Hours Of Coronary Occlusion Research Articles

Abstract 18781: Targeting GPR39 in Pericytes for Preventing No Reflow After Acute Myocardial Infarction

Background: No reflow (NR) continues to contribute towards morbidity and mortality in acute myocardial infarction (AMI). Currently, there is no treatment specific to NR. We demonstrated that NR is caused by pericyte-inducted capillary constriction and identified the G-protein coupled receptor, GPR39, through which the vasoconstrictor 15-Hydroxyeicosatetraenoic acid (15-HETE) results in pericyte contraction during myocardial ischemia. GPR39 knockout mice demonstrate a marked reduction in NR after AMI associated with less pericyte-induced capillary constriction. Consequently, we developed a drug candidate, VC108, that inhibits GPR39 with high specificity (antagonist potency, fpki=7.9) and no effect on 87 other receptors involved in cardiovascular regulation. Methods: Forty-nine Wild-type Sprague Dawley rats (3-4 weeks old) of both sexes underwent 1 hour of coronary occlusion followed by 1 hr of reperfusion. Either vehicle (n=13) or VC108 (in-vivo half-life of 2 hr) at 3 different doses: 0.3 (n=11), 0.5 (n=13), and 1.0 mg/kg (n-12) was injected 5 min before reperfusion. Risk volume (as %of LV volume) was derived from 4-6 short axis slices using Evans Blue staining and NR volume was measured using Thioflavin S. Results: There was no significant difference in the risk volume in animals treated with vehicle and the 3 doses of VC108 (Figure 1). In contradistinction, compared to vehicle, VC108 showed marked reduction in NR at all doses (Figure 2) with a trend towards lower NR volume at the highest dose. Conclusion: Pharmacological inhibition of GPR39 results in marked reduced in NR after AMI. These findings open up a novel approach to treating AMI.

Heart Rate Reduction With Ivabradine Protects Against Left Ventricular Remodeling by Attenuating Infarct Expansion and Preserving Remote-Zone Contractile Function and Synchrony in a Mouse Model of Reperfused Myocardial Infarction.

BackgroundIvabradine selectively inhibits the pacemaker current of the sinoatrial node, slowing heart rate. Few studies have examined the effects of ivabradine on the mechanical properties of the heart after reperfused myocardial infarction (MI). Advances in ultrasound speckle‐tracking allow strain analyses to be performed in small‐animal models, enabling the assessment of regional mechanical function.Methods and ResultsAfter 1 hour of coronary occlusion followed by reperfusion, mice received 10 mg/kg per day of ivabradine dissolved in drinking water (n=10), or were treated as infarcted controls (n=9). Three‐dimensional high‐frequency echocardiography was performed at baseline and at days 2, 7, 14, and 28 post‐MI. Speckle‐tracking software was used to calculate intramural longitudinal myocardial strain (Ell) and strain rate. Standard deviation time to peak radial strain (SD Tpeak Err) and temporal uniformity of strain were calculated from short‐axis cines acquired in the left ventricular remote zone. Ivabradine reduced heart rate by 8% to 16% over the course of 28 days compared to controls (P<0.001). On day 28 post–MI, the ivabradine group was found to have significantly smaller end‐systolic volumes, greater ejection fraction, reduced wall thinning, and greater peak Ell and Ell rate in the remote zone, as well as globally. Temporal uniformity of strain and SD Tpeak Err were significantly smaller in the ivabradine‐treated group by day 28 (P<0.05).ConclusionsHigh‐frequency ultrasound speckle‐tracking demonstrated decreased left ventricular remodeling and dyssynchrony, as well as improved mechanical performance in remote myocardium after heart rate reduction with ivabradine.

Severity of blood flow reduction associated with detectable T2 enhancement in the area at risk of a reperfused canine model of acute myocardial infarction

Background T2-weighted enhancement depicts the myocardial area at risk (AAR) associated with coronary occlusion. However, the severity of blood flow abnormality required to cause a detectable elevation in myocardial T2 is unknown. The aim of this study was to use microspheres to determine the severity of reduction in myocardial blood flow that results in visually detectable T2 weighted enhancement. Methods Surface coil intensity corrected T2 prepared SSFP at 1.5T was performed after 2 hours of coronary occlusion followed by 4 hours of reperfusion in a canine model. Myocardial blood flow during ischemia was determined by administering microspheres. A mid-ventricular short axis slice of the heart was divided into 16 transmural sectors for microsphere analysis. MR images were matched to the pathological slices at the sector level using papillary muscles and RV insertion as landmarks. ROIs delineated T2-enhanced and remote regions of the MR images and measurements were compared with microsphere blood flows. Results were reported as median (interquartile range [IQ]) and compared using the signed Wilcoxon rank test. Each T2-prepared sector was classified as bright (AAR) or normal (remote) by 2 independent readers and compared with absolute microsphere blood

