Injectable Drug-Releasing Microporous Annealed Particle Scaffolds for Treating Myocardial Infarction.

Intramyocardial injection of hydrogels offers great potential for treating myocardial infarction (MI) in a minimally invasive manner. However, traditional bulk hydrogels generally lack microporous structures to support rapid tissue ingrowth and biochemical signals to prevent fibrotic remodeling toward heart failure. To address such challenges, a novel drug-releasing microporous annealed particle (drugMAP) system is developed by encapsulating hydrophobic drug-loaded nanoparticles into microgel building blocks via microfluidic manufacturing. By modulating nanoparticle hydrophilicity and pregel solution viscosity, drugMAP building blocks are generated with consistent and homogeneous encapsulation of nanoparticles. In addition, the complementary effects of forskolin (F) and Repsox (R) on the functional modulations of cardiomyocytes, fibroblasts, and endothelial cells in vitro are demonstrated. After that, both hydrophobic drugs (F and R) are loaded into drugMAP to generate FR/drugMAP for MI therapy in a rat model. The intramyocardial injection of MAP gel improves left ventricular functions, which are further enhanced by FR/drugMAP treatment with increased angiogenesis and reduced fibrosis and inflammatory response. This drugMAP platform represents a new generation of microgel particles for MI therapy and will have broad applications in regenerative medicine and disease therapy.

Combining Desorption Electrospray Ionization Mass Spectrometry Imaging and Machine Learning for Molecular Recognition of Myocardial Infarction.

Lipid profile changes in heart muscle have been previously linked to cardiac ischemia and myocardial infarction, but the spatial distribution of lipids and metabolites in ischemic heart remains to be fully investigated. We performed desorption electrospray ionization mass spectrometry imaging of hearts from in vivo myocardial infarction mouse models. In these mice, myocardial ischemia was induced by blood supply restriction via a permanent ligation of left anterior descending coronary artery. We showed that applying the machine learning algorithm of gradient boosting tree ensemble to the ambient mass spectrometry imaging data allows us to distinguish segments of infarcted myocardium from normally perfused hearts on a pixel by pixel basis. The machine learning algorithm selected 62 molecular ion peaks important for classification of each 200 µm-diameter pixel of the cardiac tissue map as normally perfused or ischemic. This approach achieved very high average accuracy (97.4%), recall (95.8%), and precision (96.8%) at a spatial resolution of ∼200 µm. In addition, we determined the chemical identity of 27 species, mostly small metabolites and lipids, selected by the algorithm as the most significant for cardiac pathology classification. This molecular signature of myocardial infarction may provide new mechanistic insights into cardiac ischemia, assist with infarct size assessment, and point toward novel therapeutic interventions.

Immuno-modification of enhancing stem cells targeting for myocardial repair.

Despite the controversy in mechanism, rodent and clinical studies have demonstrated beneficial effects of stem/progenitor cell therapy after myocardial infarction (MI). In a rat ischaemic reperfusion MI model, we investigated the effects of immunomodification of CD 34(+) cells on heart function and myocardial conduction. Bispecific antibody (BiAb), consisting of an anti-myosin light chain antibody and anti-CD45 antibody, injected intravenously was used to direct human CD34(+) cells to injured myocardium. Results were compared to echocardiography guided intramyocardial (IM) injection of CD34(+) cells and PBS injected intravenously. Treatment was administered 2 days post MI. Echocardiography was performed at 5 weeks and 3 months which demonstrated LV dilatation prevention and fractional shortening improvement in both the BiAb and IM injection approaches, with BiAb achieving better results. Histological analyses demonstrated a decrease in infarct size and increase in arteriogenesis in both BiAb and IM injection. Electrophysiological properties were studied 5 weeks after treatments by optical mapping. Conduction velocity (CV), action potential duration (APD) and rise time were significantly altered in the MI area. The BiAb treated group demonstrated a more normalized activation pattern of conduction and normalization of CV at shorter pacing cycle lengths. The ventricular tachycardia inducibility was lowest in the BiAb treatment group. Intravenous administration of BiAb offers an effective means of stem cell delivery for myocardial repair post-acute MI. Such non-invasive approach was shown to offer a distinct advantage to more invasive direct IM delivery.

