Explain the special role of transesophageal echocar-diography in endovascular stent placement.
With the rapid evolution of ultrasound technology and the advent of transesophageal echocardiography (TEE), perioperative dynamic views of the cardiovascular system are now obtainable that have previously been unavailable by conventional transthoracic ultrasonography. Because the esophagus is in close approximation to the aorta, TEE has become an excellent tool for diagnosing pathology of the distal aortic arch, the descending thoracic aorta, and the proximal abdominal aorta. TEE can provide instanta-neous views of the aorta and location of the guidewires and endografts prior to deployment in relation to the normal and diseased thoracic aorta. While the long-axis view may aid in placement of the angiography catheter and delivery device, these devices may not be visualized unless they are in the precise plane of the ultrasonic beam or if there is significant artifact. To overcome these pitfalls, higher frequencies and intermittent use of the transverse imaging plane can help identify where the tip of the catheter and delivery system lie within the aorta.
TEE appears to have distinct advantages over periopera-tive angiography. TEE provides exact vessel and lesion sizing and localization, which is difficult to obtain during single-plane angiography. In contrast to angiography, both endograft leakage (using Doppler color flow imaging) and iatrogenic dissections may be diagnosed by TEE. It can also be used to estimate endograft sizing and evaluate the endo-graft location. Large intercostal arteries have been imaged, thus avoiding inadvertent obstruction by the aortic stent-graft; however, consistent visualization of intercostal arteries is not possible in all patients. After stent-graft placement, exclusion of flow from the aorta into the aneurysm can be easily confirmed using color Doppler flow imaging in most patients. Finally, since most of these patients have severe concomitant cardiac disease, perioperative TEE allows dynamic assessment of cardiac function.