Double inlet left ventricle (DILV) with double outlet right ventricle (DORV) and ventricular septal defect (VSD)

Double inlet left ventricle (DILV) is a form of functionally univentricular heart where both the left and the right atrium are connected to the morphologically left ventricle. Usually, the morphologically right ventricle is hypoplastic. The anatomic heterogeneity in the group of DILV hearts is characterized by the position of the ventricles to each other and the relationship of the great arteries to each other as well as to the ventricles [1].

The Fontan procedure is the palliative surgical procedure used in children with functionally univentricular hearts. Modification of the procedure over the years as well as improved perioperative care has led to an improvement of early survival of Fontan patients [2]. However, so far it was not possible to achieve significant improvement of long-term results of the Fontan procedure and median survival stagnates around 30 years after cavopulmonary connection [3,4]. In addition, the mode of decline and death of Fontan patients is dismal: ventricular failure, hepatic cirrhosis,carcinoma and protein losing enteropathy being the leading causes of death [5]. Survival free of such events at 25 years is only 29% [6]. Thus, both life expectancy and quality of life remain compromised in Fontan patients.

In contrast to Fontan results, a small, selected subset of DILV patients have been reported to live beyond their 4^th decade without Fontan circulation [7–9]. The inter-individual arterial oxygen saturation and therefore the clinical features amongst DILV patients vary widely due to the numerous anatomical differences and the consequent presence or absence of pulmonary and/or systemic obstruction as well as the differences in systemic and pulmonary vascular resistance. It has been suggested that unpalliated patients depend on a favorable streaming mechanism with unobstructed systemic outflow and moderate to severe pulmonary stenosis in order to live with good functional capacity and relatively few symptoms [10]. Little is known about other factors that make hearts of natural survivors superior to those of Fontan patients regarding function and survival.

Considering the aforementioned data on long-term survival of patients palliated with the Fontan procedure, we are convinced that it is highly relevant to determine further the factors that allow a small selection of patients without cavopulmonary connection to live to a comparatively high age without apparent major complaints.

In this study a series of post mortem specimens without cavopulmonary connection was investigated. The aim was to gain better understanding of the variable anatomical features of DILV hearts that would potentially facilitate favorable streaming, as it has never been done before. The fact that streamline flows as those entering into the ventricle do not have an intrinsic tendency to mix unless forced to by turbulence, is one of the basic principles of fluid dynamics, and serves as a basic paradigm for this study [11]. The focus was on anatomical characteristics that include the arrangements of the inflow and outflow tracts, the position and sizes of the great arteries, and the size and shape of the ventricular septal defect that could influence the flow and separation of deoxygenated and oxygenated blood in DILV hearts.