Eur J Cardiothorac Surg 2007;31:990-997. doi:10.1016/j.ejcts.2007.02.017
Copyright © 2007, European Association for Cardio-Thoracic Surgery. Published by Elsevier B.V. All rights reserved
Diagnosis and management of severe atherosclerosis of the ascending aorta and aortic arch during cardiac surgery: focus on aortic replacement
Bartolo Zingone*,
Elisabetta Rauber,
Giuseppe Gatti,
Aniello Pappalardo,
Bernardo Benussi,
Gabriella Forti,
Umberto Tognolli,
Marco Gabrielli
Cardiovascular Department, Cardiac Surgery Unit, Ospedali Riuniti di Trieste, Italy
Received 21 January 2007;
received in revised form 19 February 2007;
accepted 20 February 2007.
* Corresponding author. Address: 22, vicolo degli Scaglioni, 34141 Trieste, Italy. Tel.: +39 040 3994856; fax: +39 040 3994995. (Email: bartolo.zingone{at}aots.sanita.fvg.it).
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Abstract
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Objective: Severe atherosclerosis of the ascending aorta and arch frequently causes difficulties during heart operations, hindering surgical manoeuvres and potentially leading to systemic embolism. The aim of our study was to assess the safety and effectiveness of replacing the atherosclerotic ascending aorta in this setting. Methods: Aortic atherosclerosis was characterized by epiaortic ultrasonographic scanning in 90.1% of 1927 consecutive adult patients undergoing cardiac operations, and by computed tomographic chest scanning in selected cases. Thirty-six of the 152 patients requiring major derangements from our standard practice due to aortic atherosclerosis underwent replacement of the ascending aorta and constitute the study group. Replacement of the aorta was extended to the arch in 13 cases (36.1%). It was associated with single or multiple valve surgery in 34 patients (94.4%) and with coronary revascularization in 30 (83.3%). Two patients (5.6%) underwent coronary bypass grafting without valve surgery. A cryoablation procedure was associated in three patients with permanent atrial fibrillation. Deep hypothermic circulatory arrest was employed in 34 patients (94.4%), while proximal aortic disease allowed conventional distal crossclamping in 2 cases. The risk of operative mortality was estimated by the logistic EuroSCORE both with and withholding the variable ‘surgery of the thoracic aorta’. All survivors were followed-up for 1–41 months (16 ± 12). Results: Two patients died in the hospital (5.6%) and two during follow-up, for a cumulative survival of 91.3% and 85.6% at 1 and 3 years, respectively (hospital deaths included). The hospital death rate compared favourably with the expected estimates of 25.5% (p
< 0.05) and 10.3% (p
= 0.67) obtained by the EuroSCORE full model and without ‘aortic surgery’, respectively. In-hospital adverse neurologic events occurred in six patients (16.7%), including stroke in one patient (2.8%) and neurocognitive disturbances in five (13.9%), although they were all transient and cleared before discharge. Excess bleeding required re-exploration in four patients (11.1%), and one more patient underwent emergency grafting for acute postoperative coronary occlusion. Ten patients (38.5%) were intubated for longer than 24 h. Conclusion: Despite significant perioperative morbidity, replacement of the severely atherosclerotic aorta is worth consideration to avert expectedly higher death and stroke rates.
Key Words: Aorta • Aortic atherosclerosis • Porcelain aorta • Stroke • Perioperative
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Introduction
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Everything should be made as simple as possible, but not simpler (Albert Einstein).
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1. Introduction
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Atherosclerotic changes of the ascending aortic wall manifest as ‘egg-shell’ calcification, protruding atheromas, liquid intramural disease or any combination thereof [1]. They are frequently found in association with coronary artery or valvular heart disease requiring operation, in which case they heavily interfere with aortic cannulation, cross-clamping, cardioplegia and, eventually, with aortotomy reconstruction and with proximal connections of coronary grafts. Besides that, and of greater relevance to patients, they have the potential to release embolic debris [2] and eventually account for a substantial proportion of perioperative neurologic events [3,4].
