Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy

Incidence of hypertrophic cardiomyopathy (HCM) may vary from 0.02 to 0.2% in the general population. It is characterised by a hypertrophied and non-dilated left ventricle with a small cavity. The hallmark of HCM is asymmetrical septal hypertrophy (ASH) which narrows the left ventricular outflow tract (LVOT) and produces the systolic anterior motion of mitral valve (SAM) due to the Venturi effect. HCM may present with concentric left ventricular hypertrophy as well as apical cardiomyopathy with hypertrophy of left ventricular apex and adjacent myocardium.

Familial hypertrophic cardiomyopathy

HCM has an autosomal dominant pattern of inheritance, with involvement in 50% of first degree relatives. Different genes on at least 4 chromosomes have been identified, with over 3 dozen mutations. Chromosome 14 (myosin), chromosome 1 (troponin T), chromosome 15 (tropomyosin) and chromosome 11 are the various loci identified.

Pathophysiology of HCM

Pathophysiologic abnormality in systole is the dynamic LVOT gradient, which increases on standing and in situations which reduce the afterload of the left ventricle. Diastole is marked by impaired diastolic filling, with elevated filling pressures due to impaired relaxation of the hypertrophied ventricle. Atrial booster function is very important in this situation and loss of atrial booster function due to atrial fibrillation will lead to rapid hemodynamic deterioration. Myocardial ischemia can occur in HCM due to various mechanisms like increased muscle mass, filling pressure and oxygen demand; decreased vasodilator reserve and capillary density; abnormal intramural coronary arteries and systolic compression of coronary arteries.

Clinical Manifestations of HCM

HCM can be totally asymptomatic being detected by echocardiographic findings during family screening or after a routine ECG which shows gross left ventricular hypertrophy pattern. Symptomatic cases may present with dyspnea on exertion, angina pectoris, fatigue, presyncope or syncope. Palpitations, paroxysmal nocturnal dyspnoea or feature of congestive heart failure can be the presenting features in some cases. There is an increased risk of sudden cardiac death (SCD) in children and adolescents with HCM.

Natural History of HCM

Hypertrophic cardiomyopathy has an annual mortality rate of 1-3%. The risk of SCD is higher in children and may be as high as 6% per year. Clinical deterioration usually slow in HCM. Progression to dilated phase may occur in 10-15% cases of HCM. The higher left ventricular wall thickness on echocardiography and left ventricular hypertrophy with strain pattern may help in differentiation from dilated cardiomyopathy,

Risk Factors for SCD in hypertrophic cardiomyopathy

Young age (<30 years), malignant family history of SCD, certain gene mutations prone to SCD, aborted SCD, sustained ventricular tachycardia, recurrent syncope and septal thickness > 30 mm are considered to be risk factors for sudden cardiac death in hypertrophic cardiomyopathy.

Management of HCM

Beta blockers are the mainstay of treatment in hypertrophic cardiomyopathy. The negative inotropic effect is important for their role in hypertrophic cardiomyopathy with a hypercontractile state. The non-dihydropyridine calcium antagonists also have a similar role in HCM. Disopyramide useful both by its negative inotropic effect and antiarrhythmic effect in HCM. Amiodarone useful in cases with sustained ventricular arrhythmias. Sotalol has a role both as an antiarrhythmic agent and as a negative inotropic agent. DDD pacing has been advocated for long in HCM because right ventricular pacing produces paradoxical motion of the interventricular septum and reduces the LVOT obstruction. But results of various trials have been conflicting. Pacing is definitely indicated in those rare cases with associated complete AV block. While pacing in these cases, DDD mode gives a physiological advantage as the atrial booster function is important in the filling of the hypertrophied ventricle. Surgical septal myectomy has been done in the past as well as in some selected cases currently. Judging the exact amount of myocardium to removed is crucial in obtaining optimal results. Alcohol septal ablation is coming up a good way. The incidence of complete heart block with alcohol septal ablation has come down with onset of myocardial contrast echocardiography for delineation of the territory for ablation. Care has to be taken to avoid spillover of the alcohol into the parent left anterior descending (LAD) coronary artery which can have catastrophic results. Coil embolisation of septal branches of LAD is another modality for septal reduction in HCM.

Hypertensive hypertrophic cardiomyopathy of the elderly

Hypertensive hypertrophic cardiomyopathy of the elderly is an entity which resembles HCM on echocardiography. Characteristics of hypertensive HCM of the elderly are modest concentric left ventricular (LV) hypertrophy (<22 mm), small LV cavity size and associated hypertension. Ventricular morphology is distorted and the left ventricular outflow tract dimensions are reduced due to a sigmoid septum.