Funding
The authors declare that there is no external funding support for this study.
Abstract
Background and aim of the study
The Valiant NavionTM stent graft system is a third-generation low profile thoracic endograft designed for thoracic endovascular aortic repair. In this population analysis, we report on the first Asian all-comers experience and outcomes who underwent thoracic endovascular aortic repair with the use of this new stent graft system.
Methods
Between May 2019 and October 2020, 21 patients with different aortic pathologies were prospectively recruited and retrospectively analyzed. Important clinical and device-related outcomes were evaluated. The endpoints included short-term survival, technical success, access failures, major vascular and clinical complications, endoleaks, and hospital stay.
Results
The commonest indication of stenting was penetrating aortic ulcers (28.6%) and 6 (28.6%) patients had emergency stenting performed for aortic transection or rupture. 30 days of survival post-procedure was recorded and complete. There were no major vascular complications. Deployment accuracy was 100%, and the technical success rate was 94.7% (18/19) with 1 patient having a type 2 endoleak on follow-up imaging. No neurological complications were noted. The mean operative time was 95 +/- 73.6 mins and the mean fluoroscopy time was 16.2 +/- 10.8 mins. Mean hospital stay for elective zone 2, 3 and 4 stenting was 5.3 +/- 3.8 days, and only 1 patient post zone 1 TEVAR required a brief (0.5 days) ICU stay. All procedures were performed via the percutaneous transfemoral route with 100% success in percutaneous closure.
Conclusion
This first reported Asian case series demonstrated versatility, safety, and efficacy of the Valiant NavionTM stent in Asian patients with different aortic pathologies.
Abstract word count: 259
Keywords
Aorta, Thoracic aorta, Endovascular procedures, stents
Introduction
Thoracic endovascular aortic repair (TEVAR) is associated with reduced morbidity and mortality compared to open surgery in the treatment of multiple aortic pathologies [1] [2]. It is currently the mainstay treatment for a wide variety of aortic diseases in patients across all risk groups. However, not all patients are amenable to standard TEVAR. Anatomic limitations still preclude a significant number of patients from TEVAR and these include the absence of suitably sized access vessels, aortic calcification, and tortuosity, as well as the lack of adequate landing zones. The Valiant NavionTMstent graft system (Medtronic Inc. Santa Rosa, Calif.) is a third-generation low profile TEVAR device designed to allow smooth delivery via small-caliber vessels and provide better conformability on deployment. In this case series, we evaluated the short-term outcomes reflecting on our initial experience with the Valiant NavionTM stent graft system. To date, this is the first reported Asian “real world” series on the use of the novel Valiant NavionTM stent graft.
Methods
Population Characteristics
The mean age of the population was 65.4 +/- 12.4 years, with a male predominance of 90.5%. The majority of the patients were smokers (57.1%) and suffered from hypertension (71.4%). Table 1 displays the baseline characteristics of our population.
Study Design:
Between May 2019 and October 2020, 21 patients underwent TEVAR with the Valiant NavionTM endograft in the Prince of Wales Hospital, Hong Kong. All patient data were prospectively collected and retrospectively analyzed from the comprehensive Dendrite local cardiac and aortic surgery registry. Patients with variable aortic pathologies were included in the case series and relevant clinical and radiological data were recorded and analyzed.
