Effect of Ischemia Duration and Protective Interventions on the Temporal Dynamics of Tissue Composition After Myocardial Infarction
Rationale: The impact of cardioprotective strategies and ischemia duration on post ischemia/reperfusion (I/R) myocardial tissue composition (edema, myocardium at risk [MaR], infarct size [IS], salvage, intramyocardial hemorrhage [IMH] and microvascular obstruction [MVO]) is not well understood.
Objective: To study the effect of ischemia duration and protective interventions on the temporal dynamics of myocardial tissue composition in a translational animal model of I/R by the use of state-of-the-art imaging technology.
Methods and Results: Four 5-pig groups underwent different I/R protocols: 40-min-I/R (prolonged ischemia, controls), 20-min-I/R (short-duration ischemia), prolonged ischemia preceded by preconditioning, or prolonged ischemia followed by postconditioning. Serial cardiac magnetic resonance (CMR)-based tissue characterization was done in all pigs at baseline, and at 120-min, day1, day4, and day7 after I/R. Reference MaR was assessed by multidetector computed tomography during the index coronary occlusion. After the final CMR, hearts were excised and processed for water content quantification and histology. Five additional healthy pigs were sacrificed after baseline CMR as reference. Edema formation followed a bimodal pattern in all 40-min I/R pigs, regardless of cardioprotective strategy and the degree of IMH or MVO. The hyperacute edematous wave was ameliorated only in pigs showing cardioprotection (i.e. those undergoing short-duration ischemia or preconditioning). In all groups, CMR-measured edema was barely detectable at 24 hours post-reperfusion. The deferred healing-related edematous wave was blunted or absent in pigs undergoing preconditioning or short-duration ischemia, respectively. CMR-measured IS declined progressively after reperfusion in all groups. CMR-measured myocardial salvage varied dramatically according to CMR timing, ischemia duration, and cardioprotective strategy; as it was the extent of IMH and MVO.
Conclusions: Cardioprotective therapies, duration of index ischemia, and the interplay between these, greatly influence temporal dynamics and extent of tissue composition changes after I/R. Consequently, imaging techniques and protocols for assessing edema, MaR, IS, salvage, IMH and MVO should be standardized accordingly.
- ischemia reperfusion injury
- myocardial salvage
- magnetic resonance imaging
- area at risk
- Received February 28, 2017.
- Revision received June 2, 2017.
- Accepted June 8, 2017.