[1] Univ Cambridge, Addenbrookes Hosp, Div Cardiovasc Med, Cambridge CB2 0QQ, England
[2] Univ Cambridge, Addenbrookes Hosp, Dept Radiol, Cambridge CB2 0QQ, England
[3] Univ Sheffield, Dept Cardiovasc Sci, Western Bank, Sheffield S10 2TN, S Yorkshire, England
[4] Emory Univ, Dept Med, 100 Woodruff Circle, Atlanta, GA 30322 USA