Canine Myocardial Infarction Research Articles

Long-Term Stimulation of the Left Dorsal Branch of the Thoracic Nerve Improves Ventricular Electrical Remodeling in a Canine Model of Chronic Myocardial Infarction.

To evaluate the ventricular electrophysiologic effects of long-term stimulation of the left dorsal branch of thoracic nerve (LDTN) derived from the left stellate ganglion (LSG) in a canine model of chronic myocardial infarction (MI). Seventeen adult male beagles were randomly divided into three groups: the sham group (sham operated, n = 6), the MI group (n = 6), and the MI + LDTN group (MI plus LDTN stimulation, n = 5). The canine model of chronic MI was induced by the occlusion of the left anterior descending artery (LADO). The LDTN was separated and intermittently stimulated immediately after LADO for 2months. The heart rate variability (HRV) analysis, in vivo electrophysiology, the evaluation of LSG function and neural activity, histological staining, and western blotting (WB) assay were performed to evaluate the effect of LDTN stimulation on the heart. The canine MI model was successfully established by LADO, and the LDTN was separated and stimulated immediately after LADO. The HRV analysis showed that LDTN stimulation reversed the increased LF value and LF/HF ratio of the MI group. LDTN stimulation prolonged the shortening ERP and APD90, decreased the dispersion of ERP and APD90, and increased the VFT. Additionally, LDTN stimulation inhibits the LSG function and neural activity. Furthermore, LDTN stimulation suppressed the activation of Wnt/β-catenin signaling, which contributed to the LSG neuronal apoptosis by upregulation of pro-apoptotic Bax and downregulation of anti-apoptotic Bcl-2. LDTN stimulation could attenuate cardiac sympathetic remodeling and improve ventricular electrical remodeling, which may be mediated by suppressing the activated Wnt/β-catenin signaling pathway and then promoting the LSG neuronal apoptosis.

Transthoracic ultrasound-guided percutaneous intramyocardial injection combined with ultrasound-targeted microbubble destruction-mediated angiogenin 1 gene therapy in canine myocardial infarction model.

Intravenous (IV) ultrasound-targeted microbubble destruction (UTMD) has made distinct but limited progress in gene transfected therapy. Intramyocardial (IM) injection also has some effect. In this study, IM injection could be performed under the guidance of transthoracic ultrasound without thoracotomy. We aimed to evaluate the effect of combination transthoracic ultrasound-guided percutaneous IM injection and UTMD for mediating the angiogenin 1 (Ang1) gene therapy in myocardial infarction (MI) canines. Forty-two canines were divided into four groups: IM-UTMD group (intramyocardial injection of the negative control plasmid with UTMD as the sham group); IM-Ang1 group (intramyocardial injection of the Ang1 plasmid without UTMD); IM-Ang1-UTMD group (intramyocardial injection of the Ang1 plasmid with UTMD); and IV-Ang1-UTMD group (intravenous injection of the Ang1 plasmid with UTMD). The FITC green fluorescence and Ang1 protein in myocardial tissue were used for the distribution of Ang1 gene. Left ventricular dimension and systolic function were observed by echocardiography. The Masson's and Sirius Red's staining were used for evaluating the collagen fiber. The immunohistochemistry for CD31 and alpha-smooth muscle actin (α-SMA) were as the indicators of microvasculature. Myocardial contrast echocardiography was used to reflect the microvascular perfusion. More FITC-labeled plasmid was observed in the three IM injection groups than in the IV-Ang1-UTMD group, and the Ang1 protein expression was higher in the IM-Ang1-UTMD group. One month later, no significant differences in survival rate and complications were observed among all four groups. Although there were no differences in the left ventricular end-diastolic diameter among the 4 groups, the left ventricular end-systolic diameter was lower in the IM-Ang1-UTMD group than in the other groups. Then, the left ventricular ejection fraction was increased in the IM-Ang1-UTMD group, with lower collagen fiber percentage, higher blood vessel density and myocardial reperfusion intensity than those in the other groups (P<0.05). Transthoracic ultrasound-guided percutaneous IM injection combined with UTMD is a safe and effective method for mediating Ang1 plasmid therapy in MI canines.

