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Mechanical deformation of isolated rabbit hearts through passive inflation techniques have been a viable form of
replicating heart motion, but its relation to the heart's natural active contractions remain unclear. The mechanical
properties of the myocardium may show diverse characteristics while in tension and compression. In this study, epicardial
strain was measured with the assistance of computer-aided speckle interferometry (CASI)1. CASI tracks the movement of
clusters of particles for measuring epicardial deformation. The heart was cannulated and perfused with Tyrode's solution.
Silicon carbide particles were applied onto the myocardium to form random speckle pattern images while the heart was
allowed to actively contract and stabilize. High resolution videos (1000x1000 pixels) of the left ventricle were taken with
a complementary metal oxide semiconductor (CMOS) camera as the heart was actively contracting through electrical
pacing at various cycle lengths between 250-800 ms. A latex balloon was then inserted into the left ventricle via left atrium
and videos were taken as the balloon was repeatedly inflated and deflated at controlled volumes (1-3 ml/cycle). The videos
were broken down into frames and analyzed through CASI. Active contractions resulted in non-uniform circular epicardial
and uniaxial contractions at different stages of the motion. In contrast, the passive heart demonstrated very uniform
expansion and contraction originating from the source of the latex balloon. The motion of the active heart caused variations
in deformation, but in comparison to the passive heart, had a more enigmatic displacement field. The active heart
demonstrated areas of large displacement and others with relatively no displacement. Application of CASI was able to
successfully distinguish the motions between the active and passive hearts.
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