Statistical analysis
Chi-squared analysis for categorical variables, and two-tailed t-tests for continuous variables were used to evaluate whether patient and echocardiographic characteristics differed between patients who were diagnosed with bicuspid aortic valve by echocardiogram. P value of <0.05 defined statistical significance. We used GraphPad Prism for analysis (version 8, GraphPad Software, San Diego, CA).
Results:
The mean age of the cohort was 55.2 ± 15.6 years and 30.2% were female. During a median follow-up of 3.5 ± 2.2 years, 72.7% of patients had at least one visit in an outpatient cardiovascular clinic after the initial diagnosis of bicuspid aortic valve by echocardiogram. Patients followed by a cardiovascular specialist had a higher proportion of patients receiving at least one follow-up echocardiogram (78.7% vs. 34.3%, p< .0001), or at least one CT or MRI (41.0% vs. 3.0%, p < .0001), and were more likely to undergo corrective surgery (39.3% vs 4.5%, p < .0001), compared with patients not followed by a cardiovascular specialist (Table I).
Thirty-five percent (N=86) of patients in our study had a previously known BAV (as per their medical records), while the rest were given their diagnoses during the study period. Of patients with previous diagnosis of BAV, 84% (N=72) were followed by a cardiovascular specialist, while 67% (N=106) of new diagnoses were followed. In addition, many of the patients who had echocardiograms that showed a potential, but unclear bicuspid valve never received a follow-up ECHO in order to confirm or deny the diagnosis (17.9%, N=44), or never received a firm diagnosis even after multiple echocardiograms (8.6%, N=21) (Figure 1). Furthermore, follow-up echocardiograms did not always provide both aortic dimensions (aortic root or ascending aorta diameter) and mean valvular gradients (N=109, 67% of the final echocardiograms in the study period) and only 16% (N=40) of patients ever received a report on the orientation of their bicuspid valve (Type 0=2, Type 1=36, Type 2=1).
Among patients who were followed by a cardiovascular specialist, the average duration between echocardiograms was 1.11 ± 0.98 years. Patients with more severe aortic disease were not more likely to receive cardiovascular specialist follow-up than patients without severe disease. Patients with dilated aorta were not more likely to receive specialist follow-up but were more likely to receive a follow-up echocardiogram (74.2% vs. 61.8%, p=0.047), a CT or MRI (44.1% vs. 22.4%, p=0.0003), and surgery (41.9% vs. 21.1%, p=0.0005) than patients with normal aortic diameters. (Table II).
Patients were then stratified by aortic diameter and valve function to assess how these patients were followed up. Patients with moderate to severe aortic valve dysfunction (stenosis and/or regurgitation) were not more likely to have more frequent follow-up than patients with none-mild aortic valve dysfunction. Patients with moderate to severe aortic valve dysfunction were not more likely to be followed by a specialist (76.9% vs. 69.5%, p=0.198) or receive a follow-up echocardiogram (71.2% vs. 63.1%, p=0.188). However, they were more likely to receive a CT or MRI to evaluate the aorta or aortic valve (37.5% vs. 25.5%, p=0.045) and/or undergo surgery (51.9% vs. 12.1%, p < .0001). (Table II)
We assessed the impact of clinical follow-up by cardiovascular specialist on timely intervention on the valve and/ or aorta. Overall, 28.9% (N=71) of patients underwent aortic and/ or aortic valve surgery, 47.9% (N=34) of whom had already known about diagnosis prior to their inclusion in our study. Among surgical patients, 95.8% (N=68) of surgical patients were followed by cardiovascular specialist, 88.7% (N=63) received at least one follow-up echocardiogram, and 60.6% (N=43) received a CT or MRI to evaluate the aorta or aortic valve. The most common indications for surgery were ascending aortic aneurysm with or without stenosis or regurgitation (N=25, 34%), aortic stenosis (N=24, 34%), aortic regurgitation (N=10, 14%), and endocarditis with or without stenosis or regurgitation (N=5, 7%). After surgery for BAV syndrome, 85.9% (N=61) received at least one repeat echocardiogram, and 35.2% (N=25) received at least one CT or MRI for the purpose of aortic or valve surveillance. (Table III)
Conclusions:
In this study, follow-up care for patients with diagnosis of bicuspid aortic valve by echocardiogram was highly variable. Current guidelines from the The American Association for Thoracic Surgery state that the interval of follow-up imaging should be based on severity of disease (especially based on aortic dilation)9, and research has shown that bicuspid aortic valves will often progress in severity as patients age1,3,8. Therefore, once patients are diagnosed with BAV (or have a possible BAV found by echocardiogram), guidelines recommend that they should be followed by a cardiovascular specialist (cardiology/cardiac surgery) in order to determine the best schedule for imaging and/or surgical intervention. Our study shows that specialist follow-up and imaging surveillance may vary widely, and we must ensure care for patients with a possible bicuspid aortic valve diagnosis.
