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Key Concepts

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  • Hypertrophic cardiomyopathy (HCM) can be defined as left ventricular hypertrophy in the absence of an underlying cause (e.g., hypertension, aortic stenosis). Left ventricular outflow tract obstruction (LVOTO) results from septal hypertrophy combined with systolic anterior motion of the mitral valve, which also produces variable degrees of mitral regurgitation.

  • The distribution of left ventricular hypertrophy is variable in patients with HCM. The appearance and severity of the hypertrophy do not correlate with genotype; multiple ventricular morphologies may be found in the same family. The most common pattern of hypertrophy is diffuse involvement of the ventricular septum.

  • Myocardial fiber disarray is a characteristic feature of HCM.

  • Although coronary arteries are larger than normal in patients with HCM and basal coronary flow is increased at rest, coronary flow reserve is decreased in symptomatic HCM patients.

  • Two-dimensional and Doppler echocardiography is essential in the diagnosis of HCM. Cardiac MRI is useful in identifying regions of left ventricular hypertrophy not easily seen with echocardiography, specifically the anterolateral free wall and apex, and the presence and severity of myocardial fibrosis.

  • Symptoms in HCM patients are often associated with the development of LVOTO.

  • Transaortic septal myectomy is indicated in HOCM patients who continue to have limiting symptoms despite medical treatment (i.e., β-blockade, calcium antagonists, disopyramide). Mitral valve replacement is reserved for patients with intrinsic leaflet abnormalities that cannot be repaired.

  • Adequate septal myectomy usually yields 3 to 12 g of muscle. Intraoperative simultaneous aortic and left ventricular pressure measurements can be used to confirm complete relief of LVOTO after septal myectomy. The most common cause of inadequate myectomy is failure to extend the myectomy far enough toward the cardiac apex.

  • Unroofing of coronary artery muscle bridges is performed selectively, particularly in young patients and those experiencing anginal symptoms.

  • Mortality risk with septal myectomy is less than 1 percent in experienced centers with over 90 percent of patients experiencing improvement of at least two functional classes. Late recurrence of large resting left ventricular outflow tract gradients is very uncommon after successful myectomy.

  • Alcohol septal ablation is an alternative to myectomy in high-risk HCM patients. It has been associated with an 11-percent incidence of complete heart block requiring permanent pacemaker and a 1.5-percent hospital mortality.

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Introduction

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Hypertrophic cardiomyopathy (HCM) may be defined as left ventricular (LV) hypertrophy in the absence of an underlying cause such as systemic hypertension or valvular aortic stenosis.1 Left ventricular outflow tract obstruction (LVOTO) is caused by septal hypertrophy combined with abnormal systolic anterior motion (SAM) of the mitral valve, and this, in turn, produces variable degrees of mitral valve regurgitation (MR). LVOTO in HCM is distinct in morphology and prognosis from congenital membranous subaortic stenosis, which is rarely associated with SAM. Some patients with HCM will have symptoms due to mid ventricular obstruction. Hypertrophic obstructive cardiomyopathy (HOCM) is important for surgeons because obstruction may occur in over 70 percent of patients with HCM,2 and transaortic septal ...

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