Prognostic Significance of Early Aortic Remodeling in Acute Uncomplicated Type B Aortic Dissection and Intramural Hematoma

Structured Abstract

Background

Patients with Stanford type B aortic dissections (AD) are at risk of long-term disease progression and late complications. The aim of this study was to evaluate the natural course and evolution of acute type B AD and intramural hematomas (IMH) in patients who presented without complications during their initial hospital admission and who were treated with optimal medical management (MM).

Methods

Databases from two aortic centers in Europe and the US were used to identify 136 patients with acute type B AD (n= 92) and acute type B IMH (n= 44) who presented without complications during their index admission and were treated with MM. Computed tomography (CT) angiography scans were available at onset (≤ 14 days) and during follow-up for those patients. Relevant data, including evidence of adverse events during follow-up (AE; defined according to current guidelines), were retrieved from medical records and by reviewing CT scan images. Aortic diameters were measured using dedicated 3D software.

Results

The 1-, 2- and 5-year event-free survival rates of patients with type B AD were 84.3% (95% CI: 74.4 – 90.6), 75.4% (95% CI: 64.0 – 83.7) and 62.6% (95% CI: 68.9 – 73.6), respectively. Corresponding estimates for IMH were 76.5% (95% CI: 57.8 – 87.8), 76.5% (95% CI: 57.8 – 87.8) and 68.9% (95% CI: 45.2 – 83.9), respectively. In patients with type B AD, risk of an adverse event increased with aortic growth within the first six months after onset. A diameter increase of 5 mm in the first half year was associated with a relative risk for AE of 2.29 (95% CI: 1.70–3.09) compared with the median 6 months growth of 2.4 mm. In about 60% of IMH patients the abnormality resolved within 12 months and in the patients with non-resolving IMH, risk of an adverse event was highest in the first year after onset and remained stable thereafter.

Conclusions

More than one-third of patients with initially uncomplicated type B AD suffer an AE under MM within 5 years of initial diagnosis. In patients with non-resolving IMH, most adverse events are observed in the first year after onset. In patients with type B AD an early aortic growth is associated with a higher risk of AE.

Introduction

Type B aortic dissections (AD) and intramural hematomas (IMH) share the same underlying aortic wall pathology, present with the same clinical symptoms and develop similar complications.¹ While classic AD is characterized by the presence of an intimal tear and formation of a false channel within the media-layer of the aortic wall, no perfused false lumen is visible in IMH. Acute type B AD is a well-recognized clinical challenge, with a broad range of immediate clinical outcomes.^2,3 Some patients present with potentially life-threatening complications, such as rupture and organ malperfusion, some with refractory hypertension or uncontrollable pain despite medication. In these patients, urgent endovascular or open surgical repair is indicated. Patients presenting without a life-threatening event are considered uncomplicated. Traditionally, these patients are treated conservatively, with medical management (MM).^4,5 The potential role of endovascular repair for patients with uncomplicated type B AD is a much-debated topic. Patients who are medically managed require lifelong surveillance to monitor disease progression and prevent late adverse events.^6,7 Disadvantages of this strategy include the risk of poor patient compliance and incomplete follow-up. With progression of the aortic wall degeneration, aortic enlargement, and increasing stiffness of the intimal flap, treatment might become more complex and extensive at a later stage of the disease.^8,9 Finally, when a patient with chronic type B aortic dissection presents acutely, the risk of an unfavorable outcome after treatment is higher than after an elective intervention. Early thoracic endovascular aortic repair (TEVAR) has been proposed as an alternative strategy to prevent late adverse events.^10–14 Although perioperative mortality is below 5%, TEVAR for type B AD can be associated with significant complications, including paraplegia, stroke, and retrograde type A dissection.^15–17 In the context, a thorough understanding of the course of disease in dissections may be helpful. More insights into the evolution and aortic diameter growth in dissection and intramural hematoma and the associated risk of complications relating to the particular type of anatomic aortic involvement is required. It is interesting to explore whether the rate of progression in the first months after onset of the disease might be predictive of later risk of complications. The aim of this study was to evaluate the natural history and aortic remodeling in patients with initially uncomplicated acute type B AD or uncomplicated acute type B intramural hematomas (IMH).

Methods

This study was approved by the Institutional Review Boards of the participating institutions. Informed consent was waved, given the retrospective nature of this work.