Delivery of lipid micelles into infarcted myocardium using a lipid-linked matrix metalloproteinase targeting peptide.

There is a great need for delivery strategies capable of efficiently localizing drugs to the damaged myocardium that do not require direct intramyocardial injection of therapeutic molecules. In the work discussed here, we exploited the myocardium-specific upregulation of matrix metalloproteinases (MMPs) that occurs during myocardium remodeling by designing a micellar vehicle containing an MMP-targeting peptide (MMP-TP). The binding of MMP-TP to MMP was evaluated with purified MMP-2 protein and U-937 cells induced to overexpress MMP. Inhibition of MMP-2 activity was not observed in the presence of unmodified micelles but was pronounced at a 5 mol % MMP-TP ligand density. In a FACS analysis, MMP-TP micelles containing 5 mol % of the MMP-targeting peptide showed ∼10-fold higher binding to activated U937 cells than plain micelles and micelles containing a control peptide with two amino acid replacements. MMP-TP-micelles and plain micelles were injected intravenously into C57BL/6 mice 1, 3, and 7 days after the induction of a myocardial infarction (MI). Immunohistochemistry performed on heart tissue sections revealed that MMP-TP-micelles colocalize with both MMP and infiltrating macrophages. MMP-TP micelles showed significantly enhanced accumulation to the necrotic area of the heart after MI on days 3 and 7 when compared to plain micelles and negative control peptide micelles. This is coincident with the measured temporal profile of MMP gene expression in the heart after MI. These results suggest that MMP-TP micelles are candidates for the development of targeted regenerative heart therapeutics because of their ability to target the infarcted myocardium in a MMP dependent manner.

Brief exposure to secondhand smoke reversibly impairs endothelial vasodilatory function.

INTRODUCTION: We sought to determine the effects of brief exposures to low concentrations of tobacco secondhand smoke (SHS) on arterial flow-mediated dilation (FMD, a nitric oxide-dependent measure of vascular endothelial function), in a controlled animal model never before exposed to smoke. In humans, SHS exposure for 30 min impairs FMD. It is important to gain a better understanding of the acute effects of exposure to SHS at low concentrations and for brief periods of time. METHODS: We measured changes in FMD in rats exposed to a range of real-world levels of SHS for durations of 30 min, 10 min, 1 min, and 4 breaths (roughly 15 s). RESULTS: We observed a dose-response relationship between SHS particle concentration over 30 min and post-exposure impairment of FMD, which was linear through the range typically encountered in smoky restaurants and then saturated at higher concentrations. One min of exposure to SHS at moderate concentrations was sufficient to impair FMD. CONCLUSIONS: Brief SHS exposure at real-world levels reversibly impairs FMD. Even 1 min of SHS exposure can cause reduction of endothelial function.

CD45-positive cells are not an essential component in cardiosphere formation.

The cardiosphere (CS) is composed of a heterogeneous population of cells, including CD45(+) cells that are bone marrow (BM)-derived. However, whether the CD45(+) cells are an essential cell component in CS formation is unknown. The current study was undertaken to address this question. Cardiospheres (CSs) were harvested from 1-week post-myocardial infarction (MI) or non-MI hearts of C57BL/6 J mice. The process of CS formation was observed by timelapse photography. To analyze the role of BM-derived CD45(+) cells in CS formation, CD45(+) cells were depleted from populations of CS-forming cells by immunomagnetic beads. We recorded the number of CSs formed in culture from the same amount (10(5)) of intact CS-forming cells, from CD45(+)-cell-depleted CS-forming cells and from CD45(+) cells alone (n=6-9/cell type). CS-forming cells selectively aggregated together to form CSs by 35 h after plating. The depletion of CD45(+) cells from CS-forming cells actually increased the formation of CSs (67±10 CSs/10(5) cells) compared with non-depleted CS-forming cells (51±6 CSs/10(5) cells, P<0.0001). Purified CD45(+) cells from CS-forming cells did not form CSs in culture. Thus, BM-derived CD45(+) cells including BM progenitors are neither necessary nor sufficient for CS formation.

Myocardial improvement with human embryonic stem cell-derived cardiomyocytes enriched by p38MAPK inhibition.

