Inclusion Criteria:  signed informed consent form effective and stable HB or LBB pacing sinus rhythm during the intervention procedure  Exclusion Criteria:  contraindications to invasive EPS contraindications to general anesthesia contraindications to atropine administration (e.g., glaucoma) persistent atrial fibrillation or atrial flutter pregnancy diseases that may cause autonomic system neuropathy use of medications that may affect the parasympathetic system a history of cardiac surgery a history of ablation due to arrhythmia