Patients

Databases from 2 large aortic centers in the United States and Europe were used to identify patients presenting with acute type B AD or IMH between January 2002 and December 2012 and who survived their initial hospital admission without complications. Patients for whom data from computed tomography (CT) angiography scans at presentation and during follow-up visits were available were selected for further analysis. All patients were initially treated with medical management (MM) and followed up according to the standard clinical regimen. Data on patient characteristics and clinical course were retrospectively retrieved from the medical records. Relevant patient data included patients’ age, sex, presence of connective tissue disease and presence of hypertension.

Definitions

Acute uncomplicated type B AD: Classic Stanford type B aortic dissection with dissection flap. Presentation within 14 days of the symptom onset. Absence of complications, including death, aortic rupture or signs of impending rupture, organ or limb ischemia, or uncontrollable pain or hypertension at presentation and during initial hospital admission.

Acute uncomplicated type B IMH: Stanford type B intramural hematoma without dissection flap and without radiological evidence of a penetrating aortic ulcer (PAU)¹⁸. Presentation within 14 days of the symptom onset. Absence of complications, including death, aortic rupture or signs of impending rupture, organ or limb ischemia, or uncontrollable pain or hypertension at presentation and during initial hospital admission.

Aortic remodeling

CT images acquired at the time of diagnosis and during all follow-up visits were used to evaluate aortic growth. On each individual scan, aortic diameters were measured at several pre-defined levels. The parameter used to evaluate aortic growth was the maximum aortic diameter For each patient, the slope of aortic growth was calculated individually based on baseline maximum aortic diameter measurements and all repeated follow-up diameters. Baseline was considered the scan at discharge from the index hospitalization. Aortic growth rate slopes during the first 6 months were used to correlate with occurrence of adverse events during follow-up. We also recorded whether and when resolution of the dissection or IMH was observed, or whether an IMH evolved into a dissection. Resolution was defined as absence of high-density intramural aortic rim on non-contrast enhanced CT scans and absence of an intimal flap on the contrast-enhanced CT angiography.

Outcomes

The primary outcome measure was the cumulative probability of adverse event-free survival. Patients were classified as having an adverse event if one or more of the following events were diagnosed clinically and/or by CT angiography: fatal or non-fatal signs of aortic rupture, organ or limb ischemia, aortic aneurysm formation (thoracic aortic diameter ≥ 6 cm), rapid aortic diameter growth of ≥ 10 mm within 12 months of follow-up, or new refractory hypertension or pain that could not be controlled with medical therapy. In order to distinguish between clinically stable patients with asymptomatic progression of aortic diameters requiring elective intervention versus those requiring urgent treatment we also calculated the cumulative probability of event free survival from the subset of urgent late adverse events, including fatal or non-fatal signs of aortic rupture as well as organ or limb ischemia as a secondary outcome measure.

Image analysis

CT angiography images at presentation and all follow-up CT scans were reviewed for all patients. The standard scan regimen was at onset, discharge, 3 or 6 months, 12 months, and yearly thereafter, but it could differ for individual patients, depending on findings. Images were analyzed using dedicated 3D software iNtuition (TeraRecon, Inc., Foster City, CA) to measure the aortic diameters. Measurements were performed using the orthogonal method, after generating straightened multiplanar reformations (MPR). In all studies, radiological signs of adverse events, such as organ malperfusion and rupture, as well as imaging evidence of pathology resolution were reviewed.

Statistical Analysis

Baseline characteristics for the total study population and the groups with type B AD or type B IMH are described as absolute numbers and percentages for categorical variables and as mean (± standard deviation) or median with interquartile range for continuous variables. Differences between groups were tested with the chi square test for proportions and with the t-test for independent samples for continuous variables (if normally distributed) or the non-parametric Mann-Whitney U test (if not normally distributed).

Initial 6-months growth at the maximum aortic diameter of the dissections were calculated for each patient based on the repeated measurements at this landmark. The influence of growth rates in the initial 6 months on primary and secondary outcome was evaluated with a Cox proportional hazards model. In IMH patients, a distinction was made between patients with and without resorption of the IMH. Cumulative probabilities of event-free survival from all adverse events at 1 year, 2 years, and 5 years after onset were calculated using Kaplan-Meier survival analysis. Pre-specified subgroup analyses were performed for (1) patients with type B AD versus IMH, (2) patients with aortic growth rates of 0, 3, 5 and 9 mm within in the first 6 months, and (3) patients with resorbing versus non-resorbing IMH. Differences in probabilities of event-free survival between subgroups were tested for statistical significance using the log rank test. Cumulative probability of resolution of an IMH within 1, 6, and 12 months was also calculated with time-to-event analysis. Follow-up ended on the date on which an adverse event occurred or the date of the last observation (if no adverse event occurred). A p-value ≤ 0.05 was considered to indicate statistical significance. The analyses were performed using SPSS, version 21 (International Business Machines corporation, Armonk, NY) or R Core Team (2016, https://www.R-project.org) and Thernau T (2015, http://CRAN.R-project.org/package=survival).