BACKGROUND AIMS: We have shown previously that inhibition of the p38 mitogen-activated protein kinase (p38MAPK) directs the differentiation of human embryonic stem cell (hESC)-derived cardiomyocytes (hCM). We investigated the therapeutic benefits of intramyocardial injection of hCM differentiated from hESC by p38MAPK inhibition using closed-chest ultrasound-guided injection at a clinically relevant time post-myocardial infarction (MI) in a mouse model. METHODS: MI was induced in mice and the animals treated at day 3 with: (a) hCM, (b) human fetal fibroblasts (hFF) as cell control, or (c) medium control (n = 10 animals/group). Left ventricular ejection fraction (LVEF) was evaluated post-MI prior to therapy, and at days 28 and 60 post-cell therapy. Hearts were analyzed at day 60 for infarct size, angiogenesis, cell fate and teratoma formation. RESULTS: LVEF was improved in the hCM-treated animals compared with both hFF and medium control-treated animals at day 28 (39.03 ± 1.79% versus 27.89 ± 1.27%, P < 0.05, versus 32.90 ± 1.46%, P < 0.05, respectively), with sustained benefit until day 60. hCM therapy resulted in significantly smaller scar size, increased capillary bed area, increased number of arterioles, less native cardiomyocyte (CM) apoptosis, and increased CM proliferation compared with the other two groups. These benefits were achieved despite a very low retention rate of the injected cells at day 60, as assessed by immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR). Therapy with hCM did not result in intramyocardial teratoma formation at day 60. CONCLUSIONS: This study demonstrates that hCM derived from p38MAPK-treated hESC have encouraging therapeutic potential.

Second hand smoke stimulates tumor angiogenesis and growth.

Exposure to second hand smoke (SHS) is believed to cause lung cancer. Pathological angiogenesis is a requisite for tumor growth. Lewis lung cancer cells were injected subcutaneously into mice, which were then exposed to sidestream smoke (SHS) or clean room air and administered vehicle, cerivastatin, or mecamylamine. SHS significantly increased tumor size, weight, capillary density, VEGF and MCP-1 levels, and circulating endothelial progenitor cells (EPC). Cerivastatin (an inhibitor of HMG-coA reductase) or mecamylamine (an inhibitor of nicotinic acetylcholine receptors) suppressed the effect of SHS to increase tumor size and capillary density. Cerivastatin reduced MCP-1 levels, whereas mecamylamine reduced VEGF levels and EPC. These studies reveal that SHS promotes tumor angiogenesis and growth. These effects of SHS are associated with increases in plasma VEGF and MCP-1 levels, and EPC, mediated in part by isoprenylation and nicotinic acetylcholine receptors.

Treatment of pulmonary arterial hypertension with circulating angiogenic cells.

Despite advances in the treatment of pulmonary arterial hypertension, a truly restorative therapy has not been achieved. Attention has been given to circulating angiogenic cells (CACs, also termed early endothelial progenitor cells) because of their ability to home to sites of vascular injury and regenerate blood vessels. We studied the efficacy of human CAC therapy in the treatment of pulmonary arterial hypertension at two different stages of disease severity. Cells were isolated from peripheral blood and administered to nude rats on day 14 ("early") or day 21 ("late") after monocrotaline injection. The control group received monocrotaline but no cell treatment. Disease progression was assessed using right heart catheterization and echocardiography at multiple time points. Survival differences, right ventricular hypertrophy (RVH), and vascular hypertrophy were analyzed at the study endpoint. Quantitative PCR was performed to evaluate cell engraftment. Treatment with human CACs either at the early or late time points did not result in increased survival, and therapy did not prevent or reduce the severity of disease compared with control. Histological analysis of RVH and vascular muscularization showed no benefit with therapy compared with control. No detectable signal was seen of human transcript in transplanted lungs at 14 or 21 days after cell transplant. In conclusion, CAC therapy was not associated with increased survival and did not result in either clinical or histological benefits. Future studies should be geared toward either earlier therapeutic time points with varying doses of unmodified CACs or genetically modified cells as a means of delivery of factors to the pulmonary arterial circulation.

Injection of bone marrow cell extract into infarcted hearts results in functional improvement comparable to intact cell therapy.

