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(Circulation. 2004;110:1572-1578.)
© 2004 American Heart Association, Inc.
Coronary Heart Disease |
From the University of Texas Health Science Center, Houston (D.A.); Brigham and Womens Hospital, Boston, Mass (S.D.S., H.S., M.A.P.); Rigshospitalet, Copenhagen, Denmark (L.K.); Toronto Hospital, Toronto, Ontario, Canada (J.L.R.); University of Glasgow, Glasgow, United Kingdom (J.J.V.M.); The Cleveland Clinic Foundation, Cleveland, Ohio (G.S.F.); Medical Pharmaceutical Consultants, Randolph, NJ (M.H.); Duke Clinical Research Institute, Durham, NC (C.M.O., J.D.L., E.J.V, R.M.C.); Estudios Cardiologicos Latinoamerica, Santa Fe, Argentina (R.D.); Cardiology Research Institute, Moscow, Russia (Y.N.B.); and the CPR/Research Institute of Cardiology, St. Petersburg, Russia (S.V.).
Correspondence and reprint requests to Dr David Aguilar, Cardiovascular Division, University of Texas Health Science Center, 6431 Fannin, MSB 1.246, Houston, TX 77030. E-mail david.aguilar{at}uth.tmc.edu
Received January 29, 2004; revision received April 29, 2004; accepted May 18, 2004.
| Abstract |
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Methods and Results We assessed the risk of death and major cardiovascular events associated with previously known and newly diagnosed diabetes by studying 14 703 patients with acute MI enrolled in the VALsartan In Acute myocardial iNfarcTion (VALIANT) trial. Patients were grouped by diabetic status: previously known diabetes (insulin use or diagnosis of diabetes before MI, n=3400, 23%); newly diagnosed diabetes (use of diabetic therapy or diabetes diagnosed at randomization [median 4.9 d after infarction], but no known diabetes at presentation, n=580, 4%); or no diabetes (n=10 719). Patients with newly diagnosed diabetes were younger and had fewer comorbid conditions than did patients with previously known diabetes. At 1 year after enrollment, patients with previously known and newly diagnosed diabetes had similarly increased adjusted risks of mortality (hazard ratio [HR] 1.43; 95% confidence interval [CI], 1.29 to 1.59 and HR, 1.50; 95% CI, 1.21 to 1.85, respectively) and cardiovascular events (HR, 1.37; 95% CI, 1.27 to 1.48 and HR, 1.34; 95% CI, 1.14 to 1.56).
Conclusions Diabetes mellitus, whether newly diagnosed or previously known, is associated with poorer long-term outcomes after MI in high-risk patients. The poor prognosis of patients with newly diagnosed diabetes, despite having baseline characteristics similar to those of patients without diabetes, supports the idea that metabolic abnormalities contribute to their adverse outcomes.
Key Words: myocardial infarction prognosis diabetes mellitus heart failure
| Introduction |
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Most of the studies that have quantified the adverse outcomes of diabetic patients with MI have been limited to patients with a known diagnosis of diabetes at the time of infarction. During the early days after an MI, physicians often diagnose new cases of diabetes, although it is unclear whether this relates to "stress hyperglycemia" or to the discovery of previously unrecognized diabetes in the population. The characteristics and prognosis of these patients with a new diagnosis of diabetes at the time of MI have been less well defined.
We used the VALsartan In Acute myocardial iNfarcTion (VALIANT) trial to characterize further the effect of previously known and newly diagnosed diabetes on 1-year mortality and major cardiovascular events in patients with heart failure and/or left ventricular systolic dysfunction after MI.
| Methods |
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Diabetic status was assessed at presentation with MI and again at randomization into VALIANT (a median of 4.9 d after symptom onset). Investigators were asked whether patients had a known history of diabetes before the qualifying MI, referring to a recorded history of diabetes managed with diet, insulin, or oral medications. Patients with a history of diabetes or insulin use before the qualifying MI were defined as having previously known diabetes. At randomization, investigators were asked whether patients had developed diabetes from the time of MI to randomization and whether they had received insulin or oral hypoglycemic agents within 24 h before randomization. If the investigator answered yes to either of these questions and the patient did not have previously known diabetes at presentation, then the patient was considered to have newly diagnosed diabetes. The remaining participants in the study were considered not to have diabetes (Figure 1).
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Outcomes
The primary outcomes were the risks of death and major cardiovascular events within 1 year after MI. Suspected adverse cardiac events were identified by the primary investigator and were independently confirmed by the Clinical Endpoint Center. Reinfarction was confirmed in the presence of increased cardiac enzymes and typical clinical presentation or electrocardiographic changes that were consistent with MI. Heart failure was defined as an unplanned presentation for new or worsening heart failure requiring an overnight stay or admission to a healthcare facility in which the patient received intravenous inotropic, diuretic, or vasodilator therapy. Stroke was defined as a focal neurological deficit lasting >24 h or resulting in death that was presumed to be related to stroke. Resuscitated sudden cardiac arrest was defined as sudden death or cardiac arrest requiring cardioversion, defibrillation, or cardiopulmonary resuscitation. A composite cardiovascular outcome was defined as the occurrence of cardiovascular death, reinfarction, heart failure, resuscitated sudden death, and stroke.
