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J Thorac Cardiovasc Surg 1995;110:1153
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Microembolization during coronary artery bypass grafting

Centinela Hospital Medical Center
Inglewood, CA 90301

To the Editor:

The article "Microemboli During Coronary Artery Bypass Grafting" by Clark and associates ¹ discusses the genesis and effects on outcome of cerebral microemboli that occur during cardiopulmonary bypass. The authors used transcranial Doppler ultrasonography to monitor the incidence of cerebral microemboli and observed that the greatest number of microemboli occurred as a result of cardiac manipulation, removal of a partial crossclamp during construction of the proximal anastomoses, cannulation, and "unknown" causes, listed in descending order of incidence. In the published discussion of this article, the method used for venting the left ventricle and the likelihood that the incidence of microemboli was related to the method of venting were questioned. The author replied that multiple methods were used, ranging from "none, to venting the pulmonary artery, to occasionally venting the left atrium. It was rare to vent the left side of the heart, however."

My purpose is to draw attention to the "unknown"causes of microembolism and to suggest that the method of venting could affect the incidence of microembolism. In 1987, Robicsek and Duncan ² described conditions in the vented heart that facilitated retrograde air embolism through coronary arteriotomies made during coronary artery bypass operations. I ³ supported their conclusions and have since studied my own population of patients having coronary artery bypass operations with reference to the presence or absence of air in the left ventricle before the ventricle was permitted to eject.

All procedures were performed with intermittent antegrade or antegrade-retrograde infusion of cold oxygenated crystalloid cardioplegic solution with venting of the left side of the heart through the aortic root. Proximal and distal anastomoses were performed with a single period of aortic crossclamping. After removal of the crossclamp, with the patient in a deep Trendelenburg position, the venous return to the heart was partially occluded to allow the heart to fill. The elevated apex was penetrated with a 16-gauge needle and the hole was enlarged by a forceps. In a series of 328 patients, air was seen, and sometimes heard, to escape from the left ventricle in 33 or 10% of these patients.

Clark and associates used a side-biting clamp for construction of their proximal anastomoses and a variety of venting methods, none of which was specified or studied as a separate entity in their manuscript. If aortic root venting was one of the methods they used, air could have entered the left side of the heart through the open coronary arteriotomy (in one of our patients, air could be heard to be sucked into an arteriotomy). The infusion of cardioplegic solution directly into a graft may also introduce air into the left side of the heart by retrograde flow into the aorta. If the proximal anastomoses are performed with the aorta crossclamped, the interior of the aorta and the left ventricle as well (if the aortic valve is open) are exposed directly to the atmosphere.

It is clear that coronary artery bypass grafting is associated with a small but significant risk of transcoronary or transaortic entry of air into the left side of the heart. Possibly the method of venting in some of the authors' patients could have contributed to the incidence of microembolism listed under "unknown" causes. I continue to urge that the left ventricle be regarded to contain air at all times in coronary artery bypass grafting and that it be evacuated directly, if possible, before the heart is allowed to eject.

References

1. Clark RE, Brillman J, Davis DA, Lovell MR, Price RPP, Magovern GJ. Microemboli during coronary artery bypass grafting: genesis and effect on outcome. J THORAC CARDIOVASC SURG 1995;109:249-58.[Abstract/Free Full Text]
   
2. Robicsek F, Duncan GD. Retrograde air embolization in coronary operations. J THORAC CARDIOVASC SURG 1987;94:110-4.[Abstract]
   
3. Lee ME. Air embolization in coronary bypass operations. J THORAC CARDIOVASC SURG 1988;95:543.
   

This Article Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Myles Edwin Lee Permission Requests Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Lee, M. E. Search for Related Content PubMed PubMed Citation Articles by Lee, M. E.