Let's twist

Extract

In the 16th century, Leonardo DaVinci already described the rotational motion of the left ventricle (LV) ^{1 , 2} and in 1669, Richard Lower observed that myocardial contraction could be compared with ‘the wringing of a linen cloth to squeeze out the water’. ³ Three centuries later, the use of radiopaque markers in cineradiographic studies made it possible to measure this wringing motion in the human heart, as was shown by Ian McDonald and Neil Ingels. ^{4 , 5} The mechanistic basis for this wringing motion or twist lies in the complex spiral architecture of the LV as revealed by the anatomical studies of Streeter et al.⁶ and Greenbaum et al.⁷ The LV consists of obliquely oriented muscle fiber(s) that vary from a small-radius, right-handed helix at the subendocardium to a larger-radius, left-handed helix at the subepicardium. The functional result of this three-dimensional helical structure is a cyclic systolic twisting and diastolic untwisting of the LV apex relative to the base. LV twist plays a pivotal role in the mechanical efficiency of the heart, making it possible that only 15% fiber(s) shortening results in a 60% reduction in LV volume, ⁸ and untwist plays a crucial role in diastolic suction. ⁹ Studies on LV twist may yield new or additional information about cardiac (patho-)physiology, beyond the traditional measurements of radial and longitudinal function.