Q J Med 1999; 92: 619-621
© 1999 Association of Physicians
Editorial |
Echocardiography in stroke and thromboembolism: transoesophageal imaging for all?
Department of Cardiology, John Radcliffe Hospital, Oxford
Transthoracic echocardiography combines real-time two-dimensional imaging of the heart and cardiac valves with information about velocity and direction of blood flow obtained by Doppler and colour flow mapping. It is non-invasive, and a complete examination can be performed in most patients in less than 25 min. Transoesophageal echocardiography is available in regional cardiac centres and some district general hospitals. Under sedation, the ultrasound probe is passed into the oesophagus where its position next to the heart produces superior resolution, particularly of posterior cardiac structures such as the left atrium and interatrial septum.
Echocardiography is the investigation of choice when a cardiac source of embolism is suspected. However, debate persists about which patients with a stroke or thromboembolism require imaging. This is in part a result of the increasing pressure on already overloaded echo services and a need for prioritization, but it also reflects considerable variation in physicians' opinions about the potential value of the results of an echocardiogram. This diversity in practice is even more widespread in the use of transoesophageal echocardiography.
A cardiac source of thromboembolism must be excluded in patients presenting with a definite embolic occlusion of a peripheral artery, or multiple thromboembolic episodes in diverse anatomical regions. These patients should undergo transthoracic echocardiography initially and transoesophageal echo if image quality is unsatisfactory because of obesity, lung disease or chest deformity. In patients with an ischaemic stroke or patients with a possible embolic event, we advocate that the use of echocardiography should be guided by the clinical presentation, cardiac examination and the ECG.
Transthoracic echocardiography is useful to confirm the diagnosis when valvular heart disease is suspected, although many valve abnormalities, including aortic stenosis, mitral annular calcification and mitral valve prolapse, are not indications for anticoagulation if the patient is in sinus rhythm.1 Patients with mitral stenosis are at particular risk of thromboembolism, even in sinus rhythm, and any proven thromboembolic event justifies lifelong anticoagulation. Transthoracic echo has limited sensitivity for left atrial thrombus, and transoesophageal echocardiography may be necessary if embolic events occur despite therapeutic anticoagulation. In some patients with mitral stenosis, echocardiography may demonstrate spontaneous echo contrast which is the presence of dynamic smoke-like echoes produced by the interaction of erythrocytes and plasma proteins under conditions of stasis.2 These patients are at particular risk of recurrent thromboembolism, as left atrial spontaneous echo contrast is an independent predictor of left atrial thrombus and/or cardiac thromboembolic events.3–5
Transthoracic echo is commonly performed as part of the routine follow-up of prosthetic valves. However, after an embolic event, transoesophageal echo is recommended if prosthetic valve dysfunction is suspected,6 particularly for mechanical mitral valve prostheses, as attenuation artefact is reduced.7 Transoesophageal echo may reveal atrial or valvar thrombus, or evidence of endocarditis, which may not be detected by transthoracic imaging.
For patients who have already sustained a definite thromboembolic event during atrial fibrillation, anticoagulation should be lifelong unless sinus rhythm can be consistently re-established.8 Transthoracic echocardiography is valuable, as it will document underlying structural heart disease which may influence the decision about attempting cardioversion back to sinus rhythm. Whether transoesophageal echocardiography has an additional utility in the management of atrial fibrillation following an embolic event is untested. The SPAF9 and ELAT10 investigators have demonstrated that increased left atrial appendage size and spontaneous echo contrast, or left atrial thrombus detected by transoesophageal echo, are associated with a particularly high embolic risk in a mixed patient population with atrial fibrillation (one third had previously had an embolic event), but it seems unlikely that transoesophageal echo can make an additional contribution to management in those patients who already justify anticoagulation on existing clinical and echo criteria.
Both transoesophageal and transthoracic echo have limited sensitivity for detecting mural ventricular thrombus, as imaging the left ventricular apex can be particularly difficult.11 Differentiation between thrombus and myocardium may also be problematic, although this may be improved using tissue harmonic imaging and/or contrast agents. Following a recent myocardial infarct, an embolic event or detection of mural thrombus requires anticoagulation for at least 6 months.12 Anticoagulation is also recommended for patients with an embolic event and chronic heart failure when mural left ventricular thrombus is detected, particularly if it is protuberant and/or mobile.13
Echocardiography is unlikely to influence management in elderly patients with a single stroke when the electrocardiogram and clinical examination are normal. These patients should receive aspirin14 and an echo should be considered if further events occur. For young patients with ischaemic stroke and a low likelihood of atheromatous arterial disease, transthoracic echo is usually performed even in the absence of ECG or clinical abnormality, as occasionally it may demonstrate an unsuspected abnormality such as atrial myxoma. More widespread use of the improved imaging quality of transoesophageal echo has been particularly advocated in this patient group.
The inter-atrial septum is best imaged by transoesophageal echocardiography, and patency of the foramen ovale can be demonstrated in up to 30% of patients using an intravenous injection of agitated saline during a Valsalva manoeuvre. In most people this defect is asymptomatic, but if the defect in the atrial septum is large, or if right heart pressures are elevated, paradoxical embolism of venous thrombus can occur. Observational series reveal an increased incidence of patent foramen ovale in patients with otherwise unexplained stroke.15 Similarly, atrial septum aneurysm (a redundant bulge in the area of fossa ovale, with movement >10 mm) is also best identified by transoesophageal echo. A recent retrospective multicentre study found a high incidence of systemic thromboembolism in patients with atrial septal aneurysm, especially in association with a patent foramen ovale.16 Whether detection of these anomalies by transoesophageal echocardiography alters the management of these patients is unclear, as the relationship between the atrial septal abnormalities and the thromboembolic event is usually speculative. Currently, anticoagulation is the usual management following a otherwise unexplained embolic event, but some centres recommend percutaneous or surgical closure of the defect.
Transthoracic imaging of the aorta is limited to the proximal aortic root and the arch in most patients. Using transoesophageal imaging, most of the ascending and all of the descending thoracic aorta can be visualized, and image quality is improved. Several studies have suggested an association between ischaemic stroke and large, mobile or pedunculated aortic atheroma detected by transoesophageal echocardiography.17,18 Thus, transoesophageal imaging in patients with clinical evidence of peripheral vascular disease may contribute to patient management in suspected cases of cholesterol embolisation,19 or in assessing thromboembolic risk prior to cardiac intervention or surgery.20
For the majority of patients with thromboembolism, routine transoesophageal echocardiography is not indicated, since clinical examination, electrocardiography and transthoracic echocardiography provide sufficient information to determine optimal management. Transoesophageal echocardiography is indicated when embolic events occur in anticoagulated patients with native or prosthetic valvular heart disease, particularly if endocarditis is suspected, or when transthoracic images are inconclusive. In patients with embolic events but a clinically normal heart and a normal transthoracic echocardiogram, the use of transoesophageal echocardiography remains controversial. We recommend using transoesophageal imaging only when alternative pathologies such as thrombophilia or carotid stenoses have been excluded, or when embolic events despite adequate anticoagulation. Minor cardiac structural abnormalities demonstrated in these circumstances are more likely to be clinically relevant.
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