Effects of tongxinluo on mini-swine vascular endothelial integrity and myocardial no-reflow in early reperfusion of acute myocardial infarction

To assess the effects of tongxinluo on vascular endothelial integrity and myocardial no-reflow in early reperfusion of acute myocardial infarction. Forty mini-swines were divided into five groups randomly, sham group, control group, low dose (0.1 g/kg), medium dose (0.2 g/kg) and high dose (0.4 g/kg) groups of Tongxinluo. It was administered at 2 hours pre-reperfusion. Animals except in sham group were subjected to 1.5 hour of coronary occlusion followed by 3 hours of reperfusion. Content of VE-cadherin, beta-catenin, matrix metalloproteinase (MMP)-2 and 9 in myocardium were evaluated; no-reflow area was examined with myocardial contrast echocardiography (MCE) at 1.5 hour of AMI and 3 hours of reperfusion. (1) Compared with that of normal myocardium, content of VE-cadherin and beta-catenin decreased in reperfusion and no-reflow myocardium while MMP-2 and 9 increased significantly (all P < 0.05); (2) Compared with that of control group, a high dose of Tongxinluo could increase significantly the content of VE-cadherin in both reperfusion and no-reflow myocardium, (22.2 +/- 3.2)% vs (32.0 +/- 3.9)% and (14.5 +/- 2.8)% vs (28.3 +/- 2.2)% respectively, beta-catenin, (20.5 +/- 3.5)% vs (27.3 +/- 2.9)% and (13.3 +/- 2.1)% vs (20.6 +/- 2.4)%, while reduce MMP-2, (48.3 +/- 4.1)% vs (29.4 +/- 3.5)% and (57.3 +/- 4.3)% vs (38.2 +/- 4.0)% respectively, MMP-9, (55.6 +/- 4.0)% vs (34.3 +/- 3.5)% and (62.4 +/- 4.8)% vs (44.4 +/- 4.1)%, all P < 0.05; (3) Compared with that of control group, a high dose of Tongxinluo could reduce significantly both no-reflow area, (6.6 +/- 1.7) cm2 vs (4.7 +/- 1.5) cm2, P < 0.05, and percentage (90.8 +/- 3.8)% vs (71.4 +/- 4.1)%, P < 0.05, at 3 hours of reperfusion. A high dose of tongxinluo could effectively maintain the integrity of vascular endothelium and attenuate no-reflow area in early reperfusion of acute myocardial infarction.

Regional Heterogeneity of Myocardial Reperfusion Injury: Effect of Mild Hypothermia

Mild hypothermia confers a myocardial protective effect that may make it a useful adjunct to reperfusion therapy for myocardial infarction (MI). The effect of temperature on the extent and distribution of myocardial reperfusion injury in a collateral deficient ovine model was studied. Topical cooling maintained left atrial temperature at 39.5 degrees C (n = 8), 38.5 degrees C (n = 5), 37.5 degrees C (n = 6), 36.5 degrees C (n = 6), or 35.5 degrees C (n = 5) in sheep prior to 1 hour of coronary occlusion to produce an anteroapical myocardial risk area (AR) followed by 3 hours of reperfusion. A dual staining and planimetry technique was used to assess infarct size as a percentage of the AR in 3 myocardial short axis slices that included the entire AR (slice 1= most apical; slice 3= most basal). The subendocardial, midmyocardial, and subepicardial extent in short axis of the infarct was also assessed in each slice. Microspheres assessed transmural blood flow. At 39.5 degrees C there was a long-axis gradient in myocardial injury that was most severe at the apex and lessened toward the base. The midmyocardial region was most susceptible to injury at all long axis levels. Temperature reduction (as little as 1 degrees C) was associated with improved salvage that was most pronounced in the apical subendocardium and least in the basilar midmyocardium. Reperfusion at 39.5 degrees C resulted in severe transmural microvascular injury (no-reflow) that was completely obviated at temperatures below 38.5 degrees C. Myocardial reperfusion injury varies over the long and short LV axes. Mild hypothermia preferentially improves myocardial salvage at the LV apex. Small temperature changes can dramatically affect microvascular integrity.

