Organic malperfusion is a condition associated with acute Type A aortic syndrome that greatly complicates survival. Given that this pathology is dynamic and time is crucial for survival, we must address it comprehensively from the preoperative to the first hours/days of the immediate postoperative period. In fact, malperfusion can persist even after achieving successful repair of the aortic entry site. And, what may be even more concerning, it can be caused by redirecting the flow to the true lumen when some structures depended on their perfusion through the false lumen. Although this scenario is less common, it is not impossible.

The TEM classification, which has already been discussed in detail in previous blog entries, refers to the presence of malperfusion systematizing it with values for the M element (malperfusion) at 0: absent, 1: coronary, 2: of supra-aortic trunks, and 3: spinal, visceral and/or lower limbs. This classification adds nuances (+) or (-) depending on the presence of compatible clinical signs or that, during the exploration/anamnesis, the patient does not show them. It is a dynamic entity so we must always keep in mind that, what we have assessed in the tomographic study is not necessarily the exact situation we will face during the intervention minutes or even hours later.

The mechanisms by which malperfusion occurs are classified into static and dynamic. The former arise from an occlusion of the true lumen of the vessel by progression of the dissection in it and pressurization of the false lumen, generally in a cul-de-sac, which obliterates the flow in it. The dynamic form has two variants: the first understands a mechanism analogous to the previous one, but without complete obliteration of the flow, rather causing a critical or variable stenosis depending on the pressurization of the false lumen and the demands of the tributary territory; the second consists of a gate mechanism where the middle-intimal flap occludes the ostium of a collateral branch at its origin, like a cap, which can be reversible with a new balance of pressures between both lumens. Vessel thrombosis due to low flow and/or progression of native disease, generally atherosclerotic, will lead to a situation of fixed malperfusion, which can evolve from a previously dynamic one.

Coronary malperfusion must be corrected at the time of the intervention. To this effect, there is a little-used classification that systematizes it into A: ostial dissection without affecting the proximal vessel path of the right and/or left coronary, B: ostial dissection that extends through the proximal vessel, and C: rupture of the continuity of the middle-intimal membrane that separates the lumens of the affected coronary vessel. Situation C usually occurs at the level of the ostium and is necessarily corrected by coronary bypass. In the case of form A, mere obliteration of the false lumen with the reconstruction of the root (use of sealants, commissural resuspension of the aortic valve, and proximal anastomosis of the supracoronary conduit) are usually sufficient. Form B is the most doubtful and may be a candidate for repair by bypass, an attitude that can be taken from the outset or if the patient presents early ischemic changes from the emancipation of the extracorporeal circulation until the immediate postoperative period.

Cerebral malperfusion can present clinically from early stages of the dissection in the form of syncope or neurological deficits. Depending on the time elapsed and the degree of involvement, they can compromise the patient’s viability given the low tolerance of the nervous system to ischemia, making them irreversible and even worsening (hemorrhagic transformation e.g.) after correcting the dissection. On the other hand, it can be caused after redirecting the flow to the true lumen or, more frequently, by the creation of new entry points and, therefore, pressure balances in the manipulation of the supra-aortic trunks for its control, cerebral perfusion, etc.

Finally, M3 perfusion encompasses all that which may affect being tributary of the descending aorta. This is usually the most larval appearance, especially the spinal and, above all, the mesenteric forms. That of the limbs usually presents a better solution, through the performance of derivations. It is common for the affectation to predominantly involve one limb by extension of the dissection to the iliac or femoral vessels, being the best solution the performance of a femoro-femoral bypass from the contralateral donor territory. However, the main value of the affectation of the lower limbs lies in that it acts as a strong predictor of future malperfusion problems at the mesenteric level that have not yet manifested clinical signs.

The authors of the work describe their experience (University of Pittsburgh Medical Center) in the treatment of Type A aortic dissection. Regarding the surgical technique, the authors propose a quite particular approach. First, they prefer the initial perfusion by direct cannulation with Seldiger technique of the true lumen in the ascending aorta (technique recently analyzed in our blog). Criteria for exclusion from this approach are those described by other authors who carry out the same procedure with circumferential dissection, complex entry points in the aortic arch, and/or the presence of rupture or threatening signs of the same. Cerebral monitoring was carried out using INVOS and BIS systematically, performing cerebral protection by retrograde. This form of perfusion, in general more in disuse than antegrade perfusion in the last decade, has been revisited by different groups for its benefits in the prevention of embolism and by the absence of manipulation of the supra-aortic trunks as a source of embolism or creation of new reentries, which agree with the previously argued. The technique of choice was the replacement of the suprasinus ascending aorta and hemiarch. They only proposed the need to perform a complete replacement of the aortic arch in the presence of entry points in the aortic arch at its greater curvature, the presence of previous aneurysmatic pathology of the aortic arch, the circumferential dissection of the aortic arch or the presence of carotid dissection as a cause of cerebral malperfusion, with or without the presence of carotid thrombosis. In the case of procedures for complete replacement of the aortic arch, antegrade cerebral protection was carried out in order to achieve a situation closer to physiological in procedures with longer circulatory arrest times. The anastomosis of the trunks would be carried out extraanatomically to a trifurcated prosthesis, sequentially and interrupting the perfusion intermittently.