Although it is generally agreed that standard surgical procedures are best altered to overcome the risks of manipulating an atherosclerotic aorta, reports on what exactly should be done, and how that should be done, have led so far to uncertain – if not conflicting – results. A consensus indeed has been reached for isolated coronary artery surgery, generally lending itself to an off-pump, ‘no-touch’ procedure [5]. When it comes to valve procedures, however, there seems to be no recognised standard of practice as yet, and assessment of any particular approach is seriously fraught with the possibility that unfavourable results may have gone underreported. Based on considerations on the expected prevalence of the problem and the incongruously limited and controversial evidence reported so far, we felt it worthwhile to review our initial experience with the replacement of the atherosclerotic aorta, as recommended by Wareing and colleagues [6], since its inception in our unit in July 2003.
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2. Patients and methods
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2.1 Patients and selection criteria
In the period July 2003 through November 2006, 152 out of 1927 consecutively operated patients (7.9%) presented with an atherosclerotic ascending aorta for which simply moving the cannulation and/or the cross-clamp site away from the usual sites was deemed inadequate. Significant alterations of the operative strategy in respect to our standards are listed in Table 1
. This study concerns the 36 patients treated by replacement of the ascending aorta and, eventually, the arch. Their demographics and select comorbidities are listed in Table 2
. Patients signed a detailed, informed consent when replacement of the aorta was considered preoperatively. Otherwise they gave a generic consent for technical changes as required by intraoperative findings. Approval for a retrospective data review study was granted by the Ethics Committee at the Ospedali Riuniti di Trieste.
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Table 1 Procedures employed in patients with severe atherosclerosis of ascending aorta (July 2003 through November 2006)
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Patients were selected for aortic replacement on the basis of either a preoperative diagnosis of porcelain aorta or the intraoperative findings at epiaortic ultrasonographic scanning (EAS). Any hint of calcific ascending atherosclerosis by plain chest X-ray or cineangiography led to the performance of chest computed tomographic scan (CT) without contrast medium, in order to assess the extension of calcifications along the aorta and arch branches. Aortic palpation had no role in decisions, as it has long been replaced in our practice by routine intraoperative epiaortic ultrasonographic scanning. The latter was performed in 90.1% of patients in this series with a variety of transducers and machines (7.5-MHz, S8-3, L15-7io and a Sonos 2000 or a Philips HD 11 XE, Royal Philips Electronics, The Netherlands). EAS findings were coded on a 4-level scale of increasing severity and inputted separately for each of 12 ascending aortic segments. A summary score for EAS was computed (with normality = 12 and a theoretical maximum of 48) and a dichotomous variable was created for abnormal aortas, i.e. with at least 1 segment 
grade 3 (where ‘grade 3’ stands for plaques 4 mm thick, or protruding ulcerated atheromas of any size with or without mobile components).
Replacement of the ascending aorta was anticipated in 20 patients based on the extent and severity of calcifications shown by CT imaging. In the remaining 16 cases the decision was prompted by the intraoperative finding of an otherwise unmanageable atheromatous or calcified ascending aorta (n
= 6), eventually shown by EAS to host a mobile component (n
= 8), and because of an extensively calcified ascending aorta and arch distal to a known proximal aortic aneurysm scheduled for resection (n
= 2).
During the study interval aortic replacement for atherosclerosis was employed in only two patients among those submitted to isolated CABG (0.2%) and was mostly required for valve surgery (4.7%), primarily in patients undergoing combined aortic valve and coronary surgery (13.5%, Fig. 1
).
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Fig. 1. Groups of valve procedures with proportions of cases submitted to replacement of the ascending aorta for atherosclerosis. AV, aortic valve surgery; CABG, coronary artery bypass grafting; MV, mitral valve surgery; TV, tricuspid valve surgery.
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2.2 Surgical technique
In 28 patients a site to cannulate the ascending aorta or arch was selected based on EAS findings. Low velocity aortic cannulae were used (Soft-Flow cannula, Terumo Cardiovascular Systems, Ann Arbor, Michigan, or Dispersion cannula, Edwards Lifesciences, Irvine, California) with their tip oriented towards the least involved aortic wall, and eventually repositioned through the aortic graft following aortic reconstruction. In eight patients with unsuitable aorta peripheral cannulation was performed through either the right axillary (n
= 7) or the femoral artery (n
= 1).
