Simplified surgical approach to improve surgical outcomes in the center with a small volume of acute type A aortic dissection surgery

1.Introduction

Despite progressively advanced surgical strategy and techniques, surgery for acute type A aortic dissection still has high hospital mortality (12%–22%) and low 5-year survival (59%–66%) [1, 2, 3, 4] including high incidence of postoperative stroke (10%) [2, 3, 4, 5].

Recently antegrade cerebral perfusion for brain protection during circulatory arrest has significantly reduced in-hospital mortality after acute type A aortic dissection surgery [6].

The purpose of this retrospective study was to investigate surgical outcomes associated with simplified surgical approach for acute type A aortic dissection surgery in a center with small number of acute aortic type A dissection operations.

2.Methods

3.Results

The mean cardiopulmonary bypass time was 234 ± 86 min, including the mean cerebral perfusion time of 60 ± 36 min under hypothermic circulatory arrest, and the mean ischemic heart time was 162 ± 59 min. The mean lowest nasopharyngeal temperature was 15.2 ± 2.5∘C (Table 2). In-hospital mortality was 8% (8/99) in all cases; 12% (6/52) during the early 6 years and 4% (2/47) during the last 3 years that had establishment of the simplified surgical strategy (P= 0.27). The causes of the in-hospital death were myocardial infarction or arrhythmia due to coronary ostial injury associated with aortic sinus dissection in 4 patients, uncontrolled bleeding in 2 patients, and mesenteric infarction in 2 patients. Of them, 6 were died within 24 hours after surgery.

Postoperative complications included new stroke in 3 patients (3%), aggravation of previous stroke in 3 patients (3%), and prolonged ventilation > 72 hours in 38 patients (38%) (Table 4). The frequency of postoperative stroke was not different between retrograde and antegrade cerebral perfusions (2/16, 13% vs 4/78, 5%; P= 0.28). There was no paraplegia secondary to spinal cord injury. Postoperative contrast CT angiography was performed in 95% (86/91 survivors) and revealed that 56% (48/86 examiners) had false lumen thrombosis.

Univariate analyses showed that predictive factors for hospital death included preoperative shock, iliac artery involvement, poor preoperative perfusion, retrograde cerebral perfusion, all sinuses’ dissection, and longer cardiopulmonary bypass time (Table 4). Multivariate analysis showed that preoperative shock was an independent predictor of hospital death (relative risk, 9.3; 95% confidence interval 1.6–53.6; P= 0.01) (Table 5).

Between the patients who had HAR and TAR, the TAR group was significantly younger than the HAR group (53 ± 11 y vs 61 ± 14 yr; P< 0.01). Although the TAR group had significantly longer hypothermic circulatory arrest time than the HAR group (92 ± 41 min vs 43 ± 15 minutes; P< 0.001), TAR was not a risk factor for operative death (TAR, 3/32 vs HAR, 5/62; P= 1.00) and the incidences of stroke were similar for the 2 procedures (HAR, 5/62 vs TAR, 1/32; P= 0.75). Patients with additional aortic root surgery (5 replacement or 2 reimplantation) had significantly longer bypass time than those without aortic root surgery (299 ± 130 min vs. 167 ± 56 min, P= 0.04), but the aortic root surgery was not a risk factor of hospital death (0/7 vs 8/92; P= 1.00). Of the patients with aortic root surgery, 2 patients had a coronary occlusion of the right or left coronary artery caused by ostial intima disruption, respectively. Both received interposition of a short vein graft between the trimmed proximal coronary artery and the replaced aortic root.

Figure 1.

Kaplan-Meier curve showing survival after surgery for acute type A aortic dissection.

Between patients that had undergone retrograde and antegrade cerebral perfusions, patients in the two perfusion groups had a similar mean circulatory arrest time (antegrade, 60 ± 34 min: retrograde, 52 ± 39 min; P= 0.25), but the retrograde perfusion group had longer ventilation support compared with the antegrade group (146 ± 125 h vs 74 ± 69 h; P= 0.004).