Data Analysis
Continuous variables are presented as means with standard deviations unless otherwise specified. Differences in baseline demographics between groups were ascertained using Wilcoxon rank-sum tests for continuous variables and Pearson
2 tests for categorical and ordinal data. Two-sided values of P<0.01 were considered significant.
Cox proportional-hazards models were used to assess the relations between diabetic status and the outcome of interest. Both unadjusted and multivariable adjusted hazard ratios are presented. From
70 candidate variables collected at randomization, both backward elimination and stepwise selection were used to identify independent predictors of the outcome. The multivariable model for mortality included the main effects of the following variables: age, heart rate, and systolic and diastolic blood pressures; Killip classification; anterior MI; new left bundle-branch block; thrombolytic therapy, primary percutaneous intervention, or ß-blocker use with qualifying MI; history of heart failure, previous MI, stroke, dyslipidemia, stable angina, hypertension, or alcohol abuse; previous unstable angina; trial enrollment in the United States; weight; current smoking; serum creatinine; atrial fibrillation, heart failure, hypertension, renal insufficiency, cardiac catheterization, percutaneous coronary intervention, or coronary artery bypass graft surgery after the qualifying MI; and study treatment assignment. The multivariable model for the composite cardiovascular outcome included similar variables, with the exception of US enrollment and ß-blocker use with qualifying MI and the addition of gender, race, previous hospitalization, and history of peripheral vascular disease or transient cerebral ischemic event.
Log-rank tests were used to compare event curves for mortality, cardiovascular death, reinfarction, heart failure, stroke, and the composite outcome of cardiovascular death, heart failure, reinfarction, stroke, or cardiac arrest with resuscitation.
| Results |
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Clinical Characteristics
Characteristics at baseline and at randomization are described in Table 1. Baseline demographics were similar between patients with newly diagnosed diabetes and patients without diabetes, except for body mass index. In contrast, patients with previously known diabetes were older and presented with more comorbid cardiovascular conditions than did either patients with newly diagnosed diabetes or patients without diabetes.
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Patients with previously known diabetes were more likely to have a non-Q-wave MI and had lower creatine kinase levels than both patients with newly diagnosed diabetes and patients without diabetes. The initial therapy for MI was similar between patients with newly diagnosed diabetes and those without diabetes. In contrast, patients with previously known diabetes were less likely to receive aspirin, ß-blockers, thrombolytic therapy, or primary percutaneous coronary intervention than were patients without diabetes. They also were less likely to receive ß-blockers and fibrinolytic therapy than were patients with newly diagnosed diabetes.
At randomization, patients with newly diagnosed or previously known diabetes had a faster heart rate and more often had a higher Killip classification than did patients without diabetes. Patients with previously known diabetes also had a slightly lower ejection fraction than did patients without diabetes and a higher systolic blood pressure than did patients with newly diagnosed diabetes and those without diabetes.
Medications, with the exception of diabetic therapy, did not differ between patients with newly diagnosed diabetes and those without diabetes. In contrast, patients with previously known diabetes were more likely to receive calcium channel blockers and HMG-CoA reductase inhibitors but were less likely to receive aspirin and ß-blockers than were patients without diabetes. Patients with previously known diabetes also were more likely to receive calcium channel blockers, insulin, and oral hypoglycemic therapy than those with newly diagnosed diabetes.
Mortality
By 1 year, 602 patients with previously known diabetes (17.7%), 94 patients with new diagnoses of diabetes (16.2%), and 1169 patients without diabetes (10.9%) had died. Despite similarities in characteristics between patients with newly diagnosed diabetes and those without diabetes, the rate of death was greater in patients with newly diagnosed diabetes and was similar to the rate in patients with previously known diabetes (Figure 2). The 1-year mortality rate for patients with newly diagnosed diabetes was similar whether they were or were not receiving diabetic therapy within 24 h of randomization (15.7% versus 16.8%, respectively; P=0.71). After adjustment for baseline differences, patients with either previously known or newly diagnosed diabetes maintained a higher risk of death as compared with patients without diabetes (Table 2).
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Nonfatal Events
The occurrences of nonfatal adverse cardiovascular events are described in Figure 3. Patients with previously known diabetes and those with newly diagnosed diabetes had higher rates of the composite cardiovascular outcome than those without diabetes (Figure 4). Similar to total mortality, the adjusted risk for the composite cardiovascular end point in patients with newly diagnosed diabetes was similar to the risk of patients with previously known diabetes (Table 2). The incidence of the composite cardiovascular outcome also was similar between patients with newly diagnosed diabetes who were or were not receiving diabetic therapy within 24 h of randomization (30% versus 28.2%, respectively; P=0.64).
