Urgent diagnosis is crucial. A clinical prediction study indicates the following probabilities based on the three most important diagnostic variables: (1)aortic pain with sudden onset, tearing or ripping character, or both; (2) widened mediastinum, aortic widening, or both; and (3) differential pulsations, differential blood pressure, or both. The probability of dissection was high if isolated pulse or blood pressures were found or all three variables were present. Probability was intermediate with isolated findings of aortic pain or mediastinal widening. The probability of dissection was low with absence of all three variables.
B. Diagnostic Testing
1. Transesophageal Echocardiography
Because of its low cost, accuracy, speed, and use at the bedside in very ill patients, further improvement in diagnostic features would likely establish transesophageal echocardiography (TEE) as the investigation of choice, especially in patients who are unstable and in hospitals where MRI is not available. The advantages of TEE include excellent sensitivity and specificity; rapid porta¬bility; the ability to be safely performed in critically ill patients including those on ventilators; and the ability to detect and quantify undefined mechanisms of aortic insufficiency, the involvement of coronary orifices, peri-cardial effusion, and the assessment of left ventricular function. The disadvantages include missing localized dissection of the upper ascending aorta, not defining branch vessel involvement, and the reverberation of arti¬facts which can be misleading.

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