Key result
In isolated dog hearts, myocardial stunning reduced the instantaneous increase in developed pressure following sudden ventricular dilation compared to control (27 vs 35 mmHg; P=0.002).
Why the study?
Does ischaemia/reperfusion-induced stunning affect homeometric and heterometric autoregulation in isolated dog hearts?
Does ischaemia/reperfusion-induced stunning affect homeometric and heterometric autoregulation in isolated dog hearts?
Absolute Event Rate: 27% vs 35%
p-value: p=0.002
Contractile depression due to stunning proportionally reduces immediate and time-dependent enhancements of contraction evoked by sudden ventricular dilation, but does not affect inotropic stimulation from the Bowditch phenomenon.
Stunning may impair stretch-induced contractility in isolated hearts; leaves open relevance to human post-ischemic autoregulation.
AIM: To study, for the first time, the effects of stunning on homeometric and heterometric autoregulation. METHODS AND RESULTS: Ischaemia (15 min)/reperfusion (30 min) was induced in the isovolumic blood-perfused dog heart preparation. Heart rate elevations (n = 9) from 60 to 200 beats min-1, in steps of 20 beats min-1, promoted the same inotropic stimulation in control (C) and stunning (S), indicating that ischaemia/reperfusion does not affect the changes in calcium kinetics elicited by the Bowditch effect. Sudden ventricular dilation (VD) (n = 10) evoked an instantaneous increase in developed pressure (Delta1DP) followed by a continuous slow performance increase (Delta2DP) in C and S. Delta1DP (C: 35 +/- 2.2 mmHg; S: 27 +/- 2.1 mmHg; P = 0.002) and Delta2DP (C: 20 +/- 1.6 mmHg; S: 14 +/- 1.3 mmHg; P = 0.002) decreased proportionally, while Delta2/Delta1DP (C: 0.57 +/- 0.13; S: 0.58 +/- 0.14) and slow response time course (T/2) were unchanged (C: 55 +/- 6.6 s; S: 57 +/- 7.7 s) after ischaemia/reperfusion. The reduction of Delta1DP can be understood as a decline of the myofilaments calcium responsiveness, the main pathophysiological effect of stunning. The reason for the weakening of Delta2DP, due to intracellular calcium gain, was not determined but it was supposed that its complete manifestation could be restricted by cyclic adenosine monophosphate (cAMP) myocardial content reduction. As reported by others, Delta2DP depends on myocardial cAMP, and it has been shown that myocardial cAMP is decreased after ischaemia/reperfusion. CONCLUSIONS: Contractile depression due to stunning has no effect on the inotropic stimulation generated by the Bowditch phenomenon. Immediate and time-dependent enhancements of contraction evoked by sudden VD are proportionally reduced and the slow response time course is unaffected in the stunned myocardium.
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Tucci et al. (2003) studied Myocardial stunning. Ischaemia/reperfusion (stunning) vs. Control was evaluated on Instantaneous increase in developed pressure (Delta1DP) after sudden ventricular dilation (p=0.002). In isolated dog hearts, myocardial stunning reduced the instantaneous increase in developed pressure following sudden ventricular dilation compared to control (27 vs 35 mmHg; P=0.002).
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