Porcine Model Of Myocardial Ischemia Research Articles

T-wave Peak-to-End Changes Quantified by Time-Warping Predicts Ventricular Fibrillation in a Porcine Myocardial Infarction Model.

The T-peak-to-T-end ( Tpe) interval has shown potential in predicting ventricular arrhythmic risk. It is an appealing index to be measured during ischemia since it is less influenced by ST-segment changes than the early part of the T wave. A time-warping-based index, derived from a spatially transformed PCA lead, [Formula: see text], quantifying changes in the Tpe morphology, has previously demonstrated utility in tracking repolarization changes induced by a 5-minute ischemia model in humans. The value of [Formula: see text] as a predictor of ventricular fibrillation (VF) episodes is assessed in a porcine model of myocardial ischemia with ischemia maintained for 40 minutes. From 32 pigs undergoing a coronary occlusion, pre-occlusion and occlusion ECG recordings from 10 pigs suffering a VF episode after 10 min of occlusion (Delayed VF) and 16 that did not had any episode during the recording were analyzed. The [Formula: see text] series was measured by comparing Tpe morphologies at different stages of the occlusion relative to the peak-to-end morphology of a baseline T-wave. During baseline, [Formula: see text] remained stationary with an intra-recording median [IQR] value of 1.60 [1.33] ms. During artery occlusion, [Formula: see text] followed a well-marked gradual increasing trend as ischemia progressed, reaching a median of 14.58 [17.72] ms. [Formula: see text] averages were significantly higher ( ) in the VF group than in the Non-VF group at time intervals 0-5, 5-10, 10-15, 15-20, 20-25 min after occlusion onset and at 10-15, 5-10 and 5-0 minutes prior to VF episode, with median values of 12.5, 18.8, 26.8, 24.0, 31.0, 18.6, 25.0 and 28.8 vs 6.3, 7.6, 8.0, 7.8, 7.8, 8.5, 7.2 and 6.0 ms, respectively. The [Formula: see text] interval was also significantly higher in the VF group at all analyzed time periods, but with a lower significance level. Pigs with maximum [Formula: see text] ≥ 20.0 ms and [Formula: see text] ≥ 85.4 ms had significantly higher risk for VF occurring in the early 5-10 minutes interval, with 90.0%/75.0% and 80.0%/69.0% sensitivity/specificity, respectively. Univariate Cox analysis yielded hazard ratios of 12.5 for [Formula: see text] vs 5.5 for [Formula: see text]. The time-warping-based index, [Formula: see text], is a stronger VF predictor than [Formula: see text] during ischemia in a porcine model, advising for further clinical exploration studies in humans.

Veno-occlusive unloading of the heart reduces infarct size in experimental ischemia\u2013reperfusion

Mechanical unloading of the left ventricle reduces infarct size after acute myocardial infarction by reducing cardiac work. Left ventricular veno-occlusive unloading reduces cardiac work and may reduce ischemia and reperfusion injury. In a porcine model of myocardial ischemia–reperfusion injury we randomized 18 pigs to either control or veno-occlusive unloading using a balloon engaged from the femoral vein into the inferior caval vein and inflated at onset of ischemia. Evans blue and 2,3,5-triphenyltetrazolium chloride were used to determine the myocardial area at risk and infarct size, respectively. Pressure–volume loops were recorded to calculate cardiac work, left ventricular (LV) volumes and ejection fraction. Veno-occlusive unloading reduced infarct size compared with controls (Unloading 13.9 ± 8.2% versus Control 22.4 ± 6.6%; p = 0.04). Unloading increased myocardial salvage (54.8 ± 23.4% vs 28.5 ± 14.0%; p = 0.02), while the area at risk was similar (28.4 ± 6.7% vs 27.4 ± 5.8%; p = 0.74). LV ejection fraction was preserved in the unloaded group, while the control group showed a reduced LV ejection fraction. Veno-occlusive unloading reduced myocardial infarct size and preserved LV ejection fraction in an experimental acute ischemia–reperfusion model. This proof-of-concept study demonstrated the potential of veno-occlusive unloading as an adjunctive cardioprotective therapy in patients undergoing revascularization for acute myocardial infarction.