Myocardial tissue characterization by combining late gadolinium enhancement imaging and percent edema mapping: a novel T2 map-based MRI method in canine myocardial infarction

BackgroundAssessing the extent of ischemic and reperfusion-associated myocardial injuries remains challenging with current magnetic resonance imaging (MRI) techniques. Our aim was to develop a tissue characterization mapping (TCM) technique by combining late gadolinium enhancement (LGE) with our novel percent edema mapping (PEM) approach to enable the classification of tissue represented by MRI voxels as healthy, myocardial edema (ME), necrosis, myocardial hemorrhage (MH), or scar.MethodsSix dogs underwent closed-chest myocardial infarct (MI) generation. Serial MRI scans were performed post-MI on days 3, 4, 6, 14, and 56, including T2 mapping and LGE. Dogs were sacrificed on day 4 (n = 4, acute MI) or day 56 (n = 2, chronic MI). TCMs were generated based on a voxel classification algorithm taking into account signal intensity from LGE and T2-based estimation of ME. TCM-based MI and MH were validated with post mortem triphenyl tetrazolium chloride (TTC) staining. Pearson’s correlation and Bland-Altman analyses were performed.ResultsThe MI, ME, and MH measured by TCM were 13.4% [25th–75th percentile 1.6–28.8], 28.1% [2.1–37.5] and 4.3% [1.0–11.3], respectively. TCM measured higher MH and MI compared to TTC (p = 0.0033 and p = 0.0007, respectively). MH size was linearly correlated with MI size by both MRI (r = 0.9528, p < 0.0001) and TTC (r = 0.9625, p < 0.0001). MH quantification demonstrated good agreement between TCM and TTC (r = 0.8766, p < 0.0001, 2.4% overestimation by TCM). A similar correlation was observed for MI size (r = 0.9429, p < 0.0001, 6.1% overestimation by TCM).ConclusionsPreliminary results suggest that the TCM method is feasible for the in vivo localization and quantification of various MI-related tissue components.

Enhancement of Angiogenesis by Ultrasound-Targeted Microbubble Destruction Combined with Nuclear Localization Signaling Peptides in Canine Myocardial Infarction.

Objective This study aimed to develop a gene delivery system using ultrasound-targeted microbubbles destruction (UTMD) combined with nuclear localization signal (NLS) and investigate its efficacy and safety for therapeutic angiogenesis in canine myocardial infarction (MI) model. Methods Fifty MI dogs were randomly divided into 5 groups and transfected with Ang-1 gene plasmid: (i) group A: only injection of microbubbles and Ang-1 plasmid; (ii) group B: only UTMD mediated gene transfection; (iii) group C: UTMD combined with classical NLS mediated gene transfection; (iv) group D: UTMD combined with mutational NLS mediated transfection; and (v) group E: UTMD combined with classical NLS in the presence of a nucleus transport blocker. The mRNA and protein expression of Ang-1 gene, microvessel density (MVD) cardiac troponin I (cTnI), and cardiac function were determined after transfection. Results The expression of mRNA and protein of Ang-1 gene in group C was significantly higher than that of the other groups (all P < 0.01). The MVD of group C was 10.2-fold of group A and 8.1-fold of group E (P < 0.01). The cardiac function in group C was significant improvement without cTnI rising. Conclusions The gene delivery system composed of UTMD and NLS is efficient and safe.

Effect of salvianolic acid A on anesthetized canine experimental myocardial infarction

