INTEGRATED BACKSCATTER FOR QUANTIFICATION OF LEFT ATRIAL SPONTANEOUS ECHO CONTRAST

Objectives. This study was designed to develop a quantitative method o f spontaneous echo contrast (SEC) assessment using integrated backscat ter and to compare integrated backscatter SEC measurement with indepen dent qualitative grades of SEC and clinical and echocardiographic pred ictors of thromboembolism. Background. Left atrial SEC refers to dynam ic swirling smokelike echoes that are associated with low how states a nd embolic events and have been graded qualitatively as mild or severe . Methods. We performed transesophageal echocardiography in 43 patient s and acquired digital integrated backscatter image sequences of the i nteratrial septum to internally calibrate the left ventricular cavity and left atrial cavity under different gain settings. Patients were in dependently assessed as having no, mild or severe SEC. We compared int ensity of integrated backscatter in the left atrial cavity relative to that in the left ventricular as well as to the independently assessed qualitative grades of SEC. Fourier analysis characterized the tempora l variability of SEC. The integrated backscatter was compared with cli nical and echocardiographic predictors of thromboembolism. Results. Th e left atrial cavity integrated backscatter intensity of the mild SEC subgroup was 4.7 dB higher than that from the left ventricular cavity, acid the left atrial intensity of the severe SEC subgroup was 12.5 dB higher than that from the left ventricular cavity. The left atrial ca vity integrated backscatter intensity correlated well with the qualita tive grade. Fourier transforms of SEC integrated backscatter sequences revealed a characteristic dominant low frequency/high amplitude spect rum, distinctive from no SEC. There was a close relationship between i ntegrated backscatter values and atrial fibrillation, left atrial size , left atrial appendage flow velocities and thrombus. Conclusions. Int egrated backscatter provides an objective quantitative measure of SEC that correlates well with qualitative grade and is closely associated with clinical and echocardiographic predictors of thromboembolism. The relationship between integrated backscatter measures and cardioemboli c risk will be defined in future multicenter studies.