Welcome to another ultrasound-based clinical case, part of the “Ultrasound For The Win!” (#US4TW) Case Series! In this peer-reviewed case series, we focus on real clinical cases where bedside ultrasound changed the management or aided in diagnoses. In this month’s case, a 93-year-old female presents to the Emergency Department with crushing chest pain.
A 93-year-old female with no available medical history is brought to the Emergency Department by ambulance after she was noted to clutch her chest and collapse while at home. She is unable to provide any history due to altered mental status.
She is immediately brought to the ED resuscitation room, where she appears lethargic and unable to follow commands, diaphoretic, with a subtle left-sided facial droop. Bradycardia and a cardiac murmur are appreciated and asymmetric pulses are noted in her lower extremities.
- BP 110/40 mm Hg
- P 50 bpm
- RR 18 respirations/min
- O2 100% saturation on 2L nasal cannula
- T 36.9 C
- Acute Coronary Syndrome
- Aortic Dissection
- Cerebrovascular accident
- Penetrating ulcer
- Pericardial tamponade
- Pulmonary Embolism
The echo findings, taken into consideration with the clinical scenario, is concerning for acute thoracic aortic dissection stemming from aneurysmal aortic disease.
Ultrasound Image Quality Assurance (QA)
An important aspect of ultrasound is appropriate and optimal image acquisition. The clip obtained is an adequate parasternal long axis (PLAX) view of the heart. This is obtained with the phased array probe placed at the 3rd-5th intercostal space just to the left of the sternum at the sterno-costal angle. The probe marker is oriented to the patient’s right shoulder, at around 10 o’clock, which is typical of an ED echocardiogram. It is important to note that cardiology echocardiograms are done in an opposite probe indicator-to-screen orientation. For further discussion on this, please refer to a previous US4TW case, and Dr. Chris Moore’s paper,1 which is a must-read for anyone who performs echocardiograms.
In order to optimize the image, the depth should be increased slightly in order to completely visualize the cross-section of the descending thoracic aorta, allowing for measurement of the aortic diameter.
Lastly, thoracic aortic dissection is noted by the presence of the intimal flap, seen on the images here at both the aortic root and descending thoracic aorta. Thoracic aortic dissection, while a distinct entity in itself, is often preceded by the presence of a thoracic aortic aneurysm. Thoracic aortic aneurysm is defined as a diameter > 4.0-4.5 cm, and is best identified in the parasternal long axis view. Measurements should be made at the largest visualized portion, from “leading edge to leading edge”.2 To accomplish this, the calipers should be placed perpendicular to the axis of the vessel on the outside border of the aorta in the anterior field to the intimal surface of the posterior wall of the aorta in end-diastole.
For those who have an interest, a suprasternal notch view can also visualize the aortic arch, however this is out of the scope of this case series. More advanced techniques, such as color doppler and spectral doppler, can give further information about the flow (direction and velocity) in the true and false lumen.
Disposition and Case Conclusion
The concerning findings on the bedside echocardiogram prompted the team to obtain a CTA which confirmed the diagnosis of an acute thoracic aortic dissection, with extensive aneurysmal dilatation of the ascending and descending thoracic aorta through to the abdominal aorta to below the level of the aortic bifurcation!
Given the high mortality associated with acute aortic dissection, she unfortunately did not survive her condition, but the expeditious workup allowed for the appropriate patient-centered management and goals of care discussions of this grave condition to happen in a timely manner.
Thoracic aortic aneurysms are less prevalent than abdominal aortic aneurysms, however the Emergency Physician must be able to be able to identify symptomatic thoracic aortic aneurysms.2 Thoracic aneurysms are associated with aortic dissection, and have a high (>50%) mortality within the first 48 hours, making it a diagnosis that must be recognized quickly.3 Bedside trans-thoracic echocardiogram is often the initial study of choice in many emergency departments for the evaluation of a patient with concern for aortic aneurysm or dissection given its ready availability, low cost, and lack of ionizing radiation. It is within the scope of the Emergency Physician to identify thoracic aortic pathology, and recent consensus statements by ACEP and the American Society of Echocardiography (ASE) support this.
However, it is important to recognize that the entire extent of the thoracic aorta cannot be entirely visualized with ultrasound, so if there is suspicion for a symptomatic aneurysm or dissection, a CTA should be obtained. That being said, point-of-care echo can be a beneficial initial screening study; A recent retrospective study by Taylor et al showed that bedside trans-thoracic echocardiogram demonstrated good agreement with CTA measurements of maximal thoracic aortic diameter.4 Thus, it is important to be aware of the echocardiographic findings that are suggestive of a thoracic aortic aneurysm (visualizing and measuring the aortic root, and descending thoracic aorta), and findings of a dissection (visible dissection flap).
Take Home Points
- It is important to visualize regions of the thoracic aorta when performing a bedside trans-thoracic echocardiogram (TTE) to look for thoracic aneurysms or dissection.
- Although important to obtain multiple views when performing a bedside echocardiogram, the parasternal long axis view is most ideal for visualization and measurement of portions of the thoracic aorta. Make sure you have enough depth to visualize the descending thoracic aorta.
- Remember: Normal aortic root < 4.0 cm. Larger than this suggests a thoracic aortic aneurysm and possible type A aortic dissection.
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