The effect of streptokinase on intramyocardial hemorrhage, infarct size, and the no-reflow phenomenon during coronary reperfusion

Coronary No-Reflow after Primary Percutaneous Coronary Intervention-Current Knowledge on Pathophysiology, Diagnosis, Clinical Impact and Therapy

Coronary no-reflow (CNR) is a frequent phenomenon that develops in patients with ST-segment elevation myocardial infarction (STEMI) following reperfusion therapy. CNR is highly dynamic, develops gradually (over hours) and persists for days to weeks after reperfusion. Microvascular obstruction (MVO) developing as a consequence of myocardial ischemia, distal embolization and reperfusion-related injury is the main pathophysiological mechanism of CNR. The frequency of CNR or MVO after primary PCI differs widely depending on the sensitivity of the tools used for diagnosis and timing of examination. Coronary angiography is readily available and most convenient to diagnose CNR but it is highly conservative and underestimates the true frequency of CNR. Cardiac magnetic resonance (CMR) imaging is the most sensitive method to diagnose MVO and CNR that provides information on the presence, localization and extent of MVO. CMR imaging detects intramyocardial hemorrhage and accurately estimates the infarct size. MVO and CNR markedly negate the benefits of reperfusion therapy and contribute to poor clinical outcomes including adverse remodeling of left ventricle, worsening or new congestive heart failure and reduced survival. Despite extensive research and the use of therapies that target almost all known pathophysiological mechanisms of CNR, no therapy has been found that prevents or reverses CNR and provides consistent clinical benefit in patients with STEMI undergoing reperfusion. Currently, the prevention or alleviation of MVO and CNR remain unmet goals in the therapy of STEMI that continue to be under intense research.

A historical literature review of coronary microvascular obstruction and intra-myocardial hemorrhage as functional/structural phenomena

The analysis of experimental data demonstrates that platelets and neutrophils are involved in the no-reflow phenomenon, also known as microvascular obstruction (MVO). However, studies performed in the isolated perfused hearts subjected to ischemia/reperfusion (I/R) do not suggest the involvement of microembolization and microthrombi in this phenomenon. The intracoronary administration of alteplase has been found to have no effect on the occurrence of MVO in patients with acute myocardial infarction. Consequently, the major events preceding the appearance of MVO in coronary arteries are independent of microthrombi, platelets, and neutrophils. Endothelial cells appear to be the target where ischemia can disrupt the endothelium-dependent vasodilation of coronary arteries. However, reperfusion triggers more pronounced damage, possibly mediated by pyroptosis. MVO and intra-myocardial hemorrhage contribute to the adverse post-infarction myocardial remodeling. Therefore, pharmacological agents used to treat MVO should prevent endothelial injury and induce relaxation of smooth muscles. Ischemic conditioning protocols have been shown to prevent MVO, with L-type Ca ²⁺ channel blockers appearing the most effective in treating MVO.

Update on Cardioprotective Strategies for STEMI: Focus on Supersaturated Oxygen Delivery

Despite the fact that door-to-balloon times have been greatly reduced, the rates of death and the incidence of heart failure in patients with ST-segment elevation myocardial infarction (MI) have plateaued. There is still an unmet need to further reduce MI size in the reperfusion era. Most adjunctive therapies to enhance myocardial salvage have failed, but some have shown promise. Currently, the only adjunctive therapy in a pivotal trial that has demonstrated reductions in infarct size is localized delivery of supersaturated oxygen (SSO₂) therapy. This review provides background on prior infarct size reduction efforts. The authors describe the preclinical data that shows the effectiveness of SSO₂ in reducing MI size, improving regional myocardial blood flow and cardiac function, and reducing adverse left ventricular remodeling-presumably by reducing patchy areas of residual ischemia within the reperfused risk zone. Potential mechanisms by which SSO₂ is beneficial are described, including the delivery of high levels of dissolved oxygen through plasma to ischemic, but viable, vascular and myocardial cells, thus allowing their survival and function. The authors then describe the SSO₂ clinical trials, demonstrating that in patients with anterior ST-segment elevation MI, SSO₂ therapy safely and effectively reduces infarct size, improves cardiac function, and reduces adverse left ventricular remodeling.

Controlling Reperfusion Injury With Controlled Reperfusion: Historical Perspectives and New Paradigms

Cardiac reperfusion injury is a well-established outcome following treatment of acute myocardial infarction and other types of ischemic heart conditions. Numerous cardioprotection protocols and therapies have been pursued with success in pre-clinical models. Unfortunately, there has been lack of successful large-scale clinical translation, perhaps in part due to the multiple pathways that reperfusion can contribute to cell death. The search continues for new cardioprotection protocols based on what has been learned from past results. One class of cardioprotection protocols that remain under active investigation is that of controlled reperfusion. This class consists of those approaches that modify, in a controlled manner, the content of the reperfusate or the mechanical properties of the reperfusate (e.g., pressure and flow). This review article first provides a basic overview of the primary pathways to cell death that have the potential to be addressed by various forms of controlled reperfusion, including no-reflow phenomenon, ion imbalances (particularly calcium overload), and oxidative stress. Descriptions of various controlled reperfusion approaches are described, along with summaries of both mechanistic and outcome-oriented studies at the pre-clinical and clinical phases. This review will constrain itself to approaches that modify endogenously-occurring blood components. These approaches include ischemic postconditioning, gentle reperfusion, controlled hypoxic reperfusion, controlled hyperoxic reperfusion, controlled acidotic reperfusion, and controlled ionic reperfusion. This review concludes with a discussion of the limitations of past approaches and how they point to potential directions of investigation for the future.

No-reflow phenomenon in the heart and brain

The no-reflow phenomenon refers to the observation that when an organ is made ischemic by occlusion of a large artery supplying it, restoration of patency in that artery does not restore perfusion to the microvasculature supplying the parenchyma of that organ. This has been observed after prolonged arterial occlusions in the heart (30–90 min), brain, skin, and kidney. In experimental models, zones of no reflow in the heart are characterized by ultrastructural microvascular damage, including focal endothelial swelling obstructing the lumen of small vessels. Blood elements such as neutrophil plugs, platelets, and stacking of erythrocytes have also been implicated. No reflow is associated with poor healing of the myocardial infarction. In patients, no reflow is associated with a poor clinical outcome independent of infarct size, suggesting that therapy for no reflow may be an important approach to improving outcome for ST elevation myocardial infarction. No reflow occurs after reperfusion of experimental cerebral ischemia and may be observed after only 5-min episodes of ischemia. Aggregation of blood elements may play a greater role than in cardiac no reflow. No reflow in the brain may involve cortical spreading depression with disturbed local vascular control and high, vasculotonic levels of extracellular K+ concentration, postischemic swelling in endothelial cells and abutting end feet of pericytes, pericyte contraction and death, interstitial edema with collapse of cerebral capillaries, and inflammatory reaction. New guidelines suggesting that reperfusion for stroke may be considered as late as 24 h after the onset of symptoms suggest that clinicians may be seeing more no reflow in the future.

