What is the cause of hypotension in Hypoplastic Left Heart Syndrome (HLHS)?

From the Guidelines

Hypotension in hypoplastic left heart syndrome (HLHS) is primarily caused by the underdeveloped left side of the heart, which cannot effectively pump blood to the body, and the resulting dependence on the right ventricle and patent ductus arteriosus (PDA) for systemic circulation. In HLHS, the left ventricle, aorta, mitral valve, and aortic valve are severely underdeveloped, making the right ventricle responsible for pumping blood to both the lungs and the body. This creates a situation where systemic circulation depends on blood flowing through the PDA from the pulmonary artery to the aorta. When the PDA begins to close after birth, systemic blood flow decreases dramatically, leading to hypotension, as noted in guidelines from the American Heart Association and American Thoracic Society 1.

The mixing of oxygenated and deoxygenated blood in the right heart chambers results in lower oxygen content in the blood supplying the body, further compromising tissue perfusion. Pulmonary vascular changes resulting from left atrial hypertension contribute adversely to the presentation and outcome of patients with HLHS, as severe flow restriction or intact atrial septum in HLHS is associated with profound cyanosis, pulmonary artery hypoplasia, lymphangiectasis, and high mortality despite aggressive therapy 1. Management typically includes prostaglandin E1 infusion to maintain ductal patency, careful fluid management, inotropic support with medications, and balancing the pulmonary and systemic circulations by maintaining appropriate oxygen levels and sometimes using pulmonary vasodilators or vasoconstrictors as needed.

Key considerations in managing hypotension in HLHS include:

• Maintaining ductal patency with prostaglandin E1 infusion
• Careful fluid management to optimize cardiac output
• Inotropic support to enhance right ventricular function
• Balancing pulmonary and systemic circulations to ensure adequate oxygenation and perfusion of vital organs
• Surgical intervention to palliate the condition and improve long-term outcomes, with an adequate atrial septostomy (AS) being extremely important to permit adequate oxygenation and subsequent progression to cavopulmonary anastomosis, as highlighted in the guidelines 1.

From the Research

Hypotension in Hypoplastic Left Heart Syndrome

• Hypoplastic left heart syndrome (HLHS) is a complex congenital heart disease that requires multiple cardiac surgeries for survival 2.
• The management of HLHS has changed substantially over the past four decades, with the advent of the Norwood procedure improving the prognosis for these children 3.
• However, morbidity and mortality are still substantial, and careful multidisciplinary involvement in the care of these complex patients is necessary to improve their outcome 2.
• Hypotension in HLHS patients may be related to the use of certain inotropic agents, such as dobutamine, which can increase the ratio of pulmonary to systemic flow (Qp/Qs) and decrease oxygen delivery 4.
• On the other hand, epinephrine has been shown to decrease the Qp/Qs ratio and increase oxygen delivery, making it a potentially more beneficial inotropic agent in the clinical setting 4.
• The use of milrinone in the pre-operative setting has been shown to be well tolerated and associated with decreased lactate levels, but not significant hypotension or worsening of excess pulmonary blood flow 5.

Hemodynamic Aspects

• The hemodynamic aspects of various surgical stages in HLHS are crucial to understand in order to manage common pediatric problems such as dehydration and respiratory infections 2.
• The Norwood procedure and other palliative surgeries can support survival beyond the neonatal period and into early adulthood, but require careful management of hemodynamic parameters 3.
• Emerging studies have identified potential mechanisms for the disease onset, including genetic and hemodynamic causes, and current therapies are being tested clinically to improve cardiac function in patients who have undergone palliative surgeries 6.

Inotropic Agents

• Different inotropic agents may have different effects on the Qp/Qs ratio and oxygen delivery, and may not be equally effective at increasing oxygen delivery 4.
• Dopamine, dobutamine, and epinephrine all increase cardiac output, but have substantially different effects on the Qp/Qs ratio and oxygen delivery 4.
• Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery 4.