What are the dangers of hypertrophic cardiomyopathy? What is the difference between obstructive and non-obstructive cardiomyopathy?

Author: Wang Fang, Chief Physician, Beijing Hospital

Reviewer: Zhu Dan, Chief Physician, Peking University Third Hospital

Hypertrophic cardiomyopathy is a disease characterized by uneven myocardial hypertrophy, excluding other causes of myocardial hypertrophy such as hypertension and aortic valve stenosis. Previous studies have shown that one in every 500 people in my country suffers from hypertrophic cardiomyopathy.

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Under normal circumstances, the thickness of the left ventricle is generally 9-11 mm, and the thickness of the right ventricle is generally no more than 5 mm. If the myocardium exceeds the normal thickness, especially more than 15 mm, it is considered pathological thickening.

Primary hypertrophic cardiomyopathy is an autosomal dominant genetic disease with a certain genetic tendency, and of course there are sporadic cases. The immediate family members, including blood relatives, of patients diagnosed with hypertrophic cardiomyopathy should pay attention and go to the hospital for relevant examinations.

Hypertrophic cardiomyopathy is generally divided into three categories: obstructive, non-obstructive, and latent obstructive. It is more common in adults and more common in men than in women. There may be no symptoms in youth, but due to the presence of pathogenic genes and the influence of various environmental factors, symptoms may appear in adulthood.

Abnormal myocardial hypertrophy will first lead to a decrease in the volume of the heart cavity and a smaller volume to hold blood. Second, after the blood is exchanged through the lungs, the oxygen-filled blood flows back to the heart, and the heart must expand to a certain extent, that is, diastole. Due to irregular myocardial hypertrophy, the heart is like a thick ball, which cannot expand when it should, and the diastolic function is limited. Third, the myocardium can only contract very effectively when it is arranged in a consistent and synchronized manner. The muscle fibers of hypertrophic cardiomyopathy are arranged in a disorderly manner, and the myocardial contractile function will also decrease in the later stages, leading to heart failure. In addition, the irregular arrangement of muscle fibers can also lead to the occurrence of various malignant arrhythmias, which are prone to sudden death. Fourth, the heart's contraction and diastolic functions are limited, and long-term poor left ventricular filling leads to increased atrial pressure and atrial enlargement, which can easily lead to atrial fibrillation, which is also very dangerous.

What is the difference between obstructive and non-obstructive hypertrophic cardiomyopathy? During the heart's contraction, blood is pumped to the body through the aortic valve. When the ventricular septum, especially the myocardium near the aortic valve orifice, becomes thickened, it may hinder the smooth discharge of blood. This condition is called obstructive hypertrophic cardiomyopathy. However, the hypertrophy of the ventricular septum does not always lead to obstruction. Whether it causes obstruction depends on the degree of myocardial hypertrophy and whether it causes the anterior leaflet of the mitral valve to move forward during systole. Generally speaking, if the thickness of the myocardium exceeds 15 mm, it is considered to be significantly thickened and is more likely to cause outflow tract stenosis. Outflow tract stenosis can cause blood flow to accelerate, resulting in a siphon effect, which may attract the mitral valve leaflets to adhere to the outflow tract, further reducing the already restricted channel and exacerbating the obstruction. Whether it is detected by catheterization or echocardiography, if the pressure difference under the aortic valve exceeds 30 mmHg, it indicates the presence of subvalvular obstruction.

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If the hypertrophic myocardium occurs in the middle or apical segment, the effect on the outflow tract is not obvious. It is just hypertrophy without obstruction. It is non-obstructive hypertrophic cardiomyopathy.

Some patients are examined at rest and no obstruction is found, and the pressure difference is not particularly high. However, they feel breath-holding, general fatigue, black eyes, or even fainting when they are active. At this time, a provocative test is needed, such as a dobutamine stress test, an exercise test, or breath-holding, leg-lifting, and squatting. If obstruction is found at this time when blood flow increases, and the pressure difference exceeds 30 mmHg, this is called latent obstructive hypertrophic cardiomyopathy. Latent obstructive hypertrophic cardiomyopathy does not cause outflow tract obstruction in a resting state, but potential obstruction will occur when there is activity, resulting in symptoms such as chest tightness, shortness of breath, black eyes, and fainting. In severe cases, it may even cause sudden death.

Therefore, in diagnosis, it is important to distinguish between obstructive and non-obstructive. If it is non-obstructive and there is no clear family history of sudden death, this group of people will not have too many symptoms, and regular monitoring and observation are sufficient. If it is obstructive, active treatment is required.