From the Guidelines
Hypoplastic left heart syndrome (HLHS) causes metabolic acidosis due to inadequate systemic perfusion and tissue oxygenation, leading to lactic acid production and accumulation in the bloodstream. In HLHS, the left side of the heart is severely underdeveloped, including the left ventricle, aorta, mitral valve, and aortic valve, as noted in the guidelines from the American Heart Association and American Thoracic Society 1. This structural defect prevents the heart from effectively pumping oxygenated blood to the body. When the ductus arteriosus closes after birth, systemic blood flow becomes critically reduced, leading to poor tissue perfusion. As tissues receive insufficient oxygen, cells switch to anaerobic metabolism, producing lactic acid as a byproduct, which is a common cause of metabolic acidosis, as described in the BTS guideline for oxygen use in adults 1. The accumulation of lactic acid in the bloodstream leads to metabolic acidosis. Additionally, poor renal perfusion impairs the kidneys' ability to excrete acid, further worsening the acidosis. This process creates a dangerous cycle where acidosis weakens cardiac contractility, further reducing cardiac output and worsening tissue perfusion.
Some key points to consider in the management of HLHS include:
- Maintaining ductal patency with prostaglandin E1 to improve systemic blood flow
- Mechanical ventilation to improve oxygenation and reduce the workload on the heart
- Correction of acidosis with sodium bicarbonate to mitigate the effects of lactic acid accumulation
- Preparation for surgical intervention to repair or replace the defective heart structures, as the guidelines suggest that adequate atrial septostomy is crucial for adequate oxygenation and subsequent progression to cavopulmonary anastomosis 1.
It is essential to prioritize the management of metabolic acidosis in HLHS, as it can have significant implications for morbidity, mortality, and quality of life, and early recognition and treatment of metabolic acidosis are critical to improving outcomes in patients with HLHS.
From the Research
Metabolic Acidosis in Hypoplastic Left Heart Syndrome
- Metabolic acidosis in hypoplastic left heart syndrome (HLHS) is a result of decreased systemic perfusion, which occurs as the arterial duct closes 2, 3.
- This decrease in systemic perfusion leads to hypoxemia, acidosis, and shock 2.
- The underdevelopment of the left ventricle, aorta, and aortic arch, as well as mitral atresia or stenosis, contributes to the obstruction of blood flow from the left ventricular outflow tract, further exacerbating the condition 2.
- Elevated lactate levels are also a common finding in patients with HLHS, indicating impaired tissue perfusion and increased anaerobic metabolism 4.
- The use of milrinone in the pre-operative setting has been shown to decrease lactate levels and improve outcomes in patients with HLHS 4.
Pathophysiology of HLHS
- HLHS is characterized by the abnormal development of the left-sided cardiac structures, resulting in obstruction to blood flow from the left ventricular outflow tract 2, 5.
- The syndrome includes underdevelopment of the left ventricle, aorta, and aortic arch, as well as mitral atresia or stenosis 2.
- The etiology of HLHS is multifactorial, involving a complicated course of genetic and signaling cascades 6.
Clinical Implications
- HLHS is a lethal congenital heart disease if left untreated, but with current surgical interventions, survival rates have improved significantly over the past 30 years 5.
- Prenatal diagnosis, good newborn care, improved surgical skills, specialized postoperative care, and unique strategies for interstage monitoring have all contributed to increasing the likelihood of survival 5.
- Ongoing research is focused on elucidating the signaling and molecular mechanisms driving HLHS pathogenesis, with the goal of developing novel therapeutic regimens 6.