Varying Degrees of Ventricular Unloading in the Heterotopic Rat Heart Transplant Model Demonstrated by Magnetic Resonance Imaging

OBJECTIVE: Left ventricular assist device placement is an increasingly common treatment for cardiac failure, resulting in cardiac unloading and potentially reversing the remodelling changes seen in heart failure. A popular animal model for human ventricular unloading is the rodent heterotopic non-working heart transplant; the volume loading status of this preparation is important to interpreting the resulting reverse remodelling yet has not been previously investigated. This study was designed to assess the variability of left ventricular volume loading in the rodent transplant model. METHODS: Heterotopic abdominal heart transplant was performed on syngeneic rats; high resolution cine magnetic resonance imaging was subsequently performed on the heterotopic transplanted hearts in anesthetised rats, after variable post-transplant recovery times, in order to assess ventricular loading status. RESULTS: Highly variable left ventricular volume loading status was demonstrated, with some hearts exhibiting considerable ventricular filling and ejection. CONCLUSIONS: These observations call into question the assumption that studies using this model are consistently examining fully unloaded ventricles, and indicate the desirability of in vivo imaging of such hearts to quantify the degree of ventricular loading.