Aortic Dissection Risk Rises With Thoracic Aneurysm Size: Large Network Study

The findings confirm current recommendations for surgery at sizes above 5.5 cm, but the decision is multifactorial, experts say.

Aortic Dissection Risk Rises With Thoracic Aneurysm Size: Large Network Study

In patients with ascending thoracic aortic aneurysm (TAA) and no other organ-system abnormalities, the absolute risk of aortic dissection is low but increases with larger aortic sizes, according to new population data.

“One study is never enough, but our data probably contribute, I would say, some of the most robust evidence to date to help answer this question of what is the risk of dissection for patients with larger aortic aneurysms,” lead author Matthew D. Solomon, MD, PhD (Kaiser Permanente Oakland Medical Center, CA), told TCTMD. “Most of our recommendations are based upon data . . . from nearly 20 years ago, so I think our study was really an opportunity to . . . update that.”

Further, he said, the study “supports our current guidelines, which recommend surgery for nonsyndromic patients who don't have any high-risk features at 5.5 centimeters, and it cuts against the argument that says we should lower the threshold for aortic surgery.”

Mohammad Abdullah Zafar, MBBS (Yale-New Haven Hospital, CT), who commented on the study for TCTMD, agreed.

“The overall message of the study just reinforces current practice guidelines that adverse events in ascending aortas in patients—ie, type A dissection and death—happen at around 6 cm and that intervention at 5.5 cm is warranted,” he said. “It's heartening, actually, that this large population-based, really well done study lends very, very strong credence to current practice guidelines and the 5.5 centimeter criterion.”

KP-TAA Study Results

For the KP-TAA study, published online last week in JAMA Cardiology, Solomon and colleagues included 6,372 patients with nonsyndromic TAA (mean age 68.6 years; 32.3% female) from their health network who were identified between 2000 and 2016. Mean initial TAA size was 4.4 cm, with 13.0% and 4.4% of the cohort, respectively, having TAA sizes of at least 5.0 and 5.5 cm.

Over a mean 3.7 years of follow up, only 0.7% of the cohort reported aortic dissection. The unadjusted rates of both death and aortic dissection or rupture increased with initial TAA size.

Outcomes by Initial TAA Size



Aortic Dissection
or Rupture

Aortic Dissection per
100 Person-Years

Aortic Dissection/ Death per 100 Person-Years

< 4.0 cm





4.0-4.4 cm





4.5-4.9 cm





5.0-5.4 cm





5.5-5.9 cm





≥ 6.0 cm





The researchers observed a direct relationship on multivariate analysis between initial aortic size and higher risks of both aortic dissection and all-cause death, with an inflection point at 6.0 cm.

Also using multivariable models, the estimated adjusted risks of aortic dissection within 5 years were 0.3%, 0.6%, 1.5%, 3.6%, and 10.5% for patients with time-updated TAA sizes of 4.0-4.4 cm, 4.5-4.9 cm, 5.0-5.4 cm, 5.5-5.9 cm, and ≥ 6.0 cm, respectively.

Zafar commented that the “real risk” associated with TAA likely lies somewhere in between the risk of aortic dissection and the composite risk of aortic dissection or death used here. “The aortic dissection endpoint gives the absolute minimum possible aortic risk and it's probably an underestimation, because these are confirmed cases of the aortic dissection and we know that in many instances, aortic dissections are misdiagnosed as myocardial infarctions,” he explained. On the other hand, “the all-cause death endpoint [is] sort of the maximum possible aortic risk.”

‘Real Risk Numbers’

Because the patients in this study were closely followed, Solomon said it was likely they received optimal care. “When you get followed, that means that you get counseling about activity and lifestyle changes to minimize the risk of an aortic dissection, you get careful attention paid to your blood pressure, and for many patients, put on medications like beta-blockers that may be protective for the aorta,” he said. “And these interventions could potentially be also minimizing the risk of an adverse outcome over the long-term.”

Prior registries have shown an “aortic paradox” with a higher rate of dissections in patients with smaller aortas likely because “the denominator for that population is very large,” Solomon explained. “What that means is that there are likely a lot of people were not diagnosed with aortic aneurysms that are in the moderate range with the actual risk of having a dissection and your [risk] in that range is very low, nowhere near what it is when the aneurysm is larger.”

These data provide “real risk numbers that we can present to patients for what the risk of an adverse outcome will be, should we consider a watch-and-wait strategy,” he continued. “We've not really known what the risk of not doing surgery at larger aortic sizes is for a long time. So now we're able to really have better numbers to make more informed and shared decision-making.”

Prior to this study, Solomon said he kept an “open mind” as to whether prophylactic surgery would be the optimal choice for certain patients.

“I am very respectful of the fact that the aortic surgery is not a trivial matter,” he said. “Being a practicing aortic physician, it's my job to recommend that procedure to patients when I think they need it. That is always a hard conversation because just like in other areas of cardiology where patients have no symptoms but you're recommending a serious surgery, patients are often unsure whether it's the right decision for them. And the best way to convince them it's the right decision is to have very good data about what the risks of dissection over the long term are for them and those are data that were sorely lacking.”

The best way to convince them it's the right decision is to have very good data about what the risks of dissection over the long term are for them and those are data that were sorely lacking. Matthew D. Solomon

The decision to opt for surgery depends both upon the patient’s risk and preference and the experience of a center’s surgical program, Solomon said. “All of it is a complicated decision, but now we have more pieces of the puzzle to help patients make the best decisions for themselves.”

Similarly, Zafar said the “decision for aortic surgery isn't just based on size alone. There are other factors like family history, evidence of rapid growth rate, a patient's stature, [and] genetic testing even.”

“One of the good things that this study has shown [is] that aortic size retains its importance in this regard as a factor that we judge for surgical intervention,” he added, noting that at his institution, surgery is sometimes recommended for patients with TAAs in the 5.0-5.5 cm range if they have other high-risk factors.

Even with the data presented here, Zafar said he would like to see more work done looking at this population. “We recently looked at our data [of about] 400-500 dissections, and we found [that] 70% of the dissections happened below 5.5 cm,” he said. “So this criteria is still sort of problematic in that we still need to investigate this 5- to 5.5-centimeter size range a little more.”

As a population study, the current paper included patients who were operated on based on surgeon- and center-based appropriateness, Zafar said. “The real natural history was presented from expressing itself based on surgical judgment. So that surgical judgment distorts the description of the natural history, because after intervention, no further adverse events can occur.”

Ultimately, the decision boils down to balancing the risks associated with surgery versus the aneurysm itself, he continued. “Surgery has become much safer, especially over the last 20 to 30 years. So that should just be kept in mind.”

  • This study was supported by Kaiser Permanente Northern California Community Health, and by grants from the Permanente Medical Group Delivery Science and Applied Research and Physician Researcher Programs.
  • Solomon and Zafar report no relevant conflicts of interest.