Aortic dissection

I. What every physician needs to know.

Aortic dissection is a rare disease in which high pressure arterial blood is allowed to penetrate into the layers of the aorta through a defect in the aortic intima. It carries a high mortality due to a lack of distinguishing features impeding rapid diagnosis and the disease process itself. Patients often present with non-specific findings of chest, back and/or abdominal pain, requiring clinicians to have a high index of suspicion to make the diagnosis. The annual incidence is estimated to be 3-4 cases per 100,000.

Aortic dissection is classified using either the DeBakey (types I, II, or III) or Stanford (types A or B) systems. Type I (type A) dissections originate in the ascending aorta and extend to at least the aortic arch. Type II (type A) dissections originate and remain in the ascending aorta. Type III (type B) dissections originate in the descending aorta and can extend distally (or less commonly proximally).

Variants of aortic dissection include: (1) Aortic intramural hematoma—blood in the aortic wall without evidence of an intimal tear; (2) Intimal tear without intramural hematoma—the layers of the aortic wall otherwise remain intact; and (3) penetrating atherosclerotic ulcers—intimal tear with a surrounding hematoma without propagation.

II. Diagnostic Confirmation: Are you sure your patient has an aortic dissection?

Besides imaging, there is no reliable way to exclude the diagnosis of an acute aortic dissection. Von Kodolitsch et al. developed a clinical prediction tool to assist in the diagnosis using the following findings:

Immediate onset of chest pain, tearing or ripping quality, or both.

Mediastinal widening or aortic enlargement/displacement on chest x-ray (CXR), or both.

Absence of a proximal extremity or carotid pulse or blood pressure differential (greater than 20mmHg), or both.

When 2 or 3 of the above findings were present, the probability of aortic dissection was 83-100%. When all were absent, the probability was 7% (4% of patients in the study ended up having aortic dissection). While this clinical prediction tool can help you classify patients as low or high risk, it does not reliably rule out dissection and should not be used as such.

A. History Part I: Pattern Recognition:

Typically, 90% of patients will present with severe, acute pain, most often located in the chest and/or back. However, this is not specific for the diagnosis of aortic dissection. The most common to least common presenting signs and symptoms, all of which are non-specific, are as follows:

Severe and/or worst pain ever.

Abrupt onset of pain.

Chest or back pain.

Systolic blood pressure greater than or equal to 150 mmHg.

Aortic regurgitation murmur.

Abdominal pain.

Pulse deficit (weak or absent carotid, brachial or femoral pulse).

Migrating pain.

Systolic blood pressure less than 100 mmHg.

Syncope.

Painless dissection (very uncommon).

B. History Part 2: Prevalence:

Men are affected twice as often as women, with an average age of approximately 65. Women tend to present at an older age. In this age group, hypertension is the most common risk factor, followed by atherosclerosis. In patients younger than age 40, Marfan’s syndrome is the most common risk factor, followed by hypertension. Atherosclerosis is not a significant risk factor in this age group. Risk factors by category are as follows:

Cardiovascular: hypertension, atherosclerosis.

Collagen disorders: Marfan’s, Ehlers-Danlos, annuloaortic ectasia.

Vasculitis: Takayasu arteritis, giant cell arteritis, syphilis (tertiary).

Anatomic: bicuspid aortic valve, aortic coarctation, pre-existing aortic aneurysm, aortic root dilatation (Turner syndrome).

Drugs: cocaine, methamphetamine.

Iatrogenic: coronary artery bypass graft, cardiac catheterization, aortic valve replacement, strenuous exercise / high-intensity weight lifting.

C. History Part 3: Competing diagnoses that can mimic acute aortic dissection.

Acute aortic dissection is very difficult to distinguish from the more common diagnoses that present similarly—all of which present with significant chest or abdominal pain. A thorough history exploring each of the following diagnoses should help narrow down the differential:

Cardiovascular: acute coronary syndrome, pericarditis, aortic regurgitation.

Pulmonary: pneumonia, pneumothorax, pulmonary embolism, pleuritis.

Gastrointestinal: cholecystitis, pancreatitis, peptic ulcer disease, esophageal spasm/rupture.

Musculoskeletal: costochondritis, fibromyalgia.

Oncologic: mediastinal tumors (thymic, germ cell, lymphoma, thyroid, esophageal).

D. Physical Examination Findings.

The physical exam is neither sensitive nor specific for aortic dissection, and should not be used to rule out the diagnosis. Blood pressure is perhaps the most important exam finding, as it can predict the severity of aortic dissection.

Patients often present with hypertension, either due to severe pain or due to chronic hypertension. Hypotension is less common but portends a much worse outcome, usually indicating cardiac tamponade, aortic rupture or severe aortic regurgitation. Be wary of pseudo hypotension, resulting from dissection involving the brachial arteries. The rest of the exam can help predict the anatomic location of the dissection:

Pulse deficit: weak or absent carotid, brachial or femoral pulse, and/or a blood pressure difference of greater than 20mmHg between the left and right arms. It is more common in type A (type I/II) dissections, but overall presents approximately 30% of the time.

