Fibre orientation in the left ventricle and its influence on local pressure—length loop analysis in cats

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Abstract
Summary. Deviation from local fibre orientation may seriously affect quantification of myocardial segment work, as measured by implanted ultrasound crystals. Crystal pairs were positioned in mid‐wall layers with known directions to the long axis of the heart. One transmitter and four receiving crystals covered a sector on the anterior ventricular wall of 100°. The results show a strong influence of alignment to fibre direction on the pressure‐length loop area; the relation followed a cos2ψ function where ψ denotes the angle between the crystal pair direction and fibre direction established by microscopy. The angle between the mid‐wall muscle fibres on the anterior aspect of the left ventricle and the long axis of the heart varied between 62° and 90° with a mean value of 76°. This study shows that pressure‐length loop quantitation depends strongly on crystal alignment to cardiac muscle fibres through which the ultrasound passes.