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Eur J Cardiothorac Surg 2007;31:979-981. doi:10.1016/j.ejcts.2007.01.031
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved
Institut Mutualiste Montsouris, Department Cardiovasculaire, F-75674 Paris, France
* Tel.: +33 1 56616508; fax: +33 1 56616511. (Email: jean.bachet{at}imm.fr).
In an original article published in the present issue of the journal, Inoue and co-workers [1] describe and advocate the use of a rather sophisticated and complex method of arterial return of the cardiopulmonary bypass (CPB), associating several modes of cannulation and, in particular, direct cannulation of the ascending aorta, during surgery of acute type A dissection. Their experience is a variation of the experience obtained with a similar technique by the group from Hannover (Germany) and published a few years ago [2].
According to the authors, the rationale for developing and using such a technique is based on two straightforward goals: simplicity and safety.
Although the experience reported herein is limited, one may observe that the results obtained have been excellent as the hospital mortality was reduced to 3% and the rate of neurological complications did not exceed 6.5%. No case of malperfusion or thrombo-embolism induced by the technique of cannulation and perfusion was observed. One could admit, thus, that the authors have achieved their goals.
However, before being adopted on a large scale, the proposed method of cannulation may require a few words of caution as, looking twice, the reality may appear somewhat different.
It is indeed paradoxical that a technique which requires to dissect free and cannulate one femoral artery, then open the chest, cannulate the right atrium, initiate CPB, assess the possible cannulation site on the ascending aorta (possibly with the aid of epicardic echography), cannulate the ascending aorta using the Seldinger technique (and several dilators) and finally cool down the patient to deep hypothermia before starting the aortic repair, can be considered as simple. Let alone the fact that after completion of the repair, the aortic cannula must be switched to a side branch of the aortic graft to resume CPB and that de-airing of the aorta is done through the femoral cannulation, whereas the cerebral vessels are de-aired during a small period of retrograde cerebral perfusion through the superior vena cava. Obviously, all those manoeuvres imply a complex CPB circuit and an uneasy synchronisation of the various sequences.
Because ascending aorta cannulation, as described in the present article, precludes any form of direct perfusion of the brain during circulatory arrest, the authors have resorted to total circulatory arrest in profound hypothermia (DHCA) to perform the aortic repair. The drawbacks of profound hypothermia have been largely demonstrated. In particular, as acknowledged by the authors, it provides unsafe cerebral protection when the circulatory arrest exceeds 30 min. Who can ever claim that the aortic repair will be contained within this limit of time, especially during acute dissection surgery? For those many reasons, DHCA has been abandoned by most groups in favour of moderate hypothermia and selective antegrade perfusion of the brain [3].
Another important matter of concern in the reported experience is that, despite the various precautions taken by the operators, the aortic cannula was inserted in the false channel in 4 out of 32 cases (12.5%). Although the authors claim that this undue position had no consequence and that no patient suffered cerebral or visceral malperfusion because of it, this might be due to luck only and one may wonder whether a technique which is associated with such a rate of failures must be considered safe or, on the contrary, rather dangerous.
The authors question the use of the right axillary artery cannulation. They argue that the right axillary artery may be dissected, that its cannulation is more time consuming and might not provide a proper flow in patients with reduced body surface area. Instead, they consider that it is safer to use femoral cannulation which is known to be responsible for embolism, malperfusion or, even, false channel rupture.
This is not really convincing. The right axillary artery is very seldom dissected, whereas femoral arteries are often dissected. Femoral artery cannulation may be difficult and tedious in obese patients. Last, because all patients have about the same perfusion flow index (2.5 l/min m2) there is no reason why a proper flow should not be obtained in patients with a small body surface area through direct or side branched cannulation of the artery.
Right axillary artery cannulation allows antegrade perfusion of the aorta, permanent perfusion of the brain, imposes no time limit for the aortic repair, no necessity for cannula switch and no complicated de-airing process. There is no doubt, to date, that its advantages largely prevail over its disadvantages and make it the modern "gold standard" in surgery for acute type A dissection and, most probably, one of the major causes of reduction in its mortality and morbidity rates during the last decade [4,5].
Is it accurate, therefore, to state that the proposed procedure is actually simpler, less time consuming and safer than just dissecting free and cannulating the right axillary artery, performing the sternotomy, cannulating the right atrium and going to CPB in moderate hypothermia to perform a straightforward distal aortic repair during lower body circulatory arrest?
The present comments do not intend to question any technical evolution and certainly do not mean that the currently used techniques are engraved in marble and should not be challenged and replaced by newer techniques. It is quite understandable that new original methods come to the operating room because their instigators sincerely believe that they represent a progress in the operative management and a clear improvement in the outcomes of their patients. But those innovative methods should be developed and implemented because of disappointing results with conventional ones, must be based on solid anatomical or physiological elaborations and possibly developed first in the experimental laboratory.
We know that, in matters such as aortic surgery in general and acute dissection in particular, technical methods are difficult to compare, as randomised controlled studies are almost impossible, when not unethical [6,7]. We therefore must rely on observational studies to estimate the benefit of new techniques. The outstanding results obtained by Inoue and co-workers with their technique of cannulation and CPB may prove that their method is a good alternative to the simple and efficacious methods used so far and which have resulted in proven satisfactory outcomes. However, their experience is very limited in time as well as in number of patients. Common sense claims that "one swallow does not make a summer" and many techniques apparently beneficial when reported by one single group have resulted in a great number of disappointing failures when used on a large scale.
It is to be hoped that the technique proposed by Inoue and co-workers will not fall into this category.
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