Abstract
Objectives
To study the inter-physician reliability using the universal classification (UC) of acute myocardial infarction (AMI) compared to the ST-segment classification (STC). The UC is based on clinical, electrocardiographic (ECG), and pathophysiologic characteristics compared to the STC, which is mainly ECG based.
Methods
In this registry of consecutive patients with AMI presenting to a tertiary hospital, we studied the inter-physician reliability [weighted kappa (wK)] using the UC and the STC. Two physician investigators independently classified each patient with AMI according to the UC and STC, and a third senior physician investigator resolved any disagreement.
Results
The study included Type 1=226 (89.7%), Type 2=16 (6.3%), Type 3=3 (1.2%), Type 4a=1 (0.4%), Type 4b=4 (1.6%), Type 5=2 (0.8%), ST-segment-elevation AMI (STEMI)=140 (55.6%), and non-ST-segment-elevation AMI (NSTEMI)=112 (44.4%). Inter-physician reliability using the UC was very good (wK=0.84, 95% CI 0.68–0.99) and using the STC was good (wK=0.78, 95% CI 0.70–0.86). Of patients with Type 1 AMI, 57.1% were STEMI and 42.9% were NSTEMI. In contrast, of patients with Type 2 AMI, 18.8% were STEMI and 81.2% were NSTEMI.
Conclusion
The UC is a reliable method to classify patients with AMI and performs better than the STC in this study. Validation of the two classifications should be performed in large prospective studies.
1
Introduction
The 2007 universal classification (UC) of acute myocardial infarction (AMI) is based on clinical, electrocardiographic (ECG), and pathophysiologic characteristics and classifies AMI into Types 1, 2, 3, 4a, 4b, and 5 (see Methods section for details) . In contrast, the ST-segment classification (STC) is based on whether the patient has evidence of ST-segment elevation of 1.5 mm or more in two consecutive leads or new left bundle-branch block (LBBB) in the ECG and classifies the patient into ST-segment elevation AMI (STEMI) or non-ST-segment-elevation AMI (NSTEMI) . Both the UC and STC require elevation of cardiac biomarkers of myocardial necrosis, where cardiac troponin (cTn) is the preferred biomarker in the clinical setting consistent with acute myocardial ischemia .
It is recommended that research reporting outcomes of patients with AMI present the results according to different groups of UC and STC . However, the agreement between physicians using these classifications is unknown. We sought to study the inter-physician reliability using the UC and STC in consecutive patients with AMI. We also examined the proportion of patients with a particular type of AMI under both the UC and the STC.
2
Methods and materials
This is a registry study including 252 consecutive patients with AMI admitted to a single tertiary hospital. We performed a retrospective classification of AMI based on the 2007 universal definition consensus document . The methodology of data abstraction, inclusion and exclusion criteria, outcome adjudication, and statistical analysis have been published elsewhere and are briefly reviewed below .
2.1
Inclusion and exclusion criteria
We included male and female patients, age >30 years, who met the UC criteria for AMI and had angiographic documentation of ≥50% obstructive coronary artery disease (CAD). We excluded patients with elevations of cTn in the absence of overt ischemic heart disease , with metastatic cancer, on comfort care only, or refusing standard care for AMI.
Trained hospital personnel used the American College of Cardiology National Cardiovascular Data Registry’s (NCDR) instrument for data abstraction in patients with AMI ( http://www.accncdr.com/WebNCDR/Common ). The date of the AMI was confirmed by cross-checking the institutional roster list of patients admitted with AMI and the billing records. Two physician investigators (A and B) independently reviewed the medical records and classified the type of AMI. When disagreement existed, a third senior physician investigator (C) resolved the conflict.
2.2
Universal definition of AMI
The 2007 consensus document defines AMI when there is evidence of myocardial necrosis (rise and/or fall of troponin with at least one value above the 99th percentile of the upper reference limit, >0.001 μg/L) in the clinical setting consistent with myocardial ischemia, and where any of the following apply: symptoms of ischemia, ECG changes indicative of ischemia, development of pathologic Q waves on the ECG, or image with evidence of new loss of viable myocardium or new regional wall motion abnormality .
