A New Mechanism by Which an Acute Type BAortic Dissection Is Primarily Complicated,Becomes Complicated, or Remains UncomplicatedChristian Loewe, MD,* Martin Czerny, MD, MBA,* Gottfried H. Sodeck, MD,Julie Ta, MS, Maria Schoder, MD, Martin Funovics, MD, Julia Dumfarth, MD,Marek Ehrlich, MD, Michael Grimm, MD, and Johannes Lammer, MDDepartments of Cardiovascular and Interventional Radiology, Emergency Medicine, and Cardiac Surgery, Medical University of
Vienna, Vienna, Austria; Department of Cardiovascular Surgery, University Hospital Berne, Berne, Switzerland; and Departmentof Cardiac Surgery, Medical University of Innsbruck, Innsbruck, Austria
Background. This study is to evaluate if different loca-tions of the primary entry tear result in primary compli-cated, secondary complicated, or uncomplicated acutetype B aortic dissection.
Methods. Sixty-five patients were analyzed. Patientswere stratified according to the location of the primaryentry tear. Primary entry tears in axial computed tomo-graphic scans at the upper circumference (180°) of thedistal aortic arch were defined as convex (group A) andthe remaining as concave (group B). Detailed morphom-etry was done and the clinical outcome, including needfor thoracic endovascular aortic repair, was evaluated.
Results. Forty-two patients (group A) had the primaryentry tear at the convexity and 23 patients (group B) hadthe primary entry tear at the concavity of the distal aorticarch. There was a significant difference with regard to theincidence of primary complicated type B aortic dissection
(group A 21% vs group B 61%, p � 0.003) and with regard
to the development of complications in group A (9 days;9 to 37) versus group B (0 days; 0 to 13, p � 0.03). Coxregression analysis revealed a primary entry tear at theconcavity to be the only independent predictor of pri-mary or secondary development of a complicated acutetype B aortic dissection (hazard ratio, 1.8; 95% confidenceinterval, 1.0 to 3.2).
Conclusions. A primary entry tear at the concavity ofthe distal aortic arch is associated with a significantincrease of the occurrence of complicated acute type Baortic dissection. Due to low procedural risk and highsuccess rates, closure of the primary entry tear withthoracic endovascular aortic repair is strongly recom-mended in this newly defined high-risk subgroup ofpatients.
Endovascular or open surgical treatment of acute typeB aortic dissection is performed if overt complica-
tions such as rupture, malperfusion, or persistent pain dooccur [1–4]. Attempts have been made to identify predic-tors of early and late complications [5–7]. The location ofthe primary entry tear is not taken into considerationregarding the treatment strategy to date. Previous workhas shown that an entry tear at the concavity may beassociated with complicated acute type B aortic dissec-tion, including retrograde type A aortic dissection [8, 9].The aim of this study was to evaluate if different locationsof the primary entry tear result in primary complicated,secondary complicated, or uncomplicated acute type Baortic dissection.
Accepted for publication Dec 6, 2011.
*The first two authors contributed equally to this work.
Address reprint requests to Dr Loewe, Department of Cardiovascular andInterventional Radiology, Medical University of Vienna, Waehringer
Material and Methods
Patients and ImagingInitially, all patients undergoing computed tomographic(CT) follow-up or initial diagnosis of a type B aorticdissection in our hospital between 2004 and 2009 wereidentified by database search. During this time, all exam-inations were performed on a 64-slice multislice CT scan(Philips Brilliance 64; Philips Medical Systems, Best, TheNetherlands). After identifying this study group, thebaseline examinations were also retrieved and assessed.These baseline examinations were performed on differ-ent scanners, including 4-slice, 16, and 64 slice CT scan-ners (Siemens Somatom 4, 16 or 64; Siemens, Erlangen,Germany), depending on time and situation. All CT an-giographies were retrieved from the Picture Archiving andCommunication System (PACS) and were assessed onroutine PACS viewing stations (Agfa Healthcare IMPAX).Patients with acute aortic syndromes were subdivided into“classical” aortic dissections and variants of aortic dissec-tions [10]. Out of 110 consecutive patients with acute de-scending aortic syndromes, 70 patients had an acute type B
aortic dissection (Fig 1). Patients were stratified according to
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the European system for cardiac operative risk evaluationclassification [11]. The present study was approved by theMedical University of Vienna’s Institutional Review Boardand, because the study is a retrospective analysis, nowritten informed consent was obtained.
