CA-37
Is that SAM? A case of hypertrophic cardiomyopathy AND pulmonic stenosis in a patient with Noonan Syndrome.
Patel J, Kahana M
Albert Einstein-Montefiore Medical Center, Bronx, NY, USA
Noonan syndrome is a genetic disease with an incidence of 1:1000 to 1:2500 that is characterized by facial anomalies, short stature, and congenital heart defects. We describe a case of a 4 month old female with Noonan syndrome who developed systolic anterior motion (SAM) of her mitral valve after surgical correction for congenital subvalvar pulmonic stenosis (PS). Undiagnosed SAM can be life-threatening under anesthesia. Commonly used anesthetic agents act as vasodilators which decrease preload and may cause reflex tachycardia, together worsening LVOT obstruction. Inotropes that may be used to treat this hypotension increases the displacement of the mitral valve into the LVOT creating further cardiovascular collapse.
Our patient's initial echocardiogram revealed mild bilateral branch pulmonary artery (PA) stenosis with normal proximal branch PA diameters, mild RPA stenosis, qualitatively normal biventricular systolic function, no significant valvar pulmonary stenosis, and no evidence of hypertrophic cardiomyopathy (HCM) or SAM. Following a routine cardiology appointment at 4 months of age, the patient was noted to be floppy with perioral cyanosis, acutely became bradycardic, and desaturated. After resuscitation, an echo revealed progressive moderate pulmonary valvar stenosis with peak gradient across the pulmonary valve of 68mmHg (mean of 40mmHg), a mildly prominent muscle bundle in the right ventricular outflow and mild RVH with normal systolic function.The patient underwent a cardiac cath which showed a thickened pulmonic valve with additional supravalvar narrowing. Balloon dilation of her congenital subvalvar PS was unsuccessful and the decision was made to proceed with surgery. She underwent an uncomplicated pulmonary valvotomy with transannular patch that extended to the LPA. Two weeks after her cardiac surgery, mild dynamic left ventricular outflow tract (LVOT) obstruction secondary to systolic anterior motion of the mitral valve chordae and HCM was noted on follow-up echocardiogram which was an entirely new finding.
Noonan syndrome follows an autosomal dominant inheritance pattern with variable expression. It is one of the most common genetic disorders associated with congenital heart defects, second only to trisomy 21. Approximately 65-80% of patients will have a cardiac anomaly, with PS and HCM being the most common, but rarely are these two findings found in the same patient. PS in these patients is associated with a thickened, dysplastic valve that is not usually amenable to transcatheter balloon dilatation as was evidenced in our patient. HCM affects the ventricular septum primarily although the ventricular free walls may also be involved.
In summary, patients with Noonan syndrome have the potential to develop HCM despite earlier echocardiograms that do not demonstrate this abnormality. Cardiology follow up is vital in this patient population to ensure stable cardiac function even in patients with previously corrected congenital cardiac defects. As in our patient, SAM of the mitral valve can develop and does have significant anesthetic implications.
Digilio MC, Marino B. Clinical manifestations of Noonan syndrome. Images in Paediatric Cardiology. 2001; 3(2): 19-30.
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