Normal Myocardium Research Articles

Myocardial Fibrosis Assessment at 3-T versus 5-T Myocardial Late Gadolinium Enhancement MRI: Early Results.

Background Cardiac MRI at 5 T has recently become available and potentially improves tissue contrast enhancement at gadolinium chelate-enhanced T1-weighted imaging. Purpose To evaluate the feasibility of 5-T myocardial late gadolinium enhancement (LGE) MRI in assessing myocardial fibrosis by comparing image quality and LGE quantification with reference-standard 3-T myocardial LGE MRI. Materials and Methods Consecutive patients with confirmed myocardial fibrosis on previous 3-T MRI scans between January 2023 and July 2023 prospectively underwent follow-up imaging from August 2023 to November 2023. Each participant underwent follow-up 5-T imaging using an identical dose of contrast agent. Radiologist scoring of image quality using a Likert scale (range, 1-5), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contrast ratio, and semiautomatic quantitative LGE assessment were obtained and reported as medians and IQRs. Paired Wilcoxon signed rank tests were used to compare characteristics derived at 3-T and 5-T imaging. Results A total of 18 participants (mean age, 49 years ± 17 [SD]; nine male participants) were included, with a mean interval of 6.2 months ± 2.3 between undergoing 3-T and 5-T MRI. Median image quality scores were 4.0 (IQR, 3.0-4.2) at 3 T and 4.0 (IQR, 3.0-4.4) at 5 T (P = .45). SNR at 5 T was higher than at 3 T (183.7 [IQR, 147.2-255.9] vs 125.8 [IQR, 108.2-171.6], respectively; P = .002). Median CNR at 5 T was higher than at 3 T in normal myocardium (50.8 [IQR, 35.4-67.9] vs 16.5 [IQR, 11.3-24.6], respectively) and pericardial fat (21.4 [IQR, 7.1-29.3] vs -5.0 [IQR, -16.4 to -2.3], respectively) (both P < .001). There was no evidence of a difference in the percentage of LGE quantified between 5 T and 3 T (median, 11.8% [IQR, 7.7%-20.5%] vs 12.6% [IQR, 6.6%-20.4%], respectively; P = .81). Conclusion Myocardial LGE MRI at 5 T was found to be feasible, with no evidence of differences in subjective image quality and myocardial fibrosis quantification compared with 3-T myocardial LGE MRI. Furthermore, with use of identical contrast agent doses, SNRs and CNRs were improved at 5 T. Published under a CC BY 4.0 license. Supplemental material is available for this article. See also the editorial by Czum in this issue.

Assessing myocardial tissue in the acute setting with Photon-Counting CT (PCCT) in comparison with Cardiac Magnetic Resonance (CMR)

Abstract Background Cardiac magnetic resonance (CMR) characterization of myocardial tissue is routinely used in clinical practice. Compared to traditional CT, Photon counting CT (PCCT) uses photon-counting detectors offering higher spatial resolution, elimination of electronic noise and improved contrast-to-noise ratio. A comparison between CMR and PCCT for myocardial characterizazion in an urgent setting, however, has not yet been explored. Purpose The aim of this study was to compare the ability to characterize myocardial tissue between PCCT and CMR in patients presenting with acute chest pain in the emergency department (ED). Methods This single-center prospective study enrolled all consecutive patients presenting to the ED of our hospital from November 2023 to January 2024 with chest pain, ECG alterations and troponin rise consistent with myocardial injury. Patients needing urgent coronary angiography according to guidelines were excluded. PCCT was performed urgently for triple rule-out, but also for tissue characterization through post-iodine-contrast administration images. Within 24 hours, all patients underwent a CMR protocol including T2-weighted and late gadolinium enhancement (LGE) images for tissue characterization. Results Six male patients with a mean age of 20 ± 10 years were enrolled. All clinical, PCCT, and CMR parameters are presented in Table 1. All patients presented with diffuse ST-segment elevation and exhibited T2-weighted images (for edema detection) and LGE distribution (subepicardial and intramyocardial) consistent with acute myocarditis. Mean radiation exposure for PCCT was 0.8±0.1 mSv. A strong linear correlation emerged between PCCT-derived delayed enhancement (DE) volume and CMR-derived late gadolinium enhancement (LGE) volume (r = 0.970; p value 0.001) (Table 1). Similar results were achieved when comparing the number of DE and LGE myocardial segments (r = 0.871; p value 0.026). Significant correlations also emerged between DE, LGE, and high-sensitive troponin (hsTN) at presentation (respectively: PCCT-DE vs hsTN r = 0.951, p value 0.004; CMR-LGE vs hsTN r = 0.918, p value 0.010). CMR showed a much higher signal-to-noise ratio (SNR) for the delayed enhanced myocardium and contrast-to-noise (CNR) ratio between the delayed enhanced and normal myocardium with respect to PCCT in post-contrast images (respectively 7.4 ± 3.9 vs 27.2 ± 17.7, p value 0.024 and 5.5 ± 3.7 vs 38.8 ± 30.2, p value 0.023). In T2-weighted images both SNR for the hyperintense myocardium (30.3 [20.4-122.4]) and CNR between the hyperintense and normal myocardium (26.7 [13.3-60.2]) resulted to be higher compared to PCCT (p value 0.027 and 0.045, respectively) (Table 1). Conclusions PCCT appears to be reliable when compared to CMR for detecting myocardial edema through the acquisition of post-contrast images in the acute setting with an acceptable CNR.