High doses of ANP and BNP exacerbate lipolysis in humans and the lipolytic effect of BNP is associated with cardiac triglyceride content in pigs

Drugs facilitating the cardioprotective effects of natriuretic peptides are introduced in heart failure treatment. ANP and BNP also stimulate lipolysis and increase circulating concentrations of free fatty acids (FFAs); an aspect, however, thought to be confined to primates. We examined the lipolytic effect of natriuretic peptide infusion in healthy young men and evaluated the effect in a porcine model of myocardial ischemia and reperfusion.Six young healthy normotensive men underwent infusion with ANP, BNP, or CNP for 20 min. Blood samples were collected before, during, and after infusion for measurement of FFAs. In a porcine model of myocardial ischemia and reperfusion, animals were infused for 3 h with either BNP (n = 7) or saline (n = 5). Blood samples were collected throughout the infusion period, and cardiac tissue was obtained after infusion for lipid analysis.In humans, ANP infusion dose-dependently increased the FFA concentration in plasma 2.5-10-fold (baseline vs. 0.05 μg/kg/min P < 0.002) and with BNP 1.6–3.5-fold (P = 0.001, baseline vs. 0.02 μg/kg/min) 30 min after initiation of infusion. Infusion of CNP did not affect plasma FFA. In pigs, BNP infusion induced a 3.5-fold increase in plasma FFA (P < 0.0001), which remained elevated throughout the infusion period. Triglyceride content in porcine right cardiac ventricle tissue increased ∼5.5 fold in animals infused with BNP (P = 0.02).Natriuretic peptide infusion has similar lipolytic activity in human and pig. Our data suggest that short-term infusion increases the cardiac lipid content, and that the pig is a suitable model for studies of long-term effects mediated by natriuretic peptides.

Protective effects of salvianolate on microvascular flow in a porcine model of myocardial ischaemia and reperfusion

Microvascular reflow is crucial for myocyte survival during ischaemia/reperfusion injury. We aimed to assess if salvianolate, a highly purified aqueous extract from Radix salviae miltiorrhizae, could improve impaired microvascular reflow induced by ischaemia/reperfusion injury, using a porcine closed-chest model. Left anterior descending coronary artery ligation was created by balloon occlusion for 2 h followed by reperfusion for 14 days. Salvianolate was administrated intravenously for 7 days at low dose (5 mg/kg/day), high dose (10 mg/kg/day) or high dose combined with one 20 mg intracoronary bolus injection just at the beginning of reperfusion. Control-group animals were only given the same volume of saline. After 14 days of reperfusion, animals treated with high-dose salvianolate showed improved myocardial perfusion assessed by real-time myocardial contrast echocardiography and coloured microspheres. The beneficial effect was further supported by increased capillary density and decreased infarct size. All these effects eventually resulted in well-preserved cardiac function detected by echocardiography. Moreover, we also demonstrated that salvianolate administration was associated with elevated superoxide dismutase activity, thioredoxin activity and glutathione concentration, and reduced malondialdehyde concentration, which, in turn, resulted in a significant decrease in terminal deoxynucleotide transferase-mediated dUTP nick end labelling-positive cells and an increased ratio of Bcl-2 to Bax expression. Intravenous salvianolate at a dose of 10 mg/kg/day for 7 days had significant beneficial effects on myocardial microvascular reflow, which were associated with decreased oxidative stress and apoptosis.

