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Background: After myocardial infarction (MI), mitral valve (MV) tethering stimulates adaptive leaflet growth, but counterproductive leaflet thickening and fibrosis augment mitral regurgitation (MR), doubling heart failure and mortality. MV fibrosis post-MI is associated with excessive endothelial-to-mesenchymal transition (EMT), driven by transforming growth factor (TGF)-β overexpression. In vitro, losartan-mediated TGF-β inhibition reduces EMT of MV endothelial cells.Objectives: This study tested the hypothesis that profibrotic MV changes post-MI are therapeutically accessible, specifically by losartan-mediated TGF-β inhibition.Methods: The study assessed 17 sheep, including 6 sham-operated control animals and 11 with apical MI and papillary muscle retraction short of producing MR; 6 of the 11 were treated with daily losartan, and 5 were untreated, with flexible epicardial mesh comparably limiting left ventricular (LV) remodeling. LV volumes, tethering, and MV area were quantified by using three-dimensional echocardiography at baseline and at 60 ± 6 days, and excised leaflets were analyzed by histopathology and flow cytometry.Results: Post-MI LV dilation and tethering were comparable in the losartan-treated and untreated LV constraint sheep. Telemetered sensors (n = 6) showed no significant losartan-induced changes in arterial pressure. Losartan strongly reduced leaflet thickness (0.9 ± 0.2 mm vs. 1.6 ± 0.2 mm; p < 0.05; 0.4 ± 0.1 mm sham animals), TGF-β, and downstream phosphorylated extracellular-signal-regulated kinase and EMT (27.2 ± 12.0% vs. 51.6 ± 11.7% α-smooth muscle actin-positive endothelial cells, p < 0.05; 7.2 ± 3.5% sham animals), cellular proliferation, collagen deposition, endothelial cell activation (vascular cell adhesion molecule-1 expression), neovascularization, and cells positive for cluster of differentiation (CD) 45, a hematopoietic marker associated with post-MI valve fibrosis. Leaflet area increased comparably (17%) in constrained and losartan-treated sheep.Conclusions: Profibrotic changes of tethered MV leaflets post-MI can be modulated by losartan without eliminating adaptive growth. Understanding the cellular and molecular mechanisms could provide new opportunities to reduce ischemic MR. [ABSTRACT FROM AUTHOR]

Mitochondrial dysfunction plays a key role in doxorubicin-induced cardiotoxicity (DIC). In this proof-of-principle study, we investigated whether PET mapping of cardiac membrane potential, an indicator of mitochondrial function, could detect an acute cardiotoxic effect of doxorubicin (DOX) in a large animal model. Eight Yucatan pigs were imaged dynamically with [18F](4-Fluorophenyl)triphenylphosphonium ([18F]FTPP+) PET/CT. Our experimental protocol included a control saline infusion into the left anterior descending coronary artery (LAD) followed by a DOX test infusion of either 1 mg/kg or 2 mg/kg during PET. We measured the change in total cardiac membrane potential (ΔΨT), a proxy for the mitochondrial membrane potential, ΔΨm, after the saline and DOX infusions. We observed a partial depolarization of the mitochondria following the DOX infusions, which occurred only in myocardial areas distal to the intracoronary catheter, thereby demonstrating a direct association between the exposure of the mitochondria to DOX and a change in ΔΨT. Furthermore, doubling the DOX dose caused a more severe depolarization of myocardium in the LAD territory distal to the infusion catheter. In conclusion, [18F]FTPP+ PET-based ΔΨT mapping can measure partial depolarization of myocardial mitochondria following intracoronary DOX infusion in a large animal model. [ABSTRACT FROM AUTHOR]

