Speckle tracking imaging improves in vivo assessment of EPO-induced myocardial salvage early after ischemia-reperfusion in rats

Strain Analysis in the Detection of Myocardial Infarction at the Acute and Chronic Stages

BACKGROUND

Myocardial ischemia causes contractile dysfunction in ischemic, stunned, and tethered regions with larger infarcted zones having a negative prognostic impact on patients' outcomes. To distinguish the infarcted myocardium from the other regions, we investigated the diagnostic potential of circumferential strain (CS) and radial strain (RS) during the acute and chronic stages of myocardial infarction.

METHODS

Ten pigs underwent 90-minute occlusion of the left anterior descending artery, followed by reperfusion. Echocardiography was performed at baseline, after 90-minute occlusion, and at 2 hours, 30, and 60 days postreperfusion. CS and RS were measured using speckle tracking echocardiography. Subsequently, the pigs were sacrificed, and histological analysis for infarct size was performed.

RESULTS

After 90-minute occlusion, reduced strains were detected for all segments (infarcted anterior wall - baseline: CS: -17.6 ± 5.7%, RS: 54.4 ± 16.9%; 90 min: CS: -10.3 ± 3.0%, RS: 23.3 ± 7.0%; tethered posterior wall - baseline: CS: -18.4 ± 3.5%, RS: 68.7 ± 21.1%; 90 min: CS: -10.7 ± 6.4%, RS: 34.5 ± 14.7%, P < 0.001). However, postsystolic shortening was detected only in the infarcted segments, and the time-to-peak CS was 25% longer (P < 0.05). At 30 and 60 days postreperfusion, time-to-peak CS could only detect large scars in the anterior and anterior-septum walls (P < 0.05), while peak CS also detected smaller scars in the lateral wall (P < 0.05). RS failed to distinguish between normal, stunned/tethered, and infarcted myocardium.

CONCLUSIONS

During occlusion and 2 hours postreperfusion, time-to-peak CS could distinguish between infarcted and stunned/tethered myocardial segments, while at 30 and 60 days postreperfusion, peak CS was the best detector of infarction.

Erythropoietin and the heart: physiological effects and the therapeutic perspective

Erythropoietin (Epo) has been thought to act exclusively on erythroid progenitor cells. The identification of Epo receptor (EpoR) in non-haematopoietic cells and tissues including neurons, astrocytes, microglia, immune cells, cancer cell lines, endothelial cells, bone marrow stromal cells, as well as cells of myocardium, reproductive system, gastrointestinal tract, kidney, pancreas and skeletal muscle indicates that Epo has pleiotropic actions. Epo shows signals through protein kinases, anti-apoptotic proteins and transcription factors. In light of interest of administering recombinant human erythropoietin (rhEpo) and its analogues for limiting infarct size and left ventricular (LV) remodelling after acute myocardial infarction (AMI) in humans, the foremost studies utilising rhEpo are reviewed. The putative mechanisms involved in Epo-induced cardioprotection are related to the antiapoptotic, anti-inflammatory and angiogenic effects of Epo. Thus, cardioprotective potentials of rhEpo are reviewed in this article by focusing on clinical applicability. An overview of non-haematopoietic Epo analogues, which are a reliable alternative to the classic EpoR agonists and may prevent undesired side effects, is also provided.

Xenon and isoflurane reduce left ventricular remodeling after myocardial infarction in the rat

BACKGROUND

Xenon and isoflurane are known to have cardioprotective properties. We tested the hypothesis that these anesthetics positively influence myocardial remodeling 28 days after experimental perioperative myocardial infarction and compared their effects.

METHODS

A total of 60 male Sprague-Dawley rats were subjected to 60 min of coronary artery occlusion and 120 min of reperfusion. Prior to ischemia, the animals were randomized for the different narcotic regimes (0.6 vol% isoflurane, 70 vol% xenon, or intraperitoneal injection of s-ketamine). Acute injury was quantified by echocardiography and troponin I. After 4 weeks, left ventricular function was assessed by conductance catheter to quantify hemodynamic compromise. Cardiac remodeling was characterized by quantification of dilatation, hypertrophy, fibrosis, capillary density, apoptosis, and expression of fetal genes (α/β myosin heavy chains, α-skeletal actin, periostin, and sarco/endoplasmic reticulum Ca2+-ATPase).

