A Case of Noonan Syndrome with Concomitant Hypertrophic Obstruction Cardiomyopathy (HOCM) and Anomalies of the Mitral Sub Valvular Apparatus Successfully Treated With Systemic Obstruct-Reduction Therapy

Sarfraz Z and Nakata J

Published on: 2023-04-18

Abstract

Here, we report on a 13-year-old male child presenting with dysmorphic features characteristic of Noonan syndrome (NS), as well as symptomatic hypertrophic obstructive cardiomyopathy (HOCM) and localized left ventricular outflow tract obstruction (LVOTO). He complained of class III exertional according to the New York Heart Association (NYHA) criteria. Initial echocardiogram evaluation revealed localized basal septal hypertrophy causing LVOTO. We initially considered surgical septal myectomy. However, in consideration of the localized hypertrophy of the basal septal wall and the hypoplastic thorax typical of NS, we believed the space available was too narrow for myectomy. We accordingly opted to perform percutaneous trans coronary septal myocardial ablation (PTSMA). The intraventricular pressure gradient between ascending aorta and apical at rest decreased from 149 mmHg to 39 mmHg, accompanied by alleviation of the physical symptoms (dyspnea decreased from NYHA class III to I). Two years after PTSMA, however, he had complained of recurrent exertional dyspnea (NYHA class III) and syncope, accompanied by paroxysmal atrial fibrillation (Paf). Catheter pressure showed no remarkably elevated pressure gradient between ascending aorta and LVOT at rest. However, the gradient between ascending aorta and apical increased significantly after an extra-systolic ventricular provocation triggered a premature ventricular contraction (PVC) (9 mmHg at rest, 22 mmHg post-Valsalva overload and 123 mmHg post-PVC). Echocardiogram reassessment revealed regression of LVOT hypertrophy, but residual ventricular hypertrophy (20 mm) of the basal anterior septum and a pressure gradient of 26 mmHg. Mild mitral regurgitation (MR) was also present, with an anomalous mitral chorda tendinea that joined the anterolateral papillary muscle to the extruding ventricular septum. We suspected that this complex structure causes the obstruction. Systolic anterior motion (SAM) of the anterior mitral leaflet additionally caused deterioration of MR on exertion. At the age of 15 years, his development had progressed sufficiently to permit open-heart surgery. We then performed a surgical septal myectomy, resection of the sub valvular apparatus and additional implantation of implantable cardioverter defibrillator (ICD), which resulted in significant and permanent improvement of the symptoms and exercise capacity, with no recurrence of arrhythmia to date.