By Michael Crawford, MD, Editor

Professor of Medicine, Chief of Clinical Cardiology, University of California, San Francisco

Dr. Crawford reports no financial relationships relevant to this field of study.

SYNOPSIS: An observational study of patients with dilated ascending aortas not due to inflammatory or syndromic conditions supports the current guideline recommending clinicians consider prophylactic surgery at ≥ 5.5 cm in diameter, and the risk of dissection or rupture is not greater in those with bicuspid aortic valves.

SOURCES: Kim JB, Spotnitz M, Lindsay ME, et al. Risk of aortic dissection in the moderately dilated ascending aorta. J Am Coll Cardiol 2016;68:1209-1219.

Pape LA. Aortic risk redux. J Am Coll Cardiol 2016;68:1220-1222.

Current guidelines recommend elective repair of the ascending aorta when the diameter reaches 5.5 cm to prevent acute dissection or rupture. However, recent observations have shown that dissection often occurs in smaller ascending aortas, especially in patients with bicuspid valves. Thus, some have proposed lowering the surgical diameter cut point. To explore this further, investigators analyzed the echocardiography database at the Massachusetts General Hospital and identified those with ascending aortic diameters between 4.0 and 5.5 cm. Patients with connective tissue disorders, inflammatory aortic diseases, or a history of aortic surgery were excluded. Medical records were assessed to identify subsequent aortic dissection or rupture for up to five years (median 3.4) from the index echo. The study group included 4,654 adults, of whom 586 (13%) had bicuspid valves. Aortic dissection or rupture occurred in 13 and one patients, respectively, which represented a 0.1% per patient-year incidence. On multivariate analysis, aortic dissection/rupture was associated with age (hazard ratio [HR], 1.06; 95% confidence interval [CI], 1.01-1.12; P = 0.024) and baseline aortic diameter (HR, 1.2; 95% CI, 1.05-1.36; P = 0.006), but not a bicuspid valve (HR, 0.94; 95% CI, 0.10-8.4; P = 0.95). Dissection or rupture rates within five years were: 0.4% at a diameter of 4.5 cm; 1.1% at 5.0 cm; and 2.9% at 5.5 cm. The authors concluded that in subjects with moderate dilation of the ascending aorta, the risk of dissection or rupture was low at diameters < 5.0 cm and this risk was not increased in patients with bicuspid aortic valves.

COMMENTARY

Given the high morbidity and mortality rates associated with ascending aortic dissections, there has been considerable interest in indicators for prophylactic surgical replacement. Current guidelines recommend 5.5 cm (class I) and this observational study supports this cutpoint. Also, even at > 5.5 cm, the risk of dissection or rupture is low (2.9%). Prophylactic surgery makes the most sense when the risk of dissection rupture is higher than the risk of death or major morbidity from surgery. Contemporary data suggest elective ascending aortic replacement surgery has a 2-3% mortality, a 2-3% stroke rate, and a 0.5% risk of paraplegia. So even operating at 5.5 cm seems aggressive based on the dissection/rupture rates in this study.

Patients with bicuspid valves in this study had larger ascending aortic diameters and more rapid expansion rates in the subgroup (30%) with serial echoes. However, a bicuspid valve was not a predictor of dissection/rupture. This contradicts the American College of Cardiology/American Heart Association guidelines, which call for consideration of surgery at smaller diameters in bicuspid aortic valve patients (4.5-5.5 cm, class IIa). However, they updated the guidelines this year to eliminate this clause but kept the class I recommendation for surgery at 5.5 cm. Thus, surgery at < 5.5 cm is only recommended now for patients with aortic syndromic disease such as Marfan syndrome. Such patients were excluded from this study.

There are limitations to this study. The most obvious is that it is observational, but randomized trials in this area are unlikely to ever be conducted. Also, this isn’t a true population study since it is biased by referral to echo, which would include more patients with cardiovascular disease. Rates of aortic dissection or rupture likely are lower in a true community population. In addition, there were only 14 events, which makes determining predictors difficult. Finally, some patients were removed from the population for elective surgery based on a more aggressive approach to prophylactic surgery than the 5.5 cm cutoff or the need for aortic valve surgery.

The editorial accompanying this article noted that aortic size is related to age, sex, and body size, increasing with age, male sex, and larger bodies. The latter has prompted some to use aortic diameter indexed to body surface area. But others have pointed out that body surface area is heavily influenced by weight, and the typical weight gain with age may have little influence on aortic size. They have suggested indexing for height, which often changes less with aging. Thus, Pape suggested that future guidelines on prophylactic surgery for ascending aortic dilation should appropriate norms based on age, sex, and height. Until this happens, perhaps we should factor in extremes of age and body size into our decision making.