What is Free floating ball thrombus ( FFBT)? , A case of Moderate MS , mild MR and mildly dysfunctional LV and AF

Wood who first applied the term ball valve thrombus to this entity in year 1814, describe autopsy finding in 15 year old girl with rheumatic mitral valve stenosis and syncope.

Left atrial ball valve thrombus is an important pathology and left atrial (LA) ball thrombus is a rare disorder. It is most often associated with rheumatic mitral valve stenosis. However it has been reported without mitral stenosis also.

This phenomenon is seen in 17% of patients with severe mitral stenosis, and the risk doubles with atrial fibrillation.

 However, left atrial ball thrombi have rarely been reported in patients who have had no mitral valvular disease. A left atrial ball thrombus in non-rheumatic atrial fibrillation was first described in 1992.

The restricted mitral orifice encloses the free-floating thrombus in the LA. Ball valve thrombus in the left atrium (LA) is a spherical clot which is freely mobile and intermittently occludes the mitral valve orifice.

There is a potential for fatal systemic emboli or mitral valve orifice occlusion that may result in sudden death.

Almost all patients with a left atrial free floating ball thrombus have atrial fibrillation. Concomitant cardiac diseases besides of   mitral stenosis are post mitral valve replacement, myocardial infarction, myocarditis, hypertrophic cardiomyopathy and infective endocarditis.

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Pathogenesis

It is speculated that a fixed thrombus in the left atrium is formed initially, which grows gradually into the left atrial cavity and forms a spherical shape, with final disconnection of the pedicle between the thrombus and the atrial wall. As the bulbous end of thrombus enlarges the pedicle lengthens and thins until eventually the thrombus separates or fragments. Thereafter as the thrombus spins freely in the atrium, it acquires its characteristic smooth, polished appearance. During thrombus development and subsequently morphological changes, it is very likely that the patient may experience transient embolism or stroke.

Most of the thrombus are seen in LA appendage, but in 2% of cases may extend to LA body.

The presence of an enlarged chamber, atrial fibrillation, a stenotic mitral valve, low cardiac output state, and spontaneous contrast echoes, all favor blood stasis and thrombus formation.

However, in the presence of mitral stenosis or poor LV function, even patients in sinus rhythm and those with only modest LA enlargement can have LA thrombi. LA thrombi are less common in patients with mitral regurgitation, presumably because the high-velocity regurgitant jet mechanically  disrupts the area of blood stasis within the LA

Thrombus formation in the LV tends to occur in regions of blood stasis or low-velocity blood flow. The most familiar example of blood flow stasis in the LV is a ventricular aneurysm, in which low-velocity swirl­ing blood flow patterns are seen. Stasis also may occur with less severe segmental wall motion abnormalities.

The role of atrial fibrillation in the pathogenesis of ball thrombi seems to be more important. Its formation may result from an initial free-floating or mural micro thrombus, with an accretion phenomenon gradually enlarging the mass like a growing snowball.

The chronic stasis associated with atrial fibrillation should be considered an important growth factor of the ball thrombus. The surface is free from rough areas.

That explains the relative rarity of embolic manifestations with this pathology. The possibility of

sudden death due complete mitral orifice occlusion is a dreaded complication. Further such large thrombi with organized fibrin layer on the surface are unlikely to be dissolved with anticoagulation. However, there is a report of a single case wherein the thrombus dissolved completely with anticoagulation for a month.

 Clinical significance 

It has three common issues.

One: Getting confused with other more pathological entities.

Two: Risk of stroke.

Three: Nidus for normal native valve endocarditis?

Leung et al reported patients with left atrial thrombus on Transesophageal echocardiography and quantitated their embolic event rate to be about 10.4% per year and all cause mortality rate at 15.8% per year.

CMR, cardiac magnetic resonance imaging; CT, computed tomographic imaging.

*Shrestha et al: Am J Cardiol 48:954-960, 1981; Chiang et al: J Ultrasound Med 6:525-529, 1987; Bansal et al: Am J Cardiol 64:243-246, 1989.

†Aschenberg et al: JACC 7:163-166, 1986; Olson et al: J Am Soc Echo 5:52-56, 1992; Hwang et al, Am J Cardiol 72: 677, 1993. 

‡Tang et al: J Interv Card Electrophysiol 22:199, 2008; Patel et al: Heart Rhythm 5:253, 2008; Gottlieb et al: J Cardiovasc Electorphysiol 19: 247, 2008.

§Visser et al: Chest 83:228-232, 1983; Stratton et al: Circulation 66:156-165, 1982.

¶¶Ohyama et al: Stroke 34:2436, 2003.

¶Srichai et al: Am Heart J 152:75, 2006.

**Reeder GS et al: Mayo Clin Proc 56:77, 1981.

Prognosis and Clinical Implications

The importance of an LA thrombus depends on the clin­ical setting.

-  Left atrial ball valve thrombus should be suspected if the patient with severe mitral valve stenosis and atrial fibrillation have intermittent or changing murmurs , syncope, mid-diastolic or pre-systolic murmurs may increase in intensity as a ball valve thrombus encroaches on the mitral valve orifice, and a mid-diastolic murmur may disappear temporarily when the orifice become obstructed.

- In a patient with new AF and an embolic stroke, the most likely cause of the stroke is an LA thrombus whether or not one is actually imaged, and thus the demonstration of an LA thrombus would be unlikely to change clinical management.

- In contrast, in a patient with rheumatic mitral stenosis, the presence of an LA thrombus is a contraindication to mitral balloon valvotomy.

-   TEE evaluation for LA thrombus is routine before elective cardioversion and before interventional and electrophysiology procedures in which catheters or devices will be in the LA, for example, mitral valvulo­plasty or atrial fibrillation ablation.

-            Free floating dumbbell shaped thrombus in LA causing intermittent platypnea and recurrent syncope is very rare clinical presentation in patients with rheumatic mitral stenosis.

-            Usually, the free floating thrombi are small in size, ball-shaped and have endothelial-like superficial layer which

reduces the propensity to aggregate platelets and, therefore, rarely causes systemic thromboembolism.

-     -      Another important factor for reduced thromboembolism is decreased propensity of collision between the thrombus and LA wall in already dilated LA with blood stagnation.

-       -     Dyspnea is usually on exertion and is mainly because of valvular involvement whereas platypnea (dyspnea that

              occurs in an upright position) is due to intermittent obstruction of stenotic mitral valve and is an alarming bell      as these patients may succumb to sudden cardiac death.

-         -   On the other hand, giant thrombi are soft, fragile and poorly organized and are more prone

to cause systemic thromboembolism.

-           -Management of these patients needs urgent surgical removal of thrombus with correction of the underlying cause and produces long-term survival of >90%, cardiopulmonary bypass is the first therapy of choice, because it can safely prevent critical complications and further systemic embolic events.

-          -  Some reports declared management includes urgent surgical thrombus removal with underlying valvular correction and lifelong anticoagulation.

-           -Anticoagulation and thrombolytic therapy is not useful in the acute management and only helps in the prevention of its further progression.

-          - Anticoagulation therapy is mainly used for stroke prophylaxis and reduces the risk of thromboembolism by 70% and may not be effective in other 30% of patients.

-           -The clinical presentation of patients with left atrial thrombus varies depending on its size and consistency. Patient with small well endothelialized thrombus presents with presyncope or syncope, whereas those with large poorly organized thrombus presents more often with transient ischemic attack or stroke.

-        -   Echocardiography, especially transesophageal echocardiography is sensitive in detecting left atrial free floating ball thrombi.