Univentricular Heart Survival: How Morphology Impacts Outcomes
"New research highlights the critical role of ventricular morphology in predicting survival rates for patients with univentricular hearts, offering insights for improved risk stratification and treatment strategies."
Congenital heart defects (CHDs) present a significant challenge in pediatric cardiology, with univentricular hearts (UVH) representing some of the most complex cases. In UVH, one ventricle is underdeveloped, requiring a series of surgical interventions to establish a functional circulation. While advances in surgical techniques and medical management have improved survival rates, long-term outcomes remain a concern. Understanding the factors that influence survival is crucial for optimizing patient care and improving prognosis.
Among the various factors influencing outcomes in UVH, ventricular morphology has emerged as a key area of interest. Specifically, the distinction between single right ventricular morphology (SRV) and single left ventricular morphology (SLV) has garnered attention. SRV involves a dominant right ventricle with a rudimentary left ventricle, while SLV features a dominant left ventricle with a rudimentary right ventricle. The impact of these morphological variations on survival rates has been a subject of ongoing research, with conflicting evidence and a need for clearer understanding.
To address this gap in knowledge, a recent study published in Open Heart sought to investigate the prognostic significance of SRV versus SLV in patients with UVH. By analyzing data from 395 patients who underwent surgery at a single center over several decades, the researchers aimed to determine whether ventricular morphology could serve as a reliable predictor of survival. The findings of this study shed new light on the importance of ventricular morphology in risk stratification and treatment planning for patients with UVH.
Improving Survival, Growing Adult Population
The CDC identifies heart defects as the most common types of birth defects and reports that babies born with these conditions are living longer and healthier lives. Its data show improved survival over time, while also noting that medical care can be costly. Research on univentricular heart (UVH) similarly reports that improved survival has produced a large and growing adult congenital heart disease population, which now numerically exceeds the pediatric population. UVH remains one of the most complex congenital heart defects.
Staged Treatment and Persistent Risk
Children born with a functionally univentricular heart are typically managed with a staged surgical approach intended to culminate in Fontan circulation. A Norwegian retrospective study examined preoperative and postoperative survival among 595 patients with UVH, addressing mortality before surgery as well as outcomes after treatment. Other research reports that advances in surgical techniques and treatment modalities have considerably improved survival. Nevertheless, UVH has the highest mortality among complex congenital heart defects, with substantial mortality both around initial treatment and during long-term follow-up.
From First Descriptions to Modern Classification
Chemineau described the first univentricular heart in 1699, an event that prompted longstanding debate about embryology and nomenclature. A later historical report identifies Thore's 1842 description in Paris as the first case of a single ventricle and common atrium, followed by a second case in Nantes in 1887. The American Heart Association notes that inconsistent nomenclature and classification have complicated population estimates. One New England registry reported an incidence of 54 cases per million live births, although more recent estimates are substantially higher.
SRV vs. SLV: Unveiling the Survival Disparity in Univentricular Hearts
The study, conducted at Oslo University Hospital, prospectively included 395 patients with UVH who underwent surgical intervention between 1972 and 2016. The patient cohort comprised 195 individuals with SRV, 166 with SLV, and 34 with mixed or indeterminate ventricular morphology. Data collected included diagnoses, UVH morphology, types of operations performed, and the timing and causes of death or heart transplantation (HTX). The primary endpoint of the study was death or HTX.
- Increased Mortality in SRV Patients: The study revealed a significant disparity in survival rates between patients with SRV and SLV. Among the 111 non-Fontan patients, 88 deaths occurred, with a disproportionately higher number in the SRV group (62 vs. 20 in the SLV group, p<0.0001). Heart failure was identified as a major contributor to mortality, with 23 deaths attributed to heart failure in the SRV group compared to only 5 in the SLV group (p=0.0012).
- Impact of Fontan Procedure: Among the 284 patients who underwent the Fontan procedure, 25-year cumulative survival rates were significantly higher in the SLV group (87.9%) compared to the SRV group (66.9%, p=0.0027). This difference was partly attributed to a higher incidence of death or HTX due to heart failure among patients with SRV (p=0.0006).
- SRV as a Strong Predictor: Multivariable proportional hazards analyses confirmed that SRV was a strong predictor of death or HTX, with a hazard ratio of 3.3 (95% CI 1.6 to 6.6). This finding underscores the independent association between ventricular morphology and adverse outcomes in patients with UVH.
Morphology and Fontan Outcomes
Recent Fontan research continues to examine whether dominant ventricular morphology affects outcomes. One study reported a median follow-up of 16 years after the Fontan operation; at that point, 3 patients (6%) were in NYHA classes III or IV, 4 (8%) underwent Fontan conversion, 2 (4%) were listed for heart transplantation, and 2 (4%) died. Research comparing right and left single-ventricle morphology notes that some patients have a systemic morphological left ventricle while others have a systemic morphological right ventricle. Although right-ventricle morphology has been hypothesized to produce worse outcomes, the evidence remains mixed, while other reviews report higher rates of death or transplantation for heart failure among patients with a systemic right ventricle.
Early Evidence Behind the Systemic Right-Ventricle Concern
Concern about systemic right-ventricle morphology is not based only on recent speculation. A 2008 editorial predicted increased long-term mortality from heart failure in patients with a systemic right ventricle. That prediction was based on a retrospective study of 261 Fontan patients treated in Boston between 1973 and 1991. The finding illustrates why earlier evidence has continued to influence debate about morphology-related risk, even as later research has produced mixed results.
Surgical Separation Versus Natural History
Univentricular heart is a rare congenital cardiac malformation, and prognosis without surgical intervention is considered poor, with survival into late adulthood described as unusual. When feasible, the goal during childhood is to separate systemic and pulmonary circulation through a total cavopulmonary connection. The American Heart Association defines univentricular heart broadly as congenital cardiac malformations in which both atria connect entirely or almost entirely to one functionally single ventricular chamber. Long-term results after Fontan-type operations remain an important part of comparison because surgical circulation changes survival but does not eliminate later risks.
Translating Findings into Clinical Practice: A Call for Personalized Care
This study provides compelling evidence that ventricular morphology plays a critical role in determining survival outcomes for patients with UVH. The identification of SRV as a strong predictor of mortality and heart failure underscores the need for incorporating ventricular morphology into risk stratification algorithms and treatment strategies. Clinicians should consider ventricular morphology during the initial evaluation of patients with UVH and tailor their management plans accordingly.
Tracking Survival Into Adulthood
A Swedish study aims to determine long-term survival in patients with UVH, including those who were not operated on, compared with a control population. It identified patients with UVH born between 1970 and 2017 through national registers and matched them by birth year and sex with 10 individuals without congenital heart disease. The growing number of patients reaching adulthood is also highlighted in a 2024 review of univentricular heart in adults. Together, these studies point toward continued emphasis on adult outcomes and long-term follow-up.
Progress With Continuing Mortality
Substantial advances in surgical techniques and other treatment modalities have improved survival for patients with univentricular hearts. However, UVH accounts for about 20% of patients with complex heart defects and has the highest mortality among them. Mortality remains high both around initial treatment and during long-term follow-up. The condition is also described as a rare and complex congenital heart defect, while improved pediatric survival is creating a larger population of adults who require ongoing care.