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Chapter: Medicine and surgery: Cardiovascular system

Hypertrophic cardiomyopathy - Disorders of the myocardium

Hypertrophic or hypertrophic obstructive cardiomyopathy (HOCM) is a condition of the myocardium with massive hypertrophy of the ventricular walls.- Definition, Incidence, Aetiology, Pathophysiology, Clinical features, Complications, Investigations, Management, Prognosis.

Hypertrophic cardiomyopathy

 

Definition

 

Hypertrophic or hypertrophic obstructive cardiomyopathy (HOCM) is a condition of the myocardium with massive hypertrophy of the ventricular walls.

 

Aetiology

 

Half the cases are due to an autosomal dominant inherited point mutation of the β myosin heavy chain, which codes for a component of the cardiac muscle fibre.

In families with a history of sudden cardiac death from HOCM, there is an association with the angiotensin converting enzyme (ACE) genotype DD.

 

Pathophysiology

 

There is marked hypertrophy of one or both ventricles particularly affecting the ventricular septum. This may result in obstruction to the outflow of the left ventricle, which is made worse on contraction of the ventricle. The muscle fibres relax poorly and as a result there is poor left ventricular filling and contraction, with disordered mitral valve movement.

 

Clinical features

 

Hypertrophic cardiomyopathy often presents similarly to aortic stenosis with dyspnoea, angina, syncope, or sudden death. Signs of heart failure are common but occur at a late stage. Initially the pulse is jerky with a rapid outflow due to hypertrophy, in the late stages obstruction results in a slow rising pulse. The JVP shows an increase in the size of the ‘a’ wave (atrial contraction). Palpation reveals a prominent thrusting apex, which may be double (palpable atrial contraction). There may be a systolic murmur (and thrill) due to ventricular outflow obstruction maximal at the left sternal edge. This may be varied by dynamic maneouvres or drugs that can alter the degree of functional obstruction. A fourth heart sound is often heard caused by ventricular filling due to atrial contraction.

 

Complications

 

Thrombosis and consequent systemic embolisation may occur requiring anticoagulation. Prophylaxis is required against infective endocarditis. It is associated with Wolff– Parkinson–White Syndrome. Ventricular arrhythmias are common and may lead to sudden cardiac death.

 

Macroscopy/microscopy

 

Hypertrophy is asymmetrically distributed. The increase in thickness occurs particularly of the interventricular septum. Disorganised branching of abnormal, short, thick muscle fibres, in which there are large nuclei.

 

Investigations

ECG shows ST, and T wave changes with evidence of hypertrophy (anterior Q wave, T wave inversion and increased QRS voltage).

Echocardiography shows a small left ventricular cavity with generalised or asymmetrical hypertrophy of the septum. Mitral valve movement is also characteristic. Twenty-five per cent of patients have outflow tract obstruction.

 

MRI scanning is of particular value if echocardiography cannot obtain adequate views particularly in apical hypertrophy.

 

24-hour ECG monitoring is used to detect episodes of ventricular tachycardia.

 

Exercise testing is helpful for risk assessment, i.e. loss of rise in blood pressure or onset of arrhythmia during exercise are high risk features for sudden cardiac death.

 

Management

 

β-blockade is the mainstay of treatment as this lowers the pressures within the left ventricle.

 

Arrhythmias: β-blockers and amiodarone are used to prevent ventricular arrhythmias and there is increasing use of automatic implantable cardiac defibrillators (AICD). Atrial fibrillation is preferably treated with DC synchronised cardioversion. Refractory atrial fibrillation is treated with digoxin.

 

Surgical treatment: Occasionally resection of the hypertrophied septal wall (myotomy/myectomy) is indicated with, where necessary, a mitral valve replacement. Surgical intervention is usually reserved for severely symptomatic patients.

 

Septal ablation by selective alcohol injection into a sizeable septal branch of the left anterior decending artery has been shown to achieve similar results to surgery.

 

If patients have angina nitrates should be avoided, and diuretics should only be used with care as these increase the degree of functional obstruction.

 

Prognosis

 

Factors suggesting a worse prognosis include young age or syncope at presentation and a family history of sudden death due to HOCM.

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