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Echocardiographic Evaluation of Patients With a Systemic Embolic Event
Background
Cardiac Embolism
The heart and the aorta are a potential source of embolism to the systemic circulation. Because the brain is the most frequent target, investigation of cardiac embolic sources is especially aggressive after a cerebral embolic event. Most data on outcome and prevention of recurrences come from the stroke literature. The same embolic sources and principles for investigating them also apply to peripheral embolic events, with the addition of the descending aorta.
Cardioembolic and Cryptogenic Stroke
Stroke is the third leading cause of death in the United States, after cardiac diseases and cancer (pre-COVID-19 era). Approximately 7.0 million Americans 20 years of age or older have had a stroke. Each year, approximately 795,000 people experience a stroke; it occurs as a first event in 75% of cases. The estimated prevalence of silent cerebral infarction is 6% to 28%. That of transient ischemic attacks (TIAs), which are temporary episodes of neurologic dysfunction that have risk factors similar to those of stroke and often precede it, is 2.3%, which probably is an underestimation. Most strokes (87%) have an ischemic origin, involving blockage of the blood supply to the affected territory. The remainder are accounted for by intracerebral (10%) or subarachnoid (3%) hemorrhage.
Ischemic stroke has a cardioembolic source in approximately 20% of cases. Cases that have no apparent cause (i.e., cryptogenic strokes) often have a clinical presentation and neurologic imaging findings that suggest an embolic event and are also known as embolic strokes of undetermined source , or ESUS. Identification of new cardioembolic sources has led to the involvement of cardiologists, especially echocardiographers, in stroke diagnosis and prevention. Their efforts have reduced the proportion of strokes labeled as cryptogenic and changed treatment and secondary prevention strategies.
Basic Principles and Echocardiographic Approach
Transthoracic echocardiography (TTE) and especially transesophageal echocardiography (TEE) are widely used to investigate cardioembolic sources in patients with stroke or TIA. TTE is indicated for screening because it can detect some embolic sources (i.e., left ventricular [LV] apical thrombus in particular but also large valvular vegetations and intracardiac masses) and aid the decision whether to proceed to the more invasive TEE. TEE is preferred when TTE cannot clearly visualize the cardiac or aortic structures and in all instances in which high-resolution imaging of structures is needed.
TEE is superior to TTE for visualization of the atrial septum and cardiac valves. It allows a more accurate diagnosis of patent foramen ovale (PFO) or infective endocarditis (IE). TEE also provides accurate visualization of structures such as the left atrial appendage and the proximal thoracic aorta, which are important potential embolic sources. Table 38.1 shows a clinically useful classification of embolic sources and the most appropriate echocardiographic technique for each of them.
TABLE 38.1
Echocardiographic Evaluation of Cardioaortic Embolic Sources.
| Embolic Source | Possibly Associated Conditions | Age Group | Best Diagnostic Study |
|---|---|---|---|
| LV thrombus | Prior myocardial infarction, dilated cardiomyopathy | Any | TTE |
| LA thrombus or spontaneous echocardiographic contrast | Atrial fibrillation, mitral valve disease | Any | TEE |
| Valvular vegetations | Infective endocarditis (fever, murmur, systemic symptoms), lupus erythematosus | Any | TEE/TTE (less sensitive) |
| Valvular disease | Varies | Any | TTE for initial evaluation TEE for further assessment, especially for prosthetic valves |
| Cardiac tumors (myxoma, fibroelastoma, secondary malignancies) | None or nonspecific systemic symptoms | Any | TTE for screening TEE if suspicion is high despite nondiagnostic TTE |
| Patent foramen ovale | None | Any; more frequent in patients < 55 y | TTE with contrast for screening TEE if more detail is needed |
| Atrial septal aneurysm | None | Any; more frequent in patients < 55 y | TTE for screening TEE for better imaging |
| Valve strands | None | Any | TEE |
| Aortic plaques | Diffuse atherosclerosis | >60 y | TEE |
Technical Aspects: TEE Versus TTE in Cryptogenic Cerebral Ischemia
TEE has greater sensitivity than TTE for detection of cardioembolic sources. Among 231 patients with cryptogenic stroke or TIA, a potential source of embolism was observed in 55% by TEE but in only 16% by TTE. A major embolic source, with an absolute indication for anticoagulation, was found in 20% of patients by TEE and in only 4% by TTE. The superior diagnostic yield of TEE was confirmed in 702 consecutive patients with ischemic stroke or TIA. TEE produced relevant findings in 52.6% of the patients; PFO (21.7%) and previously undiagnosed valvular disease (15.8%) were the most common findings.