2.3
Acute myocardial infarction types
The UC defines several types of AMI as follows: Type 1 , as “spontaneous myocardial infarction related to ischemia due to a primary coronary event such as plaque erosion and/or rupture, fissuring, or dissection”; Type 2 , as “myocardial infarction secondary to ischemia due to either increased oxygen demand or decreased supply, e.g., coronary artery spasm, coronary embolism, anemia, arrhythmias, hypertension, or hypotension”; Type 3 , as “sudden unexpected cardiac death, including cardiac arrest, often with symptoms suggestive of myocardial ischemia, accompanied by presumably new ST elevation, new LBBB, or evidence of fresh thrombus in a coronary artery by angiography and/or at autopsy, but death occurring before blood samples could be obtained, or at a time before the appearance of cardiac biomarkers in the blood”; Type 4a as “myocardial infarction associated with percutaneous coronary intervention (PCI) with increase in cTn greater than 3×99th percentile of the upper reference limit (URL)”; Type 4b as “myocardial infarction associated with stent thrombosis as documented by angiography or at autopsy”; and Type 5 as “myocardial infarction associated with coronary artery bypass graft with increase in cTn greater than 5×99th percentile of the URL” .
Standard definitions were used for STEMI and NSTEMI according to currently published guidelines . STEMI was defined as presence of new ST-segment elevation at the J-point in two consecutive leads of ≥0.2 mV in men or ≥0.15 mV in women in leads V 2 –V 3 and/or ≥0.1 mV in other two consecutive leads, or evidence of new or presumed new left bundle branch block in the initial electrocardiogram, and meeting the universal definition of AMI . NSTEMI was defined as the absence of ST-segment elevation criteria on the electrocardiogram and meeting the universal definition of AMI .
2.4
Statistical analysis
Continuous variables were summarized as mean±S.D. and compared using the t test, while categorical variables were summarized as frequencies and compared using the χ 2 test. The inter-physician reliability using each classification of AMI was measured with weighted kappa (wK) analysis. All tests were two sided, with P <.05 considered significant. Statistical analyses were performed using MedCalc for Windows, version 9.5.0 (MedCalc Software, Mariakerke, Belgium). The study was carried out according to the principles of the Declaration of Helsinki and was approved by the institutional review board. Informed consent was not necessary due to the observational nature of the study. The authors had full access to the data and take full responsibility for its integrity. All authors have read and agree with the manuscript as written .
2
Methods and materials
This is a registry study including 252 consecutive patients with AMI admitted to a single tertiary hospital. We performed a retrospective classification of AMI based on the 2007 universal definition consensus document . The methodology of data abstraction, inclusion and exclusion criteria, outcome adjudication, and statistical analysis have been published elsewhere and are briefly reviewed below .
2.1
Inclusion and exclusion criteria
We included male and female patients, age >30 years, who met the UC criteria for AMI and had angiographic documentation of ≥50% obstructive coronary artery disease (CAD). We excluded patients with elevations of cTn in the absence of overt ischemic heart disease , with metastatic cancer, on comfort care only, or refusing standard care for AMI.
Trained hospital personnel used the American College of Cardiology National Cardiovascular Data Registry’s (NCDR) instrument for data abstraction in patients with AMI ( http://www.accncdr.com/WebNCDR/Common ). The date of the AMI was confirmed by cross-checking the institutional roster list of patients admitted with AMI and the billing records. Two physician investigators (A and B) independently reviewed the medical records and classified the type of AMI. When disagreement existed, a third senior physician investigator (C) resolved the conflict.
2.2
Universal definition of AMI
The 2007 consensus document defines AMI when there is evidence of myocardial necrosis (rise and/or fall of troponin with at least one value above the 99th percentile of the upper reference limit, >0.001 μg/L) in the clinical setting consistent with myocardial ischemia, and where any of the following apply: symptoms of ischemia, ECG changes indicative of ischemia, development of pathologic Q waves on the ECG, or image with evidence of new loss of viable myocardium or new regional wall motion abnormality .
2.3
Acute myocardial infarction types
The UC defines several types of AMI as follows: Type 1 , as “spontaneous myocardial infarction related to ischemia due to a primary coronary event such as plaque erosion and/or rupture, fissuring, or dissection”; Type 2 , as “myocardial infarction secondary to ischemia due to either increased oxygen demand or decreased supply, e.g., coronary artery spasm, coronary embolism, anemia, arrhythmias, hypertension, or hypotension”; Type 3 , as “sudden unexpected cardiac death, including cardiac arrest, often with symptoms suggestive of myocardial ischemia, accompanied by presumably new ST elevation, new LBBB, or evidence of fresh thrombus in a coronary artery by angiography and/or at autopsy, but death occurring before blood samples could be obtained, or at a time before the appearance of cardiac biomarkers in the blood”; Type 4a as “myocardial infarction associated with percutaneous coronary intervention (PCI) with increase in cTn greater than 3×99th percentile of the upper reference limit (URL)”; Type 4b as “myocardial infarction associated with stent thrombosis as documented by angiography or at autopsy”; and Type 5 as “myocardial infarction associated with coronary artery bypass graft with increase in cTn greater than 5×99th percentile of the URL” .
