Coronary artery reperfusion in acute myocardial infarction: beneficial effects of intracoronary streptokinase on left ventricular salvage and performance

Don't go breakin' my heart: cardioprotective alterations to the mechanical and structural properties of reperfused myocardium during post-infarction inflammation

Myocardial infarctions (MIs) kickstart an intense inflammatory response resulting in extracellular matrix (ECM) degradation, wall thinning, and chamber dilation that leaves the heart susceptible to rupture. Reperfusion therapy is one of the most effective strategies for limiting adverse effects of MIs, but is a challenge to administer in a timely manner. Late reperfusion therapy (LRT; 3 + hours post-MI) does not limit infarct size, but does reduce incidences of post-MI rupture and improves long-term patient outcomes. Foundational studies employing LRT in the mid-twentieth century revealed beneficial reductions in infarct expansion, aneurysm formation, and left ventricle dysfunction. The mechanism by which LRT acts, however, is undefined. Structural analyses, relying largely on one-dimensional estimates of ECM composition, have found few differences in collagen content between LRT and permanently occluded animal models when using homogeneous samples from infarct cores. Uniaxial testing, on the other hand, revealed slight reductions in stiffness early in inflammation, followed soon after by an enhanced resistance to failure for cases of LRT. The use of one-dimensional estimates of ECM organization and gross mechanical function have resulted in a poor understanding of the infarct's spatially variable mechanical and structural anisotropy. To resolve these gaps in literature, future work employing full-field mechanical, structural, and cellular analyses is needed to better define the spatiotemporal post-MI alterations occurring during the inflammatory phase of healing and how they are impacted following reperfusion therapy. In turn, these studies may reveal how LRT affects the likelihood of rupture and inspire novel approaches to guide scar formation.

Doppler echocardiographic myocardial stunning index predicts recovery of left ventricular systolic function after primary percutaneous coronary intervention

BACKGROUND

Myocardial stunning is responsible for partially reversible left ventricular (LV) systolic dysfunction after successful primary percutaneous coronary intervention (PPCI) in patients with acute ST-elevation myocardial infarction (STEMI).

AIM

To test the hypothesis that early coronary blood flow (CBF) to LV systolic function ratios, as an equivalent to LV stunning index (SI), predict recovery of LV systolic function after PPCI in patients with acute STEMI.

METHODS

Twenty-four patients with acute anterior STEMI who had successful PPCI were evaluated and compared to 96 control subjects. Transthoracic echocardiography with measurement of LV ejection fraction (EF), LV, and left anterior descending (LAD) coronary artery area wall-motion score index (WMSI) as well as Doppler sampling of LAD blood velocities, early after PPCI and 5 days later, were performed. SI was evaluated as the early ratio of CBF parameters in the LAD to LV systolic function parameters.

RESULTS

Early SI-LVEF well predicted late LVEF (r=.51, P<.01) and the change in LVEF (r=.48, P<.017). Early SI-LVMSI predicted well late LVEF (r=.56, P<.006) and the change in LVEF (r=.46, P<.028). Early SI-LADWMSI predicted late LVEF (r=.44, P<.028). Other SI indices measured as other LAD-CBF to LV systolic function parameters were not predictive of late LV systolic function.

CONCLUSIONS

LV stunning indices measured as early LAD flow to LVEF, LVWMSI, and LADWMSI ratios well predicted late LVEF and the change in LVEF. Thus, greater early coronary artery flow to LV systolic function parameter ratios predict a better improvement in late LV systolic function after PPCI.

Analytic Review: Thrombolytic Therapy in Acute Myocardial Infarction

The salvage of myocardium in the setting of acute myocardial infarction has long been a goal of physicians involved in the care of patients with coronary artery disease. Understanding the role of thrombosis in the pathogenesis of acute myocardial infarction has led the way to an entirely new approach to the treatment of this entity. Thrombolytic therapy has now become a widely used form of treatment with encouraging results. Both intravenous and intracoronary administration of thrombolytic agents have been shown to promote recanalization of acutely occluded coronary arteries. Results of studies using the clot-specific agent, tissue plasminogen activator, intravenously have been most encouraging; successful reperfusion has been obtained in approximately 70% of patients treated. In addition, a recent large-scale trial has shown a reduction in morbidity and mortality with the early use of thrombolytic agents.

Ongoing trials should help delineate the precise role and timing of these agents as the initial form of therapy for acute myocardial infarction. Other issues that remain unresolved are the frequency of restenosis and the role of percutaneous transluminal coronary angioplasty in addition to thrombolytic therapy in the treatment of acute myocardial infarction.

Computed tomography assessment of myocardial perfusion, viability, and function

In addition to coronary artery assessment, contrast-enhanced multidetector spiral computed tomography (CE-MDCT) can provide valuable information about myocardial perfusion. Using CE-MDCT, myocardial perfusion defects are often observed in the early phase of the contrast bolus (early defect (ED)), with residual defects (RDs) and late enhancement (LE) observed in the late phase in myocardial infarction (MI). However, the clinical significance of EDs, RDs, and LE has not yet been fully described. This work reviews myocardial viability and function by CE-MDCT based on our prior data by including contrast-enhanced single-slice (detector) CT (CE-SSCT) and CE-MDCT. Recently, equivalent results were obtained, as seen in CE-SSCT with images by CE-MDCT. In this review, images that were acquired by MDCT will be presented. In this work, the following items will be the focus: myocardial enhancement patterns (EDs, LE, and RDs), early perfusion defects and their relationship to wall thickness (WT) and wall motion, early CT perfusion defects vs. Tl-201 single photon emission CT (SPECT), the protocol for performing dual-phase contrast CT, classification of enhancement patterns, enhancement patterns on dual-phase CE-MDCT vs. left ventricular functional recovery and WT, changes in enhancement patterns in conjunction with healing stage, enhancement patterns on dual-phase CE-MDCT vs. 201Tl/99mTc-pyrophosphate (dual-isotope SPECT), the clinical meaning of each enhancement pattern, pitfalls of enhancement patterns and other diseases, and study limitations and the future of MDCT.

Assessment of myocardial viability using coronary zero flow pressure after successful angioplasty in patients with acute anterior myocardial infarction

OBJECTIVES

To investigate the relation between coronary flow reserve (CFR), coronary zero flow pressure (Pzf), and residual myocardial viability in patients with acute myocardial infarction.

DESIGNS

Prospective study.

SETTING

Primary care hospital.

PATIENTS

27 consecutive patients with acute anterior myocardial infarction.