The median follow-up time was 44 months (range, 4–124 m; mean, 50 ± 36 m), with a complete follow-up of 91 survivors. In all patients, the survival rates at 1 and 5 years after surgery were 88% and 77%, respectively (Fig. 1).

After the first surgery, 3 patients (3%) had aortic reinterventions: 1 patient had resection of a noncoronary sinus aneurysm and graft replacement at 35 months after the first operation, and 2 patients had resection of thoracoabdominal aortic aneurysm at 19 months and 24 months each after the dissection surgery and survived.

4.Discussion

During the 9 years of surgery for aortic dissection, we have tried to unify the surgical protocol as one of the efforts to obtain a low surgical mortality in our institute that had a small volume of acute type A aortic dissection operations. Our patient cohort had an overall in-hospital mortality of 8%. In the 3 years since January 2014, in-hospital mortality decreased to 4%, which is similar to the results of a recent study [13]. These improved outcomes may be secondary to simplified surgical strategy, such as right axillary artery perfusion, sufficient excision of dissected aortic wall, proper approximation of the remaining dissected aortic walls, bilateral selective antegrade cerebral perfusion during circulatory arrest, hemostatic anastomosis, and appropriate use of Carrel or modified Carrel patch technique.

Surgical centers participating in a small volume of aortic dissection operations may show high mortality because of insufficient surgical experiences. During our experience of 9 years, surgical strategy had been unified to improve surgical outcome. The simplified surgical approach has made surgeons more familiar with the operative procedures of acute aortic dissection. Application of different surgical protocols to every case cannot predict the surgical outcome.

We performed ascending aorta clamping and aortic root repair during cooling, confirming absence of malperfusion by monitoring blood pressure in 3 different arterial cannulation sites. With aortic cross-clamping in the middle level of the ascending aorta, we did not see malperfusion sign, even in patients who had the entry site in the ascending aorta.

According to data from the International Registry of Acute Aortic Dissection, independent variables associated with death include advanced age, hypotension, shock, previous heart disease, and preoperative renal, mesenteric or myocardial ischemia [1]. In our study, preoperative unresolved shock was the only independent risk factor of hospital death, but advanced age was not a risk factor. Recently even in octogenarians, surgical outcome was favorable [14].

Total arch replacement for acute aortic dissection was reported to cause hospital mortality, and the main causes of death were neurologic deficits and low cardiac output [2, 4]. The causes of death may be related to inadequate cerebral perfusion and myocardial protection during cardiopulmonary bypass and circulatory arrest. The incidence of temporary and permanent neurologic deficits has been reduced by antegrade cerebral perfusion [15, 16]. Our brain protection method was bilateral selective antegrade cerebral perfusion. The neurologic complications could be reduced by deep hypothermia and integrated antegrade cerebral perfusion during circulatory arrest [15, 17]. Recently, moderate hypothermia (23∘C) has showed less operative mortality and neurologic complications than deep hypothermia (17∘C) in emergent and elective aortic arch surgery [18]. In another study, mild hypothermia (28–30∘C) and antegrade cold blood cerebral perfusion (20∘C) showed low operative mortality without neurologic complications [19]. We used deep hypothermia, but the addition of the antegrade or retrograde cerebral perfusion showed low neurologic deficit, except delayed wakening in patients who had retrograde cerebral perfusion. In future, we should also consider the proper use of mild to moderate hypothermia. Until November 2013, we frequently used retrograde cerebral perfusion with a mean circulatory arrest time of 52 minutes. Retrograde cerebral perfusion did not affect neurologic deficits and hospital mortality rates, but delayed awakening of the patients caused prolonged mechanical ventilation time. Retrograde cerebral perfusion may be safe in the circulatory arrest time < 45 min [20], but in cases that require longer circulatory arrest, antegrade cerebral perfusion should be considered. We thought the unique disadvantage of deep hypothermia associated with cerebral perfusion is extended cardiopulmonary bypass time due to cooling and rewarming times.