Background--Ischemic mitral regurgitation (MR) is a frequent complication of myocardial infarction associated with left ventricular (LV) dilatation and dysfunction, which doubles mortality. At the molecular level, moderate ischemic MR is characterized by a biphasic response, with initial compensatory rise in prohypertrophic and antiapoptotic signals, followed by their exhaustion. We have shown that early MR repair 30 days after myocardial infarction is associated with LV reverse remodeling. It is not known whether MR repair performed after the exhaustion of compensatory mechanisms is also beneficial. We hypothesized that late repair will not result in LV reverse remodeling. Methods and Results--Twelve sheep underwent distal left anterior descending coronary artery ligation to create apical myocardial infarction and implantation of an LV-to-left atrium shunt to create standardized moderate volume overload. At 90 days, animals were randomized to shunt closure (late repair) versus sham (no repair). LV remodeling was assessed by 3-dimensional echocardiography, dP/dt, preload-recruitable stroke work, and myocardial biopsies. At 90 days, animals had moderate volume overload, LV dilatation, and reduced ejection fraction (all P<0.01 versus baseline, P=NS between groups). Shunt closure at 90 days corrected the volume overload (regurgitant fraction 6±5% versus 27±16% for late repair versus sham, P<0.01) but was not associated with changes in LV volumes (end-diastolic volume 106±15 versus 110±22 mL; end-systolic volume 35±6 versus 36±6 mL) or increases in preload-recruitable stroke work (41±7 versus 39±13 mL mm Hg) or dP/dt (803±210 versus 732±194 mm Hg/s) at 135 days (all P=NS). Activated Akt, central in the hypertrophic process, and signal transducer and activator of transcription 3 (STAT3), a critical node in the hypertrophic stimulus by cytokines, were equally depressed in both groups. Conclusions--Late correction of moderate volume overload after myocardial infarction did not improve LV volume or contractility. Upregulation of prohypertrophic intracellular pathways was not observed. This contrasts with previously reported study in which early repair (30 days) reversed LV remodeling. This suggests a window of opportunity to repair ischemic MR after which no beneficial effect on LV is observed, despite successful repair. [ABSTRACT FROM AUTHOR]

Objectives: We examined whether mitral regurgitation (MR) augments post-myocardial infarction (MI) remodeling. Background: MR doubles mortality after MI, but its additive contribution to left ventricular (LV) remodeling is debated and has not been addressed in a controlled fashion. Methods: Apical MIs were created in 12 sheep, and 6 had an LV-to-left atrial shunt implanted, consistently producing regurgitant fractions of ∼30%. The groups were compared at baseline, 1, and 3 months. Results: Left ventricular end-systolic volume progressively increased by 190% with MR versus 90% without MR (p < 0.02). Pre-load–recruitable stroke work declined by 82 ± 13% versus 25 ± 16% (p < 0.01) with MR, with decreased remote-zone sarcoplasmic reticulum Ca2+-ATPase levels (0.56 ± 0.03 vs. 0.76 ± 0.02, p < 0.001), and decreased isolated myocyte contractility. In remote zones, pro-hypertrophic Akt and gp130 were upregulated in both groups at 1 month, but significantly lower and below baseline in the MR group at 3 months. Pro-apoptotic caspase 3 remained high in both groups. Matrix metalloproteinase (MMP)-13 and membrane-type MMP-1 were increased in remote zones of MR versus infarct-only animals at 1 month, then fell below baseline. The MMP tissue inhibitors rose from baseline to 3 months in all animals, rising higher in the MI + MR–group border zone. Conclusions: In this controlled model, moderate MR worsens post-MI remodeling, with reduced contractility. Pro-hypertrophic pathways are initially upregulated but subsequently fall below infarct-only levels and baseline; with sustained caspase 3 elevation, transformation to a failure phenotype occurs. Extracellular matrix turnover increases in MR animals. Therefore, MR can precipitate an earlier onset of dilated heart failure. [Copyright &y& Elsevier]

