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.