- The carvedilol hibernation reversible ischaemia trial, marker of success (CHRISTMAS) study. Methodology of a randomised, placebo controlled, multicentre study of carvedilol in hibernation and heart failure. Pennell, D.J., Ray, S.G., Davies, G., Burgess, M., Webster, J., Slomka, P., Atkinson, P., Cleland, J.G. International journal of cardiology. (2000)