CT-perfusion quantitation of cardiac infarct size - a novel technique

Abstract Introduction Cardiac infarct size is associated with cardiac prognosis after AMI. Cardiac CT is able to delineate both coronary anatomy and myocardial pefusion. Thus far, CT identification of infarction has been qualitative. We describe a novel technique for quantitation of myocardial infarct size in CT-perfusion imaging. Methods Patient Population comprised 51 patients that were previously clinically diagnosed with myocardial infarction on the basis of clinical presentation, ECG findings and elevated cardiac enzymes. CTP Imaging All patients had undergone dynamic rest, vasodilator-stress, rest, delayed enhancement CT perfusion imaging performed on a dual-source, third generation scanner (FORCE, Siemens Healthcare). Image Analysis 2 trained investigators independently quantified the infarct volume in 51 patient studies using Siemens SmartSimulator software. Mean ± SD HU were taken from a 1cm² circular ROI of normal myocardium used in a thresholding method. The epicardium and endocardium of infarcted areas were manually contoured from apex to base. Volumetric measurements were obtained of the infarct and total myocardium. Interpolation of contours for segmentation objects was performed. Subtraction of left ventricle cavity from total left ventricle allowed volumetric measurements of total left ventricular myocardium. ROIs of the infarct were estimated using SDs above mean HU of normal myocardium (0.5, 1, 1.5 and 2 SDs) in delayed imaging. Selection of optimal threshold HU was based on visual assessment that best mapped the hyperenhanced infarct area. This allowed volumetric asessment of infarct and total myocardium. Inter-investigator variability was evaluated with Bland-Altman and Intra-Class Correlation Coefficient (ICC). Results Patient characteristics are follow: Age 60.20±11.35 years, 41(89%)male, BMI 25.41±4.17kg/m², Hypertension 23(50%), diabetes 10(22%), hyperlipidemia 40(87%), smoking 7(15%), family history of premature CAD 4(8.7%), previous PCI 45(97.8%). In 51 patients, 23(41%), 24 (46%) &amp; 5(10%) of the infarctions were quantitated as being medium-sized (10%-20%), large (20% -30%) and very large (&amp;gt;30%). Thirty-seven (70%), 6 (11%) &amp; 10(19%) involved the LAD, LCx and RCA territories respectively. 49 (94%) of infarctions were transmural. Identical thresholding was selected by both investigators for each SD above mean (mean 1.42; SD 0.46). 93% of the total cases were within a set threshold of 1 to 2 SDs above the mean HU for both. Interclass correlation coefficient was 0.95, CI range 0.90 – 0.97. Bland-Altman analysis did not demonstrate systemic variations or proportional bias from the plot. Conclusion The study suggests that a method of quantifying cardiac infarct size using a threshold technique and delayed hyperenhancement images with dynamic perfusion imaging is clinically feasible and consistent.Rest-Stress-Delayed Enhancement infarct

A novel method in myocardial injury risk stratification using intravenous fat emulsion as sole rapid preparation for unfasted patients to suppress myocardial 18F-fluorodeoxyglucose uptake for optimal cardiac PET imaging: a proof-of-concept randomized-crossover trial.

Optimal imaging of ischemic or inflammed myocardium via 18F-FDG PET imaging requires suppression of background carbohydrate metabolism in normal myocardium. Sole administration of intravenous lipid emulsion has not previously been used to rapidly prepare unfasted patients, such as in emergent clinical situations. In this proof-of-concept pilot, we posited that intravenous fat emulsion suppresses physiological metabolic uptake of in non-ischemic, non-inflammatory myocardium in unprepared and unfasted setting for enhanced cardiac positron emission tomography (PET) imaging. We conducted an ethics-approved, single-blind, prospective randomized crossover trial of 10 healthy volunteers from January 2020 to June 2021. Participants were unfasted and rendered hyperglycemic before being administered either high dose intravenous lipid emulsion-1.5 ml kg of 20% lipid emulsion, followed by 15 ml/kg/hr for 30mins-or saline prior to 18F-FDG injection and subsequent cardiac PET imaging. Assessors undertook image analysis for maximum standard uptake value (SUVmax), minimum standard uptake value (SUVmin) and qualitative assessment, and groups were compared using univariate analysis. The study population age was 44.5 years [IQR 32.5-56.5], with 50% male and a median BMI of 22.75 [IQR 25.0-28.5] kg/m2. The study was feasible and there were no adverse side effects from the interventions. In these participants with normal myocardium, 18F-FDG uptake was reduced by intravenous lipid emulsion as assessed by SUVmax and qualitative assessment (p = 0.042, r = 0.454 and p = 0.009, r = -0.581, respectively). Intravenous lipid emulsion suppresses background metabolic uptake of 18F-FDG even in unprepared and unfasted patients. Our findings prove and expand the possible applications for cardiac 18F-FDG PET in various settings, including in emergent settings as a means of rapid preparation in place of current more time-consuming standard protocols, allowing time-critical management to be effected.

