Keywords

Left atrial thrombus, left atrial myxoma, floating bodies

Two-dimensional echocardiography (2D-echo) is used to diagnose a number of abnormalities pertaining to the left atrium. It is more sensitive than the M-mode echo in detecting floating bodies of the left atrium. These floating bodies are found incidentally or while screening for a source of emboli in the left atrium.

A left atrial thrombus is a common indication for screening with an echocardiogram. Left atrial myxoma usually presents as a pedunculated mass with a pedicle. However, prolapsing type of left atrial myxomas present as free-floating bodies in the left atrium. A left atrial mass may lead to embolism of the major arteries.¹ 2D-echo helps in determining the nature, size, spatial orientation of these masses before surgical removal.² Mentioned below are a few differential diagnoses of a free-floating body in the left atrium.

• Left atrial thrombus
• Prolapsing type of left atrial myxoma
• Papillary fibroelastomas
• Lambl’s excrescences
• Fragments of vegetations
• Bacterial vegetations
• Fungal vegetations
• Aseptic vegetations
• Displaced pacemaker leads

LEFT ATRIAL THROMBUS

The left atrium and its appendage is a common site of formation of thrombi in patients with mitral stenosis and atrial fibrillation who are not on anticoagulation. This is due to stasis of blood or a poorly contracting left atrium. The left atrial thrombus may break into a number of smaller pieces, leading to embolic events such as a stroke. However, total or partial obstruction of the mitral valve may present as a low output state. 2D-echo is sensitive in detecting thrombi of the left atrium. The thrombus is initially attached by a pedicle, enlarges gradually and spins off in the left atrium and it acquires the characteristic rounded appearance. Further deposition of thrombotic material in layers over the thrombi contributes to the shape. These have been described as the ‘Ball valve thrombus’.

2D-echo also allows the detection of a possibility of a thrombus formation by the presence of a spontaneous echo contrast. Those described as the `Ball valve thrombus’ must fulfill certain rigid criteria as defined by Welch³ namely, there must be:

• Entire absence of attachment with consequent free motility
• Imprisonment in consequence of an excess in the diameter of the first narrowing in the circulatory passage ahead of it
• Such consistency and shape that the thrombus will not of necessity lodge as an embolus in the passage.

Case example

A 45-year-old female, a case of rheumatic mitral stenosis, presented with quadriparesis and altered sensorium.  ECG of the patient showed features of atrial fibrillation with controlled ventricular rate. 2D-echo findings of the patient are shown in (Figures 1-3). The trapping of the thrombus in the mitral valve predisposes the patient to sudden cardiac death. The patient was referred immediately for cardiac intervention. It is important to stress that oral anticoagulation may lead to fragmentation of the thrombus, leading to showers of emboli, which may be fatal.

PROLAPSING TYPE OF LEFT ATRIAL MYXOMA

Primary cardiac tumors of the heart are less common compared to metastatic disease of the heart. A three out of four, of these primary tumors are benign and a left atrial myxoma is the commonest (Fig. 4). Two different anatomic types of myxoma have been determined by means of echocardiography:

• Round, which is solid and round with a non-mobile surface
• Polypoid, which is soft and irregular in shape with a mobile surface.⁴ Ha and co-workers showed that prolapsing and polypoid tumors were associated with embolism.

The incidence of systemic embolism is higher in tumors with an irregular and friable surface than in those with a smooth surface.⁵

PAPILLARY FIBROELASTOMAS

Papillary fibroelastomas account for 8-10% of the primary cardiac tumors. They are small, solitary and motile bodies, which are of <1 cm in size and often confused with vegetations (Fig. 5). They may become as large as 4 cm. They usually arise from the mid-portion of the valve frequently involving the aortic valve followed by the mitral valve. Patients with papillary fibroelastomas are usually asymptomatic and these are identified, while screening for cardiac surgery or other indications.

Although symptoms related to fibroelastomas are uncommon, there is a potential for serious morbidity, particularly among patients with large, mobile, left-sided lesions.⁶ Cardiac papillary fibroelastomas are present on valves, away from valvular lines of closure, and also on the endocardial surfaces of the atria and ventricles.⁷

LAMBL’S EXCRESCENCES

Lambl’s excrescences are filiform fronds that occur at sites of valve closure. They are fine thread like strands and originate as small thrombi on endocardial surfaces and have the potential to embolize to distant organs.⁸ In contrast to papillary fibroelastomas, they involve the mitral valve more frequently followed by the aortic valve.

FRAGMENTS of Vegetations

Bacterial Vegetations

2D-echo is very specific in detecting vegetations of infective endocarditis (Fig. 6). The specificity is as high as 98%.⁹ However, the sensitivity ranges between 40-50%. Detection of these vegetations is a part of three major criteria of the Duke’s criteria for infective endocarditis.

The appearance and site of the vegetations depend on the etiology. Vegetations affect both the native and prosthetic valve. Detection of vegetations of the prosthetic valve is difficult. This is because of the echogenic nature of the prosthetic valves.

Bacterial vegetations as a complication of rheumatic fever are small, less friable, sterile and are known as verrucae. Vegetations, primarily due to infective endocarditis are large, bulky, more friable and are destructive in nature. They are most commonly seen in the upper parts of the valve cusps.

Fungal Vegetations

Fungal vegetations are less common than bacterial vegetations and are easily identified by 2D-echo. They are larger than bacterial vegetations. They are friable and have an easy tendency to break into smaller pieces and present as septic emboli.

Aseptic Vegetations

Aseptic vegetations may be due to nonbacterial thrombotic endocarditis or systemic illnesses such as systemic lupus erythematosus (SLE) and antiphospholipid antibody syndrome. Nonbacterial thrombotic endocarditis is also known as marantic endocarditis, which literally means ‘wasting away’.

The vegetations are small masses of fibrin and platelets, which are easily friable and are seen along lines of closure of valves. They commonly affect the mitral and the aortic valves.

Common predisposing factors are hypercoagulable states such as malignancy, sepsis and burns. Libmann sack`s endocarditis is seen in patients with SLE. These vegetations are small, warty and have destructive potential. They are commonly associated with the mitral and tricuspid valve along the atrial and ventricular surfaces and do not have a predilection for the lines of closure.

PACEMAKER LEADS

Pacemaker leads can produce an echocardiographic beam width artefact, but can be reduced by imaging from a different acoustic window.

Infection of the pacemaker leads makes it difficult to confirm whether vegetations are present or not, and to differentiate them from the vegetations of infective endocarditis. Displaced pacemaker leads may also present as a floating body in specific chambers  (Fig. 7). Early displacements are more frequent than late displacements and they usually affect atrial leads.¹⁰

SUMMARY

A free-floating left atrial mass may be a major source of emboli or may be an incidental finding. The size, site of occurrence, the nature of the surface (e.g., smooth rounded or irregular) and its relation to lines of closure of valves, by 2D-echo, helps in determining the nature, characteristics and identification of the underlying condition. 3D-echo, transesophageal Echo and the more recent 4D-echo provide more detail and throw light on the hemodynamic threat these bodies pose. Early surgical removal and histopathological examination of these masses may be indicated in a majority of these cases. Anticoagulation may harmful in the case of a large left ball valve thrombus.

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