Sir Humphry Davy Department of Anaesthesia, Bristol Royal Infirmary, Bristol, UK
* Corresponding author. E-mail: slewis{at}talk21.com
Accepted for publication November 22, 2004.
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Abstract |
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Keywords: arteries, aortic dissection ; monitoring, echocardiography ; pregnancy
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Introduction |
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Case report |
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The patient re-presented urgently a week later with sudden onset of numbness and weakness of her left arm and leg. This had been immediately preceded by the development of right-sided neck and jaw pain during sexual intercourse. On examination she was pale and apyrexial with heart rate 80 min1, arterial pressure 100/60 mm Hg and tenderness over her right carotid artery. Auscultation demonstrated an ejection systolic murmur, an early diastolic murmur and a right carotid bruit. Neurological examination revealed decreased power (3/5) and sensation of the left arm and leg. Cranial nerve examination was normal and there was no meningism. A consultant neurologist diagnosed a cerebrovascular accident, probably of thromboembolic aetiology. CT scan of the brain and carotid Doppler studies were normal. A transthoracic echocardiogram was scheduled for the following morning. In view of the diagnosis and the possible requirement for anticoagulant therapy a decision was made to expedite delivery by Caesarean section. This was performed under combined spinalepidural anaesthesia. The operation was uneventful, with the delivery of a healthy infant. Ten hours after Caesarean section the patient developed acute pulmonary oedema, which responded to diuretic therapy. At the same time it was noted that she had diminished pulses in her right arm with differential right and left non-invasive arterial pressures of 70/40 mm Hg and 100/50 mm Hg respectively. A transthoracic echo showed an enlarged aortic root, aortic regurgitation, a proximal dissection flap and a volume-overloaded left ventricle (Fig. 1). A left radial arterial line was inserted and an intravenous infusion of labetalol was commenced to maintain systolic blood pressure <100 mm Hg. The patient was transferred to the regional cardiothoracic centre.
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Discussion |
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Our patient's symptoms and examination findings were suggestive of aortic dissection but the diagnosis was not made until 3 weeks after presentation. Despite this our patient survived and made a full recovery. A number of studies have shown this to be unlikely. Mészáros and colleagues16 showed a pre-hospital mortality of 21%. The mortality rate for untreated proximal aortic dissections increases by 1 to 3% per hour after presentation and is approximately 25% during the first 24 h, 70% at 1 week and 80% at 2 weeks.2 In our patient the dissection propagated slowly, with extension into the brachiocephalic trunk and hemiparesis occurring 3 weeks after her initial presentation. Crucially, she was not given excessive vasopressor or fluids during her Caesarean section. This could have resulted in rapid progression of the dissection, acute valvular disruption and intra-operative cardiac decompensation, with potentially disastrous consequences for mother and fetus.
Although the clinical manifestations of acute aortic dissection are well described, the diagnosis is often overlooked. A study over a 27 year period showed that misdiagnosis occurred in 85% of patients presenting with acute dissection.16 This is supported by a number of case reports in which the diagnosis was initially missed in the peripartum period.58 The most common presenting feature is sudden onset of severe back or chest pain (up to 96% of cases) that is characteristically stabbing, tearing or ripping. The pain is frequently migratory, generally following the path of propagation of the dissection.17 In our case the initial back pain moved to the scapula.
Signs on physical examination may reflect the location of the dissection and its extent. Organ ischaemia results from obstruction of branch arteries originating from the aorta. Vessel occlusion can be caused by extension of the dissection into the artery wall or direct compression by the expanding false lumen. Our patient's left hemiparesis was caused by propagation of the dissection into the brachiocephalic artery, probably brought about by the cardiovascular response that accompanies sexual intercourse.18 Importantly, our patient was also noted to have a diastolic murmur and aortic regurgitation. Acute aortic valve incompetence accompanies 1850% of proximal aortic dissections and is the second most common cause of death (after aortic rupture) in dissections. Although echocardiography demonstrated good ventricular function in our case, regional wall motion abnormalities occur in 1015% of patients with proximal dissection and are primarily caused by low coronary perfusion. The right coronary artery is involved more commonly than the left, and occasionally dissection and myocardial infarction can occur together.19 Thrombolysis in this setting can be fatal.
