Reperfusion therapy in patients with acute myocardial infarction and prior coronary artery bypass graft surgery (National Registry of Myocardial Infarction-2)

We reviewed data from the National Registry of Myocardial Infarction-2 to determine the differences in characteristics and outcomes in patients with acute myocardial infarction (AMI) who have undergone previous coronary artery bypass grafting (CABG), and those who have not, and between post-CABG patients who were treated with alteplase (recombinant tissue-type plasminogen activator [rt-PA]) and those who were treated with primary percutaneous transluminal coronary angioplasty (PTCA). Demographic, therapeutic, and outcome data from patients with AMI were collected at > 1,000 hospitals in the United States in collaboration with National Registry of Myocardial Infarction-2. Of the 45,925 patients receiving reperfusion therapy, 2,544 of the 39,574 treated with rt-PA (6.4%) had a history of CABG, and 375 of the 6,351 treated with primary PTCA (5.9%) had a history of CABG. Patients with a history of CABG were older, more likely to be men, and had more comorbidities, but prior CABG was still an independent predictor of mortality after multivariate regression analysis (odds ratio 1.23; 95% confidence interval 1.05 to 1.44). Among the post-CABG patients who received rT-PA or underwent PTCA, there was no significant difference in in-hospital mortality rate or the combined end point of death and nonfatal stroke. Thus, (1) prior CABG is an independent predictor of mortality, and (2) for post-CABG patients with AMI who are not in shock and who are lytic-eligible, reperfusion therapy with rt-PA and PTCA result in similar outcomes with regard to in-hospital mortality and the combined end point of death and nonfatal stroke.

Comparison of outcomes research with clinical trials using preexisting data

Outcomes research using analysis of preexisting data is a relatively new field with the potential to improve the quality and effectiveness of medical care, and may provide a useful complement to randomized studies. Motivated by the growth of this research in the cardiovascular literature, this review offers a framework to identify the core concepts of outcomes research from database analyses by comparing and contrasting it with the randomized clinical trial.

Beta-blockade improves adjacent regional sympathetic innervation during postinfarction remodeling

The effect of beta-blockade on left ventricular (LV) remodeling, when added to angiotensin-converting enzyme inhibition (ACEI) after anterior myocardial infarction (MI), is incompletely understood. On day 2 after coronary ligation-induced anteroapical infarction, 17 sheep were randomized to ramipril (ACEI, n = 8) or ramipril and metoprolol (ACEI-beta, n = 9). Magnetic resonance imaging was performed before and 8 wk after MI to measure changes in LV end-diastolic, end-systolic, and stroke volume indexes, LV mass index, ejection fraction (EF), and regional percent intramyocardial circumferential shortening. (123)I-labeled m-iodobenzylguanidine (MIBG) and fluorescent microspheres before and after adenosine were infused before death at 8 wk post-MI for quantitation of sympathetic innervation, blood flow, and blood flow reserve in adjacent and remote noninfarcted regions. Infarct size, regional blood flow, blood flow reserve, and the increase in LV mass and LV end-diastolic and end-systolic volume indexes were similar between groups. However, EF fell less over the 8-wk study period in the ACEI-beta group (-13 +/- 11 vs. -22 +/- 4% in ACEI, P < 0.05). The ratio of adjacent to remote region (123)I-MIBG uptake was greater in ACEI-beta animals than in the ACEI group (0.93 +/- 0.06 vs. 0.86 +/- 0.07, P < 0.04). When added to ACE inhibition after transmural anteroapical MI, beta-blockade improves EF and adjacent regional sympathetic innervation but does not alter LV size.

The sleep disorder canine narcolepsy is caused by a mutation in the hypocretin (orexin) receptor 2 gene

Narcolepsy is a disabling sleep disorder affecting humans and animals. It is characterized by daytime sleepiness, cataplexy, and striking transitions from wakefulness into rapid eye movement (REM) sleep. In this study, we used positional cloning to identify an autosomal recessive mutation responsible for this sleep disorder in a well-established canine model. We have determined that canine narcolepsy is caused by disruption of the hypocretin (orexin) receptor 2 gene (Hcrtr2). This result identifies hypocretins as major sleep-modulating neurotransmitters and opens novel potential therapeutic approaches for narcoleptic patients.

