Transthoracic impedance in adult Thoroughbred horses is similar to other species.

Equine TTI is comparable to other species, suggesting it may not limit transthoracic cardioversion success.

This study investigated transthoracic impedance (TTI) in adult Thoroughbred horses using an exponential biphasic defibrillator, examining patient and technique factors that influence TTI measurements. Using a randomized crossover design with two phases, 19 adult Thoroughbred horses were evaluated. Phase 1 examined TTI in deceased horses immediately post-euthanasia across different positions (dorsal vs. lateral recumbency) and with or without manual electrode pressure. Phase 2 measured TTI during different respiratory phases (inspiration vs. expiration) in anesthetized live horses from terminal studies. The median TTI across all horses and conditions was 56 Ω (range 44–133 Ω), which is comparable to values reported in other species such as humans and small animals. Key findings revealed that successive shocks significantly reduced TTI (shock 4 was lower than shocks 1 and 2), and body weight positively influenced TTI by approximately 0.2% per kilogram. Notably, patient position, manual electrode pressure, and respiratory phase did not significantly affect TTI. The terminal study allocation also influenced TTI measurements. Study limitations included convenience sampling and the terminal study design, which may limit generalizability. These findings suggest that TTI in horses is not substantially different from other species, implying that high TTI is likely not the primary barrier to successful transthoracic cardioversion in horses. This has meaningful clinical implications for equine cardiac arrhythmia management, particularly in exploring defibrillation as a viable intervention.

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