Positron Emission Tomography to Assess the Effect of Camzyos on Ischaemia in HOCM: PEACH Trial

Inclusion Criteria: 1. Written informed consent. 2. Aged 18 and over. 3. Confirmed diagnosis of Hypertrophic Obstructive Cardiomyopathy (HOCM) based on diagnostic criteria, such as unexplained left ventricular hypertrophy with a maximal wall thickness ≥15 mm in the absence of uncontrolled hypertension, valvular heart disease, or HCM phenocopies such as amyloidosis and storage disorders, and presence of either a resting or provoked peak left ventricular outflow tract (LVOT) gradient ≥30 mmHg. 4. Symptoms suggestive of myocardial ischaemia (chest pain, shortness of breath on exertion) with a clinical indication for Rb-PET. 5. Eligible for Mavacamten treatment according to standard clinical guidelines. \[see: https://www.nice.org.uk/guidance/ta913/chapter/1-Recommendations\]. Mavacamten is part of participants' regular clinical treatment and is not being supplied, administered, or influenced by the study in any way. 6. PET-CT performed for clinical reasons at any time in the preceding 18 months if reported as abnormal. Exclusion Criteria: 1. Patients with obstructive coronary artery disease (epicardial coronary stenosis \>50%, assessed by either invasive coronary angiography or computed tomography angiography (CTCA). Patients will undergo the initial PET study as part of their routine clinical care. If evidence of ischaemia is identified, the standard next step would involve either CT coronary angiography or, in some cases, invasive angiography to guide further clinical management. If the angiography reveals a clear lesion responsible for the ischaemia identified on PET, the patient will not be eligible for inclusion in the study and will not be approached. Conversely, if the angiography does not identify a definitive cause for the ischaemia, it will be presumed to be of microvascular origin. In such cases, the patient becomes eligible for the study and will be approached to discuss participation and provide consent at this stage. It is important to emphasize that any angiographic procedure occurs prior to consent and as part of routine clinical care. No angiographic investigations are planned or conducted as part of the study protocol. Data from the clinical angiogram will not be included in the study, except to note a 'positive angiogram' as a reason for patient exclusion. 2. Contraindications to Mavacamten, including left ventricular ejection fraction (LVEF) less than 55%, hypersensitivity or allergic reaction to the drug. 3. Contraindication to Rubidium PET-CT, including: * Pregnancy or breastfeeding. * Severe claustrophobia. * Morbid obesity when the patient dimensions are beyond the scanning chamber capacity. 4. Any medical condition, which in the opinion of the Investigator, may place the patient at higher risk from his/her participation in the study, or is likely to prevent the patient from complying with the requirements of the study or completing the study.