Nitric Oxide Inhalation Improves Microvascular Flow and Decreases Infarction Size After Myocardial Ischemia and Reperfusion

The purpose of this study was to test if nitric oxide (NO) could improve microvascular perfusion and decrease tissue injury in a porcine model of myocardial ischemia and reperfusion (I/R). Inhaled NO is a selective pulmonary vasodilator with biologic effects in remote vascular beds. In 37 pigs, the midportion of the left anterior descending coronary artery was occluded for 50 min followed by 4 h of reperfusion. Pigs were treated with a saline infusion (control; n = 14), intravenous nitroglycerin (IV-NTG) at 2 microg/kg/min (n = 11), or inhaled nitric oxide (iNO) at 80 parts per million (n = 12) beginning 10 min before balloon deflation and continuing throughout reperfusion. Total myocardial oxidized NO species in the infarct core was greater in the iNO pigs than in the control or IV-NTG pigs (0.60 +/- 0.05 nmol/mg tissue vs. 0.40 +/- 0.03 nmol/mg tissue and 0.40 +/- 0.02 nmol/mg tissue, respectively; p < 0.01 for both). Infarct size, expressed as percentage of left ventricle area at risk (AAR), was smaller in the iNO pigs than in the control or IV-NTG pigs (31 +/- 6% AAR vs. 58 +/- 7% AAR and 46 +/- 7% AAR, respectively; p < 0.05 for both) and was associated with less creatine phosphokinase-MB release. Inhaled NO improved endocardial and epicardial blood flow in the infarct zone, as measured using colored microspheres (p < 0.001 vs. control and IV-NTG). Moreover, NO inhalation reduced leukocyte infiltration, as reflected by decreased cardiac myeloperoxidase activity (0.8 +/- 0.2 U/mg tissue vs. 2.3 +/- 0.8 U/mg tissue in control and 1.4 +/- 0.4 U/mg tissue in IV-NTG; p < 0.05 for both) and decreased cardiomyocyte apoptosis in the infarct border zone. Inhalation of NO just before and during coronary reperfusion significantly improves microvascular perfusion, reduces infarct size, and may offer an attractive and novel treatment of myocardial infarction.

Intramyocardial gene transfer of vascular endothelial growth factor 121 improves myocardial perfusion and function in the ischemic porcine heart

Vascular endothelial growth factor (VEGF) is an endothelial cell-specific mitogen that is angiogenic in vitro and in vivo . Several studies report on gene transfer of VEGF 121 to promote angiogenesis in the ischemic myocardium of animals and patients. We hypothesized that intramyocardial administration of naked plasmid DNA encoding VEGF 121 could improve myocardial perfusion and function in a porcine model of myocardial ischemia. Yorkshire swine underwent thoracotomy and placement of an ameroid constrictor on the circumflex coronary artery. Four weeks later, pVEGF 121 plasmid was administered into the ischemic myocardium. Four weeks after gene transfer, SPECT imaging demonstrated significant reduction in the ischemic area in pVEGF 121 -treated animals compared with controls. In the pVEGF 121 group, most of the animals evolved from light ischemia to a normal perfusion. In contrast, control animals exhibited similar or impaired ischemic conditions. Our results indicate that intramyocardial gene transfer of VEGF 121 as naked plasmid DNA results in significant improvement in myocardial perfusion and function.

High pressure, retrograde, coronary venous delivery of FGF-2 protein improves coronary blood flow in a porcine model of myocardial ischemia

High pressure, retrograde, coronary venous delivery of FGF-2 protein improves coronary blood flow in a porcine model of myocardial ischemia

