Although the incidence of and mortality after ST-segment elevation myocardial infarction (STEMI) is decreasing, time trends in anatomical location of STEMI and associated short-term prognosis have not been examined in a population-based community study. We determined 22-year trends in age- and race-adjusted gender-specific incidences and 28-day case fatality of hospitalized STEMI by anatomic infarct location among a stratified random sample of 35- to 74-year-old residents of 4 communities in the Atherosclerosis Risk in Communities study. STEMI infarct location was assessed by 12-lead electrocardiograms from the hospital record and was coded as anterior, inferior, lateral, and multilocation STEMIs using the Minnesota code. From 1987 to 2008, a total of 4,845 patients had an incident STEMI; 37.2% were inferior STEMI, 32.8% were anterior, 16.8% occurred in multiple infarct locations, and 13.2% were lateral STEMI. For inferior, anterior, and lateral STEMIs in both men and women, significant decreases were observed in the age-adjusted annual incidence and the associated 28-day case fatality. In contrast, for STEMI in multiple infarct locations, neither the annual incidence nor the 28-day case fatality changed over time. The age- and race-adjusted annual incidence and associated 28-day case fatality of STEMI in anterior, inferior, and lateral infarct locations decreased during 22 years of surveillance; however, no decrease was observed for STEMI in multiple infarct locations. In conclusion, our findings suggest that there is room for improvement in the care of patients with multilocation STEMI.
Detailed evaluation of temporal trends in myocardial infarction (MI) rates is essential to monitor the population burden of cardiovascular disease and to understand the determinants of coronary heart disease mortality over time. During an ST-segment elevation MI (STEMI), the distribution of ST elevations on a surface electrocardiogram (ECG) corresponds to anatomic locations of ischemic myocardium and has prognostic importance. Recent studies have demonstrated decreases in the incidence, severity, and mortality after an MI. Some STEMI consensus treatment guidelines and clinical practice monographs draw from historic patterns in STEMI infarct location and suggest that STEMI treatment may differ by infarct location. However, whether patterns of STEMI infarct location by electrocardiography have changed and apply to STEMI in the contemporary era is unknown. We describe herein 22-year trends in rates of incident STEMI by electrocardiographic infarct location and associated survival in a community setting.
Methods
Since 1987, the Atherosclerosis Risk in Communities (ARIC) study has conducted surveillance of hospitalized MI and deaths due to coronary heart disease among residents aged 35 to 74 years in 4 communities: Forsyth County, North Carolina; Jackson, Mississippi; suburban Minneapolis, Minnesota; and Washington County, Maryland. The combined study population of these 4 communities was approximately 396,000 subjects in 2008. Twenty-four percentage of the population in the ARIC communities under surveillance were black. Subjects in the Forsyth County, North Carolina and the city of Jackson, Mississippi were 20% and 50% black, respectively, whereas those in the remaining 2 communities in the ARIC Community Surveillance were predominantly white. Details of the surveillance methods used have been previously reported and are only briefly described here.
A stratified random sample of suspected hospitalized MIs was identified from electronic discharge lists obtained from all hospitals (n = 23) serving the 4 communities. Trained ARIC staff abstracted data from medical records, selected on age, community of residence, and discharge code ( International Classification of Diseases, Ninth Revision, Clinical Modification codes 402, 410 to 414, 427, 428, and 518.4). Detailed descriptions of investigation and validation of selected International Classification of Diseases codes used in the ARIC Community Surveillance have been provided elsewhere. Sampling probabilities varied by race, gender, field center, and discharge code stratum and were adjusted periodically. Medical records were abstracted for presence of chest pain, history of MI or cardiovascular disease, and cardiac biomarkers. Copies of up to 3 ECGs (first, last, and third) were obtained from each hospitalization and sent to the University of Minnesota Electrocardiographic Reading Center for classification by the Minnesota code. A computerized algorithm was applied to data on chest pain, biomarkers, and electrocardiographic findings to classify MI. Criteria for each of these 3 diagnostic elements in the algorithm remained constant during the study period and have been described in detail. All eligible hospitalized events were classified as definite, probable, suspect, or no MI. Definite and probable MI events were combined to define MI events for this analysis. Definite and probable MI events with abnormal biomarkers were further classified by the Minnesota code of the ECGs obtained as STEMI or non–ST-segment elevation MI (NSTEMI). This analysis was restricted to validated STEMI events without a history of previous MI noted in the medical record.
