Silent MI and the Risk of Heart Failure
What is the association between silent myocardial infarction (SMI) and clinically manifested MI (CMI) and heart failure (HF)?
The authors performed an analysis of the ARIC (Atherosclerosis Risk in Communities) study in patients who were free of cardiovascular disease at their initial visit.SMI was defined as electrocardiographic (ECG) evidence of new MI at subsequent ARIC visits that was not present at the first visit. CMI was determined by physician review of medical records. Definite CMI met >1 of the following: diagnostic ECG pattern; diagnostic ECG with abnormal enzymes; or cardiac pain and abnormal enzymes plus evolving ST-T pattern or equivocal ECG. Probable MI met >1 of the following: cardiac pain and abnormal enzymes; cardiac pain and equivocal enzymes and either evolving ST pattern or diagnostic ECG pattern; or abnormal enzymes and evolving ST-T pattern. Definite and probable CMI were combined for analysis. Incident HF was defined as the first occurrence of HF hospitalization based on International Classification of Diseases (ICD)-9 code. Cox proportional hazard analysis examined the association between CMI and SMI (compared to no MI) with HF. Models adjusting for demographics, and demographics plus body mass index, smoking status, heart rate, systolic blood pressure, use of blood pressure-lowering medications, and diabetes mellitus were used. Patients with known coronary artery disease (CAD) were excluded. The first ARIC visit occurred from 1987 to 1989, and individuals were censored at the time of HF, death, or December 31, 2010, whichever occurred earlier.
The analysis included 9,243 individuals (mean age 53.7 ± 5.7 years, 57.2% women, 20.4% black). The no MI group had 8,607 participants, CMI group had 331 participants, and SMI group had 305 participants. The SMI group had more women, blacks, and nonsmokers. Compared to individuals without MI, those with CMI and SMI had a higher prevalence of CAD risk factors. The median follow-up was 13.0 years (interquartile range, 12.2; 13.9 years), during which there were 976 cases of HF: 104 HF cases among the CMI group; 54 HF cases among the SMI group; and 818 HF cases among the no MI group. Incidence rate of HF was higher in both CMI and SMI compared to no MI (incidence rate per 1,000 person-years was 30.4, 16.2, and 7.8, respectively; p value < 0.001). Multivariable adjusted Cox proportional hazard models demonstrated both CMI and SMI, compared to no MI, significantly were associated with HF (incidence rate per 1,000 person-years was 2.85 and 1.35, respectively; p value < 0.001 and 0.35). The magnitude of risk of HF for CMI was larger than the risk associated with SMI.
SMI is associated with increased risk of HF, although the magnitude of this risk is less compared to individuals with CMI.
SMI is common and accounts for approximately half of the total number of MIs. This analysis from the ARIC study showed that SMI is associated with a significantly increased risk of HF, after controlling for demographics and common risk factors. Future studies are needed to examine whether screening for SMI is cost-effective and whether preventative therapies in patients with SMI would be beneficial in reducing the risk of HF.
Keywords: Acute Coronary Syndrome, Angina Pectoris, Atherosclerosis, Blood Pressure, Body Mass Index, Coronary Artery Disease, Diabetes Mellitus, Electrocardiography, Heart Failure, Heart Rate, Medical Records, Myocardial Infarction, Primary Prevention, Risk Factors, Smoking, Diagnostic Imaging
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