CONTRIBUTION OF ASYNCHRONY AND NONUNIFORMITY TO MECHANICAL INTERACTION IN NORMAL AND STUNNED MYOCARDIUM

In anesthetized pigs, we investigated whether asynchrony (Delta T) and nonuniformity (regional differences) in contractility (Delta E) could describe the interaction between normal and stunned myocardium. Mecha nical interaction was evaluated by regional postsystolic work (PSW) be fore and after production of stunning by a 5-min occlusion of the left circumflex coronary artery [LCX (LCX stunning)] and a subsequent 10-m in occlusion of the left anterior descending coronary artery [LAD (LAD stunning)]. Delta T and Delta E were intensified by intracoronary (LA D) infusions of dobutamine. From regional end-systolic pressure-segmen t length relationships, systolic segment shortening (SS), end-systolic elastance (E), external work (EW), and PSW were determined. LCX stunn ing decreased SSLCX from 14 +/- 2 (mean +/- SE, n = 9) to 10 +/- 2% an d E-LCX from 103 +/- 25 to 52 +/- 7 mmHg/mm, whereas the LAD region wa s unaffected. EWLCX decreased from 165 +/- 16 to 138 +/- 20 mmHg.mm, w hereas PSWLCX increased from -4 +/- 6 to 8 +/- 3 mmHg.mm. Additional L AD 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, PSWLAD, increased and PSWLCX decreased, but, during local LAD dobutamine infusions after stunning, both PSWLCX and PSWLAD increased. In normal myocardium, the changes in PSWLCX could be descr ibed by Delta T (65 +/- 11%) and Delta E (37 +/- 15%). After stunning of the LAD area, the contribution of Delta E increased to 55 +/- 14% a t the expense of Delta T (37 +/- 15%). Similar contributions of Delta E (54 +/- 13%) and Delta T (57 +/- 13%) were found when both the LCX a nd LAD distribution areas were stunned. In normal myocardium, both Del ta T and Delta E modulate mechanical interaction, with the contributio n of Delta T exceeding that of Delta E. In stunned myocardium, both fa ctors contribute, but the contribution shifts in favor of Delta E.