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  Always consider aortic dissection in patients presenting with the acute onset of chest or thoracic back pain.

  
  
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  Initiate a rapid reduction in heart rate and blood pressure in all patients with a high clinical suspicion for aortic dissection before obtaining confirmatory diagnostic imaging.

  
  
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  Stanford type A (proximal) dissections typically require surgical intervention, whereas Stanford type B (distal) dissections are managed medically.

  
  
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  Complications of acute dissection include myocardial infarction, cardiac tamponade, aortic valve insufficiency, stroke, renal failure, paralysis, limb ischemia, and death.

Acute aortic dissection is a rare but potentially life-threatening condition. Although the true incidence is unknown, it is estimated that there are between 6,000 and 10,000 new cases annually in the United States. Aortic dissection is more prevalent in men and in patients with advanced age, with approximately 75% occurring in patients between 40 and 70 years of age. Younger patients with aortic dissection usually have a history of an underlying connective tissue disease. Of note, about half of all aortic dissections in women under the age of 40 years occur in the third trimester or early postpartum period.

Risk factors for acute aortic dissection include chronic hypertension, a bicuspid aortic value, coarctation of the aorta, or inherited connective tissue disorders such as Ehlers-Danlos and Marfan syndromes. Vascular inflammatory disorders such as giant cell arteritis or Takayasu arteritis are additional risk factors for dissection.

Aortic dissection results from a tear in the intimal layer of the vessel wall. Common inciting factors include the chronic conditions listed previously, as well as illicit drug use or blunt thoracic trauma. High-pressure pulsatile blood will travel through this tear into the media layer of the aorta, thereby separating the intima from the adventitia. This creates a false lumen for aortic blood flow that can extend distally (antegrade), proximally (retrograde), or in both directions. Rarely, the false lumen will rupture through the adventitia, resulting in immediate hemodynamic collapse. The majority of aortic dissections originate in the ascending aorta (65%), the aortic arch (10%), or just distal to the ligamentum arteriosum (20%). The Stanford classification system divides aortic dissections clinically into types A and B. Type A dissections involve the ascending aorta, whereas type B dissections involve only the distal aorta (origin of the intimal tear is distal to the left subclavian artery) (Figure 17-1).

History

The classic presentation of an acute thoracic aortic dissection is that of a 55- to 65-year-old male with chronic hypertension who develops a sudden onset of severe sharp or tearing chest pain radiating to the intrascapular area. Keep in mind that this is a fairly rare condition that often presents in an atypical manner. When obtaining the history, identify relevant risk factors and inquire about the quality, radiation, and intensity at onset of the pain. Type A dissections present most commonly with anterior chest pain (71%) and less commonly with either back (47%) or abdominal pain (21%). Additional presenting complaints include syncope (13%) and stroke-like symptoms (6%). Type B dissections present most often with acute back (64%) and chest (63%) pain with increasing rates of abdominal pain (43%). Atypical presentations include patients with intermittent symptoms, pleuritic or positional pain, and isolated syncope. Painless aortic dissections have also been reported. Corresponding visceral symptoms including diaphoresis, nausea, vomiting, and pallor are often present.

Physical Examination

The physical examination should initially focus on the general appearance of the patient and an assessment of his or her vital signs. Patients with acute dissections are typically very uncomfortable and ill-appearing. Palpate peripheral pulses in all 4 extremities and measure the blood pressure in both arms, taking note of any discrepancies. The presenting blood pressure cannot be used to either diagnose or exclude this condition, as roughly half of patients will have an elevated blood pressure, whereas an equal proportion will be either normotensive or hypotensive. Although a small percentage of the normal population will exhibit a blood pressure differential between the upper extremities, a blood pressure differential ≥20 mmHg in this clinical context should be considered highly suspicious. That said, the absence of a blood pressure differential does not exclude aortic dissection.

The cardiac examination should focus on any abnormal heart sounds. Consider pericardial tamponade in patients with distant heart tones and associated hypotension, jugular venous distention, and tachycardia. The presence of a diastolic murmur suggests secondary aortic regurgitation. Perform a focused neurologic examination, looking for signs of hemiplegia or paraplegia.