1. Department of Allergy and Clinical Immunology, Guy’s and St Thomas’ NHS Foundation Trust , London SE1 9RT, UK
2. Department of Cardiology, Karolinska University Hospital and Karolinska Institute , Stockholm 171 77, Sweden
3. Imperial Syncope Unit, Imperial College Healthcare NHS Trust , London W12 0HS, UK
4. National Heart and Lung Institute, Imperial College London , London SW3 6LY, UK
5. Cutrale Perioperative and Ageing Group, Department of Bioengineering, Imperial College London , London W12 0BZ, UK