New and revisited approaches to preserving the reperfused myocardium

Early coronary artery reperfusion improves outcomes for patients with ST-segment elevation myocardial infarction (STEMI), but morbidity and mortality after STEMI remain unacceptably high. The primary deficits seen in these patients include inadequate pump function, owing to rapid infarction of muscle in the first few hours of treatment, and adverse remodelling of the heart in the months that follow. Given that attempts to further reduce myocardial infarct size beyond early reperfusion in clinical trials have so far been disappointing, effective therapies are still needed to protect the reperfused myocardium. In this Review, we discuss several approaches to preserving the reperfused heart, such as therapies that target the mechanisms involved in mitochondrial bioenergetics, pyroptosis, and autophagy, as well as treatments that harness the cardioprotective properties of inhaled anaesthetic agents. We also discuss potential therapies focused on correcting the no-reflow phenomenon and its effect on healing and adverse left ventricular remodelling.

Delayed therapeutic hypothermia protects against the myocardial no-reflow phenomenon independently of myocardial infarct size in a rat ischemia/reperfusion model

BACKGROUND

Adjunctive therapies, given in addition to reperfusion to reduce myocardial infarct size, have been disappointing based on clinical trials. New therapeutic targets independent of infarct size modification are needed. The no-reflow phenomenon occurs commonly after the infarct-related coronary artery is opened and predicts poor clinical outcome. We investigated the effects of a single application of delayed (post-reperfusion) therapeutic hypothermia (TH) in a rat model of coronary artery occlusion/reperfusion.

METHODS

Rats were subjected to 60min of coronary artery occlusion followed by 3h of reperfusion. Rats were divided into normothermic (n=5) and TH (n=5) groups. In the TH, hypothermia was initiated at 1min after coronary artery reperfusion by pumping room-temperature (22°C) saline into and out of the thoracic cavity for 1h. This decreased intrathoracic temperature to around 26°C within 12min. At 3h after reperfusion, hearts were excised for infarct size and no-reflow zone measurement.

RESULTS

Ischemic risk area and infarct size were similar between the 2 groups. No-reflow area (expressed as % of risk area) was significantly reduced in TH group (18.0±4.4%) compared with normothermic group (39.5±2.9%,P=0.005). When expressed as % of necrotic area, no-reflow area was reduced by more than half in TH group (25.5±6.4%) versus innormothermic group (54.4±5.3%,P=0.01).

CONCLUSIONS

In this preliminary study, hypothermia initiated after reperfusion following 60min of coronary artery occlusion had no effect on infarct size yet substantially reduced the extent of no-reflow.

No-Reflow Phenomenon: Maintaining Vascular Integrity

The no-reflow phenomenon relates to the inability to reperfuse regions of the myocardium after ischemia, despite removal of the large epicardial coronary artery occlusion. The mechanism involves microvascular obstruction. In experimental studies, using markers for flow (thioflavin S, carbon black, microspheres), perfusion defects associated with no-reflow demonstrated ultrastructural evidence of localized endothelial swelling and blebs that appeared to obstruct flow. In humans no-reflow is more complicated due to the microemboli of atherosclerotic debris and thrombi generated by percutaneous coronary intervention. The no-reflow zone expands during the first few hours of reperfusion suggesting an element of reperfusion injury. In animal models, extensive no-reflow was associated with worse infarct expansion. The phenomenon of no-reflow following reperfusion therapy for myocardial infarction in humans has been demonstrated by magnetic resonance imaging, echo contrast agents, thallium, technecium-99m-labeled albumin microspheres, Thrombolysis In Myocardial Infarction (TIMI) scores, and myocardial blush grade. Patients exhibiting no-reflow following reperfusion therapy for myocardial infarction have greater left ventricular dilation and remodeling, more congestive heart failure, shock, and reduced survival. Certain vasodilators (adenosine, nitroprusside, nicorandil, and calcium blockers) are used acutely in the catheterization laboratory and appear to improve no-reflow, but systematic studies on therapy for no-reflow are needed. There is now clinical evidence that no-reflow is a strong predictor of long-term mortality that is independent of and beyond that provided by infarct size. Identifying and treating no-reflow may have important benefits including enhancing delivery of nutrients and cells required for healing and reducing infarct expansion and ventricular remodeling, which ultimately may reduce congestive heart failure and mortality.

Dissecting the Effects of Ischemia and Reperfusion on the Coronary Microcirculation in a Rat Model of Acute Myocardial Infarction

BACKGROUND

Microvascular injury (MVI) after coronary ischemia-reperfusion is associated with high morbidity and mortality. Both ischemia and reperfusion are involved in MVI, but to what degree these phases contribute is unknown. Understanding the etiology is essential for the development of new potential therapies.

METHODS AND FINDINGS

Rats were divided into 3 groups receiving either 30 minutes ischemia, 90 minutes ischemia or 30 minutes ischemia followed by 60 minutes reperfusion. Subsequently hearts were ex-vivo perfused in a Langendorff-model. Fluorescence and electron microscopy was used for analysis of capillary density, vascular permeability and ultrastructure. Most MVI was observed after 30 minutes ischemia followed by 60 minutes reperfusion. In comparison to the 30' and 90' ischemia group, wall thickness decreased (207.0±74 vs 407.8±75 and 407.5±71, p = 0.02). Endothelial nuclei in the 30'-60' group showed irreversible damage and decreased chromatin density variation (50.5±9.4, 35.4±7.1 and 23.7±3.8, p = 0.03). Cell junction density was lowest in the 30'-60' group (0.15±0.02 vs 2.5±0.6 and 1.8±0.7, p<0.01). Microsphere extravasation was increased in both the 90' ischemia and 30'-60' group.

CONCLUSIONS

Ischemia alone for 90 minutes induces mild morphological changes to the coronary microcirculation, with increased vascular permeability. Ischemia for 30 minutes, followed by 60 minutes of reperfusion, induces massive MVI. This shows the direct consequences of reperfusion on the coronary microcirculation. These data imply that a therapeutic window exists to protect the microcirculation directly upon coronary revascularization.

