Introduction: For heart transplantation, optimal size matching is desirable, especially for infants. Both undersizing and oversizing may jeopardize the outcome of the procedure. Due to organ shortage, the size match is often suboptimal in human allotransplantation. In xenotransplantation, donors may be specifically selected for a perfect size match. For our own experiments, we usually estimate organ weight by either donor age or total body weight. Here, we investigate if preoperative transthoracic echocardiography (TTE) may be used to estimate organ size as compared to standard parameters such as total body weight (TBW) and donor age. 

Methods: Juvenile genetically modified pigs (GGTA1KO, hCD46, hTHBD) of cross-bred genetic background (German Landrace and Large White, 10-25kg TBW) serving as donors for pig-to-baboon cardiac xenotransplantation experiments were examined by TTE. The pigs were either sedated (n=10) or accustomed to tolerating the procedure during breeding (n=5). Left ventricular (LV) wall thickness and LV diameters were measured to calculate LV mass. TBW, age and LV mass were correlated with the actual donor heart weight. 

Results: In all sedated and 4 of 5 hand-tamed animals TTE loops could be acquired for measurements. In the non-sedated pigs, the examination was more demanding; in 1 animal the image quality was too poor for analysis, mostly due to movement artifacts and insufficient coupling. Preliminary analyses indicate that the heart weights at explantation correlate significantly with donor age, TBW, and LV mass estimated by TTE, with LV mass showing the strongest correlation (Pearson r=0.84, 0.88, and 0.95, respectively; p<0.001).

Conclusions: Whereas age and TBW of pigs are good predictors of actual heart size, TTE has the potential to estimate the organ weight with even more accuracy. As TTE should be performed routinely prior to xenotransplantation to evaluate cardiac function and assess possible congenital heart failures, the LV mass is easy to obtain. TTE examination can be performed in non-sedated animals after habituation, but for high quality imaging intensive medical training or sedation is preferable. For clinical trials size matching by age and TBW may be sufficient for adults, but heart transplantation of infants will benefit from higher accuracy provided by TTE.