What is "obstruction"in HCM?
The term obstruction refers to the blood’s inability to leave the left ventricle (and rarely the right ventricle) of the heart in a normal and unimpeded manner. In the HCM heart there are a number of different mechanisms that can cause “obstruction” to occur. The most typical forms of obstruction occur when the anterior leaflet of the mitral valve makes contact with the septum. In other cases obstruction can occur when the left free wall of the heart makes contact with the septum or when papillary muscles interfere with the flow of blood in the left ventricle. Obstruction is measured in millimeters of mercury (mmhg) and is referred to as a “gradient”.
In a normal heart, there is no gradient and in patients with HCM with no obstruction the gradient is 0. If obstruction is present in HCM a small or mild gradient is approximately 10-25mmhg, a moderate gradient 25-50mmhg, and significant is 50mmhg +. Gradients can increase to numbers up to 200+mmhg in some patients. Gradients can increase under stress and therefore tend to be measured both by resting echocardiogram and stress echocardiograms.
The presence of obstruction is not a “bad” thing, and conversely the absence is not a “good” thing. Those with obstruction are treated with medication. In the event symptoms related to obstruction are not managed well with medication, more invasive therapy may be investigated including surgical myectomy (the Gold standard) or catheter based alcohol septal ablation. The choice between methods of septal reduction therapy to reduce gradient are based mostly on the anatomy of the individual heart, age of patient and co-existing medical conditions.
Although HCM is a genetic condition, members of the same family may have both obstructed and non-obstructed HCM.
One presentation of HCM with obstruction. Please keep in mind each heart may vary.
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Gersh, B.J., Maron, B.J., Bonow, R.O., Dearani, J.A., Fifer, M.A., Link, M.S., et al. (2011). 2011 ACCF/AHA guidelines for the diagnosis and treatment of hypertrophic cardiomyopathy. A report of the American College of Cardiology Foundation/American Heart Asociation Task Force on practice guidelines. Journal of the American College of Cardiology and Circulation, 58, e212-260.