Thrombus formation in the left atrial appendage in the course of atrial fibrillation.

Background. Thromboembolism in patients with nonvalvular atrial fibrillation is secondary to emboli arising from atrial cavities, particularly left atrial appendage. Stroke Prevention Atrial Fibrillation (SPAF) III study showed washing flow, left appendage ejection fraction, natural echocontrast, and left ap- pendage volume and morphology, as risk para- meters of thromboembolism. Methods. The authors examined 69 patients by transesophageal echocardiography, subdi- viding them into 3 groups: 26 patients in sinus rhythm in Group A (Gr.A), 22 patients in atrial fibrillation without thrombi in the left atrial ap- pendage in Group B (Gr.B), 21 patients with tromboembolism and with thrombus in the left atrial appendage (Gr.C) Results. Atrial volume in sinus rhythm (SR) patients (41.9 ± 23.4 cm 3 ) was lower than the one in Gr.B (86.2 ± 47.9 cm 3 , p 0.05). No difference was found between Gr.A and Gr.B left atrial appendage fraction (31.8% versus 29.1%, p > 0.05), whereas it was found re- lated to Gr.C (31.8% versus 15.4% p < 0.01). Flow velocity within left atrial appendage was signifi- cantly higher in Gr.A in relation to the other two groups (p < 0.001); flow velocity in Gr.B was low- er than in Gr.A but higher than in Gr.C and in all cases such differences were statistically signifi- cant (p < 0.001). Gr.A flow duration was approxi- mately twice as much compared to the one in Gr.B (616.8 ± 94.1 msec vs. 483.3 ± 172.6 msec, p < 0.01), whereas it was approximately four times higher compared to the one in Gr.C (616.8 ± 94.1 msec vs. 165.7 ± 53.7 msec; p < 0.001). Such duration, if related to the corresponding cardiac cycle, indicates the percentage of time during which blood flows through a cycle within the left atrial appendage; this value is about 85% of cardiac cycle in Gr.A, while it is 65% in Gr.B (p < 0.01) and about 21% in Gr.C (p < 0.001). Conclusions. Such results add a new parame- ter to the ones suggested in the SPAF III study for the evaluation of TE risk, that is flow duration