Unroofing of LAD Myocardial Bridge Combined With Right Ventricular Septal Myectomy in a Child With Noonan Syndrome and HCM

This is a 10-year-old boy with Noonan syndrome and HCM who presented with exertional chest pain that required repeat hospitalization. His exercise treadmill stress test had to be discontinued due to chest pain. He underwent previous left ventricular septal myectomy via combined transaortic and transventricular approaches for LVOTO and had frequent PVCs that were being treated with combination antiarrhythmic medications. He also had previous device closure of an ASD. Preoperative echocardiography showed no LVOTO with preserved biventricular function and a right ventricular midcavitary gradient of 32 mm Hg.

Due to the persistence of his chest pain, a coronary angiogram was performed that showed a significant LAD myocardial bridge and confirmed the gradient in the RVOT. His cardiac catheterization showing the RVOTO and the LAD myocardial bridge is marked by double headed arrow. Due to his impaired quality of life and persistence of chest pain, the decision was made to proceed with unroofing of this myocardial bridge.

A repeat median sternotomy was performed and direct pressure measurement across the RVOT confirmed the preoperative gradient. CPB was then initiated via aortic and bicaval cannulation in the standard fashion. The authors proceeded to identify the LAD, which was quite challenging due to the mediastinal adhesions and the significant adherence of the left ventricular apex to the pericardium due to the previous apical incision. Using a combination of electrocautery at low settings and sharp dissection, the LAD was identified distally as it exited beyond the myocardium and was traced back to the intramyocardial segment. It was unroofed using Potts scissors and electrocautery.

In these cases, it is important to perform this procedure with the heart standstill to minimize risk of injury to the coronary artery, and it is also important to be precise with the direction of unroofing to avoid inadvertent entry into any ventricular cavity. The entire myocardial segment has to be unroofed. Sometimes the authors are faced with epicardial veins that needs to be clipped or divided. They administered a test dose of cardioplegia to ensure no significant bleeding from the myocardium, epicardial veins, or the unroofed coronary artery prior to removal of the aortic cross clamp. Once the unroofing was completed, attention was directed to the right ventricular outflow tract. The RV septal myectomy is a bit different from standard left ventricular myectomy.

A right ventriculotomy was performed and the RV side of the IVS was shaved, paying attention to the tricuspid apparatus, and a bovine pericardial patch was used to augment the RVOT. It was sewn in using running 4/0 prolene suture. The heart was then de-aired and the AXC was removed. The patient was then weaned off cardiopulmonary bypass in the standard fashion. Postbypass TEE showed good biventricular function with no RVOT gradient. Drains were placed and the chest was closed in the standard fashion. The patient was extubated in the operating room and transferred to the CVICU in a stable hemodynamic fashion. The AXC time was 107 minutes, and the CPB time was 274 minutes

The postoperative course was complicated with vasoplegia that responded to methylene blue and there was a need for chest re-exploration with evacuation of a posterior pericardial hematoma 24 hours later. He was discharged two weeks later. He continued to do well as an outpatient with his most recent echocardiogram showing good biventricular functions and no evidence of RVOTO, and his antiarrhythmic medications are being weaned.

References

1. Möhlenkamp S, Hort W, Ge J, Erbel R.. Update on myocardial bridging. Circulation. 2002;106:2616-2622.
2. Said SM, Dearani JA, Burkhart HM, Schaff HV. Surgical management of congenital coronary arterial anomalies in adults. Cardiol Young. 2010;20:68-85.
3. Roberts AE, Allanson JE, Tartaglia M, Gelb BD. Noonan syndrome. Lancet. 2013;381(9863):333-342.

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