Longitudinal echocardiographic systolic changes in dogs receiving doxorubicin-based chemotherapy

Doxorubicin is widely used in veterinary oncology but carries a risk of cumulative cardiotoxicity. Serial echocardiographic evaluation is commonly used to monitor dogs receiving potentially cardiotoxic chemotherapy; however, evidence remains limited regarding which indices best capture early longitudinal systolic changes. Conventional monitoring relies largely on fractional shortening and M-mode estimated ejection fraction, which are based on geometric assumptions and may have limited sensitivity for subtle systolic change. This study evaluated whether Simpson-derived left ventricular ejection fraction better captures longitudinal echocardiographic systolic changes than conventional indices in dogs receiving doxorubicin-based chemotherapy. Twenty-nine client-owned dogs were prospectively enrolled, including 23 females and 6 males, with a median age of 10.0 years (IQR, 7.0–11.0) and median body weight of 13.2 kg (IQR, 7.0–21.6). Twelve dogs received doxorubicin as monotherapy and 17 received combination protocols. Echocardiography was performed before the first cycle (D0) and after three consecutive cycles (D1, D2, D3). Simpson-derived left ventricular ejection fraction (LVEF) showed a progressive numerical decline from 72.0 ± 7.3% at baseline to 66.5 ± 7.7% at D3; however, no individual time-point estimate reached statistical significance in the mixed-effects model (D1, p = 0.183; D2, p = 0.618; D3, p = 0.206). M-mode estimated LVEF and fractional shortening did not show comparable directional patterns or significant longitudinal changes. A decline greater than 10% points in Simpson-derived LVEF was identified in 9 of 29 dogs (31.0%), all while absolute values remained within conventional reference limits. Six of these dogs were not identified by either conventional index. Serial, baseline-referenced Simpson-derived LVEF identified more longitudinal echocardiographic systolic changes than conventional indices in this cohort. These findings suggest that Simpson-derived LVEF may provide complementary information for tracking baseline-referenced systolic changes in dogs receiving doxorubicin. However, these changes should not be interpreted as definitive evidence of myocardial injury, and their clinical relevance requires confirmation in larger prospective studies.