1. Institute of Clinical Medicine; University of Oslo; Oslo Norway
2. Division of Paediatric and Adolescent Medicine; Oslo University Hospital; Oslo Norway
3. Department of Paediatric Cardiology; Skåne University Hospital; Lund Sweden
4. Division of Paediatric Cardiology; University Hospital of Iceland; Reykjavik Iceland
5. Institute of Clinical Sciences; Gothenburg University; Gothenburg Sweden
6. Division of Tertiary Pediatrics; Helsinki University Hospital; Helsinki Finland