RESULTS

Whereas xenon and isoflurane impeded the acute effects of ischemia-reperfusion on hemodynamics and myocardial injury at a comparable level, differences were found after 4 weeks. Xenon in contrast to isoflurane or ketamine anesthetized animals demonstrated a lower remodeling index (0.7 ± 0.1 vs. 0.9 ± 0.3 and 1.0 ± 0.3g/ml), better ejection fraction (62 ± 9 vs. 49 ± 7 and 35 ± 6%), and reduced expression of β-myosin heavy chain and periostin. The effects on hypertrophy, fibrosis, capillary density, and apoptosis were comparable.

CONCLUSIONS

Compared to isoflurane and s-ketamine, xenon limited progressive adverse cardiac remodeling and contractile dysfunction 28 days after perioperative myocardial infarction.

Longitudinal strain impairment as a marker of the progression of heart failure with preserved ejection fraction in a rat model

BACKGROUND

Recent advances in very high frame rate use of ultrasonography have enabled the application of two-dimensional speckle-tracking echocardiography (STE) to small animal cardiac functional assessments. In this study, two-dimensional STE was applied to a rat model of hypertensive heart failure with preserved ejection fraction to clarify consequences of left ventricular (LV) wall deformation in the progression of heart failure with preserved ejection fraction.

METHODS

STE was performed every 2 weeks in Dahl salt-sensitive rats fed a 0.3% (control group) or 8% (hypertension [HT] group) sodium chloride diet from 6 to 14 weeks of age. Longitudinal, radial, and circumferential global strain and strain rate were measured, and the time courses of these parameters were observed.

RESULTS

Deterioration of longitudinal strain occurred in the early phase of the progression of LV hypertrophy and continued to worsen until congestive heart failure developed (longitudinal strain in the HT group: 25 ± 3% at 10 weeks, 21 ± 4% at 12 weeks, and 18 ± 2% at 14 weeks; longitudinal strain in controls was preserved during the experimental period). At 12 weeks, radial strain (HT group, 35 ± 7%; controls, 41 ± 10%) had deteriorated at the late stage of manifest diastolic dysfunction. Throughout the experiments, circumferential strain was preserved (HT group, 35 ± 6%; control group, 35 ± 5%), and no significant increase in short-axis function was observed.

CONCLUSIONS

STE is applicable to the small animal heart and detected LV wall long-axis dysfunction preceding short-axis dysfunction or overt congestive heart failure in the progression of hypertensive LV hypertrophy in a rat model.

Myocardial infarction: cardioprotection by erythropoietin

Extensive research during the last decade demonstrated that a single systemic administration of -erythropoietin (EPO) lead to significant attenuation of myocardial infarction (MI) induced in animals, mostly small rodents, either by a myocardial ischemia followed by reperfusion or by a permanent ligation of a coronary artery. Both methods are critically reviewed with the aim of helping the reader in appreciating key issues in the translation of experimental results to the clinic. Results of several clinical trials in patients with acute MI completed to date failed to demonstrate beneficial effects of EPO, and thus put into question the validity of results obtained in animal models. Comprehensive review of design and results of animal experiments and clinical trials presented here allowed authors to postulate that therapeutic window for EPO during developing MI is very narrow and was possibly missed in negative clinical trials. This point was illustrated by the negative outcome of experiment in the rat model of MI in which timing of EPO administration was similar to that in clinical trials. The design of future clinical trials should allow for a narrow therapeutic window of EPO. Given current standards for onset-to-door and door-to-balloon time the optimal time for EPO administration should be just prior to PCI.

