Ventricular wall stress mapping proves the dualistic organization of the myocardial structure

Needle force probes have been developed for the direct assessment of stress in any measuring site in the free wall of the left ventricle. In 12 untrained dogs and 7 dogs 6–18 weeks after aortic banding forces were mapped in up to 20 sites and 7–12 layers from the epicardium to the endocardium. In the untrained hearts subepi- and subendocardial forces were almost identical with a minimum in the middle layers. Left ventricular hypertrophy induced a definite increase in local force development. Highest forces were measured subendocardially with an almost monotonous drop towards the epicardium. In the subendocardium, furthermore, there was a high incidence (30%) of tracings which showed an increment in force during systolic ventricular emptying. These unexpected results are partially explained by a subendocaridal accumulation of myocardial fibres which follow an oblique transmural fibre path instead of being strictly surface parallel orientated.