With the support of EAS the aorta could be cross-clamped throughout the operation in two patients with proximal disease. In the 34 remaining patients deep hypothermic circulatory arrest (DHCA) was required. In six patients the ascending aorta was temporarily occluded though the operation could not be completed without circulatory arrest due to a large, mobile atheroma in the distal ascending aorta (one), plaque rupture from a balloon endoclamp (one), difficulties with aortotomy reconstruction (two) and lack of a suitable edge for suturing downstream a proximal ascending aneurysm (two). In 28 patients no aortic occlusion was employed before DHCA.
Under circulatory arrest the ascending aorta was opened and carefully inspected from inside. It was then distally transected in a stepwise, conservative manner until a satisfactory stump was reached and/or atheromas with mobile components had been resected. In the majority of cases the resection could be limited to the ascending segment, though it had to be extended through the mid or full arch in eight and five patients, respectively. Among the latter, a strip bearing the arch branches could be left in continuity with the descending aorta in the two patients with ascending aneurysm, while in three more cases the aorta was transected past the left subclavian artery on appreciation of the involvement of the arch branches (Fig. 2
).
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Fig. 2. Surgical specimen portraying arch vessels with severe atherosclerosis. This patient was scheduled for mitral and tricuspid valve surgery plus coronary revascularization and was diagnosed ascending aortic disease on preoperative work-up. Epiaortic ultrasonographic scanning identified, in addition, a large protruding atheroma with a mobile component (arrow) at the origin of the brachiocephalic artery. With deep hypothermia, circulatory arrest and retrograde cerebral perfusion the arch was first resected past the brachiocephalic trunk and then further downstream on appreciation of carotid and subclavian involvement. Proximal arch branches were also resected to normal tissue and reconstructed with interposition grafts before catheterization for antegrade brain perfusion. Arch reconstruction was then performed and the operation successfully completed as planned. The patient was discharged on postoperative day 21.
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A properly sized Hemashield vascular graft (Boston Scientific, Natick, Massachussets) was then anastomosed to the distal aortic stump with a continuous monofilament 3/0 suture, taking large bites away from the aortic edge and ensuring that the graft was telescoped inside the aorta so as to cover intimal irregularities. If a plaque was raised during suturing additional, widely spaced figure of eight sutures were placed. In three cases with full arch replacement the origins of arch branches were resected and individually reconstructed by short interposition grafts. One patient was treated by the elephant trunk technique due to a descending aortic aneurysm.
After thorough de-airing systemic perfusion was resumed and the patient slowly rewarmed. The valve procedures were then completed and coronary arteries grafted as needed. Finally, the aortic graft was anastomosed to either the sinotubular junction (n
= 32), a valved conduit (n
= 2) or to the sinuses underneath the right coronary ostium (n
= 2). Further details of cardiac procedures are presented in Table 3
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2.3 Cerebral and cardiac protection
Brain protection during DHCA varied (Table 4
). No particular measure was undertaken in one patient who underwent a 34 min circulatory arrest at 16 °C. Eight patients had the brain perfused antegrade by either the axillary route (one case, with the innominate artery clamped after inspection from inside) or by selectively perfusing the brachio-cephalic artery alone (one case) or together with the left carotid artery. Twenty-five patients were managed by retrograde superior vena cava perfusion during DHCA. Four of them were eventually switched to antegrade perfusion due to prolongation of the arrest time.
Cold blood cardioplegia was administered at 20–30 min intervals retrograde through the coronary sinus in all cases. Antegrade administration through the coronary ostia was only performed when they were devoid of disease, otherwise saphenous vein coronary bypass grafts, if any, were perfused instead.
2.4 Data acquisition and analysis
Clinical, procedural and postoperative data were prospectively recorded into a divisional, supervised database and retrieved for this retrospective review. Deaths occurring at any time during the hospital stay or anywhere within 30 days since surgery were categorized as early deaths. Stroke was defined as a new focal neurologic deficit or coma appearing during the post-operative stay, and at least partially evident more than 24 h after its onset. Non-focal neurological derangements, such as confusion and psychosis, were recorded as neurocognitive defects. Neurologic assessment was performed by trained intensivists supported by consulting neurologists if necessary. Individual probabilities of death were computed by the EuroSCORE logistic model both with and withholding the variable ‘surgery of the thoracic aorta’. The latter estimated the risk of the core procedure as if the aorta were normal and would not require attention.
