Sinus function tests: Sinoatrial conduction time (by Narula method), the sinus node recovery time (SNRT) and the corrected sinus node recovery time (CSNRT)). For the SNRT, it is stimulated to several cycle lengths for one min, with decreases of 100 ms up to 430 ms, and the longest pause is considered as the recovery time; if greater than 1500 ms is considered abnormal.