1. Keele Cardiovascular Research Group, School of Medicine, Keele University, Staffordshire, United Kingdom.
2. Academic Unit of Obstetrics and Gynaecology, University Hospital of North Midlands, Stoke-on-Trent, United Kingdom.
3. The Heart Centre, University Hospital of North Midlands, Stoke-on-Trent, United Kingdom.
4. Division of Cardiology, University of Arizona, Phoenix, Arizona, USA.