Comparison of dog and pig models for testing substernal cardiac compression devices

Subtle anatomic differences between species can be a critical consideration when determining whether a given animal model is appropriate for surgical research purposes, especially when testing biomechanical implants. This study compares the effectiveness of two common animal models (dogs and pigs) in testing a balloon based cardiac compression device designed for substernal placement. Pigs were used in acute studies using an infarction model of heart failure, whereas dogs were used in chronic experiments in which heart failure was induced via rapid pacing. Systolic cardiac compression was accomplished in both species using identical balloons inflated between the sternum and right ventricle with every heartbeat. Results showed the device to be much more effective in pigs, where cardiac stroke volumes returned to normal with balloon assistance (14.7 +/- 1.9 to 37.8 +/- 9.2 mL, p < 0.005). Stroke volumes in dogs, however, remained essentially unaltered by balloon activation (28.1 +/- 14.1 to 29.6 +/- 14.7 mL, p = NS). Retrospective comparisons showed pig models to be a much closer approximation to the human anatomy because of a more similar thoracic cavity shape and heart orientation. These findings suggest that certain large animal models should not be used in research in which chest wall shape or cardiac orientation within the thoracic cavity may influence outcomes.