MAIN OUTCOME MEASURES

F-fluorodeoxyglucose (FDG) positron emission tomography (PET) was used in 27 patients who underwent successful intervention within 12 hours of onset of a first acute anterior myocardial infarction. Within three days before discharge they had < 25% stenosis in the culprit lesion as determined by angiography 24 (3) days after acute myocardial infarction. Pzf and the slope index of the flow-pressure relation (SIFP) were calculated from the simultaneously recorded aortic pressure and coronary flow velocity signals at peak hyperaemia.%FDG was quantified by comparing FDG uptake in the infarct myocardium with FDG uptake in the normal myocardium.

RESULTS

There was a correlation between %FDG and CFR, where y = -1.477x + 62.517, r = -0.072 (NS). There was also a correlation between %FDG and SIFP, where y = -0.975x + 60.542, r = -0.045 (NS), and a significant correlation between %FDG and Pzf, where y = -0.98x + 85.108, r = -0.696 (p < 0.001).

CONCLUSIONS

CFR does not correlate with FDG-PET at the time of postreperfusion evaluation of residual myocardial viability. The parameter that correlates best with residual myocardial viability is Pzf and this may be a useful index for predicting patient prognosis.

Reversible myocardial dysfunction in critically ill, noncardiac patients: a review

OBJECTIVE

To review reversible myocardial dysfunction affecting critically ill patients without cardiac pathology.

DATA SOURCES

The bibliography for the study was compiled through a search of different databases for the period 1966-2001. References cited in the selected articles also were reviewed.

STUDY SELECTION

The selection criteria included all articles published on reversible myocardial dysfunction in critically ill patients.

CONCLUSIONS

Reversible myocardial dysfunction may develop in a situation of critical pathology, but the etiology of reversible myocardial dysfunction is not fully understood. This dysfunction may be accompanied by increases in enzyme concentrations and electrocardiographic changes. Reversible myocardial dysfunction probably is underdiagnosed, although its presence is associated with a worsening of the prognosis and with more specific therapeutic options. Further studies are necessary to define its true incidence and clinical implications.

Clinical importance of stunned and hibernating myocardium

Myocardial stunning and hibernation are states of potentially reversible myocardial dysfunction, which were first described more than 20 years ago (c.1980). Important advances have now been made in the ability to detect stunned and hibernating myocardium, as well as in the understanding of the impact of these conditions on patient outcomes. We discuss here the clinical importance of stunned and hibernating myocardium for patients with several common cardiac conditions.

Assessment of Regional Viability in the Infarct Zone Following Myocardial Infarction

The goal of reperfusion strategies in patients with acute myocardial infarction is to salvage myocardium within the infarct zone at risk from the acute occlusion. The status of wall motion and thickening within the infarct zone is an imprecise guide to the extent of salvage and viability within the infarct zone, based on the well-described phenomenon of myocardial stunning. However, knowledge of significant salvage and preserved viability within an infarct zone soon after infarction has important implications regarding clinical decision making for catheterization and potential revascularization: given preserved viability, restoration of normal coronary flow in the setting of a severe residual stenosis or occlusion would be expected to result in significant recovery of regional, and possibly global left ventricular function, with attendant implications for prognosis and outcome.This review will critically explore imaging techniques regarding their ability to discern myocardial viability within the infarct zone soon after myocardial infarction, including electrocardiography, angiography, echocardiography, and radionuclide studies of myocardial perfusion, metabolism and cell membrane integrity.

Myocardial scintigraphy in acute myocardial infarction treated with systemic thrombolysis: how far are we from obtaining reliable information for rescue PTCA?

All noninvasive tests have an unsatisfactory accuracy in assessing patency of the infarct related vessel after systemic thrombolysis. In large infarctions, the prompt knowledge of the amount of jeopardized myocardium, as well as the eventual success of thrombolysis on the culprit lesion are major clinical needs in the subsequent decision making process, including the indication to rescue PTCA. Several reasons preclude a meaningful use of thallium scintigraphy in this setting: the most important one is the need to perform pre-thrombolytic images before the administration of the active agent, implying a delay in the administration of thrombolysis that is clinically not acceptable. SestaMIBI perfusion scintigraphy at rest seems more suitable in this regard. SestaMIBI practically does not redistribute in the myocardium, and this implies that after an administration at admission in the CCU, the pre-thrombolysis images can be acquired later, without any interference with the therapeutic schedule. The estimate of myocardial salvage can be obtained by the comparison of the perfusion pattern derived from a later sestaMIBI injection with the pre-lysis images. Both planar and tomographic reconstructions have satisfactory positive and negative predictive accuracy for the patency of the culprit vessel. Difficulties are related with the necessity of having this information timely; we describe a few protocols, appeared in the literature, that might contribute in solving such problems. SestaMIBI imaging in patients with acute myocardial infarction should be encouraged and extended, given its potential to represent one of the best tool to judge the amount of jeopardized myocardium, the obtained salvage, and to guide the decision making after systemic thrombolysis.

Prospective identification of myocardial stunning using technetium-99m sestamibi-based measurements of infarct size

OBJECTIVES

We sought to prospectively identify patients with stunning and hyperkinesia at hospital discharge on the basis of mismatches between left ventricular (LV) function and infarct size as assessed by technetium-99m (Tc-99m) sestamibi perfusion tomographic imaging.

BACKGROUND

Mechanical indexes of LV function may not accurately reflect myocardial damage after acute myocardial infarction (MI) because of myocardial stunning and compensatory hyperkinesia in noninfarct-related territories. Myocardial perfusion techniques are unaffected by these variables.

METHODS

Eighty-four patients with acute MI underwent hospital admission and discharge Tc-99m-sestamibi tomographic imaging. Global LV ejection fraction (LVEF) was measured at hospital discharge and 6 weeks later. The perfusion defect size was quantified and expressed as a percentage of the LV. The discharge perfusion defect, which is a measure of infarct size, was used to predict the 6-week LVEF for each patient based on a previously reported regression equation. Patients were classified into one of three groups depending on whether their LVEF at hospital discharge fell within, above or below one standard error (6.8 LVEF points) of the predicted 6-week LVEF.