Effect of microvascular obstruction and intramyocardial hemorrhage by CMR on LV remodeling and outcomes after myocardial infarction: a systematic review and meta-analysis

The goal of this systematic analysis is to provide a comprehensive review of the current cardiac magnetic resonance data on microvascular obstruction (MVO) and intramyocardial hemorrhage (IMH). Data related to the association of MVO and IMH in patients with acute myocardial infarction (MI) with left ventricular (LV) function, volumes, adverse LV remodeling, and major adverse cardiac events (MACE) were critically analyzed. MVO is associated with a lower ejection fraction, increased ventricular volumes and infarct size, and a greater risk of MACE. Late MVO is shown to be a stronger prognostic marker for MACE and cardiac death, recurrent MI, congestive heart failure/heart failure hospitalization, and follow-up LV end-systolic volumes than early MVO. IMH is associated with LV remodeling and MACE on pooled analysis, but because of limited data and heterogeneity in study methodology, the effects of IMH on remodeling require further investigation.

Usefulness of cardiac MRI in the prognosis and follow-up of ischemic heart disease

Cardiac magnetic resonance imaging (MRI) is an important tool that makes it possible to evaluate patients with cardiovascular disease; in addition to infarction and alterations in myocardial perfusion, cardiac MRI is useful for evaluating other phenomena such as microvascular obstruction and ischemia. The main prognostic factors in cardiac MRI are ventricular dysfunction, necrosis in late enhancement sequences, and ischemia in stress sequences. In acute myocardial infarction, cardiac MRI can evaluate the peri-infarct zone and quantify the size of the infarct. Furthermore, cardiac MRI's ability to detect and evaluate microvascular obstruction makes it a fundamental tool for establishing the prognosis of ischemic heart disease. In patients with chronic ischemic heart disease, cardiac MRI can detect ischemia induced by pharmacological stress and can diagnose infarcts that can be missed on other techniques.

The REFLO-STEMI trial comparing intracoronary adenosine, sodium nitroprusside and standard therapy for the attenuation of infarct size and microvascular obstruction during primary percutaneous coronary intervention: study protocol for a randomised controlled trial

BACKGROUND

Microvascular obstruction (MVO) secondary to ischaemic-reperfusion injury is an important but underappreciated determinant of short- and longer-term outcome following percutaneous coronary intervention (PCI) treatment of ST-elevation myocardial infarction (STEMI). Several small studies have demonstrated a reduction in the degree of MVO utilising a variety of vasoactive agents, with adenosine and sodium nitroprusside (SNP) being most evaluated. However, the evidence base remains weak as the trials have had variable endpoints, differing drug doses and delivery. As such, the results regarding benefit are conflicting.

METHODS

The REperfusion Facilitated by LOcal adjunctive therapy in STEMI (REFLO-STEMI) trial is a multicentre, prospective, randomised, controlled, open label, study with blinded endpoint analysis: Patients presenting within 6 h of onset of STEMI and undergoing planned primary PCI (P-PCI) with TIMI 0/1 flow in the infarct-related artery (IRA) and no significant bystander coronary artery disease on angiography, are randomised into one of three groups: PCI with adjunctive pharmacotherapy (intracoronary adenosine or SNP) or control (standard PCI). All receive Bivalirudin anticoagulation and thrombus aspiration. The primary outcome is infarct size (IS) (determined as a percentage of total left ventricular mass) measured by cardiac magnetic resonance imaging (CMRI) undertaken at 48 to 72 h post P-PCI. Secondary outcome measures include MVO (hypoenhancement within infarct core) on CMRI, angiographic markers of microvascular perfusion and MACE during 1-month follow-up. The study aims to recruit 240 patients (powered at 80% to detect a 5% absolute reduction in IS).

DISCUSSION

The REFLO-STEMI study has been designed to address the weaknesses of previous trials, which have collectively failed to demonstrate whether adjunctive pharmacotherapy with adenosine and/or SNP can reduce measures of myocardial injury (infarct size and MVO) and improve clinical outcome, despite good basic evidence that they have the potential to attenuate this process. The REFLO-STEMI study will be the most scientifically robust trial to date evaluating whether adjunctive therapy (intracoronary adenosine or SNP following thrombus aspiration) reduces CMRI measured IS and MVO in patients undergoing P-PCI within 6 h of onset of STEMI.

TRIAL REGISTRATION

Trial registered 20th November 2012: ClinicalTrials.gov Identifier NCT01747174.

CMR of microvascular obstruction and hemorrhage in myocardial infarction

Microvascular obstruction (MO) or no-reflow phenomenon is an established complication of coronary reperfusion therapy for acute myocardial infarction. It is increasingly recognized as a poor prognostic indicator and marker of subsequent adverse LV remodeling. Although MO can be assessed using various imaging modalities including electrocardiography, myocardial contrast echocardiography, nuclear scintigraphy, and coronary angiography, evaluation by cardiovascular magnetic resonance (CMR) is particularly useful in enhancing its detection, diagnosis, and quantification, as well as following its subsequent effects on infarct evolution and healing. MO assessment has become a routine component of the CMR evaluation of acute myocardial infarction and will increasingly play a role in clinical trials of adjunctive reperfusion agents and strategies. This review will summarize the pathophysiology of MO, current CMR approaches to diagnosis, clinical implications, and future directions needed for improving our understanding of this common clinical problem.

Detection and quantification of myocardial reperfusion hemorrhage using T2*-weighted CMR

OBJECTIVES

The purpose of this study was to validate T2*-weighted cardiac magnetic resonance (T2*-CMR) for the detection and quantification of reperfusion hemorrhage in vivo against an ex vivo gold standard, and to investigate the relationship of hemorrhage to microvascular obstruction, infarct size, and left ventricular (LV) functional parameters.

BACKGROUND

Hemorrhage can contribute to reperfusion injury in myocardial infarction and may have significant implications for patient management. There is currently no validated imaging method to assess reperfusion hemorrhage in vivo. T2*-CMR appears suitable because it can create image contrast on the basis of magnetic field effects of hemoglobin degradation products.

METHODS

In 14 mongrel dogs, myocardial infarction was experimentally induced. On day 3 post-reperfusion, an in vivo CMR study was performed including a T2*-weighted gradient-echo imaging sequence for hemorrhage, standard sequences for LV function, and post-contrast sequences for microvascular obstruction and myocardial necrosis. Ex vivo, thioflavin S imaging and triphenyl-tetrazoliumchloride (TTC) staining were performed to assess microvascular obstruction, hemorrhage, and myocardial necrosis. Images were analyzed by blinded observers, and comparative statistics were performed.

RESULTS

Hemorrhage occurred only in the dogs with the largest infarctions and the greatest extent of microvascular obstruction, and it was associated with more compromised LV functional parameters. Of 40 hemorrhagic segments on TTC staining, 37 (92.5%) were positive for hemorrhage on T2*-CMR (kappa = 0.96, p < 0.01 for in vivo/ex vivo segmental agreement). The amount of hemorrhage in 13 affected tissue slices as determined by T2*-CMR in vivo correlated strongly with ex vivo results (20.3 ± 2.3% vs. 17.9 ± 1.6% per slice; Pearson r = 0.91; r(2) = 0.83, p < 0.01 for both). Hemorrhage size was not different between in vivo T2*-CMR and ex vivo TTC (mean difference 2.39 ± 1.43%; p = 0.19).

