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Invited Commentary
Cardiology
August 24, 2018

Drawing the Line on Prophylactic Aortic Replacement: Primum Non Nocere

Author Affiliations
  • 1Corrigan Minehan Heart Center, Division of Cardiac Surgery, Massachusetts General Hospital, Harvard Medical School, Boston
JAMA Netw Open. 2018;1(4):e181289. doi:10.1001/jamanetworkopen.2018.1289

Guo and colleagues1 have pursued an important clinical question using the best available evidence. Examining data encompassing 8800 patients and providing almost 32 000 patient-years of follow-up from 20 studies lasting between 2.5 and 16 years, they have concluded that the risk of aortic catastrophe associated with moderate aortic dilatation is, in fact, low. The linearized all-cause mortality rate was 1.99% per patient-year, and the linearized rate of composite outcome, including aortic dissection, aortic rupture, and all-cause mortality, was 2.16% per patient-year. Furthermore, there was no significant relationship between mean initial aneurysm size and incidence of dissection, rupture, or all-cause mortality. Intriguingly, there was also no relationship between size and incidence of elective aortic surgery, with elective aortic surgery undertaken in 13.82% of patients over a median follow-up of 4.2 years. Importantly, there were no significant differences between aneurysms associated with tricuspid vs bicuspid valves. For patients with tricuspid valves, the pooled mean annual growth rate was only 0.34 mm/y. The pooled mean annual growth rate for patients with bicuspid valves was higher at 0.76 mm/y; however, this was driven by the inclusion of the study by Davies et al,2 which indicated rates considerably higher than those of other studies.

Over the past decade there has been a trend toward a more and more aggressive approach to prophylactic aortic replacement in the setting of moderate dilatation. Motivated by recognition of mortality rates as high as 25% associated with acute dissection involving the ascending aorta3 and the observation that as many as 50% of dissections may occur among people with aortic diameters below the commonly accepted threshold of 5.5 cm,4 aortic specialists have encouraged earlier intervention, particularly among those with bicuspid aortic valve–associated aortopathy.5 In support of this position, surgeons point to ever lower operative mortality rates for elective aortic intervention; the result has been a significant increase nationally in rates of such interventions.6 But is this a good thing?

Missing from the data cited earlier is natural history. As physicians—particularly surgeons—we “live in the numerator,” seeing those who come to medical attention with complications of their condition but blissfully unaware of the asymptomatic multitude unseen. The increase in noninvasive imaging has changed the landscape to some degree, bringing to our attention more of those carrying silent disease and challenging us to consider prophylactic intervention, but still falling short of defining the entire population. Furthermore, as our attitudes toward such interventions change, defining the fate of the untreated condition becomes less and less accessible. How, then, can we be sure that our intervention is not worse than the disease? The only individuals on earth unafraid of heart surgery are heart surgeons. Surely there is a point at which the balance of risks and benefits no longer favors intervention regardless of how low we claim the risk to be. We may disagree on the definition of that point, but surely it exists. And to define both sides of the risk equation—the risk of surgery vs the risk of the disease—we need some sense of the denominator: the natural history of the moderately dilated ascending aorta. This study helps us get closer to that answer.

What is the impact? The problem is most vexing among patients with bicuspid aortic valve–associated dilatation, particularly when the valve itself is functioning well. As Guntheroth7 highlighted in his criticism of the 2006 American College of Cardiology/American Heart Association (ACC/AHA) Practice Guidelines on Bicuspid Aortic Valve With Dilated Ascending Aorta recommendation on bicuspid aortic valve–associated aortopathy, given a population frequency of bicuspid valve of 1% to 2%, the implications are enormous. Those guidelines advocated aortic replacement at 5.0 cm8; the more recent 2010 ACC/AHA Guidelines for the Diagnosis and Management of Patients With Thoracic Aortic Disease5 were even more aggressive, advocating intervention at 4.5 cm. As it is widely recognized that the ascending aorta is most often larger in individuals with bicuspid than tricuspid valves, this ever-broadening definition of aneurysm exacerbates the problem. If somewhere between 30% and 60% of patients with bicuspid valves are classified as having aneurysms, cardiac surgeons in the United States will be quite busy replacing between 1 and 4 million aortas prophylactically.

Since the publication of the 2010 guidelines, the pendulum has begun to swing back, with the 2014 ACC/AHA Guideline for the Management of Patients With Valvular Heart Disease9 aligning with our European counterparts10 at 5.5 cm. This suggestion met with concerns, leading to a task force effort to compromise at a threshold of 5.0 to 5.5 cm depending on local surgical expertise.11 This leads to the most intriguing part of the story. Why is it so hard to roll back the threshold?

To be sure, for patients, once they have been told they have an aneurysm (read, “time bomb in your chest”) it is very hard to turn back the clock and reassure them that the likelihood of a catastrophe is low. I suspect the same is true, to some degree, among caregivers. Who among us wants to sit by watching and hoping that we do not get a phone call that an aorta has dissected? Furthermore, our outcome information is asymmetric. The absence of dissection is a nonevent; we do not see it because there is nothing to see. And, of course, we can never know how many of those aortas we replace would or would not have dissected.

For me, the most impactful message from Guo and colleagues is the challenge to conduct a prospectively randomized study of small aneurysms. It is easy to find reasons not to do so, but these authors appropriately point to our siblings in vascular medicine and surgery who have in fact done so and shown that for abdominal aneurysms smaller than 55 mm, the risk of early surgery outweighs the risk of rupture during surveillance. Isn’t it time for us to do the same?

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Article Information

Published: August 24, 2018. doi:10.1001/jamanetworkopen.2018.1289

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2018 Sundt TM. JAMA Network Open.

Corresponding Author: Thoralf M. Sundt, MD, Division of Cardiac Surgery, Massachusetts General Hospital, Harvard Medical School, Cox 652, 55 Fruit St, Boston, MA 02114 (tsundt@partners.org).

Conflict of Interest Disclosures: None reported.

References
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