Hypertrophic obstructive cardiomyopathy, also known as idiopathic hyper-trophic subaortic stenosis (IHSS), is a autosomal dominant disease in which there is hypertrophy of the interventricular septum classically in the cephalad portion, hence the term asymmetric septal hypertrophy. Systolic anterior motion of the anterior leaflet of the mitral valve occurs due to the free edge of the anterior leaflet bulging close to the septum, causing an abnormal motion seen on echocardiography. An echocardiogram is the most helpful diagnostic maneuver in evaluating IHSS. If the patient is refractory to medical treatment (Inderal, calcium channel blockers and diuretics), then the patient should undergo cardiac catheterization with a view to surgery.
The treatment of hypertrophic obstructive cardiomyopathy is transaortic myomectomy. If the extent of intraventricular hypertrophy is deeper in the left ventricular outflow tract than usual, or when residual muscle is left behind, a left ventricular approach is used also. Cardiopulmonary bypass is established with a single venous cannula, a left ventricular vent is used and antegrade followed by retrograde cardioplegia is used to arrest the heart using cold blood cardioplegia. The aortic root is opened. A sponge is placed over the right ventricle to push the septum down and an incision is made down the interventricular septum from a point just to the left of the nadir of the right coronary cusp and continued toward the intercoronary commissure in the "Morrow procedure". A wedge of muscle is thus excised.
Generally, surgical treatment is reserved for patients in Class III or IV failure, angina or syncope, or those with a gradient greater than 50 mm, i.e. similar to that for aortic stenosis, or those patients not relieved with Inderal, calcium channel blockers or diuretics. Even if there is no gradient at rest, if there is a greater than 50 mm gradient on exercise, surgery is indicated.
Mitral valve replacement may be necessary for some cases of IHSS but this is only done when myomectomy has not decreased the dynamic left ventricular outflow tract gradient. Left bundle branch block occurs in up to two-thirds of patients, but a complete AV block should not occur because one stays to the left of the nadir of the right coronary cusp and, hence, away from the membranous septum and the bundle of His at the anterior commissure.
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