**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
David S. Katzianera
aDepartment of Cardiovascular Medicine, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio

**Main Body of the Abstract**
Background
Cardiac amyloidosis (CA) and hypertrophic cardiomyopathy (HCM) can share the phenotypic characteristic of increased left ventricular wall thickness and dynamic left ventricular outflow tract obstruction. Surgical myectomy for LVOT obstruction is a well-proven therapy to alleviate symptoms.
Objective
To determine the incidence of CA in a large cohort of patients undergoing myectomy for presumed HCM.
Methods
We reviewed the myectomy database at our institution to characterize patients who underwent myectomy and were ultimately discovered to have CA on pathology.
Results
A total of 27 of 3,292 (0.8%) were found to have CA on pathologic examination of myectomy specimens. The majority (24 patients) had ATTR-CA with three patients being of the AL-lambda subtype. Most cases of ATTR-CA were wildtype; no genetic mutations for genes commonly associated with HCM were detected among patients who underwent genetic testing. Many patients had pre-operative imaging consistent with HCM with asymmetric hypertrophy (mean septal/posterior wall ratio of 1.39) and LVOT obstructive physiology (mean resting and provoked LVOT gradients of 34.7 and 93.9 mmHg, respectively). Histopathologic examination of the myectomy specimen showed presence of myocyte disarray, intramural coronary artery dysplasia, myocyte hypertrophy and interstitial fibrosis compatible with HCM in only three of 27 patients; twenty of 27 patients showed no microscopic features of HCM with the remaining four cases being equivocal.
Conclusions
Nearly 1% of patients referred for myectomy were found to have amyloid deposits on pathology. With the advent of targeted therapies for HCM and CA, recognition of this overlap is important for long-term management.



**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
David S. Katzianer^a^
^a^Department of Cardiovascular Medicine, Heart, Vascular and Thoracic Institute, Cleveland Clinic, Cleveland, Ohio

**Main Body of the Abstract**
**Background**
Cardiac amyloidosis (CA) and hypertrophic cardiomyopathy (HCM) can share the phenotypic characteristic of increased left ventricular wall thickness and dynamic left ventricular outflow tract obstruction. Surgical myectomy for LVOT obstruction is a well-proven therapy to alleviate symptoms.
**Objective**
To determine the incidence of CA in a large cohort of patients undergoing myectomy for presumed HCM.
**Methods**
We reviewed the myectomy database at our institution to characterize patients who underwent myectomy and were ultimately discovered to have CA on pathology.
**Results**
A total of 27 of 3,292 (0.8%) were found to have CA on pathologic examination of myectomy specimens. The majority (24 patients) had ATTR-CA with three patients being of the AL-lambda subtype. Most cases of ATTR-CA were wildtype; no genetic mutations for genes commonly associated with HCM were detected among patients who underwent genetic testing. Many patients had pre-operative imaging consistent with HCM with asymmetric hypertrophy (mean septal/posterior wall ratio of 1.39) and LVOT obstructive physiology (mean resting and provoked LVOT gradients of 34.7 and 93.9 mmHg, respectively). Histopathologic examination of the myectomy specimen showed presence of myocyte disarray, intramural coronary artery dysplasia, myocyte hypertrophy and interstitial fibrosis compatible with HCM in only three of 27 patients; twenty of 27 patients showed no microscopic features of HCM with the remaining four cases being equivocal.
**Conclusions**
Nearly 1% of patients referred for myectomy were found to have amyloid deposits on pathology. With the advent of targeted therapies for HCM and CA, recognition of this overlap is important for long-term management.



 Prevalence of amyloid deposition in patients undergoing surgical myectomy for presumed hypertrophic cardiomyopathy OB7 (#532)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.