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Department of Surgery, Duke University Medical Center, Durham, North Carolina
Accepted for publication September 15, 2009.
* Address correspondence to Dr Hughes, Division of Thoracic and Cardiovascular Surgery, Department of Surgery, Box 3051, Duke University Medical Center, Durham, NC 27710 (Email: gchad.hughes{at}duke.edu).
Presented at the Fifty-fifth Annual Meeting of the Southern Thoracic Surgical Association, Austin, TX, Nov 5–8, 2008.
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Abstract |
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Methods: Between June 2005 and November 2008, 55 patients (41 men) with a mean age of 59 ± 12 years (range, 31 to 77 years) underwent TEVAR for the management of complicated acute (n = 22) or chronic (n = 33) type B dissection. Indications in acute dissection included impending or frank rupture in 11 and malperfusion syndromes in 11; the indication in chronic dissections was aneurysmal degeneration in 33.
Results: Primary technical success was 100%. In-hospital and 30-day rates of death, stroke, and permanent paraplegia/paresis were 2% (n = 1), 0%, and 2% (n = 1), respectively. Median follow-up was 7.1 months (range, 1 to 38 months). Overall actuarial midterm survival was 63% at 38 months, with an aorta-specific actuarial survival of 94%. Two patients (4%) required late conversion to open repair. Postoperative type I or III endoleak occurred in 3 (6%) and type II endoleak in 7 (15%). Two patients underwent subsequent endovascular occlusion. The composite reintervention rate in follow-up was 23.4% (n = 13).
Conclusions: Endovascular repair for complicated acute and chronic type B dissection is safe and effective at early midterm follow-up. TEVAR for type B dissection requires more secondary interventions and imaging surveillance than conventional open reconstruction. Longer-term follow-up is needed to determine the durability of this approach.
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Introduction |
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Of patients with acute uncomplicated type B dissections managed medically, approximately 20% to 40% [3] will require an operation for secondary aneurysmal degeneration of the chronically dissected aorta in long-term follow-up. Although open repair for aneurysmal degeneration secondary to chronic dissection is associated with improved outcomes compared with open repair for acute complicated cases, a 30-day mortality rate of 3% to 5% is quoted in most series, with a paraplegia risk approaching 3% [4, 5].
Significant perioperative morbidity and mortality in acute complicated type B dissections has prompted alternative therapies to address this pathophysiology. First described in 1997 [6], the use of thoracic endografting for the treatment of complicated Stanford B dissections has accelerated [7–12], even though it remains an off-label indication for technology currently approved by the United States Food and Drug Administration solely for thoracic degenerative aneurysmal disease. Limited data exist with regards to endograft use for management of complex descending thoracic aortic dissections.
The rationales for treating acute (<2 weeks from symptom onset) and chronic (>2 weeks from symptom onset) type B dissections are disparate [13]. In the acute phase, endografts abrogate impending aortic rupture and relieve dynamic malperfusion. Delayed benefit involves potentiating thrombosis of the thoracic false lumen, thereby mitigating the risk of aneurysmal dilatation and subsequent aortic rupture [13]. Hence, the purpose of this study was to examine our institutional experience with endovascular stent graft therapy for treatment of complicated type B dissections and detail 30-day and early midterm outcome data.
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Patients and Methods |
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Between June 2005 and November 2008, 55 patients underwent TEVAR for management of complicated acute (n = 22) or chronic dissection (n = 33) of the descending thoracic aorta at a tertiary referral university hospital. Indications in the acute subset were frank or impending rupture in 11 patients or malperfusion syndromes in 11. For chronic dissections, the primary indication was aneurysmal degeneration, specifically an absolute aortic diameter of 5.5 cm or more in 26 patients, rapid expansion of aortic diameter exceeding 5 mm during a 6-month period in 6, or saccular aneurysm with a diameter exceeding 2 cm in 1. In the chronic subset, the average preoperative descending aortic diameter was 5.9 ± 1.3 cm.