Salvianolic acid A (SAA), one of the major active water-soluble salvianolic acids of traditional Chinese medicine Salvia miltiorrhiza Bunge, has been reported to be effective on anti-myocardial ischemia, anti-oxidation and anti-thrombus. This study aimed to investigate appropriate administration route on dogs with acute myocardial ischemia(AMI). Twenty-four dogs were randomized into four groups (n=6), model, oral administration of SAA (8 mg•kg⁻¹), intravenous administration of SAA (4 mg•kg⁻¹), intravenous administration of Herbesser(0.5 mg•kg⁻¹) as positive drug group. AMI model was established by ligating left anterior descending coronary arteries(LAD) of dogs. Changes of ST segment were determined by epicardial electrocardiogram(ECG), coronary blood flow (CBF) and myocardial oxygen consumption were measured by ultrasonic Doppler flow meter, serum creatine kinase (CK) and lactate dehydrogenase (LDH) were observed by fully automatic biochemical analyser. Myocardial infarct size was assessed by nitro blue tetrazolium (NBT) staining. Both oral and intravenous administration of SAA reduced the myocardial infarct area/left ventricle area significantly [(16.73±6.52)% and (13.19±2.38)%, compared with (24.35±4.89)% in model group, P<0.01). Oral administration of SAA improved the ECG performance of Σ-ST from 30-190 min after ischemia (P<0.05-0.01), while intravenous SAA had a rapid onset (10-190 min after ischemia, P<0.05-0.01). Compared with model group, oral and intravenous SAA both decreased serum CK and LDH significantly (P<0.05-0.01), while the difference of intravenous administration is more significant. SAA protects myocardium in canine experimental myocardial infarction models. Intravenous administration of SAA alleviates myocardial infarction with greater significance than oral route.

Relationship between new-onset atrial fibrillation and sympathetic neural remodeling in a canine acute myocardial infarction model

To establish the canine model of new-onset atrial fibrillation (AF) after acute myocardial infarction (AMI), and explore the relationship between new-onset AF and sympathetic neural remodeling in this model. Twenty four adult mongrel dogs were randomly divided into 4 groups by applying random number table. Group A (n=6): ligate the left circumflex artery (LCX). Group B (n=6): ligate the LCX and right atrial anterior artery and right atrial middle artery. Group C (n=6): ligate left anterior descending artery.Group D (n=6): sham operation.Sequential electrophysiology study was performed in all dogs to determine the AF induction rate, AF duration, effective refractory period (ERP), the density of tyrosine hydroxylase (TH) and norepinephrine transporter (NET) before AMI or sham operation, and at 30 min, 2 hours and 4 hours after AMI or sham operation. (1) The highest AF induction rate of right atrium and left auricle was 96.7%(58/60) and 95.0%(57/60) in group B, 81.7%(49/60) and 38.3%(23/60) in group A, 28.3%(17/60) and 35.0%(21/60) in group C, 20.0%(12/60) and 33.3%(20/60) in group D. (2) At 4 hours after AMI, AF duration was significantly prolonged in group B(193.50±54.67) s, compared with group A(53.83±9.37) s, group C(45.00±19.50) s, and group D(16.67±4.50) s (all P<0.05). (3) In group B, the ERP of AF was prolonged at 30 minutes after AMI and shortened at 2 hours and 4 hours after AMI compared with baseline level(all P<0.05). (4) The TH density of left atrium ((3 485±694) µm2/mm2) and left auricle((2 645±454) µm2/mm2) in group A and the TH density of left atrium ((7 873±1159) µm2/mm2) and left auricle((3 070±605) µm2/mm2) in group B were significantly higher than those in group C ((1 474±475) µm2/mm2, (1 177±277) µm2/mm2) and group D ((678±206) µm2/mm2, (489±125) µm2/mm2) (all P<0.05), and the TH density of right atrium and right auricle in group B were higher than group A (all P<0.05). The NET density of left atrium((476±75) µm2/mm2) and left auricle ((414±52) µm2/mm2) in group A and the NET density of left atrium((527±81) µm2/mm2) and left auricle((429±85) µm2/mm2) in group B were lower than that in group C ((1 044±105) µm2/mm2, (867±67) µm2/mm2) and group D ((1 438±60) µm2/mm2, (1 027±119) µm2/mm2) (all P<0.05). Ligating the LCX, right atrial anterior artery and right atrial middle artery at the same time can significantly increase the success rate in establishing the canine model of new-onset atrial fibrillation after acute myocardial infarction and can also increase the AF duration.Cardiac sympathetic remodeling after acute myocardial infarction is associated with induction and duration of AF.

