Thrombus is defined as a discrete echo dense mass with defined margins that are distinct from the endocardium and seen througout systole and diastole. Thrombi represent the most frequently found intracardiac masses.
Risk factors for intracardiac thrombi formation
Intracardiac thrombi tend to form when there is stasis of blood flow.
- Atrial fibrillation
- Mitral valve disease
- Dilated cardiomyopathies
- Systemic disease: Behçet disease, Löffler’s endocarditis, Churg-Strauss syndrome, collagen vascular diseases, amyloid, *Inflammatory bowel disease, coagulopathies.
- Tumors (Surface thrombus)
Classification of intracardiac thrombi
- Left ventricular thrombi
- Left atrial thrombi
- Right sided thrombi
- Valvular thrombi
Left ventricular thrombi
Left ventricular thrombus is defined as a discrete echo dense mass in the left ventricle with defined margins that are distinct from the endocardium and seen througout systole and diastole. Left ventricular thrombi are typically located in areas of severe wall motion abnormalities.
They can develop in any situation in which low flow and blood stasis occur
- Myocardial infarction is the most common cause of left ventricular thrombi formation.
- Most often large anterior ST elevation infarctions with anteroapical aneurysm formation and akinesis or dyskinesis.
- Incidence is lower with smaller infarctions and those involving other myocardial regions.
- Reduced LV ejection fraction, a greater degree of wall motion abnormalities, and LV aneurysm formation are other risk factors for thrombus development.
- Chronic dilated cardiomyopathies
- Chronic left ventricular aneurysm
Thrombi typically involve the apex of the left ventricle but rarely in the other noncontracting segments they may be located.
Diagnosis and Echocardiographic features
- Transthoracic echocardiography (TTE) has been the standard procedure for the diagnosis of LV thrombus.
- Sensitivity and specificity of the echocardiographic diagnosis of left ventricular thrombi are aproximately 86-95%. Apical views that position the left ventricular apex in the near field are optimal views.
- For the diagnosis of thrombus the mass must be seen at least in two views sometimes modified apical transducer positions are needed.
- Contrast use may improve image quality and allows more accurate diagnosis.
- Left ventricular thrombi (especially in the apex) are better assessed by transthoracic echocardiography than by transesophageal echocardiography as the apex is often foreshortened and not well visulized with transesophageal echocardiography. However especially in the presence of poor transthoracic image quality transgastric views may permit apex evaluation.
- Care must be taken to rule out other conditions mimicking mass formation especially artefacts.
- Echocardiographic apperance of intracardiac thrombi is heterogenous: they can vary from a small, immobile mural thrombus to a large protruding mobile thrombi. Echodensity and shape of the thrombi depend on age and degree of thrombus organization. They may be homogenously echogenic or may have heterogenous texture with lucent areas. An echolucent center suggests that the thrombus is relatively new and actively growing. Very fresh thrombi tend to protrude into the center of the cavity and are highly mobile. Older thrombi generally have smooth cavitary surfaces and they are less likely to change or embolize. In some cases vascularization or layer formation can be found. Sometimes thrombi may be flat lying along the left ventricular wall even in some cases it may be very diffucult to differenciate thrombus from myocardium.
Left atrial thrombi
Left atrial thrombi, most often associated with atrial fibrillation (AF) and/or rheumatic mitral stenosis.
LocalizationMost common location for the thrombus formation in the left atrium is the left atrial appendage. The LAA has been the site in the left atrium where more than 90% of thrombi were detected in patients with non-valvular atrial fibrillation in transoesophageal studies. The LAA has therefore been considered by some our ‘most lethal human attachment’
- Transesophageal echocardiography (TOE) is the preferred technique for detection of left atrial thrombi and this tecnique offers detailed visualization of the left atrium, including the atrial appendage where most atrial thrombi reside. The sensitivity and specificity of TEE for thrombi were 100 and 99 percent, respectively.
- The ability of transthoracic echocardiography to identify or exclude left atrial or atrial appendage thrombi is limited, with a reported sensitivity of 40 to 60 percent, due largely to poor visualization of the left atrial appendage, where most atrial thrombi reside
- Left atrial thrombi are often multiple and vary in size and, although they attach to the atrial wall, they usually demonstrate some degree of independent motion.
- Small thrombi must be distinguished from the normal trabeculations (pectinate muscles) of the left atrial appendage, and larger thrombi may be difficult to distinguish from tumor.
- The finding of spontaneous echo contrast, indicative of predisposing stasis, mostly accompanies thrombus formation. There is a very strong association between left atrial spontaneous echo contrast and left atrial thrombi; among patients with AF and left atrial thrombi, for example, spontaneous echo contrast is seen in almost 80 percent of cases.
The presence of spontaneous echo contrast may be helpful in differentiating thrombi from tumor or normal anatomy.
Right sided thrombi
- Thrombus formation is less common in the right sided cardiac chambers compared to the left.
- They mostly occur in association with catheters and pacemaker electrodes.
- Thrombi also can form in the right atrial appendage in patients with atrial fibrillation or prothrombotic states. However, the anatomy of the right atrial appendage makes it a less likely site for thrombus formation.
Floating right heart thrombi are uncommon and are in transit from the legs to the pulmonary artery. On occasion, an embolus will become enmeshed in the foramen ovale as it paradoxically passes from right atrium to left atrium.
Thrombus formation and subsequent embolization are common in patients with prosthetic valves, especially in those with a mitral or tricuspid prosthesis and suboptimal anticoagulation. Evaluation of prosthetic valves, especially mitral prostheses, is best performed by transesophageal echocardiography. The distinction between thrombus and pannus formation is essential if thrombolytic treatment is considered. For the differential diagnosis transesophageal findings and clinical findings are important. Thrombi in general larger and have soft ultrasound density similar to myocardium but pannus formation is usually more dense and small in apperance. Thrombus formation is also associated with inadequate anticoagulation.
- Vegetations (Infectious masses)
- Cardiac tumors (primary or secondary)
- Normal structures/variants (Structures Mistaken for Abnormal Cardiac Mass)
Thrombi are important clinically because they can lead to:
- Serious embolic complications including stroke, peripheral embolization and pulmonary embolization.
- According to localization they may cause obstruction or regurgittaion in a valve.
- Echocardiography can identify thrombi that are most likely associated with embolic risk. Thrombus morphology correlates with the risk of embolization. major and well known risk factors for embolization are:
- Large size,
- Protrusion into the cavity
- Pepi M, Evangelista A, Nihoyannopoulos P et al. on behalf of the European Association of Echocardiography Recommendations for echocardiography use in the diagnosis and management of cardiac sources of embolism 2010;11:461-476.
- Galiuto L, Badano L, Fox K, Sicari R, Zamorano JL. The EAE Textbook of Echocardiography. 1st edition. Oxford, Oxford University Press;2011
- Armstrong WF, Ryan T. Feigenbaum's Echocardiography. 7th edition. Philadelphia, PA:Lippincott Williams and Wilkins;2009.