CONCLUSIONS

T2*-CMR accurately quantified myocardial reperfusion hemorrhage in vivo. Hemorrhage was associated with more severe infarct-related injury.

The use of cardiovascular magnetic resonance in acute myocardial infarction

Acute myocardial infarction (MI) results in reversible and irreversible injury to the myocardium, including stunning, edema, myocyte necrosis, and microvascular obstruction. Because of its unique tissue characterization capabilities, cardiovascular magnetic resonance provides a reliable means of visualizing and quantifying the extent of these injuries. Such characterization is readily achieved through a comprehensive examination including function, first-pass perfusion, T2 (edema), and late enhancement imaging sequences. This helps to predict the prognosis, assess the success of reperfusion, detect acute phase complications, localize the area of the acute event, and confirm the diagnosis in clinical scenarios with clinical presentations similar to that of acute MI. Finally, one emerging application is the role cardiovascular magnetic resonance (CMR) may play in detecting some infarcts very early on in their evolution. This article covers the established and emerging clinical applications of CMR in the settings of reperfused and nonreperfused infarcts and in acute myocardial ischemia, the step immediately preceding actual irreversible injury.

Prediction of the no-reflow phenomenon during percutaneous coronary intervention using coronary computed tomography angiography

Coronary computed tomography angiography (CTA) can assess plaque characteristics and plaque size noninvasively. The purpose of this study was to investigate whether coronary CTA before percutaneous coronary intervention (PCI) can predict the no-reflow phenomenon during PCI. Seventy-eight patients [acute coronary syndrome (ACS) = 43, stable angina pectoris (SAP) = 35, male/female = 72/6, age: 65 ± 10 years] who underwent 16- or 64-slice CTA in the 4 weeks before PCI were enrolled. The low attenuation plaque size on CTA was compared between patients with (NR+) and without the no-reflow phenomenon (NR-). No-reflow phenomenon was observed in 11 patients, including 10 patients with ACS and 1 patient with SAP. Low attenuation plaque was detected in 9 (82%) NR(+) lesions and 35 (52%) NR(-) lesions. The length of low attenuation plaque was significantly longer in NR(+) than in NR(-) patients (9.0 ± 6.5 vs. 1.6 ± 2.7 mm, p < 0.0001). On step-wise regression analysis, ACS (p = 0.036, 95% CI = 0.009-0.258) and the presence of low attenuation plaque with a length >4.7 mm (p < 0.001, 95% CI = 0.447-0.778) were significant independent predictors of NR(-) no-reflow phenomenon. Low attenuation plaque with lesion length of >4.7 mm on coronary CTA and ACS were the significant predictors for the no-reflow phenomenon during PCI. Coronary CTA assessment before PCI would be useful to predict coronary events during PCI in advance.

The no-reflow phenomenon: A basic mechanism of myocardial ischemia and reperfusion

Both animal models of experimental myocardial infarction and clinical studies on reperfusion therapy for acute myocardial infarction have provided evidence of impaired tissue perfusion at the microvascular level after initiation of reperfusion despite adequate restoration of epicardial vessel patency. Characteristics of this "no-reflow" phenomenon found in basic science investigations, such as distinct perfusion defects, progressive decrease of resting myocardial flow with ongoing reperfusion and functional vascular alterations are paralleled by clinical observations demonstrating similar features during the course of reperfusion. In experimental animal investigations of coronary occlusion and reperfusion, this no-reflow phenomenon could be characterized as a fundamental mechanism of myocardial ischemia and reperfusion. Major determinants of the amount of no-reflow are the duration of occlusion, infarct size, but also the length of reperfusion, as rapid expansion of perfusion defects occurs during reperfusion. Moreover, no-reflow appears to persist over a period of at least four weeks, a period when major steps of infarct healing take place. The significant association of the degree of compromised tissue perfusion at four weeks and indices of infarct expansion, found in chronic animal models of reperfused myocardial infarction, might be the pathoanatomic correlate for the prognostic significance observed in the clinical setting.

MRI relaxation fluctuations in acute reperfused hemorrhagic infarction

MRI evaluations of intramyocardial hemorrhage in acute infarction have relied on T(2) and T(2)(*) shortening only. We propose a more comprehensive evaluation of hemorrhagic infarction based on the concept that fluctuations in T(2) and T(1) relaxation in acute reperfused infarction will reflect transient edema and hemoglobin oxidative denaturation to uncompartmentalized methemoglobin. Anteroapical infarction was created via percutaneous balloon in young swine (22-25 kg, N = 12). T(2), T(1), diastolic wall thickness (DWT), and the Gd-DTPA partition coefficient (lambda) were measured on days 0, 2, and 7. DWT was elevated at 1 hr postreperfusion (128% +/- 53%, P = 0.0001), and alleviated on days 2 and 7 (48% +/- 10%, P = 0.008; 53% +/- 24%, P = 0.003). T(2) and T(1) elevations were coincident with early edema (DeltaT(2) = 55% +/- 24%, P < 0.0001; DeltaT(1) = 27% +/- 18%, P < 0.04). T(2) and T(1) were nearly normal on day 2 (DeltaT(2) = 8% +/- 8%, P = 0.27; DeltaT(1) = 0% +/- 1%, P = 0.65). On day 7, T(2) increased while T(1) decreased (DeltaT(2) = 27% +/- 16%, P = 0.005; DeltaT(1) = -14% +/- 10%, P = 0.02). Lambda was elevated by >150% at all time points (P < or = 0.002). Histology verified hemorrhagic injury. T(1) and T(2) fluctuations are consistent with transient edema, as well as hemoglobin oxidative denaturation to decompartmentalized methemoglobin. This methodological development may broaden our understanding of hemorrhagic microvascular injury and improve its detection in clinical populations.

