Response to Letters Regarding Article, "Clinical Usefulness, Angiographic Characteristics, and Safety Evaluation of Intracoronary Acetylcholine Provocation Testing Among 921 Consecutive White Patients With Unobstructed Coronary Arteries". Issue 4 (27th January 2015) - Ong, Peter; Athanasiadis, Anastasios; Borgulya, Gabor; Vokshi, Ismail; Bastiaenen, Rachel; Kubik, Sebastian; Hill, Stephan; Schäufele, Tim; Mahrholdt, Heiko; Kaski, Juan Carlos; Sechtem, Udo