Diastolic murmur: due to dissection involving the aortic valve or root. Seen in type A (type I/II) dissections.

Focal neurologic deficits: due to dissection involving the cerebrospinal vessels. Seen in type A (type I/II) dissections.

Pulsus paradoxus and jugular venous distension: due to cardiac tamponade from aortic rupture into the pericardial space.

Friction rub: due to pericardial effusion, usually from aortic rupture into the pericardial space.

E. What diagnostic tests should be performed?

1. What laboratory studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

There are no laboratory studies helpful for the diagnosis of aortic dissection. Biomarkers, including D-dimer, soluble elastin fragments (sELAF), matrix metalloproteinases (MMPs), and smooth muscle myosin heavy chain show potential for diagnosing of acute aortic dissection. D-dimer levels below, less tahn 500 ng/mL may rule out acute aortic dissection in low-risk patients, however more investigation is needed.

2. What imaging studies (if any) should be ordered to help establish the diagnosis? How should the results be interpreted?

There are numerous imaging options available to rule in or out the diagnosis of aortic dissection. CXR has minimal value in the diagnosis of aortic dissection, but is often performed first given its speed, availability and cost.

Abnormal findings include a widened mediastinum (greater than 8 centimeters at the level of the carina) on a posteroanterior (PA) film and abnormal appearance of aortic contour. However, these are only seen in roughly half of patients with dissection.

Electrocardiogram (EKG) also has limited value in dissection; most commonly showing left ventricular hypertrophy and non-specific ST-T wave changes. One-third of patients have a normal EKG and a quarter of patients have findings consistent with ischemia. Therefore, additional imaging is needed and the decision on which test to obtain depends on the patient’s clinical status and contraindications.

A good rule of thumb is to use TEE or CTA in patients presenting with acute dissection and to reserve MRA for stable patients or for those with a contraindication to TEE or CTA. TEE is the best option for unstable patients, as it can be done bedside or in the operating room. Additional considerations are:

MRA of the chest, abdomen and pelvis: the sensitivity and specificity of MRA approaches 100% and it can often identify the intimal flap. Issues: (1) not suitable for unstable patients given it is time intensive; (2) cannot be used in patients who are claustrophobic or who have pacemakers; (3) Requires gadolinium contrast placing patients with a glomerular filtration rate (GFR) greater than 30mL/min at risk for nephrogenic systemic fibrosis.

CT angiography (CTA) of the chest, abdomen and pelvis: the sensitivity and specificity of standard CTA is around 95%, and spiral or multidetector CTA is at least as good as MRA. It often does not identify the intimal flap. Issues: (1) requires nephrotoxic intravenous (IV) iodinated contrast; (2) may require a second study to guide surgical intervention; (3) source of ionizing radiation.

Transesophageal echocardiography (TEE): while transthoracic echocardiography (TTE) is of minimal utility in diagnosing aortic dissection, TEE has a sensitivity and specificity equivalent to CTA and MRA. It also provides information about the intimal flap, aortic valve and heart function. Issues: (1) requires sedation and esophageal intubation which may exacerbate hypotension; (2) dependent on echocardiography technician; (3) often not readily available.

Aortography: the prior “gold standard”, now it is usually reserved only when non-invasive imaging techniques are inconclusive. Issues: (1) invasive; (2) requires nephrotoxic IV iodinated contrast; (3) highly operator dependent; (4) not readily available and time-consuming.

F. Over-utilized or “wasted” diagnostic tests associated with this diagnosis.

Laboratory testing, EKG, CXR, and TTE are not useful for the diagnosis of aortic dissection, however, they may help determine severity (i.e. pericardial effusion, ischemia) or help make an alternative diagnosis. Obtaining only chest imaging (CTA chest, MRA chest) does not exclude abdominal dissections and is an incomplete study.

III. Default Management of Acute Aortic Dissection.

A. Immediate management.

Immediate management involves admission to the intensive care unit (ICU), intubation and mechanical ventilation if in respiratory failure, placement of IV access, and blood pressure monitoring continuously (using an arterial line) or every 5-10 minutes initially, in both arms (use the higher reading to guide management).

Obtain a complete blood count (CBC), basic metabolic panel, troponin, brain natriuretic peptide (BNP), EKG, and portable CXR. It is important to manage the patient’s pain and anxiety, as this reduces blood pressure and improves comfort. Use IV morphine and IV lorazepam as needed.

Further acute management depends on the patient’s blood pressure.