Follow-up phone interviews were conducted by the authors early in January 2007. Descriptive statistics, two-tailed Pearson's chi-square or Fisher's exact test as appropriate and Kaplan–Meier survival curves were developed by SPSS 14.0 (SPSS Inc., Chicago, Illinois).
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3. Results
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3.1 Early results: hospital mortality
Two patients (5.6%) died on the second postoperative day from severe respiratory failure and cardiogenic shock, respectively. In neither case did post-mortem examination provide any additional information.
3.2 Early results: operative times and complications
Extracorporeal perfusion and cardiac ischemia times averaged 203 ± 58 and 168 ± 42 min, respectively. Duration of circulatory arrest and brain perfusion management during DHCA are shown in Table 4. Postoperative blood losses averaged 731 ± 731 ml/m2 (median 396, range 137–2998 ml/m2), and reoperation for excessive bleeding was required in four cases (11.1%). Length of stay in the intensive care unit and total postoperative hospital stay for survivors averaged 3.9 ± 3.3 and 15.3 ± 7.8 days, respectively.
There were six patients with central neurologic complications (16.7%) but no case of permanent brain damage. One patient (2.8%) exhibited a right hemiparesis on delayed awakening though the CT scan did not show any abnormality and symptoms cleared before discharge. Transient agitation and psychosis of milder degree were noted in five patients. Right upper limb dysfunction attributed to inadvertent nervous injury during mobilization of the right axillary artery was recorded in one case.
Complete heart block requiring pace-maker implantation occurred in one patient (2.8%) and perioperative myocardial infarction in two more (5.6%).
The left ventricular ejection fraction at pre-discharge echocardiography, on average, did not change significantly from baseline in the 34 survivors. In greater detail, it decreased from 58 ± 8 to 50 ± 10% in 7 patients, increased from 42 ± 12 to 55 ± 15% in 12 patients and changed less than 4% points in the remaining cases, all but one within normal limits. Notwithstanding, low-dose dobutamine was employed in the majority of patients and a dose greater than 5 µg/kg/min was temporarily required in 10 patients (34.5%).
Time on respirator averaged 39 ± 53 h, and lasted longer than 24 and 48 h in 10 (38.5%) and 6 (16.7%) patients, respectively.
Serum creatinine frequently increased after surgery and in seven cases (19.4%) more than doubled its preoperative value. It then returned to baseline levels with no need for extracorporeal filtration in any patient.
3.3 Late results
Follow-up was obtained in the 34 discharged patients at a mean interval of 16 ± 12 months after surgery (1–41 months, 572 patient-months). Two late deaths occurred at 4 and 17 months due to diabetic coma and probable myocardial infarction, respectively, leading to an actuarial survival of 91.3% and 85.6% at 1 and 3 years, hospital deaths included (Fig. 3
). The patient with the elephant trunk prosthesis successfully underwent the second stage procedure 3 months later. One patient experienced a right-sided hemiparesis during a febrile illness in connection with suspected endocarditis. Four patients had dyspnoea on mild effort (NYHA class 3), though the left ventricular ejection fraction was normal in all and had actually improved compared with preoperative in two of them. One more patient complained of mild angina. Overall, among survivors, 56% were asymptomatic and 34% only had mild dyspnoea on effort.
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4. Discussion
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The incidence of a significantly atherosclerotic aorta has been reported to vary widely from 1.2% to 28% of the cardiac surgical population [1,6–10], depending on the definition of ‘significant’ pathology, on the sensitivity of the diagnostic methods, and, to a certain extent, on the subset of procedures considered. A higher prevalence of atheromas has generally been detected when epiaortic scanning was systematically used [6,7]. We found at least 1 of 12 ascending aortic segments with severe atheromas in 21.4% of 690 nearly consecutive, unselected patients submitted to epiaortic scan [11]. Quite pertinent to this discussion, that rate rose to 54.1% in the subset of combined aortic valve replacement and CABG, largely higher than in any other procedural subset. Incidentally, this was also the setting in which replacement of the ascending aorta was more frequently required during the time frame of this study.
