2.3. Outcomes
The primary outcome was SSS. SSS was defined from any discharge diagnoses or two outpatients visits (ICD-10 codes for SSS and tachybradycardia syndrome [I495]). The secondary outcomes were pacemaker implantation or atrioventricular (AV) block. AV block was defined from any discharge diagnoses or two outpatient visits [I441 (Second-degree AV block, Mobitz type Ⅰ and Ⅱ), I442 (Complete AV block), I443 (AV block NOS), I453 (Trifascicular block), I458 (AV dissociation), I459 (Stokes-Adams syndrome, Heart block NOS)] (eTable 1 in the Supplement). To evaluate the accuracy of the outcome definitions, we conducted a validation study using hospital administrative data from two hospitals. The positive predictive values were found to be 91.1% (307/337) and 95.7% (264/276) for SSS and AV block, respectively.