Aortic dissection: Clinical sciences

Aortic dissection occurs often due to long-standing untreated high blood pressure, when blood tears through the intimal layer of the aortic wall and bleeds into the muscular layer, creating an intraluminal flap and a double lumen, which means that there is a true and a false lumen of the aorta.

Acutely, blood will flow into the false lumen because there’s less resistance, which can lead to obstruction of the true lumen, resulting in malperfusion of end-organs, such as the brain, bowel, or kidneys. In addition, as blood accumulates in the false lumen with no way out, it may clot leading to the formation of thrombi.

Lastly, as blood keeps flowing into the false lumen, the shear stress on the aortic wall can cause the tear to expand, or in the worst cases even lead to aortic rupture, causing mortality from cardiac tamponade or internal hemorrhage.

According to the Stanford classification, aortic dissection is either classified as Type A, which always involves the ascending aorta with or without involving the descending aorta; and Type B, which only involves the descending aorta.

Let’s first look at an unstable case. When approaching a patient who presents with signs and symptoms suggestive of an acute aortic dissection, your first step is to do an ABCDE assessment in order to determine if the patient is unstable or stable. If the patient is unstable, you need to stabilize their airway, breathing, and circulation first. This means that you should secure their airway, obtain IV access, and begin fluid resuscitation while continuously monitoring their vital signs, especially their blood pressure and heart rate.

Next, take a focused history and physical exam. Patients with unstable aortic dissections typically report an acute and severe “tearing” or “ripping” chest pain, and since the aorta is mostly a retroperitoneal organ, the pain can radiate to the back. In fact, the location of the pain depends on which area of the aorta is affected, and sometimes the pain can evolve and migrate as the dissection expands.

If the ascending aorta is involved, your patient will typically report acute onset of severe chest pain and upper back pain. If the descending aorta is involved, the pain can radiate to the upper, mid, and lower back. Lastly, in addition to pain, patients may also report diaphoresis or syncope. On physical exam, you’ll typically note tachycardia and hypotension.

Additional findings may depend on the areas impacted by the dissection. For example, if the dissection is more proximal, it may reach and involve the aortic valve, so you could hear a murmur from aortic regurgitation, and you may also see signs of cardiac tamponade, like jugular venous distension.

Other findings may depend on the area of the body that’s not getting adequate blood supply. For example, if the aortic arch or spinal arteries are involved, your patient may develop neurologic defects like limb paresthesia or paraplegia. There may also be asymmetric pulses or blood pressure measurements between extremities, which can cause acute limb ischemia. Lastly, if the renal arteries are involved, your patient may develop anuria.

Your next step in an unstable patient is to obtain a transesophageal echocardiogram, or TEE for short, to help confirm diagnosis, since these patients may not be stable enough for other types of imaging like a CT angiogram, or CTA for short. TEE might show a double lumen, with the true lumen and a false lumen in the dissected portion, and an intraluminal flap between them. The TEE may also show a thrombus in the false lumen. Finally, the most severe cases may even reveal an aortic rupture, and if the ascending aorta is involved, you may see cardiac tamponade. These TEE findings indicate an aortic dissection, and because this patient is unstable, they’ll typically need emergent surgical repair regardless of the Stanford classification.

Here’s a clinical pearl! Patients with type A aortic dissections are almost always hemodynamically unstable, while patients with type B dissections can become unstable, but are most often stable at presentation.