Uncertainty on the Use of Aldosterone Antagonists for Primary Therapy for Sudden Cardiac Death in the Setting of Implanted Devices

In the early development of therapy for acute myocardial infarction, it was thought that once the necrotic process had been completed (usually within 24 hours of coronary artery occlusion), additional therapies could not affect outcome. However, after completion of the necrotic process, the myocardial infarction may thin and stretch (involving lengthwise slippage of myocytes), a phenomenon referred to as myocardial infarct expansion. This process causes local left ventricular cavity dilatation followed by gradual global left ventricular dilatation and lengthwise (eccentric) hypertrophy of the noninfarcted tissue. Apoptosis (programmed cell death) and some attempt of the myocardium to regenerate, especially at the infarct border zone, may also contribute to this remodeling process of the ventricle. If the left ventricle remodels in such a way that it becomes very dilated, then the prognosis is poor, and heart failure is more likely to occur.1 These later processes of myocardial infarct expansion and left ventricular remodeling became the target of therapies such as angiotensin-converting enzyme (ACE) inhibition that could be initiated after 24 hours of coronary occlusion. ACE inhibition, angiotensin receptor blockade, and long-term β-blockade have become standard pharmacological approaches for postinfarction left ventricular dysfunction and heart failure. Response by Pitt and Pitt p 2989 Ventricular arrhythmias can occur in both the acute and chronic phases of acute myocardial infarction and can lead to sudden cardiac death (SCD). Reentrant arrhythmias may arise at the border zone of infarcts, causing monomorphic ventricular tachycardia that may occur years after the index infarction. Recurrent myocardial ischemia resulting in an unstable substrate may contribute to polymorphic ventricular tachycardia or ventricular fibrillation. Agents such as β-blockers that are anti-ischemic may reduce sudden death by quieting this unstable substrate. In the Multicenter Automatic Defibrillator Implantation Trial (MADIT) II, implantable defibrillators were shown to reduce mortality in post–myocardial infarction patients with …

Beneficial effects of diltiazem on myocardial no-reflow in a mini-swine model of acute myocardial infarction and reperfusion

To evaluate the beneficial effects of diltiazem on myocardial no-reflow. Twenty-four mini-swine were randomized into 3 equal groups: diltiazem-treated group subjected to 3 hours of coronary occlusion to cause acute myocardial infarction (AMI), followed by 60 minutes of reperfusion and injected with diltiazem into the coronary artery 1 minute before reperfusion, control group undergoing coronary occlusion followed by 60 minutes of reperfusion and injected with normal saline, and sham operation group. 5 minutes before AMI in all groups and 180 minutes after AMI and 60 minutes after re-perfusion in the diltiazem and control groups, hemodynamic data, such as heart rate (HR), left ventricular systolic pressure (LVSP). Left ventricular end diastolic pressure (LVEDP), +/- dp/dt(max), cardiac output (CO), and coronary blood volume (CBV) were measured. Myocardial contrast echography (MCE) was used to measure the left ventricle wall area (LVWA) and ligation area (LA) so as to calculate LA and to measure the area of no-reflow (ANR) so as to calculate ANR. 60 minutes after reperfusion thioflavin-S was injected into left ventricle so as to color the reperfused area and then the descending anterior branch was re-ligated and Evan's blue was injected into the left ventricle to color the area outside the ligation area. The heart was taken out to undergo histological examination. (1) In comparison with the values before AMI the LVSP, +/- dp/dt(max), and CO of the control group significantly declined (P < 0.05, 0.01), while the LVEDP significantly increased (P < 0.01) by the end of 3 hours after LAD occlusion; and the LVSP significantly increased and the +/- dp/dt(max) further significantly declined (both P < 0.05) 60 minutes after reperfusion. In the diltiazem group, the changes of LVSP, +/- dp/dt(max), CO, and LVEDP were the same as those in the control group after 3 hours of AMI, while the +/- dp/dt(max), CO, and LVEDP recovered significantly, more significantly than those in the control group, 60 minutes after reperfusion (all P < 0.05). (2) In the control group, the sizes of coronary ligation area (LA) measured by both MCE in vivo and histopathological evaluation were similar (P > 0.05), and the values of area of no-reflow (ANR) measured by MCE in vivo and histopathological evaluation were 78.5% and 82.3% respectively with the final necrosis area (NA) reaching 99% of the LA. There was no significant difference in LA measured by both MCE and histopathological evaluation between the control and diltiazem groups, while the values of ANR measured by both methods was significantly decreased to 19.9% and 20.6% that before AMI respectively in the diltiazem group (both P < 0.01). There was no significant difference in NA between the control and diltiazem groups (P > 0.05). The CBV of the control group was significantly declined to 45.8% and 50.6% of the baseline value respectively immediately and 60 minutes after reperfusion (both P < 0.01), while the CBV of the diltiazem group became 80.4% and 79.3% of the baseline value respectively immediately and 60 minutes after reperfusion (both P < 0.05), both significantly higher than those of the control group (both P < 0.01). Diltiazem is effective both in preventing myocardial no-reflow and improving left ventricular function, but not in reducing MI size during AMI and reperfusion.