Somatostatin Receptor Type 2 as a Potential Marker of Local Myocardial Inflammation in Myocardial Infarction: Morphologic Data on Distribution in Infarcted and Normal Human Myocardium.

Nuclear imaging modalities can detect somatostatin receptor type 2 (SSTR2) in vivo as a potential marker of local post-MI inflammation. SSTR2+ macrophages are thought to be the main substrate for SSTR-targeted radioimaging. However, the distribution of SSTR2+ cells in the MI patients' myocardium is unknown. Using immunohistochemistry, we investigated the distribution of SSTR2+ cells in the myocardium of patients who died during the MI inflammatory phase (n = 7) compared to the control group of individuals with fatal trauma (n = 3). Inflammatory cellular landscapes evolve in a wave front-like pattern, so we divided the myocardium into histological zones: the infarct core (IC), the border zone (BZ), the remote zone (RZ), and the peri-scar zone (PSZ). The number of SSTR2+ neutrophils (NPs), SSTR2+ monocytes/macrophages (Mos/MPs), and SSTR2+ vessels were counted. In the myocardium of the control group, SSTR2+ NPs and SSTR2+ Mos/MPs were occasional, SSTR2+ vessels were absent. In the RZ, the picture was similar to the control group, but there was a lower number of SSTR2+ Mos/MPs in the RZ. In the PSZ, SSTR2+ vessel numbers were highest in the myocardium. In the IC, the median number of SSTR2+ NPs was 200 times higher compared to the RZ or control group myocardium, which may explain the selective uptake of SSTR-targeted radiotracers in the MI area during the inflammatory phase of MI.

Patient selection, ventricular tachycardia substrate delineation and data transfer for stereotactic arrhythmia radioablation. A Clinical Consensus Statement of the European Heart Rhythm Association (EHRA) of the ESC and the Heart Rhythm Society (HRS).

Stereotactic arrythmia radioablation (STAR) is a novel, non-invasive and promising treatment option for ventricular arrythmias (VA). It has been applied in highly selected patients mainly as bail-out procedure, when (multiple) catheter-ablations, together with anti-arrhythmic drugs, were unable to control the VAs. Despite the increasing clinical use there is still limited knowledge of the acute and long-term response of normal and diseased myocardium to STAR. Acute toxicity appeared to be reasonably low but potential late adverse effects may be underreported. Among published studies, the provided methodological information is often limited, and patient selection, target volume definition, methods for determination and transfer of target volume, and techniques for treatment planning and execution differ across studies, hampering pooling of data and comparison across studies. In addition, STAR requires close and new collaboration between clinical electrophysiologists and radiation oncologists, which is facilitated by shared knowledge in each collaborator's area of expertise and a common language. This clinical consensus statement provides uniform definition of cardiac target volumes. It aims to provide advice in patient selection for STAR including etiology specific aspects, and advice in optimal cardiac target volume identification based on available evidence. Safety concerns and the advice for acute and long-term monitoring including the importance of standardized reporting and follow-up are covered by this document. Areas of uncertainty are listed, which require high-quality, reliable pre-clinical and clinical evidence before expansion of STAR beyond clinical scenarios in which proven therapies are ineffective or unavailable.

MicroPET Imaging of Riboflavin Transporter 3 Expression in Myocardial Infarction/Reperfusion Rat Models with Radiofluorinated Riboflavin.

