Interpretation of myocardial contraction recorded from local segments

An attempt to quantify the influence of extra-segmental contraction upon external mechanical work of a segment was made in cat hearts. By placing four ultrasound crystals across a borderline between normal and ischaemic myocardium, the pressure-length loop area of segments with different ischaemic contents were recorded. The relation between a normalised segment work index and the amount of ischaemic tissue within the segment showed a negative correlation. Assuming that the contributions to the segment work index from ischaemic and normal tissue coupled in series within the segment add up by cancelling each other, the extra-segmental influence of adjacent fibre contraction could be established. In six cats the extra-segmental influence which affected a typical segment of 10.0 mm corresponded to 1.5 to 3.7 mm of adjacent myocardial musculature on either side of the segment.