Contrast echocardiography can assess risk area and infarct size during coronary occlusion and reperfusion: experimental validation

ObjectivesWe sought to validate the ability of real-time myocardial contrast echocardiography (MCE) measures of opacification defect and contrast refilling parameters to estimate risk area (RA) and infarct area (IA) during coronary occlusion and reperfusion. BackgroundNo data exist establishing the accuracy of MCE in determining RA and IA size. We hypothesized that in the setting of coronary occlusion, MCE should identify RA as a perfusion defect early after bubble destruction, collateral flow to viable myocardium as opacification late during refilling and IA as absent opacification. MethodsThree hours of coronary occlusion and reperfusion were each produced in 11 dogs in which real-time MCE was performed during intravenous infusion of Sonovue (Bracco). Real-time contrast echocardiography was performed at baseline, during occlusion and reperfusion. Early (BEGIN) and end (END) images from a FLASH refilling sequence were acquired, as well as late refilling images (LATE) 1 min after FLASH. Real-time contrast echocardiography defect size and quantitative refilling parameters were compared with RA and IA determined by tissue staining. ResultsDuring occlusion, defect size varied with refilling time; defects from BEGIN images correlated best to RA and those from LATE images to IA. Refilling parameters, but not LATE peak intensity, did not predict the IA size during occlusion. During reperfusion, defects from BEGIN images were well correlated to RA and END images to IA, whereas peak plateau intensity and refilling slope parameters predicted IA size. ConclusionsReal-time contrast echocardiography defect size varies throughout microbubble refilling. Appropriately selected defect sizes and refilling parameters provide estimates of RA and IA during coronary occlusion and reperfusion.

Effect of Poloxamer 188 on Collateral Blood Flow, Myocardial Infarct Size, and Left Ventricular Function in a Canine Model of Prolonged (3-Hour) Coronary Occlusion and Reperfusion.

Poloxamer 188 is a surfactant with hemorheological, antithrombotic, and neutrophil-inhibitory properties. This agent has been demonstrated to reduce infarct size and to improve left ventricular function in animal models of myocardial infarction and reperfusion, and recently in a randomized trial of patients receiving thrombolytic therapy for acute myocardial infarction. In addition to reducing reperfusion injury, poloxamer 188 might be beneficial by increasing collateral blood flow. The purpose of this study was to determine the effect of poloxamer 188 on collateral blood flow, myocardial infarct size, and left ventricular function in a canine model of prolonged (3 hours) coronary occlusion and reperfusion. Closed-chest dogs (n = 21) underwent a 3-hour coronary occlusion and 3 hours of reperfusion. At 1 hour of occlusion, dogs received poloxamer 188, 75 mg/kg IV bolus, followed by 150 mg/kg/h IV for the final 2 hours of coronary occlusion and throughout reperfusion, or a saline placebo. Regional myocardial blood flow was measured using colored microspheres. Myocardial infarct size and area at risk were determined by postmortem histochemical staining. Compared with controls, poloxamer 188-treated dogs showed no significant increase in collateral blood flow during the final 2 hours of a 3-hour coronary artery occlusion. In addition, poloxamer 188 treatment had no beneficial effect on infarct size or left ventricular function in this model. Increased collateral blood flow is unlikely to be a beneficial mechanism of poloxamer 188 in myocardial infarction. These data also question the benefit of this agent to reduce reperfusion injury in the setting of more prolonged (3-hour) coronary occlusion.

Is calcium a mediator of infarct size reduction with preconditioning in canine myocardium?

The cellular mechanisms by which brief episodes of ischemia protect or "precondition" the heart and limit infarct size caused by a later period of sustained coronary artery occlusion remain unresolved. We propose that calcium may be an important mediator in eliciting this cardioprotection. To test this hypothesis, anesthetized dogs received a 15-minute intracoronary infusion of 20 mmol/L CaCl2 or saline before undergoing 1 hour of coronary occlusion and 4 hours of reperfusion (protocol 1). Collateral blood flow during occlusion was measured with radiolabeled microspheres, area at risk of infarction (AR) was delineated by injection of blue dye, and area of necrosis (AN) was determined by tetrazolium staining. AN/AR was reduced from 20+/-5% in the saline-treated controls to 9+/-3% in CaCl2-treated dogs (P<.05). Additional animals underwent 10 minutes of preconditioning ischemia or a comparable waiting period before the 1-hour test occlusion (protocol 2). Administration of 5-(N,N-dimethyl)-amiloride (an inhibitor of calcium influx via Na+-H+ and Na+-Ca2+ exchange) before the preconditioning stimulus attenuated the protective effect of ischemic preconditioning: AN/AR was 12+/-1%, larger than the value of 4+/-1% observed in preconditioned dogs that received saline (P<.05) and comparable to the values of 12+/-3% and 14+/-3% seen in saline- and dimethylamiloride-treated controls. Brief intracoronary infusion of CaCl2 mimicked, whereas treatment with dimethylamiloride blocked, infarct size reduction with preconditioning, thereby implicating calcium as a mediator of preconditioning in this canine model.

