Natural History of a Bicuspid Aortic Valve
Natural History of a Bicuspid Aortic Valve
Abstract & Commentary
By Michael H. Crawford, MD
Source: Michelena HI, et al. Natural history of asymptomatic patients with normally functioning or minimally dysfunction bicuspid aortic valve in the community. Circulation. 2008;117:2776-2784.
Bicuspid aortic valve is a common congenital abnormality that can progress to significant aortic stenosis or regurgitation, and is associated with aortic aneurysm and dissection. These associations are derived from tertiary care centers and autopsy series. The natural history of subjects in the community with bicuspid aortic valve (BAV), with little or no symptoms, is unknown. Thus, Michelena and colleagues from the Mayo Clinic longitudinally studied 212 subjects with isolated BAV, no initial symptoms, and normal or minimal valve dysfunction. The average age at diagnosis was 32 years, and 72% had echocardiograms due to positive auscultatory findings. The valves on echo were scored for degeneration (thickening, calcification, reduced mobility; 0-3 points each), and the mean score was low (0.8, range 0-6). Most (87%) had no degeneration (score < 3). Age and cholesterol levels correlated with degeneration; the detection of a systolic click on auscultation correlated with no degeneration. In 93% of patients, follow-up was complete over 20 years. Survival was 97% at 10 years and 90% at 20 years; there was no difference from the expected survival of an age- and sex-matched population. During follow-up, heart failure occurred in 7%, new cardiac symptoms (dyspnea, syncope, angina) in 26%, infective endocarditis in 4%, and stroke in 5%. Aortic valve replacement was eventually performed in 24%, mainly for stenosis. Mean age at surgery was 49 years. A few patients (3%) had surgery for ascending aortic aneurysm or coarctation. Aortic dissection was not observed. Cardiovascular events were not predicted by age and valve degeneration. Michelena et al concluded that subjects with BAV have an excellent survival, but do have cardiovascular events, mainly related to valve dysfunction; valve degeneration on echo identifies patients who need more careful follow up.
Commentary
How aggressively to follow patients with bicuspid aortic valve is revealed in this study. Those with evidence of more than mild valve thickening, calcification, or leaflet immobility are more likely to progress to significant valvular disease and should be followed more closely. Eventually, 40% of BAV subjects will develop some cardiac event and 24% will need valve replacement, mainly for stenosis. Despite the fact that 40% of the BAV subjects eventually reached an ascending aortic diameter > 4cm, only 3% required surgery for aortic aneurysms and none experienced aortic dissection. Thus, the appropriate follow-up protocol for dilated aortas is not clear and should follow standard guidelines. Finally, infective endocarditis was rare, which supports the new guidelines that do not recommend antibiotic prophylaxis for BAV.
The strength of this study is that it is as close to a real natural history study as one can get. It would be ideal to study subjects found by mass screening instead of those with worrisome auscultation findings and some type of symptoms. Unfortunately, this would require screening a lot of subjects, which could be rather impractical. However, such a population might even have a better prognosis. Also, the length of the follow-up was very long, yet encompassed a time when aortic valve disease diagnosis and treatment had not changed appreciably. In fact, in analyzing the early and late periods of the study independently, there was no change in the results. One weakness of the study was that the study population was from a small community in Minnesota, which would not be racially diverse. Whether the results would be the same in other populations is not known, but could be different since there are other studies from tertiary care centers in larger cities that have different results. Perhaps these results are not distorted by the tertiary hospital selection bias, but rather are reflective of a more diverse population. Finally, the diagnosis of BAV by transthoracic echo is sometimes difficult, and there were no confirmatory tests done unless the patient was being considered for, or had, surgery.
There are two major findings in this study. First, aortic valve disease is progressive in BAV, so patients need routine follow-up predicated by the initial anatomic characteristics of their valve. Those with more degenerated valves need to be more closely followed than those without degeneration. Second, the incidence of serious aortic complications is low, despite the frequent occurrence of a dilated ascending aorta. Thus, follow-up of aortic dilation need not be more intense than that for any patient with a dilated ascending aorta.
Bicuspid aortic valve is a common congenital abnormality that can progress to significant aortic stenosis or regurgitation, and is associated with aortic aneurysm and dissection.Subscribe Now for Access
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