Hypertrophic cardiomyopathy

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Introduction0:00–0:28

Cardiomyopathy translates to “heart muscle disease,” so cardiomyopathy is a broad term used to describe a variety of issues that result from disease of the myocardium, or heart muscle.
When cardiomyopathy develops as a way to compensate for some other underlying disease like hypertension or valve diseases, it’s called secondary cardiomyopathy, but when it develops all by itself it’s called primary cardiomyopathy.

Pathophysiology0:28–1:55

Now, hypertrophic cardiomyopathy is when the walls get thick, heavy, and hypercontractile, essentially the muscles grow a lot larger, because new sarcomeres are being added in parallel to existing ones.
Usually the left ventricle’s affected, and in most cases, this muscle growth is asymmetrical, meaning that the interventricular septum grows larger relative to the free wall.
These larger muscles do two things, (1) the walls take up more room, and so less blood can fill into the ventricle, and (2) they become more stiff and less compliant, and essentially, they can’t stretch out as much, again leading to less filling.
When they don’t fill as much, they don’t pump as much out and so stroke volume goes down. So the heart can fail to pump enough blood to the body, called heart failure, and since this is due to a dysfunction in filling, which happens during diastole, this is a type of diastolic heart failure.
In some patients, the muscle growth of the interventricular septum essentially gets in the way of the left ventricular outflow tract during systole, or ventricular contraction, and this increases blood velocity through the smaller opening and pulls the anterior leaflet of the mitral valve toward the septum—called the venturi effect—which further obstructs the left ventricular outflow tract, for this reason Hypertrophic cardiomyopathy is sometimes called hypertrophic obstructive cardiomyopathy.

Signs and symptoms1:55–4:09

An obstructed left ventricular outflow tract means blood is forced through a tiny opening, right? Which tends to cause a crescendo-decrescendo murmur, where it gets louder as blood first rushes out, and then softer, and this is very similar to the murmur in aortic valve stenosis.
The intensity of the murmur with Hypertrophic cardiomyopathy, though, can change, depending on how much the outflow tract is obstructed.
If the person squats down or does a handgrip maneuver, systemic vascular resistance increases, which makes it harder to eject blood out and increasing afterload—which means that the ventricle has more blood stretching it out and so it becomes less obstructed and the murmur becomes less intense.
If the person stands upright or does a valsalva maneuver, though, venous return decreases, which decreases preload, meaning less blood’s stretching out the ventricle before ejection and the obstruction gets larger, which means the murmur’s intensity increases.
Also people with obstructive Hypertrophic cardiomyopathy might have a bifid pulse, where two pulses are felt, and this is from the mitral valve moving toward the outflow tract and causing increased obstruction mid-systole.
So with larger muscle mass, the ventricles become less compliant, which remember means that they don’t stretch as easily when filled with blood.
If listening on auscultation, often an S4 sound can be heard from the atria contracting and pushing blood into a non-compliant ventricular wall during diastole.
And another thing is that those larger muscles need oxygen, like a lot of oxygen. Well, remember how we just talked about how the heart has a harder time getting blood (and therefore oxygen) to the tissues?
Well without oxygen they can become ischemic, and this is thought to be why people with hypertrophic cardiomyopathy sometimes develop dangerously fast arrhythmias, and why hypertrophic cardiomyopathy’s the most common cause of sudden death in young individuals, especially young athletes.
A little less severe symptoms of Hypertrophic cardiomyopathy might be things like dyspnea (which is difficulty breathing) or syncope (which is fainting) Now, the majority of cases of hypertrophic cardiomyopathy are inherited as an autosomal dominant trait, and caused by a genetic missense mutation, where a single nucleotide is swapped, causing a different amino acid to be coded for.

Causes4:09–4:57

This type of mutation usually happens in one of the genes that encode for proteins in the sarcomere of heart muscle, the beta-myosin heavy chain is the most common, but it could also be mutations in the myosin binding protein C and Troponin T.
A classic finding on histology is myocyte disarray, where instead of making nice parallel lines, myofibers don’t line up.
Also, people with Friedreich's Ataxia, which is an autosomal recessive neurodegenerative disease, often develop hypertrophic cardiomyopathy.

Treatment4:57–5:30

Now treatment of hypertrophic cardiomyopathy might involve medications like beta blockers, which help slow down the heart rate.
If those aren’t tolerated well, though, calcium channel blockers like verapamil or diltiazem might be used. Digoxin, however, a medication used occasionally for heart conditions, is contraindicated, since it tends to increase force of contraction, which can actually increase the obstruction as blood’s forced out of the ventricle.
Besides pharmacological treatments, some people with Hypertrophic cardiomyopathy might have surgery. All right, as a quick recap....

Review5:30–6:19

Hypertrophic cardiomyopathy is when the walls of the heart get thick, heavy, and hypercontractile. It usually affects the left ventricle, causing symptoms like a lower stroke volume, an obstructed left ventricular outflow tract during systole, a variable crescendo-decrescendo murmur, a bifid pulse, and dangerously fast arrhythmias.
It is most commonly caused by a genetic mutation affecting proteins in the sarcomere of heart muscle.