Surgical technique
Surgical technique corresponds to the standard David procedure, with a few exceptions related to the minimal access, and it can be performed without any specialized equipment.2,6,10,13 Upper hemisternotomy (down to the 3rd or 4th intercostal space) is performed to approach the aortic root and ascending aorta. Special care is taken to avoid injury of the right internal thoracic artery and vein. Following systemic heparinization, cardiopulmonary bypass (CPB) is established with central cannulation under mild hypothermia (32-34°C). It may be easier to achieve venous drainage via superior caval vein cannulation rather than right atrium, as it enables better exposure despite the limited access. Also, some surgeons prefer femoral venous cannulation with the Seldinger technique under echocardiographic guidance to provide better exposure of the operative field. In the case that additional drainage is needed, “Y” femoral venous line can be used.16 A CO2 insufflation is used. Left heart is vented via the right upper pulmonary vein. After an aortic cross-clamp (ACC) is applied and aortotomy performed, heart is arrested using direct intermittent antegrade cardioplegia (Buckberg, Del Nido or Custodiol).6,10,13 As multiple cardioplegia redosing might be time-consuming particularly, Custodiol cardioplegia can be beneficial as a single dose can provide up to 90-120 mins of myocardial protection.16
After the transection of the ascending aorta just above the commissures, AV is carefully assessed. Strategically positioned pericardial traction sutures can bring the aorta closer and provide optimal exposure. The aortic root is mobilized in a standard manner, commissural sutures are applied for exposure of the root, and the coronary ostia are excised as buttons (Figure 1). If necessary, aortic valve repair is performed. Sizing of the aortic annulus is performed using Hegar’s dilator and graft diameter is determined by using +2 mm larger size. Interrupted pledgeted Ethibond 2-0 sutures are applied below the AV from the inside out to anchor the graft. Either the Dacron or Valsalva graft can be used for aortic root replacement. The mobilized aortic root with residual free margins of the aortic sinuses is sutured to the inside of the Dacron graft using continuous 4-0 polypropylene sutures. Cor-Knot can be used for securing the graft to facilitate suturing, particularly in the limited space of a mini-sternotomy, although this technology still requires continued surveillance.16
A water-test is performed to assess the coaptation of the reimplanted native AV. Additional AV leaflet repair is performed if needed. The coronary buttons are reinserted using a continuous 5-0 polypropylene suture. Finally, the valve and hemostasis are tested by pressurizing the aortic root with cardioplegia. Meticulous hemostasis is particularly important factor during minimally invasive David procedure.
The distal anastomosis is performed, and the aortic clamp removed after de-airing. AV function is assessed by intraoperative TOE. Complete rewarming of the patient is achieved while in the operating room.
Postoperative management and outcomes
Patients undergoing minimally invasive David procedure can experience faster recovery as expected after minimally invasive surgery. A summary of perioperative data compared to the full sternotomy groups in several studies is available in a Table 1. Interestingly, Charchyan and colleagues reported significantly decreased intraoperative blood loss (710±171 mL vs. 1065±288 mL, p=0.001), 48-hour postoperative drainage (317±101 mL vs. 647±300 mL, p=0.001), mechanical ventilation time (5±1.9 h vs. 9.2±1.3 h, p=0.001) in the group of patients who underwent minimally invasive procedure when compared to the full sternotomy group.15 On the other hand, Shrestha and colleagues reported no difference in mechanical ventilation time, while they observed lower intraoperative need for red blood cells (1.0±1.7 vs. 2.1±1.8 units) in the minimally invasive group.10 In addition, 65% of patients could be operated without any blood transfusions.10 Similarly, Monsefi and colleagues observed significantly lower need for red blood cells in the minimally invasive group (1.6±3 vs. 3.7±6 units, p<0.01) when compared to the full sternotomy group.11 Immediate perioperative anesthetic management individualized to each patient and early extubation represent important adjuncts in the early postoperative care of these patients. Patients require long-life antiplatelet therapy with aspirin, if not contraindicated.3 Repeat transthoracic echocardiography is recommended before discharge. In the event of significant bleeding, re-exploration should be accomplished through the same incision. Importantly, re-exploration for bleeding rate was reported to be lower than in the full sternotomy groups across several studies (Table 1.). 10, 11, 15
 Recent studies reported postoperative clinical outcomes with minimally invasive David procedure comparable to the conventional technique.10-11, 13-16 Postoperative outcomes and characteristics of included studies are demonstrated in a Table 2. 30-day mortality was reported between 0% and 3.3%, although all the published series had a sample size of less than 100 patients.10-11, 13-16 Furthermore, selection of patients might have positively influenced outcomes as minimal access was performed in elective patients with noncalcified aortic valves. Notably, Marfan syndrome was reported in 3.9-18.8% of patients while patients with bicuspid AV in 7.7-38.7% of patients.10-11, 13-16   As these patients present at relatively young age, Shrestha and colleagues report that it could be beneficial to provide minimal access surgery as cosmesis is considered an important factor by these younger patients.10 In addition, it also has the potential to enable faster return to normal activities which is another important factor for younger patients.25
Aortic cross clamp and CPB time ranged from 110.6 to 168.5 minutes and from 139 to 199.5 minutes, respectively.10-11, 13-16 Charchyan and colleagues reported significantly longer ACC and CPB time in the minimally invasive when compared to the full sternotomy group after matching (147±14 vs. 134±31 mins, p=0.044; 130±17 vs. 115±21 mins, p=0.004 respectively), while Shrestha and colleagues found longer ACC and CPB time although the difference was not significant (115.6±30.3 vs 114.1±19.9 mins, 175±8 vs. 163±24.5 mins, respectively).10, 15 On the other hand, Shah and colleagues found no significant differences in ACC and CPB time when compared to the full sternotomy group (169 [155–179] vs. 188 [155–199] min, p=0.128); (200 [183–208] vs. 212 [183–223] min, P=0.309, respectively). However, they have used significantly more Cor-Knot (100% vs. 0%) and Custodiol cardioplegia (94% vs. 37%) in the minimally invasive group to facilitate the procedure and this can explain why the timings were not prolonged in the minimally invasive group.16 However, it seems that this has not negatively influenced postoperative clinical outcomes. Several studies reported decreased requirements for blood products, relatively shorter ICU length of stay (1.1-3 days) and low 30-day stroke rate (0-3.3%).10, 11, 15 Despite the fact that most centers emphasized importance of meticulous hemostasis, re-exploration for bleeding was reported up to 9% in some of the studies.10,11,13
Excellent early echocardiographic outcomes were reported in most studies with postoperative aortic insufficiency (AI) ≤1 observed in 84.6-100% of patients.10, 11, 13, 14, 16 Monsefi and colleagues reported echocardiographic results at mid-term follow-up (3±2 years) and demonstrated excellent findings in 99% of patients, while only one patient had to be reoperated due to severe AI.11 In addition, Hou and colleagues observed that 2 (4.5%) of patients developed moderate or severe AI during the cumulative follow-up of 9±7.8 months.14
In summary, our review of available literature on the topic of minimally invasive David procedure demonstrated that minimally invasive access could facilitate recovery of selected elective patients with isolated aortic root aneurysm along with similar early postoperative outcomes to conventional surgery. However, there are many potential pitfalls in minimally invasive David procedure and recent studies highlighted challenges of the learning curve. Sufficient experience at centers with adequate case volumes in both conventional aortic root surgery and minimal access AVR are necessary before progressing to the next step to avoid potential vulnerability and performance obstacles.