RESULTS

There were 48 patients classified as having a "match" between function and infarct size; these patients demonstrated no significant change in LVEF at 6 weeks. There were 21 patients (25%) classified as "mismatch stunned" who had discharge LVEFs lower than those predicted by infarct size. These patients demonstrated a significant improvement in mean LVEF at 6 weeks (mean [+/-SD] discharge LVEF 0.41 +/- 0.08, 6-week LVEF 0.47 +/- 0.10; p = 0.003). Fifteen patients (18%) were classified as "mismatch-hyperkinetic." The mean LVEF for these patients significantly declined at 6 weeks (discharge LVEF 0.64 +/- 0.06, 6-week LVEF 0.58 +/- 0.09; p = 0.002). There was a marked increase in LVEF within the infarct zone (8 +/- 15 LVEF points; p = 0.03) for patients predicted to have stunning and a marked decline in LVEF outside the infarct zone (9 +/- 15 LVEF points; p = 0.06) in patients predicted to have hyperkinesia. Both discharge LVEF (p < 0.0001) and group classification (p = 0.005) were independent predictors of LVEF 6 weeks later.

CONCLUSIONS

Perfusion imaging with Tc-99m-sestamibi can identify post-MI patients at hospital discharge in whom LV function is discordant with the measured infarct size. Patients with stunning have late increases in LVEF; patients with hyperkinesia have late decreases. This methodology, performed at discharge, is predictive of late changes in LV function.

Diagnostic performance of myocardial contrast echocardiography for detection of stunned myocardium

Improvement in regional wall motion after acute myocardial infarction has been described up to 2 to 3 weeks after the acute event despite restoration of blood flow by early successful reperfusion therapy. The prospective identification of potentially reversible ventricular dysfunction caused by stunned myocardium has significant clinical implications. Twenty-seven patients with acute myocardial infarction underwent myocardial contrast echocardiography (MCE) before, immediately after, and 4 weeks after successful reperfusion therapy. MCE was performed by imaging a parasternal short-axis view during intracoronary arterial injection of 2 ml sonicated ioxaglate (Hexabrix-320). The contrast defect area and contrast-filled area before reperfusion were defined as the risk area and noninfarct area, respectively. The normalized gray level was defined as the ratio of the gray level in the risk area/gray level in the noninfarct area. In 21 patients, wall motion was akinetic or dyskinetic immediately after reperfusion, and 10 of 21 patients in whom wall motion recovered during the chronic stage were defined as patients with stunned myocardium. In patients who showed asynergic wall motion immediately after reperfusion, MCE predicted the recovery of left ventricular wall motion (stunned myocardium) during the chronic stage with a sensitivity of 77%, specificity of 100%, and predictive accuracy of 86%, when a normalized gray level of more than 0.4 was presumed to predict stunned myocardium. We conclude that MCE provided the prospective identification of potentially reversible ventricular dysfunction caused by stunned myocardium, and wall motion in the area of nonenhanced myocardium on MCE immediately after reperfusion is not expected to show reversible dysfunction.

An evaluation of streptokinase therapy in early coronary reperfusion in a primate model

Efficacy of streptokinase (SK) administered beyond the period of coronary occlusion with regard to ultimate infarct size and the extent of hemorrhagic infarction was assessed in primates. Eleven macaques underwent coronary occlusion for two hours and were then reperfused. Five of them were given a 2,000 U IV bolus of SK followed by a 10,000 U IV infusion over ninety minutes. The remaining 6 served as controls. Macaques were sacrificed seven days postocclusion. The left ventricle was sectioned parallel to the minor axis, and these were examined histologically for infarct size and hemorrhage. Multiplying the planimetric values by the thickness of the sections yielded the total volumes of left ventricle, infarction, and hemorrhage. The mean percentage of left ventricle involved in infarction in the treated group was not significantly different from the controls (14.06 +/- 6.35 versus 16.50 +/- 4.67, P > 0.10). SK-treated animals had a significantly greater volume of infarct involved with hemorrhage as compared with controls (27.1 +/- 10.8 versus 4.0 +/- 1.4, P < 0.05). SK infusions done concurrently with reperfusion following a two-hour occlusion did not result in a significant reduction or increase in the size of infarct. However, SK infusions resulted in a significant increase in the amount of hemorrhagic infarction.

The use of perfusion imaging in acute myocardial infarction: applications for clinical trials and clinical care

The use of perfusion imaging in the acute phase of myocardial infarction has been facilitated by the introduction of technetium 99m-labeled sestamibi (99mTc-sestamibi). Because of minimal redistribution, myocardium at risk can be quantified without delaying reperfusion therapy. The use of perfusion imaging with 99mTc-sestamibi has been extensively validated in a series of important animal studies in contrast to other methods used to assess outcome from acute myocardial infarction. This has important implications regarding the assessment of reperfusion therapy. With an accurate means to define myocardium at risk, myocardial salvage can be measured for specific therapies or patient subsets. Such measures also have clinical utility for the care of individual patients. Infarct size measures with 99mTc-sestamibi are accurate and predictive of subsequent left ventricular remodeling as well as prognosis. The identification of jeopardized myocardium in patients with nondiagnostic electrocardiograms and the noninvasive prospective measurement of collateral blood flow before reperfusion therapy are two new areas where perfusion imaging has special clinical use. Because of the ability of perfusion imaging with 99mTc-sestamibi to measure most of the variables known to determine infarct size, comparative clinical trials can be accomplished by using relatively small sample sizes. This has important implications regarding the assessment of new therapies for acute myocardial infarction.

Frequency of inclusion of patients with cardiogenic shock in trials of thrombolytic therapy

The purpose of this study was to determine the extent to which patients with cardiogenic shock have participated in trials of thrombolytic therapy, to examine factors associated with their exclusion from these trials, and to summarize data on the efficacy of thrombolysis in these patients. Previous publications were searched for all randomized, controlled studies involving the use of thrombolytic medications used in the treatment of acute myocardial infarction. Data were abstracted for year of trial publication, performance location, sample size, maximal allowable delay between symptom onset and treatment, and exclusion criteria. Of the 94 trials included in the analysis, 22% included patients with cardiogenic shock, 37% excluded them, and the remainder contained no information on their inclusion or exclusion. Only 2 trials provided data on the efficacy of thrombolytic therapy in patients with cardiogenic shock. Multivariate analysis revealed that studies conducted exclusively in the U.S. were significantly more likely to exclude patients in cardiogenic shock than those conducted outside of the U.S., as were studies that excluded patients with a previous myocardial infarction, studies published more recently, and smaller trials. Patients with cardiogenic shock have frequently been excluded from clinical trials of thrombolytic agents. As a result, data on the efficacy of thrombolytic agents in these patients is extremely limited.

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.

Does reperfusion injury exist in humans?

