HOCUM: Hypertrophic Obstructive Cardiomyopathy
HOCUM is an outdated abbreviation for Hypertrophic Obstructive Cardiomyopathy, a term that is no longer recommended because it incorrectly implies that left ventricular outflow tract obstruction is an invariable feature of the disease. 1
Current Preferred Terminology
The term "HCM" (Hypertrophic Cardiomyopathy) is now the universally accepted nomenclature, whether or not outflow tract obstruction is present. 1
The older terms HOCUM, HOCM (Hypertrophic Obstructive Cardiomyopathy), and IHSS (Idiopathic Hypertrophic Subaortic Stenosis) are potentially misleading because they suggest obstruction is always present, when in fact one-third of patients have no obstruction either at rest or with physiologic provocation. 1
Since the 1980s, "HCM" has become the predominant formal term to designate this disease, allowing for both obstructive and nonobstructive hemodynamic forms. 1
Why the Terminology Changed
At least 80 different names, terms, and acronyms have been used historically to describe HCM, creating significant confusion in the medical and non-medical community. 1
The nomenclature popular in the 1960s and 1970s (IHSS, HOCM, HOCUM) falsely implied that left ventricular outflow tract obstruction was an obligatory component of the disease. 1
Most patients with HCM do not demonstrate outflow obstruction under resting (basal) conditions, although many may develop dynamic subaortic gradients with provocative maneuvers. 1
Clinical Distinction
When obstruction is present, the condition should be described as "HCM with left ventricular outflow tract obstruction" rather than using the outdated HOCUM/HOCM terminology. 1
It remains clinically important to distinguish between obstructive and nonobstructive forms based on the presence or absence of a left ventricular outflow gradient under resting and/or provocable conditions, as management strategies are traditionally tailored to the hemodynamic state. 1