We compared therapeutic benefits of intramyocardial injection of unfractionated bone marrow cells (BMCs) versus BMC extract as treatments for myocardial infarction (MI), using closed-chest ultrasound-guided injection at a clinically relevant time post-MI. MI was induced in mice and the animals treated at day 3 with either: (i) BMCs from green fluorescent protein (GFP)-expressing mice (n = 14), (ii) BMC extract (n = 14), or (iii) saline control (n = 14). Six animals per group were used for histology at day 6 and the rest followed to day 28 for functional analysis. Ejection fraction was similarly improved in the BMC and extract groups versus control (40.6 +/- 3.4 and 39.1 +/- 2.9% versus 33.2 +/- 5.0%, P < 0.05) with smaller scar sizes. At day 6 but not day 28, both therapies led to significantly higher capillary area and number of arterioles versus control. At day 6, BMCs increased the number of cycling cardiomyocytes (CMs) versus control whereas extract therapy resulted in significant reduction in the number of apoptotic CMs at the border zone (BZ) versus control. Intracellular components within BMCs can enhance vascularity, reduce infarct size, improve cardiac function, and influence CM apoptosis and cycling early after therapy following MI. Intact cells are not necessary and death of implanted cells may be a major component of the benefit.

Standard peak-to-peak bipolar voltage amplitude criteria underestimate myocardial scar during substrate mapping with a novel microelectrode catheter.

BACKGROUND: Ventricular bipolar voltage values <0.5 and <1.0/1.5 mV (epi- and endocardium) correlating with dense scar and border zone, respectively, were established using a 3.5-mm tip catheter. Novel microelectrode catheters promise improved mapping resolution; however, whether standard voltage criteria apply to catheters with smaller electrode size and interelectrode distance remains unclear. OBJECTIVE: The purpose of this study was to determine whether traditional bipolar voltage criteria for scar apply during substrate mapping with a microelectrode catheter. METHODS: Paired bipolar and microbipolar voltage values were acquired from control swine (n = 2) using the microelectrode catheter and assessed for systemic differences. In a postinfarction swine model (n = 6), scar characteristics were compared between the bipolar maps and microbipolar maps using both standard and adjusted voltage criteria derived from the control animals. RESULTS: In control swine, although 5th percentile values for bipolar and microbipolar voltage were similar (1.12 vs 1.22 mV [left ventricular (LV) endo]; 0.88 mV vs 0.98 mV [epi]), median values were significantly greater when acquired by microbipolar electrodes (3.60 vs 6.76 mV, P = .002 [LV endo]; 2.61 vs 2.72 mV, P = .02 [epi]). Microbipolar values were systematically larger by 2.0× and 1.4× in the LV endocardium and epicardium, respectively. Application of standard voltage values to microbipolar maps in postinfarct swine underestimated scar area by approximately 41% in the LV endocardium (13.7 vs 33.4 cm2, P = .004). CONCLUSION: Bipolar voltage values acquired from microelectrodes are systemically larger than those acquired from standard catheters. New reference values should be established for these novel catheters.

Site-Specific Epicardium-to-Endocardium Dissociation of Electrical Activation in a Swine Model of Atrial Fibrillation.

OBJECTIVES: This study sought to define the extent and spatial distribution of endocardial-epicardial dissociation (EED) in a swine model. BACKGROUND: The mechanisms underlying persistent atrial fibrillation (AF) remain unclear. METHODS: Sixteen swine underwent simultaneous endocardial and epicardial mapping using 32-electrode grid catheters. This included 6 swine with rapid atrial pacing-induced atrial remodeling. Three right atrial (RA) and 3 left atrial (LA) regions were mapped during sinus rhythm, atrial pacing, acute or persistent AF, and AF in the presence of pericardial acetylcholine. Unipolar electrogram recordings over 10-s epochs underwent offline phase analysis using customized software. Regional activation patterns on paired surfaces and the instantaneous phase at each matched electrode location were analyzed. EED was defined as paired electrodes out of phase by ≥20 ms. RESULTS: The mean distance between matched endocardial-epicardial electrode pairs was 4.4 ± 1.8 mm. During episodes of AF, rotational activations with ≥3 full rotations were not seen. EED was seen during 34.4 ± 16.4% of mapped time periods: LA > RA, persistent > acute AF in the LA, and acetylcholine-induced > acute AF in both atria (p < 0.05 for each). Most marked EED in persistent AF was in the LA appendage (47.2 ± 3.7%) and the LA posterior wall (50.3 ± 4.7%). CONCLUSIONS: Marked EED was seen in a swine model of AF, particularly during persistent AF. There was significantly more EED in the LA than the RA and, particularly, in the LA PW and LAA. Mapping approaches limited to the endocardium may not sufficiently characterize the complexity of AF.