Results

Figure 1 presents a flow diagram of patient inclusion. Out of 207 eligible patients with acute uncomplicated aortic dissection, 71 patients had to be excluded because their care was transferred back to the referring center for further follow-up. The final study population consisted of 136 patients, including 92 patients with uncomplicated type B AD and 44 patients with uncomplicated type B IMH. Three of the type B AD dissections were iatrogenic, following cardiac and other arterial catheterizations; 6 of the dissections affected only the abdominal aorta. Two or more follow-up CT scans were available for 90.2% of patients with type B AD and for 90.9% of patients with IMH. Follow-up was based on 6 or more CT scans in 33.6 % and 22.7% of type B AD and IMH patients, respectively.

Figure 1.

Flowchart of patient inclusion. Numbers in brackets show number of patients from each center. MM: Medical management.

Baseline patient characteristics are shown in table 1. Patients with type B AD were significantly younger at presentation than patients with IMH (p = 0.049) and presence of hyperlipidemia was significantly less common compared to patients with IMH (p = 0.038). In the type B AD group, 16 patients (17.4%) had connective tissue disease, whereas in the IMH group there were only 3 affected patients (6.8%), but this difference was not significant (p = 0.166).

Table 1.

Baseline patient characteristics for all patients as well as for the groups classic type B AD and IMH.

	All patients (n = 136)	Type B AD (n = 92)	IMH (n = 44)	p-value
Male gender (n)	86 (63.2 %)	61 (66.3 %)	25 (56.8 %)	.343
Age at onset (in years, mean ± SD)	60 ± 16	55 ± 16	69 ± 12	.049
Connective tissue disease (n)	19 (14 %)	16 (17.4 %)	3 (6.8 %)	.117
Hypertension (n)	119 (87.5 %)	79 (85.9 %)	40 (90.9 %)	.581
Hyperlipedemia (n)	64 (47 %)	38 (41.4 %)	26 (59.1 %)	.038
Diabetes (n)	9 (6.6 %)	7 (7.6 %)	2 (4.5 %)	.39
Smoker (active and former) (n)	77 (56.6 %)	47 (51.1 %)	30 (68.2 %)	.157
Iatrogenic dissection / Trauma (n)	3 (2.2 %)	3 (2.2 %)	0 (0%)	0.225
llicit drug use (n)	1 (0.7 %)	1 (1.1 %)	0 (0%)	0.89
Vasculitis (n)	1 (0.7 %)	1 (1.1 %)	0 (0%)	0.89
Pregnancy (n)	0 (0%)	0 (0%)	0 (0%)	1
Inheritet conditions (Turner syndrome, polycystic kidney disease, other) (n)	0 (0%)	0 (0%)	0 (0%)	1

The types and frequencies of adverse events observed over a median follow up of 861 days in patients with uncomplicated type B AD and IMH are presented in Table 2.

Table 2.

Overview of events during follow-up for all patients and by groups: type B AD and IMH.

