Intravascular ultrasound and ultrasonic flow ratio-guided zero-contrast percutaneous coronary intervention: first report of a novel technique treating a patient with obstructive coronary artery disease and contrast allergy

aDepartment of Cardiology, Fu Wai Hospital, National Center for Cardiovascular Diseases bCatheterization Laboratories, Fu Wai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, National Clinical Research Center for Cardiovascular Diseases, Beijing, China Received 3 February 2021 Accepted 9 May 2021 Correspondence to Lei Song, MD, Department of Cardiology, Fu Wai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China. No. 167 North Lishi Road, Xicheng District, Beijing, China, Tel: +86 10 88322415; e-mail: [email protected]