Question 4
A 45 year old presents with sudden onset of severe acute central chest and back pain suggestive of acute dissection. Discuss the role of transthoracic and transoesophageal echo –cardiography in the initial assessment and ongoing management
Role of ECHO in initial assessment:
- Differentiate between aortic dissection and other causes of chest pain such as PE or AMI
- Differentiate between Type A and type B dissection
- Identify complications of dissection
Role in ongoing management affected by diagnosis:
- Type A dissection cardiothoracic to be involved first and then vascular surgeons if extended down aorta.
- Type B dissection , vascular surgeons to be called first.
Problems
- Dependent on operator experience
- Difficult to assess if there are poor cardiac views
- If the aorta appears normal this doesn’t exclude a dissection
- TTE not very accurate when compared to CTA and TEE.
Signs of dissection using TTE include
1. Intimal flap in ascending aorta. Differentiation between true lumen and false lumen
Features of true lumen:
- Surrounded by calcifications (if present)
- Smaller than false lumen
Features of false lumen:
- Flow or occluded by thrombus (chronic)
- Delayed enhancement
- Wedges around true lumen (beak-sign)
- Collageneous media-remnants (cobwebs)
- Larger than true lumen
- Circular configuration (persistent systolic pressure)
- Found at the outer curve of the archSurrounds the true lumen in Type A dissection
2. Ascending aorta size of > 4cm , however an aortic dissection may be present with a smaller aortic diameter if the patient is small (based on body size)
3. Aortic regurgitation
4. Pericardial effusion
5. Abdominal aorta may show flap if dissection has involved the aorta more distally
Views to image the aorta
- Best view for ascending aorta is PLAX. To visualise the aorta best move up one rib space from PLAX and move probe towards sternum. May be able to visualise flap and measure aorta in suprasternal notch with probe orientated at 1.00 o’clock
- May see aortic root in 3 or 5 chamber view
- May see descending aorta deep to LA in Apical 2 C view and may see descending aorta in chest before it leaves the chest with probe at 12.00 o’clock through the sternum distally.
Consider other diagnoses:
PE:
- large RV
- poorly contracting RV
- D shaped ventricle PSAX
- septal flattening in PLAX
- M’connels sign, RV pressures of < 60 if , PVAT of < 60 msec +/- midsystolic notch
AMI
- Regional wall abnormalities although with a dissection involving the coronary arteries then regional wall abnormalities will be present also
Can assess LV function
- Fractional shortening.
- Eyeballing of LVF
- Ejection fraction (EF) – Simpson method
- Stroke volumeSystolic index of contractility dP/dt
- Longitudinal contraction using tissue Doppler or M mode MAPSE
TEE
- More accurate
- Confirms diagnosis
- Classifies and delineates the dissection
- Localised the intimal tear
- Differentiates true from false lumen
- Can assess complications – AR, Pericardial effusion
- Can assess LV function
- TEE can be used intraoperatively and postoperatively to assess aorta with great accuracy
Drawbacks
- Inadequate visualisation of a portion of the aorta
- Misinterpreting a non aortic structure such as an innominate vein or an azygos vein as a false lumen
- Difficulties in differentiating flap from artifact