Several studies have established the role of the atherosclerotic aorta as a precursor of brain embolism during cardiac operations [2–4,6,7,11,12]. It is worth emphasizing that stroke rates as high as 7.4–8.4% have been recorded following combined valve and coronary procedures in otherwise unselected patients managed according to aortic palpation [13,14]. Stern and colleagues [12] reported a stroke rate of 11.6% in 225 patients with severe arch atheromas detected by trans-esophageal echocardiography and mostly submitted to coronary revascularization by conventional techniques. What rates would be observed as a consequence of casual aortic manipulation in selected patients with ascending aortic atherosclerosis undergoing valve surgery is only subject to speculation as it has never been reported, nor will it likely ever be. Thus, both the prevalence of the disease and its role as a precursor of perioperative embolism [2], and of perioperative strokes in particular [2–4,6,7,11,12], point to the importance of accurate screening and proper surgical management of this condition. In fact, no operative complication carries more devastating sequelae than stroke, which also heavily contributes to operative mortality [11,13,14]. In addition, perioperative embolism probably occurs more often than clinically signalled by stroke events, particularly following aortic valve procedures [15], and may explain a significant proportion of cognitive disturbances [4] previously regarded as transient and benign. Thus, an overwhelming evidence on the prevalence of ascending aortic atherosclerosis and on its role as a precursor of brain injury and death direly combines with the growing proportion of elderly patients requiring aortic valve surgery eventually associated with coronary revascularization. Every effort is therefore justified to develop effective surgical manoeuvres to prevent systemic embolism.
4.1 Management options for extensive aortic atherosclerosis
There is probably no single way of dealing with all bad ascending aortas. Moving cannulations and cross-clamping away from the involved sites may suffice when the disease is well localized [1]. Isolated revascularization can be carried out without cardiopulmonary bypass, or at least without cross-clamping, while in situ arterial grafts help avoiding aortic connections and may also act as a source for additional conduits [1,5]. Mitral procedures, on the other hand, can also be performed without aortic cross-clamping by lowering body temperature and perfusion flow and pressure, so as to relax structures and minimize retraction-induced aortic regurgitation. It is when the aortic valve needs to be replaced that the greatest derangement from usual techniques is in order, because aortic cross-clamping can only be avoided by arresting the circulation under hypothermia.
Quite understandably, there may be some reluctance to considering DHCA in the setting of advanced age, frequently with significant comorbidities, facing a combined valve and coronary procedure. The perception of increasing, in so doing, the length and the complexity of the operation, and therefore the operative risk, is certainly well-grounded. Predicted mortality in our series was in fact quite high even simulating the absence of aortic replacement, and further increased when accounting for aortic replacement as well. Yet, the risk of ignoring the aortic problem may be even higher, while the protection offered by minor deviations from standard procedures as prompted by epiaortic scanning has proved to be largely incomplete [6,7]. An appealing strategy to keep close to standard plans would combine axillary artery cannulation and endoaortic balloon occlusion, though our own unfavourable experience with endoaortic occlusion has lead us to abandon this particular technique [16].
DHCA thus emerges as the core method to approach the truly bad aortas during aortic valve surgery, and may also be necessary in other settings when an aortotomy is not strictly required. Which specific technique yields the greatest chances of success remains a moot question however. Conceptually at least, the simplest approach appears to be that of replacing the aortic valve during DHCA without an aortic cross-clamp [8,9,17–19] (Table 5
). Coronary bypass, if needed, can be fashioned during cooling while the left ventricle is vented and perfusion flow is temporarily lowered as needed to lift the heart. Time constraints, however, may negatively affect the surgeon's accuracy in minimizing and carefully retrieving all debris from the aortic wall and annulus. In fact this technique is associated with a significant incidence of adverse events and has gained little popularity [8,9].