Background: Mitral leaflet enlargement has been identified as an adaptive mechanism to prevent mitral regurgitation in dilated left ventricles (LVs) caused by chronic aortic regurgitation (AR). This enlargement is deficient in patients with functional mitral regurgitation, which remains frequent in the population with ischemic cardiomyopathy. Maladaptive fibrotic changes have been identified in post-myocardial infarction (MI) mitral valves. It is unknown if these changes can interfere with valve growth and whether they are present in other valves.Objectives: This study sought to test the hypothesis that MI impairs leaflet growth, seen in AR, and induces fibrotic changes in mitral and tricuspid valves.Methods: Sheep models of AR, AR + MI, and controls were followed for 90 days. Cardiac magnetic resonance, echocardiography, and computed tomography were performed at baseline and 90 days to assess LV volume, LV function, mitral regurgitation and mitral leaflet size. Histopathology and molecular analyses were performed in excised valves.Results: Both experimental groups developed similar LV dilatation and dysfunction. At 90 days, mitral valve leaflet size was smaller in the AR + MI group (12.8 ± 1.3 cm2 vs. 15.1 ± 1.6 cm2, p = 0.03). Mitral regurgitant fraction was 4% ± 7% in the AR group versus 19% ± 10% in the AR + MI group (p = 0.02). AR + MI leaflets were thicker compared with AR and control valves. Increased expression of extracellular matrix remodeling genes was found in both the mitral and tricuspid leaflets in the AR + MI group.Conclusions: In these animal models of AR, the presence of MI was associated with impaired adaptive valve growth and more functional mitral regurgitation, despite similar LV size and function. More pronounced extracellular remodeling was observed in mitral and tricuspid leaflets, suggesting systemic valvular remodeling after MI. [ABSTRACT FROM AUTHOR]

Background: In patients with myocardial infarction (MI), leaflet tethering by displaced papillary muscles induces mitral regurgitation (MR), which doubles mortality. Mitral valves (MVs) are larger in such patients but fibrosis sets in counterproductively. The investigators previously reported that experimental tethering alone increases mitral valve area in association with endothelial-to-mesenchymal transition.Objectives: The aim of this study was to explore the clinically relevant situation of tethering and MI, testing the hypothesis that ischemic milieu modifies mitral valve adaptation.Methods: Twenty-three adult sheep were examined. Under cardiopulmonary bypass, the papillary muscle tips in 6 sheep were retracted apically to replicate tethering, short of producing MR (tethered alone). Papillary muscle retraction was combined with apical MI created by coronary ligation in another 6 sheep (tethered plus MI), and left ventricular remodeling was limited by external constraint in 5 additional sheep (left ventricular constraint). Six sham-operated sheep were control subjects. Diastolic mitral valve surface area was quantified by 3-dimensional echocardiography at baseline and after 58 ± 5 days, followed by histopathology and flow cytometry of excised leaflets.Results: Tethered plus MI leaflets were markedly thicker than tethered-alone valves and sham control subjects. Leaflet area also increased significantly. Endothelial-to-mesenchymal transition, detected as α-smooth muscle actin-positive endothelial cells, significantly exceeded that in tethered-alone and control valves. Transforming growth factor-β, matrix metalloproteinase expression, and cellular proliferation were markedly increased. Uniquely, tethering plus MI showed endothelial activation with vascular adhesion molecule expression, neovascularization, and cells positive for CD45, considered a hematopoietic cell marker. Tethered plus MI findings were comparable with external ventricular constraint.Conclusions: MI altered leaflet adaptation, including a profibrotic increase in valvular cell activation, CD45-positive cells, and matrix turnover. Understanding cellular and molecular mechanisms underlying leaflet adaptation and fibrosis could yield new therapeutic opportunities for reducing ischemic MR. [ABSTRACT FROM AUTHOR]