The presence of a connective tissue disorder, such as Marfan or Loeys-Dietz syndrome, was an absolute contraindication for TEVAR in the chronic setting. Although not encountered in this series, we would not consider this a contraindication in the acute setting, where endograft therapy could be used as a bridging technique to subsequent definitive open repair [14]. TEVAR is the preferred treatment strategy for chronic descending dissection with aneurysm at our institution, and no other exclusion criteria, save a lack of adequate endograft landing zone, are delineated.
The interval from diagnosis to stent graft repair in the subset of chronic dissections was a median of 48 months (range, 2 to 216 months). Data were collected through the last follow-up by the study termination date of November 2008.
Endografts used were the Gore TAG device (W. L. Gore and Associates, Flagstaff, AZ) in 54 and the Zenith TX2 (Cook Medical Inc, Bloomington, IN) in 1. Details regarding the devices, techniques of delivery, and deployment have been described [15]. The TeraRecon System (TeraRecon Inc, San Mateo, CA), which allows accurate centerline measurements of the flow lumen diameter to evaluate landing zones as well as access vessels, was used in preoperative assessment. Intravascular ultrasound (Volcano Corporation, San Diego, CA) imaging was routinely used to verify true lumen access, identify the primary entry tear and areas of distal fenestration, and evaluate proximal and distal landing zones, as previously described [16].
All procedures were performed in the operating room under general anesthesia; adjunctive transesophageal echocardiography (TEE) was used in all cases. An iliac or abdominal aortic conduit was required use for vascular access in 10 patients (18%). The left subclavian artery (LSCA) was partially or fully covered in 38 (69%), of whom, 13 (34%) underwent adjunctive left carotid-subclavian bypass at the time of TEVAR for previously described indications [17].
On-line monitoring of spinal cord function with somatosensory (SSEP) and motor evoked potentials (MEP) was used intraoperatively in elective cases and when available for 40 urgent/emergent cases (73%), comprising 12 acute and 28 chronic patients, as previously described [18]. Cerebrospinal fluid (CSF) drainage was used selectively in 12 patients (22%) for previously cited indications [17]. One patient received a preoperative lumbar drain for paraparesis secondary to dissection-induced spinal cord malperfusion.
All procedural outcomes and complications were prospectively recorded, and follow-up was performed at the Duke University Center for Aortic Surgery. Patient follow-up protocol was similar to prior clinical trials [19, 20] and included clinical examination, 4-view chest roentgenogram, and computed tomography angiography (CTA) at 1, 6, and 12 months postoperatively and annually thereafter. Additional 3-month imaging was pursued if an endoleak was identified at the 1-month follow-up. Noncontrast enhanced magnetic resonance imaging was obtained in lieu of contrast-enhanced CTA in patients with serum creatinine levels of 2.0 mg/dL or higher.
The Social Security Death Index (http://ssdi.rootsweb.com/) was queried to confirm all deaths and survey patients lost to follow-up. Survival analyses were performed using the Kaplan-Meier method. All data are presented in accordance with cited reporting standards [21].
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Results |
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Operative death, defined as death within 30 days of the procedure or during the same hospital admission, was 1.8% (n = 1). This isolated case was a salvage procedure performed in an elderly man transferred to our institution with established visceral malperfusion secondary to an acute type B aortic dissection. Emergency TEVAR successfully reestablished mesenteric flow; however, a second-look laparotomy demonstrated extensive mesenteric infarction and support was withdrawn.
The mean hospital length of stay for the entire dissection cohort was 6 ± 5 days with an intensive care unit stay of 2 ± 2 days.
No strokes were documented. One patient (2%) with an acute dissection presented with new permanent paraparesis/paraplegia. Transient paraparesis developed in 1 patient that resolved with blood pressure augmentation and did not require CSF drainage. Another acute patient manifested a clinically silent minor subarachnoid hemorrhage attributable to iatrogenic insult (CSF drainage).
Four patients presented with device-related complications requiring additional endovascular or open procedures within 30 days of the original endovascular repair for a rate of 7%. These included intraoperative partial left common carotid artery (LCCA) coverage requiring LCCA stent placement in 1 (acute subset), intraoperative iliac arterial rupture requiring covered stent repair in 1 (chronic subset), intraoperative proximal endograft migration requiring covered stent placement in the innominate artery to restore cerebrovascular flow in 1 (acute subset), and intraoperative LCCA dissection with compromised flow after ballooning of the proximal endograft, requiring open carotid endarterectomy/fenestration through an additional neck incision without neurologic sequelae in 1 (chronic subset).