Coronary reserve abnormalities in the infarcted myocardium. Assessment of myocardial viability immediately versus late after reflow by contrast echocardiography.

The aim of this study was to determine whether myocardial contrast echocardiography (MCE) during exogenous vasodilation can accurately delineate infarct size, and hence the extent of myocardial viability, both immediately (15 minutes) and late (3 hours) after reperfusion when postreflow coronary hyperema is still present. Twenty-one open-chest anesthetized dogs underwent 3 to 6 hours of coronary occlusion followed by reperfusion. MCE was performed 15 minutes after reflow before and during infusion of 0.2 mg.kg-1.min-1 adenosine i.v.. In 12 dogs, infarct size was measured at this time. In the remaining 9 dogs, reperfusion was continued for 3 hours, when MCE was repeated before and after an infusion of 0.56 mg.kg-1.min-1 dipyridamole i.v. and infarct size was measured. In the absence of adenosine, MCE perfusion defect at 15 minutes underestimated infarct sizes at both 15 minutes and 3 hours, whereas in the presence of adenosine, the estimate of infarct size was more accurate. Similarly, in the absence of dipyridamole, although MCE perfusion defect underestimated infarct size (both measured 3 hours after reflow), in the presence of dipyridamole, the estimate of infarct size was more accurate. By unmasking abnormalities in flow reserve within the infarct bed, MCE in conjunction with coronary vasodilators can accurately predict infarct size both 15 minutes and 3 hours after reperfusion. Thus, MCE can be used for assessing the extent of myocardial viability both immediately and late after reperfusion when postreflow coronary hyperemia is still present.

1H NMR spectroscopic imaging of myocardial triglycerides in excised dog hearts subjected to 24 hours of coronary occlusion.

Myocardial ischemic insult causes depression of fatty-acid beta-oxidation and increased fatty-acid esterification with triglyceride (TG) accumulation. This accumulation has been demonstrated to occur in the territory with diminished blood flow surrounding an infarct, ie, the region at risk. To evaluate whether the extent of TG accumulation in the canine heart after 24 hours of ischemia could be detected, we applied myocardial 1H nuclear magnetic resonance (NMR) spectroscopic imaging (SI). Seven adult mongrel dogs underwent 24 hours of left anterior descending coronary artery occlusion. Postmortem, the hearts were excised and the size and location of the infarct were determined. With a Philips 1.5-T clinical NMR imaging/spectroscopic system, two-dimensional (2D) 1H NMR SI was performed. TG 1H NMR chemical shift images were reconstructed from the frequency domain spectra by numerical integration. A statistically significant (P < .05) increase in TG signal intensity was demonstrated in the region at risk compared with the nonischemic control region. There was an intermediate quantity of TG in the infarct region. Biochemical determination of tissue TG content (milligrams per gram wet weight) in the control, at-risk, and infarct regions confirmed the 1H NMR measurements. Histological evaluation with oil red O staining also demonstrated graded TG accumulation in myocytes. The highest TG levels were found in the at-risk region and the lowest levels in the control region. By use of 2D 1H NMR SI, the present study confirms and extends previous work that demonstrates preferential accumulation of TG in the reversibly injured myocardium after 24 hours of coronary occlusion. This study provides an important step toward the clinical application of TG imaging. When TG imaging is ultimately possible, resultant data would have diagnostic, prognostic, and therapeutic implications.

Benefits of late coronary artery reperfusion on infarct expansion progressively diminish over time: Relation to viable islets of myocytes within the scar

To define the time limit and mechanism of the effects of late coronary artery reperfusion on infarct expansion, rats were randomized into one of four groups: permanent left coronary artery occlusion; and 2, 8, and 16 hours of left coronary artery occlusion followed by reperfusion. Two weeks after coronary occlusion, morphometric and histologic analyses were performed. Benefits of late reperfusion on infarct expansion progressively diminished after increasingly long periods of coronary occlusion and were minimal but present after 16 hours of coronary occlusion. The extent of the benefits of late reperfusion on infarct expansion were related to preservation and hypertrophy of small islets of still viable myocytes located mainly in the subepicardium of the scar.

