What Is Hypoplastic Left Heart Syndrome?
Hypoplastic left heart syndrome (HLHS) is a lethal form of inborn defect, where the affected child will be born with gross distortion and disfigurement, particularly involving the left side of the heart. The normal anatomy of the heart illustrates two distinct chambers on either side of it. In hypoplastic left heart syndrome, the anatomy of the heart's left side shows deviation from what is identified to be normal. These abnormalities can be in the form of collapsed chamber size, constricted valvular connections between the chambers, and limited communication across the lower chamber (left ventricle) and the connected blood vessel (aorta). Sometimes, the left side may lack distinct upper and lower chambers and appear underdeveloped. The extent of underdevelopment varies from person to person and directly determines the severity of the condition.
Since the left side is defective, all the functions carried out by the heart on the left side get hindered and impaired. The heart's left side is usually concerned with the driving out of blood to different cells and organs. Prompt blood pumping keeps the vitality of the cells and maintains their functions. In HLHS, the left side is nonfunctional and abnormal. As a result, it becomes incapable of driving blood to the central artery aorta, which distributes the oxygen-rich blood to all other areas within the body. Hence, it is crucial to establish circulatory patency in HLHS patients to ensure survivability, without which, it will be challenging for the affected baby to survive. Studies have concluded that HLHS babies hardly survive for a few weeks without surgical intervention.
What Is a Norwood Procedure?
Norwood procedure is the most preferred form of surgical intervention for patients diagnosed with a specific condition of inborn defect called hypoplastic left heart syndrome.
Norwood procedure is a highly complex open-heart surgical intervention performed during the neonatal period, particularly within two weeks after birth. It is quite a lengthy procedure that entails extreme caution while performing. It is recognized as the first step in the staged palliation program for babies with HLHS.
The primary aim of the Norwood procedure is to reestablish the circulation in the body, which gets hampered due to stunted growth of the left side of the heart. In the Norwood procedure, the right side of the heart is surgically modified to take up the function of the left side. The anatomical and structural defect in hypoplastic left heart syndrome cannot be rectified, and hence, Norwood's procedure focuses on redirecting the blood flow to ensure circulatory patency. Dr. Norwood first illustrated and successfully demonstrated the procedure in a child patient, and later, it was recognized as the Norwood procedure.
Norwood procedure alone cannot completely fix the defect in HLHS patients. It is often followed by two other surgical techniques: the Glenn and Fontan procedures. These two procedures are performed in specific stages of life to ensure longevity and better survivability.
What Are the Techniques Involved in the Norwood Procedure?
Norwood procedure is an invasive and explorative procedure, which requires hours to complete successfully.
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Anesthesia: The surgery is carried out with the help of general anesthesia (induces sleepiness and makes the child unconscious). The child's blood flow is maintained throughout the surgery with the help of an external machine that bypasses the heart and lungs.
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Chest Incision: Once the child achieves sufficient anesthesia, the surgeon begins the procedure with an incision on the chest to procure access to the heart.
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Creation of Atrial Septal Defect: The upper two heart chambers (right atrium and left atrium) have a muscular wall, technically known as the interatrial septum, separating them. In the Norwood procedure, an opening is purposefully created on the septum, allowing oxygen-rich blood flow from the upper left to the upper right chamber.
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Modifying the Aorta: In the majority of HLHS cases, the valve that guards the entry of blood from the lower left chamber (left ventricle) to the aorta exhibits remarkable constriction and shrinkage, which limit the blood flow to the aorta. In addition, the lower left chamber needs to be better developed and miniature in size, which can accommodate only minimal blood volume. To compensate for this, the pulmonary artery (concerned with the blood flow from the lower right chamber to the lungs) is made to join with the aorta at a specific point. This procedure enhances the aortic blood flow, facilitating systemic circulation to all the body parts.
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Establishing Shunt: As the pulmonary artery is diverted to join with the aorta, an additional shunt pathway must be created to guide the blood to the lungs. Sano shunt and Blalock-Taussig-Thomas shunt are two shunt techniques employed in the Norwood procedure, which guide a part of the blood to flow into the lungs for oxygenation.
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Shutting Down the Patent Ductus Arteriosus: Through the patent ductus arteriosus (fetal blood vessel), the child's body receives blood in the womb stage. Normally, after birth, it will shut down automatically. In HLHS patients, patent ductus arteriosus acts as an alternative source of oxygenated blood flow to the body till the surgical intervention is initiated. Since aortic modification and shunting are made into action, patent ductus arteriosus can be surgically locked, which is done during the Norwood procedure.
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Closure of the Surgical Site: Once all the procedures are done, the right ventricle takes up the functions of both the right and left ventricles, and the surgical site can be secured and closed.
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Post-surgical Monitoring: After the Norwood procedure, the baby must be hospitalized for another three to four weeks to check for immediate complications. It allows thorough monitoring of the infant.
What Are the Complications Associated With the Norwood Procedure?
Norwood procedure is an intricate and complex surgical technique. Hence, it carries the risk of certain complications following the surgery. Some of the potential complications include the following:
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Constriction of the Aorta: The aortic vessel undergoes drastic constriction, restricting the blood flow through it, which can develop post-surgically.
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Arrhythmia: It refers to the unrhythmic beating of the heart. The heart loses its beating rhythm and may beat faster or slower.
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Neurodevelopmental Delay: Cases of neurodevelopmental delays, where the child exhibits a delay in the expected neurological growth as per the age, are also noted with the Norwood procedure.
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Constriction of Pulmonary Artery: The pulmonary artery may sometimes develop constriction in response to the surgical intervention undertaken during the Norwood procedure.
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Shunt Failure: There are chances for the failure of the shunt pathways created in the Norwood procedure.
Conclusion
In the Norwood procedure, the right ventricle is responsible for both the right and left ventricle functions, as the left ventricular function is considerably compromised in hypoplastic left heart syndrome. It offers a better prognosis and survivability for patients reported with this inborn condition. It is reported to have a success rate of 90 percent and extend the person's survivability to even adulthood. It bypasses the need for heart transplantation, a highly demanding and complicated treatment alternative. The parents are instructed to closely monitor the child to check the development of adverse complications. It is reported to be the most preferred and successful treatment initiative for HLHS patients.
