cm/s or absence of color flow in the IMA.
You may need to get your magic wand out for this one!
Diagnostic Criteria Reference: Moneta, et al
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2. Scanning and trying to find those ovaries can prove to be a challenge with a pregnant uterus! Even though it is not our focus, we can’t forget those ovaries! Making sure to image those along with the uterus and fetal images will ensure that you’re not missing potential pathology, but it can definitely be tough with that pregnant uterus in the way. Best methods are to bring the transducer laterally to the patient’s side and to scan in a transverse plane along the lateral side of the uterus, starting pretty high up and moving down toward the patient’s cervix. That transverse plane will give you an increased field of view and will allow you to identify structures more easily.
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