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Table 5 Operative management of atherosclerotic aorta during valve surgery. Relevant literature and main outcomes
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An alternative option is to proceed with aortic endarterectomy preliminary to aortic cross-clamping [8–10,12,20,21] (Table 5). With the notable exception of the series reported by Vogt and colleagues [10], however, results have generally been poor (Table 5). In particular, the alarming stroke rate following endarterectomy reported by Stern and colleagues [12] may have been partly due to their focusing on arch debridement, although one may wonder whether their choice of threading a long aortic perfusion cannula through the arch may have contributed as well. Also, the often posed question as to the fate of the endarterectomised aorta remains so far unanswered.
Finally, a more radical approach of replacing the atherosclerotic ascending aorta under DHCA has been first reported by Wareing and colleagues [6] and succinctly updated by Kouchoukos [24]. Their original technique included peripheral arterial cannulation, avoidance of any aortic manipulation prior to circulatory arrest, and crossclamping the tube graft following completion of the distal anastomosis. Coronary grafts, when needed, were fashioned during the cooling period, while proximal anastomoses and eventual valve procedures were carried out while rewarming. Results have again been variable [6,8,9,22–24], with a mortality rate collectively similar to other techniques and a trend for a lower stroke rate (Table 5).
A number of reasons help understanding the wide variation of outcomes across the studies. In principle, outcomes in small series of high-risk patients submitted to complex procedures may be intrinsically unstable due to chance variation. At least as importantly, a whole host of technical details may further act as confounders. Aortic cannulation at soft spots for instance, as reported in the majority of series, is associated with a higher risk of complications compared with axillary artery cannulation [25]. Use of EAS may help selecting a safe site with greater chances of success compared with simple palpation or to blind ‘distal arch’ cannulation, though its use has not been uniform across the studies. We would also regard threading a long cannula along the arch as an hazardous manoeuvre despite real-time echo monitoring, and the risk of dislodging embolic material may be further compounded by the subsequent counter-current perfusion of the atheromatous arch. A similarly hazardous choice may be femoral cannulation, as most of these patients present with advanced arteriopathy. Temporary aortic occlusion, eventually using an endoaortic balloon, is a further detail whose results have been conflicting [10,16] and may contribute to failures. Brain perfusion by arterial catheters, or clamping the innominate artery when the axillary artery is cannulated, are only safe under well selected, favourable circumstances. In many patients, coexisting disease at the origin of arch branches makes their casual manipulation quite dangerous.
4.2 Current study
In our small series of relatively heterogeneous conditions is also embedded our learning curve with replacement of atherosclerotic aorta and the multiple subtle changes in technical details evolved during the study interval. Therefore, much as for other published series, it cannot support strong conclusions. Notwithstanding, chances being low that a properly designed prospective trial will ever be set up to provide a better evidence, we felt it worthwhile contributing with a few comments.
The first issue pertains to the selection criteria for ascending aortic replacement, which remain largely subjective. No patient in our series was treated by aortic replacement without having at least one aortic segment involved by a severe atheroma as prospectively defined, though that only emerged retrospectively. Also, rather than a measure in itself, it probably stands out to signal a more extensive disease along the aorta, while its being compatible or not with conventional procedures or with just minor modifications thereof was left to the surgeon's decision. Although it is difficult to establish firm selection criteria, it is now obvious that only accurate diagnosis by epiaortic scanning can support such a difficult decision and should therefore be implemented as a standard of practice [11].
Overall, a diagnosis of significant aortic atherosclerosis could be established preoperatively in the majority of our patients due to the extent of aortic calcifications. At the same time, EAS was instrumental in identifying protruding atheromas not shown by preoperative investigations, additionally demonstrating large mobile components in 22% of cases. On the other hand, it is also possible that a ‘permissive’ interpretation of EAS findings to select aortic cannulation and occlusion sites may have played a role in generating neurologic complications in our series. In fact, five of the six patients involved had aortic cannulation and two, including the single case with transient hemiparesis, had in addition their aorta occluded preliminary to circulatory arrest. In retrospect, we might have underestimated the potential of injuring atheromas close to the healthy aortic sites identified by the ultrasonographic scan. Consideration should in fact be given to the possibility of blast injury from the arterial perfusion jet, a risk perhaps not completely controlled by the special low-velocity cannulae used in this series. Orienting the cannula tip towards the best preserved aortic wall may be useful though axillary cannulation is probably a safer alternative and we plan to use it more frequently than hitherto. Crossclamping a healthy aortic circumference, on the other hand, alters the aortic curvature in adjacent areas as well and may therefore fracture atheromatous plaques nearby without necessarily crushing them directly, eventually leading to distal embolism. For this reason temporary aortic occlusion has been sparingly used early in this series and then abandoned, as initially recommended by Wareing and colleagues [6].