Riboflavin transporter 3 (RFVT3) represents a potential cardioprotective biotarget in energetic metabolism reprogramming after myocardial infarction/reperfusion (MI/R). This study investigated the feasibility of noninvasive real-time quantification of RFVT3 expression after MI/R with an radiolabeled probe 18F-RFTA in a preclinical rat model of MI/R. The tracer 18F-RFTA was radio-synthesized manually and characterized on the subjects of radiolabeling yield, radiochemical purity, and stability in vivo. MI/R and sham-operated rat models were confirmed by cardiac magnetic resonance imaging (cMRI) and single-photon-emission computed tomography (SPECT) myocardial perfusion imaging (MPI) with technetium-99m sestamibi (99mTc-MIBI). Positron emission tomography (PET) imaging of MI/R and sham-operated rat models were conducted with 18F-RFTA. Ex vivo autoradiography and RFVT3 immunohistochemical (IHC) staining were conducted to verify the RFVT3 expression in infarcted and normal myocardium. 18F-RFTA injection was prepared with high radiochemical purity (>95%) and kept stable in vitro and in vivo. 18F-RFTA PET revealed significant uptake in the infarcted myocardium at 8 h after reperfusion, as confirmed by lower 99mTc-MIBI perfusion and decreased intensity of cMRI. Conversely, there were only the tiniest uptakes in the normal myocardium and blocked infarcted myocardium, which was further corroborated by ex vivo autoradiography. The RFVT3 expression was further confirmed by IHC staining in the infarcted and normal myocardium. We first demonstrate the feasibility of imaging RFVT3 in infarcted myocardium. 18F-RFTA is an encouraging PET probe for imaging cardioprotective biotarget RFVT3 in mitochondrial energetic metabolism reprogramming after myocardial infarction. Noninvasive imaging of cardioprotective biotarget RFVT3 has potential value in the diagnosis and therapy of patients with MI.

Abstract We090: Antagonistic and Cooperative Dynamics of Irx3 and Irx4 in Ventricular Compaction

Left ventricular non-compaction cardiomyopathy (LVNC) is a rare heart condition characterized by excessive trabeculae and intertrabecular recesses in the left ventricle of the heart. It is believed to be caused by abnormal trabecular compaction process, which involves trabecular remodelling to form a thick myocardial wall. Embryonic trabeculae consist of bipotent progenitors that differentiate into the ventricular conduction system (VCS) and contractile cardiomyocytes, yet it remains to be further understood how the pathways involved in trabecular cell specifications play a role in the compaction process. Here we present two transcription factors, Iroquois homeobox 3 ( Irx3 ) and Irx4 , playing antagonistic and cooperative roles during trabecular specification and maturation, thereby facilitating proper ventricular compaction. Our single-cell RNA sequencing analysis revealed that the differentiation of trabecular cells into VCS cells was accompanied by increased Irx3 but decreased Irx4 expression. In addition, we found that the loss of Irx4 led to both an increased expression level of Irx3 and an expansion in the number of Irx3 -expressing cells. Conversely, the loss of Irx3 resulted in an upregulation of Irx4 expression within VCS cells. Next, to investigate the functional importance of the antagonistic relationship between Irx3 and Irx4 in trabecular differentiation, we generated Irx3 and Irx4 compound knockout (KO) mice and examined the structure and function of their hearts. Notably, unlike Irx3 KO hearts showing normal ventricular myocardium, Irx4 KO hearts exhibited mild LVNC, and Irx3 and Irx4 double knockouts ( Irx3 /4dKO) hearts displayed severe LVNC. Multiome sequencing of E14.5 ventricles revealed that Irx3 /4dKO ventricles contained an increased number of trabecular cells, expressing higher levels of cell proliferation markers and altered trabecular identity genes, compared to littermate controls. Collectively, our results demonstrate that balanced antagonism between Irx3 and Irx4 is crucial for establishing trabecular identity. This highlights the importance of proper differentiation of trabeculae into the VCS and non-VCS contractile cells during ventricular compaction, thereby preventing noncompaction cardiomyopathy.

Extended survival of 9- and 10-gene-edited pig heart xenografts with ischemia minimization and CD154 costimulation blockade-based immunosuppression

BackgroundXenotransplantation has made significant advances recently using pigs genetically engineered to remove carbohydrate antigens, either alone or with addition of various human complement, coagulation, and anti-inflammatory ‘transgenes’. Here we evaluated results associated with gene-edited (GE) pig hearts transplanted in baboons using an established costimulation-based immunosuppressive regimen and a cold-perfused graft preservation technique. MethodsEight baboons received heterotopic abdominal heart transplants from 3-GE (GalKO.β4GalNT2KO.hCD55, n=3), 9-GE (GalKO.β4GalNT2KO.GHRKO.hCD46.hCD55. TBM.EPCR.hCD47.HO-1, n=3) or 10-G (9-GE+CMAHKO, n=2) pigs using Steen’s cold continuous perfusion for ischemia minimization. Immunosuppression (IS) included induction with anti-thymocyte globulin and αCD20, ongoing αCD154, MMF, and tapered corticosteroid. ResultsAll three 3-GE grafts functioned well initially, but failed within 5 days. One 9-GE graft was lost intraoperatively due to a technical issue and another was lost at POD 13 due to antibody mediated rejection (AMR) in a baboon with a strongly positive pre-operative cross-match. One 10-GE heart failed at POD113 with combined cellular and antibody mediated rejection. One 9-GE and one 10-GE hearts had preserved graft function with normal myocardium on protocol biopsies, but exhibited slowly progressive graft hypertrophy until elective necropsy at POD393 and 243 respectively. Elevated levels of IL-6, MCP-1, C-reactive protein, and human thrombomodulin were variably associated with conditioning, the transplant procedure, and clinically significant postoperative events. ConclusionRelative to reference genetics without thrombo-regulatory and anti-inflammatory gene expression, 9- or 10-GE pig hearts exhibit promising performance in the context of a clinically applicable regimen including ischemia minimization and αCD154-based IS, justifying further evaluation in an orthotopic model.

Evaluation of Ablation Parameters to Predict Irreversible Lesion Size During Pulsed Field Ablation.

During pulsed field ablation (PFA), relationships between ablation parameters (contact force [CF], number of burst pulses, impedance decrease, and electrode temperature) and lesion size in beating hearts have not been well validated. A 7.5F-catheter with a 3.5-mm ablation electrode and CF sensor (ThermoCool SmartTouch SF-Dual-Energy, Biosense Webster, Inc, Irwindale, CA) was connected to a PFA system (TRUPULSE2, Biosense Webster, Inc). In 11 closed-chest swine, biphasic PFA current was delivered between the ablation electrode and the skin patch at 219 sites in left ventricle and right ventricle using 12, 18, and 24 burst pulses with 4 different levels of CF: (1) low (n=57; CF, 4-15g; median, 10g); (2) moderate (n=60; CF, 16-30g; median, 22.5g); (3) high (n=68; CF, 32-65g; median, 40g); and (4) no electrode contact (n=34), 2 mm away from the endocardium. Swine were euthanized 2 hours after ablation, and lesion size was measured using triphenyl tetrazolium chloride staining. All PFA lesions with electrode-myocardium contact were well demarcated with triphenyl tetrazolium chloride staining, demonstrating (1) pale central zone (contraction band necrosis with minimal coagulation necrosis), (2) dark brown zone (contraction band necrosis with hemorrhage), and (3) hyperstained red zone by triphenyl tetrazolium chloride (unaffected normal myocardium with preserved mitochondrial activity, consistent with reversible zone). Lesion depth increased significantly with increasing CF and the number of PFA burst pulses. An exponential/logarithmic formula combined with CF and the number of PFA burst pulses correlated lesion depth with high accuracy: R=0.809, P<0.0001, ±1.0-mm accuracy in 128 of 163 (79%) lesions, and ±1.5-mm accuracy in 153 of 163 (94%) lesions. Impedance decrease and electrode temperature were poor predictors of lesion size. There were no detectable lesions resulting from ablation without electrode contact. Acute PFA ventricular lesions demonstrate irreversible and reversible lesion boundaries. Electrode-tissue contact is required for effective lesion formation. Lesion depth increases significantly with increasing CF and PFA burst pulses. A new exponential/logarithmic formula combined with CF and the number of PFA burst pulses correlates lesion depth with high accuracy.

Additional value of CMR parametric mapping in tissue characterization of common benign pediatric cardiac tumors.

Cardiac Magnetic Resonance (CMR) parametric mapping is underexplored in cardiac tumors. To evaluate the contribution of mapping sequences on the characterization of pediatric tumors. All pediatric patients referred for cardiac tumors at Bambino Gesù Children's Hospital from June 2017 to November 2023, who underwent CMR with mapping sequences, were included. The diagnosis of tumor type was performed according to signal characteristics on different sequences. Mass parametric mapping for each subtype and interobserver variability was assessed. Sixteen patients were enrolled. The mean age at CMR was 7 ± 5 years. "Traditional" mass-type assessment diagnosed hemangioma (Group A) in 3 patients (19%), fibroma (Group B) in 4 patients (25%), rhabdomyoma (Group C) in 6 patients (37%), and lipoma (Group D) in 3 patients (19%). The ANOVA analysis revealed significant differences in mass native T1 and mass extracellular volume (ECV) values among the four subgroups (p<0.001 for both comparisons). The mean native T1 and ECV values were respectively 1465 ± 158 msec and 54 ± 4% for Group A, 860 ± 118 msec and 93 ± 4% for Group B, 1007 ± 57 msec and 23 ± 5% for Group C, and 215 ± 13 msec and 0 ± 0% for Group D. Mass mapping analysis is feasible and reproducible in children. ECV values provide the most accurate differentiation. Mass ECV consistently resembles normal myocardium in rhabdomyoma, is extremely high (approaching 100%) in fibroma, equals to zero in lipoma, and matches blood pool ECV (1-Hct) in hemangioma.

A machine learning algorithm improves the diagnostic accuracy of the histologic component of antibody mediated rejection (AMR-H) in cardiac transplant endomyocardial biopsies

BackgroundPathologic antibody mediated rejection (pAMR) remains a major driver of graft failure in cardiac transplant patients. The endomyocardial biopsy remains the primary diagnostic tool but presents with challenges, particularly in distinguishing the histologic component (pAMR-H) defined by 1) intravascular macrophage accumulation in capillaries and 2) activated endothelial cells that expand the cytoplasm to narrow or occlude the vascular lumen. Frequently, pAMR-H is difficult to distinguish from acute cellular rejection (ACR) and healing injury. With the advent of digital slide scanning and advances in machine deep learning, artificial intelligence technology is widely under investigation in the areas of oncologic pathology, but in its infancy in transplant pathology. For the first time, we determined if a machine learning algorithm could distinguish pAMR-H from normal myocardium, healing injury and ACR. Materials and MethodsA total of 4,212 annotations (1,053 regions of normal, 1,053 pAMR-H, 1,053 healing injury and 1,053 ACR) were completed from 300 hematoxylin and eosin slides scanned using a Leica Aperio GT450 digital whole slide scanner at 40X magnification. All regions of pAMR-H were annotated from patients confirmed with a previous diagnosis of pAMR2 (>50% positive C4d immunofluorescence and/or >10% CD68 positive intravascular macrophages). Annotations were imported into a Python 3.7 development environment using the OpenSlide™ package and a convolutional neural network approach utilizing transfer learning was performed. ResultsThe machine learning algorithm showed 98% overall validation accuracy and pAMR-H was correctly distinguished from specific categories with the following accuracies: normal myocardium (99.2%), healing injury (99.5%) and ACR (99.5%). ConclusionOur novel deep learning algorithm can reach acceptable, and possibly surpass, performance of current diagnostic standards of identifying pAMR-H. Such a tool may serve as an adjunct diagnostic aid for improving the pathologist's accuracy and reproducibility, especially in difficult cases with high inter-observer variability. This is one of the first studies that provides evidence that an artificial intelligence machine learning algorithm can be trained and validated to diagnose pAMR-H in cardiac transplant patients. Ongoing studies include multi-institutional verification testing to ensure generalizability.

Cardiac Magnetic Resonance Imaging as a Risk Stratification Tool in COVID-19 Myocarditis.

The aim of this retrospective study was to identify myocardial injury after COVID-19 inflammation and explore whether myocardial damage could be a possible cause of the persistent symptoms following COVID-19 infection in previously healthy individuals. This study included 139 patients who were enrolled between January and June 2021, with a mean age of 46.7 ± 15.2 years, of whom 68 were men and 71 were women without known cardiac or pulmonary diseases. All patients underwent clinical work-up, laboratory analysis, cardiac ultrasound, and CMR on a 1.5 T scanner using a recommended protocol for morphological and functional assessment before and after contrast media application with multi-parametric sequences. In 39% of patients, late gadolinium enhancement (LGE) was found as a sign of myocarditis. Fibrinogen was statistically significantly higher in patients with LGE than in those without LGE (4.3 ± 0.23 vs. 3.2 ± 0.14 g/L, p < 0.05, respectively), as well as D-dimer (1.8 ± 0.3 vs. 0.8 ± 0.1 mg/L FEU). Also, troponin was statistically significantly higher in patients with myocardial LGE (13.1 ± 0.4 ng/L) compared to those with normal myocardium (4.9 ± 0.3 ng/L, p < 0.001). We demonstrated chest pain, fatigue, and elevated troponin to be independent predictors for LGE. Septal LGE was shown to be a predictor for arrhythmias. The use of CMR is a potential risk stratification tool in evaluating outcomes following COVID-19 myocarditis.

426 A Beat Away from Precision Medicine: Characterizing Human Cardiac Fibroblast Responsiveness to Hemodynamic Unloading in Heart Failure with Reduced Ejection Fraction

OBJECTIVES/GOALS: Myocardial interstitial fibrosis leads to high hemodynamic load resulting in heart failure (HFrEF). Previous studies show that treatment with a left ventricular assist device (LVAD) does not reduce fibrosis. We hypothesize that human cardiac fibroblasts are highly activated in HFrEF and remain unresponsive to hemodynamic unloading by LVAD. METHODS/STUDY POPULATION: Forty human subjects with HFrEF undergoing LVAD implantation were enrolled to provide a portion of myocardium routinely removed during LVAD placement. In addition, 7 biopsies previously collected from transplanted hearts with extended LVAD treatment were also evaluated (LVEX). RESULTS/ANTICIPATED RESULTS: Quantification of PSR-stained sections reveals a significant increase in collagen content in the HFrEF tissue (CVF = 2.8) compared to control tissues (CVF = 0.9) that remained elevated in LVEX hearts (CVF = 3.1). HCFs from LV biopsies were isolated and grown to confluence. HCFs from HFrEF patients and control HCFs were plated on substrates with stiffnesses reflective of normal myocardium (2kPa) or HFrEF myocardium (8kPa). Cells were collected at 4- and 7-day time points and levels of collagen I and alpha-smooth muscle actin were quantified by western blot analysis. Control HCFs were responsive to changes in substrate stiffness producing more Col I and a-SMA on 8kPa versus 2kPa, HCFs from HFrEF patients were unresponsive to changes in stiffness exhibiting no significant difference in protein production on 2 vs. 8kPa. DISCUSSION/SIGNIFICANCE: Our data suggests that HCFs isolated from the failing myocardium do not respond to changes in mechanical load and might contribute to persistent increases in fibrosis. These findings bring us one step closer to elucidating mechanisms behind fibrosis in HFrEF which could lead to targeted therapies to improve patient outcomes from LVAD support.