The association between the on-site availability of cardiac procedures and the utilization of those services for acute myocardial infarction by payer group. The National Registry of Myocardial Infarction 2 Investigators

BACKGROUND

Prior studies have suggested that in-hospital availability may be an important determinant for the use of invasive cardiac services; however, whether this association is influenced by payer status remains unclear.

HYPOTHESIS

The interaction of payer status and the on-site availability of coronary arteriography is associated with increased utilization of this procedure.

METHODS

In-hospital availability and utilization of coronary arteriography was ascertained in 275,046 patients with acute myocardial infarction (AMI) enrolled in the National Registry of Myocardial Infarction 2 from June 1994 to April 1996. Logistic regression analyses were performed to determine the association between the on-site availability of cardiac catheterization at the initial hospital and subsequent utilization of coronary arteriography. Similar analyses were performed within Medicare, Medicaid, Commercial, Health Maintenance Organization (HMO), and Uninsured payer groups.

RESULTS

Patients initially admitted to hospitals having on-site cardiac catheterization facilities were almost twice as likely to receive coronary arteriography as patients admitted to hospitals without such facilities and later transferred out [un-adjusted odds ratio (OR) = 1.69, 95% confidence interval (CI) 1.66-1.73, p < 0.0001; adjusted OR = 2.08, 95% CI 2.01-2.15, p < 0.0001]. Furthermore, this relationship of increased utilization with greater availability was evident within each payer group, but was highest among those with Commercial insurance and lowest among Medicaid recipients: [Commercial insurance (OR = 2.19, 95% CI 2.07-2.31, p < 0.0001); Uninsured (OR = 1.74, 95% CI 1.57-1.92, p < 0.0001); HMO (OR = 1.67, 95% CI 1.54-1.82, p < 0.0001); Medicare 1.60, 95% CI 1.55-1.64, p < 0.0001); Medicaid (1.46, 95% CI 1.29-1.65, p < 0.0001)].

CONCLUSIONS

Our results show a strong association between in-hospital availability and subsequent utilization of invasive cardiac procedures following AMI among all patients, but the strength of these associations varied among payer status.

Clinical correlates of the initial and long-term cost of coronary bypass surgery and coronary angioplasty

BACKGROUND

Medical costs vary substantially among patients. Understanding the baseline factors that predict subsequent cost may allow better selection of therapy for individual patients. Understanding the postprocedure events that increase cost should help to improve efficiency and effectiveness of coronary revascularization.

METHODS

Data on 4-year costs were collected from patients randomly assigned to coronary angioplasty or bypass surgery as part of the BARI (Bypass Angioplasty Revascularization Investigation) trial. Regression models first examined factors known at the time of randomization that prospectively predicted initial procedure cost and long-term cost. Subsequent models tested the value of postrandomization events as explanatory variables for cost.

RESULTS

The independent baseline predictors of higher initial percutaneous transluminal coronary angioplasty cost included 3-vessel disease (+12%) and acute presentations (+22%), whereas the independent predictors of higher initial coronary artery bypass grafting cost included the number of comorbid conditions (+5% per condition) and female sex (+7%). The independent baseline predictors of 4-year cost included heart failure (+26%), diabetes (+22%), comorbidity (+10%), and angioplasty assignment in patients with 2-vessel disease (-15%). Postrandomization models showed higher initial and long-term costs were strongly correlated with the number of repeat revascularization procedures (+30% to +128%) and the occurrence of clinical complications (+8% to +131%).

CONCLUSIONS

Two-vessel disease identifies patients likely to have lower costs after angioplasty, whereas heart failure, comorbid conditions, and diabetes identify patients likely to accrue higher costs after either angioplasty or bypass surgery. Long-term costs can be potentially reduced by interventions that decrease procedural complications or reduce the need for repeat revascularization.

Coronary flow velocity response to adenosine characterizes coronary microvascular function in women with chest pain and no obstructive coronary disease. Results from the pilot phase of the Women's Ischemia Syndrome Evaluation (WISE) study

OBJECTIVES

We sought to develop and validate a definition of coronary microvascular dysfunction in women with chest pain and no significant epicardial obstruction based on adenosine-induced changes in coronary flow velocity (i.e., coronary velocity reserve).

