Temporal Association Between Intrathoracic Impedance and Tachyarrhythmia Occurrence

This study examined whether daily intrathoracic impedance is temporally associated with the occurrence of atrial fibrillation (AF) and ventricular tachycardia (VT).

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.

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.

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.