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J Thorac Cardiovasc Surg 2003;126:304
© 2003 The American Association for Thoracic Surgery
Letter to the editor |
a Department of Cardiothoracic Surgery, University of Tokyo, Tokyo, Japan
To the Editor
We read with interest the article entitled "Epicardial 10-MHz Ultrasound in Off-Pump Coronary Bypass Surgery: A Clinical Feasibility Study Using a Minitransducer" by Eikelaar and associates1 in the October 2002 issue of the Journal. Epicardial echocardiography for intraoperative assessment of native coronary artery and graft anastomosis is not a new approach, and many investigations related to the technique have already been performed in conventional coronary artery bypass grafting (CABG).2 Although the use of off-pump CABG has been increasing recently, performance of the graft-to-coronary anastomosis is definitely more difficult during the off-pump CABG procedure than during conventional CABG. Epicardial echocardiography therefore appears to be more valuable and effective in off-pump CABG than in conventional CABG.
The echocardiographic equipment that Eikelaar and associates1 used was described as a 10-MHz linear array color Doppler minitransducer (UST5531; Aloka Co, Tokyo, Japan). Its precise properties, however, are 5.0-MHz to 10.0-MHz in B-mode and 5.0-MHz to 7.5-MHz in color Doppler mode. It never works at 10-MHz in color Doppler mode, and the description in the article is thus somewhat confusing.
Although Eikelaar and associates1 scanned the native coronary artery and graft anastomosis in B-mode and color Doppler mode, the vessels run parallel to the echocardiographic probe, which may result in underestimation of the real lumen or the quality of the anastomoses because of artifacts. Power Doppler mode, on the other hand, is efficient in visualizing coronary arteries.3 Power Doppler ultrasonography is based on the total integrated power of the Doppler spectrum and has several advantages relative to conventional color Doppler echocardiography. It is more sensitive to visualization of smaller vessels, is angle independent, and does not produce signal aliasing. For those reasons we used the B-mode and power Doppler mode in our previous study.4
The transducer that we used was larger than their minitransducer, and its size limited the visualization of the posterior and inferior coronary arteries because of the restricted working space. Thus, although Eikelaar and associates1 used it only for the bypass for the left anterior artery, it would be more effective for visualization of the posterior and inferior coronary arteries.
We have been developing two new types of echocardiographic probes and systems, in cooperation with the research laboratory of Aloka Co. One probe is a higher frequency echocardiographic probe (7.5-13.0 MHz in B-mode) measuring 16 x 6 x 9 mm, the same as the probe of Eikelaar and associates.1 The high-frequency modality should enable more detailed visualization of the anatomy of the coronary artery and the quality of the graft anastomoses. The other probe is an original real-time 3-dimensional echocardiography system that reconstructs the power Doppler signals obtained from 2-dimensional image data into 3-dimensional image data sets.5 The 2-dimensional imaging technique is time-consuming because all planes are not imaged simultaneously, and surgeons or sonographers require additional technical skills to acquire and evaluate the 2-dimensional images. Three-dimensional echocardiography is therefore expected to overcome these limitations of 2-dimensional echocardiography, although the time resolution to image distal anastomoses still needs to be improved.
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