Mechanical protection of cardiac microcirculation during percutaneous coronary intervention of saphenous vein grafts

Saphenous vein bypass grafts permeability is one of the most important limitations of open heart surgery. The risks associated with surgical re-intervention are greater than those associated with the initial procedure. While native coronary arteries usually have fixed, fibrotic or calcified atherosclerotic plaques, the disease in the vein grafts contains soft material. When this material is compressed during percutaneous angioplasty, there is an unfavorable immediate outcome due to distal embolization of thrombus and plaque debris. In addition, the risk of post-procedure adverse events are higher when the grafts have a long time of implantation, due to a greater risk of branch occlusion or no-reflow at the adjacent microcirculation. The clinical consequence is a Non-Q-Wave Myocardial Infarction that is reflected in the increased serum cardiac enzymes. It is because of this complication that the distal protection devices were developed. The purpose of this paper is to review and discuss the current data on the distal protection devices available now for the treatment of degenerative saphenous vein graft disease. Currently, there are two distal protection devices approved in the United States: the Guardwire Balloon and Aspiration (Export) System and the Filter Wire EX. Other devices like the Triactiv System, Angioguard XP/ECW, DOW, MedNova Cardioshield, Medtronic-AVE DPD and the E-Trap Filter are still being studied. The first observational studies showed the safety and efficacy of the approved devices. A large randomized trial initially confirmed a significant decrease of in-hospital and 30-day cardiac adverse events, mainly Non-Q-Wave Myocardial Infarction, when angioplasty was performed with the assistance of the Guardwire System. Subsequently, another randomized study showed an equivalence between the Guardwire System and the Filter Wire EX. Distal protection devices have an acceptable performance, however, further technological improvements are warranted for a quick preparation, delivery and/or retrieval of these devices.

Treatment of slow/no-reflow phenomenon with intracoronary nitroprusside injection in primary coronary intervention for acute myocardial infarction

Slow/no-reflow phenomenon is a serious problem complicating primary percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI) and is associated with a poor prognosis. From January 2002 to November 2002, 11 of the 70 consecutive patients with ST elevation AMI who were subjected to primary PCI using balloon angioplasty and/or stenting developed slow/no-reflow phenomenon (TIMI 1 flow in 2, TIMI 2 in 8, and TIMI 2.5 in 1). They were 10 men and 1 woman, aged 64 +/- 11 years (range, 46-81). The culprit vessels were six in the left anterior descending coronary artery, three in the right coronary artery, one in the left circumflex coronary artery, and one in saphenous vein graft. Multiple bolus doses (100 microg) of nitroprusside were injected into the index artery through the guiding catheter using a 3 ml syringe until the TIMI flow grade improved by at least one grade or the systolic pressure decline below 80 mm Hg (one patient). The total drug dose varied from 100 to 700 microg. Following the drug treatment, angiographic TIMI flow grade improved by at least one grade in 9 (82%) of the 11 patients (P = 0.007). The TIMI frame counts significantly decreased from 36 +/- 17 frame counts to 16 +/- 11 frame counts (P = 0.012). All patients were discharged without major adverse cardiovascular events. Intracoronary bolus injection of nitroprusside using a 3 ml syringe appears to be a feasible, safe, and effective technique for the management of slow/no-reflow phenomenon complicating primary PCI.

Histopathological Findings of the No-reflow Phenomenon Following Coronary Intervention for Acute Coronary Syndrome

Although no-reflow phenomenon may occur in patients that experience reperfusion after ischemia, there have been no reports describing the postmortem findings in these patients. We describe the findings of an autopsy in a 56-year-old man who experienced acute coronary syndrome with no-reflow phenomenon after coronary intervention. Macroscopic study demonstrated myocardial infarction with diffuse hemorrhage, and microscopic analysis revealed vascular damage and microembolization in the no-reflow area. In conclusion, coronary microembolization and damage to the small coronary artery may contribute to the pathogenesis of no-reflow phenomenon following coronary intervention in humans.

No-reflow following dilatation of a coronary lesion with a large lipid core

Radiolucent findings of coronary angiogram are believed to usually represent intracoronary thrombus, but in the present case, were atheromatous plaque with a large lipid core. A 62-year-old man who suffered from an inferior acute myocardial infarction was admitted to hospital 6 h after onset. The first cine angiograms showed TIMI-1 flow in the distal-portion of the right coronary artery, so thrombectomy was initially carried out and TIMI-2 flow achieved. However, the radiolucent lesion did not disappear and so adjunctive mechanical dilatation of the lesion was prformed, which resulted in 'no-reflow' (TIMI-0). Finally, aspiration of the material from the stagnated lesion was attempted and immediately obtained TIMI-3 flow. The retrieved materials were macrophages (foam cells) and many cholesterol crystals, both of which are considered to be atheromatous gruel. Therefore, the sudden flow reduction following percutaneous transluminal coronary angioplasty was caused by mechanical disruption of an atheromatous plaque with a large lipid core.

Can streptokinase produce beneficial effects additional to coronary recanalization? Quantitative microvascular analysis of critically injured reperfused myocardium

The aim of this study was to evaluate whether streptokinase (SK) may produce beneficial effects at the level of microvascular circulation in addition to coronary recanalization. Twenty mongrel dogs weighing 28.4 +/- 4.6 kg were randomized to receive SK (16,000-72,000 U/kg) or 20 ml saline (control) in an open-chest anterior descending artery occlusion (3 h) and reperfusion (2 h) model. Myocardial blood flow was measured by the radioactive microsphere technique and the state of microvascular circulation (red blood cell containing capillary counts and tissue red blood cell content) was evaluated in the infarcted subendocardial zone using computerized image analysis. The percentage (mean +/- SE) of cell-containing vessels normalized to nonischemic control areas was 166.5 +/- 7.5 in SK-treated infarcts while in untreated control infarcts it was more variable (130.0 +/- 15.6%) (2P > 0.1). The red blood cell content of infarcts treated with 2.0 megaunits SK was 3.9 +/- 0.6% compared with 6.7 +/- 0.9% in untreated control infarcts (2P = 0.029). Plasma viscosity was slightly reduced in SK-treated dogs (2P = 0.05), but no significant changes in blood fibrinogen, hemoglobin, blood flow, and high energy phosphate levels between control and SK-treated infarcts were observed. SK reduces congestion and results in more even reperfusion of the microvasculature in severely ischemic myocardium to which blood flow has been restored. This effect may be beneficial in the salvage and healing of clinical infarctions.

The isolated blood and perfusion fluid perfused heart

The isolated heart is deservedly one of the most popular experimental models in cardiovascular research, both in terms of cost and the quality and quantity of data it provides. However, it is a deceptively simple model, capable of throwing many problems in the path of the inexperienced or unwary perfuser. The following article discusses the advantages and disadvantages of the various types of isolated heart perfusion (Langendorff and working; blood and buffer perfused). We attempt to give an insight into the many factors which must be taken into consideration when first establishing these preparations, we identify the range of indices that can be measured and the potential pitfalls which, with a little care, can be readily avoided.