BACKGROUND

Chest pain is frequently not caused by fixed obstructive coronary artery disease (CAD) of large vessels in women. Coronary microvascular dysfunction is an alternative mechanism of chest pain that is more prevalent in women and is associated with attenuated coronary volumetric flow augmentation in response to hyperemic stimuli (i.e., abnormal coronary flow reserve). However, traditional assessment of coronary volumetric flow reserve is time-consuming and not uniformly available.

METHODS

As part of the Women's Ischemia Syndrome Evaluation (WISE) study, 48 women with chest pain and normal coronary arteries or minimal coronary luminal irregularities (mean stenosis = 7%) underwent assessment of coronary blood flow reserve and coronary flow velocity reserve. Blood flow responses to intracoronary adenosine were measured using intracoronary Doppler ultrasonography and quantitative angiography.

RESULTS

Coronary volumetric flow reserve correlated with coronary velocity reserve (Pearson correlation = 0.87, p < 0.001). In 29 (60%) women with abnormal coronary microcirculation (mean coronary flow reserve = 1.84), adenosine increased coronary velocity by 89% (p < 0.001) but did not change coronary cross-sectional area. In 19 (40%) women with normal microcirculation (mean flow reserve = 3.24), adenosine increased coronary velocity and area by 179% (p < 0.001) and 17% (p < 0.001), respectively. A coronary velocity reserve threshold of 2.24 provided the best balance between sensitivity and specificity (90% and 89%, respectively) for the diagnosis of microvascular dysfunction. In addition, failure of the epicardial coronary to dilate at least 9% was found to be a sensitive (79%) and specific (79%) surrogate marker of microvascular dysfunction.

CONCLUSIONS

Coronary flow velocity response to intracoronary adenosine characterizes coronary microvascular function in women with chest pain in the absence of obstructive CAD. Attenuated epicardial coronary dilation response to adenosine may be a surrogate marker of microvascular dysfunction in women with chest pain and no obstructive CAD.

Dobutamine stress echocardiography in women with chest pain. Pilot phase data from the National Heart, Lung and Blood Institute Women's Ischemia Syndrome Evaluation (WISE)

OBJECTIVES

The aim of this project was to assess the utility of dobutamine stress echocardiography (DSE) for evaluation of women with suspected ischemic heart disease.

BACKGROUND

Most investigations addressing efficacy of diagnosis and treatment of coronary artery disease (CAD) have been performed in predominantly male populations. As part of the Women's Ischemia Syndrome Evaluation (WISE) study, DSE was assessed in women participating at the University of Florida clinical site.

METHODS

Women with chest pain or other symptoms suggestive of myocardial ischemia and clinically indicated coronary angiography were eligible for the WISE study. Enrolled subjects underwent DSE using a modified protocol. Coronary stenosis was assessed by core laboratory quantitative coronary angiography (QCA).

RESULTS

The 92 women studied ranged in age from 34 to 82 years (mean 57.5). All women had > or = 1 major risk for CAD, and most (89, 97%) had > or = 2 risk factors. In 78 women (85%), left ventricular wall motion was normal at baseline and during peak infusion. The remaining 14 women had wall motion abnormalities during DSE. By QCA, 25 women (27%) had > or = 50% coronary stenosis, including 10 with single-vessel obstruction. Dobutamine stress echocardiography was abnormal in 10 of these 25 women, yielding overall sensitivity of 40%, and 60% for multivessel stenosis. Exclusion of women with inadequate heart rate response yielded overall sensitivity of 50%, and 81.8% for multivessel stenosis. Dobutamine stress echocardiography was normal in 54 of the 67 women with < 50% coronary narrowing, specificity 80.6%.

CONCLUSIONS

Dobutamine stress echocardiography reliably detects multivessel stenosis in women with suspected CAD. However, DSE is usually negative in women with single-vessel stenosis, and in the larger subset without coronary stenosis. Ongoing protocols of the WISE study are expected to improve diagnostic accuracy in women with single-vessel disease, as well as provide important data in the substantial number of women with chest pain but without epicardial coronary artery stenosis.

