Composite outcomes; why to be wary Critical Appraisal Lowdown

From a recent paper from Gottlieb's paper regarding agents for restoration of sinus rhythm and published in the Annals of Emergency Medicine on SVT, why should we be wary of composite outcomes and how should we interpret them?
 
References and relevant resources
http://CriticalAppraisalLowdown.co.uk
http://theresusroom.co.uk/papers-of-january-18