Pathobiology and Clinical Impact of Reperfusion Injury

Reperfusion injury refers to cellular death or dysfunction caused by restoration of blood flow to previously alchemic tissue. This should be differentiated from the normal reparative processes that follow an ischemic insult. Four types of reperfusion injury have been described in the literature: (1) lethal reperfusion injury, (2) nonlethal reperfusion injury, (myocardial stunning), (3) reperfusion arrhythmias, and (4) vascular injury (including the "no-reflow" phenomenon). There is continued debate whether reperfusion itself is capable of killing viable myocytes, which otherwise would have survived the ischemic insult. However, there is firm evidence for the existence of myocardial stunning following various ischemic syndromes, including reperfusion therapy for acute myocardial infarction, unstable angina pectoris, vasospastic angina, effort-induced ischemia, coronary artery bypass surgery, and cardiac transplantation. Reperfusion arrhythmia is more common after short ischemic episodes than after long ischemic periods. Thus, while reperfusion arrhythmias in the setting of acute myocardial infarction are relatively rare, reperfusion arrhythmias may be an important cause of sudden death. The "no-reflow" phenomenon has been described following reperfusion in patients with acute myocardial infarction. Three major components have been proposed as mediators of reperfusion injury: (1) oxygen free radicals, (2) the complement system, and (3) neutrophils. Numerous experimental studies have shown short-term benefit by blocking various stages of the postischemic inflammatory response. Oxygen free radicals scavengers, complement inhibition, leukocyte depletion, and the use of antibodies against various adhesion molecules have shown a reduction of infarct size in many ischemic/reperfusion experimental models. However, many of these agents failed to show a benefit in the clinical setting. Moreover, the long-term benefit of such intervention is still unknown.

Pathobiology and Clinical Impact of Reperfusion Injury

Reperfusion injury refers to cellular death or dysfunction caused by restoration of blood flow to previously ischemic tissue. This should be differentiated from the normal reparative processes that follow an ischemic insult. Four types of reperfusion injury have been described in the literature: (1) lethal reperfusion injury, (2) nonlethal reperfusion injury (myocardial stunning), (3) reperfusion arrhythmias, and (4) vascular injury (including the "no-reflow" phenomenon). There is continued debate whether reperfusion itself is capable of killing viable myocytes, which otherwise would have survived the ischemic insult. However, there is firm evidence for the existence of myocardial stunning following various ischemic syndromes, including reperfusion therapy for acute myocardial infarction, unstable angina pectoris, vasospastic angina, effort-induced ischemia, coronary artery bypass surgery, and cardiac transplantation. Reperfusion arrhythmia is more common after short ischemic episodes than after long ischemic periods. Thus, while reperfusion arrhythmias in the setting of acute myocardial infarction are relatively rare, reperfusion arrhythmias may be an important cause of sudden death. The "no-reflow" phenomenon has been described following reperfusion in patients with acute myocardial infarction. Three major components have been proposed as mediators of reperfusion injury: (1) oxygen free radicals, (2) the complement system, and (3) neutrophils. Numerous experimental studies have shown short-term benefit by blocking various stages of the postischemic inflammatory response. Oxygen free radicals scavangers, complement inhibition, leukocyte depletion, and the use of antibodies against various adhesion molecules have shown a reduction of infarct size in many ischemic/reperfusion experimental models. However, many of these agents failed to show a benefit in the clinical setting. Moreover, the long-term benefit of such intervention is still unknown.

Limitation of myocardial infarct size after primary angioplasty: is a higher patency the only mechanism?

BACKGROUND

Several studies demonstrate a better outcome after primary angioplasty compared with thrombolysis. The mechanism is assumed to be a higher rate of open infarct-related vessels.

METHODS AND RESULTS

We conducted a randomized trial of primary coronary angioplasty compared with thrombolysis. A total of 401 patients with acute myocardial infarction were randomly assigned to either primary angioplasty or thrombolytic therapy. Radionuclide left ventricular ejection fraction was performed before hospital discharge. Infarct size was estimated by measurement of serial lactate dehydrogenase activity (LDH Q72). Separate analyses were performed in patients with an open infarct-related vessel, either after thrombolysis or angioplasty. Baseline characteristics were comparable between the 2 treatment groups. Of the 197 patients treated with angioplasty, 176 (89%) had an open infarct-related vessel compared with 126 (62%) of the 204 patients treated with thrombolysis (P <.001). In patients with an open infarct-related vessel, those treated with primary angioplasty had a lower enzyme release compared with those treated with thrombolysis: LDH Q72 949 (748) and 1200 (1117), respectively (P <.05). Compared with angioplasty, patients treated with thrombolysis had a lower left ventricular ejection fraction. In the subgroup of patients with an open infarct-related vessel, after thrombolysis or angioplasty, patients treated with thrombolysis still had a lower ejection fraction (47% vs 50%, P <.05). Multivariate analysis, adjusting for differences in several clinical variables, did not change these results. Patients with an open infarct-related vessel and thrombolysis had a higher risk of an ejection fraction <40% compared with patients treated with primary angioplasty (relative risk 1.9, 95% confidence interval 1.0 to 2.7).

CONCLUSIONS

Despite successful thrombolysis, with sustained patency of the infarct-related vessel, primary angioplasty remains superior to thrombolytic therapy with regard to left ventricular function and enzymatic infarct size. This may be caused by adverse effects of fibrinolytics on infarcted myocardium.

The distinction between coronary and myocardial reperfusion after thrombolytic therapy by clinical markers of reperfusion

OBJECTIVES

We sought to examine the hypothesis that rapid resolution of ST-segment elevation in acute myocardial infarction (AMI) patients with early peak creatine kinase (CK) after thrombolytic therapy differentiates among patients with early recanalization between those with and those without adequate tissue (myocardial) reperfusion.

BACKGROUND

Early recanalization of the epicardial infarct-related artery (IRA) during AMI does not ensure adequate reperfusion on the myocardial level. While early peak CK after thrombolysis results from early and abrupt restoration of the coronary flow to the infarcted area, rapid ST-segment resolution, which is another clinical marker of successful reperfusion, reflects changes of the myocardial tissue itself.

METHODS

We compared the clinical and the angiographic results of 162 AMI patients with early peak CK (< or =12 h) after thrombolytic therapy with (group A) and without (group B) concomitant rapid resolution of ST-segment elevation.

RESULTS

Patients in groups A and B had similar patency rates of the IRA on angiography (anterior infarction: 93% vs. 93%; inferior infarction: 89% vs. 77%). Nevertheless, group A versus B patients had lower peak CK (anterior infarction: 1,083+/-585 IU/ml vs. 1,950+/-1,216, p < 0.01; and inferior infarction: 940+/-750 IU/ml vs. 1,350+/-820, p=0.18) and better left ventricular ejection fraction (anterior infarction: 49+/-8, vs. 44+/-8, p < 0.01; inferior infarction: 56+/-12 vs. 51+/-10, p=0.1). In a 2-year follow-up, group A as compared with group B patients had a lower rate of congestive heart failure (1% vs. 13%, p < 0.01) and mortality (2% vs. 13%, p < 0.01).