Cardiac repair using chitosan-hyaluronan/silk fibroin patches in a rat heart model with myocardial infarction

The cardiac repair of myocardial infarction (MI) hearts of rats using chitosan-hyaluronan/silk fibroin (chitosan-HYA/SF) cardiac patches was examined after eight weeks of implantation. Rats with implantations of chitosan-HYA/SF patches (CHS group) significantly (P<0.05) reduced the dilation of the inner diameter of left ventricle (LV) (4.27 ± 0.29 mm), increased wall thickness of LV (1.5 ± 0.13 mm) and improved the fractional shortening of LV of hearts (LVFS) (42.8 ± 2.4%) compared with those values of LVs of rats without implants (MI group) (e.g., 5.92 ± 0.39 mm, 1.2 ± 0.06 mm and 31.5±1.4%, respectively). Moreover, blood vessel-like structures in MI regions of LVs in the CHS group were widely distributed while none was found in the MI group. The CHS group significantly improved the secretion of paracrine factors, such as VEGF in the MI regions of LVs (P<0.05, n=4), relative to that in the MI group. In conclusion, chitosan-HYA/SF cardiac patches are promising biomaterials for the cardiac repair of MI rat hearts.

Layer-specific strain analysis: investigation of regional deformations in a rat model of acute versus chronic myocardial infarction

Myocardial infarction (MI) injury extends from the endocardium toward the epicardium. This phenomenon should be taken into consideration in the detection of MI. To study the extent of damage at different stages of MI, we hypothesized that measurement of layer-specific strain will allow better delineation of the MI extent than total wall thickness strain at acute stages but not at chronic stages, when fibrosis and remodeling have already occurred. After baseline echocardiography scans had been obtained, 24 rats underwent occlusion of the left anterior descending coronary artery for 30 min followed by reperfusion. Thirteen rats were rescanned at 24 h post-MI and eleven rats at 2 wk post-MI. Next, rats were euthanized, and histological analysis for MI size was performed. Echocardiographic scans were postprocessed by a layer-specific speckle tracking program to measure the peak circumferential strain (S(C)(peak)) at the endocardium, midlayer, and epicardium as well as total wall thickness S(C)(peak). Linear regression for MI size versus S(C)(peak) showed that the slope was steeper for the endocardium compared with the other layers (P < 0.001), meaning that the endocardium was more sensitive to MI size than the other layers. Moreover, receiver operating characteristics analysis yielded better sensitivity and specificity in the detection of MI using endocardial S(C)(peak) instead of total wall thickness S(C)(peak) at 24 h post-MI (P < 0.05) but not 2 wk later. In conclusion, at acute stages of MI, before collagen deposition, scar tissue formation, and remodeling have occurred, damage may be nontransmural, and thus the use of endocardial S(C)(peak) is advantageous over total wall thickness S(C)(peak).

Cardiac repair achieved by bone marrow mesenchymal stem cells/silk fibroin/hyaluronic acid patches in a rat of myocardial infarction model

Bone marrow mesenchymal stem cells/silk fibroin/hyaluronic acid (BMSC/SH) patches were implanted into myocardial infarction (MI) rat hearts to investigate the efficacies of them on enhancing left ventricular (LV) remodeling and cardiac repair. 45 rats were divided into four groups: Sham, MI (MI hearts, induced by a cryo-injury technique), SH and BMSC/SH (MI hearts with implantations of SH and BMSC/SH patches, respectively). After eight weeks of post-implantation, the patches for the SH and BMSC/SH groups were intact and well adhered on the MI zones with no and minor immunological responses, respectively, examined by a CD68 marker, while severe inflammation on the zones was observed for the MI group. The SH group showed the efficacy of cardiac repair on MI zones. Moreover, BMSC/SH group significantly improved the wall thickness of LV, assessed by echocardiography, and had high viability of delivery BMSC, largely reduced apoptosis, significantly promoted neo-vascularization and stimulated the secretions of various paracrine factors such as VEGF, examined by real-time PCR, in MI zones compared with those of the SH and MI groups. In conclusion, the therapeutic efficacies of using BMSC/SH patches for repairing MI hearts were demonstrated by showing the advantages of both bioactive SH patches and BMSC-based therapy.

