Abstract 12443: Different Histopathologic Diagnoses in Clinically Diagnosed Hypertrophic Cardiomyopathy Patients Following Surgical Myectomy to Relieve Dynamic Left Ventricular Outflow Tract Obstruction.

Background: Dynamic left ventricular outflow tract obstruction (LVOTO), which is typically relieved by surgical myectomy (SM), is the hallmark of obstructive hypertrophic cardiomyopathy (HCM). However, dynamic LVOTO is occasionally seen in other disorders like hypertensive heart disease (HHD). In a patients with severe dynamic LVOTO who underwent SM, we sought to study the incidence of various histopathologic diagnoses. Methods: We studied 2472 consecutive patients ≥ 18 years (56±14 years, 54% men, excluding 63 patients with subaortic membrane) with symptoms related to severe dynamic LVOTO who underwent SM at our center between 1/2002-3/2018. Baseline clinical and echocardiographic data (including resting and provocable LVOT gradients) were recorded. Following a thorough evaluation, all patients were clinically diagnosed with HCM. All SM specimens were evaluated by cardiac pathologists. In-hospital mortality was recorded. Results: The breakdown of histopathologic findings in the current study was as follows: a) HCM (n=2108, 82%) b) HHD (n=280, 11%) c) storage disease (SD, n=33, 1.3%) d) concomitant myocarditis (n=123, 5%) and e) Amyloidosis (n=18, 1%). Figure 1 shows the relevant baseline clinical and echo data in the study cohort. There were no significant differences in basal septal thickness and LVOT gradients between different groups. There were 7 (0.3%) in-hospital deaths (4 in HCM, 1 in amyloid and 2 in HHD groups). Conclusions: In a large cohort of symptomatic patients with a clinical diagnosis of HCM and severe dynamic LVOTO undergoing SM, ~ 1 in 5 patients had different histopathologic diagnoses including HHD, amyloid, SD and concomitant myocarditis. These findings may have implications in longer-term treatment, family screening and prognosis. [ABSTRACT FROM AUTHOR]