Definition of Complicated Acute Type B AorticDissectionPrimary complicated acute type B aortic dissection wasdefined as rupture, contained rupture, retrograde extentinto the arch or into the ascending aorta; furthermore,visceral, renal, or limb malperfusion, or persistent pain[12]. Secondary complicated type B aortic dissection wasdefined according to the same surrogates, however, be-ing not present at the time of primary diagnosis.
Morphometric DefinitionsTo assess the potential impact of the localization of theprimary entry tear on immediate and long-term clinicaloutcome, the following parameters were assessed on thebaseline CT angiographies using a standardized evalua-tion sheet: (1) distance of the primary entry tear to the lastaortic arch branch (typically left subclavian artery); (2)localization of the primary entry tear at the inner (“con-cave”) or outer (“convex”) curvature of the distal aortic
Fig 1. Flow chart for study screening, patientselection, and evaluation.
arch (Fig 2); (3) retrograde dissection component; and (4)
morphologic signs for acute complications being im-pending or ongoing rupture or visceral, renal, or periph-eral ischemia due to malperfusion. The method of assess-ment is detailed below.
Fig 2. Scheme of different sites of the primary entry tear of acute typeB aortic dissections. (A) Primary entry tear at the outer circumference ofthe distal aortic arch defined as “convex.” The retrograde component ofthe dissection is stopped by left subclavian artery. (B) Primary entrytear at the inner circumference of the distal aortic arch defined as “con-cave,” allowing progression of the retrograde component of the dissec-
tion into the aortic arch and the ascending aorta.
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The distance to the left subclavian artery was mea-sured on parasagittal maximum intensity projectionsangulated across the aortic arch. The distance from theprimary entry tear to the offspring of the left subclavianartery was measured. Patients with a primary entry tearin the distal descending aorta (distance to the subclavianartery of more than 5 cm) were excluded from furtherevaluation. Also excluded were patients where the pri-mary entry tear could not be clearly identified.
The exact location of the site of the primary entry tearwas assessed using the parasagittal maximum intensityprojections as well as the axial source data. Primary entrytears within the inner 180 degrees of the lesser curvatureat axial slices were defined as primary entry tears at theconcavity and primary entry tears within the outer 180degrees of the greater curvature were defined as primaryentry tears at the convexity.
A retrograde component was defined as an extent ofthe dissection cranially of the primary entry tear into theaortic arch. Also, intramural hematoma propagating cra-nially to the site of the primary entry tear was defined asa retrograde component. The presence or absence of aretrograde component was assessed as well as the extentup to the level of the subclavian artery, into the aorticarch, or up to the level of the ascending aorta.
From a morphologic point of view, primary compli-cated type B aortic dissection was defined as the presenceof aortic rupture indicated by hematothorax, hematoperi-cardium, or paraaortic extravasation. Furthermore, mor-phologic signs for end-organ ischemia such as ileus,intestinal wall thickening, and hypoperfusion as well aspneumatosis were assessed.
Definition of Development of ComplicationsThis parameter was defined as the time from diagnosis tothe development of complicated type B aortic dissectionneeding treatment as defined above. If complicationswere already present at the time of diagnosis, the time todevelopment of complications was classified as 0. In thesubacute phase, the definition of development of compli-cations was further extended by an increase of the initialdiameter of the proximal descending aorta exceedingbaseline measurements by 20% [13–16].
Statistical MethodsContinuous data are presented as the median and theinterquartile range (range from the 25th to the 75thpercentile) or as the mean and standard deviation (SD),as appropriate. Discrete data are given as counts andpercentages. Comparisons of continuous data were per-formed by the Mann Whitney U tests and groups ofcategoric data were compared by �2 tests. Univariate Coxregression analysis was primarily performed to assessthe prognostic impact of the site of the primary entry tearupon the future need for thoracic endovascular aorticrepair (TEVAR), followed by a multivariate Cox regres-sion model to assess the strongest independent predictorafter adjustment for possible confounding factors. Re-sults of the regression model are given as the hazard ratio
(HR) and the 95% confidence interval (CI). Interaction
was assessed using multiplicative interaction terms andlikelihood ratio tests. Regression diagnostics and overallmodel fit were performed according to standard proce-dures. A 2-sided p value less than 0.05 was consideredstatistically significant. Calculations were performedwith SPSS for Mac OSX (version 16.0; SPSS, Chicago, IL).
Results
DemographicsThe demographics of the entire cohort are depicted inTable 1. Forty-two patients (group A) had the primaryentry tear at the convexity (Fig 3), and 23 patients (groupB) had the primary entry tear at the concavity of the distalaortic arch (Fig 4). Chronic health conditions and riskfactors in both groups are depicted in Table 2. Riskfactors were assessed according to the European systemfor cardiac operative risk evaluation definitions [11].
