The effect of a myocardial infarction on the normalized time-varying elastance curve

Abstract

It has been suggested that the shape of the normalized time-varying elastance curve [En( tn)] is conserved in different cardiac pathologies. We hypothesize, however, that the En( tn) differs quantitatively after myocardial infarction (MI). Sprague-Dawley rats ( n = 9) were anesthetized, and the left anterior descending coronary artery was ligated to provoke the MI. A sham-operated control group (CTRL) ( n = 10) was treated without the MI. Two months later, a conductance catheter was inserted into the left ventricle (LV). The LV pressure and volume were measured and the En( tn) derived. Slopes of En( tn) during the preejection period (αPEP), ejection period (αEP), and their ratio (β = αEP/αPEP) were calculated, together with the characteristic decay time during isovolumic relaxation (τ) and the normalized elastance at end diastole (Eminn). MI provoked significant LV chamber dilatation, thus a loss in cardiac output (−33%), ejection fraction (−40%), and stroke volume (−30%) ( P < 0.05). Also, it caused significant calcium increase (17-fold), fibrosis (2-fold), and LV hypertrophy. End-systolic elastance dropped from 0.66 ± 0.31 mmHg/μl (CTRL) to 0.34 ± 0.11 mmHg/μl (MI) ( P < 0.05). Normalized elastance was significantly reduced in the MI group during the preejection, ejection, and diastolic periods ( P < 0.05). The slope of En( tn) during the αPEPand β were significantly altered after MI ( P < 0.05). Furthermore, τ and end-diastolic Eminnwere both significantly augmented in the MI group. We conclude that the En( tn) differs quantitatively in all phases of the heart cycle, between normal and hearts post-MI. This should be considered when utilizing the single-beat concept.