Magnetic resonance has been shown to define the normal and abnormal cardiovascular structures in the preoperative patient with ascending thoracic aortic aneurysm and dissections. We have tried to assess the value of MR as a noninvasive means of postoperative assessment in patients who have had composite graft valve placement. It has been suggested that the long-term prognosis will be determined primarily by the risks associated with prosthetic aortic valves.
However, our findings present new information about the appearance of composite valve grafts. Increased signal intensity within the ascending aorta often is found. This may represent thrombus between the conduit wall and the native wrapped aorta. Even echo rephasing was present in some cases in which increased signal was identified and this may represent slow blood flow in addition to thrombus in the space between conduit and native aorta. Phase display images as well as techniques using gradient recalled echos may be a way to differentiate slow blood flow from thrombus. This thrombus and/or slow blood flow could be secondary to perioperative bleeding, early or late leakage, chronic partial dehiscence, or late new tears. In some patients, not only is increased signal identified, but the ascending aortic vascular lumen diameter is compromised. This luminal narrowing could be flow-restrictive, leading to a pressure gradient from the proximal portion of the repair to the distal aorta. Emerging MR techniques should be able to evaluate this possibility. Current echo-Doppler techniques are often unable to assess the entire ascending aorta and arch because of the retrosternal position of the aorta limiting the acoustic window. Transesophageal echocardiography is not a noninvasive technique. It is uncomfortable for the patient and may require sedation to perform; CT scanning does not have the same ability as MR imaging to assess blood flow patterns in a conduit and requires iodinated contrast material as well as radiation. buy cialis soft tabs
The clinical studies cited indicate excellent clinical prognosis with few instances of composite graft dysfunction. In our study, this clinical success rate also was apparent. However, MR imaging of patients postoperatively detected increased periluminal signal with and without luminal narrowing. Thus, MR imaging may be a sensitive noninvasive tool to detect thrombosis and abnormal blood flow and may identify groups at increased risk (groups 2 and 3) for developing late complications. The different MR patterns suggest that clinical success is not always accompanied by uncom- promised anatomic correction. To determine the clinical significance of these abnormal MR patterns will require longer term follow-up in larger numbers of patients. In addition, noninvasive MR imaging of the postoperative patient is seen to be a viable alternative to repeat angiography.