IDIOPATHIC HYPERTROPHIC SUB-AORTIC STENOSIS FOR THE USMLE
Let’s take some time to discuss a disease that is becoming more popular in the media – IHSS. Everytime you hear of a young person dying while playing sports, it is probably IHSS.
Some important ‘must know’ information about IHSS:
– Is an autosomal dominant disease (if you have it, there’s a 50% chance your kids will have it – if you live long enough)
– Muscle fibers are hypertrophied but disorganized (will have an S4 due to hypertrophy) *fibers are disorganized and this is what causes the pathology… septum is thick and is ‘top heavy‘ –> so it wants to fall into the ventricle (thus we need to ensure ventricle can fill adequately to move larger muscle away)
– Any young athlete who dies suddenly, especially during peak exercise, probably has IHSS
– The septum is asymmetrically thick, especially the top –> causes SUBAORTIC stenosis (this part wants to fall down into the ventricle) – and is why we need to allow the ventricle to fill with plenty of blood… as ventricle contracts the hypertrophied part moves out of the way, when its done it falls back, and then the ventricle squeezes again (bulsus bisferens – ie. we’ll hear 2 pulses)
– Excessive hypertrophy compresses the coronary arteries
– Excessive hypertrophy obliterates the ventricular space
– Murmur LOUDER when standing or with valsalva, decreased with increased TPR
Let’s explain the statement above more in-depth: If we are looking for a murmur, we know that they are going to be louder when there is more blood in the heart simply because more blood = more turbulence through the valve… Now, the opposite is true for hearing a heart with IHSS because when there is plenty of blood in the heart there will be no way the hypertrophied septum will fall into the ventricle. So in order to hear this with a stethoscope the patient would have to have less blood in the heart (so we’ll do it purposely with the valsalva maneuver – more on this later)
******is the MCC of sudden death in athletes –> any athlete who drops dead at a young age during play –> it is IHSS.
WHY do they die at peak of exercise? Because at the peak of exercise the HR is too fast, they are spending most time in systole, thus little time in diastole and the septum falls into the ventricle and there’s not enough blood to move it out of the way –> they drop dead.
**30% will present with syncope, 70% will die suddenly. This 30% are the lucky ones, and if this is found before they die there are some absolutely ESSENTIAL steps they must follow:
#1 – Give a beta blocker – the reason for this is to decrease the contractility of the heart so there is more time for the ventricles to fill adequately.
#2 –> Bar them from organized sports (it is simply too risky for them to play competitively)
#3 –> Plasma volume must remain very high – (adequate fluid intake a must – life depends on it)
***do an ECHO on the entire family
The thing to realize is that we cannot simply do an ECHO on anybody who asks for it because they cost quite a bit of money…. So, instead of an echo, there’s a simple test we can do in the clinic to diagnose this test
Do the valsalva maneuver –> pushing down on a closed glottis – it prevents blood from coming from the leg veins so that we have less blood coming into the heart while performing the maneuver, and it will make IHSS sound louder – this is because there is not enough blood in the ventricle and thus we can hear this problem more prominently. *** the first 2 seconds of performing the valsalva we have to ignore, because just in case there was lots of blood in the heart at that moment, we’ll be hearing the increased sound of aortic stenosis and a softening of IHSS, so we wait a couple seconds then listen to see what happens!
***things making aortic stenosis louder will make the IHSS softer (because there is more fluid and thus less of the septum falling into the ventricle.)
*If you’re given a question about this and there is the option of doing an echo or the valsalva, pick the valsalva.
SO –> IHSS gets louder with the valsalva because there isn’t enough blood in the left ventricle to keep the septum from falling into the ventricle, and thus it iss louder.
Be sure you know how to manage a patient who is diagnosed with IHSS.
Be sure you answer IHSS when a youngster falls dead while playing sports.