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| Discussion |
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Patients with acute MI and a history of diabetes have poorer outcomes than such patients without diabetes,25,8 a finding confirmed in the present study. As in other studies, previously known diabetic patients in VALIANT were more likely to be older and female and to have more comorbid conditions than patients without diabetes. Despite having smaller MIs, as measured by creatine kinase levels, patients with diabetes also were more likely to have a greater degree of heart failure in conjunction with and in the first year after MI.
Multiple mechanisms have been implicated in the increased number of adverse outcomes in patients with diabetes. These mechanisms include an abnormal metabolic response to ischemia with inefficient energy use and accumulation of deleterious oxygen-free radicals,9 greater endothelial dysfunction,10 and abnormalities of thrombosis and fibrinolysis.11 Patients with diabetes are known to have a greater burden of atherosclerotic disease, with more diffuse and more multivessel coronary artery disease.5,12 The presence of a "diabetic cardiomyopathy" may lead to greater degrees of heart failure.8 Finally, although they derive similar therapeutic benefit, patients with diabetes have been demonstrated to be less likely to undergo thrombolysis13 or receive ß-blocker therapy14,15 than were patients without diabetes, a finding seen in the present study.
In our study, the 4% of patients who received a new diagnosis of diabetes during the early phase of acute MI displayed an increased risk of death and adverse cardiovascular events. It is important to consider this hazard in light of the differences that may exist in the group of patients with newly diagnosed diabetes. Because no uniform definition was specified and no blood glucose values were available for review, new cases of diabetes were diagnosed by individual physician assessments. Given this likely heterogeneity, as well as difficulties establishing a new diagnosis of diabetes in the early post-MI setting,16 patients with newly diagnosed diabetes likely composed a spectrum of patients from those with true unrecognized diabetes to those without diabetes but with stress hyperglycemia.
Population-based studies1719 and recent analyses of patients who were referred for cardiac catheterization20,21 have shown that the prevalence of previously unrecognized diabetes may range from one third to one half of the people with diabetes in the population studied and that the presence of unrecognized diabetes is associated with an increased risk of death.19,20,22 Overall, in studies in which survivors of an acute MI have undergone oral glucose tolerance testing, fasting blood glucose testing 2 to 3 months after MI, or both, the prevalence of undiagnosed diabetes has been estimated at 4% to 6%,16,23,24 although a recent prospective study using oral glucose testing after acute MI demonstrated a prevalence of unrecognized diabetes and impaired glucose tolerance of 31% and 35%, respectively.25 It is important to note that patients with newly diagnosed diabetes have been shown to have a significantly increased risk for coronary artery disease.21 Additionally, vascular wall abnormalities have been demonstrated in patients before the onset of diabetes mellitus.26
A significant proportion of patients with acute MI have hyperglycemia at presentation, a significant risk factor for adverse outcomes in both diabetic27,28 and nondiabetic patients.27,29 The mechanisms underlying the adverse association between hyperglycemia and acute MI are not fully understood, but multiple hypotheses have been proposed. Hyperglycemia may simply be a marker of stress hormones, which occur because of a catecholamine response to more extensive infarction or more severe heart failure. In our study, patients with newly diagnosed diabetes and previously known diabetes had similar heart rates and Killip classifications, suggesting that heart rate and degree of heart failure with infarction, both markers for deranged hemodynamics, may be common components between the two groups.
In addition to being a marker of stress hormone response, hyperglycemia may contribute directly to adverse outcomes. Acute hyperglycemia has been linked to impaired endothelial function,30 reduced collateral coronary blood flow,31 and, after reperfusion therapy for acute MI, increased microvascular dysfunction.32 Acute hyperglycemia also may increase thrombus formation; blood glucose levels have been shown to independently predict platelet-dependent thrombosis.33 Finally, hyperglycemia may itself be a marker for the degree of insulin resistance or insulin deficiency at the time of the acute MI and the subsequent associated metabolic consequences.
The present study has several limitations. As noted, blood glucose values were not available to allow a direct correlation of hyperglycemia with adverse outcomes. The lack of blood glucose levels and a uniform definition for diabetes likely led to some heterogeneity in the group with newly diagnosed diabetes. Also, individuals who were diagnosed with diabetes after randomization into the trial would not be captured in this analysis. Finally, these analyses were limited to those high-risk patients who fulfilled criteria for entry into the VALIANT trial.
| Conclusion |
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The poorer outcomes of patients with newly diagnosed diabetes, a diagnosis likely based on the presence of hyperglycemia, support the hypothesis that metabolic abnormalities early after MI contribute to the adverse outcomes. Although it is often difficult to confirm a diagnosis of diabetes early after MI, this study underscores the importance of screening for diabetes after MI to identify a group of patients who are at high risk for adverse outcomes and deserve particular medical attention to lower their risk.
| Disclosure |
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| Acknowledgments |
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| References |
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