Structure and function in HCM
HCM is a genetic disease caused by sarcomeric contractile proteins mutations. It is characterized by left ventricular (LV) hypertrophy, myocardial fibrosis and myocyte disarray which result in ischemia, diastolic dysfunction and arrhythmias. Many patients with HCM experience functional limitation due to symptoms such as syncope, dyspnea and chest pain. Although abnormal peripheral responses, reduced stroke volume, diastolic dysfunction, LV hypertrophy and left ventricular outflow tract obstruction have all been implicated, the exact mechanism of exercise intolerance is still uncertain. Subjective NYHA functional classification, although very practical, has been shown to underestimate the severity of exercise intolerance in various populations affected by cardiac diseases, including HCM population. Symptom-limited cardiopulmonary testing (CPX) with breath-by-breath gas analysis can therefore help identify potential determinants of functional limitation by providing an accurate and objective expression of exercise capacity. Because some authors have demonstrated an association between LVOT gradients and exertional symptoms, combining CPX with stress echocardiography can provide very valuable information since stress imaging can quantify ventricular performance, gradients as well as valvular abnormalities.
