Evidence for Left Ventricular Outflow Tract Obstruction With Minimal Septal Hypertrophy

Hypertrophic cardiomyopathy (HCM) is the most common genetic heart disease caused by mutations in genes encoding proteins of the cardiac sarcomere and is associated with substantial heterogeneity in phenotypic expression and clinical course.1,2 Over the last 55 years, numerous advances have contributed enormously to our understanding of the diagnosis and treatment of patients with this disease.2–5 Throughout this continuum of progress, cardiovascular imaging has had a central role. Indeed, there is perhaps no other cardiovascular disorder more uniquely suited to noninvasive imaging than HCM, particularly given the enormous diversity in morphology, particularly with respect to the pattern and extent of left ventricular (LV) wall thickening and dynamic LV outflow obstruction.6,7See Article by Patel et al For nearly all of this time, echocardiography has been the principal imaging technique in HCM. In the early 1970s, M-mode echocardiography was introduced and HCM could be diagnosed for the first time by demonstrating ventricular septal hypertrophy and the characteristic asymmetrical pattern of LV wall thickening.5 Introduction of 2-dimensional echocardiography provided enhanced capability for imaging the overall LV chamber and the pattern of hypertrophy more extensively and recognition of the nonobstructed form of the disease.8 The emergence of Doppler provided the opportunity to reliably measure LV outflow tract gradients rapidly both at rest and with provocation, information critical for determining which HCM patients are candidates for select treatment options, such as septal reduction therapy.8,9 Indeed, after 35 years, echocardiography remains the fundamental imaging technique for HCM diagnosis and assessment.1However, the past 2 decades have witnessed a new era of imaging for this disease, with the emergence of cardiovascular MRI (CMR). This contemporary imaging technique provides 3-dimensional tomographic imaging, high spatial resolution, and sharp contrast between the blood pool …