Assessment of Retrograde Coronary Venous Infusion of Mesenchymal Stem Cells Combined with Basic Fibroblast Growth Factor in Canine Myocardial Infarction Using Strain Values Derived from Speckle-Tracking Echocardiography

Speckle-tracking echocardiography was used to assess retrograde coronary venous infusion of mesenchymal stem cells (MSCs) combined with basic fibroblast growth factor (bFGF) in a canine model of acute myocardial infarction (AMI). AMI was induced by ligation of the left anterior descending coronary artery. Coronary venous retroperfusion was performed at 1 wk after AMI. Twenty-eight animals were randomized into four groups: saline, bFGF+saline, saline+MSCs and bFGF+MSCs. Echocardiography was performed before AMI, at 7 d post-AMI and 40 d after retroperfusion. Apoptotic cardiomyocytes in the border zone of the ischemic region were evaluated by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling. Vascular endothelial growth factor and factor VIII concentrations were measured by western blotting. The left ventricular end-systolic volume increased significantly, whereas the left ventricular ejection fraction and global and segmental strain values decreased significantly after AMI. After retroperfusion, the strain values of the infarct zone, but not conventional echocardiographic parameters, were significantly different between control and bFGF+MSC groups. Cardiomyocyte apoptosis decreased, whereas vascular endothelial growth factor and factor VIII concentrations were higher in the bFGF+MSC, bFGF and MSC groups. Cardiomyocyte apoptosis was well correlated with the strain values. Although retrograde coronary venous infusion of bFGF and MSCs promoted neo-vascularization of the infarcted myocardium and inhibited apoptosis, there was only a slight strain improvement without a substantial increase in global cardiac functions.

Adenovirus-mediated expression of human sodium-iodide symporter gene permits in vivo tracking of adipose tissue-derived stem cells in a canine myocardial infarction model

IntroductionIn vivo tracking of the transplanted stem cells is important in pre-clinical research of stem cell therapy for myocardial infarction. We examined the feasibility of adenovirus-mediated sodium iodide symporter (NIS) gene to cell tracking imaging of transplanted stem cells in a canine infarcted myocardium by clinical single photon emission computed tomography (SPECT). MethodsBeagle dogs were injected intramyocardially with NIS-expressing adenovirus-transfected canine stem cells (Ad-hNIS-canine ADSCs) a week after myocardial infarction (MI) development. 99mTc-methoxyisobutylisonitrile (99mTc-MIBI) and 99mTc-pertechnetate (99mTcO4−) SPECT imaging were performed for assessment of infarcted myocardium and viable stem cell tracking. Transthoracic echocardiography was performed to monitor any functional cardiac changes. ResultsLeft ventricular ejection fraction (LVEF) was decreased after LAD ligation. There was no significant difference in EF between the groups with the stem cell or saline injection. 125I uptake was higher in Ad-hNIS-canine ADSCs than in non-transfected ADSCs. Cell proliferation and differentiation were not affected by hNIS-carrying adenovirus transfection. 99mTc-MIBI myocardial SPECT imaging showed decreased radiotracer uptake in the infarcted apex and mid-anterolateral regions. Ad-hNIS-canine ADSCs were identified as a region of focally increased 99mTcO4− uptake at the lateral wall and around the apex of the left ventricle, peaked at 2 days and was observed until day 9. ConclusionsCombination of adenovirus-mediated NIS gene transfection and clinical nuclear imaging modalities enables to trace the fate of transplanted stem cells in infarcted myocardium for translational in vivo cell tracking study for prolonged duration.

Transendocardial Delivery of HGF Via Microbubbles and Ultrasound to Treat Acute Myocardial Infarction

To enhance the safety of transendocardial delivery and the efficacy of intramyocardial angiogenic gene expression, a visible, less invasive, targeted, high-efficiency gene delivery strategy was tested. Progress toward clinical approval of systemic administration of genes and microbubbles (MBs) has been limited. The feasibility of transendocardially delivering MBs as extracellular markers and gene carriers in conjunction with intracardiac ultrasound (US) treatment remains unknown. In a canine acute myocardial infarction (MI) model, a naked plasmid encoding 500 μg human hepatocyte growth factor (HGF) was delivered transendocardially to the myocardium via US/MB (HGF-US/MB), insonation (HGFUS), or alone (HGF alone). Control MI dogs received saline without US/MB (control group). During US/MB, intracardiac insonation was performed for 30 s with a 10-s pause, at 4.3-MHz, 1-W/cm(2), for 60 s at each site. Gene and MB distribution in the myocardium was visualized. Compared to the HGF alone group at 28 days, the HGF-US/MB group had an average 7.1-fold enhancement in gene expression (P < 0.01). Compared to the control group, there were 16% decreases in the ratio of left ventricle (LV) weight/body weight in the HGF-US/MB group and decreases in collagen volume fraction (CVF) of type I (33%) and type III (23%) collagen. Capillary density increased from 22.8 ± 6.3/mm(2) in the control group to 154.3 ± 42.9/mm(2) in the HGF-US/MB group (P < 0.01). This less invasive catheter-based US therapeutic procedure offers observable gene delivery with higher therapeutic efficiency, enhanced angiogenesis, and improved myocardial perfusion and ventricular function following MI.

