Severe mitral annular calcification and TAVR: not an innocent bystander

This editorial refers to ‘Concomitant mitral annular calcification and severe aortic stenosis: prevalence, characteristics and outcome following transcatheter aortic valve replacement’†, by Y. Abramowitz et al., on page 1194. There are no innocent bystanders… what are they doing there in the first place? William S. Burroughs In this issue of the journal, Abramowitz et al. evaluated the prevalence of MAC among patients with severe AS and assessed for the first time the clinical implications of MAC following transcatheter aortic valve replacement (TAVR).9 MAC was a common finding in half of the patients undergoing TAVR, and severe MAC was present in 10% of patients. As shown previously, patients with MAC were older, mainly female, had higher incidence of chronic kidney disease, higher STS (Society of Thoracic Surgeons) scores, higher pressure gradients over the aortic valve, and increased LV outflow tract (LVOT) calcifications. MAC was found to affect important endpoints after TAVR, including mortality and post-procedural pacemaker (PPM) implantation. We propose a new risk score that includes severe mitral annular calcification (MAC), frailty indices such as the 5-m gait speed, and quality of life measures such as the Kansas City Cardiomyopathy Questionnaire to the actual TVT Registry score. CKD, chronic kidney disease; COPD, chromic obstructive pulmonary disease; STS, Society of Thoracic Surgeons; TAVR, transcatheter aortic valve replacement; TF, transfemoral. There is no doubt that important variables are not accounted for in risk stratification of patients undergoing TAVR. Frailty indices such as the 5-m gait speed and quality of life measures such as the Kansas City Cardiomyopathy Questionnaire are generally recognized as potentially important factors and are not yet included in any risk score.14 However, the TVT Registry is currently collecting frailty and quality of life data to include in future 30-day and 1-year risk models. In this study, MAC was an independent risk factor for mortality irrespective of the STS score. One-year all-cause mortality and cardiovascular mortality were increased in patients with severe MAC compared with patients undergoing TAVR with no MAC (21.7% vs. 12.3%, P = 0.03; and 11.6% vs. 4.7%, P = 0.02, respectively). Therefore, severe MAC should not be overlooked when evaluating patients with TAVR and may be considered in future risk stratification models as severe MAC is a marker of more advanced disease and atherosclerotic burden, and is responsible for the increased mortality seen in this subset of patients after TAVR. New PPM implantation remains one of the Achilles heels of TAVR. Studies evaluating the outcomes of conduction abnormalities after TAVR have yielded inconsistent results, but some limited data suggest a potential effect on mortality and LV function.15 Furthermore, PPM carries a risk of infective endocarditis. An increased rate of conduction abnormalities has been reported for some of the newer transcatheter heart valves and could potentially be a barrier towards wide adoption in younger and lower risk patients. As shown previously, right bundle branch block (RBBB), use of self-expanding valves, and LVOT calcifications were independent predictors for new PPM implantation in this study. In addition, severe MAC was found to be a strong predictor of new PPM implantation following TAVR (odds ratio 2.83). The higher incidence of conduction disease is most likely to be due to calcification in the vicinity of the atrioventricular node and the bundle of His, as well as diffuse degenerative conduction system disease that is frequently associated with MAC. In patients with severe MAC, no pre-dilation or pre-dilation with an undersized balloon, relatively high implant, use of transcatheter heart valves with a record of low PPM rates, and avoidance of post-dilation seem to be prudent to avoid interaction with the disease conduction system. Mitral regurgitation (MR) is not uncommon in TAVR patients and is a main driver of subsequent clinical outcomes.16 However, the predictors of MR improvement are not well defined. In a recent study, calcification of the mitral apparatus by multidetector CT (MDCT) was the strongest parameter for predicting lack of MR improvement post-TAVR.17 Although not statistically significant, subgroup analysis revealed a trend towards less improvement in patients with severe MAC (33.2% of patients with non-severe MAC had one grade or more MR improvement vs. 22.0% of patients with severe MAC, P = 0.14). A probable mechanism for this association is the calcium infiltration at the base of the posterior leaflet which reduces leaflet mobility, increases traction on the chordae, and lifts the leaflets. Indeed, MAC can potentially impinge and restrict leaflet motion and is associated with lack of reduction in MR improvement after TAVR.18 Severe MAC was associated with an elevated gradient to>5 mmHg in around half of patients, and 6.9% had a gradient >10 mmHg consistent with severe mitral stenosis. This is an important consideration especially when MAC is associated with severe mitral stenosis as this could affect the decision-making and can identify a subset of patients that can benefit from mitral valve intervention after TAVR, or surgical approach to both valves although associated with high operative morbidity and mortality in the setting of severe MAC.19 Moreover, transcatheter mitral valve replacement for severe MAC is associated with prosthesis anchoring issues, LVOT obstruction, and paravalvular leak, and is technically challenging. The presence of MAC in patients referred for TAVR should not go unnoticed, and careful quantification, proper risk assessment, and careful procedural planning should be undergone in order to maximize outcomes. Conflict of interest: L.S. has received institutional research grants from Medtronic, St. Jude Medical, Boston Scientific, Symetis, and Edwards Lifescience; and is a proctor for Medtronic, St. Jude Medical, Boston Scientifi, and Edwards Lifescience. F.J.S. has no conflict of interest to declre.