	All (n = 136)	TBAD (n = 92)	IMH (n = 44)
All Adverse Events
Rupture	3 (2.2 %)	1 (1.1 %)	2 (4.5 %)
Renal ischemia	5 (3.7 %)	4 (4.3 %)	1 (2.3 %)
Bowel ischemia	1 (0.7 %)	1 (1.1 %)	0 (0 %)
Limb ischemia	2 (1.5 %)	2 (2.2 %)	0 (0 %)
Spinal cord ischemia /Neurologic impairment	0 (0 %)	0 (0 %)	0 (0 %)
Aortic diameter ≥ 6 cm	18 (13.2 %)	17 (18.5 %)	1 (2.3 %)
Rapid aortic diameter growth ≥ 10 mm /year	10 (7.4 %)	8 (8.7 %)	2 (4.6 %)
New refractory pain, uncontrollable with medication	3 (2.2 %)	0 (0%)	3 (6.8 %)
Urgent Adverse Events	42 (30.9 %)	33 (35.9 %)	9 (20.5 %)
Rupture	3 (2.2 %)	1 (1.1 %)	2 (4.5 %)
Renal ischemia	5 (3.7 %)	4 (4.3 %)	1 (2.3 %)
Bowel ischemia	1 (0.7 %)	1 (1.1 %)	0 (0 %)
Limb ischemia	2 (1.5 %)	2 (2.2 %)	0 (0 %)
Other Events	11 (80.1%)	8 (8.7%)	3 (6.8%)
Resolution of the IMH	26 (59.1%)	0 (0 %)	26 (59.1 %)
Resolution of dissection flap	2 (1.5 %)	2 (2.2 %)	0 (0 %)

Aortic Remodeling and Adverse Events in patients with AD

A total of 33 of 92 (36%) patients with type B AD developed an adverse event during follow-up, of which 26 of 33 (78.8%) were related to aortic critical diameter progression. Urgent severe adverse events occured in 8 patients (9%). None of the 6 patients with an isolated abdominal aortic dissection developed an adverse event. Resolution occurred in 2 patients with aortic dissection; both of which were iatrogenic. During follow-up, 15 patients were treated with open surgical aortic graft replacement, 9 patients were treated endovascularly, and 3 patients were treated with a hybrid approach. In one patient, a single nephrectomy was performed. Five patients died during hospitalizations related to a late adverse event.

With respect to aortic remodeling, 30.4% (28/92) of patients with type B AD had a growth rate of 5 mm or higher over the first 6 months; this percentage was higher in patients with connective tissue disease, in whom 50% (7/14) of patients had a 5mm or higher 6-months aortic growth rate. Figure 2 illustrates the relationship between the 6-month aortic growth and relative risk of (a) all adverse events and relative risk of (b) urgent adverse events (excluding patients with clinically stable critical size progression) over a period of 5 years for type B AD. We found that faster aortic growth in the first 6 months, is associated with an increased relative risk (RR) for late adverse events. This effect was significant for all adverse events and for urgent severe adverse events only (p < 0.001 and p = 0.002, respectively). Compared with a median growth of 2.4 mm/half year as reference value (RR = 1), no growth (0 mm/half year) was associated with a relative risk of adverse events (including size progression) of 0.44 (95% CI: 0.32–0.60). Six-month growths of 3 mm, 5 mm and 9 mm were associated with RR of 1.22 (95% CI: 1.14–1.32), RR of 2.29 (95% CI: 1.70–3.09) and RR of 7.09 (95% CI: 3.62–13.91), respectively. The initial aortic diameter was not independently significantly correlated with the occurrence of adverse events (p = 0.168). For acute adverse events only, no growth was associated with a relative risk of 0.56 (95% CI: 0.31–1.00). Growth rates of 3 mm, 5 mm and 9 mm per first half year were associated with RR of 1.16 (95% CI: 1.01–1.13), RR of 1.81 (95% CI: 1.04–3.16) and RR of 4.04 (95% CI: 1.17–13.99), respectively.

Figure 2.

Relationship between aortic growth rate over the first 6 months and log relative risk for (a) all adverse events including critical size progression and (b) urgent adverse events excluding critical size progression. The median value of growth is 2.4 mm in the first half year and this value was chosen as reference value. Blue dotted lines show 95% confidence intervals. Red dotted vertical lines aid in reading the log RR for four exemplary slopes of 0, 3, 5 and 9 mm aortic growth in the first half year.

