Aortic dissection is a disease that commands a lot of respect. Thankfully it’s also quite rare, and as a result, we don’t cross its path very often. While the scarcity of this disease is good for the population at large, it ends up being quite detrimental to our individual patients because we simply don’t have a lot of experience identifying it. What follows are just some ideas I’ve picked up over the past few years that I figure are worth sharing and considering…
Why is it so important?
Rare, atypical, and scary: that’s probably the best way to summarize aortic dissection.
Rare – When understanding its incidence, the most usable figure I’ve come across states that it occurs around once per 10,000 patients admitted to the hospital. By my estimate, that means that your average ED with an annual census of 50,000 patients might see one patient per year with this disease. So, if you haven’t seen anyone with a dissection yet, you’re not alone.
Atypical – Of the diseases that can result in your imminent demise, this is probably the most deserving of that title given to so many conditions: “The Great Masquerader.” We all know the classic chief-complaint of “tearing mid-scapular back pain,” but if that’s the only symptom that catches your ear,you’re bound to miss some. It’s been reported that maybe 4.5% of dissection present PAIN FREE, and since the aorta has branches to every part of the body, the constellation of signs and symptoms you encounter can be quite varied.
Scary – Data from the IRAD database suggests an in-hospital mortality of 27.4% for all-comers with a dissection, and that’s without counting all the patients who died prior to arrival or were missed and sent home to perish. A commonly quoted figure is that an acute dissection is associated with a mortality of 1 to 2% per hour for the first 24-48 hours.
The “Dissecting Aortic Aneurysm”
You may disagree, and feel free to state your case, but I absolutely abhor this phrase. When someone uses it I can’t help but infer that they don’t understand the pathophysiology of either a dissection or an aneurysm. By definition and common understanding, an aortic aneurysm is a bulging of all three walls of the aorta.
On the other hand, a dissection occurs when the intima (inner layer) of the aorta separates from the adventitia (outer layer) by the media (middle) being torn and filled with blood. In the latter condition the outside dimension of the aorta is likely to change, but all three layers do not do so equally, and thus it does not meet the definition of a true aneurysm in my book. I hope we can put that behind us.
Not done yet? Well you’re technically right, you can have a baseline aortic aneurysm that eventually leads to a dissection, but such an entity is quite rare—especially considering that plain-ole dissections are rare enough—so I think the term should not be bandied-about unless there is imaging to confirm the diagnosis. In every other case, aortic aneurysm and aortic dissection are two very distinct diseases with differing pathological findings and management.
The IRAD Database
One of the really interesting things going on in this field right now is the International Registry of Acute Aortic Dissection (IRAD). You can read more about it here but basically it’s grown to a group of 30 large referral hospitals in 11 countries that are collecting data on pretty much everything you ever wanted to know about aortic dissections. In 2000 they published one of their seminal works in JAMA, covering the initial registry data on 464 patients with aortic dissection. Most of the numbers I quote in this article come from that study unless otherwise noted.
You Can’t Diagnose Every Dissection
As I stated earlier, 4.5% of the patients in the IRAD registry presented with ABSOLUTELY NO PAIN. If you can’t handle the fact that you’re eventually going to miss one of these, you should probably find a different line of work.
“Sudden and Severe”
The classic teaching is that the pain of dissection is described as “tearing,” but that’s only present in 50.6% of cases. In fact, more patients presented with “sharp” pain (64.4%). More useful, instead, is a history of pain that was sudden (84.8%) and severe (90.6%) in origin.
In fact, I actually like to think of aortic dissection as a lot like subarachnoid hemorrhage. They both initiate with sudden and severe pain (maybe maximal at onset?), often with atypical presentations, and both are diagnoses that significantly benefit from early identification and treatment. Also, in my limited experience (maybe two or three cases of each), they are both also very easy to dismiss as “malingering” or “over-dramatic” presentations as a slightly uncooperative patient moves around on the gurney, unable to get comfortable. That is, until you see the CT results and very quickly reverse your opinion.
The “Chest Pain and…” Syndrome
As mentioned in the title, one of the most important points of this discussion is that you should consider the diagnosis of dissection in any patient complaining of chest (72.7%) and/or back (53.2) pain AND something else. What can that something else be?
Abdominal pain (29.6% reported any) – also a possibility on its own.
Arm or leg pain.
Focal neurological findings: any stroke-like presentations (4.7% presented as cerebrovascular accidents), including arm, leg, or facial paresthesia, weakness, or paralysis.
Altered mental status.
Or pretty much anything else that strikes you as weird and not typically related to the chest and back pain we encounter.
Why This Myriad of Presentations?
Consider for a moment what this giant artery connects to: everything! If you tear apart the layers of your aorta, you can also block blood-flow through any of the arteries coming from it.
Disrupt flow through a renal artery and that kidney is going to die.
Dissect into an iliac and the patient may experience leg pain, weakness, or hypo-perfusion.
Same goes for the bracheocephalic or left subclavian arteries, affecting the arms.