Enhanced TfR1 Recognition of Myocardial Injury after Acute Myocardial Infarction with Cardiac Fibrosis via Pre-Degrading Excess Fibrotic Collagen.

The fibrosis process after myocardial infarction (MI) results in a decline in cardiac function due to fibrotic collagen deposition and contrast agents' metabolic disorders, posing a significant challenge to conventional imaging strategies in making heart damage clear in the fibrosis microenvironment. To address this issue, we developed an imaging strategy. Specifically, we pretreated myocardial fibrotic collagen with collagenase I combined with human serum albumin (HSA-C) and subsequently visualized the site of cardiac injury by near-infrared (NIR) fluorescence imaging using an optical contrast agent (CI, CRT-indocyanine green) targeting transferrin receptor 1 peptides (CRT). The key point of this strategy is that pretreatment with HSA-C can reduce background signal interference in the fibrotic tissue while enhancing CI uptake at the heart lesion site, making the boundary between the injured heart tissue and the normal myocardium clearer. Our results showed that compared to that in the untargeted group, the normalized fluorescence intensity of cardiac damage detected by NIR in the targeted group increased 1.28-fold. The normalized fluorescence intensity increased 1.21-fold in the pretreatment group of the targeted groups. These data demonstrate the feasibility of applying pretreated fibrotic collagen and NIR contrast agents targeting TfR1 to identify ferroptosis at sites of cardiac injury, and its clinical value in the management of patients with MI needs further study.

Gene expression and cellular changes in injured myocardium of Ciona intestinalis.

Ciona intestinalis is an invertebrate animal model system that is well characterized and has many advantages for the study of cardiovascular biology. The regulatory mechanisms of cardiac myocyte proliferation in Ciona are intriguing since regeneration of functional tissue has been demonstrated in other organs of Ciona in response to injury. To identify genes that are differentially expressed in response to Ciona cardiac injury, microarray analysis was conducted on RNA from adult Ciona hearts with normal or damaged myocardium. After a 24- or 48-h recovery period, total RNA was isolated from damaged and control hearts. Initial results indicate significant changes in gene expression in hearts damaged by ligation in comparison to control hearts. Ligation injury shows differential expression of 223 genes as compared to control with limited false discovery (5.8%). Among these 223 genes, 117 have known human orthologs of which 68 were upregulated and 49 were downregulated. Notably, Fgf9/16/20, insulin-like growth factor binding protein and Ras-related protein Rab11b were significantly upregulated in injured hearts, whereas expression of a junctophilin ortholog was decreased. Histological analyses of injured myocardium were conducted in parallel to the microarray study which revealed thickened myocardium in injured hearts. Taken together, these studies will connect differences in gene expression to cellular changes in the myocardium of Ciona, which will help to promote further investigations into the regulatory mechanisms of cardiac myocyte proliferation across chordates.

The active papillary muscle sign in 18F-FDG PET/CT cardiac sarcoidosis exams and its relationship with myocardial suppression.

Papillary muscle (PM) activity may demonstrate true active cardiac sarcoidosis (CS) or mimic CS in 18FDG-PET/CT if adequate myocardial suppression (MS) is not achieved. We aim to examine whether PM uptake can be used as a marker of failed MS and measure the rate of PM activity presence in active CS with different dietary preparations. We retrospectively reviewed PET/CTs obtained with three different dietary preparations. Diet-A: 24-h ketogenic diet with overnight fasting (n = 94); Diet-B: 18-h fasting (n = 44); and Diet-C: 72-h daytime ketogenic diet with 3-day overnight fasting (n = 98). Each case was evaluated regarding CS diagnosis (negative, positive, and indeterminant) and presence of PM activity. MaxSUV was measured from bloodpool, liver, and the most suppressed normal myocardium. Linear mixed-effects models were used to compare these factors between those with PM activity and those without. PM activity was markedly lower in the Diet-C group compared with others: Diet-C: 6 (6.1%), Diet-A: 36 (38.3%), and Diet-B: 26 (59.1%) (p < 0.001). MyocardiumMaxSUV was higher, and MyocardiummaxSUV/BloodpoolmaxSUV, MyocardiummaxSUV/LivermaxSUV ratios were significantly higher in the cases with PM activity (p < 0.001). Among cases that used Diet-C and had PM activity, 66.7% were positive and 16.7% were indeterminate. If Diet-A or Diet-B was used, those with PM activity had a higher proportion of indeterminate cases (Diet-A: 61.1%, Diet-B: 61.5%) than positive cases (Diet-A: 36.1%, Diet-B: 38.5%). Lack of PM activity can be a sign of appropriate MS. PM activity is less common with a specific dietary preparation (72-h daytime ketogenic diet with 3-day overnight fasting), and if it is present with this particular preparation, the likelihood that the case being true active CS might be higher than the other traditional dietary preparations.