Dyssynchrony and Fibrosis Persist After Resolution of Cardiomyopathy in a Swine Premature Ventricular Contraction Model.

OBJECTIVES: This study sought to prospectively study the development and then regression of premature ventricular contraction (PVC)-induced cardiomyopathy, with the hypothesis that structural left ventricular (LV) changes that are of potential clinical significance may endure beyond the period of exposure to PVCs. BACKGROUND: Recovery of LV function after eradication of PVCs in PVC-induced cardiomyopathy is incompletely defined. METHODS: Fifteen swine were exposed to: 1) 50% paced PVCs from the LV lateral epicardium for 12 weeks (LV PVC, n = 5); 2) no pacing for 12 weeks (Control, n = 5); or 3) 50% paced LV PVCs for 12 weeks followed by pacing cessation for 4 weeks (Recovery, n = 5). LV function was quantified biweekly in sinus rhythm with echocardiography. Dyssynchrony was measured from pressure-volume loops at baseline and terminal studies. LV fibrosis was quantified after sacrifice. RESULTS: LV ejection fraction during sinus rhythm fell between baseline and terminal studies in the LV PVC group (65.8 ± 3.0 to 39.3 ± 3.2; p < 0.05), whereas there was no significant change in the Control group (69.6 ± 3.0 to 72.2 ± 3.0; p = NS) or after Recovery (64.5 ± 3.4% to 61.4 ± 3.4%; p = NS) groups. There was a significant increase in LV dyssynchrony measured during sinus rhythm between baseline and terminal studies in the LV PVC group (4.0 ± 1.5% to 9.0 ± 1.5%; p < 0.05); there was a similar increase in dyssynchrony that persisted 4 weeks after PVC cessation in the Recovery group (4.4 ± 1.7% to 12.8 ± 1.7%; p < 0.05). After sacrifice, percent fibrosis was higher in the LV PVC group compared with Control (5.7 ± 0.3% vs. 3.0 ± 0.3%; p < 0.05) and remained elevated in Recovery (4.1 ± 0.3% vs. 3.0 ± 0.3%; p < 0.05) despite return to baseline LV ejection fraction. CONCLUSIONS: In a swine model of PVC-induced cardiomyopathy, cessation of PVCs for 4 weeks leads to normalization of LV systolic function but significant changes in myocardial fibrosis and LV dyssynchrony during sinus rhythm persist.

Development of Injectable Amniotic Membrane Matrix for Postmyocardial Infarction Tissue Repair.

Ischemic heart disease represents the leading cause of death worldwide. Heart failure following myocardial infarction (MI) is associated with severe fibrosis formation and cardiac remodeling. Recently, injectable hydrogels have emerged as a promising approach to repair the infarcted heart and improve heart function through minimally invasive administration. Here, a novel injectable human amniotic membrane (hAM) matrix is developed to enhance cardiac regeneration following MI. Human amniotic membrane is isolated from human placenta and engineered to be a thermoresponsive, injectable gel around body temperature. Ultrasound-guided injection of hAM matrix into rat MI hearts significantly improves cardiac contractility, as measured by ejection fraction (EF), and decrease fibrosis. The results of this study demonstrate the feasibility of engineering as an injectable hAM matrix and its efficacy in attenuating degenerative changes in cardiac function following MI, which may have broad applications in tissue regeneration.

Reevaluation of the role of VEGF-B suggests a restricted role in the revascularization of the ischemic myocardium.