SkM1 and Cx32 improve conduction in canine myocardial infarcts yet only SkM1 is antiarrhythmic

Reentry accounts for most life-threatening arrhythmias, complicating myocardial infarction, and therapies that consistently prevent reentry from occurring are lacking. In this study, we compare antiarrhythmic effects of gene transfer of green fluorescent protein (GFP; sham), the skeletal muscle sodium channel (SkM1), the liver-specific connexin (Cx32), and SkM1/Cx32 in the subacute canine infarct. Immediately after ligation of the left anterior descending artery, viral constructs were implanted in the epicardial border zone (EBZ). Five to 7 days later, efficient restoration of impulse propagation (narrow QRS and local electrogram duration) occurred in SkM1, Cx32, and SkM1/Cx32 groups (P< 0.05 vs. GFP). Programmed electrical stimulation from the EBZ induced sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) in 15/22 GFP dogs vs. 2/12 SkM1, 6/14 Cx32, and 8/10 SkM1/Cx32 (P< 0.05 SkM1 vs. GFP). GFP, SkM1, and SkM1/Cx32 had predominantly polymorphic VT/VF, whereas in Cx32 dogs, monomorphic VT predominated (P< 0.05 for Cx32 vs. GFP). Tetrazolium red staining showed significantly larger infarcts in Cx32- vs. GFP-treated animals (P< 0.05). Whereas SkM1 gene transfer reduces the incidence of inducible VT/VF, Cx32 therapy to improve gap junctional conductance results in larger infarct size, a different VT morphology, and no antiarrhythmic efficacy.

In Vivo SPECT Quantification of Transplanted Cell Survival After Engraftment Using 111In-Tropolone in Infarcted Canine Myocardium

Current investigations of cell transplant therapies in damaged myocardium are limited by the inability to quantify cell transplant survival in vivo. We describe how the labeling of cells with (111)In can be used to monitor transplanted cell viability in a canine infarction model. We experimentally determined the contribution of the (111)In signal associated with transplanted cell (TC) death and radiolabel leakage to the measured SPECT signal when (111)In-labeled cells were transplanted into the myocardium. Three groups of experiments were performed in dogs. Radiolabel leakage was derived by labeling canine myocardium in situ with free (111)In-tropolone (n = 4). To understand the contribution of extracellular (111)In (e.g., after cell death), we developed a debris impulse response function (DIRF) by injecting lysed (111)In-labeled cells within reperfused (n = 3) and nonreperfused (n = 5) myocardial infarcts and within normal (n = 3) canine myocardium. To assess the application of the modeling derived from these experiments, (111)In-labeled cells were transplanted into infarcted myocardium (n = 4; 3.1 x 10(7) +/- 5.4 x 10(6) cells). Serial SPECT images were acquired after direct epicardial injection to determine the time-dependent radiolabel clearance. Clearance kinetics were used to correct for (111)In associated with viable TCs. (111)In clearance followed a biphasic response and was modeled as a biexponential with a short (T(1/2)(s)) and long (T(1/2)(l)) biologic half-life. The T(1/2)(s) was not significantly different between experimental groups, suggesting that initial losses were due to transplantation methodology, whereas the T(1/2)(l) reflected the clearance of retained (111)In. DIRF had an average T(1/2)(l) of 19.4 +/- 4.1 h, and the T(1/2)(l) calculated from free (111)In-tropolone injected in situ was 882.7 +/- 242.8 h. The measured T(1/2)(l) for TCs was 74.3 h and was 71.2 h when corrections were applied. A new quantitative method to assess TC survival in myocardium using SPECT and (111)In has been introduced. At the limits, method accuracy is improved if appropriate corrections are applied. In vivo (111)In imaging most accurately describes cell viability half-life if T(1/2)(l) is between 20 h and 37 d.

