Polar organization of collagen in human cardiac tissue revealed with polarimetric second-harmonic generation microscopy.

Polarimetric second-harmonic generation (P-SHG) microscopy is used to characterize the composition and polarity of collagen fibers in various regions of human cardiac tissue. The boundary between the cardiac conduction system and myocardium is shown to possess a distinct composition of collagen compared to other regions in the heart. Moreover, collagen fibers in this region are macroscopically organized in a unipolar arrangement, which may consequently aid in effective propagation of the electrical signal through the cardiac conduction system.