CT aortography has the advantage of imaging adjacent chest structures for alternative diagnoses.5 It can delineate extent of dissection and branch compromise and is helpful in planning definitive surgical management.2 Sensitivity and specificity are 94% and 77%, respectively.26 New EKG gating can eliminate motion artifact in structures close to the heart and may allow simultaneous imaging of the coronary and pulmonary arteries. This creates potential for a novel, single “triple rule-out” test for AAD, PE, and coronary artery disease, which is currently being studied.26
Explore This IssueACEP News: Vol 28 – No 07 – July 2009
TEE has a sensitivity of 98% and specificity of 83%, and can image the entire descending thoracic aorta, unlike transthoracic echocardiogram (TTE).26 The advantage of TTE is ease of performance from lack of sedation and airway monitoring. The major drawback of echocardiography is dependence on an experienced operator and limited availability in small institutions and at off hours.
Conventional aortography and magnetic resonance imaging (MRI) are not currently recommended as first-line diagnostic modalities. Aortography has limited availability, sensitivity less than 80% when compared to CT or TEE, and important technical limitations in diagnosing an intimal flap or thrombosis in the false lumen.26 Although MRI is highly accurate (98% sensitive and specific) and lacks radiation exposure, it requires potentially unstable patients to stay in undermonitored settings for long durations. Accordingly, MRI is best used for postoperative follow-up and assessment of chronic dissection.26
No randomized clinical trials exist to guide initial management of AAD. The European Society of Cardiology provided a consensus statement in 2001: Once AAD is highly likely or confirmed, therapy includes analgesia, heart rate control, blood pressure control, and surgical evaluation.5
Morphine is the preferred analgesic, as it decreases sympathetic output as well. Reductions in heart rate and blood pressure will reduce overall aortic wall tension and limit the extent of dissection. Short-acting IV beta-blockers such as labetalol or esmolol are ideal, with esmolol preferred if the subject is potentially intolerant of beta-blockers (chronic obstructive pulmonary disease, bradycardia, congestive heart failure). The goal heart rate is 60-80 bpm. No data for calcium-channel blockers exists, but IV dihydropyridines such as nicardipine may be used to reduce blood pressure. Vasodilators such as nitroprusside may be necessary to decrease systolic blood pressure to 100-120 mm Hg once heart rate is controlled.5
The emergency physician should consult cardiothoracic and vascular surgery early in patients with confirmed AAD. Establishment of Stanford classification is extremely important to direct management and prognosis. Stanford Type A dissections should be treated surgically, and Stanford Type B dissections initially should be treated medically. Most patients with Stanford Type A dissections managed surgically will return to independent living. Because most patients with Stanford Type A dissections managed nonsurgically will die, medical management should be pursued only in the presence of severe comorbidities or patient refusal.2