Contribution of asynchrony and nonuniformity to mechanical interaction in normal and stunned myocardium

Abstract

In anesthetized pigs, we investigated whether asynchrony (Δ T) and nonuniformity (regional differences) in contractility (Δ E) could describe the interaction between normal and stunned myocardium. Mechanical interaction was evaluated by regional postsystolic work (PSW) before and after production of stunning by a 5-min occlusion of the left circumflex coronary artery [LCX (LCX stunning)] and a subsequent 10-min occlusion of the left anterior descending coronary artery [LAD (LAD stunning)]. Δ T and Δ E were intensified by intracoronary (LAD) infusions of dobutamine. From regional end-systolic pressure-segment length relationships, systolic segment shortening (SS), end-systolic elastance ( E), external work (EW), and PSW were determined. LCX stunning decreased SSLCX from 14 ± 2 (mean ± SE, n = 9) to 10 ± 2% and E LCX from 103 ± 25 to 52 ± 7 mmHg/mm, whereas the LAD region was unaffected. EWLCX decreased from 165 ± 16 to 138 ± 20 mmHg ⋅ mm, whereas PSWLCX increased from −4 ± 6 to 8 ± 3 mmHg ⋅ mm. Additional LAD stunning reduced SSLAD from 16 ± 2 to 9 ± 3% and E LAD from 79 ± 10 to 31 ± 6 mmHg/mm, without affecting SSLCX and E LCX. In the normal myocardium, PSWLADincreased and PSWLCX decreased, but, during local LAD dobutamine infusions after stunning, both PSWLCX and PSWLAD increased. In normal myocardium, the changes in PSWLCXcould be described by Δ T (65 ± 11%) and Δ E(37 ± 15%). After stunning of the LAD area, the contribution of Δ E increased to 55 ± 14% at the expense of Δ T (37 ± 15%). Similar contributions of Δ E (54 ± 13%) and Δ T (57 ± 13%) were found when both the LCX and LAD distribution areas were stunned. In normal myocardium, both Δ T and Δ E modulate mechanical interaction, with the contribution of Δ Texceeding that of Δ E. In stunned myocardium, both factors contribute, but the contribution shifts in favor of Δ E.