Funding Acknowledgements Type of funding sources: None. Background The mitral valve (MV) has an important contribution to left ventricular outflow tract obstruction (LVOTO) in patients with hypertrophic obstructive cardiomyopathy (HOCM). Several parameters were described to be significantly different between obstructive and non-obstructive forms of HCM, like the aortomitral angle, anterior mitral leaflet (AML) and LVOT size, anterior displacement of the coaptation line, annular related parameters, etc. The redundant length of the AML beyond the coaptation point and the entire AML length are important in the decision to also approach the mitral valve when surgical septal reduction therapy (SRT) is considered, to increase the success rate. Data is scarce regarding mitral valve related predictors of interventional SRT response. This is important as certain patients have a suboptimal response regardless of the proper coronary anatomy and branch targeting. Purpose To evaluate the possible differences in certain mitral valve parameters in interventional SRT responders versus non-responders. Methods We retrospectively included in the study a number of 21 consecutive HOCM patients treated with alcohol septal ablation (ASA). All the procedures were guided with contrast echocardiography besides fluoroscopy and all patients had a proper distribution of at least 1 septal branch. They were divided in two groups- responder group (15 patients) with a non-significant residual LVOT PG (<50mmHg/>50% reduction) and non-responder group (6 patients) with a significant residual LVOT PG (>50mmHg/<50% reduction) and/or early rebound. We accounted for the residual LVOT PG evaluated by continuous Doppler at least 6 months after SRT. The groups were compared regarding LV dimensions and ejection fraction and mitral valve annulus/ leaflet size and displacement of the coaptation line, evaluated by bidimensional transthoracic echocardiography, before the intervention. Results The most hypertrophied part of the LV was the basal interventricular septum (IVS). The two groups were similar regarding age, comorbidities, LV dimensions and ejection fraction and baseline LVOT PG. Also, there was no significant difference between AML length, posterior mitral leaflet (PML) length, AML/PML, MV annulus. The redundant length of the AML was significantly lower in responders whereas anterior displacement of the coaptation point (projection of AML/projection of PML on the MV annulus) was less intense in responders and almost reached statistical significance. (Table) Interestingly, we found a baseline AML/PML projection <1 in all non-responder patients and only in 2 responder patients (13.33%) (p<0.001). Conclusion So far, significant anterior displacement of the coaptation point and the residual AML length may have an important impact on the response to ASA in HOCM patients. This pilot study could be an important start point for larger prospective studies to confirm and evaluated the prediction value of these parameters among others.

(1) Background: Complete atrioventricular block is a well-known complication of alcohol ablation as a septal reduction therapy, implemented in selected patients with hypertrophic obstructive cardiomyopathy (HOCM). It usually occurs during or immediately after the intervention. Rare cases of late complete atrioventricular block (CAVB) have been reported, but data are still scarce in the literature regarding this issue. (2) Case report: We report the case of a 70-year-old male patient, with mild aortic stenosis, but with a significantly degenerated valve and perivalvular tissue, and a nonspecific intraventricular conduction delay, which developed intensely symptomatic CAVB, four months after alcohol septal ablation (ASA) for HOCM, along with left ventricular pressure gradient recurrence. Both problems were resolved by implantation of a dual chamber pacemaker, with pacing optimization to a short atrioventricular interval, along with a maximal tolerated betablocker therapy. With the description of the patient’s treatment and evolution in comparison with other reports and studies, this case report highlights the fact that a close clinical, electrical and echocardiographic surveillance is warranted for this kind of patients, as late CAVB may be a life-threatening complication. Previous electrical conduction problems and degenerated aortic valve and perivalvular tissue may be predisposed for this type of complication, independent of betablocker therapy. This treatment has several other beneficial effects and thus it should not be interrupted after the procedure.