The wall-to-wall outer diameter of vessels was used to measure the maximal aortic diameter (MAD) and the minimal iliofemoral access diameter. Vessels with circumferential calcification at any site were severely calcified. Any sequential aortic or vascular segments with angulation of > 45 degrees between adjacent curves were defined as tortuous vessels. TEVAR done within 1 day of admission were emergency procedures. Outcomes of interest included short term survival and important post TEVAR complications such as major vascular complications, stroke, spinal cord injury (SCI), renal dialysis, and endoleak. Procedural related death was defined as death during the index hospital stay. Survival analysis included 30-day mortality rates. Technical success was defined as successful access and deployment of the stent-graft with no major vascular complications, mortality, and the absence of endoleak on follow-up computed tomography (CT) scan. Deployment accuracy was defined as stent deployment within 5mm of intended proximal landing location on fluoroscopy and follow up CT scan. Access failure was defined as the inability to insert the device due to mechanical failure, or the need for anatomic exclusion of the iliofemoral vessels for access. Major device-related complications included aortic rupture, conversion to open surgery, need for salvage procedure, endoleak, and mortality. Major access site-related complications included access vessel dissection, pseudoaneurysm, limb ischemia, and the need for unintended adjunctive procedures such as conduits or cutdown. Neurological complications included stroke, transient ischemic attack (TIA), and spinal cord ischemia (SCI). Procedural related stroke was defined as a modified Rankin score (mRS) of 2 or more or an increase in 1 category from baseline within index episode of hospitalization. SCI was defined as new onset paraparesis or paraplegia following TEVAR. Positive aortic remodeling did not apply to transection cases and was defined as a complete penetrating aortic ulcer (PAU) or stent- induced new entry (SINE) tear coverage, or MAD reduction in aneurysmal disease. Thrombosis outside TEVAR stent in the absence of aortic size reduction was not considered positive aortic remodeling. All procedures were performed under general anesthesia in a state-of-the-art hybrid theatre. TEVAR was jointly performed by cardiac surgeons and interventional radiologists. For all patients, a proximal and distal landing of 2 cm or more was mandatory. In zone 2 cases, a left carotid-axillary artery bypass was performed for patients with the dominant left vertebral artery. Zone 1 patients required double de-branching with a carotid-carotid bypass and a left carotid-axillary bypass. The left subclavian artery was not routinely embolized during zone 2 TEVAR unless bypass was required or in the presence of type II endoleak on completion aortogram. All grafts were deployed under strict systolic blood pressure control < 100mmHg to prevent migration and wind-socking phenomenon. All femoral access was performed percutaneously and closed with percutaneous closure devices.
Ethical Approval:
The local registry was approved by the Hong Kong Hospital Authority and the Government of Hong Kong SAR to allow collection, analysis, reporting, and outcome tracking of patient data since its introduction in 2007. No informed consent from patients was sought for this retrospective analysis as there were no identifiers in this manuscript that could disclose individual patient confidentiality. Patient anonymity was preserved in this study and all patient data were kept confidential and secured.
Statistical Analysis:
Continuous variables were reported as mean +/- standard deviations (SD). Categorical variables were reported as frequencies and percentages. Data analysis was performed with IBM SPSS Statistics Version 25.
Results
21 patients were recruited for this study. The commonest indication for TEVAR was symptomatic penetrating aortic ulcers (PAU) (28.6%) (Figure 1a,b &c), followed by aortic transections (23.8%) (Figure 2a &b), stent induced new-entry (SINE) tears (23.8%), Thoracic aortic aneurysm (19%) and aortic rupture (4.8%). All aortic transection cases were grade 3 injuries, which required emergent stenting. The mean maximal thoracic aortic diameter was 45.5 +/- 16.1 mm. Most patients had a MAD of less than 50mm (71.4%). The minimum iliofemoral access diameter was 9.7 +/- 1.57mm, and 14.3% had access vessels smaller than 8mm. Severe vessel tortuosity and calcification occurred in 14.3% and 23.8% of patients, respectively. The mean follow-up period was 268 +/- 179 days.
Operative Characteristics
Table 2 displays the procedural characteristics. Most procedures were done on an elective basis (71.4%). TEVAR with zone 4 landing was most commonly performed (52.4%), followed by zone 2 landing (33.3%) and zone 3 landing (9.5%). 1 patient had a zone 1 TEVAR (4.8%). 28 stents were utilized, and 7(33%) patients had more than one stent. Most patients did not require adjunctive bypass procedures. Head and neck vessels debranching were performed in 2 patients, with 1 patient requiring a double bypass with carotid-carotid bypass and left carotid-axillary bypass (Figure 3a-d). The left subclavian artery was embolized with Nester Embolization Coils (Cook Medical, Bloomington, Indiana) in 3 patients (14.3%) and 1 patient had coil embolization of the aneurysmal sac. The overall mean operation time was 95 +/- 73.6mins, and the mean operation time for zone 3 and 4 TEVAR was 75.1 +/- 20.1 mins. Mean fluoroscopy time was 16.2 +/- 10.8 mins, and 11.2 +/- 4.5 mins for zone 3 and 4 TEVAR alone. All patients had a percutaneous femoral approach for TEVAR.
