Frozen elephant trunk in acute type A aortic dissections: frontiers and challenges

Abstract

Acute type A aortic dissection (ATAAD), a surgical emergency, has high mortality and morbidity. More than half of the patients die within 2 weeks and the 30-day mortality is 90%. Frozen elephant trunk in ATAAD addresses the primary and secondary goals — resection of the primary tear in the ascending aorta and promoting remodelling in the downstream aorta. Though the literature supports this fact, in reality these literatures emerge from high-volume centres. But in the “real world” most of the ATAAD are operated on in the low-volume centres. Furthermore, in India, there are unique challenges including the financial burden, transport, emergent availability of the hybrid prosthesis and aortic supercentres.

Introduction

Acute type A aortic dissection (ATAAD), the most common surgical aortic emergency, is burdened by high mortality and morbidity. Masuda et al. had demonstrated the dismal prognosis of this disease; if treated medically, the survival rates at 24 h and 2 weeks were 72% and 43% respectively [1]. The 30-day mortality is as high as 90% in these patients [2]. Though no randomized clinical trial exists for this dreadful clinical condition, analysis for various clinical experiences establishes that emergent surgical interventions are the only option available to modify the dismal natural history of ATAAD to a 70–80% chance of survival [1]. The mainstay of the surgical treatment is resection of the entry point in the ascending aorta and directing the blood from the left ventricle into the true lumen. Over the last 25–30 years, there has been considerable improvement in morbidity and mortality in patients who undergo surgical repair for ATAAD at high-volume centres [3]. A positive volume-outcome relationship in regard to mortality has been demonstrated by multiple studies [4, 5]. With the incidence of morbidity and mortality continuing to remain stable across the high-volume centres, the present debate is being shifted to the optimal management of the aortic arch and descending thoracic aorta in ATAAD. While few centres argue to reduce the operative and postoperative morbidity and mortality, performing a limited arch procedure, others justify an extended arch repair/frozen elephant trunk (FET) to mitigate the risk of patent false lumen.

FET in ATAAD: raison d'être

FET has been in use for aortic pathologies for the last decade and a half. Though initially it was presumed that it was an industry-driven technology use, as more literature emerge, it is now evident that FET has multiple advantages over the limited resection surgeries.

The primary goal of the ATAAD is resection of the primary tear in the ascending aorta with replacement of the ascending aorta and directing blood to the true lumen. Emergent repair of the proximal aorta let fall between the cracks the fact that nearly one-third of the patients have an additional tear in the aortic arch of the proximal descending aorta [6]. Though the primary goal is achieved, nearly two-thirds of the patients have a patent distal false lumen (FL), which accounts for future complications like compression of the true lumen (TL) by the dilated FL, malperfusion or rupture in the range of up to 30% within 10 years [7–9]. Surgeons from South Korea analysed 122 ATAAD patients postoperatively. They demonstrated a high incidence of descending aortic dilatation during follow-up in these patients. The group identified patent FL and a relatively larger size of FL in regard to TL as significant risk factors for dilation [10]. Fattori et al. demonstrated that patent FL is a significant risk factor for the dilation of the distal aorta (3.7 mm/year as compared to 1.1 mm/year) [11]. Hence, the secondary goal of ATAAD repair is to promote remodelling in the downstream aorta to avoid further intervention and complication.

FET in ATAAD seems to achieve the primary and secondary goals. The endograft in the descending aorta expands the TL and seals the additional entry points in the aortic arch and proximal descending aorta, prompting FL thrombosis. This reduces the late complications of ATAAD, including downstream aortic dilation, malperfusion and rupture. A recent publication from Essen claims an excellent follow-up with FET in ATAAD [12]. The freedom from reintervention at 5-year and 10-year favours FET (87% vs 68% and 74% vs 48%, respectively) as compared to limited arch repair in a near 100% follow-up of their patients. There was 90% positive aortic remodelling with FL thrombosis in ATAAD in their cohort.