All ECGs were visually coded using the Minnesota code categories of ST-segment elevations into 1 of 4 anatomic locations based on conventional anatomic grouping of surface electrocardiographic leads: V 1 to V 5 ; II, III, aVF; or I, aVL, V 6 . Using these 3 lead groups, 4 anatomic locations (anterior, inferior, lateral, or multiple) were derived for this study. Anterior STEMI was defined as an ST-segment elevation of ≥2.0 mm in any of the leads V 1 to V 4 or an ST-segment elevation of ≥1.0 mm in V 5 ; inferior STEMI as an ST-segment elevation of ≥1.0 mm in any of the leads II, III, or aVF; and lateral STEMI as an ST-segment elevation of ≥1.0 mm in any of the leads I, aVL, and V 6 alone or in the presence of anterior ST-segment elevations. ST elevations in the anterior and lateral electrocardiographic lead groups were combined to increase sensitivity to detect lateral STEMI, as ischemia of the lateral wall may be poorly represented by the lateral leads (I, aVL, and V 6 ) alone. Finally, to represent ischemia in multiple anatomic locations, a multilocation STEMI was defined as ST-segment elevations in ≥2 of anterior, inferior, or lateral locations.
Vital status after hospital discharge was determined through linkage with the National Death Index. Twenty-eight-day case fatality was determined for all incident STEMI cases and, because of limited events by infarct location, we grouped 28-day case fatality into 2 time period categories (1987 to 1996 and 1997 to 2007) for comparison. Case fatality results are not reported for 2008 because of a lag in the National Death Index reporting.
All analyses were weighted and standard errors were computed using stratified random sampling method to account for the sampling scheme. Descriptive statistics for baseline characteristics were computed by year group and by STEMI infarct locations. The annual percent changes in event rates were computed across the year groups for each baseline characteristics and the corresponding standard errors were approximated by the delta method. Wald tests were used to compare baseline characteristics between STEMI locations. Age- and race-adjusted, gender-specific, annual incidence per 10,000 subjects of STEMI by anatomic location were computed based on population denominator estimates using interpolation and extrapolation of 1990 and 2000 US Census population estimates. Age and race adjustments were by the direct method using the 2000 US population estimates as the standard. Twenty-two-year trends in incident STEMI are reported by location and gender based on linear or quadratic Poisson regression models. Quadratic trends are reported only when the quadratic term in the model is significant at the 0.05 level. Pairwise comparisons of the bootstrapped average annual percent change estimated from the location-specific linear regression models were made at the 0.05 level with Bonferroni adjustment for multiple comparisons. Logistic regression was used to model age- and race-adjusted 28-day case fatality percentages as a function of location, time interval (1987 to 1996 and 1997 to 2007), and gender. Contrasts were specified to test differences in case fatality between year groups for each location. The differences of trends in case fatality trends between genders were tested; gender-specific trends were not reported because of insignificant p values and small numbers of events. Event rate trends analysis was conducted in the statistical package SUDAAN Loglink and case fatality analyses were conducted in SUDAAN Logistic (Research Triangle Institute, Research Triangle Park, North Carolina).
Results
From 1987 to 2008, there were an estimated 4,845 incident hospitalized STEMIs in the 4 ARIC study communities among residents aged 35 to 74 years. During the 22-year study period, 31.3% of STEMIs occurred in women. There were statistically significant changes in both the characteristics of patients with STEMI and the methods used to treat these patients during the study duration ( Table 1 ).
