**4.4 Postoperative atrial fibrillation**

Rhythm disturbances often accompany cardiac valvular procedures. The reported incidences of postoperative atrial fibrillation (POAF) are from 12.8% to 32.2% [13, 15–17].

## **4.5 Mechanical ventilation**

Mechanical ventilation is significantly shorter in patients undergoing minimally invasive aortic valve surgery (5 vs. 6 h; p = 0.04) [17] and only 4.3% required prolonged ventilation >24 h [16].

### **4.6 Intensive care unit and hospital stay**

Intensive care unit (ICU) and hospital length of stay are perhaps the most evident advantages of minimally invasive aortic valve surgery. Both parameters are shorter in comparison to median sternotomy aortic valve surgery [15]. Semsroth et al. reported a mean duration of ICU to stay 22 h for upper mini-sternotomy and 21 h for ART patients [18]. Although, Ghanta et al. reported longer ICU stays, early discharge defined by discharge by the 4th postoperative day (POD) was achieved in 15.8% in the minimally invasive group compared to only 4.2% in the median sternotomy group (p < 0.01) [17]. About 52.8% of minimally invasive surgery patients are discharged by the 6th POD and only 7.9% have a prolonged stay over 12 days [16].

### **4.7 Acute kidney injury**

Acute kidney injury (AKI) incidence ranges from 1% to 4.7% [16, 17] with hemodialysis from 0.5% to 13.2% [15, 18]. The large differences are a consequence of different AKI definitions and acquired protocols for renal replacement therapy. The highest reported incidence of hemodialysis comes from the report by Semsroth et al. Their explanation lies in the necessity of a preoperative CT imaging for patients receiving minimally invasive aortic valve surgery through ART, as contrast enhancement is nephrotoxic and might increase the risk for AKI [18].

However, a word of caution is proper. Not all patients are suitable for minimally invasive approaches, especially for ART which is technically more demanding. The reported exclusion criteria for ART are concomitant ascending aortic aneurysms, ascending aorta located completely retrosternal or relatively left lateral, pathological calcification of the ascending aorta (soft plaques) or prior cardiac surgery, history of right-sided pleuritis, a deep chest or women with large breasts [10, 19]. On the other hand, this approach is highly beneficial for disabled patients on crutches or those with deformed sternum due to radiation or injury.

### **5. Aortic valve repair and valve-sparing procedures through a minimally invasive approach**

All of the information on minimally invasive approaches so far have been regarding AVR. In recent years, some authors have published their experience with performing aortic valve repair or aortic valve-sparing procedures through minimally invasive approaches.

The Beijing group reported their results in upper mini-sternotomy aortic root surgery. A relatively small sample of 18 patients was matched with an equally large median sternotomy group. There were no differences in the categories of surgery, as aortic root surgery was combined with ascending aorta replacement or aortic arch replacement. Aortic cross-clamp was significantly longer in the minimally invasive group. Regarding postoperative outcomes, fewer transfusions, lower drainage volume, shorter mechanical ventilation time as well as shorter ICU and hospital stay were observed [20].

The ART approach was tested for the treatment of ascending aortic pathology. The Houston group compared 74 patients who operated through an ART with 103 patients with median sternotomy. In a matched cohort, a trend towards longer aortic cross-clamp time as well as significantly higher numbers of the bicuspid aortic valves in the ART group was observed. Again, fewer transfusions, shorter ventilation time, shorter ICU and hospital stay were experienced. Interestingly, short-term mortality was similar between the two groups [21].

A systematic review of the results of the minimally invasive aortic root, ascending aorta or aortic arch performed by the Bristol group revealed similar mortality, decreased length of cardiopulmonary bypass, shorter ICU and hospital stay, fewer reoperations due to bleeding and lower incidence of postoperative AKI in the minimally invasive group. A major limitation of this review is very low-quality non-randomized evidence [22].

The Warsaw group reported their experience with 167 upper mini-sternotomy aortic root or ascending aorta operations. About 49% undergone ascending aortic replacement, 26% a combination of ascending aortic and aortic valve replacement and 25% one of the aortic valve-sparing procedure (reimplantation/remodeling). Short- and long-term mortality was 1% and 5%, respectively. Seven % reoperations for bleeding, 1.7% prolonged ICU stays and 4.8% postoperative AKIs were observed [23].

### **6. Pitfalls in minimally invasive surgery**

As already mentioned in the text above, there are some specific pitfalls encountered in minimally invasive aortic valve surgery. Let us summarize and emphasize the most frequently seen:

