Quantification Of Infarct Size Research Articles

Deep learning segmentation model for quantification of infarct size in pigs with myocardial ischemia/reperfusion.

Infarct size (IS) is the most robust end point for evaluating the success of preclinical studies on cardioprotection. The gold standard for IS quantification in ischemia/reperfusion (I/R) experiments is triphenyl tetrazolium chloride (TTC) staining, typically done manually. This study aimed to determine if automation through deep learning segmentation is a time-saving and valid alternative to standard IS quantification. High-resolution images from TTC-stained, macroscopic heart slices were retrospectively collected from pig experiments (n = 390) with I/R without/with cardioprotection to cover a wide IS range. Existing IS data from pig experiments, quantified using a standard method of manual and subsequent digital labeling of film-scan annotations, were used as reference. To automate the evaluation process with the aim to be more objective and save time, a deep learning pipeline was implemented; the collected images (n = 3869) were pre-processed by cropping and labeled (image annotations). To ensure their usability as training data for a deep learning segmentation model, IS was quantified from image annotations and compared to IS quantified using the existing film-scan annotations. A supervised deep learning segmentation model based on dynamic U-Net architecture was developed and trained. The evaluation of the trained model was performed by fivefold cross-validation (n = 220 experiments) and testing on an independent test set (n = 170 experiments). Performance metrics (Dice similarity coefficient [DSC], pixel accuracy [ACC], average precision [mAP]) were calculated. IS was then quantified from predictions and compared to IS quantified from image annotations (linear regression, Pearson's r; analysis of covariance; Bland-Altman plots). Performance metrics near 1 indicated a strong model performance on cross-validated data (DSC: 0.90, ACC: 0.98, mAP: 0.90) and on the test set data (DSC: 0.89, ACC: 0.98, mAP: 0.93). IS quantified from predictions correlated well with IS quantified from image annotations in all data sets (cross-validation: r = 0.98; test data set: r = 0.95) and analysis of covariance identified no significant differences. The model reduced the IS quantification time per experiment from approximately 90min to 20s. The model was further tested on a preliminary test set from experiments in isolated, saline-perfused rat hearts with regional I/Rwithout/with cardioprotection (n = 27). There was also no significant difference in IS between image annotations and predictions, but the performance on the test set data from rat hearts was lower (DSC: 0.66, ACC: 0.91, mAP: 0.65). IS quantification using a deep learning segmentation model is a valid and time-efficient alternative to manual and subsequent digital labeling.

82Rb-PET is feasible in rodent AMI model after positron range correction

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Prof. Andreas Kjær Department of Clinical Physiology, Nuclear Medicine & PET and Cluster for Molecular Imaging, Department of Biomedical Sciences, Rigshospitalet and University of Copenhagen, Copenhagen, Denmark Background Myocardial infarction (MI) remains a leading cause of morbidity and mortality worldwide, necessitating innovative approaches for accurate diagnosis and treatment. Positron emission tomography (PET) using 82-Rubidium (82Rb) is well-established as non-invasive myocardial perfusion imaging (MPI). However, the long position range of 82Rb disables MPI and analysis of MI through 82Rb-scans in rats. Exact assessment of myocardial infarction (MI) in small animal models is important for translational research. Purpose To investigates if positron range correction (PRC) of 82Rb PET can improve the quantification of infarct size in a rat model of MI. Method 10 Sprague-Dawley rats were included. 8 rats with MI established through coronary artery ligation and 2 rats with sham operations, where the rats underwent the same open chest procedure as the MI-rats except for the ligation of the coronary artery. Rats were PET scanned with ~ 60 MBq 82Rb PET one week after MI induction/sham operation (acute scan) in a preclinical PET/CT scanner. At 30-days following MI induction/sham operation the rats were re-scanned with 82Rb PET and 18 flu-deoxy-glucose (18F-FDG) to assess final infarct size. 82Rb PET data were reconstructed both with and without positron range correction. All acquisitions were gated by pulse and respiratory frequency. The image analysis of the static reconstructions was conducted using Corridor4DM version 2023. Infarct size was quantified by summed rest score (SRS). Due to n=10 Spearman’s rank correlation was used. Results Acute 82Rb SRS without PRC showed no correlation to the SRS of 18F-FDG follow-up PET (r=0,015 and p=0,67). Nor was there a correlation between the acute 82Rb with PRC and 18F-FDG-scans (r=0,067, p= 0,85). (Figure1) However, the follow up scan at 30 days post MI induction showed a significant correlation between infarct size of 82Rb with PRC and infarct size of the 18F-FDG scans (r=0,71 and p=0,02). No such correlation was found 82Rb results without PRC and the 18F-FDG results (r=0,51 and p=0,13) (Figure2). The 82Rb PRC scans revealed a significant correlation with 18F-FDG scans, indicating improved alignment between the two in assessing infarct size. This contrasted with the original 82Rb-images. Conclusion In this study we show the possibility of utilizing 82Rb-PET as a cardiac perfusion radioisotope in small animal research by applying positron range correction. 82Rb-PET with positron range correction provides a useful tool to delineate perfusion defects more accurately in a rodent MI-model and shows significant correlation to 18F-FDG results. Further research is warranted to validate the translational potential of these findings.Figure 1Figure 2

Abstract WP310: Pharmacological Inhibition of 6-Phosphofructo-2-Kinase/Fructose-2,6-Biphosphatase 3 (PFKFB3) is Neuroprotective in an Acute Mouse Model of Ischemic Stroke

Background: A major hallmark of stroke is the dysregulation of normal metabolic functions. In the ischemic environment, cells shift towards glycolysis, a metabolic pathway associated with a prolonged inflammatory response and delayed apoptotic cell death. One primary driver of glycolysis is 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3). This enzyme is upregulated after injury and synthesizes fructose-2,6-biphosphate, an allosteric regulator of phosphofructokinase-1, which catalyzes the first rate-limiting step in glycolysis. Studies in other disease models support a neuroprotective effect of PFKFB3 inhibition. Hypothesis: Because aberrant glycolysis contributes to inflammation and cell death and PFKFB3 upregulates glycolysis after injury, inhibition of PFKFB3 is neuroprotective in stroke. Methods: We administered a 45-minute transient middle cerebral artery occlusion in male C57BL/6J mice, followed by treatment with a highly selective PFKFB3 inhibitor AZ67 (N=10) or vehicle (N=11). The vehicle or the inhibitor (30mg/kg) were administered starting at the onset of reperfusion via the jugular vein with three repeated retro-orbital doses over the course of 48h. Open field, vertical grid, weight test, and neural deficit scorings were conducted at 24 and 48h post-stroke, after which the mice were euthanized by perfusion with saline and stained with TTC to quantify infarct size. Results: Our findings show a neuroprotective effect of PFKFB3 inhibition in ischemic stroke with improved functional and behavioral recovery and smaller infarct sizes. These results support the hypothesis that PFKFB3 inhibitors may be used as a novel pharmacological treatment for reducing delayed cell death after ischemic stroke. Future studies are underway to investigate the molecular mechanisms and cell types involved in the protection conferred by PFKFB3 blockade in the context of ischemic stroke.

Abstract 15814: Imaging Local and Systemic Reactive Oxygen Species After Ischemia-reperfusion Injury in Swine With Multimodal 18 F-ROStrace PET/CT and CMR

Introduction Reperfusion injury after myocardial infarction (MI) can cause additional tissue damage and is associated with adverse outcomes, and inflammation of extra-cardiac tissue may occur post-MI. In this study, we used positron emission tomography (PET) radiotracer [18F]ROStrace to image reactive oxygen species (ROS) in myocardium and in extra-cardiac tissues in a swine model of subacute ischemia-reperfusion injury. Methods The mid left anterior descending coronary artery was occluded in three swine for 90 minutes, followed by reperfusion. Baseline and post-MI ROStrace data were acquired 3 days post-MI on the long axial field-of-view PennPET Explorer PET/CT system. A [82]Rb scan was acquired to calculate myocardial blood flow (MBF). Regions of interest (ROIs) were drawn in brain, lungs, bone marrow, spleen, skeletal muscle, myocardium (baseline) and infarcted and non-infarct myocardium (post-MI). ROStrace fractional uptake rate (FUR) was calculated in all ROIs. Cardiac FUR was corrected for MBF. Paired T-tests and Cohen's d effect size (ES) were used to evaluate the effect of MI on ROStrace activity in cardiac and extra-cardiac tissues. Cardiac MRI was done to quantify infarct size. Results In extra-cardiac tissues, MI had a nonsignificant medium effect on ROS in bone marrow (ES = 0.54, p = 0.45) and spleen (ES = 0.60, p=0.41), and a nonsignificant large effect in skeletal muscle (ES = 1.24, p = 0.17). No effect was seen in brain and lungs. In the heart, MI had a significant large effect on ROS in the region of the infarct, compared to baseline (ES = 3.84, p = 0.02) (Fig. 1). Infarct size on late gadolinium enhanced MRI ranged from 16.73 to 33.62% of the myocardium. Conclusion For the first time, systemic and local effects on ROS after MI were directly imaged using whole-body [18F]ROStrace PET. We found that ROS are increased in the infarcted myocardium in the subacute phase, and MI leads to moderate-to-large effects in ROS levels in hematopoietic tissues and skeletal muscle.

Inflammatory Bowel Disease Increases the Severity of Myocardial Infarction after Acute Ischemia-Reperfusion Injury in Mice.

(1) Background: Increased risk of myocardial infarction (MI) has been linked to several inflammatory conditions, including inflammatory bowel disease (IBD). However, the relationship between IBD and MI remains unclear. Here, we implemented an original mouse model combining IBD and MI to determine IBD's impact on MI severity and the link between the two diseases. (2) Methods: An IBD model was established by dextran sulfate sodium (DSS) administration in drinking water, alone or with oral C. albicans (Ca) gavage. IBD severity was assessed by clinical/histological scores and intestinal/systemic inflammatory biomarker measurement. Mice were subjected to myocardial ischemia-reperfusion (IR), and MI severity was assessed by quantifying infarct size (IS) and serum cardiac troponin I (cTnI) levels. (3) Results: IBD mice exhibited elevated fecal lipocalin 2 (Lcn2) and IL-6 levels. DSS mice exhibited almost two-fold increase in IS compared to controls, with serum cTnI levels strongly correlated with IS. Ca inoculation tended to worsen DSS-induced systemic inflammation and IR injury, an observation which is not statistically significant. (4) Conclusions: This is the first proof-of-concept study demonstrating the impact of IBD on MI severity and suggesting mechanistic aspects involved in the IBD-MI connection. Our findings could pave the way for MI therapeutic approaches based on identified IBD-induced inflammatory mediators.

Reassessing the clinical significance of electrocardiographically unrecognized myocardial infarctions: Radionuclide infarct size and its impact on long-term prognosis.

Silent or unrecognized myocardial infarction (UMI) diagnosed by surveillance electrocardiography (ECG) carries similarly poor prognosis as recognized MI (RMI) for poorly understood reasons. This study included 5430 consecutive patients who presented to the nuclear laboratory and underwent 2-day stress and rest Tc-99m sestamibi and ECG studies between March 1991 and June 1999. UMI was diagnosed if ECG showed Q-wave MI in the absence of a history of RMI. We measured infarct size (% defect size as compared with the entire left ventricular sestamibi uptake), ejection fraction (EF, %), and summed difference score (SDS, sestamibi uptake by myocardium in stress minus sestamibi uptake in rest images as a marker of ischemia). Survival was determined by follow-up survey (median 6 years). We identified 346 UMIs, 628 RMIs, and 4456 subjects without MI (No MI). As compared with RMI, UMI patients had lesser abnormalities on nuclear scans (p < .0001 for all), including smaller infarct size (5.7% vs. 12.2%), higher EF (58% vs. 53%), and lesser ischemia (SDS; 3.9% vs. 2.7%). UMI prognosis was as poor as that of RMI (annual mortality rate 4.7% vs. 4.8% with No MI rate of 2.9%; p < .001 for all comparisons), and this persisted after multivariate analysis. Infarct size quantification successfully risk-stratified ECG-UMI patients, but UMI patients continued to predict mortality even if the infarct size was 0%. Although UMI patients have lesser abnormalities on nuclear scans, ECG-based UMI continues to independently predict mortality, indicating the continuing relevance of ECG in clinical practice.

An Experimental Model of Myocardial Infarction for Studying Cardiac Repair and Remodeling in Knockout Mice.

Cardiovascular disease is the most prevalent cause of death in Western countries, with acute myocardial infarction (MI) being the most prevalent form. This paper describes a protocol for studying the role of galectin 3 (Gal-3) in the temporal evolution of cardiac healing and remodeling in an experimental animal model of MI. The procedures described include an experimental model of MI with a permanent coronary ligature in male C57BL/6J (control) and Gal-3 knockout (KO) mice, an echocardiography procedure to study cardiac remodeling and systolic function in vivo, a histological evaluation of interstitial myocardial fibrosis with picrosirius red-stained and rhodamine-conjugated lectin-stained sections for studying myocyte hypertrophy by the cross-sectional area (MCSA), and the quantification of infarct size and cardiac remodeling (scar thinning, septum thickness, and expansion index) by planimetry in slices stained with Masson's trichrome and triphenyl tetrazolium chloride. Gal-3 KO mice with MI showed disrupted cardiac remodeling and an increase in the scar thinning ratio and the expansion index. At the onset of MI, myocardial function and cardiac remodeling were also severely affected. At 4 weeks post MI, the natural evolution of fibrosis in infarcted Gal-3 KO mice was also affected. In summary, the experimental model of MI is a suitable model for studying the temporal evolution of cardiac repair and remodeling in mice with the genetic deletion of Gal-3 and other animal models. The lack of Gal-3 affects the dynamics of cardiac repair and disrupts the evolution of cardiac remodeling and function after MI.

The Incidence and Impact of Permanent Right Ventricular Infarction on Left Ventricular Infarct Size in Patients With Inferior ST-Segment Elevation Myocardial Infarction

Mounting evidence shows that right ventricle (RV) function carries independent prognostic influence in various disease states. This study aimed to investigate the incidence and impact of permanent RV infarction in patients with inferior ST-segment elevation myocardial infarction (STEMI) and culprit lesion in the right coronary artery (RCA). In this substudy of the DANAMI-3 (DANish Study of Optimal Acute Treatment of Patients with ST-segment Elevation Myocardial Infarction) trial, cardiac magnetic resonance was performed in 291 patients at day 1 and follow-up 3 months after primary percutaneous coronary intervention of 674 patients with STEMI with the culprit lesion in the RCA. Final infarct was assessed using late gadolinium enhancement on cardiac magnetic resonance at 3 months. Patients with permanent RV infarction (20%) had lower ventricular function at follow-up; RV ejection fraction (EF) 47% ±6 versus 50% ± 5 (p <0.005) and left ventricular (LV) EF 56% ± 8 versus 60% ± 9 (p <0.006). Furthermore, patients with permanent RV infarction had a higher incidence of microvascular obstruction 39 (67%) versus 81 (39%) (p <0.001), larger final LV infarct size 16% ±8 versus 10% ± 8 (p <0.001) and larger LV area at risk 33% ± 10 versus 29% ± 9 (p <0.001). Permanent RV infarction was an independent predictor of final LV infarct size (p <0.001) but was not associated with LVEF (β=-0.0; p=0.13) in multivariable analyses. In conclusion, permanent RV infarction was seen in 20% of patients with inferior STEMI and culprit lesion in RCA and independently predicted final LV infarct size. However, permanent RV infarction did not predict overall LV function. LGE was used to detect infarct location and quantify infarct size.17 LGE in RV free wall on follow-up CMR was considered as permanent infarction. LGE images were obtained 10 minutes after intravenous injection of 0.1-mmol/kg body weight of gadolinium-based contrast (Gadovist; Bayer Schering, Berlin, Germany) using an electrocardiogram (ECG)-triggered inversion-recovery sequence. The inversion time was adjusted to null the signal from the normal myocardium. Short-axis images were acquired from the atrioventricular plane to the apex with adjacent 8-mm slices. The remaining protocol has been described previously.16.

Epicardial adipose tissue, infarct size, microvascular obstruction and ventricular remodelling after ST-segment elevation myocardial infarction

Abstract Background Epicardial adipose tissue (EAT) is a biologically active fat deposit contained beneath the pericardium promoting coronary atherosclerosis. EAT can be accurately measured through cardiac magnetic resonance (CMR), which also enables an accurate quantification of infarct size, microvascular obstruction (MVO), left ventricular (LV) ejection fraction (EF) and volumes in patients with ST-elevation myocardial infarction (STEMI). Purpose We performed a systematic assessment of the correlates of EAT volume at baseline and after 6 months in a homogeneous cohort of patients with STEMI. Methods We prospectively enrolled patients with a first anterior STEMI reperfused within 12 hours from symptom onset. These patients underwent a first CMR exam after 1 week from the MI and after 6 months. Results Patients (n=138) were more often men (81%), with a median age of 58 years (interquartile range 48–66). EAT volume was 30 mL/m2 (23–41). Patients with EAT &amp;gt;30 mL/m2 (n=69) were older (60±12 vs. 55±11 years, p=0.02), more often diabetic (26% vs. 12%, p=0.03), and showed a worse baseline risk profile (Thrombolysis in Myocardial Infarction risk score 3 [2–5] vs. 2 [1–4], p=0.05). Patients with EAT &amp;gt;30 mL/m2 also displayed a larger IS (33±15 vs. 23±16% of LV mass, p=0.001) and MVO (1.5 [0–6.8] vs. 0% [0–2.2], p=0.008). Again in patients with EAT &amp;gt;30 mL/m2, EAT volume independently predicted infarct size (standardized beta coefficient=0.30, p&amp;lt;0.001) and MVO area (standardized beta coefficient=0.36, p&amp;lt;0.001) after adjusting for age, sex and infarct characteristics at 1 week (Figure 1). Despite these correlations with infarct size and MVO, patients with EAT &amp;gt;30 mL/m2 did not display more depressed LVEF or larger LV volumes than those with EAT ≤30 mL/m2, either at 1 week or at 6-month CMR (p&amp;gt;0.1 for all comparisons). Conclusions In a cohort of patients with first anterior STEMI undergoing timely reperfusion, those with a greater EAT volume have a larger infarct size and a larger area of MVO. Despite these correlates of EAT volume size, patients with larger EAT do not have a higher risk of adverse LV remodelling. Funding Acknowledgement Type of funding sources: None.

Histopathological validation of semi-automated myocardial scar quantification techniques for dark-blood late gadolinium enhancement magnetic resonance imaging.

To evaluate the performance of various semi-automated techniques for quantification of myocardial infarct size on both conventional bright-blood and novel dark-blood late gadolinium enhancement (LGE) images using histopathology as reference standard. In 13 Yorkshire pigs, reperfused myocardial infarction was experimentally induced. At 7 weeks post-infarction, both bright-blood and dark-blood LGE imaging were performed on a 1.5 T magnetic resonance scanner. Following magnetic resonance imaging (MRI), the animals were sacrificed, and histopathology was obtained. The percentage of infarcted myocardium was assessed per slice using various semi-automated scar quantification techniques, including the signal threshold vs. reference mean (STRM, using 3 to 8 SDs as threshold) and full-width at half-maximum (FWHM) methods, as well as manual contouring, for both LGE methods. Infarct size obtained by histopathology was used as reference. In total, 24 paired LGE MRI slices and histopathology samples were available for analysis. For both bright-blood and dark-blood LGE, the STRM method with a threshold of 5 SDs led to the best agreement to histopathology without significant bias (-0.23%, 95% CI [-2.99, 2.52%], P = 0.862 and -0.20%, 95% CI [-2.12, 1.72%], P = 0.831, respectively). Manual contouring significantly underestimated infarct size on bright-blood LGE (-1.57%, 95% CI [-2.96, -0.18%], P = 0.029), while manual contouring on dark-blood LGE outperformed semi-automated quantification and demonstrated the most accurate quantification in this study (-0.03%, 95% CI [-0.22, 0.16%], P = 0.760). The signal threshold vs. reference mean method with a threshold of 5 SDs demonstrated the most accurate semi-automated quantification of infarcted myocardium, without significant bias compared to histopathology, for both conventional bright-blood and novel dark-blood LGE.

No sex-related differences in infarct size, no-reflow, and protection by ischaemic pre-conditioning in Göttingen minipigs.

