Evaluation of cardiac dysfunction in adult zebrafish using high frequency echocardiography

Aims: Recently, the zebrafish has gained attention as an innovative experimental model to decipher molecular and cellular mechanisms involved in cardiovascular development and diseases. Nevertheless, the use of zebrafish models has been challenged because the transparency of these fish, which allows for accurate cardiac evaluation, disappears in adulthood. In this study, the epicardial outline method was performed to investigate the feasibility of echocardiography in assessing cardiac function in pathological adult zebrafish. Materials and methods: We attempted to estimate heart failure in adult zebrafish treated with three distinct regulators of cardiac function: phenylhydrazine hydrochloride (PHZ), doxorubicin (DOX), and ethanol. B-mode and Doppler images were evaluated at frequencies of up to 50 MHz and 40 MHz, respectively. The correlation between alterations in cardiac function, haemoglobin concentration, and myocardial histopathology were assessed. Key findings: Cardiac output (CO) in PHZ-treated zebrafish was significantly higher than that in control zebrafish (151 +/- 67 vs. 84 +/- 37 mu l/min, P = 0.004), whereas ejection fraction (EF) was lower (36.3 +/- 10.9 vs. 50.9 +/- 8.7%, P < 0.001), indicating typical high output heart failure derived from anaemia. Additionally, ventricular dysfunction in DOX-treated zebrafish was characterised by low CO (57 +/- 38 mu l/min) and EF (28.8 +/- 10.4%), accompanied by an enlarged ventricle in diastole and systole, representing low output heart failure. For ethanol-treated zebrafish, EF was markedly reduced (39.6 +/- 7.2%) indicating a dilated heart, while CO remained unchanged (90 +/- 40 mu l/min). Significance: The epicardial outline method is an effective way of using echocardiography to assess cardiac dysfunction in pathological adult zebrafish, unlocking a major bottleneck in this research field with limited cardiac functional assays.