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Eur J Cardiothorac Surg 2005;28:831-832
© 2005 Elsevier Science NL
Department of Surgery, Ulleval University Hospital, 0407 Oslo, Norway
(Email: i.j.vaage{at}medisin.uio.no).
The first coronary artery bypass surgery I witnessed as a resident was with intermittent aortic cross-clamping and ventricular fibrillation and with a large vent into the left ventricular apex as myocardial protection. During subsequent years and in parallel with the advances and improvements of cardioplegia, it was always a mystery to me how good results could be reported with intermittent cross-clamping as myocardial protection. Many cardiac surgeons who are strong believers in cardioplegia as the technique of choice for myocardial protection have been surprised and puzzled by the good clinical results presented by surgeons using intermittent cross-clamping [1,2,3]. However, the present study by Fuji and Chambers [4] provides strong data to support what some of us have believed in the back of our minds – that intermittent cross-clamping with ventricular fibrillation may represent a way of preconditioning the heart. The present study is an excellent research report using the classic, isolated Langendoff-perfused rat heart. It is from a research center that for decades has been in the front of research efforts on myocardial protection. The study is well conducted, well designed, and well written. Altogether there are three different series of isolated, perfused rat hearts with several groups in each. It is a large study, and it is to the authors’ credit that they did not try to split this up into more than one solid article.
The study demonstrates that preconditioning is an integrated part of myocardial protection afforded by using intermittent cross-clamping with ventricular fibrillation. The investigators show that this protection is attenuated by glibenclamide, a non-specific -channel blocker. Furthermore, inhibition of more specific mechanistic components of preconditioning such as protein kinase and mitochondrial -channels also attenuated the cardioprotective effects of intermittent cross-clamping. However, although this work "proves" that one of the protective effects of intermittent cross-clamping is by inducing preconditioning, it is not totally a new concept, as preconditioning induced by intermittent cross-clamping was suggested by Abd-Elfattah et al. [5].
By demonstrating that intermittent cross-clamping in reality is a way of preconditioning the heart, Fuji and Chambers [4] have brought this old technique into the modern era of organ protection. There is now strong evidence that the human heart may be preconditioned both in cardiology and in cardiac surgery [6]. Pharmacologically exploiting the mechanisms of the endogenous cell defense which includes both pre- and postconditioning [6] may be the future of organ protection. Unfortunately, in spite of 20 years of research on preconditioning, there is still no effective and clinically acceptable technique of routinely preconditioning patients in cardiac surgery. The endogenous cell defense has a considerable potential of "making the cells stronger" and more resistant towards injury, but we cannot use its possibility in clinical surgery. This unfortunate situation ought to be changed.
Does intermittent cross-clamping represent a way of introducing the endogenous cell defense into routine use in cardiac surgery? Definitely not! Intermittent cross-clamping is a 30-year-old technique [7], and it was introduced at a time when coronary artery bypass surgery was performed in patients around 50 years of age. Today the average age of these patients is close to 70 years in some centres in Western Europe and USA. The ascending aorta is a dangerous organ, it becomes more and more atherosclerotic with age. Clamping and declamping the ascending aorta is one of the manoeuvres causing embolism and neurologic injury including fulminant stroke [8,9]. The risk of stroke increases almost exponentially with age, and this risk is strongly correlated with atherosclerosis of the ascending aorta [8]. In contrast to intermittent cross-clamping, a surgical technique with no touch of the ascending aorta may be one of the most powerful ways to prevent perioperative stroke in cardiac surgery.
Consequently, in the surgical practice of Europe today, repeated clamping and declamping of the aorta should be avoided. It may work reasonably well in a patient population below 60, but in older patients this technique represents an unjustifiable risk of stroke as long as we have good – or probably even better – techniques of myocardial protection during coronary artery bypass grafting.
Explaining the positive cardioprotection of intermittent cross-clamping with preconditioning is an interesting and important scientific finding, and the present work may become a classic in the field. However – to use a cliché – introducing preconditioning into intermittent cross-clamping is like giving old wine a new bottle. But does the new bottle mean that we should drink the wine? Definitely not, the wine is now too old, the bottle with its content should be regarded as a collector's item. The old wine should be placed on a shelf where we can memorize and watch it, while we taste and enjoy some better wine, which still may be stored for some years until it becomes too acidic by the passing of time and progress.
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