Aortic dissections are insidious killers that are often undetectable by history and physical exam alone. Obviously, providers must have a high index of suspicion for these as their presentations are highly variable. CT angiography, and less often, transesophageal echocardiography are classically the diagnostic modalities that providers use to identify this rare, deadly diagnosis. However, getting a patient over to CT can sometimes be delayed whether it is for transportation, or stabilizing the patient before CT scan.
A 73 year old lady with only a past medical history of hypertension that presented to our emergency department with intermittent focal left upper extremity numbness and weakness, and bilateral lower extremity pain. She presented hypotensive and tachycardic. The astute clinician had a high index of suspicion of dissection and while the patient was getting prepared to go to CT scan obtained the following clip of the parasternal long axis of the heart:
It is obvious here that the aortic outflow tract is dilated (usually, it should be the size of the left atrium).
Then the physician obtained a suprasternal view of the aortic arch and obtained the following clip:
Then, given the focal neurologic symptoms, she got the following images of the right carotid, in which you can see an intimal flap and also more distally, a blood clot in the carotid:
To investigate the distal extension of the clot, the following views were obtained of the abdominal aorta with an actual intimal flap:
Finally, at the level of the bifurcation, extension of the dissection into the bilateral iliacs is visualized
CT surgery was notified before the CT scan and the patient was taken directly from the CT scanner (which revealed the image below) to the OR..
Tips on POCUS for aortic dissection:
- A parasternal long axis view can be helpful to visualize a dilated aortic root and/or a pericardial effusion in the setting of a suspected dissection
- Evaluating carotid arteries, the distal aorta, or the iliac arteries can help diagnose an extensive dissection.
- Point of care ultrasound should be used to quickly make a diagnosis, speed further imaging, or get a consultant involved expeditiously. Similar to much of what we do with point of care ultrasound, this tool should be used to rule in a diagnosis, rather than to rule out a diagnosis.
- Point of care ultrasound can be used to make a quick diagnosis at the bedside before more consultative imaging, making it an invaluable tool in identifying this covert killer.
The subxiphoid four chamber view is commonly used in cardiac assessments and the FAST exam and for many is the initial “go-to” view of the heart. Difficulty obtaining this window can frustrate novice and seasoned operators, and there are a few tips which can help optimize the view.
- It’s called SUB-xiphoid for a reason. Don’t jam the probe up against the xiphoid process. Imaging through bone is difficult, the patient will be in pain, and the angle is too steep. Instead, place the probe a few centimeters south of the xiphoid process and work up from there.
- Get a good view of the liver, THEN use that to get a good view of the heart. You may find that starting to the patient’s right of midline gives a better liver window, since the stomach tends to obscure the subxiphoid view as you go further left.
This video illustrates the huge difference that left vs. right can make. It was taken with the probe in a midline subxiphoid position. Starting with the probe angled towards the patient’s left, the entire screen is obscured by gas in the stomach. As the operator changes the angle towards the patient’s right, we see the liver come into view. This yields an excellent window through which the heart can be visualized.
The figure below, taken from the midpoint of the video, illustrates the point a bit more clearly. To the right of the green line (patient left), superficial stomach gas (arrow) obscures everything behind it, creating a terrible view. On the other side of the green line, liver (L) is visualized which creates a good window for viewing the heart behind it.
One of the major indications for bedside cardiac ultrasound is the detection of pericardial effusion and its extreme form, cardiac tamponade. You may remember that Beck’s Triad (hypotension, jugular venous distension, and muffled or distant heart sounds) is pathognomonic for cardiac tamponade. You should also remember (to say to your colleagues who recite that tamponade is a clinical diagnosis) that the triad is present in about one-third of cases.
If you can spot tamponade clinically in a hypotensive, tachycardic patient with muffled heart tones and JVD, congratulations! You may pass your boards, save a simulated patient, or impress a junior medical student. But how does one diagnose this condition a bit earlier in its natural history?
Pulsus parodoxus is not as hard to assess as it sounds- inflate a blood pressure cuff as you normally would. Slowly deflate the cuff and listen for Korotkoff sounds. If they are present during inspiration and expiration, there is no pulsus parodoxus and you are done. If you only hear Korotkoff sounds during expiration, note the pressure reading and keep slowly deflating until they are present throughout the respiratory cycle. What is the pressure difference between sounds during expiration only and sounds throughout the entire cycle? If it is greater than 10 mmHg, pulsus paradoxus is present.
But you read this far down because you want to know how to find tamponade using ultrasound, right? There are some earlier findings of cardiac tamponade which are detectable with ultrasound before hemodynamic instability ensues. They are:
- Pericardial effusion
Diastolic collapse of right atrium and right ventricle
- Hard to have tamponade without this
Inferior Vena cava plethora
- Ideally diastole can be recognized with EKG monitoring on ultrasound, or using M-Mode
Atrio-ventricular valve Doppler inflow velocities
- Dilated IVC with loss of respiratory variation
- If these words are unfamilar, use the first three findings instead! Respiratory variation in inflow across the atrioventricular valves (like a valvular pulsus parodoxus) can be a sign of early tamponade physiology. However this is an advanced technique.
The video below shows the first three findings nicely:
Large Pericardial Effusion from Sinai EM Ultrasound on Vimeo.
Note the subxiphoid view with large effusion, followed by the parasternal long axis view. Finally, a transverse view of the IVC demonstrates dilatation and loss of respiratory variation.
- Schairer JR, Biswas S, Keteyian SJ, et al. A systematic approach to evaluation of pericardial effusion and cardiac tamponade. Cardiol Rev. 2011 Sep-Oct;19(5):233-8.
- Nagdev A, Stone MB. Point-of-care ultrasound evaluation of pericardial effusions: does this patient have cardiac tamponade? Resuscitation. 2011 Jun;82(6):671-3.