Abstract 4144794: Effects of Myectomy on Cardiac Magnetic Resonance Parameters in Obstructive Hypertrophic Cardiomyopathy

Introduction: Cardiac magnetic resonance (CMR) analyses in patients from the EXPLORER-HCM study showed that cardiac myosin inhibitors (CMIs) have favorable effects in obstructive hypertrophic cardiomyopathy (oHCM) characterized by decreased left ventricular (LV) maximal thickness, decreased left ventricular mass index (LVMI), decreased left atrial volume index (LAVI), and cessation of replacement fibrosis progression based on late gadolinium enhancement (LGE). Question: Do surgical and alcohol myectomy lead to less favorable LV remodeling and cessation of scar formation than CMIs using CMR findings from EXPLORER-HCM as the comparison reference? Hypothesis: We hypothesized that the extent of CMR changes observed with CMIs in oHCM would not be observed with myectomy. Methods: We identified patients who underwent surgical or alcohol myectomy at our center of excellence with pre- and postprocedural CMR. We analyzed changes in LAVI, LVMI, LV maximal thickness, LV ejection fraction (LVEF), percent scar volume (LGE%), and scar mass by LGE (LGE% x LV mass). We normalized these changes by LV mass for comparison with CMR findings with CMIs reported in EXPLORER-HCM. Results: Characteristics of five patients with CMR before and after surgical or alcohol myectomy are shown in Table 1. Median (IQR) time to postprocedural CMR was 6.6 (2.5-28.9) months. LV maximal thickness decreased by 2.0 ± 1.4 mm (p = 0.03) following myectomy (EXPLORER-HCM: 2.4 mm decrease), LVMI decreased by 13.2 ± 15.5 g/m 2 (p = 0.13)(EXPLORER-HCM: 15.8 g/m 2 decrease), LAVI decreased by 11.9 ± 13.3 g/m 2 (p = 0.12)(EXPLORER-HCM: 10.3 g/m 2 decrease), and LVEF decreased by 6.4 ± 9.2% (p = 0.20)(EXPLORER-HCM: 6.4% decrease). Myectomy patients had an increase in LGE% of 2.5 ± 3.3% (p = 0.16) and in LGE mass of 2.4 ± 6.9 g (p = 0.48). Corrected for LV mass change, there was decreased mean LV maximal thickness (-1.7 mm), trends toward decreased mean LVMI (-11.3 g/m 2 ), LAVI (-10.2 g/m 2 ), LVEF (-5.5%), and trends toward increased mean LGE% (2.1%) and LGE mass (2.0 g). Conclusions: Surgical or alcohol myectomy resulted in trends toward positive remodeling, with overall similar effects to those seen with CMIs. Limitations include small sample size and variable timing of CMRs. There was an increase in LGE during follow-up with myectomy, consistent with continued disease activity with myectomy compared to CMI. This plausible difference in scar formation merits further prospective investigation with a larger sample size.