ESSENTIALS OF DIAGNOSIS
May present with dyspnea, chest pain, syncope.
Though LV outflow gradient is classic, symptoms are primarily related to diastolic dysfunction.
Echocardiogram is diagnostic. Any area of LV wall thickness > 1.5 cm defines the disease.
Increased risk of sudden death.
In 2020, an ACC/AHA joint committee on clinical practice guidelines issued updated guidelines for the diagnosis and treatment of HCM. The guidelines address many clinical scenarios and provide a host of clinically relevant suggestions. HCM is noted when there is LVH unrelated to any pressure or volume overload. The definition has evolved over time; while it traditionally was defined by LV outflow obstruction due to septal hypertrophy, currently it is considered present any time that any portion of LV wall is measured at more than 1.5 cm thick on an echocardiogram. This allows for many forms to be considered that do not create LV outflow obstruction. The increased wall thickness reduces LV systolic stress, increases the EF, and can result in an “empty ventricle” at end systole. The interventricular septum may be disproportionately involved (asymmetric septal hypertrophy), but in some cases the hypertrophy is localized to the mid-ventricle or to the apex. In a normal heart, the LV apex may be paper thin; in HCM, the LV obstruction may trap blood just above the apex and the LV pressure may be very high there. This can result in the apex becoming aneurysmal. The LV outflow tract is usually narrowed during systole due to the hypertrophied septum and systolic anterior motion of the mitral valve occurs as the anterior mitral valve leaflet is pulled into the LV outflow. The obstruction is worsened by factors that increase myocardial contractility (sympathetic stimulation, digoxin, and postextrasystolic beat) or that decrease LV filling (Valsalva maneuver, peripheral vasodilators). The amount of obstruction is preload and afterload dependent and can vary from day to day. The consequence of the hypertrophy is elevated LV diastolic pressures rather than systolic dysfunction. Rarely, systolic dysfunction develops late in the course of the disease. The LV is usually more involved than the RV, and the atria are frequently significantly enlarged.
HCM is inherited as an autosomal-dominant trait with variable penetrance and is caused by pathogenic variants of one of a large number of genes, most of which code for myosin heavy chains or proteins regulating calcium handling. The prognosis is related to the specific gene pathogenic variant. Patients usually present in early adulthood. Elite athletes may demonstrate considerable hypertrophy that can be confused with HCM, but generally diastolic dysfunction is not present in the athlete and this finding helps separate pathologic disease from athletic hypertrophy. The apical variety is particularly common in those of Asian descent. An HCM in older adults (usually in association with hypertension) has also been defined as a distinct entity (often a sigmoid interventricular septum is noted with ...