Follow-Up Outcomes
Median duration of follow-up was 7.1 months (range, 1 to 38 months). Overall actuarial midterm survival was 63% at 38 months, with an aorta-specific actuarial survival of 94% (Fig 1). Of late deaths, 1 (2%) was aortic-related and the remaining 8 were due to comorbid conditions, including failure to thrive in 2 (1 acute and 1 chronic subsets), sepsis in 1 (acute subset), myocardial infarction in 1 (chronic subset), complications secondary to femoral neck fracture in 1 (acute subset), chronic renal failure sequelae in 1 (chronic subset), presumed overdose in patient with psychiatric comorbidity in 1 (chronic subset), and an unknown cause in 1 (chronic subset, contact attempted but unsuccessful) but presumed secondary to comorbid conditions because the 18-month radiologic follow-up demonstrated a thrombosed descending aneurysm and decreasing aortic dimensions.
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Overall, 48 patients (87%) underwent at least one follow-up CT scan; of the 7 who did not, 1 died in the perioperative period, and 6 did not return for scheduled follow-up. The incidence of type I or III endoleak at any follow-up visit was 6% (n = 3; 2 acute and 1 chronic); all were seen on the initial postoperative CT scan and were treated with additional endovascular repair, with complete resolution at most recent follow-up. An additional 7 type II endoleaks (15%; 4 acute, 3 chronic) were noted on follow-up imaging. Of these, 2 (both chronic subset) were due to retrograde flow from the LSCA and were successfully treated with late coil embolization. The remaining 5 were due to intercostal vessels and are being followed up with decreasing (n = 1) or stable (n = 4) aortic diameters.
At the latest follow-up, 17 of the 33 patients (52%) undergoing endovascular repair for chronic dissection with aneurysmal dilation have decreasing (>5 mm) aortic dimensions, 6 (18%) exhibit stable aortic dimensions, 1 (3%) has enlarging aortic dimension, and 9 (27%) lack 6-month follow-up because 3 were lost to follow-up and in 6 the procedure was performed within 6 months before data harvest. Of the 24 with follow-up imaging at 6 months or more, the aortic dimensions in 17 (71%) decreased by at least 5 mm, consistent with aortic remodeling of the chronic dissection (Fig 2). Of the 33 patients in the chronic subset, 32 had at least one follow-up CT scan and 55% exhibited false lumen thrombosis of at least the entire thoracic aorta. Only 9% continue to have some retrograde false lumen flow through distal fenestrations along some portion of the endografts (Table 3).
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Actuarial freedom from reintervention was 90% at 30 days, 83% at 1 year, and 55% at 38 months after TEVAR (Fig 3). Two patients (both chronic subset) required Palmaz bare-metal stent placement to reexpand proximal (n = 1) and distal (n = 1) partial TAG graft collapse at 2 and 1.5 months postoperatively, respectively. Additional distal endografting was required in 3 patients (1 acute and 2 chronic) for false lumen dilation developing downstream to the initially placed endograft. Two patients (1 acute and 1 chronic) underwent additional endografting for the development of metachronous descending aortic pathology separate from the initially treated dissection. Including all additional late procedures (open conversion, treatment of endoleaks, Palmaz, additional distal pavement), 13 patients (4 acute, 9 chronic; 23.36%) in this series required late intervention during midterm follow-up, and 12 of these procedures were successful, with the open conversion for AEF and perioperative death cited as a reintervention failure.
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Comment |
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Debate exists regarding extensive "paving" of the descending thoracic aorta in the acute setting to mitigate potential retrograde false lumen flow by downstream fenestrations [22]. A caveat is that extensive aortic coverage may increase neurologic morbidity. We prefer to minimize aortic paving to the extent necessary to relieve the malperfusion syndrome and reestablish true lumen flow. In the case of rupture, we individualize the degree of endografting and do not hesitate to extend aortic coverage to the level of the celiac axis if necessary; of note, the single case of paraplegia observed in this series was an acute dissection patient who had undergone aortic paving from the innominate artery to the celiac axis. Regardless, this equates to a permanent paraplegia/paresis rate of 4.5% (1 of 22) for complicated acute dissection, comparable to rates cited in open series [1, 2, 4].