Postoperative neurologic complications may be associated with retrograde arterial perfusion from the femoral artery [15, 16]. Compared with femoral artery cannulation for arterial perfusion, right axillary artery cannulation reduced the risk of poor visceral and cerebral perfusion and embolism from the thoraco-abdominal aorta to the brain [21, 22]. Our practice for arterial perfusion in acute aortic dissection surgery is right axillary artery perfusion using an 8-mm vascular graft. However, in patients who have unresolved hypotension, right femoral artery cannulation is inevitable for emergency cardiopulmonary bypass. In these patients, after distal aortic anastomosis of the graft under antegrade cerebral perfusion, we converted the femoral artery perfusion to the antegrade systemic perfusion through a side branch of the aortic graft.

Myocardial protection during cardiac arrest is an important tool to prevent postoperative low cardiac output. The longer the operation time, the more emphasis is placed on myocardial protection [23]. In all cases, we performed retrograde cardioplegia every 20–30 minutes through a 12-Fr catheter, which was directly placed in coronary sinus with a purse-string suture through a short right atriotomy. This method does not require operative interruption for the infusion of cardioplegic solution, and it can induce perfusion of the entire myocardium through the middle cardiac vein by positioning the cannula balloon at the aperture of coronary sinus as possible [24].

In patients who had aortic regurgitation combined with aortic root dilation, aortic root reimplantation or replacement can be aggressively performed according to the pathology of the aortic valve during the initial procedure [13, 25]. Aortic root surgery associated with acute type A aortic dissection surgery did not affect surgical outcomes of acute dissection surgery [13].

We had aortic reintervention in 3 patients only: resection of a sinus aneurysm in 1 patient and resection of descending thoracic aortic aneurysm in 2 patients. Such a low reintervention rate may be due to sufficient resection of the dissected aortic tissues and proper approximation of the dissected aortic walls. In TAR for aortic dissections extending to the thoracoabdominal aorta, we did not use elephant trunk technique because it was difficult to insert the elephant graft into the unexpanded intima of the aortic dissection. Instead, a graft length of 3 cm between the left subclavian artery and the distal aortic anastomotic suture line was left as a clamping site for future descending aortic operations.

Survival rates after surgery are similar in most reports [5, 26, 27], and risk factors for long-term survival included preoperative diabetes, advanced age, and postoperative dialysis [27]. However, our study population had a high survival curve after discharge, probably due to more younger patients in our study and low incidences of risk factors of late death.

Limitations of the present study included retrospective and nonrandomized design and a small number of the study cases. The small sample size and low mortality and morbidity rates can limit the statistical power for evaluating risk factors for events. Because the various parts of the surgical protocol have been simplified step by step at different times, it is difficult to determine an exact time point to compare early and late surgical outcomes. Although our surgical strategy was not modernized, including levels of hypothermia, we tried to perform the acute dissection surgery with reasonable surgical protocol. We achieved reasonable surgical outcomes with deep hypothermia, but recently the improved results were reported with mild to moderate hypothermia, which we need further studies about.

5.Conclusion

Emergent surgery for acute type A aortic dissection yielded acceptable early and intermediate results. Preoperatively uncorrected severe hypotension was an independent risk factor of in-hospital death in acute aortic type A dissection surgery. The causes of postoperative mortality or morbidity could be reduced with improved brain and myocardial protection. Bilateral selective antegrade cerebral perfusion is a reliable way to protect the brain during circulatory arrest. Our surgical strategy, including antegrade systemic arterial perfusion, effective myocardial protection, deep hypothermia and antegrade bilateral cerebral perfusion has been gradually simplified over a period of 9 years. With the simplified surgical approach, we could obtain satisfactory surgical outcomes in a hospital with a small number of type A aortic dissection operations. The majority of in-hospital deaths occurred because of preoperative acute myocardial injury and mesenteric ischemia, which were not related to surgical procedures during the last 3 years.