Inhomogeneities in wall stress measured by microergometry in the heart muscle in situ.

Microergometry is a method which we have developed as a tool to measure local mesh-tension within the myocardial weave at any measuring site of both ventricles and the septum on the beating heart in situ. In a mapping procedure on pig and dog hearts, both in control conditions and in the hypertrophied state after aortic banding, local mesh-tension was measured in several areas and in up to eight depths proceeding from the epicardium to the endocardium: Probe-to-fibre coupling is definitely more stable in the canine myocardium than in the porcine heart muscle, probably due to a more effective connective tissue fettering of the canine myocardial weave. The observed longitudinal gradient, with the highest tension in the base, of control dog hearts was levelled out in the hypertrophied hearts. Furthermore, in control dog hearts mesh-tension in the subepi- and subendocardial layers was higher than in the midlayers. This pronounced midlayerhypotension was smoothed in the hypertrophied hearts. Further studies will be dedicated to the question of whether the impact of ventricular size and shape on intersegmental stress transmission is determined by the Frank-Starling mechanism alone or whether protracted remodelling processes on the level of the local fibre weave cause slow coupling alterations.