Although suggested by the clinical findings, the diagnosis of aortic dissection must be confirmed by investigation. Diagnostic modalities include chest radiography, echocardiography, contrast-enhanced computed tomography, aortography and magnetic resonance imaging. Although chest radiography lacks specificity it can be useful for the initial prediction of dissection when used in combination with the history and examination findings. The classic radiographic feature of mediastinal widening occurs in up to 50% of cases.20 Concern about fetal radiation exposure meant that our patient did not undergo chest radiography at first presentation. Transthoracic echocardiography diagnosed the dissection in our patient. This investigation is useful in the initial screening of patients with suspected aortic dissection. The sensitivity and specificity can be up to 75% and 90%, respectively. Transoesophageal echocardiography overcomes many of the limitations associated with transthoracic echocardiography and has sensitivity and specificity data as high as 99% and 98%, respectively.1 CT and aortography involves the risk of i.v. contrast administration and radiation.
The main predisposing factor for aortic dissection is degeneration of the collagen and elastin in the intima media. Systemic hypertension is the main risk factor. Other well-established risk factors include hereditary connective tissue disease (e.g. Marfan's syndrome and EhlersDanlos syndrome), coarctation of the aorta, bicuspid aortic valve, aortitis and arch hypoplasia. On the basis that 50% of aortic dissections in women under 40 years of age occur in pregnancy or the puerperium, it is frequently stated that pregnancy is an independent risk factor for aortic dissection.21 22 However, a recent review by Oskoui and Lindsay23 has questioned the causal relationship between pregnancy and aortic dissection. Hypertension and Marfan's syndrome are the most commonly occurring risk factors in cases of aortic dissection during pregnancy. The most common site of pregnancy-associated dissection is the proximal aorta, and aortic rupture usually occurs during the third trimester or first stage of labour.1
In our patient neither clinical nor histological examination showed any evidence of hereditary connective tissue disease. Syphilis serology was normal and there was no documented evidence of hypertension. The only abnormal finding was a floppy aortic valve with idiopathic myxoid degeneration. Floppy aortic valves occur less commonly than floppy mitral valves, but both can be associated with myxoid degeneration. This degeneration is defined as significant disruption of the valve fibrosa and its replacement by acid mucopolysaccharides together with cystic change. The underlying cause can be rheumatic, endocarditic or idiopathic, or connective tissue disorders. Idiopathic myxomatous degeneration is rare, with patients mainly in their fifties and sixties, although younger cases have been reported. There is a male preponderance. Most patients present with severe aortic regurgitation, with the diagnosis made after valve replacement.24 25 This is the first reported case of pregnancy and acute aortic dissection occurring in association with this valvular pathology in a non-Marfinoid patient.
In conclusion, this case highlights some important learning points. Despite a clinical presentation suggestive of aortic dissection, our patient was initially diagnosed with a thromboembolic stroke. This may have been the result of a lack of awareness of peripartum aortic dissection or the unavailability of out-of-hours echocardiography. This culminated in a Caesarean section being performed in the presence of an acute type A dissection. As the consequences of missing an acute aortic dissection can be fatal, it is imperative that any patient presenting with a suggestive clinical history is thoroughly investigated. Echocardiography is an effective diagnostic tool with high specificity and sensitivity that avoids the added risk of fetal radiation exposure and is the investigation of choice in pregnancy. Furthermore, the American College of Cardiology and American Heart Association state that any patient under 45 years of age who is thought to have suffered a cerebrovascular event should be routinely investigated with echocardiography to exclude a cardiac cause.26 Once aortic dissection is diagnosed the definitive management is dependent on the gestation. This report is a reminder to anaesthetists that, although rare, acute aortic dissection can present during pregnancy.
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References |
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