Nejm 2004;350:1320; Jama 2002;287:1308
Cause:Genetic, over 10 different mutations can cause, one on chromosome 14 (Nejm 1992;326:1108; 1989;321:1372), autosomal dominant with nearly complete penetrance when measure thickness of interventricular septum (Ann IM 1986;105:610)
Pathophys:50% due to mutations in the myosin heavy chain gene (Nejm 1992;326:1108; 1991;325:1753). Abnormal intraventricular septum produces dynamic aortic root obstruction and subaortic stenosis; mitral regurgitation is due to anterior mitral leaflet being distorted by the septum; obstruction is worsened by diuresis and vasodilators, and increases in contractility, eg, by digoxin, PVCs, catechols, and exercise. Reentrant PVCs because of different refractory periods in different muscle groups (Nejm 1980;302:97). Increased calcium channels increase the muscle sensitivity and contraction strength (Nejm 1989;320:755). Myocardial bridging of epicardial coronary arteries also occur (Nejm 1998;339:1201) and cause myocardial ischemia/infarcts and coronary microvascular dysfn (Nejm 2003;349:1027)
Prevalence = 1/500; male/female = 4:1 in sporadic type, but equal in genetic type (E. Braunwald, 1978); higher incidence in Fabry's disease (Nejm 1982;307:926)
Sx:Onset age 15-46 yr, positive family hx in 1/3 (E. Braunwald, 1978); syncope (3/18), dyspnea (13/18), chest pain (7/18), angina, which starts when exercise stopped, palpitations
Si:
LVH by palpation and double PMI, with diphasic arterial systolic peak murmur
Aortic murmur without radiation into neck (Nejm 1988;318:1575), decreases with leg elevation and squatting, which increase venous return, worse with isoproterenol, exercise, standing, amyl nitrite inhalation, alcohol ingestion, and Valsalva maneuver
Two types: slowly progressive and generally benign (Jama 1999;281:650; Nejm 1989;320:749); and "malignant," with premature death in young adulthood w myosin heavy chain mutation (Nejm 1992;326:1108). Outlet obstruction makes prognosis worse (Nejm 2003;348:295)
Sudden death by Vtach/fib (Nejm 1988;318:1255) correlates w LV wall thickness (Nejm 2000;342:1778); Afib in 20-25%; endocarditis
r/o "ATHLETE'S HEART" w LV wall thickness always <16 mm, rarely >13 mm (Nejm 1991;324:295), which overlaps w IHSS in men but not in women (Jama 1996;276:210); and glycogen storage disease hypertrophic cardiomyopathy (Nejm 2005;352:362)
r/o causes of sudden death in athletes (Nejm 1998;339:364): cardiomyopathy (22%), ASCVD (15%), anomalous coronary artery (12%), IHSS (2%) (see screening cardiac exam)
Lab:
Noninv:EKG shows LVH, big Qs in V1-2 (hypertrophied septum)
- Holter for malignant PVCs. Nonspecific EKG changes occur in affected children before echo changes (Nejm 1991;325:1753)
- Echo shows hypertrophied septum and LV wall and systolic anterior motion of mitral valve; Doppler shows subvalvular gradient
Path:Endocardial bx shows chaotic muscular disorder (Nejm 1977;296:135). Genetic PCR studies of peripheral lymphocytes can detect in presymptomatic stage (Nejm 1991;325:1753)
Xray:Chest shows LVH
Rx: (Jama 2002;287:1308)
Avoid competitive sports
Avoid digoxin, diuretics, catechols, alcohol (Nejm 1996;335:938), nitrates, and other vasodilators.
Implantable cardiovertor defibrillator (ICD) (Nejm 2000;342:365, 422) to prevent Vtach/sudden death; cardioverts 11%/yr when used as secondary (after VT) and 5% as primary prevention in high-risk pts
Antiarrythmic rx, not justified in asx pts by efficacy trials
Iatrogenic anteroseptal MI effective (Nejm 2002;347:1326) but often causes complete heart block, 50% need pacer
Surgical myotomies when resting obstruction >75 mm or class II sx despite medical rx; 80% success (Ann IM 1972;77:515); dual chamber pacing; and angiographic septal ablation?
of CHF: neg inotropes like 
-blockers, verapamil (Mod Concepts Cardiovasc Dis 1990;59:1; Ann IM 1982;96:670), disopyramide (Norpace—Nejm 1982;307:997) 150-200 mg po qid
of Afib: amiodarone and warfarin anticoag