Discussion Author: Eric Jones
Hypertrophic Cardiomyopathy (HCM) is an autosomal dominantly inherited disorder in which the thickness of the ventricular wall is substantially increased in the absence of altered loading conditions that would fully account for the problem. Although only occurring in an estimated 0.2% of the population, it is the leading cause of sudden death (Sudden Cardiac Death [SCD]) among young athletes. Due to varying mutations, genetic analysis may only identify up to 50% of close relatives with the condition; therefore, accurate imaging techniques are essential in identifying this disorder.
Typically, the left ventricle is not dilated and the left ventricular ejection fraction is increased. Normal thickness of the left ventricular myocardium is from 0.6 to 1.1 cm (as measured at the very end of diastole.) Patients with HCM typically far exceed this value, with severe hypertrophy exceeding 30 mm. The ventricular septum and the anterior LV wall are preferentially involved in most patients, with abnormalities most prominent in the basal segments (thus asymmetric).
Mutations in sarcomere proteins lead to fibrosis of cardiac myocytes, which can be detected by late gadolinium enhancement through CMR imaging techniques. Contrast agent is readily washed out of normal myocardium, but resides in areas of myocardium with increased extracellular space. Typically, late gadolinium enhancement is located at the insertion points of the right ventricle into the septum. This pattern is observed in approximately 80% of HCM patients.
HCM requires an accurate diagnosis and determination of the distribution of hypertrophy and its functional consequences. An assessment of the likelihood of SCD is obtained by focusing on the presence of the following:
1. Extreme LV hypertrophy (>30 mm);
2. Blunted blood pressure response to exercise in patients younger than 40 years;
3. A family history of SCD;
4. Unexplained syncope;
5. Nonsustained ventricular tachycardia on 24-hour Holter monitoring.
The nonpathological form of LV hypertrophy, as observed in athletes, can be distinguished from pathological hypertrophy, based on the maximal end-diastolic wall thickness to volume ratio. An end diastolic wall thickness to volume ratio <0.15 mm*m2/ml was found to have a 99% specificity to differentiate an athleteâ€™s heart from pathological hypertrophy (Germans et al., 2010).
Alpha-blockers are the mainstay of therapy and are effective for symptomatic relief but not for the reversal of cardiac phenotype.
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