Correlation relationships of homeostasis indicators in dogs with myxomatous mitral valve degeneration

Myxomatous mitral valve disease (MMVD) in dogs is accompanied by electrolyte disturbances, oxidative stress, and low-grade systemic inflammation, which may affect cardiac geometry and electrophysiology. This study presents a secondary analysis of prospectively collected data from our previous work to evaluate correlations between homeostatic markers and cardiovascular parameters in dogs with MMVD. We compared a control cohort (healthy dogs, n = 6) with two cohorts of ACVIM stage C patients: standard therapy (ST, n = 6) and standard therapy plus humic substances (STH, n = 6). We assessed clinical–laboratory, electrocardiographic, and echocardiographic indices on days 1 and 21. In controls, we identified physiological associations between catalase activity and heart rate (HR; r = 0.93; p = 0.008) and between P-wave duration and catalase (r = 0.82; p = 0.046). In ST, HR showed no significant associations with antioxidants; however, QRS duration correlated inversely with catalase on day 1 (r = −0.93; p = 0.008), while R-wave amplitude correlated positively with superoxide dismutase (r = 0.84; p = 0.036) and later with malondialdehyde (r = 0.99; p = 0.002). In STH on day 1, we observed HR–catalase (r = 0.83; p = 0.042) and P-wave amplitude–total antioxidant capacity (TAC; r = 0.94; p = 0.005) correlations, which disappeared by day 21; the QT interval showed a biphasic association with catalase (r = −0.84; p = 0.036 on day 1; r = 0.82; p = 0.046 on day 21). Under diuretic therapy in STH, serum chloride correlated positively with P-wave duration (r = 0.84; p = 0.038), underscoring the role of electrolyte balance in atrioventricular conduction. In the pooled sample on day 1, HR correlated moderately with malondialdehyde (r = 0.51) but this association faded over time; inorganic phosphorus was associated with left-ventricular dilatation in ST at study end (r = 0.94; p = 0.021) and lost this dependence in STH. Collectively, these findings indicate that humic substances generate short-lived yet notable “antioxidant–ECG” correlations and may attenuate pathological links driven by electrolyte imbalance and oxidative stress.