**5. Conclusion**

Several reasons may explain this finding. First, subepicardial left ventricular twist may reflect the positive effects of cardiac resynchronization therapy better than subendocardial left ventricular twist, because the subepicardial layer is the major determinant of left ventricular twist. Second, left ventricular pacing in cardiac resynchronization therapy is applied from the epicardial surface, which may be more closely related to mechanical changes in the subepi‐

Sun et al. [68] subjected 7 pigs to myocardial infarction by occlusion of the left anterior descending coronary artery. After 8 weeks, left ventricular twist was decreased significantly in the left anterior descending coronary artery territory areas, whereas there was no change in twist in adjacent and remote left ventricular areas. Therefore, the authors proposed that left ventricular twist may be suitable for noninvasive quantification of left ventricular regional function in ischemic heart disease. Kroeker et al. [69], using an optical device coupled to the left ventricular apex in 16 open-chest dogs, also found a decrease of left ventricular apical rotation with ischemia caused by occlusion of the left anterior descending coronary artery. Interestingly, in the first 10 seconds of occlusion, there was a paradoxical increase in left ventricular apical rotation, which was attributed to isolated subendocardial ischemia leading

In clinical studies in patients with a prior anterior myocardial infarction it was found that, although left ventricular basal rotation was preserved, left ventricular apical rotation was decreased, leading to decreased left ventricular twist [70]. In patients with a left ventricular aneurysm, left ventricular apical rotation was nonexistent or even inverted, leading to severely

In the majority of left ventricular twist studies in congenital heart disease, investigators focused on patients with a congenital transposition of the great arteries. In patients operated with atrial switch, the systemic right ventricle shows absence of twist, whereas the subpulmonary left ventricle shows reduced twist [71,72]. Furthermore, there are regional differences of apical rotation of the subpulmonary left ventricular, whereas apical rotation is homogeneous in a normal left ventricle [73,74]. In a theoretical model of situs inversus totalis, and in 8 patients with this condition [75,76] it was shown that, although gross anatomy is mirror imaged, this is not the case for left ventricular systolic deformation. Both the left ventricular base and apex rotated in a counterclockwise direction, whereas the midventricular section exhibited hardly any rotation. These findings may be explained by the arrangement of myofibres in these patients. Anatomical studies have revealed that in situs inversus totalis arrangement of myofibres is normal in the apical regions leading to normal counterclockwise rotation, whereas at the basal level a partly mirror-imaged pattern of the normal transmural change in fibre angle

to loss of the counteractive action of the subendocardial helix of myofibres.

cardial than the subendocardial left ventricular layer.

**4.5. Ischemic heart disease**

38 Cardiomyopathies

decreased left ventricular twist.

**4.6. Congenital heart disease**

is seen.

Even though left ventricular twist is indispensable for proper left ventricular function, little is known about it in "the cardiology community". Mainly due to the development of speckle tracking echocardiography, allowing accurate, reproducible and rapid bedside assessment of left ventricular twist, interest in this important mechanical aspect of left ventricular deforma‐ tion has been rapidly increasing.

Although the vital physiological role of left ventricular twist is indisputable, the clinical relevance of assessment of left ventricular twist in cardiomyopathies still needs to be con‐ firmed. Nonetheless, left ventricular twist evaluation has already provided significant pathophysiological insight in a broad variety of cardiomyopathies. It has become clear that increased left ventricular twist in for example HCM, AS, and diabetics, but also in a healthy ageing population, may serve as a compensatory mechanism to preserve ejection fraction. Furthermore, demonstration of left ventricular rigid body rotation in NCCM may provide a unique way to objectively confirm this difficult diagnosis. Diastolic left ventricular untwisting represents the elastic recoil caused by the release of restoring forces that have been generated during the preceding systolic left ventricular twist and has an important contribution in left ventricular filling through suction generation. Measurement of left ventricular untwisting may become an important element of diastolic function evaluation in cardiomyopathies in the future.
