Data and Cohort Identification
For this analysis, Medicare claims (inpatient, outpatient, and carrier) and enrollment data were used to identify Medicare fee-for-service (FFS) beneficiaries implanted with a leadless VVI or transvenous VVI pacemaker from March 9, 2017 (the first date of Medicare coverage for leadless VVI pacemakers) through December 31, 2018. Pacemaker implants were identified using the International Classification of Diseases, 10th Revision, Procedure Coding System (ICD-10) and the Current Procedural Terminology (CPT) codes for inpatient and outpatient implants respectively (Appendix Table 1 ). The index date for outcomes ascertainment was defined as the date of each patient’s first observed pacemaker implant procedure during the study period. Patients with evidence of a prior cardiovascular implantable electronic device (CIED) were excluded to facilitate comparison ofde novo pacemaker implants and to reduce the risk of misattribution of outcomes related to a prior device. Patients with less than 12 months of continuous enrollment in FFS Medicare were excluded to ensure that patient baseline clinical and demographic characteristics could be adequately captured. Among the patients implanted with a transvenous VVI pacemaker, the cohort was limited to patients implanted in facilities with evidence of leadless implants over the same time period, to increase the likelihood that patients in the study cohort would have had access to and a chance to receive either system. SeeAppendix Figure 1 for the study cohort diagram.