Antegrade selective perfusion for brain protection during DHCA in this setting also evokes the risk of embolism due to inadvertent trauma to diseased arch branches. Indeed our patients with adverse neurologic events shared both aortic cannulation and selective cerebral perfusion as a potential mechanism of brain injury, making it impossible to decide which of them contributed most. It is therefore fortunate that ascending aortic reconstruction could be accomplished in most cases within the safe time limits allowed by deep hypothermia and venous retroperfusion alone, with the arterial back-flow minimizing the risk of debris and air embolism. When supra-aortic branches also had to be reimplanted they were first resected and reconstructed by small interposition grafts during venous retroperfusion. The grafts, and not the arteries themselves, were then cannulated and perfused antegrade during subsequent arch reconstruction. So we have come to rely on antegrade perfusion only in those few cases who require reimplantation of arch branches.
The rates of death and stroke were quite low in our series, supporting the safety of aortic replacement in this setting. Although the 5.6% mortality rate was not negligible, it was lower than the expected 25.5% estimated by EuroSCORE and also lower, though only numerically so, than the 10.3% estimate with the aortic procedure withheld from the model. The stroke rate was also low at 2.8% though there is no reference to compare it with but the emotional expectation of what could have happened otherwise.
On the other hand, an alternative and more thorough assessment of outcomes in our series points to the frequent occurrence of multiple serious postoperative complications. However transient, adverse neurologic events occurred in 16.7% of our patients. Excess bleeding, temporary renal impairment and prolonged intubation time were recorded in a substantial proportion of cases, and perhaps it was only fortunate that more patients were not brought on a less favourable course. Still, albeit in the short-term, survival was stable with no new neurologic events, and the majority of patients enjoyed a satisfactory functional status.
4.3 Future developments and new technologies
Intra-aortic filtration has been shown to be effective in retrieving particulate material released anywhere upstream, though at best incompletely so in preventing neurologic injury. In its present format it requires that the distal ascending aorta and proximal arch can be safely cannulated, crossclamped and instrumented with the filtering device, all of which are hardly compatible with extensive atherosclerosis as discussed herein. As a matter of fact the currently available device is not intended for use in classic porcelain aorta.
Apico-aortic conduits have also been revived in order to circumvent the ascending aortic difficulties by a somewhat less-invasive approach through the left chest. It is too early to say whether connections to the descending thoracic aorta, generally involved with more advanced disease compared with the ascending segment, will make this approach reproducible and dependable, but this option is certainly worth further study.
Finally, it is only pertinent to note that emerging new technologies exploring the endovascular approach may find the atherosclerotic aortic model particularly suitable for their application. Eventually combined with percutaneous coronary intervention, they promise to avoid the risks of aortic cannulation and crossclamping, not to mention the omission of extracorporeal circulation. The transventricular approach in particular can obviate the problem of instrumenting bad aortas with stiff devices and may be worth a prospective comparative assessment with alternative methods.
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5. Conclusion
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Replacement of the ascending aorta under deep hypothermic circulatory arrest has a long-established role in the management of chronic aneurysms and acute aortic syndromes. It can also be readily applied to the treatment of the severely atherosclerotic aorta during valve surgery and compares quite favourably with available alternatives in regard of neurologic injury. The results from small retrospective, uncontrolled studies such as our own and the few more reported so far should be interpreted with caution, and the possibility of negative results going unreported should not be discounted. Still, they encourage the adoption of aortic resection and grafting as a comparatively safe and effective strategy for managing the severely atherosclerotic aorta during cardiac surgery.
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Abstract
Introduction
