Determining the impact of 24/7 phone support on hospital readmissions after aortic valve replacement surgery (the AVRre study): study protocol for a randomised controlled trial oleh Irene Lie, Stein Ove Danielsen, Theis Tønnessen, Svein Solheim, Marit Leegaard, Leiv Sandvik, Torbjørn Wisløff, Jonny Vangen, Tor Henning Røsstad, Philip Moons