Written by Gill Douglas, Shameer Rafee, Department of Neurology, St Vincent’s University Hospital
Management of Cardioembolic stroke
Stroke remains a leading cause of death and disability globally. While 10-15% of strokes are haemorrhagic in nature, ischaemic stroke, due to thrombosis, embolism or systemic hypoperfusion, accounts for over 80% of cases. Acute ischaemic strokes are time sensitive due to the reperfusion treatments like thrombolysis and thrombectomy. Accurately identifying stroke mechanism is important as it allows for evidence based recommendations for therapy and developing future preventative strategies. The TOAST classification is commonly used in stroke research and subdivides ischaemic stroke into 5 categories – a) large artery atherosclerosis, b) cardioembolism, c) small vessel occlusion, d) stroke of other determined aetiology and, e) stroke of undetermined aetiology (cryptogenic). Approximately 20% of ischaemic strokes are cardioembolic.
Cardioembolic strokes are associated with a worse prognosis and are often more disabling. Emboli originating from cardiac chambers are capable of occluding larger, more proximal cerebral arteries. Cardioembolic strokes have been associated with both short and long term recurrence, with incidence expected to rise worldwide due to aging populations and increasing life expectancy. They classically present with stroke of worse severity (higher NIHSS scores). Ischaemic strokes in different vascular territories are suggestive of a cardiac source, as well as stroke following valsalva manoeuvre, the presence of decreased levels of consciousness and cortical signs such as Wernicke’s aphasia, global aphasia without hemiparesis and visual field defects.
Many cardiac disorders are recognised as potential sources of embolism- atrial fibrillation (AF) remains the most significant. It’s the most common sustained arrythmia, with its prevalence increasing in the older person. It is recognised as precipitating 50% of cases of cardioembolic strokethis may be preventable with early identification and treatment. The CHADS2VASC score can be used to predict the risk of ischaemic stroke in patients with AF. Treatment with anticoagulation can significantly reduce morbidity and mortality and can prevent around 70% of strokes in those with AF.
While atrial fibrillation is the leading cause of cardioembolic stroke, it is important to recognise other potential cardiac sources of embolism such as chamber dysfunction, valvular disease or a mechanical prosthetic valve, and infectious aetiologies like endocarditis. Myocardial infarction (MI) can lead to left ventricular dysfunction and focal areas of dyskinesia. This can result in stasis and formation of mural thrombi, leaving these patients at high risk of embolic stroke. Acute MI is considered aetiological if stroke occurs within one month of the MI.
Valvular disease, including mechanical valves, also carry a high risk of embolic events and while the incidence of rheumatic mitral valve disease has decreased in recent times, it still carries a significant burden of disease in endemic and developing regions. Embolism should also be a consideration in infective endocarditis. While infective endocarditis is itself a relatively uncommon, it’s important to note that 20% of cases of endocarditis with intracardiac vegetations are complicated by embolic stroke, with the mitral valve the most frequent source of emboli. Prompt antibiotic therapy typically reduces this potential.
While there is no defined clinical criteria for the diagnosis of cardioembolic stroke, the clinical approach should include a detailed history, clinical exam, neuroimaging, ECG and, importantly, echocardiography. Inpatient telemetry can be used to diagnose paroxysmal atrial fibrillation. Prolonged monitoring with outpatient holter monitors are recommended if suspicion remains for a cardioembolic source. Longer automated cardiac monitoring has been shown to be useful in detecting paroxysmal AF- even a 30-day recording can improve AF detection rates 5-fold (EMBRACE trial).
In 2014, the term “embolic stroke of undetermined source” (ESUS) was introduced as a subset of cryptogenic strokes for patients with non-lacunar strokes and no identifiable mechanism. The most prevalent source of emboli is thought to remain cardiac. Although initially AF was considered a major factor, it is now thought to be less important for a number of reasons: studies have shown that embolic events are not temporally close to AF captured on monitoring, ESUS patients are phenotypically different from AF related strokes and, incidence of AF detection in ESUS patients is similar to non- ESUS strokes. This is an area that warrants targeted research.
Transthoracic echocardiography (TTE) is often performed as a matter of routine. Transoesophageal echocardiography (TOE) is most reliable in detecting ventricular dysfunction and dysmotility, as well as interatrial shunts, atrial septal defects, and thrombosis at the atrial appendage. TOE is also useful in detecting patent foramen ovale (PFO). The association between PFO as a cause of cardioembolic stroke can be tenuous. PFO is present in about 25% of the population, and may serve as a channel for the shunting of a thrombus from the venous to the arterial circulation, a phenomenon known as paradoxical embolism. It is believed that only a small minority of strokes can be linked causally with PFO e.g. stroke after valsalva in the presence of a PFO or presence of deep vein/ pulmonary thromboses. A history of obstructive sleep apnoea can also be suggestive as it increases right to left shunting. The extent of shunting can be assessed intra-procedurally during TTE or TOE with agitated saline. The presence and size of the shunt can help with deciding which patients should undergo closure. The Gore-REDUCE trial showed that, with careful patient selection, PFO closure was associated with lower risk of recurrence.
Cardiac embolism should be recognised as an important source of ischaemic stroke. It carries a high mortality and risk of complications as well as a high incidence of stroke recurrence. Inpatient assessment may be insufficient to diagnosis of AF; longer term monitoring is often warranted, particularly in cases of cryptogenic strokes. Anticoagulation is a safe and effective method or reducing stroke recurrence. Targeting cardioembolic strokes through improved detection and early treatment can reduce the global burden of stroke.
References available on request
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