Aortic remodeling and adverse events in patients with IMH

Out of 44 patients with IMH, 9 patients (21%) developed an adverse event, with new refractory pain being the most common (3 patients, 33.3%), followed by aortic rupture (2 patients, 22.2%), and rapid aortic growth (2 patients, 22.2%). One patient reached an aortic aneurysm size of 6 cm during follow-up (without rupture) and one patient developed renal tissue malperfusion related to the IMH. Seven IMH patients (16%) developed an intimal tear with dissection flap and false lumen flow during follow-up, and 3 of those patients developed an adverse event. Resolution of the IMH was observed in 26 patients. The probability of resolution at 1 month, 6 months, and 12 months was 9.5% (95% CI: 3.7% – 23.4%), 39.2% (95% CI: 25.2% – 57.4%), and 58.9% (95% CI: 42.7% – 75.8%), respectively. During follow–up, 5 patients underwent endovascular aortic repair and 4 patients were treated with open aortic graft replacement. Two patients died during hospital admission related to a late adverse event. Median aortic growth rate in patients with resorbing IMH was −0.04 mm / month (IQR: − 0.39 – 0.00). In patients with non-resorbing IMH, the median growth was 1.49 mm / month (IQR: 0.11 − 2.79). The initial dimeter in patients with non-resorbing IMH was significantly larger than in patients with resorbing IMH In patients without resorption the mean baseline aortic diameter (± standard deviation) was 42.2 ± 6.4 mm versus 36.1 ± 5.3 mm in patients with resorption was, (p = 0.0018). Resorption occurred in 35% (6/17) of patients with an initial aortic dimeter of 40 mm or greater, whereas resorption occurred in 74% (20/27) of patients with initial aortic diameter smaller than 40 mm (p = 0.03).

Adverse event-free survival estimates between subgroups of AD and IMH

Figure 3 shows the Kaplan Meier survival curves for patients with classic type B AD versus IMH. The cumulative probability of event-free survival for patients with initially uncomplicated type B AD was 84.3% (95% CI: 74.4 – 90.6%) within the first year, 75.4% (95% CI: 64.0 – 83.7 %) within the first 2 years, and 62.6% (95% CI: 68.9 – 73.6%) within the first 5 years after onset, respectively. The 1-, 2- and 5-year probability of event-free survival for patients with IMH was 76.5% (95% CI: 57.8 – 87.8%), 76.5% (95% CI: 57.8 – 87.8%), and 68.9% (95% CI: 45.2 – 83.9%), respectively. The probability of event free survival was not different for type B AD versus IMH (log rank: p = 0.963). The temporal pattern of events appears different, however, between those groups and even within IMH patients. Figure 4 shows that all adverse events in patients with IMH occurred in patients without resorption, whereas in patients with resorbing IMH no adverse events were observed (log rank: p < 0.001). In IMH patients without resorption, the majority of adverse events occurred within the first year after onset. In patients with type B AD on the other hand, the cumulative probability of adverse events continues to increase gradually over time. Figure 5 shows the Kaplan Meier survival estimate from the Cox model for four different aortic 6-months growth rates in patients with type B AD. Patients with faster aortic growth in the first 6 month show higher rates of adverse events at 1, 2 and 5 years after onset compared to patients with slower aortic growth. The risk of an adverse event within 2 years after onset is greater than 20% for patients with growth rates of 5 mm and higher.

Figure 3.

Five- year Kaplan Meier survival curves with confidence intervals (dotted lines) for patients with classic type B AD (Dissection) versus intramural hematoma (IMH). Numbers at risk for each year shown in table below. Log rank: p = 0.9629.

Figure 4.

Five- year Kaplan Meier survival curves with confidence intervals (dotted lines) for patients with intramural hematoma (IMH) with and without resorption. Numbers at risk for each year shown in table below. Log rank: p < 0.001.

Figure 5.

Five- year Kaplan Meier survival curves for four aortic growth rates of 0 mm, 3 mm, 5 mm. and 9 mm within the first 6 months from the Cox model.

Discussion

Acute type B aortic dissection is one of the most challenging aortic diseases. Optimal treatment for patients without complications in the acute phase is the subject of ongoing debates, surrounding the choice between medical management and preventive TEVAR. Whether optimal medical treatment with a wait and see approach represents appropriate care depends on the risk of adverse events during follow-up. Unfortunately, neither the clinical course, nor the morphologic evolution of uncomplicated type B aortic dissections and IMH are completely understood. Several analyses have been performed in the past for medically treated type B AD, but none of them have provided a comprehensive picture of clinical evolution over time based on aortic morphology and aortic growth patterns shortly after the acute event.^{6, 19–26} Even less is known about the aortic evolution of acute type B IMH.²⁷ Through this retrospective analysis of data gathered in a time when uncomplicated patients were treated conservatively and preventive interventions were relatively uncommon, we attempt to provide insight into the natural history of initially uncomplicated and medically managed acute type B classic aortic dissections and IMH, with a focus on the probability of event-free survival during follow-up in relation to early aortic remodelling..

