Ischemic Myocardial Positron Emission Tomography Perfusion Without Epicardial Coronary Disease in Hypertrophic Obstructive Cardiomyopathy.

The presence of impaired microvascular coronary flow (MCF) identified by positron emission tomography myocardial perfusion imaging (PET-MPI) has been described in hypertrophic obstructive cardiomyopathy (HOCM) patients, contributes to blunted myocardial perfusion during vasodilator stress, and is a strong predictor of poor prognosis. A 45-year-old female with hypertension and obesity presented with angina. Her PET-MPI displayed vasodilator stress-induced global LV ischemia. However, her coronary angiogram revealed no obstructive coronary disease. These contradictory findings triggered a more thorough cardiac MRI with diffuse myocardial fibrosis, indicating high-risk HOCM. She underwent implantable cardioverter-defibrillator (ICD) placement due to non-sustained ventricular tachycardia and syncope. While this patient lacked epicardial coronary disease, her PET-MPI demonstrated global LV ischemia due to decreased MCF, leading to inadequate augmentation of myocardial perfusion during hyperemia. This is a well-described phenomenon responsible for anginal symptoms in HOCM patients. HOCM hearts have abnormally thick coronary arterioles and decreased capillary density, leading to increased oxygen diffusion distances and reduced perfusion. The presence of vasodilator-induced, global ischemia on PET-MPI without epicardial stenosis should raise suspicion for HOCM with impaired MCF, which represents a high-risk population with an almost 10 times greater risk of cardiovascular mortality compared to hypertrophic cardiomyopathy with preserved MCF.