We believe that at the present time TEVAR should be reserved for complicated cases of acute descending aortic dissection. Initial (30-day) mortality is 10% or less with medical therapy in acute uncomplicated type B dissection, and preliminary data from the Investigation of Stent Grafts in Patients With Type B Aortic Dissection (INSTEAD) trial suggest no therapeutic advantage to indiscriminate endograft placement (10% 1-year mortality) vs standard medical therapy (3% 1-year mortality) for uncomplicated Stanford type B dissection [2, 22, 23]. The INSTEAD trial does have several limitations, however, including a high crossover rate from medical to surgical therapy and thus should not be considered the final word on this subject. Rather, current reports highlight the need for additional well-planned and executed studies of endovascular therapy for acute type B dissection.
Up to 40% of patients with initially uncomplicated type B dissection are subject to aneurysmal degeneration in late follow-up [3], and the role of TEVAR for the subset of uncomplicated patients with a predilection for this complication remains undefined. Marui and colleagues [24] reported an actuarial freedom from late aortic events of only 8% at 10 years in 141 patients with acute uncomplicated type B dissections who initially presented with an aortic diameter exceeding 4 cm and a patent false lumen on radiographic evaluation. Further study is warranted to identify subset(s) of uncomplicated patients who may benefit from early endovascular repair.
TEVAR for chronic type B dissection is generally undertaken for late aneurysmal complications, as performed in 33 patients in the current series. Perioperative outcomes are excellent, with no deaths, strokes, or spinal cord complications in this chronic cohort; results that are superior to open repair for this pathology [1, 4]. Our results, consistent with other series published within the last year [11–13], support the use of TEVAR in chronic cases.
Despite these results, TEVAR application in chronic dissection patients remains controversial, with some investigators ascribing its use for this indication as "futile" [22]. The controversy is partly because endografting eliminates antegrade false lumen flow by coverage of the primary tear, although distal reentry tears and fenestrations persist that provide retrograde false lumen flow. Further, in the chronically dissected aorta, the intimal flap thickens and does not readily reapproximate to the native aortic wall. Therefore, complete false lumen thrombosis is less likely in this setting [25]. In the current series, however, decreases in aortic dimensions were typically seen in this cohort in follow-up. Specifically, 17 of 33 patients with chronic aortic dissections treated using endovascular means demonstrated decreasing aortic dimensions in follow-up, including 17 of 24 patients (71%) with CT imaging at 6 months or longer after implantation. Similar results have been published by Rodriguez and colleagues [11] in the largest reported single-institution series of endovascular treatment of type B aortic dissection to date.
Although TEVAR for complicated type B dissection maintains excellent 30-day outcomes, the results of the current study highlight an increased need for reintervention compared with open repair. For example, 3 patients (5%) required late reintervention with additional distal endografting for downstream dilatation. We now have a low threshold to pave down to the celiac axis in chronic dissection patients even if the aneurysmal segment is limited to the proximal descending thoracic aorta. Even this strategy, however, will not prevent the late although less common scenario of abdominal aortic dilation [26]. Our results concur with other published results, which have reported reintervention rates of approximately 12% [10]. Dissection-specific devices to address these issues are clearly needed [27].
In summary, TEVAR for acute complicated type B aortic dissection reliably relieves malperfusion and effectively mitigates impending and frank rupture with results far superior to those previously reported for open repair. It would appear that endovascular therapy represents a clear advance in the management of this morbid condition. Further, our data and the data from other published series [11] suggest a potential benefit for endovascular therapy in chronic type B dissections complicated by aneurysmal degeneration. Potential benefits are tempered by the need for reintervention, which appears higher than conventional open repair. Fortunately, almost all of these reinterventions are successfully managed with endovascular techniques.
Questions persist about durability and optimal patient selection, which can be answered with additional studies and a longer duration of follow-up. Drawing upon parallel results from other series and longer-term data currently available for other TEVAR indications (eg, aneurysmal disease), this technology appears to have secured a firm position in the surgical armamentarium for the treatment of acute and, potentially, chronic descending thoracic aortic dissection.
