Chapter 4 Cardiac Embolism
Cardiac embolism represents one of the most common mechanisms of ischemic stroke. It is most common in the elderly as a consequence of the high incidence of atrial fibrillation, but it is also one of the most frequent causes of stroke in the young. Yet several factors often make the diagnosis of cardiac embolism complicated: (1) cardiac embolism can produce infarctions in any vascular distribution; (2) some of the potential sources of cardiac embolism are prevalent in the general population; (3) cardioembolic sources often coexist with atherosclerotic vascular lesions in the cerebral vasculature. Furthermore, even when the diagnosis of a cardioembolic stroke is typically followed by the initiation of anticoagulation for secondary prevention, this intervention has only been scientifically validated for atrial fibrillation and mechanical valve prosthesis. With these caveats in mind, Table 4-1 lists the potential causes of cardiac embolism divided according to the strength of the evidence supporting the pathophysiological association.
TABLE 4-1 Cardiac sources of embolism.
Definite |
Atrial fibrillation (chronic and paroxysmal)* |
Mechanical valve prosthesis |
Rheumatic valve disease |
Infective endocarditis |
Nonbacterial thrombotic endocarditis |
Dilated cardiomyopathy with severely reduced left ventricular ejection fraction |
Acute transmural myocardial infarction (especially of the anterior wall) |
Mural thrombi |
Apical aneurysm |
Left atrial thrombus |
Atrial myxoma |
Probable |
Patent foramen ovale with atrial septal aneurysm |
Biological prosthetic valves (early after surgery) |
Possible |
Patent foramen ovale |
Spontaneous echo contrast |
Left atrial enlargement |
Degenerative mitral or aortic valve disease |
Valve strands |
Mitral annular calcification |
Valvular fibroelastoma |
Nondilatated cardiomyopathies |
Sick sinus syndrome |
Brain infarctions caused by cardiac embolism tend to share similar radiological characteristics regardless of the type of cardiac disease responsible for the embolism. These general characteristics are listed in Table 4-2 and illustrated in Figure 4-1. The pattern of acute multiple bilateral infarctions on diffusion-weighted imaging (DWI), especially when involving the anterior and posterior circulation territories, is strongly associated with cardiac embolism.1,2 Infarctions with embolic appearance and acute multiple brain infarctions on DWI2–4 should raise suspicion of a cardiac source but may also be produced by artery-to-artery embolism. In fact, it is essentially impossible solely on the basis of brain imaging to distinguish cardioembolic infarctions from infarctions due to aortic embolism. It is important to keep in mind that cardioembolic strokes can have atypical presentations, such as relatively small subcortical infarctions.5 Thus the presence of radiological features highly suggestive of cardiac embolism should prompt comprehensive cardiac assessment, but their absence does not exclude the possibility of a cardioembolic mechanism.
TABLE 4-2 Radiological characteristics of cardioembolic strokes.
Wedge-shaped infarctions based in the cortex |
Concurrent acute bilateral infarctions |
Concurrent acute infarctions in the anterior and posterior circulations |
Multiple cortical infarctions in various vascular distributions (even if infarctions are of different ages) |
Greater tendency to hemorrhagic transformation |
The advent of echocardiography, particularly transesophageal echocardiography (TEE), has provided a wealth of information on various cardiac abnormalities that may increase the risk of ischemic stroke. Transthoracic echocardiography (TTE) provides better visualization of the left ventricle and mitral valve, but it typically adds little to TEE in the evaluation of stroke patients. TEE offers better visualization of the left atrium, left atrial appendage, interatrial septum, aortic valve, and aortic arch. The superiority of TEE for the study of the cardiac structures more commonly associated with embolism makes it the preferred choice for the evaluation of cardiac embolism in combination with electrocardiography (to detect myocardial ischemia and arrhythmias) and Holter monitoring (to recognized paroxysmal arrhythmias not apparent on the electrocardiogram [ECG]).6 TTE is justified when myocardial ischemia, areas of ventricular hypokinesis/akinesis, or dilatated cardiomyopathy are suspected by the history or the initial ECG. Although we strongly advocate the use of TEE for the study of cardiac sources of embolism after a transient ischemic attack (TIA) or stroke, in this chapter we present several examples of diagnostic TTE, because it was the institutional practice at Jackson Memorial Hospital’University of Miami to perform a transthoracic study first.
ATRIAL FIBRILLATION
A 72-year-old man with history of hypertension, dyslipidemia, and coronary artery disease presented with sudden left-sided weakness. Examination revealed an irregularly irregular pulse, left visual field deficit, left hemiparesis, and left hemihypoesthesia with neglect. ECG confirmed the suspicion of atrial fibrillation, and brain imaging showed a right middle cerebral artery infarction (Figure 4-2). TEE was remarkable for left atrial enlargement but did not show any atrial thrombus or dense spontaneous echo contrast. The patient was initially treated with aspirin because of concerns about possible hemorrhagic transformation of the cerebral infarction. Beta-blockers were successful in maintaining the ventricular rate controlled. Warfarin was started 3 days after the stroke without complications. The patient evolved favorably and remained free of stroke recurrence 3 years later.
DILATED CARDIOMYOPATHY
MYOCARDIAL INFARCTION
INFECTIVE ENDOCARDITIS
A 46-year-old man with recent community-acquired pneumonia and history of diabetes presented with worsening dyspnea. Examination revealed that the patient was confused and febrile, and careful cardiac auscultation denoted a new systolic murmur with characteristics suggestive of mitral regurgitation. Brain imaging showed scattered, small, acute ischemic infarctions in cortical locations. Echocardiography disclosed a vegetation attached to the mitral valve (Figure 4-10, F and G), and blood cultures grew Staphylococcus aureus. The patient was successfully treated with vancomycin and rifampin first and later switched to nafcillin with rifampin when susceptibilities proved that the organism was not methicillin-resistant. The patient did not have recurrent episodes of systemic or cerebral embolism, and repeat echocardiography 4 weeks later confirmed resolution of the vegetation.
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