Baseline patient characteristics in our retrospective cohort are mostly similar for type B AD and IMH. However, there were more patients with Marfan syndrome and other connective tissue diseases in the classic type B AD group, explaining the significantly younger mean age at onset and lower percentage of patients with hyperlipidemia in this group compared to the IMH group. We found clear differences in the natural history between the type B AD and IMH. More than half of the IMH patients (26/44) showed resorption of the hematoma within the first year. However, in patients in whom the hematoma did not resolve, both the initial aortic diameter and aortic growth rates were higher than in the resorbing IMH subgroup as well as in the type B AD group. Most adverse events occur in the first year after onset and the risk of having an adverse event in that first year is about 60% in patients with non-resorbing IMH. This evaluation might suggest that IMH should be followed closely in the first year, either to diagnose resolution (and allow for a less frequent follow-up imaging regimen) or to detect early signs of adverse events. Once patients have survived the first year without complications, they have a high probability of remaining stable during later follow-up. Especially patients with an IMH and an initial diameter > 40 mm seem to be at increased risk for unfavorable evolution.

For patients with type B AD, the risk of an adverse event in the first year is about 15%, but patients remain at risk during later years. An important finding is that the patients with a faster aortic growth rate within the first 6 months represent a group with a significantly higher risk of rupture, mal-perfusion, or late significant aneurysm formation. This finding strongly suggests that rapid early aortic growth itself seems to be a strong indicator for an unfavorable outcome and – if confirmed - could be considered as an indication for elective intervention.

Definitions of late complications and indications for surgery in chronic dissections based upon aortic diameter criteria vary between European and American guidelines, some of which have undergone changes over the past few years. Based on our clinical practice during the study period, a 6 cm maximum aortic diameter of the descending thoracic aorta was considered an adverse event.²⁸ This is in accordance with the current European guidelines²⁹ on chronic dissections and American guidelines with respect to degenerative descending thoracic aortic aneurysm³⁰. The newest American guidelines on chronic dissection recommend elective surgical intervention at an aortic diameter of 55 mm, and other studies discuss intervention at even smaller diameters^31,32. If the 55 mm threshold had been applied to our study, 2 more adverse events would have been recorded, with one patient reaching the 55 mm threshold after 5.1 years and another after 8.9 years. Similarly, differences exist for the definition of rapid aortic growth, as the definition of this complication varies in guidelines from > 4mm over a year to > 10 mm over a year.^5,29,30 We used a > 10mm increase in aortic diameter over a year as the definition of an adverse event.²⁹

Our study is limited by its retrospective design, the variation in the follow-up regimen and number of CT scans between patients, but most importantly the potential selection bias associated with studies carried out in high-volume referral centers, and by the incomplete follow-up. Approximately one-third of patients admitted to our institutions for treatment of uncomplicated type B aortic dissection or IMH were followed clinically by outside referring health-care providers after hospital discharge. Choice of follow-up in other centers was typically based on the location of patient’s residence or insurance coverage. We informally compared the baseline characteristics of our study population (Table 1) with those patients followed elsewhere and did not find a significant difference in any of the baseline characteristics, except for the fact that all patients with connective tissue diseases were followed at the two participating aortic centers, and none of these patients was followed outside. This is not unexpected, and underscores the limits of generalizability of our findings to patients seen in expert aortic centers.

Conclusion

More than one third of patients with acute type B AD who survive the initial hospitalization without complication and who are medically managed undergo an AE within five years. In patients with non-resolving IMH, most adverse events are observed in the first year after onset, and in patients with type B AD a rapid early aortic growth is associated with a high risk of AE.

Supplementary Material

supplement. VIDEO.

In this short (2 min 45s) introductory video the paper’s senior author – Dr Dominik Fleischmann – explains the motivation and key findings of this study.

Central Message.

Most adverse events in patients with non-resolving IMH occur in the first year. Aortic growth in the first 6 months is associated with late AE in patients with uncomplicated type B AD.

Perspective Statement.

Non-resolving IMH should be followed closely in the first year, because this is when most adverse events occur. Resolving IMH typically remain stable. In patients with initially uncomplicated type B AD, a faster growth within the first 6 months under medical management (MM) is associated with a higher risk of adverse events.

Abbreviation glossary

AD

Aortic dissection

IMH

Intramural hematoma

MM

Medical management

AE

Adverse event

CT

Computed Tomography

IQR

Interquartile range

TEVAR

Thoracic endovascular aortic repair

RR

Relative Risk