Echocardiographic imaging in conscious, unsedated sheep: a novel approach enabling apical views for advanced cardiac assessment

Accurate echocardiographic assessment in large-animal models is essential for translational cardiovascular research. In sheep, imaging has been limited by the inability to obtain diagnostic apical views, restricting analyses to parasternal measures. This study aimed to develop a reproducible echocardiographic protocol for conscious sheep. Female Welsh Mountain sheep underwent transthoracic echocardiography using a systematic approach to probe orientation and positioning. Using a modified left-lateral thoracic approach, apical views were consistently obtained in conscious, unsedated animals, enabling comprehensive evaluation. Baseline values were established before animals underwent rapid ventricular pacing to induce heart failure with weekly assessments. The protocol enabled comprehensive imaging of chamber dimensions, systolic and diastolic function, and tissue Doppler indices. Baseline values were reproducible across animals. During tachypacing, left-ventricular ejection fraction declined from 66 ± 3% to 31 ± 3% (<i>P</i> < 0.001). Left ventricular (LV) systolic performance declined most rapidly within the first ∼60% of pacing duration, identifying a critical window for therapeutic intervention. Left atrial area increased from 9.8 ± 1.6 cm² to 16.9 ± 2.3 cm² (<i>P</i> < 0.001), consistent with global systolic impairment and elevated filling pressures. Right ventricular dilatation and dysfunction paralleled LV changes, mirroring the biventricular phenotype of human dilated cardiomyopathy. This study establishes the first reproducible echocardiographic protocol for comprehensive cardiac phenotyping in conscious sheep. By defining normative values and characterizing temporal biventricular and atrial remodeling in a tachypacing model, it enhances the translational fidelity of ovine heart failure studies and provides a robust platform for testing therapeutic strategies.<b>NEW & NOTEWORTHY</b> We establish the first protocol for high-fidelity echocardiography in conscious sheep, overcoming the long-standing barrier of apical view acquisition. This enables advanced indices, including volumetric ejection fraction and tissue Doppler, and provides reproducible reference values. Applied to a tachypacing model, it revealed progressive biventricular and atrial remodeling and an early therapeutic window, offering a powerful and clinically relevant platform for translational heart failure research.