Female sex has been proposed to be cardioprotective per se. Studies with myocardial ischaemia/reperfusion and infarct size as endpoint have demonstrated cardioprotection in female, castrated male, and male pigs. These studies are difficult to compare, given the different pig strains, models, durations of ischaemia, and methods of infarct size quantification. The few studies using both female and male pigs reported no differences in infarct size and cardioprotection. We, therefore, prospectively compared infarct size in Göttingen minipigs undergoing ischaemia/reperfusion (I/R) without and with ischaemic pre-conditioning (IPC) between female, castrated male, and male pigs. In a prospective, randomized approach, 28 Göttingen open-chest, anaesthetized minipigs underwent 60 min ischaemia by distal left anterior descending artery (LAD) occlusion and 180 min reperfusion without and with IPC by three cycles of 5 min LAD occlusion/10 min reperfusion. Infarct size with I/R was not different between female, castrated male, and male pigs (45 ± 8 vs. 45 ± 13 vs. 41 ± 9% area at risk), as was the reduction in infarct size with IPC (25 ± 11 vs. 30 ± 8 vs. 19 ± 10% area at risk). In addition, the area of no-reflow was not different between female, castrated male, and male pigs with I/R (57 ± 13 vs. 35 ± 7 vs. 47 ± 26% infarct size) or IPC (4 ± 10 vs.12 ± 20 vs. 0 ± 0% infarct size). Phosphorylation of signal transducer and activator of transcription 3 was increased at 10 min reperfusion by IPC but not by I/R to the same extent in female, castrated male, and male pigs (198 ± 30 vs. 230 ± 165 vs. 179 ± 107% of baseline). Our data do not support the notion of sex- or castration-related differences in infarct size, coronary microvascular injury, and cardioprotection by IPC. The translation of successful preclinical studies on cardioprotection to the benefit of patients with reperfused myocardial infarction has been difficult. The difficulties have been attributed to confounders such as co-morbidities and co-medications which patients typically have but animals don´t, but also to age and sex. Notably, female sex has been considered as protective per se. We have now, using our established and clinically relevant pig model of reperfused acute myocardial infarction and ischaemic preconditioning as the most robust cardioprotective intervention looked for sex-related differences of infarct size, no-reflow and cardioprotection by ischaemic preconditioning in a prospectively powered approach but found none such difference.

Quantification of murine myocardial infarct size using 2-D and 4-D high-frequency ultrasound.

Ischemic heart disease is the leading cause of death in the United States, Canada, and worldwide. Severe disease is characterized by coronary artery occlusion, loss of blood flow to the myocardium, and necrosis of tissue, with subsequent remodeling of the heart wall, including fibrotic scarring. The current study aims to demonstrate the efficacy of quantitating infarct size via two-dimensional (2-D) echocardiographic akinetic length and four-dimensional (4-D) echocardiographic infarct volume and surface area as in vivo analysis techniques. We further describe and evaluate a new surface area strain analysis technique for estimating myocardial infarction (MI) size after ischemic injury. Experimental MI was induced in mice via left coronary artery ligation. Ejection fraction and infarct size were measured through 2-D and 4-D echocardiography. Infarct size established via histology was compared with ultrasound-based metrics via linear regression analysis. Two-dimensional echocardiographic akinetic length (r = 0.76, P = 0.03), 4-D echocardiographic infarct volume (r = 0.85, P = 0.008), and surface area (r = 0.90, P = 0.002) correlate well with histology. Although both 2-D and 4-D echocardiography were reliable measurement techniques to assess infarct, 4-D analysis is superior in assessing asymmetry of the left ventricle and the infarct. Strain analysis performed on 4-D data also provides additional infarct sizing techniques, which correlate with histology (surface strain: r = 0.94, P < 0.001, transmural thickness: r = 0.76, P = 0.001). Two-dimensional echocardiographic akinetic length, 4-D echocardiography ultrasound, and strain provide effective in vivo methods for measuring fibrotic scarring after MI.NEW & NOTEWORTHY Our study supports that both 2-D and 4-D echocardiographic analysis techniques are reliable in quantifying infarct size though 4-D ultrasound provides a more holistic image of LV function and structure, especially after myocardial infarction. Furthermore, 4-D strain analysis correctly identifies infarct size and regional LV dysfunction after MI. Therefore, these techniques can improve functional insight into the impact of pharmacological interventions on the pathophysiology of cardiac disease.

Cross-modality analysis of left ventricular function and volume in patients with st-segment elevation myocardial infarction: impact of infarct patterns

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): Sonderforschungsbereich 1116, University Düsseldorf Background Left ventricular (LV) function is considered of major importance to estimate prognosis of patients with ST-segment elevation myocardial infarction (STEMI) [1]. Although transthoracic echocardiography (TTE) after STEMI is recommended to assess for LV function and identify patients at high risk for rehospitalisation due to heart failure, Cardiovascular Magnetic Resonance (CMR) is still considered the gold standard for an adequate quantification of volumes, function and infarct size (IS) [2]. In addition, unenhanced TTE has been shown to underestimate LV function [3]. It is complicating that parameters such as IS and area-at risk (AAR) are thought to further deteriorate prognosis [4,5]. Purpose To test the hypothesis that cross-modality 2D/3D analyses using TTE, CMR and cineventriculography are comparable for the determination of LV-function in STEMI and that infarct patterns influence the determination of LV-function and volumes across modalities. Methods In a group of 70 patients after STEMI, estimation of LV function and volumes was performed by biplane cineventriculography during acute catheterization, biplane (2D) CMR 28 ± 16 hours (1 day) as well as 2D/3D-CMR and TTE 114 ± 31 hours (5 days) post STEMI. 3D-TTE after STEMI was only performed in a subset of 36 patients respectively. IS and AAR were assessed by T2-weighted and contrast enhanced CMR (1.5T) as percentage of the LV mass. Results Both, 2D- and 3D-, LV ejection fraction (LVEF) were comparable between the single modalities. Stroke volume (SV) and LV end-diastolic volume (LVEDV) were underestimated when comparing 2D- to 3D-CMR and when comparing TTE/cineventriculography to CMR. Correlating IS to the difference of 2D- and 3D-CMR, higher IS/AAR did not alter previous results, except from a fairly increased difference in SV (R = 0.3). For 2D-TTE versus 2D-CMR, higher IS/AAR increased differences in LVEDV (IS &amp; AAR: p &amp;lt;0.001 both, R = -0.58, R=-0.54). For 3D-TTE and 3D-CMR, IS and AAR increased the difference in LVEF (p = 0.009, R = 0.50; p &amp;lt; 0.001, R = 0.60) and LVEDV (p = 0.021, R=-0.5; p = 0.027, R=-0.46). A general linear model (GLM) for repeated measures including IS as covariate supported this finding by showing a significant interaction effect between the imaging modalities (TTE/CMR) for LVEF estimation and IS. AAR increased the difference in LVEF comparing cineventriculography and 2D-CMR as well (p = 0.001, R = 0.47). This was again supported by a significant interaction effect as detected by the GLM. Conclusions There is good agreement between LVEF analysis across dimensions (2D and 3D) and different modalities (TTE, cineventriculography and CMR) whereas the comparison of SV and LVEDV is hampered. However, with increasing IS or AAR, LVEF differences between modalities increase and 3D-CMR, if available, or alternatively 3D-TTE should be used for the most accurate estimation of LVEF.

Functional and prognostic implications of cardiac magnetic resonance feature tracking-derived remote myocardial strain analyses in patients following acute myocardial infarction

BackgroundCardiac magnetic resonance myocardial feature tracking (CMR-FT)-derived global strain assessments provide incremental prognostic information in patients following acute myocardial infarction (AMI). Functional analyses of the remote myocardium (RM) are scarce and whether they provide an additional prognostic value in these patients is unknown.Methods1034 patients following acute myocardial infarction were included. CMR imaging and strain analyses as well as infarct size quantification were performed after reperfusion by primary percutaneous coronary intervention. The occurrence of major adverse cardiac events (MACE) within 12 months after the index event was defined as primary clinical endpoint.ResultsPatients with MACE had significantly lower RM circumferential strain (CS) compared to those without MACE. A cutoff value for RM CS of − 25.8% best identified high-risk patients (p < 0.001 on log-rank testing) and impaired RM CS was a strong predictor of MACE (HR 1.05, 95% CI 1.07–1.14, p = 0.003). RM CS provided further risk stratification among patients considered at risk according to established CMR parameters for (1) patients with reduced left ventricular ejection fraction (LVEF) ≤ 35% (p = 0.038 on log-rank testing), (2) patients with reduced global circumferential strain (GCS) > − 18.3% (p = 0.015 on log-rank testing), and (3) patients with large microvascular obstruction ≥ 1.46% (p = 0.002 on log-rank testing).ConclusionCMR-FT-derived RM CS is a useful parameter to characterize the response of the remote myocardium and allows improved stratification following AMI beyond commonly used parameters, especially of high-risk patients.Trial registrationClinicalTrials.gov, NCT00712101 and NCT01612312Graphic abstractDefining remote segments (R) in the presence of infarct areas (I) for the analysis of remote circumferential strain (CS). Remote CS was significantly lower in patients who suffered major adverse cardiac events (MACE) and a cutoff value for remote CS of − 25.8% best identified high-risk patients. In addition, impaired remote CS ≥ − 25.8 % (Remote −) and preserved remote CS < − 25.8 % (Remote +) enabled further risk stratification when added to established parameters like left ventricular ejection fraction (LVEF), global circumferential strain (GCS) or microvascular obstruction (MVO).

Impact of Administration Time and Kv7 Subchannels on the Cardioprotective Efficacy of Kv7 Channel Inhibition.

PurposeThe mechanism of cardioprotection by Kv7.1–5 (KCNQ1-5) channels inhibition by XE991 is unclear. We examined the impact of administration time on the cardioprotective efficacy of XE991, the involvement of key pro-survival kinases, and the importance of the Kv7 subchannels.MethodsIsolated perfused rat hearts were divided into five groups: 1) vehicle, 2) pre-, 3) post- or 4) pre- and post-ischemic administration of XE991 or 5) chromanol 293B (Kv7.1 inhibitor) followed by infarct size quantification. HL-1 cells undergoing simulated ischemia/reperfusion were exposed to either a) vehicle, b) pre-, c) per-, d) post-ischemic administration of XE991 or pre-, per- and post-ischemic administration of e) XE991, f) Chromanol 293B or g) HMR1556 (Kv7.1 inhibitor). HL-1 cell injury was evaluated by propidium iodide/Hoechst staining. Pro-survival kinase activation of Akt, Erk and STAT3 in XE991-mediated HL-1 cell protection was evaluated using phosphokinase inhibitors. Kv7 subtype expression was examined by RT-PCR and qPCR.ResultsXE991, but not Chromanol 293B, reduced infarct size and improved hemodynamic recovery in all isolated heart groups. XE991 protected HL-1 cells when administered during simulated ischemia. Minor activation of the survival kinases was observed in cells exposed to XE991 but pharmacological inhibition of kinase activation did not reduce XE991-mediated protection. Kv7 subchannels 1–5 were all present in rat hearts but predominately Kv7.1 and Kv7.4 were present in HL-1 cells and selective Kv7.1 did not reduce ischemia/reperfusion injury.ConclusionThe cardioprotective efficacy of XE991 seems to depend on its presence during ischemia and early reperfusion and do not rely on RISK (p-Akt and p-Erk) and SAFE (p-STAT3) pathway activation. The protective effect of XE991 seems mainly mediated through the Kv7.4 subchannel.