Several studies have shown that TEE findings directly affect the therapeutic choices for approximately 20% of cryptogenic stroke patients ( Table 38.2 ). , , Criteria for appropriate use of echocardiography in patients with a recent embolic event were issued in 2011 by the American College of Cardiology Foundation (from the consensus of the major imaging and medical societies in the United States). More recently, guidelines on appropriate use were issued by the American Society of Echocardiography. These guidelines, which have more emphasis on the inappropriateness of imaging in cases of low pretest probability or when the results are unlikely to affect management, are summarized in Table 38.3 .
TABLE 38.2
Therapeutic Changes Resulting From the Use of TEE to Investigate Cardiac Embolic Sources in Patients With Acute Ischemic Stroke or Transient Ischemic Attack.
| Study | Patient Characteristics | Most Common Findings | Therapeutic Changes | Type of Change | |||
|---|---|---|---|---|---|---|---|
| N | M/F | Age | N | % | |||
| de Bruijn et al. (2006) | 231 | N/A | 39 pts ≤ 45 y; 192 pts > 45 y | Aortic plaques 30%; LAA thrombus 16% | 46 | 20 | Initiation of OAC |
| Harloff et al. (2006) | 212 | 125/87 | 58.2 ± 13.9 y | PFO 20.3%; aortic plaque 17.6% | 65 | 22.6 | Initiation of OAC |
| Khariton et al. (2014) | 1458 | 792/726 | 60.5 y (range, 17–93 y) | PFO 11.9%; IE 1.4%; aortic plaque 1%; tumor or mass 0.5% |
243 | 16.7 | Initiation of OAC, PFO closure, antibiotics for IE, cardiac surgery |
IE , Infective endocarditis; LAA, left atrial appendage; N/A , information not available; OAC , oral anticoagulation; PFO , patent foramen ovale; pts , patients.
Table 38.3
Appropriate Use Criteria for Echocardiography in Evaluation of Cardiac Sources of Emboli.
From Saric M, Armour AC, Arnaout S, et al. Guidelines for the use of echocardiography in the evaluation of a cardiac source of embolism. J Am Soc Echocardiogr. 2016;29:1–42.
| Appropriate Use: TTE |
| Symptoms or conditions potentially related to suspected cardiac etiology, including but not limited to chest pain, shortness of breath, palpitations, TIA, stroke, or peripheral embolic event |
| Suspected cardiac mass |
| Suspected cardiovascular source of embolus |
| Initial evaluation of suspected IE with positive blood culture results or new murmur |
| Reevaluation of IE at high risk for progression or complication or with a change in clinical status or cardiac examination results |
| Known acute PE to guide therapy (e.g., thrombectomy and thrombolytic therapy) |
| Reevaluation of known PE after thrombolysis or thrombectomy for assessment of change in RV function and/or pulmonary artery pressure |
| Appropriate Use: TEE |
| As initial or supplemental test for evaluation for cardiovascular source of embolus with no identified noncardiac source |
| As initial or supplemental test to diagnose IE with a moderate or high pretest probability (e.g., staph bacteremia, fungemia, prosthetic heart valve, or intracardiac device) |
| As initial test for evaluation to facilitate clinical decision making with regard to anticoagulation, cardioversion, and/or radiofrequency ablation |
| Uncertain Indication for Use: TEE |
| Evaluation for cardiovascular source of embolus with a previously identified noncardiac source |
| Inappropriate Use: TTE |
| Transient fever without evidence of bacteremia or new murmur |
| Transient bacteremia with a pathogen not typically associated with IE and/or a documented nonendovascular source of infection |
| Routine surveillance of uncomplicated IE when no change in management is contemplated |
| Suspected PE to establish diagnosis |
| Routine surveillance of prior PE with normal RV function and pulmonary artery systolic pressure |
| Inappropriate Use: TEE |
| Evaluation for cardiovascular source of embolus with a known cardiac source in which TEE would not change management |
| Routine use of TEE when diagnostic TTE is reasonably anticipated to resolve all diagnostic and management concerns |
| Surveillance of prior transesophageal echocardiographic finding for interval change (e.g., resolution of thrombus after anticoagulation, resolution of vegetation after antibiotic therapy) when no change in therapy is anticipated |
| To diagnose IE with low pretest probability (e.g., transient fever, known alternative source of infection, negative blood culture results, or atypical pathogen for endocarditis) |
| Evaluation when a decision has been made to anticoagulate and not to perform cardioversion |
IE, Infective endocarditis; PE, pulmonary embolism; TIA, transient ischemic attack.
Clinical Utility and Outcome Data
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