Value of segmental myocardial strain by 2-dimensional strain echocardiography for assessment of scar area induced in a rat model of myocardial infarction

OBJECTIVES

Two-dimensional strain echocardiography (2DSE) technique has enabled accurate quantification of regional myocardial function. This experimental study was aimed to investigate the value of 2DSE in detection of segmental regional myocardial dysfunction induced by fibrosis following myocardial infarction in a small animal (rat) model.

METHODS

A rat model of myocardial infarction was established by ligation of the proximal left anterior descending coronary artery in 17 SD rats. Regional myocardial function was detected by 2DSE at baseline and 4-weeks post-infarction, including end-systolic radial strain and strain rate (SR and SrR) and end-systolic circumferential strain and strain rate (SC and SrC) of each of six segments at papillary level. According to the size of scar found by histologic Masson staining, the optimal cutoff points of parameters for detecting scar area were analyzed and the sensitivity and specificity of every parameter to detect myocardial scar were obtained using ROC.

RESULTS

(1) Comparing with parameters measured at baseline, there were significant decreases in SR, SrR, SC and SrC of each segment at 4 weeks post-infarction, with the worst in the infarct area (32.90 ± 8.79 vs 11.18 ± 3.89, 6.28 ± 1.35 vs 3.18 ± 0.47, -14.46 ± 2.21 vs -6.30 ± 2.17 and 4.93 ± 0.95 vs 2.59 ± 1.16, respectively) (all P < 0.05). (2)By 4 weeks, the myocardium of infarct area (anteroseptum, anterior and anterolateral) had fibrosis (31.33 ± 9.89, 73.42 ± 13.21 and 13.99 ± 3.24%, respectively) with minimal fibrosis in inferoseptal segment (0.32 ± 0.19%), no fibrosis was found in the inferior and inferolateral segments. (3)Significant negative correlations were found between the size of segmental scar and 2DSE parameters (r-value -0.61 ~ -0.80, all P < 0.01) with the strongest correlation in SR. SR less than 10% has 84% sensitivity and 98% specificity for detecting segments of scar area greater than 30% with AUC = 0.97.

CONCLUSIONS

2DSE is able to assess regional myocardial dysfunction in a rat model of myocardial infarction and has high accuracy in detecting infarct segments with scar area greater than 30%.

Single high-dose erythropoietin administration immediately after reperfusion in patients with ST-segment elevation myocardial infarction: results of the erythropoietin in myocardial infarction trial

BACKGROUND

Preclinical studies and pilot clinical trials have shown that high-dose erythropoietin (EPO) reduces infarct size in acute myocardial infarction. We investigated whether a single high-dose of EPO administered immediately after reperfusion in patients with ST-segment elevation myocardial infarction (STEMI) would limit infarct size.

METHODS

A total of 110 patients undergoing successful primary coronary intervention for a first STEMI was randomized to receive standard care either alone (n = 57) or combined with intravenous administration of 1,000 U/kg of epoetin β immediately after reperfusion (n = 53). The primary end point was infarct size assessed by gadolinium-enhanced cardiac magnetic resonance after 3 months. Secondary end points included left ventricular (LV) volume and function at 5-day and 3-month follow-up, incidence of microvascular obstruction (MVO), and safety.

RESULTS

Erythropoietin significantly decreased the incidence of MVO (43.4% vs 65.3% in the control group, P = .03) and reduced LV volume, mass, and function impairment at 5-day follow-up (all P < .05). After 3 months, median infarct size (interquartile range) was 17.5 g (7.6-26.1 g) in the EPO group and 16.0 g (9.4-28.2 g) in the control group (P = .64); LV mass, volume, and function were not significantly different between the 2 groups. The same number of major adverse cardiac events occurred in both groups.

CONCLUSIONS

Single high-dose EPO administered immediately after successful reperfusion in patients with STEMI did not reduce infarct size at 3-month follow-up. However, this regimen decreased the incidence of MVO and was associated with transient favorable effects on LV volume and function.