Prognostic Impact of Ischemic Mitral Regurgitation Severity and Myocardial Infarct Quantification by Cardiovascular Magnetic Resonance

ObjectivesThis study sought to evaluate the role of cardiac magnetic resonance (CMR) for the quantification of ischemic mitral regurgitation (IMR) and myocardial infarct size (MIS) in patients with ischemic cardiomyopathy (ICM). This study also sought to explore the interaction between IMR severity and MIS and its association with outcomes in patients with ICM. BackgroundIMR occurs secondary to a disease of the left ventricle and is associated with poor outcomes. The role of CMR for the evaluation and risk stratification of patients with ICM and IMR remains uncertain. MethodsConsecutive patients with ICM who underwent baseline CMR were included. MIS was quantified on late gadolinium enhancement imaging as the proportion of left ventricular mass. IMR was quantified with CMR by calculating the mitral regurgitant fraction (MRFraction). Cox proportional hazards models were built to assess the association of IMR and MIS quantification with the combined endpoint of all-cause death or heart transplant. ResultsWe evaluated 578 patients (mean age: 62 ± 11 years, 76% males). The mean left ventricular ejection fraction was 25 ± 11%, with an MIS of 24 ± 16% and MRFraction of 18 ± 17%. Over a median follow-up time of 4.9 years, 198 (34%) patients experienced death or cardiac transplant. On multivariable analysis, after comprehensive medical risk score, subsequent revascularization, implantable cardioverter-defibrillator insertion, and surgical mitral valve intervention were controlled for, the interaction of IMR severity and MIS emerged as a powerful predictor of adverse outcomes (p = 0.008). For patients with significant IMR (MRFraction: ≥35%), the hazard ratio comparing moderate MIS (15% to 29%) versus small MIS (<15%) was 1.51 (0.57 to 3.98), and the hazard ratio comparing large MIS (≥30%) versus small MIS was 5.41 (2.34 to 12.7). ConclusionsRisk associated with IMR is more comprehensively described as an interaction between IMR severity and MIS. Further studies in patients IMR using comprehensive CMR evaluation are needed to verify whether this approach can improve patient selection and procedural outcomes to address IMR.

P5389Limited regenerative potential of the neonatal porcine heart after myocardial infarction

Abstract Background Neonatal murine hearts possess -for a brief period after birth- a robust capacity for spontaneous myocardial regeneration following cardiac injury. Whether hearts of neonatal large mammals possess similar regenerative potential is a matter of active investigation. Recently, two studies reported that 1-day-old and 2-day-old neonatal pigs exhibit a significant cardiac regenerative response post-myocardial infarction (MI), characterized by minimal cardiac fibrosis and spontaneous recovery of left ventricular (LV) function; this regenerative capacity is purportedly lost after the first two days of life. Purpose We sought to evaluate the regenerative potential of neonatal porcine hearts after MI. Methods Twenty-one neonatal farm pigs were randomly assigned to undergo MI by permanent ligation of the left anterior descending artery on postnatal day 1 (P1) or postnatal day 3 (P3). Infarcted P1 and P3 pigs were euthanized either at 1 week or at 7 weeks post-MI. Hearts explanted at 1 week post-MI underwent fluorescent immunohistochemistry for Ki67 and alpha-sarcomeric actinin to quantify myocyte cell cycle re-entry. Transthoracic echocardiography was performed at 7 weeks post-MI to quantify fractional shortening and systolic thickening of the anterior (infarcted) LV wall and the posterior (non-infarcted) LV wall. Hearts explanted at 7 weeks post-MI underwent staining with triphenyl-tetrazolium chloride and Masson's Trichrome to quantify infarct size, infarct circumference and infarct transmurality. Results Fourteen animals successfully completed the protocol. Infarct size (P1: 9.5±2.2% vs P3: 8.9±3.6% of LV, p=0.797), infarct circumference (P1: 33.8±7.1% vs P3: 29.8±10.6% of LV, p=0.566) and infarct transmurality (P1: 38.1±4.3% vs P3: 40.4±13.7% of anterior wall, p=0.764) were comparable in P1 and P3 animals at 7 weeks post-MI. LV fractional shortening (an index of global LV systolic function) was similar in P1 and P3 animals at 7 weeks post-MI (P1: 25.5±2.9% vs P3: 23.7±4.5%, p=0.662). Furthermore, systolic thickening in the anterior (infarcted) LV wall was depressed to a similar degree in P1 and P3 animals (P1: 31.8±5.3% vs P3: 32.3±8.5%, p=0.914) compared to systolic thickening in the posterior (non-infarcted) wall (P1: 72.5±9.0% vs P3: 69.0±11.4%, p=0.666) at 7 weeks post-MI. Myocyte cell cycle re-entry in the infarct border zone was increased in P1 animals compared to P3 animals (P1: 4.5±1.3 vs P3: 2.3±0.6 per field of view, p=0.045) at 1 week post-MI. Conclusions In contrast to recently-published reports, we did not observe a robust cardiac regenerative response in neonatal porcine hearts post-MI. Hearts of both 1-day-old and 3-day-old neonatal pigs exhibited substantial scarring and significant hypokinesia of the infarcted myocardium post-MI. Additional research is warranted to assess the cardiac regenerative potential of neonatal large mammals. Acknowledgement/Funding Co-financed by Greece and the European Union - European Social Fund

Improvements in left ventricular regional and global systolic function following treatment with S100A4-shRNA after myocardial infarction in mice.