Timely coronary reperfusion as treatment for acute myocardial infarction reduces myocardial infarct size, improves left ventricular function and survival. There is still concern that at the time of reperfusion, a further injury occurs to the myocardium. Theoretically, if this "reperfusion injury" could be treated and eliminated, the outcome for patients with myocardial infarction might further improve. The concept of reperfusion injury is closely tied to the concept that oxygen radicals generated at the time of reperfusion cause tissue damage. There are four basic forms of reperfusion injury. Lethal reperfusion injury is described as myocyte cell death due to reperfusion itself rather than to the preceding ischemia. This concept continues to be controversial in both experimental animal and clinical studies. Vascular reperfusion injury refers to progressive damage to the vasculature over time during the phase of reperfusion. Manifestations of vascular reperfusion injury include an expanding zone of no reflow and a deterioration of coronary flow reserve. This form of reperfusion injury has been documented in animal models and probably occurs in humans. Stunned myocardium refers to postischemic ventricular dysfunction of viable myocytes and probably represents a form of "functional reperfusion injury." This phenomenon is well documented in both animal models and humans. Reperfusion arrhythmias represent the fourth form of reperfusion injury. They include ventricular tachycardia and fibrillation that occur within seconds to minutes of restoration of coronary flow after brief (5 to 15 min) episodes of myocardial ischemia. True reperfusion arrhythmias occur in only a small percentage of patients receiving thrombolytic therapy for acute myocardial infarction and are not a sensitive indicator for successful reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Stunning: damaging or protective to the myocardium?

There are several potential outcomes of myocardial ischemia. When ischemia is severe and prolonged, irreversible damage occurs and there is no recovery of contractile function. Interventions aimed at reducing mechanical activity and oxygen demand, either before ischemia or during reperfusion, have been shown to delay the onset of ischemic damage and to improve recovery on reperfusion. When myocardial ischemia is less severe but still prolonged, myocytes may remain viable but exhibit depressed contractile function. Under these conditions, reperfusion restores complete contractile performance. This type of ischemia, leading to a reversible, chronic left ventricular dysfunction, has been termed hibernating myocardium. Depression of mechanical activity is, actually, a protective mechanism whereby the hibernating cells reduce their oxygen demands in the setting of reduced oxygen supply. A third possible outcome after a short period of myocardial ischemia is a transient postischemic ventricular dysfunction, a situation termed stunned myocardium. As in the case of hibernating myocardium, the depressed contractile function occurring during stunning could be a protective mechanism, allowing the reperfused cells to gradually recover their metabolism and function.

The stunned and hibernating myocardium: a brief review

DEFINITIONS

Stunned myocardium is viable myocardium salvaged by coronary reperfusion that exhibits prolonged postischemic dysfunction after reperfusion. Hibernating myocardium is ischemic myocardium supplied by a narrowed coronary artery in which ischemic cells remain viable but contraction is chronically depressed.

CLINICAL EVIDENCE

Stunned myocardium has been identified in the following patient groups: (1) thrombolysis or percutaneous transluminal coronary angiography (PTCA) in patients with acute evolving infarction; (2) unstable angina; (3) exercise-induced angina; (4) coronary artery spasm; (5) platelet aggregation or transient thrombosis of a coronary artery; (6) PTCA for chronic myocardial ischemia; and (7) immediately following coronary artery bypass graft (CABG). Evidence of hibernating myocardium (LV dysfunction) is found in the patient with severe coronary artery stenosis, even in asymptomatic patients at rest. Stunned myocardium returns to normal after a prolonged period of time (hours to weeks). Hibernating myocardium returns to normal function rather quickly if the cause is removed.

DIFFERENTIATION

Stunned myocardium can be differentiated from hibernating myocardium by three clinical parameters, namely, LV wall motion, myocardial perfusion, and myocardial metabolism. Stunned myocardium has abnormal wall motion that tends to normalize in response to inotropes and postextrasystolic potentiation. Perfusion is adequate and metabolism is also adequate. Hibernating myocardium also has abnormal wall motion, which normalizes after nitrates, inotropes, post extrasystolic potentiation (PESP), PTCA, or CABG. Myocardial perfusion is reduced but can be reversed with PTCA or CABG and metabolism is adequate.

Comparison of tomographic and planar imaging for the evaluation of thrombolytic therapy in acute myocardial infarction using pre- and post-treatment myocardial scintigraphy with technetium-99m sestamibi

Pre- and post-treatment myocardial scintigraphy with technetium-99m hexakis 2-methoxy-isobutyl-isonitrile (Tc-99m sestamibi) was performed in patients who underwent thrombolytic therapy for acute myocardial infarction comparing planar imaging and single-photon emission computed tomography (SPECT). Twenty-one patients were injected with Tc-99m sestamibi before thrombolytic treatment. SPECT and planar imaging were acquired after completion of the treatment. The scintigraphy was repeated 5 days later in 20 subjects. Planar and SPECT studies were evaluated using an uptake score. Patients were divided according to the status of the infarct-related vessel (patent in 13 patients, group 1, and occluded in seven, group 2) and to the presence of functional recovery in serial echocardiographic controls (present in 10 patients, group A, and absent in 10, group B). The scintigraphic defect extent in the 5-day images correlated with the enzymatic infarct size: SPECT: r = 0.75, p less than 0.0002; planar: r = 0.68, p less than 0.002. The decrease of the uptake defects correlated with the reduction of the left ventricular wall asynergy (admission versus 1 month echocardiogram): SPECT: r = 0.92, p less than 0.000001; planar: r = 0.82, p less than 0.00001. The percent decrease of the uptake defects was significantly higher in patients in group 1 and group A compared with group 2 and, respectively, group B--SPECT: group 1: 51.4 +/- 27.7 versus group 2: 13.1 +/- 8.6, p less than 0.02; group A: 64.2 +/- 15.3 versus group B: 11.9 +/- 8.1, p less than 0.0002; planar group 1: 41 +/- 30.4 versus group 2: 7.7 +/- 6.2, p less than 0.05; group A: 52.5 +/- 24.3 versus group B: 6.1 +/- 6, p less than 0.0002. This study confirms the reliability of pre- and post-treatment myocardial scintigraphy with Tc-99m sestamibi for evaluating the outcome of thrombolytic treatment in myocardial infarction. The results seems slightly more accurate using SPECT, but a simple three-view planar study also gives useful data.

