Discussion:
The LAA is the only area within the left atrium that is composed of
pectinate muscle and creates an environment that is conducive to blood
stasis and thrombus formation [6]. LAA also is a
contractile reservoir and decompression chamber that acts as a suction
during ventricular systole and as a conduit during diastole[7]. Functioning as an endocrine organ, when it
stretched, the LAA produces approximately 30% of atrial natriuretic
peptides [8]
The morphology of LAA varies greatly from individual to individual which
is generally divided into 4 types, including “chicken
wing,”“cauli-flower,” “cactus,” and “windsock”. Research shows
the LAA accounts for 91% of the thrombus sources in nonvalvular AF and
15% to 38% in non-AF patients with a cardiomyopathy who have developed
stroke [9,10]. A multicenter study has found that
patients with the chicken wing morphology are significantly less likely
to have an embolic event compared to those with cactus, windsock, and
cauli-flower morphologies [11]. In clinical
practice, therefore, long term oral anticoagulants are needed to prevent
cerebrovascular accidents for those high risk patients. Given that
AF-related thrombi occurs predominantly in the LAA, surgical and
percutaneous procedures for LAA exclusion have been developed especially
for the patients who are not candidates for anticoagulation[12], which include the patients with prior
hemorrhagic strokes and untreated bleeding disorders.
The congenital absence of LAA is quite rare cardiac anomaly, which can
be found in multi-imaging processes intended for other purposes. The
accurate prevalence and incidence of this condition is unknown. Its
diagnosis needs to be considered on detail evaluation of patient’s
surgical and medical history as total thrombotic occlusion, uncommon
anatomical features, surgical or percutaneous exclusion, as well as poor
imaging quality could cause misdiagnosis. Additionally, considering the
variations of LAA position and morphology, multimodality imaging is
often needed for confirmation [13]. TEE is the
technique of choice to visualize LAA due to its higher spatial
resolution and real-time performance. Two-dimensional TEE can more
accurately evaluate the morphology and function of the left atrial
appendage, as well as the adjacent structure of the LAA, meanwhile
Three-dimensional TEE provides more specific information, which may be
helpful in the differential diagnosis of LAA with thrombus or other
findings. RT 3D TEE is a novel and valuable imaging modality in the
percutaneous catheter-based LAA occlusion in AF patients, which could be
recommended for routine clinical application [14].
Theoretically, the risk of embolic events in patients with AF with
congenital absence of left atrial appendage is low, but clinical
significance of the anomaly was not elucidated. In our case, It’s worth
to mention that various etiologies can evoke stroke events and defining
stroke mechanisms is crucial for effective stroke prevention.