The influence of afterload on uniformity of segment shortening in feline left ventricles. Importance of cross-fibre contraction.
Previous studies have shown that the combined increase of preload and afterload leads to a more uniform wall contraction. As our previous information with a stable afterloaded situation showed considerable increase of left ventricular end-diastolic pressure, we have as yet no information of how afterload per se effects uniformity of segment shortening. We therefore analysed maximal systolic shortening of cross-oriented segments for three consecutive beats during abrupt elevation of afterload in 12 open-chest cats. Peak left ventricular systolic pressure increased during the three beats from 154 +/- 5 mmHg (mean +/- SEM) to 167 +/- 5 mmHg and 186 +/- 5 mmHg. Left ventricular end-diastolic pressure remained unchanged. Maximal systolic shortening was reduced for both segments with increasing afterload, in longitudinal segment (LONG) from 7.6 +/- 1.1 to 6.1 +/- 1.0% (P < 0.005), and more pronounced for circumferential segments (CIRC) from 12.2 +/- 0.7 to 8.3 +/- 0.9% (P < 0.0005). Uniformity of maximal systolic shortening, LONG/CIRC, increased from 0.63 +/- 0.08 in the first beat to 0.73 +/- 0.10 and 0.82 +/- 0.12 in the following beats (P < 0.02). We conclude that uniformity of contraction for cross-oriented segments in the anterior left ventricular wall is increased during increased afterload. We propose that this can be explained by reduction of the effect of cross-fibre contraction with increasing afterload.
Hexeberg
E
E
Department of Surgery, Haukeland Hospital, University of Bergen, Norway.
Birkeland
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S
D000704:Analysis of Variance; D000818:Animals; D002415:Cats; D003971:Diastole; D006321:Heart / Q000502:physiology*; D009200:Myocardial Contraction; D013599:Systole; D016277:Ventricular Function, Left