OBJECTIVE: The endogenous role of the VEGF family member vascular endothelial growth factor-B (VEGF-B) in pathological angiogenesis remains unclear. METHODS AND RESULTS: We studied the role of VEGF-B in various models of pathological angiogenesis using mice lacking VEGF-B (VEGF-B(-/-)) or overexpressing VEGF-B(167). After occlusion of the left coronary artery, VEGF-B deficiency impaired vessel growth in the ischemic myocardium whereas, in wild-type mice, VEGF-B(167) overexpression enhanced revascularization of the infarct and ischemic border zone. By contrast, VEGF-B deficiency did not affect vessel growth in the wounded skin, hypoxic lung, ischemic retina, or ischemic limb. Moreover, VEGF-B(167) overexpression failed to enhance vascular growth in the skin or ischemic limb. CONCLUSIONS: VEGF-B appears to have a relatively restricted angiogenic activity in the ischemic heart. These insights might offer novel therapeutic opportunities.

Left Ventricular Dyssynchrony Predicts the Cardiomyopathy Associated With Premature Ventricular Contractions.

BACKGROUND: The pathophysiology of cardiomyopathy associated with premature ventricular contractions (PVCs) remains unclear. OBJECTIVES: This study prospectively explored cardiomyopathy development in a swine model of paced ectopic beats. METHODS: A total of 35 swine underwent pacemaker implantation. A group exposed to paced bigeminy from the right ventricular apex (RVA) for 14 weeks (RVA PVC) (n = 10) were compared with a group exposed to regular pacing from the RVA at 140 beats/min (RV-140) (n = 5) and a control group (n = 5). To test the role of ectopic beat dyssynchrony, further groups were exposed for 12 weeks to bigeminy from the right ventricular free wall (RVFW PVC) (n = 5), the left ventricular epicardium (LV Epi PVC) (n = 5) or the right atrium (premature atrial complex) (n = 5). RESULTS: After 14 weeks, the mean left ventricular ejection fraction (LVEF) was significantly lower in the RVA PVC group than in the RV-140 or control groups (p < 0.05). LVEF declined significantly in the LV Epi PVC (65.2 ± 2.4% to 39.7 ± 3.0%; p < 0.01) and RVFW PVC (66.1 ± 2.6% to 48.6 ± 2.7%; p < 0.01) groups, with final LVEF significantly lower and ventricular fibrosis significantly higher in the LV Epi PVC group compared with all others (p < 0.05). Protein levels of pRyR2, NCX-1, CaMKII-α, and PLN were up-regulated and levels of SERCA2a were down-regulated in the LV Epi PVC group compared with the control group (p < 0.05). Longer ectopic beat QRS duration and greater LV dyssynchrony were significantly associated with larger declines in LV systolic function. CONCLUSIONS: In a swine model of paced ectopic beats, PVC-induced cardiomyopathy is phenotypically distinct from a tachycardia-induced cardiomyopathy. Cardiomyopathy severity is strongly associated with severity of the hemodynamic derangement associated with the paced ectopic beats, particularly the extent of LV dyssynchrony.

Injectable hyaluronic acid based microrods provide local micromechanical and biochemical cues to attenuate cardiac fibrosis after myocardial infarction.

Repairing cardiac tissue after myocardial infarction (MI) is one of the most challenging goals in tissue engineering. Following ischemic injury, significant matrix remodeling and the formation of avascular scar tissue significantly impairs cell engraftment and survival in the damaged myocardium. This limits the efficacy of cell replacement therapies, demanding strategies that reduce pathological scarring to create a suitable microenvironment for healthy tissue regeneration. Here, we demonstrate the successful fabrication of discrete hyaluronic acid (HA)-based microrods to provide local biochemical and biomechanical signals to reprogram cells and attenuate cardiac fibrosis. HA microrods were produced in a range of physiological stiffness and shown to degrade in the presence of hyaluronidase. Additionally, we show that fibroblasts interact with these microrods in vitro, leading to significant changes in proliferation, collagen expression and other markers of a myofibroblast phenotype. When injected into the myocardium of an adult rat MI model, HA microrods prevented left ventricular wall thinning and improved cardiac function at 6 weeks post infarct.

Myocardial infarct size measurement in the mouse chronic infarction model: comparison of area- and length-based approaches.

