This study aimed to investigate the relationship between the LVIO angle and an increase in BNP levels post-TAVI. The major findings are as follows: First, the systolic LVIO angle, which was measured using MDCT with a popular software and was highly reproducible, was associated with increase in BNP levels post-TAVI, independent of pre-procedural AS severity and post-procedural transvalvular gradient. Second, the systolic LVIO angle had a significant inverse correlation with both the amount and rate of change in BNP levels pre and 30 days post-TAVI, regardless of pre-procedural BNP levels.
Limited data exists on the increase in BNP level post-TAVI, despite its frequent occurrence and its association with poor clinical outcomes [5–7]. We identified the anatomical features affecting the change in BNP levels pre- and post-TAVI. In this study, a small systolic LVIO angle was associated with increase in BNP levels post-TAVI, independent of pre-procedural AS severity and post-procedural transvalvular gradient. The association between a small LVIO angle and an increase in BNP levels post-TAVI can be explained by the left intracavitary ventricular pressure. Kwon et al. [9] have demonstrated that the left ventricle to aortic root angle, which is almost the same as the LVIO angle in this study, had a significant inverse correlation with a maximal LVOT gradient in patients with hypertrophic cardiomyopathy, independent of basal septal thickness. They have also indicated that a steep left ventricle to aortic root angle increases the left intracavitary ventricular pressure, owing to increased turbulence of blood flowing from the left ventricle into the aorta. In this study, the systolic LVIO angle had a significant inverse correlation with the peak LVOT velocity both pre and 30 days post-TAVI (Fig. 3), whereas the diastolic LVIO angle did not. Furthermore, as Fig. 4 shows, the systolic LVIO angle significantly affected the amount and rate of changes in BNP level pre and 30 days post-TAVI. Additionally, parameters that affected circulating BNP level, including the body mass index, atrial fibrillation, hypertension, peripheral artery disease, and renal impairment [24, 25], did not significantly differ between the groups. These results support our hypothesis.
A previous study showed that greater left ventricle to aortic root angles, including the angulation between the left ventricle to ascending aorta or LVOT, were associated with a risk of greater than moderate aortic regurgitation, leading to poor clinical outcomes after TAVI [8]. However, our results conflict with the results of the previous study. The divergent results are probably associated with the difference in THV, particularly the grade of residual aortic regurgitation. In this study, we mainly used third-generation valves, such as SAPIEN3 and Evolut Pro/Pro + valves, with attached outer skirts to reduce paravalvular regurgitation [26], while first-generation valves, such as Edwards-SAPIEN (Edwards Lifesciences) and Corevalve (Medtronic), were used in the previous study. Third-generation valves dramatically reduced paravalvular regurgitation after THV deployment [26]. In fact, the incidence of moderate or worse aortic regurgitation, reportedly associated with poor clinical outcomes after TAVI [27], was 2.1% in this study and 15.4% in the previous study.
In the BNP-rise group, the rate of balloon-expandable valve implantation was higher than in the non BNP-rise group. This was related to the pre-procedural AS severity, especially in the calcium volume of the AV. Patients in the BNP-rise group had a significantly lower total calcium volume of the AV, including the non-coronary leaflet, than those in the non BNP-rise group. In cases with less calcification of the non-coronary leaflet, implantation of a self-expandable valve was a risk factor for valve embolization or migration [28]. Therefore, a balloon-expandable valve was more frequently used in the BNP-rise group, and the use of a balloon-expandable valve exhibited no significant difference in the multivariate analysis.
Post-procedural MDCT examinations were not evaluated in this study because of the high incidence of renal impairment. THV implantation without complete coaxiality with the native aortic root may change the LVIO angle after valve deployment. However, a previous study using three-dimensional echocardiography showed that an aortic-mitral annular angle did not change pre- and post-TAVI [29]. Therefore, the effects of valve deployment appeared to be small.
This study had several limitations. First, this was a single-center observational study with a small number of patients. However, the incidence of increased BNP levels post-TAVI (BNP-rise group) was 31% (45/144), which was comparable to that in previous reports [5–7], increasing the validity of our data. Additionally, we could not completely exclude the possibility of overlooking new-onset atrial fibrillation, as it is impractical to implant a cardiac monitor in all patients for arrhythmia detection. Therefore, we devised our follow-up method of 48-hour telemetry monitoring and electrocardiography at days 1 and 30 post-TAVI, in addition to self-pulse rate monitoring for palpitations after discharge. Our findings are thought-provoking and further investigations are required to evaluate our results.