Clinical OutcomeTwo patients died due to retrograde type A aortic dissec-tions, and 1 patient underwent iliac artery stent implan-tation due to limb ischemia. Two patients underwentsmall bowel resection due to extensive visceral ischemia.The remaining patients had an uneventful aortic-relatedclinical course. Early type Ia endoleaks were rare (groupA, 7% versus group B, 4%; p � 0.64).
Table 1. Descriptive Characteristics of the Entire Cohort
Characteristics No. Overall � 70
DemographicsAge, years; median (IQR) 58 (51–65)Female, n (%) 11 (16%)
Chronic health conditions and riskfactorsa
Hypertension, n (%) 70 (100%)Chronic obstructive pulmonary disease,
n (%)20 (14%)
Diabetes, n (%) 1 (1%)Renal insufficiency, n (%) 1 (1%)Extracardiac arteriopathy, n (%) 2 (3%)Previous aortic surgery, n (%) 3 (4%)
In-hospital clinical assessmentEmergency, n (%) 13 (18%)Logistic EuroSCORE, median (IQR) 10 (8–24)Suitable for open surgery, n (%) 20 (29%)
Dissection entryConvex, n (%) (group A) 42 (60%)Concave, n (%) (group B) 23 (33%)Descending, n (%) 4 (6%)Unclear, n (%) 1 (1%)Distance to subclavian artery (cm),
mean (SD)2.3 (2.2)
a Classification of chronic health conditions and risk factors according toEuroSCORE criteria.
Unless otherwise indicated, data are number (percentage).
EuroSCORE � European system for cardiac operative risk evaluation;IQR � interquartile range; SD � standard deviation.
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Morphometric OutcomeThere was no significant difference with regard to thedistance to the left subclavian artery (group A, 2.2 � 1.8cm versus group B, 1.6 � 2.0 cm; p � 0.14). Retrogradecomponents of aortic dissection were common (group A,57% versus group B, 65%; p � 0.60). In group A theretrograde component stopped at the level of the leftsubclavian artery in all patients, whereas in group B, 17%progressed to the level of the aortic arch and 34%progressed as an intramural hematoma up to the level ofthe ascending aorta.
Development of ComplicationsThere was a significant difference with regard to theincidence of primary complicated acute type B aorticdissection (group A, 21% versus group B, 61%; p � 0.003)and with regard to the development of complications(group A, 9 days [9 to 37] versus group B, 0 days [0 to 13];p � 0.03) (Fig 5). Of these, 20 patients underwent primaryTEVAR. In patients with primary complicated type Baortic dissection at the time of referral, malperfusion(61%) was the leading cause, followed by a retrogradetype A intramural hematoma (IMH; 34%). Intractable painwas rare (5%). Within 14 days, a further 16 patients (groupA 30% versus group B 13%) underwent TEVAR. In this timeframe, newly developed malperfusion (44%) was also theleading cause, followed by retrograde type A IMH (19%),diameter progression (25%), and finally, impending rupture
Fig 3. Figure shows a 63-year old male pa-tient with acute severe chest pain and no elec-trocardiographic changes. (A) Parasagittalthin maximum intensity projection (thinMIP)computed tomography angiographic imageshowing an acute type B aortic dissection witha primary entry tear at the convexity of thedistal aortic arch. (B) Axial image at the levelof the distal aortic arch showing the primaryentry tear at convexity. (C) Axial image of thesame patient at the level of the renal arteriesshowing only slight compression of the truelumen. No signs of malperfusion of bothkidneys.
(12%). Between 14 and 30 days, another 7 patients under-
went TEVAR because of a diameter increase of more than20%, compared with baseline, at the proximal descendingaorta. Another 12 patients underwent TEVAR after 30 daysfor the same reason. Nine patients (group A, 14% versusgroup B, 13%; p � 0.99) were primarily uncomplicated andremained uncomplicated.
Cox Regression AnalysisUnivariate Cox regression analysis revealed that a pri-mary entry tear at the concavity was a predictor ofprimary or secondary development of complicated acutetype B aortic dissection, with a HR of 1.8 (95% CI, 1.0 to3.1). Although the presence of a retrograde component ofthe dissection and a short distance of the primary entrytear to the subclavian artery were significant confoundersin the univariate analysis, the predictive effect of the siteof the primary tear was sustained after adjustment HR 1.8(95% CI, 1.0 to 3.2).
Follow-UpLate type Ia endoleak formation was observed in 5% ofpatients in group A and in 4% of patients in group B (p �0.45). Late open surgical conversion was performed in12% in group A and in 13% in group B (p � 0.92) (Table3). Reasons for surgical conversion were retrograde typeA dissections in 3 patients. Two patients had isolatedtype A dissections as a new unrelated event, and 4patients underwent thoracoabdominal replacement due
to aneurysm formation in downstream aortic segments.