Background: Ischemic mitral regurgitation (MR) is a frequent complication of myocardial infarction associated with left ventricular (LV) dilatation and dysfunction, which doubles mortality. At the molecular level, moderate ischemic MR is characterized by a biphasic response, with initial compensatory rise in prohypertrophic and antiapoptotic signals, followed by their exhaustion. We have shown that early MR repair 30 days after myocardial infarction is associated with LV reverse remodeling. It is not known whether MR repair performed after the exhaustion of compensatory mechanisms is also beneficial. We hypothesized that late repair will not result in LV reverse remodeling.Methods and Results: Twelve sheep underwent distal left anterior descending coronary artery ligation to create apical myocardial infarction and implantation of an LV-to-left atrium shunt to create standardized moderate volume overload. At 90 days, animals were randomized to shunt closure (late repair) versus sham (no repair). LV remodeling was assessed by 3-dimensional echocardiography, dP/dt, preload-recruitable stroke work, and myocardial biopsies. At 90 days, animals had moderate volume overload, LV dilatation, and reduced ejection fraction (all P<0.01 versus baseline, P=NS between groups). Shunt closure at 90 days corrected the volume overload (regurgitant fraction 6 ± 5% versus 27 ± 16% for late repair versus sham, P<0.01) but was not associated with changes in LV volumes (end-diastolic volume 106 ± 15 versus 110 ± 22 mL; end-systolic volume 35 ± 6 versus 36 ± 6 mL) or increases in preload-recruitable stroke work (41 ± 7 versus 39 ± 13 mL mm Hg) or dP/dt (803 ± 210 versus 732 ± 194 mm Hg/s) at 135 days (all P=NS). Activated Akt, central in the hypertrophic process, and signal transducer and activator of transcription 3 (STAT3), a critical node in the hypertrophic stimulus by cytokines, were equally depressed in both groups.Conclusions: Late correction of moderate volume overload after myocardial infarction did not improve LV volume or contractility. Upregulation of prohypertrophic intracellular pathways was not observed. This contrasts with previously reported study in which early repair (30 days) reversed LV remodeling. This suggests a window of opportunity to repair ischemic MR after which no beneficial effect on LV is observed, despite successful repair. [ABSTRACT FROM AUTHOR]

Purpose: The lipophilic cationic compound, (4-[¹⁸F]fluorophenyl)triphenylphosphonium ion (¹⁸F-FTPP) was synthesized and evaluated as a potential positron emission tomography (PET) myocardial perfusion agent.Procedure: ¹⁸F-FTPP was prepared from (4-nitrophenyl)triphenylphosphonium nitrate and ammonium [¹⁸F]fluoride by nucleophilic aromatic substitution and was purified by high performance liquid chromatography before use. Biodistribution studies were performed in rats at 5, 30, 60 min (five rats per time point). Three rats were evaluated by microPET imaging after injection of ¹⁸F-FTPP. In addition, microPET imaging in rabbits (three) was performed before and after occlusion of the left anterior descending (LAD) artery with ¹³NH₃ (111 MBq) and ¹⁸F-FTPP (74 MBq).Results: Biodistribution data in rats showed rapid blood clearance and high levels of accumulation in the heart; 75:1 heart-to-blood ratio at 30 min. Uptake of radioactivity in the heart was 1.64% ID/G, 1.51% ID/g, and 1.57% ID/g at 5, 30, and 60 min. At 5, 30, and 60 min, lung activity was 0.69% ID/g, 0.03% ID/g, and 0.38% ID/g, and liver uptake was 0.34% ID/g, 0.18% ID/g, and 0.17% ID/g. Heart-to-lung ratios at 5, 30, and 60 min were 2, 5, and 4. Bone accumulation was minimal. MicroPET imaging in both rats and rabbits after injection of ¹⁸F-FTPP demonstrated an initial spike of activity in the myocardium corresponding to blood flow followed by a plateau after 1 min. Region of interest analysis of microPET images of normal and LAD-occluded rabbits with ¹³NH₃ and ¹⁸F-FTPP indicated similar distributions of the two tracers in both normal and altered blood flow regions.Conclusion: The excellent heart-to-blood ratio of ¹⁸F-FTPP and its correlation with ¹³NH₃ distribution in normal and LAD-occluded rabbits suggest that this radiopharmaceutical may have potential as a PET agent for characterizing mitochondrial damage and/or myocardial blood flow. [ABSTRACT FROM AUTHOR]

