**8. Latent obstruction**

A subgroup of HCM patients have symptoms despite what appears to be a low LVOT gradient at rest and it is important to differentiate between diastolic dysfunction and labile LVOT gradient as an etiology for their symptoms. It is critical in evaluating these patients, to perform provocative maneuvers such as exercise, amyl nitrite, and/or Valsalva maneuver. If provocative maneuvers revealed significant LVOT gradient, the patient should be offered septal myectomy as symptoms in these patients are related to a latent form of obstruction rather than to diastolic dysfunction.

A report of 249 patients with latent obstruction (gradient <30 mmHg at rest) was compared to those who had severe LVOT gradient at rest and both underwent septal myectomy. Early mortality was 1% with comparable long-term survival to that of an age-matched population [23].