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Comment
A primary entry tear at the concavity of the distal aorticarch is associated with a significant increase of theoccurrence of complicated acute type B aortic dissection.Due to low procedural risk and high success rates,closure of the primary entry tear with TEVAR is stronglyrecommended in this newly defined high-risk subgroupof patients.
The clinical idea for this study originated from theobservation that a certain percentage of retrograde typeA dissections have their entry tear in the descendingaorta [17]. As such, it seemed obvious that the localiza-tion of the primary entry tear must have an impact on thepropagation, and consequently, on the required treat-ment strategy in acute type B aortic dissection. The factthat small entry tears at the concavity of the distal aorticarch in patients with acute intramural hematoma (IMH)can lead to IMH within the ascending aorta, furthersubstantiating the need for an exact evaluation of thelocation of the primary entry tear [8, 9].
Clinical outcome corresponds well to the recent liter-ature. Rupture remains a threat, as does retrograde typeA aortic dissection after TEVAR, being observed morecommonly in dissections than in any other acute andchronic aortic pathology [18]. A rarely observed indica-tion for treatment in this series was recurring or persis-tent. Despite being rare, this issue warrants attention.Recurring or persistent pain is an indispensable surro-
gate for an active mechanism irrespective of the under-
lying disease and should therefore not be underesti-mated. It is clear that the natural course of dissection-related pain should be a declining one the longer theacute event has passed. However, recurring peaks of painmay well give an important clinical hint for an impendingcatastrophe. It would be worthwhile to think upon apain-scale evaluation of patients after acute type B aorticdissection and to correlate this pain scale to outcome.This could well be a task of future investigation.
Notably, retrograde components of dissections werecommon in both primary entry tears at the convexity as wellas at the concavity. This is in line with previous reports [8,9, 17]. However, previous reports linked the location of theprimary entry tear with retrograde type A dissection but notwith complicated type B aortic dissection.
An anatomic barrier seems to be decisive with regardto the clinical consequences of retrograde propagation[19]. This may well explain our findings that the aorticarch and the ascending aorta were not affected in any ofour patients with a primary entry tear at the convexity,but, in more than half of the patients with a primary entrytear at the concavity the aortic arch and the ascendingaorta were affected. Furthermore, it was interesting toobserve that retrograde components presented as pro-gressive IMH, thus substantiating the clinical suspicionthat IMH is an intermediate stage of classical dissection[8, 20]. It may well be assumed that these IMH may havepropagated to classical retrograde type A aortic dissec-
Fig 4. Figure shows a 56-year old male pa-tient with acute severe chest pain and no elec-trocardiographic changes. (A) Parasagittalthin maximum intensity projection computertomography angiographic image showing anacute type B aortic dissection with a primaryentry tear at the concavity of the distal aorticarch. (B) Axial image at the level of the distalaortic arch showing the primary entry tear atconcavity. (C) Axial image of the same patientat the level of the origin of the superior mes-enteric artery shows compression of the aortictrue lumen due to expansion of the false lu-men and subsequent malperfusion of the leftkidney.
tion without treatment.
ORE
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A significant difference between both groups with regardto the time of development of complications could beobserved, with a substantial need for urgent or emergentTEVAR in the majority of patients with a primary entry tearat the concavity. Nevertheless, delayed complications weredeveloped in an additional 16 patients with type B aorticdissections within 14 days. Of these, the majority had a
Fig 5. Kaplan-Meier calculation of freedom from development ofcomplications for both groups showing significant differences relatedto the site of the primary entry tear. (CI � confidence interval;
Table 2. Distribution of Patients by Different Chronic HealthOrigin of the Primary Dissection Entry
Variable
DemographicsAge, median (IQR)Female sex, n (%)
Chronic health conditions and risk factorsa
Hypertension, n (%)Chronic obstructive pulmonary disease, n (%)Extracardiac arteriopathy, n (%)Previous aortic surgery, n (%)Suitable for open surgery, n (%)Logistic EuroSCORE, median (IQR)
CT- morphology of dissectionMax. ascending aortic DM (cm), median (IQR)Max. descending aortic DM (cm), median (IQR)Retrograde dissection component, n (%)Distance to subclavian artery (cm), mean (SD)
a Classification of chronic health conditions and risk factors according to
Unless otherwise indicated, data are number (percentage).
primary entry tear at the convexity, which was quite clear asnearly all patients with a primary entry tear at the concavityhad already been treated. This finding further underlinesthe necessity of hospitalizing patients with a primary un-complicated type B aortic dissection for 14 days, whichremains the critical period.
ditions and In-Hospital Risk Assessment Stratified to the
Unless otherwise indicated, data are number (percentage).