Hit those same arteries and the dissection can in-turn extend into a carotid, causing the patient to present like a stroke.
Cut off flow to part of the spinal cord and you’re going to see weakness, paresthesia, or paralysis affecting the downstream extremities.
Hit a mesenteric (gut) artery and the patient will experience severe, unremitting abdominal pain, and eventually dead bowel.
Dissect back into the pericardium and it’s going to fill with blood and lead to tamponade, with signs of obstructive shock.
Here’s a SCARY – but rare – one: hit a coronary artery, usually the RCA, and you’re going to see a STEMI on the ECG (3.2%). So, in that case, you’ll have a patient who presents with chest pain and an acute MI, maybe even in CHF (6.6%), but their underlying problem is actually an aortic dissection. Give them heparin or lytics and that’s what Dr. Amal Mattu likes to call a “clean kill.” I like to call it an impossible diagnosis.
So How Do You Die from Dissection?
The quickest way is through aortic rupture, which carries a 50% prehospital and 80% overall mortality.
As mentioned earlier, you can also dissect back into the pericardium, fill it with blood, and die from tamponade.
Or, from that last scenario, there’s also a small chance you can block one or more coronary arteries, and perish from a heart attack and sudden cardiac arrest.
Severe aortic insufficiency from poor flow through the aorta, combined with an incompetent aortic valve, can also lead to poor perfusion and death.
Then there’s slower routes, like infarcting a kidney, some gut, or your brain, and passing away from the sequelae that those conditions bring.
How Does Blood Pressure Fit Into the Patient Assessment?
Chronic hypertension is a well-known risk factor for developing a dissection, but what does it mean if the patient in front of you is hyper- or normo-tensive?
Almost nothing. 49% had a systolic BP >149 mmHg (hypertensive), and 34.6% had a BP from 100-149 mmHg (normotensive), so the patient’s current BP doesn’t do much to help you out. Unless, that is, it’s low, in which case you’ll hopefully be able to recognize that something catastrophic is happening.
What is the Role of Bilateral Blood-Pressure Measurement?
Here’s one of my favorite topics…
When I first heard of doing bilateral blood pressures to look for pseudohypotension in ascending aortic dissection I thought it was the greatest idea ever. If the patient managed to kink off one of the arteries going to an arm it would result in a false-low blood-pressure reading. As a result I did a lot of bilateral pressures, got a lot of false-positives, and didn’t save anyone.
One problem arises when trying to decide just what constitutes an abnormal difference, with various sources quoting 10, 15, 20, or 30 mmHg as worrisome levels. I’d say 20 mmHg is the most common value cited, but that raises another issue.
Maybe 19% of the general population also has a 20 mmHg difference between their arms at baseline. It gets worse when you consider that the greater a patient’s atherosclerotic burden, age, or hypertension—three of the big risk factors on our radar—the more difference you’re going to see between their limbs. Then there’s the additional variance involved in performing the same test twice, which will result in slightly different results every time. PLUS, what if the dissection is affecting both arms and as a result, both blood pressures are diminished but at equal levels.
So, What’s the Alternative?
The basic physical exam: pulses and perfusion. Simply check pulses in all four extremities, ensure that there are signs of good perfusion, and both you and the patient are in good shape from that perspective. You haven’t ruled out a dissection by any stretch, but a positive result would greatly increase the chances that there is actually a dissection. With bilateral BP’s, on the other hand, you still cannot come close to ruling out dissection, but a positive result is also a lot less useful.I don’t have exact numbers, but if you know how to think in likelihood-ratios, pulse deficits would have a much higher positive-LR than bilateral BP’s (just throwing out an example, 15 vs. 4), but both would have similarly useless negative-LR’s (again, made-up, 0.7 vs. 0.5)
Radial and femoral arteries are my sites of choice.
Radial pulses are usually readily palpable and can be compared simultaneously, so I like to start there. The lower extremities are less straight-forward, but I find the femorals are simple enough to find on most patients, easy to compare consecutively, and only inches away from the lower quadrants of your abdominal exam if you’re doing it right. On the other hand, if you try using pedal pulses, you’re likely to get a lot of false-positives when the patient simply has difficult anatomy. Still, even when using the femorals, it’s worth looking at their feet to get a feel for both symmetric and overall perfusion.
This disease is scary, rare, tough to diagnose, and easy to mimic. I guarantee that on your next shift you’re going to see at least one patient who now raises some flags on your dissection radar. Thankfully, that’s the point! It’s worth having a high suspicion for this disease.
With that said, please don’t go chasing zebras. I don’t advocate treating the patient with an exacerbation of their chronic back-pain and sciatica like they’re dissecting (but they still can…). Instead, use that encounter as an opportunity to open your differential a little and practice performing a slightly more thorough history and physical exam. The goal isn’t to rule out the disease in everyone with back pain, but rather to risk-stratify them as “not going to die in front of me.”
If you have any more pointers, or disagree with any of my opinions, let me know! As always, I’m open to discussion – yes, even with you, guy who still calls it a dissecting aneurysm.