Outcomes
Table 3 displays the survival and procedural outcomes. The procedural mortality was 0%. None of the patients died within 30 days of the procedure. There were no major vascular complications, stroke, dialysis, or conversion to open surgery. 19 patients had a follow-up CT aortogram at the time of the study. The technical success rate was 94.7%, and 1 patient had type II endoleak found on a follow-up CT scan. There were no cases of retrograde type A dissection (RTAD), SINE, and stent migration up to the time of follow up. The mean overall hospital stay was 22.9 +/- 50.4 days. Excluding polytrauma and rupture cases, the mean hospital stay was 5.8 +/- 4.12 days, and only 1 patient out of the 15 elective TEVAR cases required half a day of ICU stay. On follow up CT scan for non-transection cases, 73.3% (10/15) patients had positive aortic remodeling, while 20% (3/15) had a static aortic appearance on CT. 1 patient (7.2%) out of 15 patients had type II endoleak on follow up CT.
Discussion
This series represents the first reported all-comers, “real world” experience with the new Valiant NavionTM stent graft system (Medtronic Inc. Santa Rosa, Calif.) in an Asian population. The Valiant NavionTM stent graft system is a low- profile evolution of the Valiant thoracic stent graft with CaptiviaTM delivery system [4,5]. Comparing to prior generations of stent-grafts, the delivery system comes in smaller outer diameters and has a shorter flexible, hydrophilic-coated taper tip which facilitates navigation in small and tortuous vessels. The stent-graft comes in outer diameters of 18, 20, and 22Fr. The improvement in flexibility and trackability of the NavionTM Stent system theoretically reduces the incidence of major vascular complications and facilitates a pure percutaneous procedure. Femoral and iliac access limitations preclude 35% of cases from TEVAR [6]. Anatomical drawbacks such as the size of vessels, degree of calcification, and tortuosity are considered unfavorable for transfemoral access of TEVAR. Indeed, the risks of major vascular complications are reported to be around 15% post TEVAR [7-10]. In the Pivotal trial, the NavionTM stent graft system was implanted in 87 patients and 70.9% of the studied population had severe access artery tortuosity. Despite the challenging access to anatomy, there were no cases of access failures. The Navion study group reported 3.4% access-related complications in 160 European patients, which were all from cut-down procedures [11]. The rate of femoral pseudoaneurysm and iliac vessel dissection was 0.86% respectively. In our center, the percutaneous femoral approach is routine, and vessels are repaired with percutaneous closure devices. We report a 100% success rate in percutaneous closure of access sites with no cases of the pseudoaneurysm, dissection, or limb ischemia. It is worth noting, that despite our patients being predominantly Asian, the mean minimal iliofemoral access was 9.7mm. A minority of patients (3/21; 14.3%) had access vessels smaller than 8mm, and this can be explained by the male predominance (90.5%) in our studied population. The 3 cases of small caliber iliofemoral access were all found in patients in shock state with aortic transection and multisystem trauma. With the low-profile delivery system, NavionTM stent graft allows for safe transfemoral access in shock patients with vasoconstricted vessels, which is important and a significant advantage especially in the setting of emergency TEVAR. No cutdown procedure was required for access in all 5 of our transection cases. Around one-quarter of our patients had circumferential calcification in the access vessels, and we had no cases of limb ischemia secondary to embolus and no cases of dissection. This can be attributed to the hydrophilic smooth taper cone tip of the NavionTM Stent system, which improves the trackability of the device during navigation to the targeted landing sites.