Low-Dose IV Acetylcholine Acts As a "Preconditioning-Mimetic" in the Canine Model

Brief episodes of ischemia paradoxically protect or "precondition" the heart and reduce infarct size caused by a subsequent, more sustained, coronary artery occlusion, perhaps by stimulation of adenosine receptors coupled to muscarinic receptors via the inhibitory G protein. However, brief ischemia is not a desirable form of therapy. Using the anesthetized canine model, we therefore sought to determine if small intravenous (i.v.) doses of the muscarinic agonist acetylcholine would provide a therapeutically feasible means to mimic preconditioning. Four groups of dogs underwent a 40-minute intervention period, followed by 1 hour of coronary occlusion and 5 hours of reperfusion: 8 received two i.v. doses of acetylcholine (0.01 mg each) at 40 minutes and 5 minutes before the sustained occlusion; 8 received equipotent doses of nitroglycerin (0.05 mg; a vasodilator that does not act via the M2 muscarinic receptor); 7 received conventional ischemic preconditioning (four 5-minute episodes of coronary occlusion, each interrupted by 5 minutes of reperfusion); and 8 controls received no intervention. Coronary blood flow and hemodynamic parameters were monitored throughout the protocol, regional myocardial blood flow was measured during the sustained occlusion by injection of radiolabeled microspheres, and infarct size was assessed by tetrazolium staining. All four groups were equally ischemic during coronary occlusion. However, infarct size was reduced significantly in both the preconditioned and acetylcholine-treated dogs when compared with controls (6% +/- 2% [p < 0.01 vs controls], 10% +/- 2% [p < 0.05 vs controls], and 19% +/- 3% of the myocardium at risk).(ABSTRACT TRUNCATED AT 250 WORDS)

Aspirin Enhances the Benefits of Late Reperfusion on Infarct Shape

The time window of the benefits of late reperfusion on infarct shape is limited. In rats, these benefits diminish in a wave front over time, with minimal benefits when reperfusion follows 16 hours of coronary occlusion. The mechanism of the benefits of aspirin on survival after acute myocardial infarction is unknown. The purpose of this study was to test the ability of aspirin to enhance the benefits of late coronary artery reperfusion on infarct shape and to examine the mechanism of the benefits of aspirin on infarct shape. Rats were entered into two different protocols, the morphometric and the histological protocols. In the morphometric protocol, rats were randomized into two groups: the aspirin group, in which rats underwent left coronary artery occlusion followed by treatment with aspirin (12 mg/kg i.v.), and the control group, in which rats underwent left coronary artery occlusion followed by treatment with placebo. Rats in both groups were reperfused 8 hours after coronary occlusion. Rats in the aspirin group received aspirin in the drinking water (12 +/- 2 mg/kg daily). Morphometric analysis was performed 2 weeks after acute myocardial infarction. In the histological protocol, rats underwent the same randomization, coronary occlusion, and reperfusion protocols. Hearts were removed 24 hours after coronary occlusion, and microvessels were assessed for patency. Infarct size expressed as a percent of circumference was similar in the aspirin and placebo treatment groups (28 +/- 2% versus 33 +/- 3%, P = NS). Septal thickness was also similar in both groups (1.8 +/- 0.1 versus 2.1 +/- 0.1 mm, P = NS for aspirin versus placebo). The aspirin-treated group had thicker infarcts compared with the placebo-treated group (0.8 +/- 0.1 versus 0.5 +/- 0.1 mm, P < .05) and less expanded infarcts (expansion index, 1.2 +/- 0.1 versus 2.0 +/- 0.2, P < .05). Aspirin was associated with increased patency of the microvessels in the infarcted area compared with the placebo group (96% versus 64% of microvessels patent, P < .001). Aspirin enhances the benefit of late coronary artery reperfusion on infarct shape after 8 hours of coronary occlusion. The benefits of aspirin on infarct shape after late reperfusion are related to increased patency of the microvessels in the infarcted area.

