Choi YH, Cowan DB, Wahlers TCW, Hetzer R, Del Nido PJ, Stamm C. Calcium sensitisation impairs diastolic relaxation in post-ischaemic myocardium: implications for the use of Ca(2+) sensitising inotropes after cardiac surgery.
Eur J Cardiothorac Surg 2009;
37:376-83. [PMID:
19616444 DOI:
10.1016/j.ejcts.2009.05.030]
[Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2008] [Revised: 04/30/2009] [Accepted: 05/18/2009] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND
Calcium sensitising inotropes are increasingly being used in cardiac surgical patients. Theoretically, increasing contractile protein sensitivity to Ca(2+) prevents the Ca(2+) elevation associated arrhythmogenicity and potentiates the inotropic effect of catecholamines. On the other hand, we hypothesised that Ca(2+) sensitisation exacerbates post-ischaemic myocardial stunning by impairing diastolic relaxation, which might have deleterious effects in postoperative cardiac surgical patients.
METHODS
In an isolated rabbit heart model, 45 min normothermic ischaemia with potassium-induced cardioplegic arrest was followed by 120 min reperfusion. Isovolumetric left ventricular (LV) function and myocardial oxygen consumption (MvO(2)) were measured, and cytosolic Ca(2+) was monitored by rhod-2 surface spectrofluorometry. During reperfusion, ORG 30029 (250 microM) and levosimendan (0.5 microM) were used as Ca(2+) sensitisers (ORG, n=6, Levo, n=6), Ca(2+) de-sensitisation was induced with butanedione-monoxime (5mM, BDM, n=6), and dopamine (20 nM) served as a representative catecholamine (n=6). To counteract the PDE III inhibiting properties of ORG and Levo, IGF-1 (0.1 microM) and parathyroid hormone (0.05 microM) were used.
RESULTS
As expected, ischaemia/reperfusion induced moderate cytosolic calcium overload. Dopamine increased LV contractility and MvO(2) by augmenting the amplitude of the Ca(2+) transient, but relaxation was unchanged due to faster diastolic Ca(2+) removal. Dopamine-induced Ca(2+) handling was unchanged after uncoupling the Mg-ATPase with BDM, and MvO2 decreased in proportion with the reduced LV mechanical work load. ORG improved contractility without apparent effects on Ca(2+) handling, and MvO(2) remained constant despite increased contractile work. Conversely, ORG induced a rightward shift of the diastolic pressure-volume relationship in post-ischaemic hearts (diastolic pressure at 0.8 ml balloon volume 14.3+/-5 mmHg, p=0.01 vs control), but not in non-ischaemic control hearts. With levosimendan, the Ca(2+) sensitising effects were less pronounced (7.6+/-3 mmHg, p=0.4 vs control). By counteracting the PDE inhibiting effects of ORG and Levo using parathyroid hormone and IGF-1, the negative lusotropic effects of Ca(2+) sensitisation were unmasked.
CONCLUSIONS
Calcium sensitisation improves systolic function and energetic efficiency. However, Ca(2+) sensitisers should be used with caution during post-ischaemic reperfusion, as they may exacerbate myocardial stunning and thus impair cardiac output.
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