Bedside diagnosis of extensive aortic dissection

Acute aortic dissection (AAD) can be rapidly fatal with out early diagnosis and appropriate medical, surgical, or endovascular treatment. In fact, the mortality rate of aortic dissection approaches 1% per hour during the first 48 h [9]. If unrecognized and untreated, aortic dissection results in a 90% mortality with in the first 3 months, usually due to acute aortic insufficiency, major branch vessel occlusion, or rupture into the pericardium, mediastinum, or left hemithorax [10].

Computerized tomography, TEE, and MRI are the most commonly used modalities to diagnose AAD. The detection of an aortic dissection by CT has a sensitivity from 93 to 100% and a specificity of 87–100% with the primary diagnostic criterion being the detection of an intimal flap separating two contrast-filled lumens [10]. However, CT examination for AAD requires contrast, transportation from a monitored environment, and patient cooperation for an adequate examination.

Angiography is the most widely used modality and is preferred by surgeons prior to repair. Angiography can demonstrate the extent of the dissection, differentiate the true and false lumen, identify the entry and re-entry sites by detecting intimal tears, demonstrate the anatomy of the major arterial branches, and determining aortic regurgitation. However, angiography is an invasive procedure which is associated with morbidity, mortality, requires time for setup and performance which can be difficult in critically ill patients, and when the false lumen is totally thrombosed, the diagnosis may be obscured [11].

Magnetic resonance imaging and TEE offer modestly improved sensitivities for the detection of AAD, i.e. 95–100 and 95–98%, respectively [1]. However, these modalities are difficult to perform on the patient with AAD due to the immense pain associated with this condition. Additionally, more than one-third of patients with AAD will demonstrate signs and symptoms secondary to organ system involvement. These secondary manifestations may include acute aortic regurgitation with resultant cardiac decompensation and shock, cerebral ischemia or stroke with resultant alteration in mental status, spinal cord involvement with resultant infarction and para or quadriplegia making MRI or TEE impossible to perform emergently. To complicate matters further, these diagnostic modalities are difficult to obtain in most centers 24 h a day [1].

Transthoracic echocardiography has been used to diagnose AAD and is often the initial screening tool in unstable patients. In spite of the drastically lower sensitivity of TTE (35–80%) [5–8] as compared to that of CT, MRI, or TEE, TTE has the advantage of being able to exclude other differential diagnoses in critically ill patients. Often, TTE is being performed to rule in or out these other diagnoses such as myocardial infarction when a dissection is discovered. Therefore, the clinician must keep a high index of suspicion for AAD when performing ultrasound involving any of the vasculature such as looking for an intimal flap on an abdominal aorta exam or a dilated aortic root on a cardiac exam. As in this case, an abdominal aortic ultrasound using a curvilinear probe revealed the hallmark of AAD, an intimal flap. The discovered dissection was then traced origin of the aorta using a phased array probe utilizing both the standard TTE views and the suprasternal notch as a window to the superior portions of the aortic arch. With the use of multiple image planes including unusual imaging windows such as the right parasternal, left parasternal, and paraspinal, the thoracic aorta can be imaged in its entirety increasing the accuracy of TTE [6].