Functional mechanisms of myocardial microcirculation in left ventricular hypertrophy: a hypothetical model of capillary remodeling post myocardial infarction.

OBJECTIVES

Left ventricular (LV) remodeling after myocardial infarction (MI) is characterized by myocyte hypertrophy and a disproportional capillary growth. We developed a hypothetical model of capillary remodeling mechanisms based on quantitative data of microcirculation determined by magnetic resonance (MR) imaging techniques and histology.

METHODS

Perfusion and regional capillary blood volume (RBV) were quantified 8 and 16 weeks after MI (mean 27.0+/-2.9% of the left ventricle 16 weeks post MI) or sham operation in rats using MR imaging and were correlated with morphometric data.

RESULTS

Maximum perfusion (ml/(g min)) in the remote area decreased from 5.69+/-0.63 to 3.48+/-0.48 compared to sham animals (5.33+/-0.31, p</=0.01) and showed a close inverse relation to hypertrophy. In contrast, maximum RBV in the remote area was similar to that of sham animals (16.79+/-0.42% and 16.52+/-0.33%, respectively) and did not change over time. Thus, mean transit time (MTT) was longer in remote than in sham myocardium. Morphology revealed that hypertrophy was inversely related to capillary density which was associated with an increase in capillary cross-sections.

CONCLUSIONS

Perfusion data in synopsis with histological observations demonstrate that the functional capillary length increases during hypertrophy post MI which is consistent with the increase of the mean transit time. Despite a relative decrease in capillary density, RBV may be restored by an increase in the cross-sections. In the light of almost maximum oxygen extraction under normal conditions, this hypertrophy related remodeling may be deleterious for tissue supply.