Mismatch of left ventricular function and infarct size demonstrated by technetium-99m isonitrile imaging after reperfusion therapy for acute myocardial infarction: identification of myocardial stunning and hyperkinesia

Quantitation of perfusion defect size using tomographic imaging with technetium-99m-hexakis-2-methoxy isobutyl isonitrile was performed at the time of hospital discharge in 32 patients with a first myocardial infarction who underwent successful coronary reperfusion within 8 h of the onset of chest pain. Reperfusion was accomplished with thrombolysis or primary coronary angioplasty. Radionuclide angiography was performed at discharge and 6 weeks later. There was a close correlation between perfusion defect size and values for ejection fraction and regional wall motion both at discharge (r = -0.80 and -0.75, respectively) and 6 weeks later (r = -0.81 and -0.81, respectively). There was no overall group difference in ejection fraction between the value at discharge and at 6 weeks; however, five patients had a significant increase (greater than or equal to 0.08) and six had a significant decrease (greater than or equal to 0.08) in ejection fraction. In patients with a significant increase at 6 weeks, ejection fraction was significantly lower at discharge than the value predicted from perfusion defect size (0.37 +/- 0.09 measured versus 0.47 +/- 0.13 predicted, p less than 0.05) and it improved at 6 weeks to near predicted values (0.51 +/- 0.07). In patients with a significant decrease at 6 weeks, ejection fraction was significantly higher at discharge than the value predicted from perfusion defect size (0.60 +/- 0.10 measured versus 0.50 +/- 0.10 predicted, p less than 0.05) and it decreased at 6 weeks to near predicted levels (0.51 +/- 0.09). Left ventricular ejection fraction at the time of hospital discharge is a potentially misleading index of the efficacy of reperfusion therapy for myocardial infarction. In a significant minority (34%) of patients this index does not accurately reflect perfusion defect size, apparently because of the effects of myocardial stunning and compensatory hyperkinesia.

Single photon emission computed tomography with technetium-99m hexakis 2-methoxyisobutyl isonitrile in acute myocardial infarction before and after thrombolytic treatment: assessment of salvaged myocardium and prediction of late functional recovery

Single photon emission computed tomography (SPECT) with technetium-99m hexakis 2-methoxyisobutyl isonitrile was investigated as a method to evaluate the results of intravenous thrombolytic treatment in 14 patients (11 men and 3 women) with acute myocardial infarction admitted to the coronary care unit within 4 h of the onset of symptoms. All patients received an injection of 740 MBq of the tracer before starting the thrombolytic therapy, and isonitrile tomography was performed 3 to 4 h later. The tomographic study was repeated 5 days after the acute event. The results of thrombolytic treatment were independently evaluated taking into account the clinical, electrocardiographic (ECG) and enzymatic data and the findings of left ventricular and coronary angiography. Furthermore, all patients were studied with two-dimensional echocardiography on admission, 5 days later and 1 month later. The site and extent of the perfusion defects on admission scintigraphy were consonant with the ECG and echocardiographic findings. A good correlation could be established between the 5 day scintigraphic estimate of infarct dimension and the enzymatic infarct size (r = 0.907, p less than 0.00002). The comparison between pre- and postthrombolytic treatment images enabled the identification of successful and unsuccessful reperfusion even in patients whose other noninvasive findings were inconclusive. Finally, the reduction in defect size predicted late functional improvement that was demonstrated by echocardiography performed 1 month later (r = 0.89, p less than 0.00005). The results of the study suggest the feasibility and the possible usefulness of isonitrile tomography in demonstrating the presence and size of myocardial damage and in assessing the extent of myocardial salvage after thrombolytic therapy in acute myocardial infarction.

Deleterious effects of oxygen radicals in ischemia/reperfusion. Resolved and unresolved issues

Oxygen free radicals are known to be generated during periods of ischemia followed by reperfusion. There is still some controversy, however, concerning the use of electron paramagnetic resonance spectroscopy to accurately detect and identify the free radical species that are formed. There is no doubt that oxygen radicals are deleterious to the myocardium; free radicals cause left ventricular dysfunction and structural damage to myocytes and endothelial cells in both in vitro and in vivo preparations. Potential sources of these cytotoxic oxygen species include the xanthine oxidase pathway, activated neutrophils, mitochondria, and arachidonate metabolism, yet the crucial source of free radicals in the setting of ischemia and reperfusion is unresolved. There is little doubt that oxygen radicals play a role in the phenomenon of stunned myocardium induced by brief periods of ischemia followed by reperfusion; numerous studies have consistently observed that pretreatment with free radical scavengers and antioxidants enhances contractile function of stunned, postischemic tissue. Whether oxygen free radical scavengers administered only during reperfusion enhance recovery of stunned myocardium in models of brief ischemia remains to be determined. In models of prolonged ischemia (2 hours) followed by reperfusion, we have not observed a beneficial effect of scavengers on stunned myocardium. The issue of whether oxygen free radical scavengers are capable of reducing so-called irreversible or lethal reperfusion injury remains, in our opinion, unresolved. Although some studies have observed that agents such as superoxide dismutase and catalase reduce infarct size in ischemia and reperfusion models, many others have reported negative results. Additional studies will be needed to resolve this ongoing controversy. Oxygen free radicals may also contribute to reperfusion-induced arrhythmias in rodent heart preparations; however, less data are available in other animal models. The concept of reperfusion injury should not be considered a deterrent to reperfusion for the treatment of acute myocardial infarcts in the clinical setting. Thrombolytic therapy reduces myocardial infarct size, enhances recovery of left ventricular function, and improves survival. Whether incremental beneficial effects on these parameters will be obtained when oxygen radical-scavenging agents are used as adjuvant therapy to thrombolysis in patients remains to be determined.

