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Hypertrophic Cardiomyopathy

posted Aug 21, 2013, 6:44 AM by Purnema Madahar

Today's Monte Minute is brought to you by Mary Gover. The topic is based on a recent case presented at CRS last Friday. Thanks Mary!


Overview

Hypertrophic cardiomyopathy is the most common genetic cardiovascular disease.  It affects 0.2% of the population (or 1:500 people).  The underlying genetic mutation primarily affects sarcomere function - but also causes increased interstitial collagen, abnormal intramural arteries, and mitral valve malformations.  What is interesting about the condition is its heterogeneity in terms of phenotype.  When hearing about HCM we are conditioned to think about sudden death in a young athlete.  But, this is only one (albeit the most alarming) of the possible clinical expressions.


Clinical Course

It is likely that many patients with underlying genetic mutations do not present clinically.  In those that do, clinical manifestations can present at any age.  The three broad categories of the clinical spectrum include: sudden death, atrial fibrillation, and heart failure.  


                                    

Sudden Death:

It is thought that the disordered sarcomeric structure combined with scarring from intermittent episodes of ischemia (related to abnormal intramural coronary arteries) creates the substrate for arrhythmia and sudden death.  Most patients with HCM do not have risk factors for, and thus do not succomb to, sudden death.  That being said, sudden death does not only occur in young athletes.  When evaluating a patient with HCM in your practice, you should assess for the risk factors outlined below.  These factors have an excellent negative predictive value (ie - if your patient does not have them, it is highly unlikely that he will suffer sudden death from arrhythmia).  The positive predictive value is less clear.


Atrial fibrillation:

This is the most common sustained arrhythmia in HCM; however, it is not a predictor of sudden death.  The significance of atrial fibrillation in HCM is that it can lead to clinical deterioration.  As such, it should be treated aggressively.


Heart failure

Heart failure was the presentation seen in our CRS patient (which you can read about below).  The most likely inciting factor leading to heart failure is diastolic dysfunction.  Patients with HCM who present with heart failure are usually older, but can present at any age.  



The Case

In CRS, we had a case of a 49 year old man with 1 month progressive SOB.  His history of present illness was significant for lower extremity edema x 1-2 weeks, orthopnea x 1 week and cough x 3 days.  His past medical history was significant for malaria, typhoid, and latent TB (all s/p treatment).  He does not currently use any medications (prescribed or over-the-counter).  Per his social history, he is Nigerian - in the United States visiting family - and does not smoke, drink alcohol, or use other illicit drugs.  And, finally, his family history is only notable for hypertension and stroke.


From the above history, most groups agreed that the patient had some form of cardiomyopathy - though, the diagnosis was clenched with the physical exam.  As you might imagine, the physical exam was full of teaching points.  But, I have distilled down to two interesting cardiac findings found in patients with HOCM for your reading pleasure:


Neck Exam: ?double carotid impulse

We learned that this double pulse is a “pulsus bisferiens” - referring to two systolic beats per cardiac cycle.  Thanks to McGee, I learned that this double pulse is caused by rapidly ejected blood traveling into the aorta and causing a Venturi effect.  This Venturi effect, in HCM, pulse the anterior leaflet of the mitral valve and the interventricular septum together which momentarily reduces flow.  You can feel this double pulse by palpating the carotid pulse or by using the blood pressure cuff and listening for a “quick double tapping sound.”


Cardiac Exam: Grade 3 mid-late systolic murmur heard along the parasternal border that increases in upright position and with valsalva, and decreases when supine, with squat and with handgrip.

Let’s talk murmurs, maneuvers and likelihood ratios.  In this patient, we learned that he had a systolic murmur that increases with decreased preload and decreases with increased preload.  Preload is increased when supine and immediately after squatting.  The increase in preload increases the size of the ventricle which decreases the LV outflow tract obstruction.  Preload is decreased immediately after standing from a squat and after 20 seconds of exhaling against a closed glottis (Valsalva).  The hand grip maneuver increases afterload which would increase the size of the ventricular from the increased pressure needed for ejection.  The increased ventricular size decreases the intensity of the murmur.


And, how do these findings help us?  

The most helpful finding in terms of likelihood ratio is that the murmur is louder with Valsalva strain - LR 14.0.  

Louder with squatting-to-standing - LR 6.0

Softer with standing-to-squatting - LR 7.6

Softer with hand grip - LR 3.6


So, if the pre-test probability that our CRS patient is 0.2% (or the general prevalence), the finding of increase in the murmur with Valsalva strain + decrease with standing-to-squatting increases our post-test probability to greater than 10%.  Quite a jump!  


“Hypertrophic Cardiomyopathy: A Systemic Review.”  Barry J. Maron, MD. JAMA, March 13, 2002 - Vol 287, No 10.

“Hypertrophic Obstructive Cardiomyopathy.”  Rick A. Nishimura, MD and David R. Holmes Jr. MD.  NEJM, March 25, 2004.

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