1348773 - Massive Left Ventricular Hypertrophy in an 11-year-old Male

An 11-year-old male presented for a second opinion following a recent diagnosis of hypertrophic obstructive cardiomyopathy (HOCM). During a routine sports screening exam one month prior, he was noted to have a murmur and referred for a transthoracic echocardiogram (TTE) which revealed asymmetric septal hypertrophy. He was therefore referred for a cardiac magnetic resonance (CMR) imaging which was interpreted as septal HCM verses cardiac mass. The patient was started on Atenolol 1 mg/kg/day and recommended to undergo immediate cardiac transplant evaluation.

At his initial presentation to our institution, he reported dyspnea on exertion. He was bradycardic likely secondary to beta-blocker use. A systolic murmur was noted on the physical exam.

Diagnostic Techniques and Their Most Important Findings:

A repeat TTE at our institution confirmed asymmetric LV wall thickness involving the septum measuring approximately 40 mm. His ejection fraction was 70% and the LV outflow tract (LVOT) maximal instantaneous Doppler gradient measured 50 mm Hg at rest and 62 mm Hg with Valsalva.  Reinterpretation of the outside institution CMR was most consistent with reverse curve morphologic subtype HOCM with a maximum myocardial thickness of 42 mm in the mid anteroseptal segment and corresponding patchy mid-myocardial delayed enhancement in the septum. There was no cardiac mass.  A 48-hour Holter monitor revealed frequent PVCs but no sustained ventricular tachycardia. The patient’s genetic test revealed a mutation in MYBPC3 gene.

After a joint discussion with surgery, the patient had an extended septal myectomy via transaortic and transapical approach with implantable cardioverter-defibrillator placement. Pathology from resected myocardial tissue confirmed the diagnosis of HOCM with marked myocyte hypertrophy, myocyte disarray, interstitial fibrosis, and endocardial fibrosis.

Learning Points from this Case:

This patient’s initial TTE revealed massive LV wall thickening, which was concerning for HOCM. The differential diagnosis included intracardiac mass due to marked myocardial thickness (i.e. rhabdomyoma or fibroma) and/or a toxic, metabolic or infectious non-ischemic cardiomyopathy. Use of the 2020 ACC AHA HCM guidelines give a class 1B recommendation to obtain a CMR when the diagnosis is in question. CMR in our patient helped eliminate a cardiac mass from the differential. Additionally, the clinical picture was not consistent with other forms of cardiomyopathy previously mentions.

CMR imaging further helped characterize this patient’s HOCM subgroup as reverse septal curve which is present in approximately 40% of cases based on recent data published in the National Heart, Lung, and Blood Institute HCM Registry. Interestingly, this subgroup is more likely to have increased LGE and interstitial fibrosis which is associated with a 2-fold increase in sudden cardiac death risk and a 3-fold increase in composite events when extensive LGE ( >15%) is present.