Efficacy of potential treatments for myocardial infarction (MI) is commonly assessed by histological measurement of infarct size in rodent models. In experiments involving an acute MI setting, measurement of the infarcted area in tissue sections of the left ventricle is a standard approach to determine infarct size. This approach has also been used in the chronic infarct setting to measure infarct area several weeks post-MI. We tested the hypothesis that, because wall thinning is known to occur in the chronic setting, the area measurement approach would be less appropriate. We compared infarct measurements in tissue sections based on 1) infarct area, 2) epicardial and endocardial infarct arc lengths, and 3) midline infarct arc length. Infarct sizes from all three measurement approaches correlated significantly with left ventricular ejection fraction and wall motion abnormality. However, the infarct size values derived from the area measurement approach were significantly smaller than those from the other two measurement approaches, and the range of values obtained was compressed 0.4-fold. The midline method allowed detection of the expected size differences between infarcts of variable severity resulting from proximal vs. distal ligation of the coronary artery. Segmental infarct size was correlated with segmental wall motion abnormality. We conclude that both area- and length-based measurements can be used to determine relative infarct size over a wide range of severity, although the area-based measurements are substantially more compressed due to wall thinning, and that the estimation of infarct midlines is a simple, reliable approach to infarct size assessment.

Aging is protective against pressure overload cardiomyopathy via adaptive extracellular matrix remodeling.

When challenged by hemodynamic stress, aging hearts respond differently to young hearts. Preclinical models of heart disease should take into account the effects of age. However, in the transverse aortic constriction (TAC) model of pressure-overload cardiomyopathy, the larger aorta of aging mice has not previously been taken into account. First, we studied the aortic size in mice, and found that the aortic cross-sectional area (CSA) is 28% larger in aging mice than in young adult mice (P=0.001). We then performed TAC to make the same proportional reduction in CSA in young and aging mice. This produced the same pressure gradient across the constriction and the same rise in B-type natriuretic peptide expression. Young mice showed acute deterioration in systolic function assessed by pressure-volume loops, progressive LV remodeling on echocardiography, and a 50% mortality at 12 weeks post-TAC. In contrast, aging mice showed no acute deterioration in systolic function, much less ventricular remodeling and were protected from death. Aging mice also showed significantly increased levels of matrix metalloproteinase-3 (MMP-3; 3.2 fold increase, P<0.001) and MMP-12 (1.5-fold increase, P<0.001), which were not seen in young mice. Expression of tissue inhibitor of MMP-1 (TIMP-1) increased 8.6-fold in aging hearts vs 4.3-fold in young hearts (P<0.01). In conclusion, following size-appropriate TAC, aging mice exhibit less LV remodeling and lower mortality than young adult mice. This is associated with induction of protective ECM changes.

Diffuse fibrosis leads to a decrease in unipolar voltage: Validation in a swine model of premature ventricular contraction-induced cardiomyopathy.

BACKGROUND: Frequent premature ventricular contractions (PVCs) may lead to dilated cardiomyopathy. A leftward shift in the unipolar voltage distribution in patients with cardiomyopathy has also been described and attributed to increased fibrosis. OBJECTIVES: We established a swine model of PVC-induced cardiomyopathy and assessed (1) whether an increase in left ventricular fibrosis occurs and (2) whether increased fibrosis leads to a leftward shift in the unipolar voltage distribution. METHODS: Ten swine underwent implantation of ventricular pacemakers; 6 programmed to deliver a 50% PVC burden and 4 controls without pacing. Voltage maps were acquired at baseline and after 14 weeks of ventricular bigeminy. RESULTS: In the PVC group, left ventricular ejection fraction decreased from 67% ± 7% to 44% ± 15% (P < .05) with no change in controls (71% ± 6% to 73% ± 4%; P = .56). The fifth percentile of the bipolar and unipolar voltage distribution at baseline was 1.63 and 5.36 mV, respectively. In the control group, after 14 weeks of pacing there was no significant change in % bipolar voltage <1.5 mV (pre 1.2% vs post 2.2%; P = .34) or % unipolar voltage <5.5 mV (pre 4.0% vs post 3.5%; P = .20). In the PVC group, there was a significant increase in % unipolar voltage <5.5 mV (5.4% vs 12.6%; P < .01), with a leftward shift in the unipolar voltage distribution. Histologically, % fibrosis was increased in the PVC group (control 1.8% ± 1.3% vs PVC 3.4% ± 2.6%; P < .01). CONCLUSION: PVC-induced cardiomyopathy in swine leads to an increase in interstitial fibrosis and a leftward shift in the unipolar voltage distribution. These findings are consistent with findings in humans with PVC-induced cardiomyopathy.