Assessment of the Pulmonary-to-Systemic-Flow Ratio in Patients with Hypoplastic Left Heart Syndrome in Pre-Stage 2

Abstract

Hypoplastic left heart syndrome (HLHS) is a rare congenital heart disease that affects normal blood flow through the heart with high mortality if not treated (70% in the first week and 91% within 30 days; Morris et al., 1990). The aortic valve, aortic arch, mitral valve, and left ventricle are severely underdeveloped (Figure 1). In this condition, the right ventricle is the systemic ventricle and must pump blood to the lungs and the rest of the body through a persistent ductus arteriosus (PDA). Norwood palliation (NW) was considered the first palliation stage for patients with hypoplastic heart left syndrome (HLHS). The operation is usually performed in the first few weeks of the life. The goals of first-stage palliation are: <br /> • Unobstructed systemic blood flow to the aorta and coronary arteries; <br /> • A controlled source of pulmonary blood flow; and <br /> • Unobstructed egress of pulmonary venous return <br /> In NW, the neo-aorta is constructed by side-to-side anastomosis of the hypoplastic ascending aorta and the main pulmonary artery, a modified Blalock-Taussig shunt (MBTS) is created between the right subclavian artery and the pulmonary arteries to supply the pulmonary blood flow, and an atrioseptectomy is performed (Figure 2). A Sano shunt, a conduit created between the systemic right ventricle and the pulmonary artery, could be an alternative to the MBTS. <br /> The second palliative operation (stage 2) is called a hemi-Fontan or Glenn operation, which usually occurs within six months of birth and in which the superior vena cava (SVC) is disconnected from the right atrium and connected to the pulmonary arteries (Pas), allowing the deoxygenated blood to flow from the upper part of the body directly to the PA without passing through the heart (Figures 3 and 4). The third palliative stage is the Fontan operation (stage 3), which occurs approximately at 1.5–3 years of age. During this surgery, the inferior vena cava (IVC) is disconnected from the RA and connected to the PAs through a conduit with or without fenestration, allowing the deoxygenated blood from the lower part of the body to flow into the PAs without passing through the heart (Figures 3 and 4). <br /> In a Norwood operation, maintaining the balance between the systemic and pulmonary blood flow (Qp:Qs) postoperatively is challenging, with increased mortality and morbidity (up to 50%; John et al., 2020). An excess of one compromises the other. Increased Qp (Qp > Qs) leads to pulmonary overcirculation and heart failure, with symptoms like dyspnea, tachycardia, and sweating, and saturation increases to more than 85%. At the same time, the limited Qs leads to systemic hypoperfusion, a potential cause of coronary ischemia, mesenteric ischemia, necrotizing enterocolitis (NEC), renal insufficiency, and cerebral hypoxemia. <br /> Increased Qs (Qs > Qp) leads to pulmonary undercirculation and excessive cyanosis due to the desaturated blood in the systemic circulation, which could lead to respiratory failure, cerebral hypoxia, coronary ischemia, heart failure, and even death. Few studies have been conducted to estimate the optimal value of the Qp:Qs intraoperatively and postoperatively in which the patients are hemodynamically stable without signs of generalized tissue hypoperfusion, like an increase in lactate or decrease in blood PH, and with satisfactory saturation (Charpie et al., 2007; Malec et al., 2003; Photiadis et al., 2005, 2006; Primeaux et al., 2021; Rychik et al., 2000; Strauss et al., 2001). <br /> Other studies compared the MBTS with the Sano shunt postoperatively and in pre-stage 2 (PS2; Edward et al., 2007; Mair et al., 2003). The results showed that the Qp:Qs in patients with an MBTS was higher than in those with a Sano shunt. The same observation of the end-diastolic pressure of the right ventricle was documented. No study has been conducted to date, however, investigating the range of the Qp:Qs in patients in PS II who received routine catheter examination before the Fontan operation (total cavo-pulmonary connection) or in those who received an emergency examination due to clinical deterioration. <br /> This study aims to evaluate the range of the Qp:Qs in PS2, in which the patients are hemodynamically stable with adequate saturation and mild anticongestive therapy. In addition, the study tries to find any relationship between the Qp:Qs and the outcome in this cohort and evaluate whether the Qp:Qs could predict the outcome in the patients in PS2. The composite primary outcome was freedom from the following: death, the need for reoperation, referral to palliative care, or the need for heart transplantation. The secondary outcome was freedom from reintervention in MBTS or pulmonary arteries.