Aims: This study was designed to characterise both the systolic and diastolic mechanical properties of regions with different degrees of myocardial ischaemic injury after reperfused acute myocardial infarction (AMI).
Methods and results: Fourteen dogs underwent 90-min coronary artery occlusion followed by reperfusion. Image acquisition was performed 24 h after reperfusion using three techniques: tagged, first-pass perfusion and delayed-enhancement magnetic resonance imaging (MRI). Systolic circumferential strain and both systolic and diastolic strain rates were calculated in 30 segments/animal. Transmural AMI segments displayed reduced systolic contractility when compared to subendocardial AMI segments (systolic strain = -2.5 +/- 0.5% versus -6.0 +/- 0.9%, P < 0.01 and systolic strain rate = -0.11 +/- 0.12 versus -0.82 +/- 0.16 s(-1), P < 0.01), and both exhibited significant systolic and diastolic dysfunction compared to remote. Moreover, AMI segments presenting with microvascular obstruction ("no-reflow") displayed further compromise of systolic and diastolic regional function (P < 0.05 for both). Importantly, risk region segments only exhibited diastolic impairment (diastolic strain rate = 1.62 +/- 0.14 versus 2.99 +/- 0.13 s(-1), P < 0.001), but not systolic dysfunction compared to remote 24 h after reperfusion.
Conclusion: Reversibly injured regions can demonstrate persistent diastolic dysfunction despite complete systolic functional recovery after reperfused AMI. Moreover, the presence of no-reflow entails profound systolic and diastolic dysfunction. Finally, tagged magnetic resonance imaging (MRI) strain rate analysis provides detailed mechanical characterisation of regions with different degrees of myocardial ischaemic injury.