Diagnosis of acute thoracic aortic dissection using combined echocardiography and computed tomography

Diagnostic potential of combined transthoracic echocardiography and x-ray computed tomography in suspected aortic dissection

BACKGROUND

Transesophageal echocardiography (TEE) and magnetic resonance imaging (MRI) are considered optimal diagnostic methods in the setting of suspected aortic dissection. However, although less sensitive as single modalities, transthoracic echocardiography (TTE) and contrast-enhanced computed tomography (x-ray CT) are more widely available and less costly.

HYPOTHESIS

This study was undertaken to compare the diagnostic performance and reliability of the combined use of TTE and x-ray CT with TEE and/or MRI findings in the setting of suspected aortic dissection.

METHODS

The diagnostic power of combined TTE and x-ray CT was compared with both single use of TTE and x-ray CT and with TEE and/or MRI in a series of 168 consecutive patients with suspected aortic dissection (AD). Of these, 28 women and 58 men (mean age 53 +/- 16 years) underwent TTE and x-ray CT prior to TEE (n = 52) and/or MRI (n = 69). Diagnostic results of combined TTE/x-ray CT were retrospectively but independently reevaluated in blinded fashion; diagnostic findings were validated by angiography (n = 63), surgery (n = 52), or autopsy (n = 7).

RESULTS

Type A dissection was found in 29 patients (34%), type B dissection in 10 (12%), whereas aortic dissection was excluded in 47 (55%). With 95%, the sensitivity of TTE and x-ray CT was significantly enhanced when used in a combined access compared with 67 and 79%, respectively, when used as single methods (95%; p < 0.05). Sensitivity and specificity (95 and 91%, respectively) of combined TTE/x-ray CT evaluation were not different from TEE and/or MRI (100 and 96%, respectively; NS). Thrombus formation, side-branch involvement, aortic regurgitation, pericardial effusion or mediastinal hematoma were also detected with similar sensitivities and specificities both by combined TTE/x-ray CT and TEE and/or MRI.

CONCLUSION

This first controlled study comparing the combined information of TTE and x-ray CT with TEE and/or MRI revealed a similar diagnostic potential of both diagnostic strategies in the setting of suspected aortic dissection. Thus, in an environment with access to color Doppler TTE and x-ray CT only, the information from both tests should be combined to decide on diagnostic management of these patients.

Imaging of aortic aneurysms and dissection: CT and MRI

There are numerous approaches to the diagnosis of aortic aneurysms and aortic dissection. Echocardiography, computed tomography (CT), and magnetic resonance imaging (MRI) have enthusiastic proponents promoting each technique, which to some extent obscures the real value of each technique. This review examines the role of these techniques in the diagnosis of aortic disease, with special reference to the most recent published literature and an emphasis on the use of CT and MRI. For most patients with chronic aortic disease, MRI is the most appropriate investigation. In acute situations, CT scanning is usually the most useful technique, with echocardiography added for those with ascending aortic disease or cardiac complications.

Fast CT for aortic dissection

Results were evaluated in 81 patients with suspected acute aortic dissection who were examined on a fast CT system capable of a 1 s data acquisition time. 17 patients had Type A and nine had Type B dissections. Radiological assessment provided 78 confident reports and expressed some uncertainty about the diagnosis in three patients. Overall sensitivity for aortic dissection was 96.2% and specificity was 96.4%. When 78 confident reports alone were considered, both sensitivity and specificity reached 100%. Reconstruction of data at 100 ms intervals allowed discrimination between artefacts in the ascending aorta and Type A dissections. CT can often be used as the single investigation prior to surgery for acute Type A dissections.

Utility of transesophageal echocardiography in the diagnosis of disease of the thoracic aorta

PURPOSE

Transesophageal echocardiography (TEE) offers a rapid, minimally invasive method for diagnosing thoracic aortic disease. High-resolution images are possible because of the close proximity of the esophagus and vascular structures within the chest. Lung and chest wall components have little influence on the image quality and a virtually unobstructed view of the heart, thoracic aorta, and pulmonary vasculature is seen. The role of TEE in diagnosing diseases of the thoracic aorta is rapidly developing. The purpose of this study is to define the role of TEE in the diagnosis of thoracic aortic disease.

METHODS

Between July 1, 1989 and December 31, 1992, 1005 TEEs were performed at our center. Of these, 199 (125 men, 74 women) were entered into our aortic disease registry. Indications for the studies included 37 referrals to rule out aortic dissection, 18 to assess aortic aneurysm, 55 to assess for an intraaortic source of embolus, 9 to rule out intraaortic thrombus, and 13 with familial hyperlipidemia being followed to mark response to low-density lipoprotein apheresis. In 67 cases, subclinical aortic plaquing was found incidentally. No complications from the TEE procedure were encountered.

RESULTS

In cases of suspected aortic dissection, TEE was equal to computed tomography (CT) scanning in identifying the type (DeBakey) and extent of thoracic aortic dissection. In addition, TEE provided information regarding functional status of the aortic valve, identified interluminal communications, and assessed blood flow and thrombus burden in the false lumen. TEE correctly identified true aneurysms, intraluminal thrombus, and plaques as possible sources of emboli. One false-positive CT scan result for aortic dissection was seen and was ruled out both by TEE and angiography.

CONCLUSION

Biplane TEE can be considered the method of choice in diagnosing disease of the thoracic aorta. Information from TEE can be obtained at the patient's bedside or in the operating suite, to assess surgical results before procedure termination and afterward for follow-up. Adjunctive magnetic resonance imaging, CT scanning, or aortography may be needed to assess extension of the disease process into the abdomen or pelvis or to plan surgical intervention.

Imaging of thoracic aortic dissection

Acute thoracic aortic dissection has a high mortality if untreated, so the diagnosis must be rapidly made if mortality is to be lowered significantly. Multiple imaging techniques are often used. This retrospective study from 1988 to 1993 assesses the usefulness in diagnosis of chest X-rays, computed tomography (CT) scanning, aortography, magnetic resonance imaging (MRI), trans-thoracic (TTE) and trans-oesophageal (TOE) echocardiography. Forty-two patients with a final clinical diagnosis of dissection were studied. The diagnosis was confirmed in 16 (13 at surgery and three at autopsy). Three died with dissection given as the only cause for death. Chest X-ray abnormalities were seen in all 19 patients with surgery or death from dissection, with a widened mediastinum and/or dilated aorta being present in 17. In the group of 16 patients with surgery or autopsy proof, CT scans found dissections in 9 of 12 patients studied and correctly classified the type in only five. Aortography was performed in five, with accurate depiction of dissection and type in all. TTE found dissections in three of eight patients imaged by this method. MRI and TOE were performed each on two patients, with accurate depiction of dissection and type in each. Because of the relatively low sensitivity of CT scanning in defining aortic dissections Westmead Hospital is currently assessing the use of TOE as the prime imaging modality prior to surgical intervention.