The Women's Ischemia Syndrome Evaluation (WISE) study: protocol design, methodology and feasibility report

OBJECTIVES

The Women's Ischemia Syndrome Evaluation (WISE) is a National Heart, Lung and Blood Institute-sponsored, four-center study designed to: 1) optimize symptom evaluation and diagnostic testing for ischemic heart disease; 2) explore mechanisms for symptoms and myocardial ischemia in the absence of epicardial coronary artery stenoses, and 3) evaluate the influence of reproductive hormones on symptoms and diagnostic test response.

BACKGROUND

Accurate diagnosis of ischemic heart disease in women is a major challenge to physicians, and the role reproductive hormones play in this diagnostic uncertainty is unexplored. Moreover, the significance and pathophysiology of ischemia in the absence of significant epicardial coronary stenoses is unknown.

METHODS

The WISE common core data include demographic and clinical data, symptom and psychosocial variables, coronary angiographic and ventriculographic data, brachial artery reactivity testing, resting/ambulatory electrocardiographic monitoring and a variety of blood determinations. Site-specific complementary methods include physiologic and functional cardiovascular assessments of myocardial perfusion and metabolism, ventriculography, endothelial vascular function and coronary angiography. Women are followed for at least 1 year to assess clinical events and symptom status.

RESULTS

In Phase I (1996-1997), a pilot phase, 256 women were studied. These data indicate that the WISE protocol is safe and feasible for identifying symptomatic women with and without significant epicardial coronary artery stenoses.

CONCLUSIONS

The WISE study will define contemporary diagnostic testing to evaluate women with suspected ischemic heart disease. Phase II (1997-1999) is ongoing and will study an additional 680 women, for a total WISE enrollment of 936 women. Phase III (2000) will include patient follow-up, data analysis and a National Institutes of Health WISE workshop.

Early contrast-enhanced MRI predicts late functional recovery after reperfused myocardial infarction

BACKGROUND

We have observed 3 abnormal patterns on contrast-enhanced MRI early after reperfused myocardial infarction (MI): (1) absence of normal first-pass signal enhancement (HYPO), (2) normal first pass signal followed by hyperenhanced signal on delayed images (HYPER), or (3) both absence of normal first-pass enhancement and delayed hyperenhancement (COMB). This study examines the association between these patterns in the first week after MI and late recovery of myocardial contractile function by use of magnetic resonance myocardial tissue tagging.

METHODS AND RESULTS

Seventeen patients (14 men) with a mean age of 53+/-12 years were studied after a reperfused first MI. Contrast-enhanced images were acquired immediately after bolus administration of gadolinium and 7+/-2 minutes later. Tagged images were acquired at weeks 1 and 7. Circumferential segment shortening (%S) was measured in regions displaying HYPER, COMB, or HYPO contrast patterns and in remote regions (REMOTE) at weeks 1 and 7. At week 1, %S was depressed in HYPER, COMB, and HYPO (9+/-8%, 7+/-6%, and 5+/-4%, respectively) and were less than REMOTE (18+/-6%, P<0.003). However, in HYPER, %S improved at week 7 from 9+/-8% to 18+/-5% (P<0.001 versus week 1). In contrast, HYPO did not improve significantly (5+/-4% to 6+/-3%, P=NS) and COMB tended to improve 7+/-6% to 11+/-6% (P=0.06).

CONCLUSIONS

HYPER has partially reversible dysfunction and represents predominantly viable myocardium. COMB shows borderline improvement and likely contains an admixture of viable and necrotic myocardium. HYPO shows little functional improvement at 7 weeks, presumably because of irreversible myocardial damage.

Health status in VA patients: results from the Veterans Health Study

Recently, the Veterans Administration (VA) Under Secretary for Health has designated functional status as one of the domains of value for the system, given its increasing importance for clinical care. The Veterans Health Study (VHS) was designed to assist the VA in monitoring outcomes and measuring the case mix of patients who use the VA. The Veterans SF-36 (short form functional status assessment for veterans) was administered to 2425 veterans receiving ambulatory care. Measures of the Veterans SF-36 were strongly correlated with sociodemographics and morbidities of the veterans. Young veterans had poorer mental health status than older veterans. Veterans who used ambulatory care in the VHS reported lower levels of health status, reflecting more disease than a non-VA civilian population. These measures of health are important indicators of the disease burden or case mix of the patients and are pertinent to health systems such as the VA for resource allocation decisions and as outcomes of care.