CONCLUSIONS

Among patients in whom reperfusion appears to have taken place using an early peak CK as a marker, the coexistence of rapid resolution of ST-segment elevation further differentiates among patients with an opened culprit artery between the ones with and without adequate myocardial reperfusion.

The Open Artery Hypothesis: Past, Present, and Future

The survival benefit following a reperfusion strategy, be it pharmacologic or mechanical, appears to be due to both full and early reperfusion. While the TIMI Flow Grade classification scheme has been a useful tool to assess coronary blood flow in acute syndromes, it has several limitations. A newer method of assessing coronary blood flow called the Corrected TIMI Frame Count method has the following advantages: (1) it is a continuous quantitative variable rather than a categorical qualitative variable; (2) the flow in the non-culprit artery is not assumed to be normal as it is in the assessment of TIMI Grade 3 Flow; (3) there is simplified reporting of reperfusion efficacy through the use of a single number instead of expressing the data in 2 to 4 categories; (4) because a single number rather than 4 categories is used to report the data, there is more efficient use of the dataset by increasing the statistical power; and finally (5) coronary flow can be expressed in intuitive terms (e.g. time or cm/sec for strategy A versus time or cm/sec for strategy B). This paper reviews the history of the open artery hypothesis and recent advances in the field.

Relation between injections before 90-minute angiography and coronary patency: results of the thrombolysis in myocardial infarction 4 trial

The current goal of thrombolytic therapy is to achieve both full (Thrombolysis in Myocardial Infarction [TIMI] grade 3) and early reperfusion. Newer reperfusion strategies may now achieve a high degree of reperfusion even earlier than the traditional 90-minute end point. To determine whether injections before 90 minutes affect this traditional end point, the relation between the number of injections before 90-minute angiography and patency was examined in the TIMI 4 trial. The number of injections before 90-minute angiography was no different between occluded arteries (TIMI grade 0/1 flow) (2.46 +/- 1.78; n = 94) and patent arteries (TIMI grade 2/3 flow) (2.71 +/- 2.42; n = 295) (p = 0.24). The incidence of any injections before 90 minutes was no different in patent versus closed arteries (80.6% [77/98] vs 72.4% [22/304]; p = 0.10). The number of injections before 90 minutes was insignificantly smaller in patients with TIMI grade 3 flow (2.53 +/- 2.53 [n = 184] vs 2.76 +/- 2.03 [n = 204]; p = 0.31), but the incidence of any injections before 90 minutes was significantly smaller in patients with TIMI grade 3 flow (68.8% [132/192] vs 79.5% [167/210]; p = 0.01). No relation was identified between the number of injections before 90-minute angiography and patency at this traditional time point. This observation justifies the judicious use of a limited number of "earlier snapshots" of the infarct-related artery before 90 minutes to ascertain just how rapidly newer thrombolytic regimens achieve patency. Patients with TIMI grade 3 flow had a slightly lower incidence of injections before 90 minutes, perhaps because they did not require as urgent a definition of coronary anatomy.

Extension of hemorrhage after reperfusion of occluded coronary artery: contrast echocardiographic assessment in dogs

OBJECTIVES

The aim of this study was to elucidate the progression of intramural hemorrhage complicated by reperfusion with the use of myocardial contrast echocardiography.

BACKGROUND

Although hemorrhagic infarction is known to occur in ischemia followed by reperfusion, its onset and sequence have not been well characterized.

METHODS

In 20 anesthetized dogs, 3-h occlusion of the left circumflex-coronary artery was followed by reperfusion. The area at risk during coronary occlusion was approximately 25%. Myocardial contrast echocardiogram was examined, and the time-intensity curves for both ischemic and nonischemic areas were obtained at baseline, at 3 min after reperfusion and then at 15-min intervals until 90 min after reperfusion. The wall thickness of both areas was also measured.

RESULTS

Gross hemorrhage in the reperfused areas was observed in five dogs (Group H) but not in seven dogs (Group NH). All wall segments were opacified at 3 min after reperfusion in both groups. However, the contrast defect spread significantly with time after reperfusion in Group H but not in Group NH (18.7 +/- 3.4% and 3.3 +/- 1.8%, respectively, at 90 min after reperfusion p < 0.005). The wall of the risk area at 90 min after reperfusion had thickened to 1.3 times baseline thickness in Group H but was unchanged in Group NH. The other eight dogs were excluded from study because of fatal arrhythmias or the existence of collateral circulation during coronary occlusion.

CONCLUSIONS

Both progression of the contrast defect area on myocardial contrast echocardiography and a gradual thickening of the wall with reperfusion are characteristic of hemorrhagic infarction.

Early detection of successful coronary reperfusion based on serum concentration of human heart-type cytoplasmic fatty acid-binding protein

Both human heart-type cytoplasmic fatty acid-binding protein (H-FABPc) and myoglobin are low molecular weight proteins that are abundant in the cytoplasm of myocardial cells. Unlike myoglobin, H-FABPc content in the skeletal muscle is less than in cardiac muscle. To investigate the usefulness of the serum concentration of H-FABPc in the early detection of successful coronary reperfusion, we measured serum concentrations of H-FABPc and myoglobin in 45 patients with acute myocardial infarction treated with intracoronary thrombolysis or direct percutaneous transluminal coronary angioplasty. Coronary angiography was performed every 5 min for reperfusion therapy to identify the onset of reperfusion. Reperfusion, defined as a TIMI grade 2 or 3, was achieved within 60 min of the initiation of reperfusion therapy in 30 patients (the reperfused group), but was not achieved in 15 patients (the non-reperfused group). Blood samples were obtained before initiation of treatment and 15, 30 and 60 min after initiation of treatment in the non-reperfused group. In the reperfused group, samples were obtained before reperfusion and 15, 30 and 60 min after reperfusion. The H-FABPc ratio (the ratio of value after to value before the initiation of treatment or reperfusion) increased sharply after the onset of reperfusion, peaking at 41 +/- 18 min, and decreased rapidly thereafter. The predictive accuracy of an H-FABPc ratio of > 1.8 for the detection of reperfusion within 60 min of the initiation of treatment was 93% at 15 min after reperfusion, 98% at 30 min, and 100% at 60 min. Similar rates of predictive accuracy were observed for a myoglobin ratio > 2.4. The H-FABPc ratio detected successful reperfusion as early as 15 min after the onset of reperfusion and was highly accurate in detecting reperfusion within 60 min of the onset of reperfusion. The predictive accuracy of the H-FABPc ratio was similar to that of the myoglobin ratio for the early detection of successful coronary reperfusion.