Limited versus extended approach in ATAAD

Norton et al. studied 276 patients without cerebral malperfusion in ATAAD. They showed that there is no difference in the incidence of stroke and mortality rate in patients with or without arch branch vessel dissection. They concluded that hemiarch replacement is adequate even with patients with arch branch vessel dissection in ATAAD, though there is an increased risk of late reoperation [13]. A 10-year analysis of 156 patients in Taiwan showed total arch replacement (TAR) was significantly associated with surgery-related stroke, though the cohort had better downstream aortic remodelling [14]. The Baylor group performed a meta-analysis of 3154 patients who underwent FET looking into the neurological complications in particular. The operative mortality, stroke and spinal cord ischemia were 8.8%, 7.6%, and 4.7%, respectively [15]. On subgroup analysis, patients with ATAAD did not differ significantly from patients with non-ATAAD in pooled mortality rate or stroke. The overall composite adverse outcome was 22% in ATAAD, as compared to 16.5% in non-ATAAD patients. This higher mortality and stroke rate further tend to conceal the spinal cord ischemia, as these patients were not evaluated for the same. Though the incidence of spinal cord ischemia is similar to other meta-analyses — 5.1% [16] and 5.0% [17] — it is higher than the rate of 2.6% reported with conventional elephant trunk [5]. A recent single-centre analysis of 92 patients with ATAAD showed that TAR is an independent risk factor for mortality [18].

It is noteworthy that FET in ATAAD, at present in all probability, is being performed in specialized aortic centres, explaining the non-significant difference in unfavourable outcomes between emergent and nonemergent cases [15]. Most of the literature may not reflect the “real world” scenario — performance of the hybrid devices in less experienced centres. As the procedure is getting popular among surgeons, the device usage is inevitable. But one has to bear in mind the learning curve for FET can impose a considerable burden on hospital mortality and morbidity.

Is FET the “ace” solution for ATAAD?

This brings in questions which are yet to be answered: “Is FET the ideal way for complex aortic pathologies?” “Does FET need to be performed in all ATAAD?”.

The vascular domain of the European Association for Cardiothoracic Surgery, along with other experts in aortic surgery, provided recommendations for use of FET [19]. They recommended FET to be used in patients where there is a tear in the distal aortic arch or proximal descending aorta, presenting with malperfusion. In reality, this represents a small subset of patients. Frozen elephant trunk repair is a complex procedure even for the “master surgeons”. The complexity is increased if there is an accompanying aortic root procedure like a David or Bentall procedure. This eventually increases the cardiac ischemia time in an already long procedure. The aggregate morbidity and mortality from 97 focused publications showed a spinal cord injury of 0–21%, re-exploration because of bleeding of 2.5–30%, acute kidney injury of 4–34.8% and a stroke rate of 2.5–20% [19]. On the other hand, surgery for ATAAD has a high mortality rate even in the present era. The registries from the United Kingdom (UK) and Germany have documented operative mortalities of 23.1% and 17% respectively [20]. Any experienced surgeon would agree that operating on an ATAAD is not as similar as operating on other aortic pathologies. The characteristic of the dissected aorta and associated malperfusion coupled with the hemodynamic instability can pose challenges for the surgeon and team. Though assessment of tissue quality is subjective, it is beyond denial that the aortic tissues are fragile in a dissected aorta. This translates to the suture holding capacity and eventually postoperative bleeding in these patients. One can imagine the complexity of the procedure when performing FET in an ATAAD. The surgeon has to be well versed with FET in elective aortic pathology before venturing on the emergent situations. In ATAAD, the decision to proceed with FET has to be weighed between the risks involved in a challenging procedure against the mid-term benefits of the same. Most of the literature of FET in ATAAD emerge from high-volume centres where at least two surgeons are on call round the clock, who are competent to perform FET even in odd hours. But in the “real world” scenario, many of the ATAAD are operated on in low-volume centres. In an analysis from the UK, out of the 249 different consultant cardiac surgeons, 41 surgeons performed a single ATAAD procedure. Furthermore, during the study period of 6 years, nearly 80% of the surgeons had performed fewer than 10 procedures overall [5].

The Indian context: frontiers and challenges

The incidence of ATAAD in India has not been quantified, but through personal contact with a few high-volume centres and industrial data, we realise that the number of ATAAD repairs is significantly lower in India as compared to that in the Western world. The reason can be multifactorial including the lack of diagnosis and difficulties in transport. Furthermore, India being deemed as the world’s capital of diabetes, a lower incidence of aortic aneurysm and aortic dissection can be expected, due to the inverse association between diabetes and aortic disease including aortic dissection [21].