Arrhythmogenic Right Ventricular Cardiomyopathy in Children: A Systematic Review.

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited disease characterized by the progressive replacement of the normal myocardium by fibroadipocytic tissue. The importance of an early diagnosis is supported by a higher risk of sudden cardiac death in the pediatric population. We reviewed the literature on diagnosis, risk stratification, and prognosis in the pediatric population with ARVC. In case reports which analyzed children with ARVC, the most common sign was ventricular tachycardia, frequently presenting as dizziness, syncope, or even cardiac arrest. Currently, there is no gold standard for diagnosing ARVC in children. Nevertheless, genetic analysis may provide a proper diagnosis tool for asymptomatic cases. Although risk stratification is recommended in patients with ARVC, a validated prediction model for risk stratification in children is still lacking; thus, it is a matter of further research. In consequence, even though ARVC is a relatively rare condition in children, it negatively impacts the survival and clinical outcomes of the patients. Therefore, appropriate and validated diagnostic and risk stratification tools are crucial for the early detection of children with ARVC, ensuring a prompt therapeutic intervention.

Can native T1 mapping sequence be used as a non-invasive alternative imaging tool to LGE sequence for evaluating DCM patients?

BackgroundMyocardial fibrosis is the potential outcome of dilated cardiomyopathy (DCM). Cardiac MRI is considered one of the most essential imaging methods in DCM evaluation by using the late gadolinium enhancement (LGE) sequence and native T1 mapping technique. The study aimed to assess the diagnostic accuracy and reliability of the native T1 mapping technique for detecting myocardial fibrosis in DCM patients and correlate the values with the LGE in such a patient population.ResultsLGE was present in ten patients (33.33%) and 46 out of 480 myocardial segments (9.58%). T1 native values were significantly higher in the LGE group compared to the non-LGE group (P < 0.001). Furthermore, the non-LGE group showed higher T1 native values than the control group. Based on receiver operating characteristics (ROC) curves analysis, the best cut-off value of T1 native for the discrimination between normal myocardium and DCM was 1060 ms, while 1125 ms was the optimal cut-off value for LGE prediction among DCM patients (AUC; 0.919 and 0.904), respectively.ConclusionsNative T1 mapping technique can be used as a simple, practical, and reproducible method for characterizing myocardial fibrosis in patients with DCM with high diagnostic accuracy and specificity.

Effects of Contact Force on Lesion Size During Pulsed Field Catheter Ablation: Histochemical Characterization of Ventricular Lesion Boundaries.

Effects of contact force (CF) on lesion formation during pulsed field ablation (PFA) have not been well validated. The purpose of this study was to determine the relationship between average CF and lesion size during PFA using a swine-beating heart model. A 7F catheter with a 3.5-mm ablation electrode and CF sensor (TactiCath SE, Abbott) was connected to a PFA system (CENTAURI, Galvanize Therapeutics). In 5 closed-chest swine, biphasic PFA current was delivered between the ablation electrode and a skin patch at 40 separate sites in right ventricle (28 Amp) and 55 separate sites in left ventricle (35 Amp) with 4 different levels of CF: (1) low (CF range of 4-13 g; median, 9.5 g); (2) moderate (15-30 g; median, 21.5 g); (3) high (34-55 g; median, 40 g); and (4) no electrode contact, 2 mm away from the endocardium. Swine were sacrificed at 2 hours after ablation, and lesion size was measured using triphenyl tetrazolium chloride staining. In 1 additional swine, COX (cytochrome c oxidase) staining was performed to examine mitochondrial activity to delineate reversible and irreversible lesion boundaries. Histological examination was performed with hematoxylin and eosin and Masson trichrome staining. Ablation lesions were well demarcated with triphenyl tetrazolium chloride staining, showing (1) a dark central zone (contraction band necrosis and hemorrhage); (2) a pale zone (no mitochondrial activity and nuclear pyknosis, indicating apoptosis zone); and a hyperstained zone by triphenyl tetrazolium chloride and COX staining (unaffected normal myocardium with preserved mitochondrial activity, consistent with reversible zone). At constant PFA current intensity, lesion depth increased significantly with increasing CF. There were no detectable lesions resulting from ablation without electrode contact. Acute PFA ventricular lesions show irreversible and reversible lesion boundaries by triphenyl tetrazolium chloride staining. Electrode-tissue contact is required for effective lesion formation during PFA. At the same PFA dose, lesion depth increases significantly with increasing CF.