Distal vessel pullback angiography and pressure gradient measurement: an innovative diagnostic approach to evaluate the no-reflow phenomenon

The angiographic appearance of "no-reflow" in saphenous vein grafts or native coronary arteries has been described following administration of thrombolytic therapy or performance of percutaneous transluminal coronary angioplasty or atherectomy. Apparent occlusion may represent spasm, dissection, thrombosis, or competitive collateral circulation, all of which must be excluded to make the diagnosis of "no-reflow." We describe an innovative approach to the diagnostic dilemma created by the appearance of "no-reflow" at coronary angiography. Pressure gradient measurement with distal vessel pull-back (retrograde) angiography provides maximal information regarding the severity of disease and the etiology of "no-reflow," while exposing both the patient and angiographer to less risk compared to standard strategies.

Features and outcome of no-reflow after percutaneous coronary intervention

No-reflow is an uncommon complication that may occur after revascularization of patients with acute myocardial infarction, after interventions in saphenous vein bypass grafts, and after the use of some new interventional devices. However, the clinical impact of no-reflow after coronary intervention is unknown. Accordingly, this study examined the incidence, clinical presentation, angiographic characteristics, and outcome of no-reflow after percutaneous coronary intervention. No-reflow was defined as an acute reduction in antegrade flow (< or = 1, as defined by the Thrombolysis in Myocardial Infarction [TIMI] trial) not attributable to abrupt closure, high-grade stenosis, or spasm of the original target lesion. Among 10,676 coronary interventions performed between October 1988 and June 1993, no-reflow occurred in 66 patients (0.6%). These patients were compared with a subgroup of 500 consecutive patients who did not exhibit no-reflow. The incidence of no-reflow was 30 of 9,431 (0.3%) for percutaneous transluminal coronary angioplasty, 1 of 317 (0.3%) for excimer laser, 8 of 104 (7.7%) for Rotablator (Heart Technologies, Bellevue, Washington), 21 of 469 (4.5%) for extraction atherectomy, and 6 of 355 (1.7%) for directional atherectomy. Compared with those without no-reflow, patients with no-reflow experienced a 10-fold higher incidence of in-hospital death (15%) and acute myocardial infarction (31%). Correlates of in-hospital mortality included acute myocardial infarction on presentation (p = 0.006) and final flow < 3 (as defined by the TIMI trial) at completion of the procedure (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

Early detection of successful coronary reperfusion based on serum myoglobin concentration: comparison with serum creatine kinase isoenzyme MB activity

The usefulness of serum myoglobin (Mb) concentration for early detection of successful reperfusion was compared with that of creatine kinase isoenzyme MB (CKMB) activity in 49 patients with acute myocardial infarction. To determine accurately the time of reperfusion, we performed coronary angiography every 5 minutes during reperfusion therapy. Reperfusion was obtained in 32 patients (reperfused group) but not in 17 patients (nonreperfused group) until 60 minutes after the initiation of reperfusion therapy. Blood samples were taken before and 15, 30, and 60 minutes after the angiographic confirmation of reperfusion in the reperfused group. In the nonreperfused group, samples were taken before and 15, 30, and 60 minutes after the initiation of treatment. We calculated the Mb ratio (value after reperfusion or treatment initiation to value before) and CKMB ratio (value after to value before). When values > 2.4 for the Mb ratio or > 2.0 for the CKMB ratio were used as the criteria for reperfusion within 60 minutes after initiation of treatment, the sensitivities were 91% and 56% at 15 minutes after reperfusion, 97% and 84% at 30 minutes, and 100% and 100% at 60 minutes, respectively. For each ratio the specificity of detection was 100% at all times evaluated. Thus the Mb ratio accurately detected the success of reperfusion as early as 15 minutes after reperfusion and may be more useful than the CKMB ratio for detecting the success of reperfusion within 30 minutes.

Deterioration in myocardial blood flow following relief of sustained ischemia is not associated with release of endothelin into the coronary sinus

Numerous studies have described a progressive deterioration in resting myocardial blood flow following relief of sustained ischemia in both necrotic and salvaged myocardium (termed "no reflow" and "low reflow", respectively). We sought to determine whether release of the potent vasoconstrictor peptide endothelin-1 may play a role in these phenomena. As part of a previous study in our laboratory, 14 anesthetized open-chest dogs underwent 1 h of coronary artery occlusion and 4 h of reperfusion, while 2 dogs served as time-matched sham-operated controls (artery isolated but not occluded). Regional myocardial blood flow was measured by injection of radiolabeled microspheres at 30 min and 4 h post reflow; endothelin-1 concentrations in the coronary sinus were determined by radioimmunoassay at baseline, during coronary occlusion and at 30 min and 4 h after reperfusion; and the extent of myocardial necrosis was delineated by post-mortem tetrazolium staining. As expected, in dogs subjected to ischemia/reperfusion, regional myocardial blood flow deteriorated between 30 min and 4 h post reflow in both the subendocardium (1.40 +/- 0.30 versus 0.48 +/- 0.06 ml/min/g; p = 0.003; reflecting a mixture of no reflow and low reflow) and subepicardium (0.84 +/- 0.08 versus 0.64 +/- 0.07 ml/min/g; p = 0.03; due to low reflow). However, endothelin levels showed only a modest and nonsignificant increase during the protocol (4.1 +/- 0.5, 4.7 +/- 0.2 and 4.9 +/- 0.6 pg/ml plasma at baseline, 30 min and 4 h post reflow; p = NS), and regression analysis revealed no correlation between release of endothelin and deterioration in blood flow in either myocardial layer. Moreover, the sham-operated controls showed a similar modest increase in endothelin levels, with no change in myocardial perfusion during the course of the protocol. We therefore conclude that deterioration in myocardial blood flow following relief of sustained ischemia in the anesthetized open-chest dog is not associated with release of endothelin-1 into the coronary sinus.

Myocardial stunning: an overview

Over the past two decades, we have challenged the belief that transient ischemia is benign with little functional sequelae following resolution of ischemia. The phenomenon of prolonged postischemic contractile dysfunction, or of myocardial stunning, has been developed and is under investigation using multiple experimental and clinical models. Classifications of myocardial stunning have been suggested and include single and multiple reversible ischemic episodes, partially reversible episodes, and global ischemia. More challenging is the understanding of the mechanisms of myocardial stunning, including free radical protection, excitation-contraction uncoupling, altered calcium flux, microvascular dysfunction, and impaired energy production and use. Finally, advances have been made in the clinical arena, including development of new more sensitive technologies to detect dysfunction, and development of potentially important therapies, including free radical scavengers, adenosine-regulating agents, and calcium channel blockers. In this brief overview, we focus on myocardial stunning, including a historical perspective of coronary occlusion, and definition, classification, and clinical implications of myocardial stunning.