| Variable | Year Group | Annual Percent Change (95% CI) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1987–1988 (n = 420) ∗ | 1989–1990 (n = 474) ∗ | 1991–1992 (n = 548) ∗ | 1993–1994 (n = 630) ∗ | 1995–1996 (n = 599) ∗ | 1997–1998 (n = 516) ∗ | 1999–2000 (n = 437) ∗ | 2001–2002 (n = 290) ∗ | 2003–2004 (n = 240) ∗ | 2005–2006 (n = 334) ∗ | 2007–2008 (n = 357) ∗ | ||
| Age (yrs) | 58.8 | 58.0 | 57.8 | 58.4 | 58.4 | 57.9 | 58.6 | 57.6 | 58.1 | 58.7 | 56.8 | −0.1 (−0.2 to 0.1) |
| Women | 30.3 | 30.3 | 31.4 | 29.3 | 32.2 | 30.5 | 33.7 | 30.0 | 35.5 | 26.6 | 36.9 | 0.5 (−0.5 to 1.5) |
| Black | 11.8 | 12.0 | 14.2 | 20.8 | 21.7 | 27.4 | 23.6 | 21.5 | 25.1 | 25.5 | 36.3 | 4.6 (3.3 to 5.9) |
| Age >65 yrs | 27.8 | 25.7 | 30.4 | 30.6 | 32.0 | 28.2 | 33.2 | 27.4 | 30.3 | 25.2 | 19.8 | −0.7 (−1.8 to 0.3) |
| History of hypertension | 48.7 | 50.7 | 48.1 | 53.9 | 51.1 | 56.7 | 58.7 | 53.4 | 59.0 | 54.2 | 62.3 | 1.1 (0.4 to 1.7) |
| Diabetes Mellitus † | NA | NA | NA | 21.9 | 25.8 | 26.8 | 23.7 | 24.0 | 25.5 | 26.6 | 26.3 | 0.8 (−1.1 to 2.6) |
| PCI within 24 h † | NA | NA | NA | 15.6 | 20.8 | 23.3 | 31.3 | 52.7 | 63.2 | 59.8 | 53.9 | 9.9 (7.7 to 12.1) |
| CABG within 24 h † | NA | NA | NA | 2.3 | 4.1 | 2.0 | 2.0 | 0.8 | 0.9 | 0 | 0.7 | −14.0 (−20.6 to −7.3) |
| Thrombolytic therapy | 39.2 | 52.7 | 60.0 | 54.0 | 41.4 | 39.0 | 32.6 | 29.4 | 8.5 | 1.7 | 2.4 | −8.7 (−9.4 to −8.0) |
∗ Weighted number of incident, unadjusted hospitalized STEMI per year group.
† Data on diabetes, PCI, or CABG were unavailable before 1993.
Overall, for all years combined, 37.2% of STEMIs were inferior, 32.8% anterior, 16.8% occurred in multiple infarct locations, and 13.2% were lateral. There were differences in age and race by STEMI infarct location ( Table 2 ).
| Variable | Inferior, % (n = 1,804) ∗ | Anterior, % (n = 1,590) ∗ | Lateral, % (n = 640) ∗ | Multiple, % (n = 813) ∗ | p † |
|---|---|---|---|---|---|
| Age (yrs) | 58.6 (0.3) | 58.3 (0.4) | 57.9 (0.5) | 56.9 (0.5) | 0.03 |
| Women | 34.0 (1.3) | 29.8 (1.6) | 28.3 (1.9) | 31.5 (2.3) | 0.06 |
| Black | 12.4 (0.9) | 31.3 (1.8) | 23.7 (2.1) | 17.5 (2.0) | <0.01 |
| Center | |||||
| Jackson, Mississippi | 17.0 (1.1) | 25.5 (1.5) | 21.4 (1.8) | 23.7 (2.3) | <0.01 |
| Forsyth co., North Carolina | 41.4 (1.4) | 43.3 (1.8) | 40.5 (2.3) | 36.6 (2.4) | |
| Minneapolis, Minnesota | 24.2 (1.5) | 17.4 (1.2) | 21.8 (1.8) | 24.8 (2.0) | |
| Washington co., Maryland | 17.5 (1.0) | 13.8 (1.0) | 16.3 (1.5) | 14.9 (1.6) |
∗ Weighted number of incident, unadjusted hospitalized STEMI by infarct location.
† p Value for differences in characteristics across STEMI locations using Wald test.
For all STEMI infarct locations combined, from 1987 to 2008 there was an age- and race-adjusted average annual decrease in STEMI incidences in both men and women for inferior, anterior, and lateral STEMIs ( Table 3 and Figure 1 ). The decrease was most notable for inferior STEMI in men ( Table 3 and Figure 2 ). In contrast, there was no substantial change in the rates of STEMI in multiple infarct locations for either men or women. A quadratic trend was observed in anterior STEMIs for both genders; trends in the remaining locations and genders were linear with a statistically significant difference between the inferior and multiple location trends in both genders.
| STEMI Location | Women | Men | ||
|---|---|---|---|---|
| Average Annual Percent Change (95% CI) | p ∗ | Average Annual Percent Change (95% CI) | p ∗ | |
| Anterior | −3.2 (−5.9 to −0.5) † | 0.10 ‡ | −4.3 (−5.8 to −2.8) † | <0.001 ‡ |
| Inferior | −4.2 (−5.6 to −2.7) | <0.001 | −5.4 (−6.8 to −4.0) | <0.001 |
| Lateral | −3.1 (−5.8 to −0.4) | 0.03 | −4.5 (−6.4 to −2.5) | <0.001 |
| Multiple | −0.7 (−3.1 to 1.7) | 0.55 | −1.5 (−3.2 to 0.4) | 0.13 |
| Total | −3.1 (−4.1 to −2.1) | <0.01 | −4.0 (−4.7 to −3.3) | <0.01 |
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