Endoleaks post TEVAR can result in suboptimal aortic remodeling, lesser sac regression rates, and repeat reinterventions [12-14]. The complexity and variability in landing zones affect deployment accuracy and success, and incomplete exclusion of diseased segments of the aorta can result in endoleaks. The rate of endoleaks from TEVAR range from 3.4 % to 42.2% with type I endoleak being the commonest at 41.4% followed by type II and III endoleaks [15]. The ValiantTMNavion stent-graft comes with two proximal stent-graft configurations, the FreeFlo, and the CoveredSeal device. The Freeflo device has a bare stent proximal design, which allows for the preservation of trans-vessel flow at the proximal landing zone, while the CoveredSeal has a proximal graft fabric edge. The stent-graft is mounted onto the delivery catheter and rarely shortens or changes length during deployment. This allows for customization of the stent for different landing zones and facilitates accurate landing, better sealing, and conformability to optimize deployment accuracy and reduce endoleaks. The improvement in conformability provides correct positioning to avoid type 1 endoleaks. In our series, for all pathologies, there was 100% deployment accuracy and only one case of endoleak due to a type II endoleak from a left subclavian artery with a disproportionately large orifice which was not completely embolized with coils. In the Pivotal trial, 2 out of 87 patients had endoleaks at 1 month (2.4%), and in the Navion study group, there were no endoleaks at a median follow up of 98 days. The latter study, similar to our series, was all on types of pathologies, not limited to aneurysms, and 32.27% of patients had significant thoracic or abdominal aortic angulations of more than 45 degrees. The Design of the Valiant NavionTM stent system is suitable for a wide range of pathologies. The smaller stent option of 20mm in diameter, in combination with the low-profile design, short nose cone, and simple 3-step deployment technique makes it an ideal stent for emergency scenarios in patients who are vasoconstricted and in shock. The CoveredSeal configuration has “W” shaped internal supporting stents, which are fully enclosed within the graft. This aids in enhanced landing zone apposition and sealing and reduces graft retroflexion. The sinusoidally shaped elastic nitinol springs throughout the graft provide improved conformability and flexibility, with a balanced radial force to optimize vessel sealing. This factor, in combination with a greater allowable distal tapering of 5-6 mm, prevents stent induced new entry (SINE) tears and retrograde type A aortic dissection (RTAD), especially in the setting of fragile aortas, such as aortas with intramural hematoma. The Pivotal trial reported 1 case of RTAD and 1 case of arch rupture, in our series, there were no cases of RTAD or SINE.
The improved design of the Valiant NavionTM stent has rendered TEVAR more operator-friendly without compromising short term patient survival and procedural outcomes. In our series, the procedural risk was low and survival outcomes were excellent. No patient died from the procedure and there were no cases of stroke, new dialysis requirement, spinal cord ischemia, respiratory failure, and conversion to open surgery. A European study on the Navion stent reported a stroke rate of 4.3%, SCI rate of 2.6%, and in-hospital mortality rate of 4.3%. The Pivotal trial reported a 30-day survival rate of 97.7% and a stroke rate of 4.6%. Our population is smaller compared to the two stated trials above, but our results of superior survival and operative outcomes affirmed the safety and feasibility of the NavionTM Stent graft system. The ease of deployment has also facilitated shorter operation times, shorter fluoroscopy times, and lower contrast doses, which obviate the need to utilize intensive care unit resources post-TEVAR. 1 case of zone 1 TEVAR required a half-day ICU stay, and excluding polytrauma patients with aortic transections, none of the elective zone 2,3, and 4 TEVAR patients required ICU stay. The mean hospital stay for elective cases was 5.3 +/- 3.8 days, and all elective zone 2, 3, and 4 TEVAR patients were extubated immediately after the procedure. In our series, for standard elective TEVAR, the mean operation time was 75.1 +/- 20.1 mins, with a mean contrast dose of 63.6 +/- 19.5 mls and a mean fluoroscopy time of 11.2 +/- 4.5 mins. This is consistent with the findings of the Pivotal trial, with a mean operative time of 88.7 mins, mean contrast dose of 96.2 ml, and fluoroscopy time of 12.2 mins. The ease to percutaneously close TEVAR femoral wounds has diminished the need for open cut down procedures, which also speeds up patient recovery.
Limitations
This non-comparative study is retrospective in nature and has inherited intrinsic weaknesses such as recall and measurement bias. The population is small, and the findings serve to highlight the safety, feasibility, and versatility of the new Navion TM stent graft system in Asians. The findings are at best hypothesis-generating. Besides, only short-term outcomes were demonstrated, and these patients will be followed up for long term outcomes as controversies still exist in the durability and high future reintervention rates of TEVAR
Conclusion
Our series, to date, is the first reported Asian series on the use of the NavionTM stent graft system in all-comers with all pathologies. Most patients in our population had non-aneurysmal aortic diseases such as aortic transection, SINE, and PAU. We did not encounter a disproportionately high number of patients with small, calcified, and tortuous vessels. Nonetheless, we have demonstrated the NavionTM stent system to be safe and effective across various pathologies amongst Asians. The high rate of successful percutaneous femoral access and stent deployment accuracy facilitates shorter operative times, reduces procedural complications, and shortens hospital stay.
Author contributions
Conception and design: SC, RW , JH
Administrative support: RW , SY, CM CHU
Provision of study materials or patients: All authors
Collection and assembly of data: SC, RW , JH
Data analysis and interpretation: All authors
Manuscript drafting and writing : SC, RW, JH
Critical Revision of article : all authors
Final approval of manuscript: All authors
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Table 1. Baseline demographics