Serial quantitative planar technetium-99m isonitrile imaging in acute myocardial infarction: efficacy for noninvasive assessment of thrombolytic therapy

Technetium-99m isonitrile is a new myocardial perfusion imaging agent that accumulates according to the distribution of myocardial blood flow. However, unlike thallium-201, it does not redistribute over time. This imaging agent was used with serial quantitative planar imaging to assess the initial risk area of infarction, its change over time and the relation to infarct-related artery patency in 30 patients with a first acute myocardial infarction. Twenty-three of 30 patients were treated with recombinant tissue-type plasminogen activator (rt-PA) within 4 h after the onset of chest pain. Seven patients were treated in the conventional manner without thrombolytic therapy. Technetium-99m isonitrile was injected before or at the initiation of thrombolytic therapy, and imaging was performed several hours later. These initial images demonstrated the area at risk. Repeat imaging was performed 18 to 48 h later and at 6 to 14 days after the onset of myocardial infarction to visualize the ultimate extent of infarction. The initial area at risk varied greatly (range defect integral 2 to 61) both in patients treated with rt-PA and in those who received conventional treatment. For the total group, the initial imaging defect decreased in size in 20 patients and was unchanged or larger in 10 patients. Patients with a patent infarct-related artery had a significantly greater decrease in defect size than did patients with persistent coronary occlusion (-51 +/- 38% versus -1 +/- 26%, p = 0.0001). All patients with a decrease in defect size greater than 30% had a patent infarct-related artery. In 12 patients who also had predischarge quantitative exercise thallium-201 imaging, good agreement existed between the extent and severity of myocardial perfusion defect on the last technetium-99m isonitrile study before discharge and that noted on delayed thallium-201 imaging. It is concluded that serial planar technetium-99m isonitrile myocardial imaging in patients with acute myocardial infarction undergoing thrombolytic therapy offers a new quantitative noninvasive approach for assessment of the initial risk zone as well as the success of reperfusion.

What factors predict recovery of contractile function in the canine model of the stunned myocardium?

Recovery of contractile function of myocardium stunned by a brief, transient period of regional ischemia is highly variable. In our experience, segment shortening (an index of regional systolic contractile function) assessed during the initial hours after a 15-minute period of coronary artery occlusion in anesthetized open-chest dogs ranged from -84 to +99% of normal preocclusion values. In this retrospective study, regression analysis was used to assess the effects of various parameters on segment shortening 2 hours after reperfusion. Parameters assessed included regional myocardial blood flow both during occlusion and after reperfusion, high-energy phosphate content of previously ischemic tissue, systemic hemodynamic parameters (heart rate, mean arterial pressure and double product), occluded bed size and segment shortening measured during coronary artery occlusion. Recovery of systolic contractile function was not influenced by the degree of ischemia during coronary artery occlusion, myocardial blood flow after reperfusion, high-energy phosphate content, hemodynamic parameters or occluded bed size (correlation coefficients, r, ranged from 0.001 to 0.37 [p = not significant]). Only the degree of dyskinesia/hypokinesia exhibited during coronary occlusion significantly and reliably predicted recovery of segment shortening measured 2 hours after reflow (r = 0.70, p less than 0.001). Thus, recovery of systolic contractile function in the anesthetized canine model of the stunned myocardium is determined primarily by the degree of dysfunction exhibited during the preceding period of ischemia.

Is "stunned myocardium" a protective mechanism? Effect of acute recruitment and acute beta-blockade on recovery of contractile function and high-energy phosphate stores at 1 day post-reperfusion

There is little doubt that the "stunned myocardium" is amenable to therapeutic intervention, as a host of diverse pharmacologic agents have all been shown to improve short-term contractile function of viable, previously ischemic myocardium. However, few studies have addressed the question: Should the stunned myocardium be forced to contract? If the stunned myocardium is a protective mechanism, then acute recruitment could have later deleterious consequences on recovery of contractile function and high-energy phosphate stores. Conversely, acutely "resting" the heart (i.e. by beta-adrenergic blockade) could conceivably enhance or accelerate recovery of the stunned, postischemic tissue. We therefore sought to assess the immediate and longer-term effects of acute recruitment and acute beta-blockade on regional wall thickening (WT: using two-dimensional echocardiography) and adenosine triphosphate (ATP) content in the canine model of the stunned myocardium. Anesthetized open-chest dogs underwent 15 minutes of transient coronary artery occlusion. At 30 minutes following reperfusion, the dogs acutely received either: the ultrashort-acting beta-blocker esmolol, the afterload reducing and cardiostimulatory agent hydralazine, or saline. As anticipated, hydralazine enhanced contractile function of the stunned tissue in the short term: WT at 2 hours after treatment was 53.7 +/- 6.9% versus 7.1 +/- 6.5% in treated versus saline controls (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Newer agents for coronary thrombolysis. Perspectives from clinical studies

Myocardial infarction (MI) is a major cause of morbidity and mortality in western countries and the formation of intracoronary thrombi is recognized as a critical determinant of this ischaemic event. Since streptokinase and urokinase cause in vitro lysis of clots, it was though that these drugs were also effective in vivo in dissolving coronary thrombi. Clinical studies supported this concept. However, the beneficial effects of these drugs were, to some extent, offset by their inherent adverse reactions. Therefore new thrombolytic agents were developed, and for three of them (APSAC, tPA and proUK) there are enough clinical studies to allow for a comparison with 'old' agents. The data show that none of the new agents is safer or better than old agents with respect to easy handling, incidence of reperfusion of occluded coronary arteries, frequency of reocclusions, thrombus specificity, and bleeding complications. Thus, several directions are currently pursued to develop newer thrombolytic drugs with risk/benefit ratios better than those of 'old' agents. In this respect, it has been shown recently that the combination of aspirin with streptokinase is significantly better than streptokinase alone as far as mortality and incidence of rethrombosis is concerned. These data suggest that thrombolytic approaches safer and better than those currently available are possible and indicate that some of such new strategies are already available to enter the 'thrombolytic era' of acute MI.

Altered myocardial states. The stunned and hibernating myocardium

There are several potential outcomes of myocardial ischemia. When ischemia is severe and prolonged, myocyte cell death occurs and there is no recovery of contractile function of these cells. When myocardial ischemia is less severe but still prolonged, myocytes may remain viable but exhibit depressed contractile function, which may be a protective mechanism whereby these cells attempt to reduce their oxygen demand in the setting of reduced oxygen supply. The resultant chronic left ventricular dysfunction has been termed "hibernating myocardium." Finally, myocardial ischemia may be reversed with coronary artery reperfusion resulting in salvage of the myocytes. However, the viable myocardium may demonstrate relatively prolonged but transient postischemic contractile dysfunction, the situation termed "stunned myocardium." The concepts of stunned myocardium are reviewed as they apply to both coronary reperfusion during evolving acute myocardial infarction, as well as brief periods of ischemia that may occur during angina pectoris, or coronary vasospasm, or both. The concept of hibernating myocardium is reviewed as it applies to left ventricular function prior to and after coronary artery bypass surgery.