Consultation before thrombolytic therapy in acute myocardial infarction. Second National Registry of Myocardial Infarction (NRMI 2) Investigators

Among 57,398 thrombolytic recipients in the National Registry of Myocardial Infarction 2, consultation with another physician was sought in 64% before initiating lytic therapy, although presenting features were typical, rather than atypical, in most patients. Consultation significantly delayed the administration of lytic therapy and was associated with increased hospital mortality.

A milled implant-supported removable partial denture

Implant supported prostheses are highly successful restorations. There are multitudes of differing designs for these restorations. It is advantageous to retain some nervous input from the remaining dentition. The treatment modality presented in this paper not only has the support, stability, and retention necessary for all restorations, some of the remaining teeth are retained and are included in the restoration design.

Management and outcomes for black patients with acute myocardial infarction in the reperfusion era. National Registry of Myocardial Infarction 2 Investigators

Data from a national registry of myocardial infarction patients from June 1994 to April 1996 were analyzed to compare the presenting characteristics, acute reperfusion strategies, treatment patterns, and clinical outcomes among black and white patients. Blacks presented much later to the hospital after the onset of symptoms (median 145 vs 122 minutes, p <0.001), were more likely to have atypical cardiac symptoms (28% vs 24%, p <0.001), and nondiagnostic electrocardiograms during the initial evaluation period compared with whites (37% vs 31%, p <0.001). Also, blacks were less likely to receive intravenous thrombolytic therapy (adjusted odds ratio [OR] 0.76, 95% confidence intervals [CI] 0.71 to 0.80), coronary arteriography (adjusted OR 0.85, 95% CI 0.77 to 0.95), other elective catheter-based procedures (adjusted OR 0.87, 95% CI 0.78 to 0.96), and coronary artery bypass surgery (adjusted OR 0.66, 95% CI 0.58 to 0.75) than their white counterparts. Despite these differences in treatment, there were no significant differences in hospital mortality between blacks and whites.

Presenting characteristics, treatment patterns, and clinical outcomes of non-black minorities in the National Registry of Myocardial Infarction 2

Data from a national registry (cohort) of myocardial infarction, which has enrolled 275,046 patients from June 1994 to April 1996, were analyzed to compare the baseline demographic and clinical characteristics, treatment patterns, and clinical outcomes among Hispanics, Asian-Pacific islanders, and native Americans with those of white Americans presenting to the hospital with acute myocardial infarction. Non-black minorities were younger, had a higher proportion of men, used the emergency medical services less frequently, and presented later to the hospital after the onset of symptoms (135 vs 122 minutes, p <0.001) than whites. Also, non-black minorities were less likely to receive beta-blocker therapy at discharge (crude odds ratio 0.86, confidence interval 0.82 to 0.90) than whites, but they were generally as likely to receive intravenous thrombolytic therapy (with the exception of Asian-Pacific islanders) and undergo both coronary arteriography and revascularization procedures as their white counterparts. There were no significant differences in hospital mortality for non-black minorities compared with whites.

Risk for intracranial hemorrhage after tissue plasminogen activator treatment for acute myocardial infarction. Participants in the National Registry of Myocardial Infarction 2

BACKGROUND

The efficacy of thrombolytic therapy in reducing mortality from acute myocardial infarction has been unequivocally shown. However, thrombolysis is related to bleeding complications, including intracranial hemorrhage.

OBJECTIVE

To determine the frequency of and risk factors for intracranial hemorrhage after recombinant tissue-type plasminogen activator (tPA) given for acute myocardial infarction in patients receiving usual care.

DESIGN

Large national registry of patients who have had acute myocardial infarction.

SETTING

1484 U.S. hospitals.

PATIENTS

71073 patients who had had acute myocardial infarction from 1 June 1994 to 30 September 1996, received tPA as the initial reperfusion strategy, and did not receive a second dose of any thrombolytic agent.

MEASUREMENT

Intracranial hemorrhage confirmed by computed tomography or magnetic resonance imaging.