Epicardial Border Zone Overexpression of Skeletal Muscle Sodium Channel SkM1 Normalizes Activation, Preserves Conduction, and Suppresses Ventricular Arrhythmia

In depolarized myocardial infarct epicardial border zones, the cardiac sodium channel (SCN5A) is largely inactivated, contributing to low action potential upstroke velocity (V(max)), slow conduction, and reentry. We hypothesized that a fast inward current such as the skeletal muscle sodium channel (SkM1) operating more effectively at depolarized membrane potentials might restore fast conduction in epicardial border zones and be antiarrhythmic. Computer simulations were done with a modified Hund-Rudy model. Canine myocardial infarcts were created by coronary ligation. Adenovirus expressing SkM1 and green fluorescent protein or green fluorescent protein alone (sham) was injected into epicardial border zones. After 5 to 7 days, dogs were studied with epicardial mapping, programmed premature stimulation in vivo, and cellular electrophysiology in vitro. Infarct size was determined, and tissues were immunostained for SkM1 and green fluorescent protein. In the computational model, modest SkM1 expression preserved fast conduction at potentials as positive as -60 mV; overexpression of SCN5A did not. In vivo epicardial border zone electrograms were broad and fragmented in shams (31.5 +/- 2.3 ms) and narrower in SkM1 (22.6 +/- 2.8 ms; P=0.03). Premature stimulation induced ventricular tachyarrhythmia/fibrillation >60 seconds in 6 of 8 shams versus 2 of 12 SkM1 (P=0.02). Microelectrode studies of epicardial border zones from SkM1 showed membrane potentials equal to that of shams and V(max) greater than that of shams as membrane potential depolarized (P<0.01). Infarct sizes were similar (sham, 30 +/- 2.8%; SkM1, 30 +/- 2.6%; P=0.86). SkM1 expression in injected epicardium was confirmed immunohistochemically. SkM1 increases V(max) of depolarized myocardium and reduces the incidence of inducible sustained ventricular tachyarrhythmia/fibrillation in canine infarcts. Gene therapy to normalize activation by increasing V(max) at depolarized potentials may be a promising antiarrhythmic strategy.

Nitrite Anion Provides Potent Cytoprotective and Antiapoptotic Effects as Adjunctive Therapy to Reperfusion for Acute Myocardial Infarction

Accumulating evidence suggests that the ubiquitous anion nitrite (NO2-) is a physiological signaling molecule, with roles in intravascular endocrine nitric oxide transport, hypoxic vasodilation, signaling, and cytoprotection. Thus, nitrite could enhance the efficacy of reperfusion therapy for acute myocardial infarction. The specific aims of this study were (1) to assess the efficacy of nitrite in reducing necrosis and apoptosis in canine myocardial infarction and (2) to determine the relative role of nitrite versus chemical intermediates, such as S-nitrosothiols. We evaluated infarct size, microvascular perfusion, and left ventricular function by histopathology, microspheres, and magnetic resonance imaging in 27 canines subjected to 120 minutes of coronary artery occlusion. This was a blinded, prospective study comparing a saline control group (n=9) with intravenous nitrite during the last 60 minutes of ischemia (n=9) and during the last 5 minutes of ischemia (n=9). In saline-treated control animals, 70+/-10% of the area at risk was infarcted compared with 23+/-5% in animals treated with a 60-minute nitrite infusion. Remarkably, a nitrite infusion in the last 5 minutes of ischemia also limited the extent of infarction (36+/-8% of area at risk). Nitrite improved microvascular perfusion, reduced apoptosis, and improved contractile function. S-Nitrosothiol and iron-nitrosyl-protein adducts did not accumulate in the 5-minute nitrite infusion, suggesting that nitrite is the bioactive intravascular nitric oxide species accounting for cardioprotection. Nitrite has significant potential as adjunctive therapy to enhance the efficacy of reperfusion therapy for acute myocardial infarction.