Streptokinase and reduced plasma viscosity: a second benefit

The purpose of this pilot study on a small cohort of patients (n = 13) with acute myocardial infarction receiving systemic streptokinase (STK) thrombolytic therapy was to measure the decrease in plasma viscosity concomitant with fibrinogen depletion. The treatment group was compared with a similar control group not given thrombolytic therapy. Serial relevant blood studies were undertaken in both groups for a period of 6 d. In the treatment group, a maximum reduction in plasma viscosity of 17 +/- 9% (mean +/- S.D.) was achieved during the first 24 h. Plasma viscosity remained below baseline for the 6-d duration of the study. Conversely, in the control group, the plasma viscosity rose to a maximum of 19 +/- 14% (mean +/- S.D.) over the period of study, paralleling the rise in plasma fibrinogen as an acute-phase reactant. Correlation studies between viscosity and plasma fibrinogen were strongly positive with mean values of r of 0.74 and 0.66 in the STK-treated group and controls, respectively. We conclude that the benefit of systemic STK treatment may in part be due to reduced myocardial workload and oxygen consumption at a critical time, and improved microvascular circulation, consequent on reduced plasma viscosity.

Assessment of thallium-201 redistribution versus glucose uptake as predictors of viability after coronary occlusion and reperfusion

Both 201Tl redistribution and persistent glucose uptake have been proposed as markers of viability after reperfusion. In the present study, they have been compared in the same open-chest canine preparation of occlusion and reperfusion. Ten fasting dogs were subjected to 2 hr of left anterior descending coronary artery occlusion and 4 hr of reperfusion. Myocardial blood flow was determined by a microsphere technique 100 min after occlusion and 3 hr after reperfusion. 201Tl was injected intravenously 20 min before reperfusion. Serial biopsy samples were obtained from ischemic and normal areas. 18F-2-deoxyglucose, a tracer of exogenous glucose uptake, was injected 3 hr after reperfusion. Thirty minutes before the animals were killed, simultaneous blood samples were taken from the femoral artery and the regional coronary veins draining the reperfused and the remote areas. Dogs were killed 4 hr after reperfusion was established. Area at risk was assessed by dye injection in vivo and area of necrosis by triphenyl tetrazolium chloride (TTC) staining, with confirmation by electron microscopy. Immediately after death, endocardial and epicardial samples were taken from regions characterized as risk regions, areas of necrosis, areas of patchy necrosis, and normal areas. These samples were counted in a scintillation well counter. Four hours after reperfusion, in ischemic myocardium (TTC positive) the relative 201Tl gradient between ischemic and normal regions was 26 +/- 13%, whereas in necrotic samples, this gradient was 71 +/- 26%.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative analysis of infarct size, contraction band necrosis, and coagulation necrosis in human autopsied hearts with acute myocardial infarction after treatment with selective intracoronary thrombolysis

To assess the importance of contraction band necrosis (CBN) in patients with acute myocardial infarction (AMI) treated with selective intracoronary thrombolysis, CBN, coagulation necrosis, and infarct size (expressed as CBN + coagulation necrosis) were analyzed quantitatively in 16 autopsied hearts. Intracoronary thrombolysis was performed from 2 to 6 hr after the onset of AMI, and the time from the onset of AMI to death was 7 to 168 hr. Cineangiography revealed no evidence of good collateral circulation in any of the patients. The 16 patients were classified into three groups: six patients with successful thrombolysis (100% to 99% stenosis, group I), five patients with unsuccessful thrombolysis (100% to 100%, group II), and five patients with 99% stenosis before thrombolysis (group III). Among the three groups, there were no significant differences in the time from the onset of AMI to thrombolysis, the time from the onset of AMI to death, the cause of death, or the degree of collateral circulation. The percentage of the risk area involved by the infarct in group I (82 +/- 6%) was similar to that in group II (80 +/- 11%). Infarct size was not reduced in group I because collateral circulation was not good and because the degree of recanalization after thrombolysis was 1%. However, the percentage of the infarct area with CBN was significantly higher in group I (20 +/- 9%) then in group II (3 +/- 3%). This finding shows that diffuse CBN occurred after reperfusion in patients with AMI treated with thrombolysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Streptokinase for the treatment of acute myocardial infarction: a brief review of randomized trials

This is a review of the important randomized trials of intracoronary and intravenous streptokinase therapy for treatment of acute myocardial infarction. Trials carried out before 1980 failed to recognize the relations between early coronary reperfusion and myocardial salvage and therefore have not been included in this review. Seven studies on intracoronary streptokinase have been reviewed. The two largest of these studies, the Western Washington trial and the Netherlands trial, show a similar reduction in early mortality. Two other small studies demonstrated a trend toward a reduction in mortality with streptokinase therapy and the other three did not. One small and two large intravenous streptokinase trials are reviewed. Of these, the large GISSI trial in Italy demonstrated a 23% reduction in mortality in patients treated within 3 hours from the onset of symptoms and the Intracoronary Streptokinase in Acute Myocardial Infarction (ISAM) trial showed a similar trend toward reduced mortality. The small Western Washington trial showed an even greater trend toward reduced mortality but this benefit was limited to patients with anterior myocardial infarction who received early therapy. It is concluded that intracoronary and intravenous streptokinase therapy, when initiated within the first 6 hours of acute myocardial infarction, reduces mortality. The therapy is most beneficial for those patients with anterior myocardial infarction and those who can receive therapy within the first 2 to 3 hours from the onset of symptoms.

Appraisal of various thrombolytic agents in the treatment of acute myocardial infarction

The immediate therapeutic objective after the onset of symptoms of an evolving myocardial infarction is to stop the process from progressing. Evidence has accumulated that this can be accomplished by the early dissolution of the clot within an acutely thrombosed artery, resulting in reperfusion of the ischemic area. There are five clot-dissolving agents currently being evaluated by intravenous administration for their ability to dissolve coronary thrombi and to produce clinical benefit; all are plasminogen activators and each has distinctive properties. Streptokinase, because it has been the agent most extensively studied and its clinical benefits have been established, now serves as a standard for comparison with the others (anisoylated plasminogen-streptokinase activator complex, urokinase, recombinant tissue plasminogen activator, and recombinant pro-urokinase). It is apparent that each of the agents has advantages and disadvantages and that none has established its superiority over the others as of yet.