RESULTS

673 patients (0.95%) were reported to have had intracranial hemorrhage during hospitalization for acute myocardial infarction; 625 patients (0.88%) had the event confirmed by computed tomography or magnetic resonance imaging. Of the 625 patients with confirmed intracranial hemorrhage, 331 (53%) died during hospitalization. An additional 158 patients (25.3%) who survived to hospital discharge had residual neurologic deficit. In multivariable models for the main effects of candidate risk factors, older age, female sex, black ethnicity, systolic blood pressure of 140 mm Hg or more, diastolic blood pressure of 100 mm Hg or more, history of stroke, tPA dose more than 1.5 mg/kg, and lower body weight were significantly associated with intracranial hemorrhage.

CONCLUSIONS

Intracranial hemorrhage is a rare but serious complication of tPA in patients with acute myocardial infarction. Appropriate drug dosing may reduce the risk for this complication. Other therapies, such as primary coronary angioplasty, may be preferable in patients with acute myocardial infarction who have a history of stroke.

Employment after coronary angioplasty or coronary bypass surgery in patients employed at the time of revascularization

BACKGROUND

Patients who undergo coronary angioplasty have a shorter convalescence than those who undergo coronary bypass surgery. This may improve subsequent employment.

OBJECTIVE

To compare employment patterns after coronary angioplasty or surgery.

DESIGN

Multicenter, randomized clinical trial.

SETTING

Seven tertiary care hospitals.

PATIENTS

409 employed patients with multivessel coronary artery disease.

INTERVENTION

Coronary bypass surgery or balloon angioplasty.

MEASUREMENTS

Time to return to work and time spent working during 4 years of follow-up.

RESULTS

Patients who underwent angioplasty returned to work 6 weeks sooner than patients who underwent coronary bypass surgery (P < 0.001), but long-term employment did not differ significantly (P > 0.2). Long-term employment was significantly lower among patients who were 60 to 64 years of age (P < 0.001), those who worked less than full-time at study entry (P < 0.001), and those who had less formal education (P = 0.005). Patients with only one source of health insurance were more likely to continue working (P = 0.005).

CONCLUSIONS

Faster recovery after angioplasty speeds return to work but does not improve long-term employment, which is primarily associated with nonmedical factors.

Vessel boundary extraction based on a global and local deformable physical model with variable stiffness

Reliable and efficient vessel cross-sectional boundary extraction is very important for many medical magnetic resonance (MR) image studies. General purpose edge detection algorithms often fail for medical MR images processing due to fuzzy boundaries, inconsistent image contrast, missing edge features, and the complicated background of MR images. In this regard, we present a vessel cross-sectional boundary extraction algorithm based on a global and local deformable model with variable stiffness. With the global model, the algorithm can handle relatively large vessel position shifts and size changes. The local deformation with variable stiffness parameters enable the model to stay right on edge points at the location where edge features are strong and at the same time, fit a smooth contour at the location where edge features are missing. Directional gradient information is used to help the model to pick correct edge segments. The algorithm was used to process MR cine phase-contrast images of the aorta from 20 volunteers (over 500 images) with excellent results.

Regional myocyte hypertrophy parallels regional myocardial dysfunction during post-infarct remodeling

