Relating myocardial laminar architecture to shear strain and muscle fiber orientation

Cardiac myofibers are organized into laminar sheets about four cells thick. Recently, it has been suggested that these layers coincide with the plane of maximum shear during systole. In general, there are two such planes, whi ch are oriented at +/-45 degrees to the main principal strain axes. These p lanes do not necessarily contain the fiber axis. In the present study, we e xplicitly added the constraint that the sheet planes should also contain th e muscle fiber axis. In a mathematical analysis of previously measured thre e-dimensional transmural systolic strain distributions in six dogs, we comp uted the planes of maximum shear, adding the latter constraint by using the also-measured muscle fiber axis. Generally, for such planes two solutions were found, suggesting that two populations of sheet orientation may exist. The angles at which the predicted sheets intersected transmural tissue sli ces, cut along left ventricular short- or long-axis planes, were strikingly similar to experimentally measured values. In conclusion, sheets coincide with planes of maximum systolic shear subject to the constraint that the mu scle fiber axis is contained in this plane. Sheet orientation is not a uniq ue function of the transmural location but occurs in two distinct populatio ns.