Percent infarct mapping: An R1‐map‐based CE‐MRI method for determining myocardial viability distribution

Viability detection is crucial for the management of myocardial infarction (MI). Signal intensity (SI)-based MRI methods may overestimate infarct size in vivo. In contrast to SI, the longitudinal relaxation-rate enhancement (DeltaR1) is an intrinsic parameter that is linearly proportional to the concentration of contrast agent (CA). Determining DeltaR1 in the presence of an infarct-avid persistent CA (PCA) allows determination of the per-voxel percentage of infarcted tissue. Introduced here is a DeltaR1-based CE-MRI method, termed percent infarct mapping (PIM), for quantifying myocardial viability following delayed PCA accumulation. In a canine MI model (N=6), PIMs were generated using a persistent CA (PCA) and validated using triphenyltetrazolium-chloride (TTC) histochemistry. Voxel-by-voxel R1 maps of the entire left ventricle (LV) were generated 24 and 48 hr after PCA administration using inversion recovery (IR) with multiple inversion times (TIs). PI values were calculated voxel by voxel. Significant correlations (P<0.01, R=0.97) were obtained for PI per slice (PIS) determined using PIM vs. corresponding TTC-based values. Median deviations of PIS with PIM from that with TTC were only 1.01% and -0.53%, at 24 hr and 48 hr. Median deviations from the true infarction fraction (IF) were 1.23% and 0.49% of LV at 24 hr and 48 hr, respectively. No significant difference was found between PIM24 hr and PIM48 hr. DeltaR1-based PIM is an accurate and reproducible method for quantifying myocardial viability distribution, and thus enhances the clinical utility of CE-MRI.

Electrophysiological consequence of skeletal myoblast transplantation in normal and infarcted canine myocardium

The purpose of this study is to test our hypothesis that injection of skeletal myoblasts (SkMbs) into viable tissue may alter impulse conduction but that injections into nonviable tissue (scar) will have negligible impact. Myocardial infarction (MI) is a major public health problem. SkMb transplantation after MI has been shown to have some beneficial effect on hemodynamic function. Previous studies have indicated that SkMbs do not electrically couple with viable host myocardium in vivo. We used optical mapping to measure impulse propagation and arrhythmia inducibility in the canine left ventricular wedge preparation with and without MI. MI was created by temporary ligation of a branch of the left anterior descending coronary artery (LAD) (7.0 +/- 3.8 ng/mL troponin 24 hours after MI). Labeled SkMbs (10(8) in 4 mL of serum-free basal solution) were injected from the epicardium (20-40 0.1 mL injections) into normal myocardium (n = 8) or the central zone of the MI (n = 6). During endocardial pacing in the absence of MI, transmural conduction velocity was similar with (35.75 +/- 3.4 cm/s) and without (37.42 +/- 3.6 cm/s) SkMb transplantation. However, pacing from the epicardium resulted in conduction slowing in regions that were DiI-positive and associated with the expression of skeletal myosin (fast) but not connexin-43. In all preparations with MI (n = 13), abnormal impulse propagation was seen regardless of SkMb transplantation. Arrhythmias (at least one extra beat after standard programmed stimulation) occurred most frequently in preparations with MI independent of SkMb transplantation. In preparations without MI (n = 8), SkMb transplantation did not significantly increase arrhythmia inducibility. We conclude that SkMbs transplanted into normal myocardium can cause abnormal impulse propagation. These data suggest that the location of SkMb transplantation may influence arrhythmia vulnerability associated with MI.

Feridex-Labeled Mesenchymal Stem Cells: Cellular Differentiation and MR Assessment in a Canine Myocardial Infarction Model

Attempts to regenerate myocardium after experimentally induced acute myocardial infarction (MI) by cellular myoplasty techniques have recently provided encouraging results [1, 2]. Transplantation and mobilization of bone marrow stem cells to the area of infarction has hitherto received the most attention. In particular, culture-expanded bone-marrow-derived mesenchymal stem cells (MSCs) are a promising source for treatment of MI [3, 4]. Under the right circumstances, MSCs may “home” to injuries, engraft and differentiate [5].