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Discussion |
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Dr Parsa, I have the following questions. First, one of the criteria you used for classification and treatment of the 22 patients as acute was "impending rupture." What were your criteria to determine impending rupture for the 11 patients in this subgrouping? Second, do you obtain CT [computed tomography] scans at 24 hours or prior to hospital discharge to document no type I, type II, or type III endoleak, and why did your paper specifically exclude type II endoleaks? Third, in your manuscript you indicated the average size of the stent graft deployed was 34 mm. What was the average size of the aneurysm you were treating in this series and what size criteria for treatment did you use in the chronic group?
Again, congratulations to the authors for their important work, as we all continue to analyze critically this emerging technology and its broadening applicability to complex thoracic aortic disease.
DR PARSA: Thank you, Dr Reddy, for your comments and questions. In terms of the criteria for impending rupture, as a referral center, we get a cohort of patients that are at risk for rupture. They present with pain and may exhibit refractory pain. In our series, we treat each patient initially with pain management and blood pressure control. The majority, if not all, usually resolve symptoms. This requires transition to oral agents and transfer to the stepdown unit. In the case of acute dissection, if the initial CT scan indicates aortic dilatation (around 4 cm) and the patient exhibits a blood pressure spike while on the stepdown unit or some other incident that induces recurrent pain, this is a harbinger of a dangerous outcome, and we typically include these patients in our acute series. This comprises 10 patients in our urgent category that are done not within 24 hours of admission, but typically within 72 hours of admission.
In terms of your second question, our CT protocol, a CT scan is done 1 month postoperatively. The type I endoleak data are up here. The type II endoleak data for our series consists of 7 patients: 5 intercostal and 2 left subclavian. In our center, we will perform coil embolization of all left subclavian type II endoleaks; the intercostal endoleaks are typically followed up, one of which has resolved, with the remaining 4 cases exhibiting stable aortic dimensions over serial follow-up. If 1-month follow-up indicates a potential endoleak that does not require immediate intervention, we will add an interval 3-month follow-up. If the endoleak does require reintervention, then the surveillance schedule is restarted as 1-, 6- and 12-month follow-up, etcetera.
In terms of aneurysm size criteria for our chronic series, obviously, the aortic luminal diameter is most relevant for this subset. The number I posted up on the slide was 5.4 cm. That is the mean for all 55 patients. For the chronic series, specifically it is 5.9 cm, but I think that number underestimates our true actual average, although that meets the criteria for repair currently, because there are 6 patients in our series that have undergone rapid growth (eg, more than 5 mm growth in 6 months), which are included in that series as well. So I think that falsely depresses that mean luminal diameter somewhat.
DR HUGHES: If I could just make a comment, we don't obtain a CT scan prior to discharge routinely, as we don't typically leave the operating room with a known endoleak. Thus, if the patient is doing fine, we don't get a CT scan until the 1-month follow-up. We don't follow-up type I or III endoleaks, but rather intervene on those. Type IIs we will occasionally follow-up, although we will scan the patient again at 3 months. For the left subclavian origin type IIs, we generally go ahead and treat them because it is relatively simple to do.
With regards to the stent grafts utilized, I think what you are getting at with your question is that sizing in dissection has been based on proximal landing zone diameter only, at least if you are using the TAG graft [W.L. Gore & Assoc, Flagstaff, AZ], which does not have a tapered option. However, now that TX2 [Cook Medical, Bloomington, IN] is available and has tapered sizes, at least in the chronic dissections with aneurysm, we have gone to using a tapered device, because the true lumen distally is smaller. Further, in the chronic setting, you are not going to get complete aortic true lumen reexpansion after endovascular repair, and as outlined in the manuscript, we did have one partial distal TAG graft collapse in a small true lumen that required Palmaz [Cordis, Miami Lakes, FL] stent reexpansion. So it is a concern. Again, I think when we get dissection specific devices this will help treat this disease better.