Effect of Coronary Artery Reperfusion on Transmural Myocardial Remodeling in Dogs

The effects of reperfusion after coronary occlusion on transmural remodeling of the ischemic region early and late after nontransmural infarction must importantly affect the recovery of regional function. Accordingly, analysis of local volume and three-dimensional strain was performed using a finite element method to determine regional remodeling. Systolic and remodeling strains were measured using radiographic imaging of three columns (approximately 1 cm apart) of four to six gold beads implanted across the left ventricular posterior wall in 6 dogs. After a control study, infarction was produced by 2 to 4 hours of proximal left circumflex coronary artery occlusion followed by reperfusion. Follow-up studies were performed at 2 days, 3 weeks, and 12 weeks with the dogs under anesthesia and in closed-chest conditions. Biplane cineradiography was performed to obtain the three-dimensional coordinates of the beads. At 2 days, end-systolic strains were akinetic with loss of normal transmural gradients of shortening and thickening. Remodeling strains (RS) were determined by use of a nonhomogeneous finite element method by referring the end-diastolic configuration during follow-up studies to its control state at matched end-diastolic pressures and heart rates. Tissue volume at 2 days increased substantially, more at the endocardium (30 +/- 7%) than at the epicardium (5 +/- 12%, P < .01); the increase was associated with an average RS in the wall-thickening direction of 0.18 +/- 0.15 (P < .01) with all other RS near zero. At 12 weeks systolic function partially recovered, with normal wall thickening in the epicardium (radial strain, 0.081 +/- 0.056 [control] versus 0.113 +/- 0.088 [12 weeks]) but with dysfunction in the endocardium (0.245 +/- 0.108 [control] versus 0.111 +/- 0.074 [P < .01] [12 weeks]). This inability of the inner wall to recover function may be related to increased transmural torsional shear and negative longitudinal-radial transverse shear in the inner wall. Volume loss occurred at 12 weeks in the endocardium (-36 +/- 16%) corresponding to transmural gradients in longitudinal RS and both transverse shear RS. Negative longitudinal RS was greater at the endocardium (-0.20 +/- 0.10) than at the epicardium (-0.06 +/- 0.05, P < .01). These results indicate the presence of marked subendocardial edema 2 days after reperfusion following 2 to 4 hours of coronary occlusion. At 3 months after reperfusion, however, there was volume loss in the inner wall due to shrinkage along the myofiber direction with reduced transmural function and loss of longitudinal shortening, while both tissue volume and function recovered completely in the outer wall.

Cardioprotective effect of L-carnitine in rats submitted to permanent left coronary artery ligation.

Several studies have suggested that L-carnitine may limit the cellular alterations induced by myocardial hypoxia or ischemia. In the present study, rats were subjected to chronic treatment with L-carnitine (0, 25, 50 or 200 mg/kg/day i.p.) for 9 days prior to being submitted to permanent regional myocardial ischemia by left coronary artery ligation in situ. Following 48 hours of coronary occlusion, infarct size was measured using planimetry of transverse sections of the hearts, which had been stained with nitro-blue tetrazolium. Various functional and metabolic parameters have also been measured in isolated perfused hearts. Treatment with L-carnitine at 200 mg/kg/day i.p. for 9 days led to a significant reduction in infarct size and a better preservation of residual cardiac function. However, none of the metabolic parameters measured were modified. In conclusion, we suggest that the preservation of cardiac contractile function observed with L-carnitine pretreatment is secondary to carnitine-induced infarct size limitation.

Controlled coronary hydrodynamics at the time of reperfusion reduces postischemic injury

Background: In a canine preparation of 2 hours of coronary occlusion and 2 hours of reperfusion, we tested the hypothesis that controlled hydrodynamic conditions (coronary pressure and flow) of reperfusion would decrease infarct size and improve regional functional recovery. Methods: In 28 anesthetized, open-chest dogs, segmental contractile work and diastolic stiffness (sonomicrometry), and myocardial blood flow (15 μm microspheres) were measured in the segment per fused by the left anterior descending (LAD) and circumflex coronary arteries. After 2 hours of LAD occlusion, reperfusion was established using an extracorporeal perfusion circuit to control intracoronary pressure and blood flow. Twelve dogs did not complete the protocol or meet exclusion criteria. In eight dogs (abrupt group), blood flow was abruptly restored and continued for 2 hours of reperfusion. In eight dogs (ramp group), blood flow was adjusted so that LAD perfusion pressure was linearly incremented over the first 30 minutes of reflow, and equalized to mean arterial pressure thereafter. Results: Two hours of LAD occlusion reduced myocardial blood flow in the ischemic zone from 67.7 ± 11.7 to 11.7 ± 4.7 mL/min/100g (P Conclusions: Slowly increasing coronary pressure and blood flow during the early phase of reperfusion 1) increases postischemic systolic and diastolic functional recovery, 2) improves postischemic blood flow, and 3) reduces infarct size by 67%. These data suggest that the mode of reperfusion may be a factor in determining myocardial injury after reversible occlusion.

Assessment of postreperfusion myocardial hemorrhage using proton NMR imaging at 1.5 T.