After large myocardial infarction (MI), left-ventricular (LV) remodeling is characterized by cavity dilatation, eccentric hypertrophy, and regional mechanical dysfunction. We wished to correlate cellular hypertrophy chronically after MI with in vivo function on a regional basis within non-infarcted myocardium. Twelve sheep were studied. Seven underwent coronary ligation to create an anteroapical MI. Magnetic resonance imaging (MRI) was performed once in controls, and prior to and 8 weeks after infarction, for measurement of LV mass, volumes, ejection fraction, and regional intramyocardial circumferential shortening (%S). Myocyte morphometric indices (cell volume, length, cross-sectional area, width, and length/width ratios) were measured from myocytes isolated from regions adjacent to (within 2 cm of the infarct border) and remote from the infarct and at corresponding loci in the control animals. From baseline to 8 weeks after infarction in the infarcted animals, end-diastolic volume increased from (mean+/-s.d.) 1.9+/-0.4 ml/kg to 2.6+/-0.4 ml/kg (P<0.02) and EF fell from 49+/-6 to 35+/-6% (P<0.02). LV mass trended upwards from 2.2+/-0.4 to 2.6+/-0.4 g/kg (P=n.s.). Regionally, %S in the region adjacent to the infarct fell (from 19+/-3 to 13+/-3%, P<0.003) while remote %S did not change. Cell volume in adjacent non-infarcted regions was greater than that in remote non-infarcted regions (3.8+/-0.9x10(4) micrometer3 v 2.6+/-0. 8x10(4) micrometer3, P<0.006) and this difference (+1.2+/-0.7x10(4) micrometer3) was greater than the corresponding regional difference in controls (+0.4+/-0.2x10(4) micrometer3, P<0.05). Similarly, myocytes in adjacent non-infarcted regions were longer (138.0+/-10.1 micrometer) than in remote regions (123.7+/-10.1 micrometer, P<0.002), and this difference (+14.3+/-7.2 micrometer) was greater than that in controls (-1.4+/-5.6 micrometer, P<0.003). Adjacent %S correlated inversely with adjacent myocyte cell volume (r=-0.72, P<0.009) and cell length (r=-0.70, P<0.02). In mechanically dysfunctional non-infarcted regions adjacent to chronic transmural myocardial infarction in the remodeled LV, disproportionate cellular hypertrophy occurs, predominantly due to an increase in cell length. Mechanical dysfunction in these regions correlates with cell lengthening and hypertrophy.

Activation of the Ah receptor signal transduction pathway by bilirubin and biliverdin

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin) and related chemicals. Although no endogenous physiological ligand for the AhR has yet been described, persistent expression of hepatic CYP1A1 gene expression (an AhR-dependent response) in congenitally jaundiced Gunn rats indirectly supports the existence of such a ligand(s) in these animals. High plasma levels of the heme degradation product bilirubin (BR) in these animals prompted us to evaluate whether BR is an endogenous AhR agonist. Expression of dioxin responsive element (DRE)-driven luciferase gene expression in stably transfected mouse, guinea pig, rat, and human cells was induced by treatment with physiological concentrations of BR. Biliverdin (BV), the metabolic precursor of bilirubin, also induced luciferase activity in all species. BR and BV not only stimulated AhR transformation and DRE binding in vitro andin cells in culture, but competitive inhibition of [3H]TCDD-specific binding to the cytosolic AhR revealed that these chemicals are AhR ligands. The significantly greater inducing potency of these chemicals in intact cells, compared to their ligand binding and AhR transformation potency in vitro, suggests that BR and BV may also be converted within the cell to a more potent activator(s). Our results demonstrate that the heme degradation products BR and BV are AhR ligands which can regulate the AhR-dependent gene expression pathway.

Corrosion behavior of sensitized duplex stainless steel

The present work investigates the corrosion behavior of 2205 duplex stainless steel in 0.9% NaCl solution after various heat-treatments, and compares it to that of 316L austenitic stainless steel. Both stainless steels were heat-treated at 500, 650, and 800 degrees C in air for 1 h, followed by furnace cooling. Each heat-treated sample was examined for their microstructures and Vickers micro-hardness, and subjected to the X-ray diffraction for the phase identification. Using potentiostatic polarization method, each heat-treated sample was corrosion-tested in 37 degrees C 0.9% NaCl solution to estimate its corrosion rate. It was found that simulated sensitization showed an adverse influence on both steels, indicating that corrosion rates increased by increasing the sensitization temperatures.

Activation of the Ah receptor by tryptophan and tryptophan metabolites

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that mediates many of the biological and toxicological actions of a variety of hydrophobic natural and synthetic chemicals, including the environmental contaminant 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD, dioxin). A variety of indole-containing chemicals, such as indole-3-carbinol, indolo[3, 2-b]carbazole, and UV photoproducts of tryptophan (TRP), have previously been identified as ligands for AhR. Here we have examined the ability of endogenous metabolites of tryptophan (TRP) to bind to and activate AhR in vitro and in cells in culture. Although hydroxylated TRP metabolites were inactive, two metabolites, namely tryptamine (TA) and indole acetic acid (IAA), were shown to be AhR agonists. Not only do TA and IAA bind competitively to AhR, but they also can stimulate AhR transformation and DNA binding and induce expression of an AhR-dependent reporter gene in cells. In addition to being an AhR ligand, TA is also a competitive substrate for cytochrome P4501A1, a well-characterized AhR- and TCDD-inducible gene product. Although these compounds are relatively weak ligands, compared to TCDD, they represent some of the first endogenous hydrophilic AhR agonists identified to date.

