Patients with univentricular hearts are currently palliated with the Fontan procedures. This results in an unphysiologic circulation with poor long-term survival. On the other hand there is a small, selected subgroup of patients with univentricular hearts of the double inlet left ventricle (DILV) type that survives up to old age without ever having undergone any Fontan procedures. Considering the relatively bleak data on long-term survival of DILV patients palliated with the Fontan procedure, it seems highly relevant to investigate and determine factors that allow a selection of unoperated patients to live to a comparatively high age without apparent major complaints. This might have an impact on how (and if, at all) certain univentricular patients are selected for operation in the future. For some, a different surgical procedure, or even therapeutic nihilism might be a more viable alternative.

The investigators hypothesise that favourable intracardiac streaming plays a role in making these patients viable: certain intracardiac anatomical characteristics allow for favourable flow patterns.

The primary objective of this study is to describe the intracardiac anatomy and hemodynamics of DILV patients without Fontan circulation using 4D MRI. Furthermore, the functional status and quality of life of these patients will be assessed.

Rationale: Patients with univentricular hearts are currently palliated with a sequence of operations known as the Fontan procedure. This results in an un-physiologic circulation with poor long-term survival. On the other hand there is a small, selected subgroup of patients with univentricular hearts of the double inlet left ventricle (DILV) type that survives up to old age without ever having undergone any Fontan procedure. Considering the relatively bleak data on long-term survival of DILV patients palliated with the Fontan procedure, it is highly relevant to investigate and determine factors that allow for a selection of unoperated patients to live to a comparatively high age without apparent major complaints. This might have an impact on how (and if, at all) certain univentricular patients will be selected for operation in the future. For some, a different surgical procedure, or even therapeutic nihilism might be a more viable alternative. The investigators hypothesize that favourable intracardiac streaming plays a role in making the unpalliated patients viable: certain intracardiac anatomical characteristics allow for favourable flow patterns, resulting in higher systemic oxygen saturations than expected by mixing pulmonary and systemic venous returns.

Objective: The primary objective of this study is to describe the intracardiac anatomy and hemodynamics of DILV patients without Fontan circulation using 4D MRI. Furthermore, the functional status and quality of life of these patients will be assessed and compared to a matched cohort of Fontan patients.

Study design: This will be an observational, cross-sectional study. The investigators aim to include all DILV patients without Fontan circulation known at the congenital heart disease referral centers in the Netherlands and Flanders. The Dutch patients will undergo one 4D MRI, a physical examination, cardiopulmonary exercise testing and have a blood sample taken at the University Medical Center Utrecht. The patients from the Flemish referral centers will undergo the same protocol at the University Medical Center Leuven. Furthermore, patients over the age of 18 will be asked to fill out a quality of life questionnaire.

Study population: Included will be patients over the age of 12 with the diagnosis double inlet left ventricle, which have not undergone the Fontan trajectory. For the 4D MRI, patients with an MRI non-compatible pacemaker in situ will be excluded.

Main study parameters/endpoints: This is primarily an explorative study aiming to describe the anatomy of unpalliated DILV hearts of patients without Fontan palliation. With 4D MRI, the hearts will be grouped according to the angular relationship of the two lines connecting the atrioventricular and the ventriculo-arterial valves. This angle can be divided into three categories: 1) parallel (i.e. 0°), 2) perpendicular (i.e. 90°) or 3) an in-between variant. Accordingly, flow patterns, ranging from linear to turbulent will be measured and correlated to the anatomical variants.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The burden and risks associated with participation in this study are minimal. Patients need to visit the site of investigation only once, and the tests done at the visit (i.e. 4D MR imaging, exercise and pulmonary function testing and blood sample) are part of standard medical care and as such pose negligible risk on the patients. The quality of life survey is not part of standard medical care and might be confrontational on a psychological level. It is, however, a widely used and scientifically approved survey, which aims to keep this burden very low. Due to the extremely low prevalence of the condition to be studied, it is of great importance to include every single patient, including children under the age of 18. Excluding children from this study would further decrease the sample size to a significantly smaller number, making it difficult to draw conclusions.

Inclusion Criteria:

• Diagnosis double inlet left ventricle, established by echocardiograph or MRI
• Not undergone Fontan trajectory in the past
• Be of the age of 12 or older
• Written informed consent

Exclusion Criteria:

• previous (partial) cavopulmonary connection

The following subjects will be excluded from the MRI part of the study, but will still be asked to participate in all the other parts:

• MRI non-compatible pacemaker in situ

Included will be patients over the age of 12 with the diagnosis double inlet left ventricle, which have not undergone the Fontan trajectory. For the 4D MRI, patients with an MRI non-compatible pacemaker in situ will be excluded.