Obstruction in hypertrophic cardiomyopathy: how often does it occur? Should it be treated? If so, how?

Hypertrophic cardiomyopathy (HCM) is the most common monogenic cardiac disorder and has been estimated to occur in 1 of every 500 people in the general population, amounting to a total of ≈600 000 persons in the United States.1 Its pathophysiology and optimal management have been the subject of conjecture and debate for more than a century. The issues surrounding left ventricular outflow tract (LVOT) obstruction in HCM have evoked the most discussion. Article see p 2374 In 1907, a German pathologist, A. Schminke, described 2 hearts from women in their mid-50s. Decades before the development of left heart catheterization, and before any pressure gradients had ever been measured in humans, he wrote the following: “Diffuse muscular hypertrophy of the left ventricular outflow tract causes an obstruction. The left ventricle has to work harder to overcome the obstruction. So, the primary hypertrophy will be accompanied by a secondary hypertrophy, causing an incremental (further) narrowing of the outflow tract.”2 Thus, Schminke presciently understood the vicious circle of left hypertrophy → obstruction → more hypertrophy, etc. A half century later, Morrow and I, despite having access to left heart catheterization (but not being aware of Schmincke's insight), struggled to explain our findings in 2 patients who had subaortic pressure gradients but no evidence of obstruction in the potassium citrate–arrested heart, a condition which we initially (and awkwardly) termed functional aortic stenosis.3 However, we did conclude “that the obstruction can only be explained by muscular hypertrophy of the left ventricular outflow tract.”3 As open-heart surgery exploded in …