Temporal Association Between Intrathoracic Impedance and Tachyarrhythmia Occurrence

BACKGROUND: This study examined whether daily intrathoracic impedance is temporally associated with the occurrence of atrial fibrillation (AF) and ventricular tachycardia (VT). METHODS: This retrospective cohort study included 117 patients with cardiac implantable devices, followed for a median of 668 days, corresponding to 89 637 person-days. Recurrent AF occurred in 28% of patients (mean AF burden 0.27), while 773 VT episodes occurred in 15% of patients. Daily intrathoracic impedance, expressed relative to a reference impedance, was analyzed to identify events of impedance decrease and increase. The temporal association between impedance events and tachyarrhythmia burden was quantified using a patient-specific relational strength measure (γ), which compares post-event and pre-event tachyarrhythmia burden. RESULTS: For impedance decreases, event-related γ for AF was higher than control γ computed for randomly placed events (median 0.68 vs. 0.48, p = 0.04). For VT, event-related γ did not differ significantly from control γ (six patients; median 0.52 vs. 0.21, p = 0.82). No significant differences were observed for impedance increases in either the AF or VT analysis. In the pooled episode-level analysis, an impedance decrease was associated with a shorter time to VT occurrence than an impedance increase (median 4 vs. 7 days, p < 0.001), with 48% of VT episodes occurring within 3 days after an impedance decrease. CONCLUSION: A decrease in intrathoracic impedance is temporally associated with subsequent AF occurrence and, at the episode level, with a shorter time to VT. These findings suggest that daily intrathoracic impedance may provide information on short-term changes preceding tachyarrhythmia occurrence.