Con
5
41
11
3322
Euro
IQR � interquartile range.
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In this analysis, we did not include the primary aorticdiameter in the distal aortic arch as a risk factor for earlycomplications as its potential lies in the prediction of latecomplications [7]. However, we think that it would beappropriate to perform a study where the initial diameterrise within the first 7 or 14 days is assessed as there are nodata out on this issue. Presumably, by this approach, theratio between initial diameter and diameter after 7 or 14days may turn out to be more indicative than the absolutediameter itself.
It is obvious that the underlying need for TEVAR isdifferent in the acute and in the early chronic phase.Rupture, contained rupture, retrograde extent into thearch, or into the ascending aorta, with visceral, renal, orlimb malperfusion, and persistent pain, were not ob-served after 14 days. The only indication for TEVAR inthe chronic phase was a diameter increase of more than20% compared with baseline, taken as a surrogate fordisease progression. It will be the task of future investi-gations to define whether this indication for TEVAR isjustified [21]. Finally, 9 patients with an entry tear at theconvexity were primarily uncomplicated and remaineduncomplicated. We were not able to predict with cer-tainty whether these patients might develop an aneurys-mal formation in downstream segments in the future.According to current knowledge, these patients do wellwith medical therapy [22].
Conversion to open surgery is higher than expected fromthe current literature. Several reasons may account for thisfinding. On the one hand, the issue of retrograde type Adissection is of sad actuality and remains unpredictableeven years after the initial event [18]. Furthermore, a patentprimary entry has turned out to be an independent predic-tor of need for surgical conversion due to late aneurysmformation. Finally, a strict follow-up protocol encomprisinga CT scan of the entire aorta on an annual basis, as we do inour setting, may help in early detection of the threshold forsecondary surgical conversion.
Multivariate regression analysis revealed a significantincrease in risk for a complicated acute type B aorticdissection in patients with a primary entry tear at theconcavity. This suggests the need for a rediscussion ofthe definition of complicated, as we defined retrogradeextent into the arch or into the ascending aorta ascomplicated due to the inherent risk of classical retro-grade type A dissection. As a consequence, we do notfollow a watch and wait strategy in these patients butsubject them to treatment if the primary entry tear can beclearly localized at the concavity. Due to our results anddue to our clinical experience in this kind of pathology,location of the primary entry tear supercedes symptomsand nonsymptoms regarding the need for intervention.However, it remains a rare occasion that a patient with anacute type B aortic dissection with a primary entry tear atthe concavity is, or becomes, asymptomatic.
Limitations and StrengthsAlthough we could demonstrate that a primary entry tearat the concavity of the distal aortic arch is associated with
a significant increase in the occurrence of complicated
type B aortic dissections, the sample size is modest withregard to random variability. Because of the low inci-dence of this disease, our findings from this single-centerstudy will ideally need confirmation in multicenter stud-ies. In addition, patient management in the emergencydepartment, operating theatre, and intensive care unitmay have confounded the results. However, such con-founders are impossible to control in an observational,noninterventional study. Even the definition of an in-crease of aortic diameter of more than 20% as indicationfor TEVAR in the subacute or chronic phase is arbitraryand not defined as a cutoff marker in the literature.
The value of this study is the newly created awarenessthat the percentage of complicated type B aortic dissec-tion is by far higher than reported in the literature. Acertain benignity of type B aortic dissection with regardto the natural course has come to the mind of thescientific community and which does, in our impression,not reflect clinical reality. The main reason for this mightwell lie in the fact that many units do discharge patientswith acute type B aortic dissection after 10 days and leavethe follow-up to referring centers or even to familydoctors. As a consequence the entire complexity of thedisease is missed. It is also the focus of this manuscript toalert physicians treating this disease to closely followthese patients in the chronic phase to detect need fortreatment early and therefore to prevent adverse outcome.
In order to enable a modified standardized terminol-ogy we suggest referring to a primary entry tear at theconvexity as B1 and to a primary entry tear at theconcavity as B2 in acute type B aortic dissections. It willbe the task of future consensus documents and guide-lines to adopt this approach.
Summarizing, a primary entry tear at the concavity ofthe distal aortic arch is associated with a significantincrease of the occurrence of complicated acute type Baortic dissection. Due to low procedural risk and highsuccess rates, closure of the primary entry tear withTEVAR is strongly recommended in this newly definedhigh-risk subgroup of patients.
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