AORTIC DISSECTION

Ascending aortic aneurysms may undergo internal tearing
or dissection resulting in an extremely high mortality of
up to 1% per minute and 60% in 60 minutes. Thus,
time-consuming investigations that are not sufficiently
sensitive or specific, such as CTscans, are usually not recommended.
Emergency surgery carries the only hope of survival
for patients with dissecting aneurysms, and immediate
accurate diagnosis is mandatory to guide therapy.
A. Signs and Symptoms
Sudden onset of severe chest and interscapular pain is
common in aortic dissection. The pain is sudden like a
gunshot, while heart attack pain builds up gradually
over several minutes. The pain is described as a tearing
or ripping sensation that becomes rapidly unbearable
resulting in a shock-like state. In this state the patient’s
skin is cold and clammy with impaired sensorium.
Although the blood pressure may remain in the normal
range or sometimes be increased, hypotension may occur
from external rupture; this is an ominous sign. Syncope
usually indicates a rupture into the pericardial sac with
cardiac tamponade. A new loud aortic diastolic murmur
may be heard and the pulses may be lost in one or
more limb.
The majority of patients with aortic dissection are
hypertensive and older than 60. Normotensive younger
patients usually have associated underlying disease of the
aortic root that includes Marfan syndrome. This is a
leading cause of aortic dissection in patients under 40.
Other causes include giant cell arteritis, lupus erythematosus,
Ehlers-Danlos syndrome, Noonan and Turner’s
syndrome, and relapsing polychondritis. Approximately
15% of patients with coarctation of the aorta die from
aortic dissection.
Urgent diagnosis is crucial. A clinical prediction study
indicates the following probabilities based on the three
most important diagnostic variables: (1)aortic pain with
sudden onset, tearing or ripping character, or both; (2)
widened mediastinum, aortic widening, or both; and (3)
differential pulsations, differential blood pressure, or
both. The probability of dissection was high if isolated
pulse or blood pressures were found or all three variables
were present. Probability was intermediate with isolated
findings of aortic pain or mediastinal widening. The
probability of dissection was low with absence of all
three variables.
B. Diagnostic Testing
1. Transesophageal Echocardiography
Because of its low cost, accuracy, speed, and use at the
bedside in very ill patients, further improvement in
diagnostic features would likely establish transesophageal
echocardiography (TEE) as the investigation of choice,
especially in patients who are unstable and in hospitals
where MRI is not available. The advantages of TEE
include excellent sensitivity and specificity; rapid portability;
the ability to be safely performed in critically ill
patients including those on ventilators; and the ability to
detect and quantify undefined mechanisms of aortic
insufficiency, the involvement of coronary orifices, pericardial
effusion, and the assessment of left ventricular
function. The disadvantages include missing localized
dissection of the upper ascending aorta, not defining
branch vessel involvement, and the reverberation of artifacts
which can be misleading.
2. MRI
MRI proved remarkably useful and safe even in unstable
patients with dissection in a blinded study by Nienhaber
et al. In centers where new generation magnets are
available, MRI may be the primary procedure of choice.
New approaches to breath-hold magnetic resonance
angiography (MRA) allow rapid acquisition and produce
markedly improved images.
3. New Generation CT
Spiral or helical CT scan significantly reduces scanning
time, reduces respiration and motion artifact, and allows
more images during peak levels of contrast enhancement.
Newer scanners can image the entire aorta within seconds
displaying three-dimensional images and appearing to
have a sensitivity and specificity comparable to that of
TEE and MRI.
All three investigative methods, TEE, MRI, and CT,
possess potential pitfalls in the evaluation of dissection
and are complimentary. Two imaging modalities may be
necessary to correctly establish the diagnosis of this lifethreatening
condition.

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