OVERVIEW
Nonobstructive hypertrophic cardiomyopathy is hypertrophic cardiomyopathy without left ventricular outflow tract obstruction. Left ventricular hypertrophy usually occurs in the mid-septum, apical region, or free wall of the left ventricle, but does not cause left ventricular outflow tract obstruction. In some cases, the proximal septal hypertrophy is mild and there is no significant pressure difference in the left ventricular outflow tract, but as the septal hypertrophy worsens, it may evolve into obstructive hypertrophic cardiomyopathy.
Etiology
The disease is an autosomal dominant disorder, with 60% to 70% being familial and 30% to 40% being sporadic, with familial and disseminated cases, and pediatric and adult cases, sharing the same causative gene mutations. At least 14 gene mutations have been shown to be associated with the development of hypertrophic cardiomyopathy, 10 of which are in genes encoding structural proteins of the myocardial segments, and the vast majority of mutations are located in these genes.
Symptoms
The clinical manifestations of the disease are mild and may be asymptomatic and only detected during an electrocardiogram or echocardiogram. Common symptoms include palpitations and precordial discomfort, as well as shortness of breath after exertion, and syncope does not usually occur.
Examination
1. Electrocardiography
Electrocardiogram shows left ventricular hypertrophy.
2. Echocardiography
Transthoracic echocardiography shows hypertrophy of the middle or distal segment of the ventricular septum, which may also be combined with left ventricular free wall hypertrophy, with the ratio of the thickness of the ventricular septum to that of the left ventricular free wall <1.3, and there is no systolic forward movement of the mitral valve. The left atrium may be significantly enlarged with an E/A ratio <1, suggesting impaired left ventricular diastolic function. The left ventricular cavity is small or normal-sized in the early stages of the disease and may be significantly enlarged in the late stages of heart failure.
Diagnosis
The diagnosis of this disease relies mainly on transthoracic echocardiography, which reveals marked left ventricular hypertrophy without left ventricular outflow tract obstruction.
Differential Diagnosis
Left ventricular hypertrophy due to aortic stenosis and subaortic septum with systolic murmur in the aortic valve region should be excluded.
Treatment
1. Drug therapy
Symptomatic patients can choose β-receptor antagonists, which are effective in improving the diastolic function of the left ventricle and preventing arrhythmia and sudden death. Calcium channel blockers such as verapamil can be used in patients who cannot tolerate beta-agonist therapy. Antiarrhythmic agents such as propyzamide are the most clinically potent agents available to reduce the pressure difference in the left ventricular outflow tract and can be used in the treatment of left ventricular outflow tract obstruction. Patients at high risk for embolism in the physical circulation should be given warfarin for anticoagulation.
Whether antibiotics should be routinely applied to prevent infective endocarditis in patients with nonobstructive hypertrophic cardiomyopathy during dental procedures and other interventional procedures is inconclusive.
2. Other
Since there is no left ventricular outflow tract obstruction, surgical or chemical ablation therapy or implantation of a dual-chamber pacemaker is not required.
Prognosis
The prognosis is generally good, and female patients with good cardiac function can tolerate pregnancy and normal delivery.