How do you differentiate between obstructive and non-obstructive hypertrophic cardiomyopathy?

In the context of differentiating between obstructive and non-obstructive hypertrophic cardiomyopathy (HCM), measuring the pressure gradient across the left ventricular outflow tract during exertion or pharmacological stress is a critical diagnostic criterion. In obstructive HCM, there is a dynamic obstruction to outflow, which manifests as a significant pressure gradient between the left ventricle and the outflow tract. This gradient can vary with changes in loading conditions, particularly during physical exertion or when provoked pharmacologically with agents like dobutamine.

This assessment helps clinicians determine whether the HCM is obstructive, characterized by a resting gradient that can worsen with stress, or non-obstructive, where the gradient is absent or minimal under similar conditions. It is important to note that while left ventricular mass index, family history, and mitral valve structure all contribute valuable information in the overall assessment of HCM, they do not provide the direct measurement necessary to ascertain the presence of dynamic outflow obstruction, which is central to differentiating between the two forms of the condition.