Perfusion strategies for aortic arch surgery: trends and evidence.

Abstract

In this issue of the European Journal of Cardio-Thoracic Surgery, De Paulis et al. [1], on behalf of the EACTS Vascular Domain Group, present an interesting survey on trends in cannulation and neuroprotection during aortic arch surgery across European Cardiac Units. The report offers several opportunities for discussion. Apparently, it is one of the first of its kind from a methodological standpoint. In fact, few examples exist of voluntary questionnaires, using qualitative end-points, which are proposed as original articles. Whereas the effort to document changes in clinical practice is certainly laudable, relevance of the findings herein is lessened by the low yield of completed questionnaires returned. Although one-third of 450 European Cardiac Centres still corresponds to a sizable patient population (albeit not quantified), this result is hardly representative of current practice for aortic arch surgery in Europe. If the stride towards definition of trends in surgical management made by the EACTS Vascular Domain Group is emulated in the future by other Society domains, such as Congenital Heart Disease and Acquired Heart Disease, more rigorous assessment of survey outcomes is warranted to avoid disseminating skewed perspectives. The bias of sample significance notwithstanding, this article documents a series of changes in practice, which have occurred through the years. According to the authors, the use of deep hypothermia, in general, and deep hypothermic circulatory arrest (DHCA), in particular, has essentially vanished from the aortic surgical armamentarium in favour of regional cerebral (or multiorgan) perfusion using moderate or, more rarely, mild hypothermia. This secular trend, which has since been witnessed in neonatal aortic arch surgery, deserves a special mention as it follows the trail of a more physiological extracorporeal circulation. Whether the continuous pump flow with regional perfusion at moderate or mild hypothermia truly constitutes a more physiological perfusion than DHCA remains at present speculative. Evidence that this landmark change in neuroprotective strategy for aortic arch surgery in newborns and adults is associated with a more favourable clinical outcome has never been reported in randomized controlled trials. However, if most adult and paediatric cardiac units have abandoned DHCAwithout apparent compromise of patient care, the safety and efficacy of regional perfusion may probably be inferred. The present study is no exception in terms of lack of evidence, as the absence of clinical end-points from the ‘circulatory arrest’ and the ‘regional perfusion’ eras does not allow associating practice changes with superior or noninferior outcome. As for regional perfusion in more detail, adoption of retrograde perfusion remains negligible. It is remarkable, instead, that interest for unilateral antegrade cerebral perfusion and for concomitant visceral perfusion is surfacing in the adult surgical community, similarly to established perfusion strategies in neonatal aortic arch surgery [2–4]. Whether the taboo of unilateral cerebral perfusion due to the inadequacy of collateral flow through the Willis circle in adults will ever be demystified by clinical evidence is presently unknown. Certainly, the current survey is in line with a prior meta-analysis on over 5000 patients, where unilateral or bilateral antegrade cerebral protection proved indifferent in terms of survival and gross neurological outcome [5]. Clear-cut recommendations on selective use of unilateral versus bilateral antegrade perfusion, as well as ideal temperature, flow rate and pressure, cannot be inferred from the survey herein. Thus, judicious use of unilateral perfusion for shorter arrest durations seems only reasonable. As surveys suggest that strategies to protect the adult brain during elective arch surgery start resembling more and more solutions in use for infant arch repair, it must be remembered that advantages in terms of clinical outcome remain to be proved. Whereas patient heterogeneity has thus far hindered acquisition of any evidence in infant neuroprotection and neuromonitoring, except for the favourable influence of an adequate (>24) haematocrit value during bypass [6], an opportunity exists to set up multicentre, randomized, controlled trials in elective and emergent adult arch surgery to advance from mere trends to hard evidence.