Role of myocardial perfusion imaging in evaluating thrombolytic therapy for acute myocardial infarction

Myocardial thallium-201 scintigraphy is being increasingly employed as a method for assessing the efficacy of coronary reperfusion in acute myocardial infarction. New thallium uptake after intracoronary tracer administration after successful recanalization indicates that nutrient blood flow has been successfully restored. One may also presume that some myocardial salvage occurred if thallium administered in this manner is transported intracellularly by myocytes with intact sarcolemmal membranes. However, if one injects thallium by way of the intracoronary route immediately after reperfusion, the initial uptake of thallium in reperfused myocardium may predominantly represent hyperemic flow and regional thallium counts measured may not be proportional to the mass of viable myocytes. When thallium is injected intravenously during the occlusion phase the degree of redistribution after thrombolysis is proportional to the degree of flow restoration and myocardial viability. When thallium is injected for the first time intravenously immediately after reperfusion, an overestimation of myocardial salvage may occur because of "excess" thallium uptake in the infarct zone consequent to significant hyperemia. Another approach to myocardial thallium scintigraphy in patients undergoing thrombolytic therapy is to administer two separate intravenous injections before and 24 hours or later after treatment. Clinical studies have demonstrated that the improvement in defect size on serial images predicts improvement in regional function and patency of the infarct-related vessel. Finally, patients with acute myocardial infarction who receive intravenous thrombolytic therapy are candidates for predischarge exercise thallium-201 scintigraphy for risk stratification and detection of residual ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombolytic therapy in acute myocardial infarction. A perspective

This paper deals with the history of thrombolytic therapy from its inception to its application in acute myocardial infarction. It describes the discovery of streptococcal fibrinolysin, followed by the elucidation of the plasma proteolytic enzyme system concerned with fibrinolysis. An outline is given of the therapeutic basis for the decision to concentrate on the development of activators of the enzyme, rather than the enzyme itself. Early attempts to demonstrate the value of streptokinase and urokinase in the treatment of myocardial infarction are examined. Finally, the more encouraging approaches in current use, especially the early application of thrombolytic therapy after the onset of the morbid event, are discussed.

Myocardial thallium-201 kinetics and regional flow alterations with 3 hours of coronary occlusion and either rapid reperfusion through a totally patent vessel or slow reperfusion through a critical stenosis

Myocardial thallium-201 kinetics and regional blood flow alterations were examined in a canine model using 3 hours of coronary occlusion and different methods of reperfusion. Group I comprised 10 dogs undergoing a 3 hour left anterior descending artery occlusion and no reperfusion. Group II comprised seven dogs undergoing 3 hours of left anterior descending artery occlusion and rapid reperfusion through a totally patent vessel. Group III comprised 10 dogs undergoing 3 hours of left anterior descending artery occlusion and slow reperfusion through a residual stenosis. All dogs received 1.5 mCi of thallium-201 after 40 minutes of coronary occlusion. During occlusion and 2 hours of reperfusion, serial hemodynamic, blood flow and myocardial thallium-201 activity measurements were made. The relative thallium-201 gradient (normal zone minus ischemic zone activity when initial normal activity is expressed as 100%) during left anterior descending coronary occlusion was similar in all groups. Group I, 87 +/- 3%; Group II, 78 +/- 6%; Group III, 83 +/- 6% (p = NS). After 2 hours of either method of reperfusion, the final relative gradient had decreased to a similar level (Group II, 51 +/- 9%; Group III, 42 +/- 6%). These values were not significantly different from the final relative thallium-201 gradient seen in dogs undergoing a sustained 3 hour occlusion (Group I, 55 +/- 5%). After 2 hours of reperfusion, both methods of reflow were associated with similar degrees of "no reflow." Transmural flows in the central ischemic zone were 89 +/- 10% of normal in Group II and 71 +/- 6% of normal in Group III after reperfusion, with both flows substantially higher than the relative thallium-201 activities in these dogs. Infarct size (percent of left ventricle) determined with triphenyltetrazolium chloride was similar in all groups (Group I, 24 +/- 4%; Group II, 29 +/- 4%; Group III, 25 +/- 4%). Thus, in this experimental canine model, 3 hours of coronary occlusion followed by either rapid reperfusion through a totally patent vessel or slow reperfusion through a critical stenosis resulted in little delayed thallium-201 redistribution or myocardial salvage as assessed histologically, despite significant recovery of regional flow.

Activation of the fibrinolytic system during intracoronary streptokinase administration

Serial biochemical studies were performed in 12 patients treated with intracoronary streptokinase infusion for acute myocardial infarction, in order to study the method of activation of the fibrinolytic system during local administration of a relatively low dose of this drug and to determine correlations between systemic effects and reperfusion. Plasma samples were obtained before and every 15 minutes during the infusion of streptokinase and after completion of the therapy. Streptokinase dosage in this study was 211,000 +/- 88,000 IU (+/- SD). The average time from the onset of symptoms to the start of infusion was 2 hours 50 minutes (range 1 hour 10 minutes to 3 hours 30 minutes). Reperfusion occurred in six patients and temporary recanalization in three; in three patients no recanalization was achieved. Fibrinolytic assays of pretreatment plasma samples revealed elevated levels of plasminogen activators, presumably caused by the release of tissue-type plasminogen activator after a condition of stress. Plasminogen concentrations decreased from 94 +/- 17% to 44 +/- 30%. Alpha 2-antiplasmin fell from 84 +/- 27% to 12 +/- 19%; in seven patients no plasmin inhibitor activity was measurable at the completion of the infusion. Free plasmin occurred in samples only when this inhibitor had disappeared. This resulted in a lytic state leading to degradation of fibrinogen, the levels of which fell from 2.9 +/- 0.7% to 1.5 +/- 1.1%. Fibrinogen degradation products, measured in plasma with monoclonal antibodies, increased exponentially during streptokinase infusion in at least four patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Stabilization of a derangement in adenosine triphosphate metabolism during sustained, partial ischemia in the dog heart

Severe myocardial ischemia in dogs (perfusion 10% of normal) caused progressive deterioration in adenosine triphosphate (ATP) metabolism. Between 1/2 hour and 5 hours, myocardial ATP content fell from 55 to 6% of normal, and the sum of adenine nucleotides fell from 66 to 14% of normal. Moderate ischemia (perfusion 20 to 70%) also disturbed ATP metabolism, but to a lesser degree. Moreover, there was no significant change in the concentration of any ATP metabolite between 1/2 hour and 5 hours of moderate ischemia. ATP content was 66 and 52% of normal, and adenine nucleotide content was 73 and 59% of normal at 1/2 hour and 5 hours, respectively. Trivial ischemia (perfusion 80% or greater) barely perturbed ATP metabolism at either 1/2 hour or 5 hours. Thus, in contrast to severe or trivial ischemia, prolonged moderate ischemia produced a derangement in ATP metabolism that persisted and was relatively stable for 5 hours.