Accurate and objective infarct sizing by contrast-enhanced magnetic resonance imaging in a canine myocardial infarction model

To identify an accurate and reproducible method to define myocardial infarct (MI) size, we conducted a study in a closed-chest canine model of acute myocardial infarction, in which MI size was measured using different thresholding techniques and by imaging at different delay times after contrast administration. The MI size by contrast-enhanced magnetic resonance imaging (CE-MRI) is directly related to long-term prognosis. However, previous measurements were done using nonuniform methods and tended to overestimate nonviable areas. Thirteen animals underwent 90 min of coronary artery occlusion, followed by reperfusion. The CE-MRI data were acquired within 24 h after reperfusion and compared with triphenyltetrazolium chloride pathology. In the first nine animals, images were obtained approximately 15 min after gadolinium diethylene triamine penta-acetic acid (Gd-DTPA) using an inversion-recovery gradient-echo pulse sequence. To identify the most accurate method, MI size by CE-MRI was measured visually and by semi-automatic thresholding techniques, using different criteria. In four additional animals, images were acquired every 6 min until 30 min after Gd-DTPA. Postmortem MI size was 13.5 +/- 2.6% of left ventricular volume. Semi-automatic techniques, using full-width at half-maximum (FWHM) criterion, correlated best with postmortem data (r(2) = 0.94, p < 0.001; results confirmed by Bland-Altman plots). Using FWHM, there was no difference in MI size between different delay times after contrast (15.2 +/- 2.9% to 14.5 +/- 4.2% at 6 and 30 min, respectively; p = NS). When an objective technique is used to define MI size by CE-MRI, accurate infarct size measurements can be obtained from images obtained up to 30 min after contrast administration.

Vascular mural cells in healing canine myocardial infarcts.

Angiogenesis is a critical process in healing of myocardial infarcts, leading to the formation of highly vascular granulation tissue. However, effective cardiac repair depends on mechanisms that inhibit the angiogenic process after a mature scar is formed, preventing inappropriate expansion of the fibrotic process. Using a canine model of reperfused myocardial infarction, we demonstrated that maturation of the infarct leads to the formation of neovessels, with a thick muscular coat, that demonstrate distinct morphological characteristics. Many of these "neoarterioles" lack a defined internal elastic lamina and demonstrate irregular deposits of extracellular matrix in the media. Vascular mural cells in healing infarcts undergo phenotypic changes, showing minimal expression of desmin during the proliferative phase (1 hr occlusion/7 days reperfusion) but in the mature scar (8 weeks reperfusion) acquire a phenotype similar to that of vascular smooth muscle cells in control areas. Non-muscle myosin heavy chains A and B are induced in infarct endothelial cells and myofibroblasts, respectively, but are not expressed in neovascular mural cells. Recruitment of a muscular coat and formation of neoarterioles in mature scars may inhibit endothelial cell proliferation and vascular sprouting, stabilizing the infarct vasculature.

Accurate and objective infarct sizing by contrast enhanced magnetic resonance imaging defined in a canine myocardial infarction model

Accurate and objective infarct sizing by contrast enhanced magnetic resonance imaging defined in a canine myocardial infarction model

Superparamagnetic iron oxide MION as a contrast agent for sodium MRI in myocardial infarction.

An intravascular iron-based contrast agent was used as a sodium (23Na) MRI T2 relaxant in an effort to suppress the blood signal from the ventricular cavities in normal and infarcted canine myocardium in vivo. 23Na MRI signal decreases in blood were attributed to decreases in the fast (T2f) and slow (T2s) transverse relaxation components, which were quantified as a function of dose and MRI echo time (TE). In vivo 23Na MRI signal decreases up to 65% were noted in ventricular blood when imaging under dose and TE conditions of 10 mg/kg body weight and 5 ms, respectively. Contrast injection followed by subsequent 23Na MRI in canine myocardial infarction led to a clear delineation of the location of the injured tissue, as identified by postmortem triphenyltetrazolium chloride staining, and to an improvement in the contrast-to-noise ratio between the blood in the ventricular chamber and the infarcted tissue that was as high as 3.3-fold in the postcontrast images in comparison to the precontrast images.