S100A4 plays a vital role in cardiac fibrosis after myocardial infarction (MI), but its effects on myocardial mechanics and remodeling are unknown. We hypothesized that regional and global left ventricular (LV) systolic function as determined by speckle tracking echocardiography (STE) would be improved with inhibition of S100A4 using short hairpin (sh) RNA. This study aimed to investigate whether STE can delineate the efficacy and safety of S100A4-shRNA in MI. A total of 48 mice were randomly assigned to sham+S100A4-shRNA, sham+scrambled (Scr) sequence-shRNA, MI+S100A4-shRNA, and MI+Scr-shRNA groups (n=12 per group) and underwent intramyocardial injection of target agents after MI was produced by left anterior descending ligation. Two-dimensional STE and M-mode echocardiography were performed at baseline and at day 7, 14, and 28 post-MI by GE Vivid 7 ultrasound (il3L linear probe, 10.0-14.0 MHz) and Echopac PC software. Radial strain was analyzed from 6 segments of the mid short axis images with 20-30 frames per cardiac cycle. Post-mortem western blotting, immunohistochemistry, and Masson's trichrome stain were performed to quantify infarct size and detect suppression of S100A4. STE detected a statistically significant improvement in peak radial strain (pRS) and time to peak radial strain (pRSt) by day 14 post-MI in the MI+S100A4-shRNA group (P<0.05), especially in the LV anteroseptal wall (pRS: 23.83%±1.12% vs. 20.25%±1.02%, pRSt: 76.75±3.18 vs. 92.00±3.69 ms, P<0.05). After 1 month of S100A4-shRNA administration, cardiac function improved in the MI+S100A4-shRNA group according to both STE and M-mode tracing in mice. Additionally, both biochemical and histopathological examinations found reduced cardiac fibrosis in the MI+S100A4-shRNA group. S100A4-shRNA can be utilized as a therapeutic target to improve regional deformation and attenuate cardiac fibrosis following MI. Two-dimensional STE is useful in the early and comprehensive assessment of LV systolic function in mice.

Heart clearing opens new insights in the quantification of injured area after ischemia reperfusion

Myocardial infarction leads to ischemia reperfusion (I/R) injury. The quantification of tissue injury is essential in translational research. Although MRI or X-ray scanner can estimate injured area in live animals, their cost and their limited accessibility often restrict their use. Actually, the commonly used method is the TTC blue technique, based on the unisperse blue and performed on organ slices. However, it is partly subjective, time consuming and a volume estimation. The recent development of clearing methods in neurosciences opens new insights through giving access to high spatially resolved whole organ imaging. Indeed, tissue fixation followed by lipids removing increases the scattering of light travelling through the tissue in microscopy. To quantify infarct size in 3D we propose in this study to adapt clearing method to heart. Using X-Clarity system, mice hearts were clarified after ishemia-reperfusion sequences and imaging was performed by confocal microscopy and light-sheet imaging systems. Cleared heart can be imaged in depth (> 1.5 mm) and thus enables the tomography of 3D volumes with a high spatial resolution (300 nm in xy; 1–5 μm in z). This study provides a proof-of-concept that multi-scale imaging can be achieved on cleared heart to study cells in their native physiopathological environment. We also demonstrate that myocardium autofluorescence mainly originates from myoglobin. Myoglobin spectrum can be used to quantify oxidized area, which could actually reveal the infarct area. So we developed a half-automated algorithm on ImageJ to quantify area-at-risk and oxidized area. This technique offers a novel approach of infarct size quantification in 3D. The possibility to perform immunostaining of structures of interest and cells also allow new perspectives on the understanding of I/R injury.

Comparison of Magnetic Resonance Analysis of Myocardial Scarring With Biomarker Release Following S-T Elevation Myocardial Infarction

Late gadolinium enhancement (LGE) with cardiac magnetic resonance (CMR) is commonly assumed to represent myocardial fibrosis; however, comparative human histological data are limited, and there is no consensus on the most accurate method for LGE quantitation. We evaluated the relationship between CMR assessment of regional fibrosis and infarct size assessment using serial biomarkers after ST elevation acute myocardial infarction (STEMI). Ninety-three patients treated for STEMI (59±10 years, 86% male) underwent CMR 6 months after infarction. Infarct size was quantified by CMR-LGE using manual and range of semi-automated thresholds (range: 2-10 standard deviations [SD]) above reference myocardium and the full width-half maximum (FWHM) technique, and compared with the rise in serum biomarkers. The agreement between CMR and biomarker in the identification of large infarcts based on peak troponin (TnI) levels was also analysed. Quantification methods had a strong influence on the infarct size assessment with CMR-LGE. Significant correlations were observed between LGE and biomarkers across all of the signal intensity thresholds. Whilst there was a wide variation with respect to the estimation of total LGE size (from 6.8±7.7 to 32.1±11.3 grams), the variation in the correlation with peak troponin level was much smaller (r-values ranging from 0.670 to 0.876). There was good agreement between CMR-LGE and biomarker assessment of infarct size; the best agreement between CMR-LGE and large infarction using a threshold of 8SD for peak TnI>50ng/mL (Cohen's kappa (κ)=0.722), and a threshold of 4SD for peak TnI >95ng/mL (κ=0.761). The correlation between CMR-LGE quantification of infarct size and biomarker release following STEMI at a range of semi-automated thresholds was consistently strong, with good agreement between measures across a range of thresholds.