Background: Data on patients in emerging countries at high risk of sudden cardiac death (SCD) are lacking. The Improve SCA registry is the first prospective, global registry to evaluate this population.Methods: Patients who met guideline recommendations for implantable cardioverter-defibrillator (ICD) implantation were enrolled in 17 countries and regions in regions underrepresented in previous trials. Countries were stratified by WHO regional classification and income level based on the World Bank classification system. Primary outcomes were all-cause mortality and SCD.Findings: We enrolled 4,222 patients and 3,889 patients were included in the analysis. The mean follow-up period was 21·6±10·2 months. There were 433 (11·1%) instances of all-cause mortality and 117 (3·0%) SCD. All-cause mortality was highest in primary prevention (PP) patients from Southeast Asia (Southeast Asia/Europe, HR=3·18, 95%CI: 1·14-8·91, P=0·0275), while it was highest in secondary prevention (SP) patients from the Middle East and Africa (MEA) (MEA/Europe, HR=5·1, 95%CI 1·13-23·0, P=0·0341). The SCD rate of PP and SP patients was highest in South Asia. All-cause mortality in PP patients from upper middle income (UMI) countries was higher than high income (HI) (HR=1·38, 95% CI: 1·04-1·84, p=0·0276) and lower middle income countries (LMI) (HR=1·563, 95% CI: 1·18-2·08, p=0·0021). SCD rates of PP and SP patients of LMI countries were higher than UMI and HI (p<0·0001).Interpretation: There was significant heterogeneity among high SCD risk patients in emerging countries. Influences of both geography and income level on patient outcomes were significant. These findings emphasize the need to increase ICD/CRT-D utilization in emerging countries.Trial Registration: ClinicalTrials.gov identifier: NCT02099721Funding: This study was funded by Medtronic Inc.Declaration of Interest: S. Zhao declare no conflicts of interest. S. Zhang: speakers bureau/consulting fees: Boston Scientific, Medtronic, St. Jude Medical, Biotronik, steering committee fees: Medtronic; CK Ching: speaker fees/steering committee fees: Medtronic; D. Huang: speaker/consultant fees: Boston Scientific, St. Jude Medical; YB Liu: speaker fees/steering committee fees, Medtronic; DA. Rodriguez: proctor/lecture fees: Boston Scientific, proctorship: Biosense Webster, St. Jude Medical/Abbott, steering committee fees: Medtronic; Azlan Hussin: speaker fees/steering committee fees, Medtronic; YH. Kim: steering committee fees: Medtronic; AR. Chasnoits: steering committee fees: Medtronic; J. Cerkvenik: Employment: Medtronic; D. Lexcen: Employment: Medtronic; K. Muckala: Employment: Medtronic; M. Brown: Employment: Medtronic; A. Cheng: Employment: Medtronic; XH Zhou: Employment: Medtronic; B. Singh: steering committee fees: MedtronicEthical Approval: The protocol was approved by the ethics committee at each participating institution and associated national and local regulatory agencies. All patients provided writteninformed consent before undergoing study procedures.