The authors’ experience is summarized in the period between 2010 and 2018. During the same, 467 patients were operated on, 332 of whom (71.1%) did not present malperfusion syndrome and 135 (28.9%) did. Of those who presented malperfusion, 71.9% presented only one affected territory, while 17.8% presented two and 10.4% 3 or more territories. The most frequent form was iliofemoral involvement (n = 63), followed by cerebral (n = 51), coronary (n = 29), renal (n = 26), visceral (n = 13), and spinal (n = 6). Regarding the clinical situation, they use another, also little widespread, classification of the University of Pennsylvania consisting of class a: hemodynamic stability without signs of malperfusion (48.8% in the study), class b: hemodynamic stability with signs of local malperfusion (19.7%), class c: hemodynamic instability with tamponade, rupture or shock (24.4%). This classification makes sense since none takes into account the hemodynamic situation with which the patient is intervened, with marked prognostic sense and that, in the presence of hemodynamic compromise, it is more likely that they will worsen or that situations of malperfusion that would be detected in non-gravity contexts pass unnoticed. Indeed, 7.1% of the patients were classified in class b and transitioned to c during the evolution.

With all this, hospital mortality was 10.3%. However, this presented significant differences between patients who presented with malperfusion and those who did not (21.5% vs. 5.7%, p < 0.001), with the corresponding results of greater morbidity and hospital stays associated with a worse initial clinical condition. Indeed, the presence of malperfusion in any of its forms was identified as an independent risk factor for hospital mortality (HR 2.43, p < 0.001). Likewise, the number of territories affected by malperfusion correlated with a worse prognosis.

The authors conclude that the malperfusion syndrome is associated with higher mortality of patients operated on for acute Type A aortic syndrome and that this risk is proportional to the number of vascular territories involved.

COMMENTARY:

The acute Type A aortic syndrome, particularly in its form of dissection, is a devastating pathology that threatens the life of the patient. The correction constitutes nothing more than a palliation where the correction of the flows between the lumens seeks, at the proximal level, to prevent progression to the root that would cause the patient’s death by cardiac failure due to aortic insufficiency, coronary malperfusion, and/or cardiac tamponade. At the distal level, it aims to rebalance the pressures between the lumens and protect from the malperfusion that there is, is, or is going to take place.

The results exposed in this study are absolutely enviable, describing just over 5% mortality in patients without the presence of malperfusion syndrome. They can be explained by a remarkable mastery in the treatment of this involvement, which translates into an average of almost 60 cases per year and a greater aggressiveness in the indications for approaching the aortic arch. Precisely, this is the key aspect of the work, the results of more aggressive criteria than usual, to preferably consider surgery for replacement of the aortic arch over the hemiarch. And it is that, the presence of an entry point at the greater curvature of the arch has traditionally been the main indication, but the other three have been reason for a more conservative attitude, considering the hemiarch procedure sufficient to save the patient’s life. With this approach, the authors try to minimize in the surgical act the two problems of malperfusion that, either are present, or can present in the immediate postoperative: coronary and cerebral ischemia. This greater technical aggressiveness did not translate into an increase in postoperative morbidity and mortality, as traditionally considered. In this way, they leave the M3 type malperfusion, of a more larval presentation and with possibilities of short-term treatment, for a deferred approach if necessary, generally by endovascular procedures that, probably due to the low frequency of the same, do not provide details of their frequency. However, due to their aggressiveness with the approach to the aortic arch, they perform a significantly higher number of substitutions of the same in patients with malperfusion (28.6 vs. 48.9%, p < 0.001), with no differences in the techniques of “lax” or “frozen” elephant trunk that ranged between 6-8% and 7-10%, respectively. They also performed up to 20-23% of the cases, procedures for reimplantation of the aortic root.

In short, Type A aortic dissection teaches us that it is a dynamic pathology, so, “what we operate is not necessarily what we thought and what happens is not necessarily what we expected to leave”. Around all this uncertainty is the malperfusion, one of the main causes of morbidity-mortality of the patients intervened, even with a theoretical successful repair of the entry point in the ascending aorta. Considering extending the procedures to the aortic arch seems, along with the new trends in cannulation already commented, a new approach as to address this pathology and that contravene classical principles previously taken for granted. Yes, a greater surgical complexity may be accompanied by morbidity-mortality that could counteract the expected results, especially if the necessary experience and volume are not available, as we are discussing in this analysis. Intermediate solutions can be the application of devices like the AMDS prosthesis, which allows a more conservative approach (replacement of the ascending aorta without hemiarch in the absence of an entry point in it) and which is specially designed for the correction of cerebral and distal malperfusion by means of obliterating the false light with the implantation of an open-cell stent. Until then, we only have prudence and good practice, without losing sight of the silent killer that is malperfusion.

REFERENCE:

Brown JA, Aranda-Michel E, Navid F, Serna-Gallegos D, Thoma F, et al. Outcomes of emergency surgery for acute type A aortic dissection complicated by malperfusion syndrome. J Thorac Cardiovasc Surg. 2024 Mar;167(3):882-892.e2. doi: 10.1016/j.jtcvs.2022.04.051.