Effect of Ablation Electrode Contact Force. Introduction: Ablation electrode–tissue contact has been shown to be an important determinant of lesion size and safety during nonirrigated ablation but little data are available during irrigated ablation. We aimed to determine the importance of contact force during irrigated-tip ablation. Methods and Results: Freshly excised hearts from 11 male pigs were perfused and superfused using fresh, heparinized, oxygenated swine blood in an ex vivo model. One-minute ablations were placed using one of 3 different power control strategies (impedance control—15 Ω target impedance drop, and 20 W or 30 W fixed power) and 3 different contact forces (2 g, 20 g, and 60 g) to give a grid of 9 ablation groups. The force sensing catheter (Tacticath™, Endosense SA) was irrigated at 17 mL/min for all of the ablations. Of a total 101 ablations, no thrombus formation was noted but popping was seen in 17 lesions. The lesion depth and incidence of pops was 5.0 ± 1.3 mm /0%, 5.0 ± 1.6 mm /10% and 6.7 ± 2.5 mm /45% for the 15 Ω, 20 W, and 30 W groups (P < 0.01), respectively, and 4.4 ± 1.8 mm /3%, 5.8 ± 1.6 mm /17% and 6.6 ± 2.0 mm /37% for the 2 g, 20 g, and 60 g groups, respectively (P < 0.01). The impedance drop in the first 5 seconds was significantly correlated to catheter contact force: 9.7 ± 9.9 Ω, 22.3 ± 11.0 Ω, and 41.7 ± 22.1 Ω, respectively, for the 2 g, 20 g, and 60 g groups (Pearson's r = 0.65, P < 0.01). Conclusion: Catheter contact force has an important impact on both ablation lesion size and the incidence of pops. (J Cardiovasc Electrophysiol, Vol. pp. 806-811, July 2010) [ABSTRACT FROM AUTHOR]

Steroids have been a cornerstone in renal transplant immunosuppression. New immunosuppressive drugs have led to protocols using early steroid withdrawal or complete avoidance. A prospective protocol in 23 pediatric renal transplant (ages 2–14 yr) who received decreasing steroid doses stopping at day 7 post-Tx, FK, and MMF were compared with a CsA, AZT, historically matched steroid-based control group. Basiliximab was used in two doses. Anthropometric, biochemical variables, AR rates, and CMV infection were evaluated and compared using Student’s t-test and regression analysis. A better growth pattern was seen in steroid withdrawal group. GFR rate and serum glucose were similar in both groups. Total serum cholesterol levels were significantly lower in steroid withdrawal group. The incidence of AR at 12 months was 4.3% in steroid withdrawal group vs. 8.6% in steroid-based group (p = ns). No difference in CMV infection was observed. Hemoglobin levels were low during the first months in both groups; reached normal values after six months. SBP became higher at 12 months in steroid-based group. Patient and graft survival was 98% in both groups at one-yr post-transplant. Early steroid withdrawal was efficacious, safe, and did not increase risk of rejection, preserving optimal growth, renal function, and reducing cardiovascular risk factors. [ABSTRACT FROM AUTHOR]

