Transthoracic Echocardiography

Two-dimensional echocardiography is a useful imaging tool in the initial evaluation of patients suspected of aortic dissection21-23 for both confirming the diagnosis as well as excluding other conditions in patients presenting with similar clinical picture. Although several diagnostic criteria exist (Table 4.1), the hallmark of aortic dissection is the detection of undulating linear echoes of

Table 4.1. Echo features that aid in the diagnosis of dissection

Transthoracic echo:

• Linear echo with undulating motion (intimai flap)

• Aortic root dilatation >42 mm

• Widening of aortic walls: o Anterior 16-21 mm o Posterior 10-13 mm

Transesophageal echo:

• Linear undulating echo (intimal flap)

• Small true lumen

• Large false lumen

• Accentuated color flow Doppler in true lumen

• Spontaneous echo (swirling) and thrombus in the false lumen

• Communications demonstrated by color flow Doppler an intimalflap. When seen in multiple views, this finding increases the predictive accuracy of the diagnosis24. Several studies have shown that high-quality imaging can be obtained in many patients with aortic dissection and with the use of multiple windows including right parasternal, left parasternal, and paraspinal, the thoracic aorta can be imaged in its entirety. High left parasternal and right parasternal widows allow imaging of the aortic root and ascending aorta. Supra sternal and right supra clavicular windows permit imaging of the distal ascending aorta, arch of aorta including the neck vessels, and proximal descending thoracic aorta. The distal portion of the descending thoracic aorta can be visualized from modified apical and from the subcostal windows. However, the major limitation is inconsistent image quality of the ascending aorta and aortic arch and suboptimal imaging of the descending thoracic aorta, more so in patients with obesity, chest deformity, and emphysema23. The major issue is correctly differentiating the intimal flap from scanning artifacts that result from a calcified aortic root, catheter from the right ventricular outflow tract, and fluid in the transverse pericardial sinus25. The sensitivity and specificity for TTE is 75% and 90%, respectively21,23,26 when adequate images are obtained. However, its sensitivity is 78-100% in the ascending aortic dissection but only 31-50% in descending thoracic aortic dissection27. None-the-less, in descending thoracic aortic dissection, using all available windows has provided reliable diagnostic accuracy28. TTE in addition to identifying the inti-mal flap also provides important information pertaining to involvement of the aortic root, coronary arteries as well as impending rupture by demonstrating aortic regurgitation and its mechanism, regional wall motion, and pericardial effusion respectively. This information is essential for the timing of surgery. In

Type Dissection Echocardiography
Figure 4.9. This composite TTE images demonstrates the comprehensive assessment of the type A dissection. Note the intimal flap extends from the aortic root to the abdominal aorta. TL = true lumen, FL = false lumen, AR = aortic regurgitation, LCA = left carotid artery, and Abd. Ao = abdominal aorta.

unstable patients, the information from TTE may be sufficient to allow immediate transfer to the operating room where TEE can be used intra operatively to further refine the findings. Figure 4.9 demonstrates the ability of comprehensive assessment of Type A aortic dissection by TTE.

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