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.