Evangelista 24/7/08 12:47 Page 80
Hypertension
Diagnostic Strategies Natural History and Prognosis
Electrocardiogram Type A Dissection
This test should be performed on all patients as it helps to differentiate In-hospital mortality rate was 32.5% in type A dissection patients.
14
In-
pain from acute myocardial infarction, for which treatment may hospital complications (neurological deficits, altered mental status,
include anticoagulation, in contrast to aortic dissection, where this myocardial or mesenteric ischaemia, kidney failure, hypotension, cardiac
therapy would be contraindicated. A normal electrocardiogram (ECG) tamponade and limb ischaemia) were increased in patients who died
was seen in one-third of patients, and ECG showed non-specific ST- compared with survivors (p<0.05 for all). Logistic regression identified the
and T-wave changes in 42%, ischaemic changes in 15% and evidence following presenting variables as predictors of death: age >70 years (OR
of an acute myocardial infarction in 5% of patients with an ascending 1.70), abrupt onset of chest pain (OR 2.50) hypotension/shock/
aortic dissection. tamponade (OR 2.97), kidney failure (OR 4.77), pulse deficit (OR 2.03)
and abnormal ECG (OR 1.77); area under receiver operating curve 0.74.
Chest X-ray This analysis provides a useful and simple bedside risk prediction tool that
A routine chest X-ray is abnormal in 60–90% of cases with suspected could be used by physicians for determining the prognosis of patients
aortic dissection. However, 12% of patients have a completely normal with acute type A AAS.
chest X-ray.
1
Because of the limited sensitivity of this method, additional
imaging studies are required in all patients. Type B Dissection
Acute aortic dissection affecting the descending aorta is less lethal than
Imaging Studies type A dissection. Patients with uncomplicated type B dissection have a
During the IRAD period a shift was shown from an invasive (aortography) 30-day mortality of 10.5%.
15
However, patients who develop ischaemic
to a non-invasive diagnostic strategy for evaluating suspected thoracic complications such as renal failure, visceral ischaemia or contained rupture
aortic dissections. Most patients require multiple imaging studies to often require urgent aortic repair, which carries a mortality of 20% by day
diagnose and characterise aortic dissection. In IRAD,
10
the initial study was two and 25% by day 30. Similar to type A dissection, advanced age,
computed tomography (CT) in 61%, echocardiography in 33%, rupture, shock and malperfusion are important independent predictors of
aortography in 4% and magnetic resonance imaging (MRI) in only 2%. The early mortality. A risk prediction model with control for age and gender
mean number of studies performed per patient was 1.8. In type A AAS, showed hypotension/shock (OR 23.8), absence of chest/back pain on
transoesophageal echocardiography was the most commonly used presentation (OR 3.5) and branch vessel involvement (OR 2.9) – collectively
technique (79%), mainly in US sites. Imaging techniques revealed aortic named ‘the deadly triad’ – to be independent predictors of in-hospital
regurgitation in 62%, pericardial effusion in 46% and coronary artery death.
15
A subanalysis in elderly patients
16
(>70 years) showed that
involvement in 14%. A proximal intimal tear was identified in the aortic hypotension/shock was more common and malperfusion of a visceral
root in 39% of patients, in the ascending aorta in 55% and in the organ less frequent among the elderly cohort compared with the younger
aortic arch in 4%. For the diagnosis of acute aortic dissection, all four patients (16 versus 10%; p=0.07). A classification tree identified that
diagnostic tests (CT, transoesophageal echocardiography, MRI and elderly patients with hypotension/shock had the highest risk of death
aortography) demonstrate a high diagnostic sensitivity. However, the (56%). In the absence of this, any branch vessel involvement was
false-negative rate is still considerable, such that the diagnosis cannot be associated with the highest mortality rate (29%), followed by the presence
excluded confidently on the basis of a single test. Another imaging test is of peri-aortic haematoma (11%). In contrast, elderly patients without any
strongly recommended when the diagnosis is highly suspected clinically.
10
of these three risk factors had an extremely low mortality rate (1.3%).
IRAD contributed new imaging information that aids diagnostic accuracy. Variants
Maximum aortic diameters in acute type A dissection were <55mm in
59% of cases and <50mm in 40% of cases.
11
Independent predictors of Intramural Haematoma
dissection at diameters <55mm were history of hypertension and age. Although the clinical manifestations of intramural haematoma are similar
Marfan’s syndrome patients were more likely to dissect at larger diameters to those of acute aortic dissection, the former tends to be more of a
(odds ratio [OR] 14.3). In-hospital mortality was not related to aortic size. segmental process; therefore, radiation of pain, pulse deficits and aortic
valve insufficiency are less common.
17
The natural history of acute IMH
Peri-aortic haematoma was present in 23% of cases (26% in type A and continues to be debated. In patients with symptoms consistent with
19% in type B) and implied significantly greater mortality (33 versus acute aortic dissection, acute IMH accounts for 5–20% of cases; in IRAD
20%; p<0.001).
12
A multivariate model demonstrated peri-aortic it accounted for 5.7% of AAS. This cohort tended to be older (69 versus
haematomas to be an independent predictor of mortality in patients with 62 years of age; p<0.001) and more likely to have distal aortic
aortic dissections (OR 1.71). involvement (60 versus 35%; p<0.0001). Overall mortality was similar to
that of classic dissection (21 versus 24%). The analysis demonstrated an
Finally, a recent study showed that transoesophageal echocardiography association between increasing hospital mortality and the proximity of
provides prognostic information in type A AAS.
13
Independent predictors IMH to the aortic valve, regardless of medical or surgical treatment.
of mortality were cardiac tamponade (OR 2.7), whereas dissection flap
confined to the ascending aorta (OR 0.2) and false lumen thrombosis Treatment
(OR 0.15) were protective. When only the surgically treated patients One of the important contributions of IRAD is to show the current
were considered, peri-aortic haematoma was an independent predictor management and outcome of AAS. Type A acute aortic dissection was
of mortality. treated surgically in 81.7% of cases.
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The reasons for medical treatment
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