- What does HOCM sound like? à same as AS (mid-systolic murmur, aka crescendo-decrescendo
- What causes HOCM? à autosomal dominant mutation in beta-myosin heavy-chain gene.
- What’s the structural change in the heart with HOCM? à asymmetric septal hypertrophy that causes
the anterior mitral valve leaflet to block off the LV outflow tract under states of lesser preload à
student says, “if the LV outflow tract is blocked off (i.e., where the aortic valve is), why is it the mitral
valve leaflet that blocks it off then?” Yeah, I know, it’s weird. But the asymmetric septal hypertrophy
causes this to happen.
- What’s the cause of death in HOCM? à ventricular fibrillation (really HY!!) à the “sudden death in
young athlete” is not due to an MI à i.e., the patient has clean coronary arteries à do not select
coronary artery occlusion as the answer.
- What about if the vignette is sudden death in middle-aged patient with heart disease? à answer =
ischemic heart disease (MI), not HOCM.
- 18M athlete + 2/6 mid-systolic murmur at right sternal border 2nd intercostal space + there is
paradoxical splitting of S2 + there is no change in the murmur with Valsalva; Dx? à ”bicuspid aortic
valve” (AS), not HOCM à students say “oh em gee young athlete! HOCM!” à the USMLE will slam
you on this and wants you to know that the key way to distinguish between AS and HOCM murmurs is
that HOCM gets worse with lower volume in the heart; AS will soften or there will be no change.
Don’t just automatically jump on HOCM because it’s a young athlete.
- How to Tx HOCM à can give propranolol to keep HR from getting too fast (the slower the HR, the
more time the heart spends in diastole à more diastolic filling à greater preload à less occlusion of
LV outflow tract) à should be noted tangentially that although beta-blockers increase preload, they
decrease chronotropy + inotropy so the net effect is still decreased myocardial oxygen demand.
- Can you explain “splitting of S2”? What does that even mean? à the aortic valve normally shuts (A2)
just before the pulmonic valve (P2), so A2 will occur slightly before P2 à when we talk about changes
in splitting of the S2 heart sound (i.e., wide splitting, paradoxical splitting, etc.), if pressure in a
ventricle is greater, the sound will occur later / is protracted. So if RV pressure becomes greater for
whatever reason à P2 occurs later à wider splitting. So pulmonary artery hypertension = widesplitting. If LV pressure becomes greater à A2 occurs later, and can even occur after P2 à paradoxical splitting. So LVH = paradoxical splitting. When R or L ventricular pressure exceeds the
pulmonic arterial and aortic pressure, respectively, the valves open. Then the ventricle will lose
pressure as blood ejects, followed by isovolumetric relaxation marking the onset of diastole, and the
pressure within the ventricle falls below the pressure distal to the valve à valve shuts. Normally
splitting oscillates with the respiratory cycle. Inhalation causes P2 to occur later à decrease in
intrathoracic pressure à increased venous return to right atrium à more blood in right ventricle à
more preload à more pressure à time it takes for RV pressure to fall below pulmonic arterial
pressure is greater à P2 will occur slightly later with inhalation. With exhalation it’s the opposite. P2
occurs slightly sooner because increased intrathoracic pressure will attenuate venous return à less
preload in RV à less pressure in RV à time it takes for RV pressure to fall below pulmonic arterial
pressure is less à pulmonic valve closes slightly sooner à distance between A2 and P2 is less.