Intramyocardial hemorrhage occurs frequently after reperfusion of acute myocardial infarction. However, its significance has not yet been established, mainly because of the lack of methods for detecting such hemorrhage. The following ex vivo study was carried out to assess the potential of nuclear magnetic resonance (NMR) imaging to detect and quantitate postreperfusion intramyocardial hemorrhage. Sixteen adult mongrel dogs underwent 3 hours of coronary occlusion followed by 1 hour of reperfusion, and three dogs underwent 4 hours of occlusion without reperfusion. Radiolabeled microspheres and 51Cr-labeled red blood cells were used to assess flow and evaluate the extent of hemorrhage. These results were later compared with both NMR and histology. Spin-echo NMR imaging was performed on the excised hearts using a 1.5-T system. Macroscopic assessment of the sliced myocardium revealed the existence of hemorrhage in 14 of the 16 dogs that underwent reperfusion but in none of those with occlusion only. In all 16 dogs with reperfusion, zones of increased signal intensity (SI) ratio (1.68 +/- 0.41 compared with control, p less than 0.05) were seen in regions relating to the distribution of the occluded coronary artery, whereas in 13 of the 16 dogs, areas of decreased SI within the zone of increased SI ratio (0.81 +/- 0.16 compared with control, p less than 0.05) were also seen, corresponding to regions with macroscopic hemorrhage. In contrast, in the three dogs without reperfusion, no macroscopic hemorrhage was observed, and likewise, no NMR zones of reduced SI were detected. Hemorrhage size by NMR (decreased SI zones), correlated well with hemorrhage size calculated from tissue slices (r = 0.96, SEE = 0.92%, p less than 0.01), or by 51Cr labeling (r = 0.78, SEE = 1.5, p = 0.1). In the reperfusion group, T2 relaxation times in the infarcted hemorrhagic zone (58 +/- 9 msec) were significantly lower than the infarcted zones without hemorrhage (98 +/- 13 msec, p less than 0.001). In contrast, when compared with control (964 +/- 72 msec), T1 relaxation times were significantly increased in both infarct zones, either with (1,284 +/- 176 msec) or without (1,266 +/- 103 msec) hemorrhage. The selective shortening of T2 relaxation times in the hemorrhagic regions is consistent with the paramagnetic effects of deoxyhemoglobin. NMR imaging may provide a noninvasive approach for the detection and quantitation of intramyocardial hemorrhage. This observation may provide a means to further characterize pathological processes associated with acute myocardial infarction and assess the role of myocardial hemorrhage after reperfusion therapy.

Area-at-risk determination by technetium-99m-hexakis-2-methoxyisobutyl isonitrile in experimental reperfused myocardial infarction.

In a canine model of reperfused myocardial infarction, we tested the hypothesis that after reperfusion, technetium-99m-hexakis-2-methoxyisobutyl isonitrile (Tc-MIBI) tomographic imaging still reflects occlusion blood flow when the tracer is injected before reperfusion. Nine anesthetized dogs underwent 2 hours of coronary occlusion followed by 3 hours of reperfusion ending by being killed. Reference coronary blood flow was determined by radioactive microspheres injected during occlusion and after reperfusion. Biopsies in normal and ischemic myocardium and single photon emission computed tomography were obtained during occlusion and after reperfusion. Circumferential profiles were applied to axial slices divided into 5-degree sectors. The sectors were divided into 3 groups selected on the occlusion acquisition (normal, mildly reduced, and severely reduced) and compared with the postreperfusion acquisition. Tissular Tc-MIBI kinetics was assessed both by Tc-MIBI time-activity curves of normal and ischemic tissue obtained by biopsy and by the relative gradient between normal, ischemic, and necrotic postmortem tissue samples. In biopsy samples, Tc-MIBI content remained unchanged during occlusion and after reperfusion in normal as well as in ischemic tissue (4,662 +/- 2,237 counts/min/mg vs. 4,599 +/- 1,577 counts/min/mg in normal tissue, NS; 941 +/- 903 counts/min/mg vs. 1,087 +/- 721 counts/min/mg in ischemic tissue, NS). In postmortem tissue samples, there was a good correlation between occlusion microsphere blood flow and Tc-MIBI activity (r = 0.91). In the necrotic samples, mean normalized Tc-MIBI activity (10 +/- 17%) was slightly higher than the normalized microsphere blood flow (3 +/- 3%, p less than 0.001) but markedly lower than the normalized microsphere reperfusion blood flow (63 +/- 31%, p less than 0.001). Comparing the single photon emission computed tomographic acquisitions before and after reperfusion, Tc-MIBI activity remained unchanged in normal as well as in mildly reduced or severely reduced segments. Thus, our data are consistent with the hypothesis that Tc-MIBI traces blood flow, does not redistribute significantly despite reperfusion, and can be used for imaging the area at risk.