Dr Keenan is a Consultant Cardiologist at West Herts Teaching Hospitals NHS Trust and an Honorary Clinical Senior Lecturer at Imperial College, London. At West Herts NHS Trust he is Divisional Director for Medicine. He was previously Clinical Director for Interventional Medicine and Associate Medical Director for Quality and Innovation.

He has been Clinical Lead for the prize winning South and West Herts HCP Virtual Ward. He chairs the NHS England East of England Clinical Advisory Group for Virtual Wards, and sits on the NHS England National Steering Group for Virtual Wards.

He is President-Elect of the British Society of CMR (BSCMR) and led a recent study of the state of CMR in the UK. Since 2020 he has been a member of the Scientific Documents (Guidelines) Committee of the European Association of Cardiovascular Imaging (EACVI).