From the Guidelines
HOCM is a specific subtype of hypertrophic cardiomyopathy characterized by obstruction to blood flow, whereas hypertrophic cardiomyopathy (HCM) refers to the general condition of abnormal heart muscle thickening without necessarily implying obstruction. The main difference between the two conditions lies in the presence of obstruction to blood flow out of the heart, which is a hallmark of HOCM. In HOCM, the thickened septum between the ventricles narrows the left ventricular outflow tract, creating a pressure gradient and impeding blood flow from the left ventricle to the aorta 1. This obstruction can cause symptoms like shortness of breath, chest pain, dizziness, and fainting, particularly during exertion.
Key Differences and Management
- HCM refers to the general condition of abnormal heart muscle thickening, while HOCM specifically indicates that this thickening causes obstruction to blood flow out of the heart.
- The presence of obstruction in HOCM can lead to symptoms such as shortness of breath, chest pain, and dizziness, which may not be present in non-obstructive HCM.
- Management of HOCM often requires specific medications like beta-blockers or calcium channel blockers to reduce the obstruction, and in severe cases, procedures such as septal myectomy or alcohol septal ablation may be necessary to relieve the obstruction 1.
- Understanding this distinction is important for proper treatment selection, as non-obstructive HCM may require different management approaches, including medications to control heart failure symptoms or procedures to address other complications of the disease.
Diagnostic Considerations
- The clinical diagnosis of HCM is established most easily and reliably with two-dimensional echocardiography by demonstrating left ventricular hypertrophy (LVH) 1.
- Contemporary magnetic resonance imaging may represent an additional diagnostic modality, particularly in the presence of technically suboptimal echocardiographic studies or when segmental hypertrophy is confined to unusual locations within the LV wall 1.
- The diagnosis of HOCM specifically requires the demonstration of obstruction to blood flow, which can be assessed using echocardiography or other imaging modalities.
From the Research
Definition and Classification
- Hypertrophic cardiomyopathy (HCM) is a primary disorder of heart muscle characterized by muscular hypertrophy without recognized cause, which encroaches on the ventricular chamber, reducing chamber area and volume 2.
- HCM is classified as hypertrophic obstructive cardiomyopathy (HOCM) if a left ventricular outflow tract (LVOT) gradient is present at rest or during provocation, such as with Valsalva maneuver or exercise 3.
Mechanism of Obstruction
- The mechanism of obstruction in HOCM is primarily due to obstruction at the mitral valve level 2.
- The obstruction is caused by the hypertrophied muscle encroaching on the ventricular chamber, reducing chamber area and volume 2.
Relationship between HOCM and Hypertrophic Cardiomyopathy
- HOCM is a subset of HCM, characterized by the presence of a LVOT gradient 3.
- Patients with HCM are classified as having HOCM if they have a LVOT gradient, which can be present at rest or during provocation 3.
- The management of HCM and HOCM involves similar strategies, including activity restriction, prevention of sudden cardiac death, control of symptoms, and screening of relatives 3.
Management of HOCM
- The management of HOCM involves a stepped approach, including pharmacologic treatment, septal reduction therapy, and surgical myectomy 3, 4.
- Pharmacologic treatment includes negative inotropic drugs, such as beta blockers, disopyramide, and non-dihydropyridine calcium channel blockers 3, 4.
- Septal reduction therapy, including septal myectomy and alcohol septal ablation, is considered for patients with intolerable symptoms despite optimal conservative therapy 3, 4.