Abdominal Aortic Dissection
Detection with Echocardiography
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Background
The Cleveland Clinic reports that abdominal aortic aneurysms (AAA) are more prevalent than thoracic aortic aneurysms, affecting 1.1 million individuals in the U.S. aged 50 to 84. Detection can be difficult as aortic aneurysms often grow over time and don’t always cause symptoms; those that report symptoms typically complain of deep pain in stomach area, back pain, or a pulse near the belly button.
Aneurysms can occur anywhere along the aorta but most occur in the abdominal portion (75%) as a result of atherosclerosis, hypertension, trauma, or in rare cases infection. This diagnosis predominately affects patients over the age of 65 and is four times more common in people assigned male at birth. Smoking is a considerable risk factor as it weakens blood vessel walls (Cleveland Clinic, 2024).
The risk of an AAA is an aortic dissection, a tear in the intimal layer that allows blood to pass between the intima and the media causing them to split. This new flow channel is created and recognition with echocardiography should be thoroughly understood. The key features in this case include: systolic aortic regurgitation, left atrial compression, true and false lumen, and an intimal flap.
The Parasternal Long Axis View
This patient presented to the emergency department with crushing chest pain, altered mental status, and hypotension. A bedside transthoracic echocardiogram was ordered to assess cardiac status. The parasternal long axis view revealed a dilated left ventricular cavity with severely reduced systolic function. What is the origin of this dysfunction? A congestive heart failure exacerbation, dilated cardiomyopathy, significant coronary occlusion, volume overload, or pressure overload are some of the potential causes for this systolic impairment.
Color Doppler uncovers a severe posteriorly directed jet of aortic regurgitation (AR) and the origin is unknown at this time. Chronic aortic regurgitation results in left ventricular volume overload whereas acute aortic regurgitation causes left ventricular pressure overload. Either of these case scenarios could be contributing to the left ventricular systolic dysfunction. Compression of the left atrial cavity can also be observed here with restricted mobility of the mitral valve due to the high distal pressure.
Potential Causes of Aortic Regurgitation
Idiopathic aortic root dilation: Not attributed to any specific disease or condition, aortic annular dilation resulting in retrograde flow.
Systemic hypertension: Increased pressure exerted on the aortic wall over time causing dilation and malcoaptation of the aortic cusps. Loss of structural integrity and remodeling occurs as a result of this acquired aortic root abnormality.
Aortic dissection: A tear of the inner layer of the aortic wall allows blood to pass between the inner (intimal) and middle (media) layers. This separation is referred to as a dissection and is a life-threatening condition.
Trauma: Severe trauma, such as that from a car accident or a fall, can directly damage the aorta or aortic valve resulting in regurgitation. Sudden changes in blood pressure can also affect hemodynamics in the acute setting.
Autoimmune disease: Systemic lupus erythematosis, ankylosing spondylitis, Reiter’s syndrome.
Congenital leaflet abnormalities: Bicuspid AV, unicuspid AV, quadricuspid AV, or ventricular septal defect
Acquired leaflet abnormalities: Endocarditis, senile calcification, rheumatic valve disease, carcinoid, radiation-induced valvulopathy
Connective Tissue Disorders: Loeys Deitz, Ehlers-Danlos, Marfan Syndrome
Short Axis of Aortic Valve
The origin of this aortic regurgitation can be investigated further now that the potential causes have been discussed. The purpose of the short axis view is to look for any congenital leaflet abnormalities that could be causing the AR. The image below was captured revealing that the aortic valve is trileaflet; systolic regurgitation is noted here as well, why?
Aortic regurgitation is supposed to occur during diastole and in this case it is seen during systole. Systolic aortic regurgitation can be seen in cases of heart failure, left ventricular assist devices, and cardiac arrhythmias like atrial fibrillation. The aortic valve is prematurely opening because of the high pressure in the left ventricle; pressure equalization is disturbed by the aortic valve’s incompetence and LV dysfunction.
Subcostal 4 Chamber
The subcostal view can be obtained by rotating the probe indicator to the 3 o’clock position towards the patient’s left side. The heart is superficial so utilizing an overhand grip and a small breath is helpful here.
Once the subcostal 4 chamber view is optimized, rotate the probe indicator to the 12 o’clock position and follow the right atrium to the inferior vena cava (IVC). Differentiating between the IVC and abdominal aorta can be challenging but pulsed wave Doppler is used to confirm the continuous biphasic flow pattern within the IVC and hepatic vein.
Visualizing the Abdominal Aorta
While keeping the IVC in the center of the screen, tilt the tail of the transducer towards the patient’s right hip until the aorta comes into view. Technical factors may limit visualization but pulsatile flow within the aorta can be observed with color and pulsed wave Doppler. Keep the indicator at the 12 o’clock position and move the probe in a small circular motion to look for alternative imaging windows.
This subcostal view of the abdominal aorta gave the clinical team the necessary information to promptly treat this patient. The origin of the chest pain, systolic aortic regurgitation, and heart failure is confirmed with this one view that many cardiovascular sonographers overlook at the end of their protocol. The final diagnosis was described as severe aortic regurgitation, severely reduced left ventricular systolic function, dissection of the abdominal aorta, and a right atrial myxoma.
Labeling Lumens
True Lumen: the original channel where flow travels, systolic expansion can be seen to differentiate.
False Lumen: the new channel formed as a result of the dissection, expands in diastole and compresses during systole, SEC is possible and/or thrombus formation.
Intimal Flap: mobile linear structure, image in multiple orthogonal views, utilize x-plane if possible.
Thank you!
We would like to thank Armando Salinas for sharing this educational case for us to breakdown here on The Echo Journal. If you found this valuable, give this article a share on LinkedIn and be sure to tag us @Echo Imaging Solutions.
