By Eric E. Roselli, MD, and Lars Svensson, MD, PhD
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Although we commonly see bicuspid aortic valve (BAV) and its attendant manifestations, no textbook strategy exists for surgical management. Because the population with BAV is heterogeneous, the best surgical solution varies from patient to patient. While aortic stenosis is usually the reason we operate, aortic regurgitation, aortic dilatation and aneurysms are common as well. Determining the best strategy requires an understanding of the underlying pathophysiology and experience with diverse BAV presentations.
What causes aortic pathology?
Flow MRI studies show that aortic flow is altered in patients with a BAV, leading to increased wall shear stress. While normal flow in the aorta is laminar, BAV creates a helical and vortical pattern, with aortic stenosis further exacerbating flow abnormalities.
But this isn’t the whole story: Even after aortic valve replacement (AVR), the aorta continues to grow faster than normal. Something about the aortic wall itself appears to make patients with BAV vulnerable to dilatation.
At Cleveland Clinic, we recently used machine learning to classify BAV-related dilatation phenotypes based on preoperative analysis of 3-D CT reconstructions from 656 BAV patients undergoing ascending aorta surgery (J Thorac Cardiovasc Surg. 2018;155:461-469). Three distinct aneurysm phenotypes were identified, which correlated with patient characteristics:
- Root dilatation (13 percent) — Patients tended to be younger men and have more aortic insufficiency
- Ascending aortic dilatation (55 percent)
- Arch dilatation (32 percent) — Patients tended to be older, have more aortic stenosis and have right non-valve cusp fusion
The fact that patient characteristics and valvular dysfunction varied by phenotype suggests that the location of aortic pathology may be related to the underlying pathophysiology.
When do we repair bicuspid aortopathy?
Determining the criteria for treating the aorta when a patient with BAV undergoes AVR is an important clinical issue. A review of nearly 2,000 patients who underwent BAV surgery at Cleveland Clinic (J Thorac Cardiovasc Surg. 2011;142;622-629) shed light on the issue by suggesting that an aortic diameter greater than 4.5 cm should be considered a trigger for concurrent aortic repair, as aortic repair conferred a late survival benefit with no added risk.
But rather than having a hard-and-fast rule, decisions about aortic surgery are best tailored to the patient, based on individual risks and benefits. Surgical AVR tends to be performed in a relatively young, healthy population, but that is not always the case. Considerations should include valve indications (aortic stenosis, aortic insufficiency), aortic indications (morphology, size), nonaortic comorbidities and family history.
Further insight comes from a Cleveland Clinic study involving 1,181 patients from 1995 to 2014 who had BAV and either a sinus or ascending aortic diameter of at least 4.7 cm (Ann Thorac Surg. 2015;100:1666-1673). Of these patients, 801 had aortic surgery, and the others were followed with imaging surveillance. We found that the immediate risk of dissection started climbing above 5 percent for patients whose aortic diameter was approximately 5.0 cm or larger. A cross-sectional area-to-height ratio of at least 10 cm2/m for sinuses of Valsalva and 13 cm2/m for the tubular ascending aorta was found to be an even stronger predictor of dissection.
Based on these data, we can tell patients who meet these thresholds that they have about a two-thirds chance of having an aneurysm within a decade — or, ideally, an aortic intervention well before that.
We tend to treat aggressively and have the experience to do so confidently. Cleveland Clinic’s mortality rate for elective thoracic aorta surgery is 0.3 percent, which is less than one-tenth the benchmark expected rate of 3.8 percent (based on 2017 discharges).
Repair or replace BAV?
The choice of a conventional operation — surgical AVR combined with a Bentall root or supra-coronary graft — depends on patient pathology.
Over recent decades, however, we have become better at repairing rather than replacing the bicuspid valve, and repair can be combined with repair of the ascending aorta or root or extended to the arch. If valve leaflet tissues are healthy, we prefer to preserve a patient’s native valve, if possible, as this avoids the need for lifelong anticoagulation and prosthetic valve-related complications.
From 1985 to 2011, we followed 728 patients who underwent BAV repair at Cleveland Clinic (Ann Thorac Surg. 2014;97:1539-1548). Overall, we found that BAV repair entails a very low risk of death and stroke and is associated with good durability and long-term survival. Freedom from aortic valve reoperation at 10 years was 78 percent, which is as good as or even better than the rate with a bioprosthetic valve, especially in a young population. Survival at 10 years was 94 percent.
We also found that we improved with experience and learned to better select patients for valve repair and select which components of the operation to perform. We now employ a “CLASS” evaluation, taking into account commissures, leaflets, annulus, sinuses and the sinotubular junction, as valve function is affected by more than just leaflets.
Valve-preserving root replacement
For people who present with aortic insufficiency and a dilated aortic root, we perform a modified reimplantation procedure for valve-preserving root replacement. Orienting the two normal commissures at 180 degrees, as illustrated in the 2.5-minute operative video below, results in better durability of valve repair.
We have developed general guidelines for managing differing scenarios when a patient presents with BAV and aortopathy, as outlined below.
If the valve is the primary indication for surgery (i.e., severe aortic stenosis and/or severe regurgitation):
- Replace the aorta if >45 mm in diameter.
- Replace the root too if it is >5 cm and AVR is being done. If the native valve is being retained, it needs to be stabilized, so the diameter threshold should be lowered to >45 mm.
- Sometimes thresholds need to be lowered further, depending on the quality of tissue or for a small patient, such as an individual with Turner syndrome or other syndromic connective tissue disorder.
If the aorta is the primary indication for surgery:
- Operate if the aorta is >5 cm in diameter or the cross-sectional area-to-height ratio is >10 cm2/m.
- Consider sparing the valve if it looks healthy, but address the root if >45 mm.
- Selectively lower thresholds.
- In some cases, parts of the arch should be resected because this may be curative.
Finally, when deciding how best to treat a patient, it is important to consider the likely surgical results. Outcomes tend to be best when surgery is done at a high-volume aorta center by an experienced, multidisciplinary team.
Dr. Roselli is Chief of Adult Cardiac Surgery and Director of the Aorta Center at Cleveland Clinic. Dr. Svensson is Chair of Cleveland Clinic’s Miller Family Heart & Vascular Institute.