MRI monitoring of function, perfusion and viability in microembolized moderately ischemic myocardium

Abstract

Assessment of microembolization after coronary interventions is clinically challenging, thus we longitudinally investigated microemboli effects on moderately ischemic myocardium using MRI and histopathology. Twenty-four pigs (8/group) were divided into: group I (no intervention), group II (45 min LAD occlusion) and group III (45 min LAD occlusion with microembolization). Cine, perfusion and delayed contrast enhanced MRI (DE-MRI), using 1.5T MRI, were used for assessment at 3 days and 5 weeks. Triphenyltetrazolium-chloride (TTC) and Masson-trichrome were used as gold standard references for macro and microscopic quantification of myocardial infarction (MI). Cine MRI showed differential increase in end systolic volume (1.3 ± 0.08 ml/kg group II and 1.6 ± 0.1 ml/kg group III) and decrease in ejection fraction (45 ± 2 and 36 ± 2%, respectively) compared with controls at 3 days (2.1 ± 0.1 ml ESV and 50 ± 1% EF, P < 0.05). At 5 weeks group III, but not II, showed persistent perfusion deficits, wall thinning in the LAD territory and compensatory hypertrophy in remote myocardium. DE-MRI MI at 3 days was significantly smaller in group II (3.3 ± 2.2 g) than III (9.8 ± 0.6 g), at 5 weeks, MI were smaller by 60% (1.3 ± 0.9 g) and 22% (7.7 ± 0.5 g), respectively. TTC MI was similar to DE-MRI in group II (1.6 ± 1.0 g) and III (9.2 ± 1.6 g), but not microscopy (2.8 ± 0.4 and 10.5 ± 1.5 g, respectively). The effects of moderate ischemia with and without microembolization on myocardium could be differentiated using multiple MRI sequences. MRI demonstrated that microemboli in moderately ischemic myocardium, but not solely ischemia, prolonged ventricular dysfunction, created perfusion deficits, poor infarct resorption and enhanced compensatory hypertrophy, while moderate ischemia alone caused minor LV changes.

Coronary Embolization and Myocardial Microinfarction: MR Imaging and Histopathologic Characterization

“…In a recent proof-of-concept study, we demonstrated that mildly injured myocardium subjected to 40 min LAD occlusion then microembolization did not manifest greater susceptibility to infarction compared with solely embolized non-ischemic myocardium and 40 min LAD occlusion groups [15] (Figure 3).…”

“…In an experimental study [15], investigators found after 24 hrs PCI that plasma concentrations of CK-MB and troponin I were significantly higher after delivery of 16 mm 3 and 32 mm 3 microemboli to the LAD coronary artery compared with baseline. However, there was no significant difference at this time point in troponin I after 16 mm 3 (0.52 ± 0.28 ng/ml) and 32 mm 3 (0.68 ± 0.4 ng/ml) or CK-MB (1670 ± 370 U/L and 1060 ± 235 U/L, respectively).…”

“…Investigators found that the controlled preclinical animal models were suitable for resolving the above complexities of myocardial ischemia, reperfusion injury and coronary microembolization. Large animal models were used in many studies to recapitulate the clinical scenario of percutaneous coronary intervention [15] [27]- [30]. In these studies, coronary angiography showed normal epicardial and side branches arteries after embolization.…”

“…In these studies, coronary angiography showed normal epicardial and side branches arteries after embolization. The sizes of chosen microemboli in our studies where in the middle range of the size of microemboli escape the distal protective devices during PCI and the number of microemboli was based on previous animal studies [15] [27]- [30]. It should be noted that currently there is no animal model of spontaneous plaque rupture resulting in coronary microembolization.…”

“…DE-MR images are acquired 8 -10 min after injection of (0.1 -0.2 mmol/kg) extracellular gadolinium-chelates (Figure 1). The LV mass and extent of microinfarct are quantified using semiautomatic threshold methods [15] [29] [33] [34]. The recently developed delayed contrast enhanced three-dimensional (3D) IR-GRE has been validated against 2D IR-GRE in patients with AMI [35]- [37] and in swine hearts subjected to microinfarction.…”