The challenges faced in India are unique as compared to those in the Western world.

1. Financial burden: The healthcare in most of the European and American nations are structured in a way that the finance is taken care of by the State or the insurance, while in India, we have the public and private sectors. The private sector in healthcare account for more than half (58%) of the hospitals, and the public sector offer only 44% of the inpatient care [22]. Though health insurance is available, many fellow citizens lack such insurance policies. This eventually leads to the majority of citizens spending their money from their savings. This makes the patient pay their hospital bills, apart from being subjected to a loss of pay at work.

2. Public versus private: The above-mentioned 58% of private sector are clustered in urban India providing direct service to 35% of the nation’s population [22]. The industry data suggest that more than three-fourths of the FET repair in the country have been performed in the private sector. The scenario again diverts the patients to the private sector where they have to spend from their pocket most of the time.

3. Late presentation/delayed diagnosis: It is not unusual to encounter a misdiagnosis in ATAAD as acute coronary syndrome or a cerebral vascular accident or an acute abdomen. This not only delays the diagnosis of ATAAD, but allows the patients to cross the “golden hour” time frame.

4. Transport: India is a vast country measuring about 3214 km from north to south between the extreme latitudes and about 2933 km from east to west between the extreme longitudes. The geography of the country is complex with hills, valleys, plateaus, deserts and rivers. Though road transport is the most commonly used, it takes considerable time to reach and many times patients cannot tolerate long and cumbersome road journeys to the hospitals. In this regard, air ambulance has gained popularity in recent times even in tier II and tier III cities. Having said this, it is not without challenge. The government strategies, framework, payment structure and insurance cover have to be addressed for smooth working of air ambulances.

5. Aortic supercentres: The model of “aortic supercentres” has been in practice in the United States (USA) for quite some time. Most of the ATAAD patients are regionalized and this ensures an improved outcome of patients when confined to high-volume multidisciplinary teams [23]. In India, centralization of expertise and amenities does not exist. Furthermore, surgery for ATAAD does not follow a selective referral system, leading to a mix and match of low- and high-volume centres.

6. Emergent life-saving procedure: When the above two factors are coupled, at times it becomes extremely difficult to shift an ATAAD to a specialized centre. As the mortality keeps climbing every hour, the patients are operated on in low-volume centres, when an emergency ascending aortic replacement will suffice to save the life of the patient.

7. Warehouse: On personal contact with industry, we realise that to date fewer than 100 FET hybrid prosthesis have been used in India including elective and emergency situations. Furthermore, we realise that the stocks of FET hybrid prosthesis at present are stored in a few handful sites across the country. Even transporting these devices in acute conditions is difficult for the industry team.

Our strategy

Our practice is to keep things simple. Although our techniques have evolved over the years, in patients with ATAAD, we prefer to perform a proximal arch replacement under moderate hypothermia and bilateral antegrade cerebral perfusion. In patients who have an additional tear in the aortic arch, we perform a TAR at zone 2. In patients with connective tissue disorder, where the size of the distal aorta is expected to enlarge at a faster rate, we perform a TAR even when there is no additional tear in the aortic arch. The anastomosis is performed in such a way that there is adequate landing zone in the Dacron graft for future thoracic endovascular aortic repair (TEVAR). procedures. Although we had reported the first FET in ATAAD in the country [24], we perform FET in ATAAD in a highly selective subset of patients — those with an additional tear in the proximal descending thoracic aorta or with compressed/small true lumen in hemodynamically stable conditions. In patients who are hemodynamically unstable and/or ongoing/impending malperfusion, we tend to keep the surgery simple with a proximal arch replacement.

Conclusion

A live dog is better than a dead lion (Ecclesiastes 9:4).

ATAAD is a challenging clinical condition with high morbidity and mortality. Despite the long-term benefits of extensive repair including the TAR and FET, patients must survive the extensive surgery. In clinical practice, one size does not fit all. Given the variety of clinical presentation and scenario, the primary approach has to be tailored to the patients’ presentation with regard to the experience of the surgeon and centre.

Funding

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Declarations

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Research involving human participants/animals

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Conflict of interest

The authors declare that they have no conflict of interest.