Impact of time to treatment with tissue plasminogen activator on morbidity and mortality following acute myocardial infarction (The second National Registry of Myocardial Infarction)

This study examines the association between time to treatment with thrombolytic therapy and hospital outcomes in patients with acute myocardial infarction (AMI) enrolled in a national registry. A total of 71,253 patients hospitalized with AMI from June 1994 to July 1996 who received tissue plasminogen activator (t-PA) therapy in 1,474 United States hospitals were studied. In this study sample, approximately 39% of patients presented to participating hospitals within 2 hours of acute symptom onset and received t-PA; 36% were treated within 2.1 to 4 hours, 12% between 4.1 to 6 hours, and the remaining 13% thereafter. After controlling for potentially confounding factors, in-hospital death rates increased progressively with increasing delays in time of administration of t-PA. The lowest risk for dying during acute hospitalization was seen for those treated with t-PA within 2 hours of acute symptoms. No significant association was seen between time of administration of t-PA and in-hospital risk of recurrent AMI, myocardial ischemia, cardiogenic shock, major bleeding episodes, or stroke and/or intracranial bleeding. The incidence of sustained ventricular arrhythmias declined with progressively longer time to administration of t-PA. The results of this multihospital observational study suggest that patients with AMI treated earlier with t-PA are significantly more likely to survive the acute hospitalization than patients treated later. These data reinforce the benefits to be gained by treatment with t-PA as soon as possible following the onset of acute ischemic symptoms, and for community-wide efforts to reduce the duration of prehospital delay in patients with acute coronary disease.

Quantitative assessment of myocardial viability after infarction by dobutamine magnetic resonance tagging

BACKGROUND

The assessment of return of function within dysfunctional myocardium after acute myocardial infarction (MI) using contractile reserve has been primarily qualitative. Magnetic resonance (MR) myocardial tagging is a novel noninvasive method that measures intramyocardial function. We hypothesized that MR tagging could be used to quantify the intramyocardial response to low-dose dobutamine and relate this response to return of function in patients after first MI.

METHODS AND RESULTS

Twenty patients with a first reperfused MI (age, 53+/-12 years; 16 male; 11 inferior MIs) were studied. Patients underwent breath-hold MR-tagged short-axis imaging on day 4+/-2 after MI at baseline and during dobutamine infusion at 5 and 10 microg x kg(-1) x min(-1). At 8+/-1 weeks after MI, patients returned for a follow-up MR tagging study without dobutamine. Quantification of percent intramyocardial circumferential segment shortening (%S) was performed. Low-dose dobutamine MRI was well tolerated. Overall, mean %S was 15+/-11% at baseline (n=227 segments), increased to 16+/-10% at 5 microg x kg(-1) x min(-1) dobutamine (P=NS), 21+/-10% at peak (P<0.0001 versus baseline and 5 microg x kg(-1) x min(-1), and 18+/-10% at 8 weeks (P<0.004 versus baseline and peak). The increase in %S with peak dobutamine was greater in dysfunctional myocardium (103 segments, +9+/-10%) than in normal tissue (124 segments, +4+/-12%, P<0.0001). In dysfunctional regions, %S also increased from 6+/-7% at baseline to 14+/-10% at 8 weeks after MI (P<0.0001). In dysfunctional regions that responded normally to peak dobutamine (> or =5% increase in %S), the increase in %S from baseline to 8 weeks after MI (+9+/-9%) was greater than in those regions that did not respond normally (+5+/-9%, P<0.04). Midmyocardial and subepicardial response to dobutamine were predictive of functional recovery, but the subendocardial response was not.

CONCLUSIONS

The response of intramyocardial function to low-dose dobutamine after reperfused MI can be quantified with MR tagging. Dysfunctional tissue after MI demonstrates a larger contractile response to dobutamine than normal myocardium. A normal increase in shortening elicited by dobutamine within dysfunctional midwall and subepicardium predicts greater functional recovery at 8 weeks after MI, but the response within the subendocardium is not predictive.