DR JOSEPH E. BAVARIA (Philadelphia, PA): I would like to congratulate the Duke group for some radical, revolutionary kind of thought processes. This is a really good paper. The general audience of the Southern Thoracic Surgical Association may not understand how seminal both this paper and the previous paper are regarding aortic surgery conceptual frameworks. Anyway, this may be the largest series by a thoracic aortic group that I know of using TEVAR [thoracic endovascular aortic repair] in chronic type B dissection. Really, we kind of know what is going on with the acute type B dissection presentation vis-à-vis TEVAR, so I am going to focus my questions on the chronic side. Do you do all patients now with stent grafts, or is there a management algorithm that you use to choose between an open chronic dissection aneurysm case vs a stented case?
DR PARSA: Thank you, Dr Bavaria. Essentially in this series, there have been 3 patients who have undergone open repair. These are principally young patients with a connective tissue disorder. Otherwise, every other patient is managed by an endovascular approach. And the indication is always aneurysmal dilatation, either rapid growth or an absolute value greater than 5 cm.
DR BAVARIA: I would like to hear what Dr Coselli has to say about this, but in our experience, we have kind of drilled down on this a little bit and focused on stenting chronic dissecting aneurysms if they have: (1) all 4 visceral vessels coming off the true channel, (2) they have a known and an easily identifiable large tear site proximally, and, (3) if they don't have a very, very small distal true lumen landing zone that can create a "pseudocoarctation" as Chad just talked about. Can you comment on that focused treatment algorithm or do you just stent everybody?
DR PARSA: I will say simply that we stent everybody with that concern in mind. If there is concern about a very chronic dissection where you feel that the true lumen is very narrowed and will not expand well, a tapered device would be utilized. In terms of the visceral segments all coming off the true lumen, the majority of these patients have distal fenestrations. Therefore, even though you reexpand the true lumen and potentially thrombose the false lumen, there is enough retrograde flow from the abdominal aorta that we usually are not too concerned about that.
DR HUGHES: Basically what you see in the treated chronic dissections is thrombosis of the aneurysm along at least the length of the stent grafts, with the false lumen staying patent distal to that. The goal is to treat the area of aneurysm, which, as in the paper your group just presented, is typically in the proximal descending aorta or distal arch, immediately adjacent to the large primary tear usually there. In our experience to date, which is 33 chronic patients, in general, there is thrombosis of the false lumen along at least the length of the stent grafts and by 6 months the aorta starts to decrease in diameter, although you are still left with distal dissection. However, as long as there is no aneurysm distally, this chronic distal dissection does not pose a risk to the patient. And we don't really concern ourselves too much with what lumen the distal vessels come off of, because in the chronic setting there are fenestrations at the sites of any vessel coming off of the false lumen, which is why we don't see total false lumen obliteration ever in the chronics. We are just treating the aneurysm. We are not trying to get the whole aorta to remodel in this situation.
DR BAVARIA: This subject is a little bit debatable if you drill down a bit.
But the last question is, what about those 29% that got bigger and the 71% that got smaller? What happened to the 29% that got larger?
DR PARSA: One has passed away.
DR HUGHES: The remainder are not bigger, but rather are stable. The only enlargement in the entire series was the patient who went to open conversion and he was an acute, not chronic, patient.
DR PARSA: We have one open conversion and one death.
DR HUGHES: To further argue the point about treating chronic dissections, we have put CardioMEMs sensors in the false lumens of a number of these chronic dissections with aneurysms, and following TEVAR the pressures in the false lumen go down significantly. Typically, one will see a false lumen sac pressure of 10% systemic, which does support the concept that you are depressurizing the false lumen along the endograft. That is some data that we are going to present at the STS [Society of Thoracic Surgeons].
DR JONATHAN ELLICHMAN (Memphis, TN): Could you elaborate on your selection criteria for carotid subclavian bypasses as well as spinal drains in these patients?
DR PARSA: For spinal drainage, it involves patients that we anticipate paving below T8, and patients that have had prior abdominal or thoracic aortic procedures that place them at higher risk. As far as a carotid subclavian bypass, a patent mammary and someone who has had a CABG or a dominant left vertebral artery warrants extra-anatomic bypass. A postexclusion left upper extremity systolic blood pressure of less than 50 mm Hg is a relative indication for bypass as well.
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