Improved Visualization of the Left Atrial Appendage by Transthoracic 2-Dimensional Tissue Harmonic Compared with Fundamental Echocardiographic Imaging☆,☆☆,★

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Abstract

We compared fundamental and tissue harmonic transthoracic echocardiographic imaging for the delineation of the left atrial appendage (LAA) in 32 subjects. The LAA images recorded in the parasternal short-axis view were divided into 4 segments and 2 observers independently graded for each segment using a visual scoring system ranging from 0 to 3 (0 = no, 3 = clearly visible over the entire length of the segment). For the 128 segments, the averaged segment scores were significantly increased after switching to harmonic imaging (1.32 ± 0.69 versus 1.60 ± 0.81 for fundamental and tissue harmonic imaging, respectively; P < .0005 for observer 1, and 1.38 ± 0.65 versus 1.61 ± 0.82, respectively; P < .001 for observer 2). In a patient with LAA thrombus, the image contrast of the thrombus was improved in harmonic compared with fundamental imaging. These data suggest that tissue harmonic imaging significantly improves image quality of the LAA. (J Am Soc Echocardiogr 1998;11:1044-9.)

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Study Population

The study population consisted of 26 consecutive patients (15 women and 11 men, aged 30 to 83 years [mean age 65 ± 12 years]) and 6 healthy volunteers (2 women, and 4 men, aged 26 to 33 years [mean 30 ± 2 years]). Ten patients had ischemic heart disease, 10 had nonischemic cardiomyopathic conditions, 2 had nonrheumatic valvular heart disease, 3 had dual chamber pacemakers, and 2 patients had lone atrial fibrillation. Seven patients were in atrial fibrillation at the time of echocardiographic

Delineation of LAA Anatomy

The segment scores of the 128 segments in fundamental and harmonic modes are summarized in Table 1.When compared with fundamental imaging, harmonic imaging was associated with significantly higher averaged segment scores by both observers (1.32 ± 0.69 versus 1.60 ± 0.81, P < .0005 for observer 1, and 1.38 ± 0.65 versus 1.61 ± 0.82, P < .001 for observer 2, respectively, Table 1). The segment scores of zero were mainly observed in the apical region (segment 2 and 3) of the LAA, and the

DISCUSSION

Harmonic imaging has been initially proposed to enhance the detection of contrast agents within blood-containing cavities and vascularized tissue.15, 16, 17 During exposure to ultrasound, microbubbles undergo compression and rarefaction, resulting in a back-scattered signal composed of the fundamental frequency and its multiples (harmonics). The second harmonic of the backscattered ultrasound pulse is more prominent for microbubbles than for tissue. Newer broadband transducers have been used to

Acknowledgements

We thank Dr James B. Seward, Professor of Medicine and Pediatrics, Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic, for his helpful review of the manuscript.

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From the Fourth Department of Internal Medicine, Shimane Medical University, Izumo, Japan, and the Division of Cardiovascular Diseases and Internal Medicine, Mayo Clinic and Mayo Foundation, Rochester, Minn.

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Reprint requests: Kazuaki Tanabe, MD, Ultrasound Research, Medical Sciences 2-130, Mayo Clinic, 200 First St SW, Rochester, MN 55905.

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Copyright © 1998 American Society of Echocardiography. Published by Mosby, Inc. All rights reserved.