In this study, we found that over the mean follow-up of 3.5 years, more than a quarter of patients were never seen by a cardiovascular specialist after bicuspid aortic valve diagnosis by echocardiogram. In addition, a third of patients did not receive a follow-up echocardiogram, and only less than half of the patients who may have benefitted from CT or MRI surveillance according to some guidelines (2018 AATS) received it. Furthermore, many unclear bicuspid diagnoses, such as those labeled as “possible BAV” or “unable to rule out BAV”, did not receive a follow-up echocardiogram and/or a firm diagnosis following the initial echocardiogram. These data beg the question of how the bicuspid valves of the other patients progressed, and whether those patients would have benefitted from earlier intervention or earlier acknowledgement of the potential complications that bicuspid aortic valves can present.
Current guidelines suggest that the frequency and type of surveillance should be based on severity of aortic dilatation. Specifically, the 2018 AATS guidelines push for comprehensive serial evaluation. After the initial evaluation of the valve morphology, these guidelines state that normal aortic diameters should receive echo surveillance every 3-5years, stable aortic dilation (40-49mm) should be evaluated every 2-3 years (after an initial check at 12 months), and more advanced aortic dilation (>50mm) should be imaged yearly. It is also further recommended that aortic dilation >40mm should be investigated by echocardiogram-gated MRI or CT angiography9. ACC/AHA guidelines suggest a slightly more flexible pattern of surveillance14-15, with 2020 ACC/AHA guidelines suggesting MRI/CT for difficult to assess structures, then lifelong surveillance of patients whose aortic diameter ≥4.0cm, with intervals determined by family history and progression rate. Additionally, these guidelines suggest lifelong surveillance after aortic valve replacement if the aortic diameter is ≥4.0cm. These guidelines also suggest considering a screening TTE in the first-degree relatives of patients with BAV12. These guidelines state that TTE is usually adequate for hemodynamics and evaluation of anatomy, while TEE can provide improved 2D and 3D images. Cardiac MRI or CT provides better images of the aorta (including the sinotubular junction, sinuses, or ascending aorta) when both of those imaging modalities are not adequate to evaluate valve and aorta morphology.
In our study, patients with aortic dilation >40mm were more likely to receive a follow-up echocardiogram, CT, or MRI, but they were not more likely to have outpatient specialist follow-up. Furthermore, the severity of valvular disease at presentation (aortic stenosis or regurgitation) did not significantly affect clinical follow-up or imaging surveillance patterns. (Table II).
Patients with BAV are at risk for aortic dilation independent of valvular dysfunction, even beginning in childhood16, and aortic dilation can progress even with normally functioning valves17,18. At the same time, valvular dysfunction (especially aortic stenosis) is an independent risk factor for dissection6. It would follow that severity of disease should impact the level of outpatient surveillance by cardiovascular specialists so that both patients and providers can be aware of risks and potential complications over time and manage imaging appropriately. Unfortunately, we found that increased severity in general did not seem to lead to increased follow-up by a specialist.
Our study speaks to the stark gap in adoption of guidelines and ensuring optimal implementation in the clinical setting. They also provide a window of opportunity to improve system wide screening and institution of diagnosis triggered alerts to the right clinical practices so BAV patients are provided optimal care. This gap in quality of care attests to the importance of interdisciplinary communication between cardiology, radiology, and cardiac surgery to provide optimal care for patients with bicuspid aortic valve syndrome.