Hypoplastic Left Heart Syndrome - Norwood Operation

Definition

In hypoplastic left heart syndrome (HLHS) one or more of the structures of the left side of the heart are too small. The consequence is that this chamber cannot contribute or can only partially contribute to the supply of the body’s circulation. Typically there is high-grade narrowing or occlusion of the aortic valve (aortic stenosis, atresia) and/or mitral valve (mitral stenosis, atresia), lack of full formation of the left pumping chamber (hypoplasia or aplasia), hypoplasia or the ascending aorta and the aortic arch and an intact interventricular septum. Today the term HLHS is used for extreme forms of left hypoplasia that result in body circulation dependent on the right ventricle. However there are heart defects, such as unbalanced atrial-ventricular septal defects, double-outlet right ventricle with left ventricular hypoplasia, tricuspid atresia with transposition of the great arteries and functional single ventricle with aortic or arch hypoplastia, which are not defined as HLHS. Nevertheless the Norwood operation is the only possible therapy option for these complex heart defects.

Indication and Timing

Norwood operation
Diagnosis of a heart defect with ductus-dependent systemic circulation represents the indication for surgery. Ideally the child should be treated by a neonatologist directly after delivery and the diagnosis should be made by a pediatric cardiologist on the basis of echocardiographic examination. After intravenous administration of prostaglandins (5-10 ng/kg/min) the child should be promptly referred for surgical treatment (DHZB emergency telephone number: 030 4593-1000).
Timing: in the first weeks of life, when the newborn’s hemodynamics has been stabilized.
Hybrid operation (bilateral pulmonary artery banding and if needed ductus stenting).
Indicated when the circulation cannot be stabilized by medication preoperatively, in preterm infants weighing less than 2000g or when there is fresh cerebral bleeding.
Timing: between the third and tenth day of life, urgently in the case of heart failure and as an emergency measure in the case of intact atrial septum or other contraindications for a Norwood operation. 

Diagnosis

  • by echocardiography: visualization of the typical anatomy: aortic and/or mitral atresia or stenosis with intact ventricular septum and no antegrade flow into the ascending aorta; endocardial fibroelastosis; relation of left to right ventricle (long axis); diameter of the aortic annulus and the left ventricular outflow tract; mitral annulus (parasternal long axis).
  • by chest X-ray and, if necessary, abdominal X-ray and cranial to abdominal sonography.
  • by heart catheterization: only with unclear anatomy (suspected anomalous pulmonary venous connection).

Norwood Operation

In the Norwood operation the pulmonary artery stem is connected to the aortic arch, which has first been enlarged; the right ventricle thus becomes the systemic ventricle. To enable perfusion of the lung a GORE-TEX® conduit (shunt) is placed from the right arm artery to the right pulmonary artery (modified Blalock-Taussig Shunt). Further, the atrial septum is removed so that the blood can flow freely from the left atrium to the right side of the heart. Specialties of the DHZB: - Norwood operation without circulatory arrest with selective cerebral perfusion ,and ascending aorta perfusion and peripheral perfusion of the lower body. – Use of a BT shunt. –Postoperative monitoring of the blood flow to the lung and to the body (Qp/Qs, SvO2). Heart failure treatment with Carvedilol. Home monitoring with daily measurement of weight and oxygen saturation. Regular checks of the hemoglobin values and if necessary erythropoetin therapy or blood transfusion. Sano operation: In the case of when the pulmonary flow is supplied from the arm artery (modified BT shunt) it may be necessary to deviate from the Norwood operation and have the shunt arise directly from the right ventricular outflow tract (Sano shunt). However, in the long term arrhythmia is to be expected as the result of scar formation; therefore this type of shunt is not regularly employed at the DHZB.

HLHS Anatomy
Norwood Operation
HLHS Glenn Operation
HLHS: Fontan extracardiac conduit