Discussion
The knowledge and experience accumulated by several generations of medical specialists and researchers have led to remarkable decreases in cardiac surgery mortality rates across a wide spectrum of pathologies. However, patients presenting with ATAAD continue to represent a major clinical challenge for cardiovascular specialists. When selecting the appropriate treatment strategy for ATAAD, the modern aortic team has a wide range of surgical techniques, protective adjuncts, and monitoring tools available for any extent of aortic dissection. For correction of the dissected ascending aorta, the most commonly performed intervention is supracoronary aortic replacement with or without concomitant aortic valve replacement [12]. In younger patients with aortic root dissection and / or dilatation combined with aortic valve insufficiency, the method of choice is a valve-sparing technique (i.e. David or Yacoub procedures), provided that the operator is experienced with performing these operations. In those cases in which the aortic valve cusps are not pliable, the operator is not experienced with valve-sparing surgery, the patient is over 60 years of age, or in which prolonged ischemic times should be avoided (eg. patients with comorbidities, malperfusion, or preoperative hemodynamic instability), the Bentall procedure should be performed. Other potential, but less commonly used, approaches to the dissected / enlarged aortic root are replacement of the noncoronary sinus and the ascending aorta (also called 1/3 or “mini” Yacoub) and Florida sleeve operation (i.e. wrapping of the aortic root from the outside).
In the last years, a growing attention to valve-sparing procedures for aortic root pathology has been observed. This approach avoids structural valve degeneration (in comparison to bioprostheses) and anticoagulation (in comparison to mechanical prostheses), and is associated with excellent long-term results when performed by experienced surgeons [13]. When managing ATAAD, however, the primary treatment goal is to save the patient’s life. Valve-sparing procedures – being technically demanding and time-consuming – may be associated with increased operative risks, especially in critically ill patients. Also, these procedures require extensive preparation of the aortic root, which may increase the risk of injuring surrounding structures. Such patient- and operator-dependent issues must be weighed when considering the correct approach to the aortic root in individual ATAAD patients.
Our method of performing the modified Bentall procedure in ATAAD patients has evolved over the years. First of all, changes in types of conduits have been observed with a predominant use of biological valve conduits in recent years. While the decision about conduit type (i.e. mechanical or biological) should optimally be made by the patient and the surgeon together prior to surgery, many ATAAD patients cannot adequately participate in this decision because of neurologic or hemodynamic instability at the time of presentation. Surgeons may have therefore more frequently chosen a bioprosthesis for such patients, particularly in the current era of TAVI valve-in-valve procedures. In addition, the avoidance of postoperative coumadin is a particularly important issue to consider in those patients who will continue to have a perfused false lumen post-ATAAD repair.
We previously implanted many aortic root xenografts in ATAAD patients. However, we noted that porcine xenografts were suboptimal in regards to tissue handling. Aortic homografts (used only in 1 patient), have much better tissue handling characteristics, but are prone to heavy calcification within the first years after implantation [14-15]. Thus, our current procedure of choice for biological aortic root replacement is the use of a stented tissue valve implanted into an aortic graft prosthesis. We prefer to use an Edwards Perimount valve – because of the technical ease of securing its relatively rigid sewing ring to the aortic graft – that is sewn to a Hemashield prosthesis that is 5 mm larger than the Perimount labeled valve size. This suture line is performed with a running 3-0 Prolene (Ethicon, Bridgewater, NJ, USA), leaving a 5-8 mm skirt of Hemashield prosthesis under the sewing ring of the Perimount valve. This skirt is then secured to the native aortic annulus using pledgeted sutures that are placed in the usual fashion. Such a technique enables future redo aortic valve replacement surgery to be performed without remobilization of the coronary buttons, by simply cutting the Prolene suture and removing the stented valve.
The coronary button technique with extensive artery mobilization was used in all cases in the current series, in order to avoid tension on the anastomoses [16]. In the earlier era, dissected walls of coronary arteries were often brought together using glue injected into the false lumen, but this technique has been discontinued at our center because of the risk of tissue necrosis and embolization [17]. In case of coronary artery disruption or extensive dissection, venous graft plasty or coronary bypass surgery (with or without occlusion of the proximal ostium) was performed.
Over the analyzed time-period, we observed an improvement in operative results of aortic root replacement in ATAAD patients. This positive development is surely due to many improvements in perioperative management over time, but may also be a result of total increase of ATAAD cases treated at our institution over time. The mortality rates in the current study are similar to those reported in IRAD and GERAADA (German Registry for Acute Aortic Dissection Type A) outcomes [6, 18]. However, limited comparisons can be made to other ATAAD series for a variety of reasons. The majority of isolated Bentall studies available in the literature report the results either in a mixed aortic pathology population, or in a relatively small group of ATAAD patients with various root interventions [19, 20]. In addition, most ATAAD series include a large number of patients who underwent either very minor (eg. readaptation of the dissected noncoronary sinus layers) or absolutely no aortic root procedures. In addition, younger ATAAD patients and those without malperfusion or cardiopulmonary instability frequently undergo valve-sparing surgery at our institution. Finally, we are very aggressive with surgical management of nearly all ATAAD patients presenting at our center, regardless of age and hemodynamic status. The high-risk nature of our current Bentall patient population can be demonstrated by the fact that one-third had malperfusion of one or more organ systems, 30% were in critical preoperative state, 9% underwent preoperative cardiopulmonary resuscitation, and one-third underwent total arch or elephant trunk replacement. Nonetheless, our outcomes roughly correspond with those reported in the literature, particularly when the analysis is performed in patients with similar preoperative characteristics and distal aortic repair extent [21].
The permanent neurologic deficit rate in the current series was higher (22%) compared to our previous publications on ATAAD, (7) which could be explained by higher rates of preoperative cerebral malperfusion in the Bentall cohort of patients. In addition, one needs to consider that several patients developed permanent paraplegia/paraparesis, which is oftentimes a complication of intercostal artery malperfusion and not of the proximal aortic procedure per se . The rates of perioperative myocardial infarction and low cardiac output syndrome observed in the current study correspond with preoperative coronary malperfusion rates and the number of critically unstable patients. It has also been previously shown that approximately 20% of ATAAD patients have underlying coronary artery disease [22], which was an independent predictor for in-hospital mortality in our patients. This factor, together with critical preoperative state (both reported in our previous ATAAD series) [7] and coronary malperfusion (new predictor), emphasize the challenges presented by our Bentall cohort of ATAAD patients.