Page 84 - Medicine and Surgery

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80 Chapter 2: Cardiovascular system

beyond the brachiocephalic trunk (Type I) or not The diagnosis is best confirmed with contrast CT or
(Type II). Most thoracic aortic dissections are Type MR angiography. Transthoracic or transoesphageal
A, and these have the highest mortality. echocardiography can give valuable information
Less commonly the dissection is confined to the de- about the aorta and aortic valve, and may also be used

scending aorta (Type B or Type III). The most com- to make the diagnosis, particularly in haemodynami-
mon site for these to start is at the point of the ductus cally unstable patients.
arteriosus, i.e. opposite to the left subclavian artery.
Type I and Type III aortic dissections threaten the Management
spinal arteries as well as the arteries supplying the ab- Dissection of the aorta is a medical (and surgical) emer-
dominal viscera, e.g. mesenteric and coeliac axes and gency. In both types, urgent but careful resuscitation
the renal arteries. They may extend as far down as the is required, and importantly hypertension should be
iliac arteries. treated, aiming at a maximal systolic blood pressure of
100–120 mmHg to maintain renal and cerebral perfu-
sion without exacerbating the dissection. Intravenous
Clinical features
Dissection classically presents with excruciating sudden β-blockers, glyceryl trinitrate and hydralazine may all
onset central chest pain, which may be mistaken for an be needed. Adequate analgesia is required.
acute myocardial infarction. The pain tends to be tear- Type A dissections require emergency surgery with
ing, most severe at the onset and radiates through to cardiopulmonary bypass. The ascending aorta is re-
the back. Most patients are hypertensive at presenta- placed using a Dacron graft and the aortic valve re-
tion. Hypotension suggests significant blood loss, acute paired or replaced as necessary. The aortic arch and its
haemopericardium or disruption of the aortic valve. A branches may also need repair or replacement.
difference in the blood pressure between the arms sug- Type B dissections should be treated conservatively
gests impaired flow to one of the subclavian arteries. with antihypertensive therapy. Surgery or endovascu-
There may be reduction in the pulses distal to the lesion. lar stenting may be indicated if the dissection pro-
Auscultation may reveal the early diastolic murmur of gresses, or if rupture occurs, but the risk of paraplegia
aortic regurgitation and occasionally a pericardial rub. due to spinal artery ischaemia during surgery is high.
Haemorrhage from descending aortic aneurysms may Asymptomatic thoracic aortic aneurysms found by
cause dullness and absent breath sounds at the left lung screening, e.g. in Marfan’s syndrome, are closely moni-
base due to a left pleural effusion (haemothorax). toredwith echocardiograms and CT scans for expansion
and may be treated electively by surgical repair.
Complications
Prognosis
Dissection or formation of thrombus on the damaged
Untreated thoracic aortic dissection results in 50% mor-
endothelium may obstruct any branch of the aorta,
tality within 48 hours. In all patients long-term strict
and thus stroke, paraplegia (due to spinal artery in-
blood pressure control is needed.
volvement), renal failure and mesenteric ischaemia may
result.
Acute peripheral arterial occlusion
Investigations
ECG may be normal or show evidence of left ventric-
Definition
ular hypertrophy due to long-standing hypertension. Acute loss of the arterial supply to a limb.
Myocardial infarction may occasionally be due to dis-
section involving the coronary arteries. Incidence
Chest X-ray may show a widened mediastinum: di-
Commonest vascular emergency.
lated aorta, an enlarged heart due to pericardial ef-
fusion and calcification of the aortic intima pushed Age
further than normal within the aortic border. Increases with age.