Hypotension or shock occurs in approximately 25% of patients and predicts a poor outcome. Cardiogenic (acute aortic regurgitation, myocardial ischemia), obstructive (pericardial tamponade), distributive (spinal infarction), and hypovolemic (aortic rupture) etiologies can be present in acute aortic dissection.

Attempt to determine the etiology using exam findings (i.e. signs of fluid overload) and a bedside TEE. Volume resuscitation is key in patients without cardiogenic shock. Use IV normal saline +/- packed red blood cell transfusions through large bore (14-16 gauge) peripheral IVs or an internal jugular cordis line.

A good rule of thumb is to start with 250-500mL boluses, in case the etiology is unclear. In patients with cardiogenic shock, vasopressors can be used, but inotropes can worsen the dissection and should be avoided. Pericardiocentesis should also be avoided in pericardial tamponade as this can worsen hemorrhage. Urgent cardiothoracic surgical consultation, or transfer to a facility that provides this service, is mandatory for all etiologies.

Hypertension, present in half of patients, should be treated aggressively. While a hypertensive emergency is defined as a blood pressure >180/>120, consider all patients with acute aortic dissection and hypertension (systolic blood pressure (SBP) ≥150) to have a hypertensive emergency. Blood pressure should be lowered acutely with a goal systolic pressure of 100-110mmHg (or the lowest blood pressure that achieves organ perfusion).

Beta-blockers are the drug of choice; Esmolol is often used because of its short duration of action so that it can be turned off quickly if needed. Vasodilators (e.g., nitroprusside) can be added to achieve the target blood pressure, but should not be used without adequate beta-blockade, as the resulting reflex tachycardia can worsen the dissection. For those with contraindications or are intolerant of beta-blockers, calcium channel blockers can be used.

Urgent cardiothoracic surgical consultation, or transfer to a facility that provides this service, is mandatory for type A (types I and II) dissection, and recommended for type B (type III) dissection. Endovascular stenting is an alternative option for patients with complicated type B dissections.

Complicated type B (type III) dissections occur when limb ischemia/paresis, organ ischemia, aortic aneurysm, refractory hypertension, and/or refractory pain are present.

B. Physical Examination Tips to Guide Management.

Blood pressure monitoring in both arms is necessary to guide management. Always use the higher blood pressure reading. Since type A (types I and II) aortic dissection is a surgical emergency, no physical exam findings will otherwise change your management. Uncomplicated type B (type III) aortic dissection is not a surgical emergency.

Monitoring for limb ischemia via peripheral pulses and cyanosis, limb weakness or paresis, or continued pain is worrisome for a complicated type B dissection requiring surgical intervention.

C. Laboratory Tests to Monitor Response to, and Adjustments in, Management.

Laboratory testing should include:

Serial troponin measurements every 6-8 hours for 24 hours or until the patient is pain free. Elevated troponins portend a poor prognosis and further justify rapid surgical intervention.

Serial hemoglobin measurements every 6-8 hours. Falling levels may indicate aortic rupture.

Daily to twice daily basic metabolic panels (BMPs) to assess for renal function and for an anion gap acidosis. Worsening creatinine likely indicates poor renal perfusion. Worsening gap acidosis, likely lactic acidosis, indicates worsening organ hypo-perfusion.

D. Long-term management.

All patients, requiring surgical repair or not, require life-long oral beta-blocker therapy to achieve a goal blood pressure of 120/80mmHg. Additional antihypertensives will likely be necessary to achieve this goal. Patients should be monitored with serial MRAs to evaluate for aortic aneurysm at 1, 3, 6, and 12-month intervals, followed by annually or biannually.

Patients should be instructed to avoid strenuous physical activity, especially those activities with rapid accelerations / decelerations. In young patients, an underlying etiology (i.e. Marfan’s) should be explored.

E. Common Pitfalls and Side-Effects of Management.

Vasodilator therapy (nitroprusside, nitroglycerin) should not be started before or without beta-blockers, as it can result in a reflex tachycardia increasing shear stress on the aorta.
Thoracic surgery should be consulted immediately for recommendations regarding surgical repair.
Avoid anticoagulants and antiplatelet medications to prevent hemorrhage.
Avoid paracentesis if pericardial tamponade from hemopericardium is diagnosed, as this can worsen hemorrhage.
Avoid inotropes as they can worsen the dissection.

IV. Management with Co-Morbidities.

A. Renal Insufficiency.

TEE would be the test of choice in patients with renal insufficiency to prevent contrast nephropathy from CTA or to prevent nephrogenic systemic fibrosis from MRA.

Nitroprusside should be avoided in patients with a creatinine clearance (CrCl) less than 10 or on dialysis. Use nitroglycerin instead.

B. Liver Insufficiency.

In cases of aortic rupture and hemorrhage, fresh frozen plasma and platelets should be given depending on the severity of the liver disease and thrombocytopenia.