Low-dose inotropic stimulation during left ventricular ischaemia does not worsen post-ischaemic dysfunction

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Abstract
Inotropic agents are used clinically to improve ventricular function during ischaemia. The goal of this study was to determine whether inotropic stimulation during moderate left ventricular (LV) ischaemia exacerbates post-ischaemic LV dysfunction. Methods: In 18 open-chest, anesthetized pigs, LV pressure versus subendocardial segment length loops were used to generate regional preload-recruitable stroke work (PRSW) and LV end-diastolic pressure (EDP) versus end-diastolic segment length (EDL) relations. Ischaemia was produced by constant, partial constriction of the mid anterior descending coronary artery for 90 min. Nine pigs received dobutamine (4 μg·kg−1·min−1, i.v.) during the final 60 min of ischaemia (Group 2), while 9 other pigs did not (Group 1). Results: During unstimulated ischaemia, anterior subendocardial blood flow (Group 1, 0.27 ± .05; Group 2, 0.30 ± .07 ml·g−1·min−1, mean ± s.e.m.) and steady-state PRSW (Group 1, 30 ± 4%; Group 2, 27 ± 5% of baseline) were similar in both groups. Dobutamine stimulation during ischaemia increased heart rate, mean arterial pressure, subendocardial blood flow, oxygen consumption and steady-state PRSW of the ischaemic zone, but not lactate release. After 60 min reperfusion, steady-state ischaemic zone PRSW remained markedly and nearly equally reduced in both groups (Group 1, 28 ± 4%; Group 2, 23 ± 5% of baseline). Reduced PRSW after reperfusion was due primarily to persistent rightward shift of the PRSW intercept with only a modest contribution from reduced PRSW slope. Conclusions: Low-dose inotropic stimulation during moderate regional LV ischaemia increases aerobic, but not anaerobic energy metabolism, and does not worsen post-ischaemic dysfunction.

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