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Acute pulmonary microembolism induces different regional changes in preload and contraction pattern in canine right
B Zwissler1, H Forst, K Messmer
1Department of Experimental Surgery, University of Heidelberg, West Germany.
Study Objective:
The aim of the study was to investigate the influence of acute pulmonary embolism on local myocardial preload and contraction pattern in right ventricle.
Design:
Measurements of preload and contraction pattern were made in inflow and outflow tracts of canine right ventricular free wall by sonomicrometry. Local right ventricular preload was assessed from end diastolic segment length. Contraction pattern was assessed from pressure-length loops and quantified by calculating maximal, systolic, and postsystolic shortening, and protosystolic segment elongation. Data were obtained before and after microembolization with 100 microns glass beads in combination with oleic acid.
Subjects:
13 foxhounds of either sex were used, weight 20.4 +/- 4.0 kg.
Measurements And Main Results:
Pulmonary microembolization resulted in a rise in systolic, mean, and end diastolic right ventricular pressure and pulmonary vascular resistance. At the same time, the pressure-length loops, originally triangular or oval, became rectangular in both inflow and outflow tract. Normalised end diastolic segment length increased in the inflow tract from 10.0 to 10.3 mm (p less than 0.01), but simultaneously decreased in the outflow tract, from 10.0 to 9.6 mm (p less than 0.05). Segment shortening in the inflow tract was not affected but deteriorated in the outflow tract from 11.6 to 2.7% (p less than 0.01).
Conclusions:
Increase in afterload due to pulmonary microembolization caused regionally different changes in local preload and segment shortening in right ventricular free wall. Clinically available measures of global right ventricular preload do not assess these local differences in preload and therefore may fail to reflect the functional state of the right ventricle accurately.