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.