Gene therapy for myocardial angiogenesis

In patients in whom antianginal medications fail to provide sufficient symptomatic relief, additional interventions such as angioplasty or bypass surgery may be required. Although both types of intervention have been shown to be effective for various types of patients, a certain group of patients may not be candidates for either intervention because of the diffuse nature of their coronary artery disease. Moreover, there are many patients in whom recurrent narrowing and/or occlusion of bypass conduits after initially successful surgery has left the patient again symptomatic with no further angioplasty or surgical option. Ischemic muscle represents a promising target for gene therapy with naked plasmid DNA. Intramuscular transfection of genes encoding angiogenic cytokines, particularly those naturally secreted by intact cells, may constitute an alternative treatment strategy for patients with extensive tissue ischemia in whom contemporary therapies (antianginal medications, angioplasty, bypass surgery) have previously failed or are not feasible. This strategy is designed to promote the development of supplemental collateral blood vessels that will constitute endogenous bypass conduits around occluded native arteries, a strategy termed “therapeutic angiogenesis.” Preclinical animal studies from our laboratory have established that intramuscular gene transfer may be used to successfully accomplish therapeutic angiogenesis. More recently, phase 1 clinical studies from our institution have established that intramuscular gene transfer may be used to safely and successfully accomplish therapeutic angiogenesis in patients with critical limb ischemia. The notion that this concept could be extrapolated to the treatment of chronic myocardial ischemia was demonstrated in our laboratory by administering recombinant human vascular endothelial growth factor (VEGF) to a porcine model of chronic myocardial ischemia. Recent experiments performed in this same porcine model of myocardial ischemia have shown that direct intramyocardial gene transfer of naked plasmid DNA encoding VEGF (phVEGF 165, the identical plasmid used in our previous animal and human clinical trials) can be safely and successfully achieved through a minimally invasive chest wall incision. Finally, initial results have supported the concept that intramyocardial injection of naked plasmid DNA encoding VEGF can achieve therapeutic angiogenesis, as demonstrated by clinical improvement in patient symptoms and improved myocardial perfusion shown by single-photon emission computed tomography–sestamibi imaging. (Am Heart J 1999;138:S132-S141.)

Visualization and quantification of myocardial mass at risk using three-dimensional contrast echocardiography.

Three-dimensional echocardiographic assessment of myocardial ischemia using contrast echocardiography has been hampered by limitations of available contrast agents and analytic software. In the study presented, a three-dimensional perfusion imaging method was evaluated in the porcine model of myocardial ischemia using a novel contrast agent. Three-dimensional echocardiography was performed in eight open-chested pigs before, during and after left anterior descending (six animals) or circumflex (two animals) coronary artery occlusion. The intramyocardial contrast effect was obtained by left atrial injection of Myomap, a deposit contrast agent. Myocardial opacification was visible in all studies and retained in all three-dimensional datasets. Three-dimensional intensity analysis demonstrated a significant difference, exceeding 20 intensity units in every animal (in 127-level scale), between perfused and non-perfused myocardium. Reperfusion followed by contrast reinjection resulted in homogenous myocardial enhancement. Myocardial mass at risk was clearly delineated in all studies and measured with a mean error of -0.1 +/- 2.0 g against real mass (p = non-significant). Spatial extent of ischemia could be displayed in volume-rendered reconstruction of separate perfusion territories. Quantitative analysis of myocardial contrast enhancement from three-dimensional datasets is feasible and allows accurate measurement of myocardial mass at risk.

Retrograde Infusion of Lidocaine or l-Arginine Before Reperfusion Reduces Myocardial Infarct Size

Background. Retrograde perfusion preserves ischemic myocardium when initiated shortly after coronary artery occlusion. However, benefits diminish as the delay increases. In this study, we used this technique to deliver agents known to reduce the injury associated with the reperfusion of ischemic myocardium. We proposed that the local delivery of lidocaine or l-arginine before reperfusion would reduce the damage caused during reperfusion, even after a delay between onset of ischemia and intervention designed to approximate clinical reality. Methods. In a porcine model of myocardial ischemia, the left anterior descending coronary artery was snared immediately distal to its second diagonal branch. After 1 hour of occlusion, 34 animals were randomized into six groups: no intervention (control) (n = 6); administration of normal saline solution into the great cardiac vein (Retro-NS) (n = 6); administration of lidocaine either intravenously (IV-LID) (n = 6) or retrograde (Retro-LID) (n = 6); and administration of l-arginine either intravenously (IV- l-ARG) (n = 5) or retrograde (Retro- l-ARG) (n = 5). After 90 minutes of ischemia, the snare was released, and the myocardium was reperfused for 3 hours. Two-dimensional echocardiograms were made prior to occlusion and 60, 150, 210, and 270 minutes after occlusion. The infarct size and the area at risk were determined by lissamine green and triphenyltetrazolium chloride staining with computer planimetric quantification. Regional wall motion was assessed by a wall motion score: normal = 1; mild hypokinesia = 2.0; severe hypokinesia = 2.5; and akinesia = 3. Results. The area of the left ventricle at risk for infarction was similar in all groups and represented 25.4% (5.2% [standard deviation]) of the left ventricular mass ( p = 0.63). The percent area of infarction in the area at risk after 3 hours of reperfusion was 76.7% (7.1% for the control group, 73.9% (5.7%) for the Retro-NS group, 72.1% (8.7%) for the IV-LID group, 54.5% (10.2%) for the Retro-LID group, 58.8% (4.0%) for the IV- l-ARG group, and 54.3% (4.0%) for the Retro- l-ARG group p < 0.005, Retro-LID and Retro- l-ARG versus Control, Retro-NS, and IV-LID; p < 0.03, IV- l-ARG versus control and Retro-NS). No significant difference in wall motion scores between groups was detected by echocardiography ( p = 0.578). Conclusions. Retrograde delivery of lidocaine or l-arginine before reperfusion reduces infarct size without acutely affecting wall motion after 90 minutes of ischemia and 3 hours of reperfusion. Lidocaine must be present before reperfusion to have an effect, whereas l-arginine is beneficial if it is delivered at the time of reperfusion.