Objectives: We sought to assess the effect of sildenafil, a highly-specific type 5 phosphodiesterase (PDE5) inhibitor, on platelet-mediated cyclic coronary flow reductions occurring in a canine model of coronary thrombosis despite aspirin therapy. Background: The PDE5 inhibitors augment the antithrombotic effects of nitric oxide in vitro and in vivo, but it has been proposed that the PDE5 inhibitor sildenafil is prothrombotic. Methods: Cyclic coronary flow reductions were induced in the left anterior descending coronary artery by creation of a stenosis, endothelial injury, and thrombus formation followed by treatment with aspirin, heparin, and tissue plasminogen activator. After an initial observation period, dogs were treated with or without sildenafil (100 μg/kg bolus followed by 4 μg/kg/min infusion). Results: Cyclic coronary flow reductions ceased in five of six animals 18 ± 5 min after initiation of sildenafil but continued in all six control animals. The portion of the observation period during which the coronary artery was patent increased from 52 ± 9% to 83 ± 5% after sildenafil administration (p = 0.008) but did not differ between the first and second observation periods in untreated dogs (49 ± 11% vs. 44 ± 11%, respectively). Among animals with plasma free sildenafil levels ≥20 nmol/l, cyclic coronary flow reductions were 73 ± 12% less frequent and the time to cessation of cycling 72 ± 14% shorter than in animals with levels <20 nmol/l (p < 0.05 for both). Sildenafil transiently decreased blood pressure 7 ± 1% but did not change heart rate. Sildenafil treatment reduced ex vivo thrombin-induced platelet aggregation by 39 ± 3% (p < 0.005). Conclusions: Sildenafil improves coronary patency in a canine model of platelet-mediated coronary artery thrombosis, likely via inhibition of platelet aggregation. [Copyright &y& Elsevier]

Abstract: Objective: Diastolic dysfunction is a characteristic finding of the aged mammalian heart. Parvalbumin acts as a Ca2+ sink and enhances relaxation in skeletal muscle, and overexpression of parvalbumin in myocardium increased cardiac relaxation in vitro as well as in vivo. Therefore, the objective of this study is to test the hypothesis that in vivo gene transfer of parvalbumin will improve diastolic dysfunction in aged rat heart. Methods: We used adenovirus to transfer parvalbumin into two different rat models of aging: the Fischer 344 (F344) and the Fischer 344×Brown Norway F1 hybrid (F344×BN). Cardiac function was measured and compared after gene transfer. Results: In vivo overexpression of parvalbumin in both rat aging models had no effect on systolic parameters but reduced left ventricular diastolic pressure and the time course of pressure decline. Overexpression of parvalbumin also improved the force frequency relationship in senescent rats. Conclusion: In vivo overexpression of parvalbumin improves diastolic dysfunction in two rat models of senescence, and this effect is independent of the rat strain investigated. The results show promise that gene therapy of parvalbumin may address the impaired Ca2+ homeostasis and diastolic dysfunction without an increase in energy expenditure. [Copyright &y& Elsevier]

Generation of arachidonic acid by the ubiquitously expressed cytosolic phospholipase A[sub 2] (PLA[sub 2]) has a fundamental role in the regulation of cellular homeostasis, inflammation and tumorigenesis. Here we report that cytosolic PLA[sub 2] is a negative regulator of growth, specifically of striated muscle. We find that normal growth of skeletal muscle, as well as normal and pathologic stress-induced hypertrophic growth of the heart, are exaggerated in Pla2g4a[sup -/-] mice, which lack the gene encoding cytosolic PLA[sub 2]. The mechanism underlying this phenotype is that cytosolic PLA[sub 2] negatively regulates insulin-like growth factor (IGF)-1 signaling. Absence of cytosolic PLA[sub 2] leads to sustained activation of the IGF-1 pathway, which results from the failure of 3-phosphoinositide-dependent protein kinase (PDK)-1 to recruit and phosphorylate protein kinase C (PKC)-ζ, a negative regulator of IGF-1 signaling. Arachidonic acid restores activation of PKC-ζ, correcting the exaggerated IGF-1 signaling. These results indicate that cytosolic PLA[sub 2] and arachidonic acid regulate striated muscle growth by modulating multiple growth-regulatory pathways. [ABSTRACT FROM AUTHOR]

Provides information on a study using a catheter-based technique to achieve highly effective transgene expression in rat heart in vivo. Methodology and materials used to conduct the study; Results of the study.