Ann Thorac Surg 1995;59:802-803
© 1995 The Society of Thoracic Surgeons
Invited Commentary
INVITED COMMENTARY
Philippe Menasché, MD, PhD
Department of Cardiovascular Surgery Hopital Lariboisiere 2, rue Ambroise Pare 75010 Paris, France
See also page 795.
This article demonstrates, with the use of sophisticated hemodynamic end points, that warm continuous retrograde blood cardioplegia provides poor protection, compared with the more conventional cold antegrade technique, in a canine model of cardioplegic arrest superimposed on a previous episode of normothermic unprotected global ischemia. Van Camp and associates logically conclude that their data ``dictate cautious use of warm retrograde cardioplegia in the setting of acute ischemia.'' I think that the interpretation of this conclusion should be equally cautious because two major features of the experimental design seriously limit the clinical relevance of this study.
First, the dogs were anemic, as reflected by an average hematocrit of 15%. Because the residual oxygen requirements of a given heart never can be predicted accurately and actually may exceed theoretical calculations, it is critical to supply as much oxygen as possible. Consequently, the target hematocrit should be at least 25%, which is by far higher than that used in Van Camp and associates' experiments. This can be achieved easily by the use of a low-dilution cardioplegia delivery technique, which entails supplementation of pure blood with a limited amount of crystalloid cardioplegia. Incidentally, in the Emory study alluded to in this article, the higher incidence of stroke now is considered to be not the result of warm cardioplegia, per se, but rather the consequence of excessively high blood glucose levels caused by the infusion of unduly large volumes of a glucose-rich cardioplegic solution.
Second, in spite of Van Camp and associates' repeated allegations, the flow rates that they have used (1.5 to 1.8 mL • kg-1 • min-1) are not clinically relevant. The studies that are quoted in the article date back to the early experience with retrograde warm blood cardioplegia and do not reflect current practices. In addition, it is inaccurate to look for a support in Yau and associates' studies [17,23] as this group has reported flow data with the use of antegrade, not retrograde, cardioplegia. Indeed, all those who use warm retrograde blood cardioplegia in their clinical practice try now to keep the flow rate in the 150 to 250 mL/min range, which, assuming an average body weight of 70 kg, would yield values approximately twice as high as those used in this study. In the same line of reasoning, the observation of a coronary sinus pressure ranging from 15 to 22 mm Hg strongly suggests an inadequate driving force for the retrogradely infused cardioplegia; in clinical practice, the finding of such values would immediately lead one to look for an inadvertent dislodgement of the coronary sinus cathether. Interestingly, in the study by Horsley and associates [21] that demonstrates the adequacy of retrograde warm blood cardioplegia in a similar canine model of cardioplegic arrest superimposed on a regional infarct, the cardioplegia hematocrit averaged 24% and although the flow rates were not indicated precisely, one can infer that they were higher than in the present study from the fact that coronary sinus pressures were in the range of 40 mm Hg.
In summary, the study by Van Camp and associates is important in that it clearly demonstrates that the prerequisites for warm retrograde blood cardioplegia to be safe and effective are avoidance of hemodilution and maintenance of high retrograde flow rates.
Related Article
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Functional Recovery After Ischemia: Warm Versus Cold Cardioplegia
- Joseph R. Van Camp, Louis A. Brunsting, III, Keith F. Childs, and Steven F. Bolling
Ann. Thorac. Surg. 1995 59: 795-802.
[Abstract]
[Full Text]