Influence of coronary venous retroinfusion and vasodilatation on regional myocardial blood flow measurement with microspheres. An analysis of 'microsphere loss' from ischaemic and reperfused porcine hearts.

The influence of coronary venous retroinfusion and a vasoselective calcium antagonist felodipine on the microsphere loss in a porcine model of myocardial ischaemia and reperfusion was studied. Sixteen open-chest pigs underwent 45 min of myocardial ischaemia induced by occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Either felodipine (felo-retro group, 7 nmol kg-1, n = 6) or the corresponding amount of vehicle (vehicle-retro group, n = 5) was infused retrogradely into the coronary veins over 30 min, starting 5 min before reperfusion. In a third group, the same amount of felodipine was administered intravenously (felo-iv group, n = 5). Myocardial regional blood flow was measured with radiolabelled microspheres (phi = 15 microns) injected before ischaemia to investigate a possible loss during ischaemia. In the felo-retro group, the apparent blood flow in the ischaemic areas, expressed as a percentage of the corresponding values in the non-ischaemic areas (%-flow), were 73 +/- 15, 73 +/- 11 and 75 +/- 19 in the subendocardial, midmyocardial and subepicardial layers, respectively. The corresponding percentage flows were 64 +/- 11, 70 +/- 11 and 62 +/- 9 in the vehicle-retro group and 75 +/- 18, 77 +/- 15 and 76 +/- 11 in the felo-iv group. The differences between the groups were not statistically significant. It is concluded that in this open-chest preparation microsphere loss observed in the ischaemic and reperfused myocardium is not increased by coronary venous retroinfusion or by a concomitantly administered vasodilative agent like felodipine.

Effects of magnesium supplementation in a porcine model of myocardial ischemia and reperfusion.

We tested the hypothesis that acute, intravenous (i.v.) magnesium (Mg2+) supplementation would protect against myocardial stunning in an in situ swine model of regional ischemia and reperfusion and that a concomitant inhibitory effect on platelet aggregation would be elicited. An open-chest model was used, with transient occlusion of the left anterior descending coronary artery (LAD) for 8 min. Regional contractile function was assessed by measuring wall thickening fraction with epicardial Doppler crystals. One control group (n = 6) and two treatment groups were studied: group I (n = 6) received 750 mg MgSO4 before occlusion; group II (n = 6) received 1 g MgSO4 after the occlusion. Both protocols produced significant hypermagnesemia. In group I, platelet aggregation was measured before and after Mg2+ treatment using platelet-rich plasma (PRP) and various agonists (ADP 5 and 10 mM and collagen 1 mg/ml). As compared with controls, both treatment groups experienced significantly less postischemic dysfunction, with systolic function returning more quickly to baseline. Furthermore, platelet aggregation was significantly decreased immediately after Mg2+ infusion. Inhibition of platelet aggregation induced by Mg2+ treatment occurs concomitantly with significant amelioration of postischemic myocardial dysfunction.