Aortic Dissection

Introduction

Essentials of Diagnosis

• A history of hypertension or Marfan's syndrome is often present.
  
• Sudden severe chest pain with radiation to the back, occasionally migrating to the abdomen and hips.
  
• Patient appears to be in shock, but blood pressure is normal or elevated; pulse discrepancy in many patients.
  
• Acute aortic regurgitation may develop.

General Considerations

Aortic dissection is the most common aortic catastrophe requiring admission to a hospital. It is caused by an intimal tear, which allows creation of a false lumen between the media and adventitia. Over 95% of intimal tears occur either in the ascending aorta just distal to the aortic valve (Stanford type A) or just distal to the left subclavian artery (Stanford type B). These are points where the aorta is fixed and allow for intimal injury during shear stress.

The false lumen can rupture into the pericardial sac, left pleural space, or retroperitoneum. More commonly, the dissection propagates distally to involve aortic branch vessels, producing acute spinal cord (3%), visceral (9%), renal (12%), or lower extremity (9%) ischemia. Proximal extension of a type A dissection can stretch the aortic annulus or occlude a coronary artery orifice, producing acute aortic regurgitation, myocardial infarction, and intrapericardial rupture with tamponade. Both blood pressure and the rate of acceleration of pulsatile flow (dP/dt) are important in propagation of dissection; 80% of patients with acute dissection are hypertensive. Other risk factors for dissection are Marfan's syndrome, pregnancy, bicuspid aortic valve, and coarctation of the aorta.

When not appropriately diagnosed and treated, type A aortic dissection is a lethal disease. Untreated type A dissections are associated with 50% mortality at 48 hours and 90% mortality at 1 month - due to free rupture, tamponade, or acute left ventricular failure. Mortality with untreated type B dissection is 10-20%, usually secondary to free rupture into the pleural space, acute mesenteric ischemia, or renal failure.

Clinical Findings

A. Symptoms and Signs
Eighty-five percent of patients report sudden excruciating ("ripping") pain in the chest or upper back. The pain may radiate into the abdomen, neck, or groin. Many patients are hypertensive at presentation. Some present with syncope, hemiplegia, or lower extremity paralysis. On physical examination, peripheral pulses and blood pressures may be diminished or unequal. A diastolic murmur of aortic insufficiency may be heard.

B. Laboratory FindingsThe ECG may be normal but often reveals left ventricular hypertrophy from long-standing hypertension. Acute ischemic changes suggest coronary artery involvement. Because dissections preferentially extend into the right coronary ostium, inferior wall abnormalities predominate.