Standard definitions were used for STEMI and NSTEMI according to currently published guidelines . STEMI was defined as presence of new ST-segment elevation at the J-point in two consecutive leads of ≥0.2 mV in men or ≥0.15 mV in women in leads V 2 –V 3 and/or ≥0.1 mV in other two consecutive leads, or evidence of new or presumed new left bundle branch block in the initial electrocardiogram, and meeting the universal definition of AMI . NSTEMI was defined as the absence of ST-segment elevation criteria on the electrocardiogram and meeting the universal definition of AMI .
2.4
Statistical analysis
Continuous variables were summarized as mean±S.D. and compared using the t test, while categorical variables were summarized as frequencies and compared using the χ 2 test. The inter-physician reliability using each classification of AMI was measured with weighted kappa (wK) analysis. All tests were two sided, with P <.05 considered significant. Statistical analyses were performed using MedCalc for Windows, version 9.5.0 (MedCalc Software, Mariakerke, Belgium). The study was carried out according to the principles of the Declaration of Helsinki and was approved by the institutional review board. Informed consent was not necessary due to the observational nature of the study. The authors had full access to the data and take full responsibility for its integrity. All authors have read and agree with the manuscript as written .
3
Results
The demographic, clinical, and laboratory characteristics of these patients are summarized in Table 1 under the UC and in Table 2 under the STC. Type 1 AMI constituted the majority of the patients (89.7%) and only one patient with Type 4a AMI (0.4%) was observed. There were no differences in the mean cardiac enzymes, lipid value, or ejection fraction between the UC groups. Patients with STEMI were younger with higher proportion of smokers, higher peak cardiac enzymes, and higher low-density lipoprotein (LDL) cholesterol levels compared to NSTEMI patients. There were no differences in the prescription of discharge cardiovascular protective medications between the groups.
| Characteristics | Type 1 n =226 (89.7%) | Type 2 n =16 (6.3%) | Type 3 n =3 (1.2%) | Type 4a n =1 (0.4%) | Type 4b n =4 (1.6%) | Type 5 n =2 (0.8%) | P |
|---|---|---|---|---|---|---|---|
| Age (mean±S.D.) | 62.2±14 | 69.5±13 | 49±16 | 70±0 | 61.7± | 74.5±0.7 | .12 |
| Male (%) | 157 (62.3) | 8 (3.2) | 3 (1.2) | 0 (0) | 2 (0.8) | 0 (0) | .05 |
| Caucasian (%) | 149 (88.7) | 11 (6.5) | 2 (1.2) | 1 (0.6) | 4 (2.4) | 1 (0.6) | <.01 |
| Black (%) | 72 (91.1) | 5 (6.3) | 1 (1.3) | 0 (0) | 0 (0) | 1 (1.3) | <.01 |
| Obesity (%) | 90 (87.4) | 6 (5.8) | 2 (1.9) | 1 (1) | 2 (1.9) | 2 (1.9) | <.01 |
| Smokers (%) | 68 (95.8) | 1 (1.4) | 1 (1.4) | 0 (0) | 1 (1.4) | 0 (0) | <.01 |
| Diabetes mellitus (%) | 53 (88.3) | 5 (8.3) | 1 (1.7) | 0 (0) | 1 (1.7) | 0 (0) | <.01 |
| Systemic hypertension (%) | 125 (88.7) | 8 (5.7) | 2 (1.4) | 1 (0.7) | 3 (2.1) | 2 (1.4) | <.01 |
| Hypercholesterolemia (%) | 63 (84) | 6 (8) | 1 (1.3) | 1 (1.3) | 2 (2.7) | 2 (2.7) | <.01 |
| History of CAD (%) | 54 (87.1) | 5 (8.1) | 0 (0) | 0 (0) | 3 (4.8) | 0 (0) | <.10 |
| History of PVD (%) | 7 (77.8) | 2 (22.2) | 0 (0) | 0 (0) | 0 (0) | 0 (0) | .18 |
| Laboratory | |||||||
| Peak CK-MB (mean±S.D.) | 69±105 | 31±50 | 46.3±77 | 19.4±0 | 47.1±68.8 | 163±27 | .52 |
| Peak troponin (mean±S.D.) | 87.5±139 | 18.9±26 | 58.6±72 | 6.3±0 | 51.5±74 | 53.6±35 | .46 |
| LDL cholesterol (mean±S.D.) | 81.2±58 | 54.4±49 | 45.3±48 | 190±0 | 56.8±45 | 59.5±84 | .13 |
| HDL cholesterol (mean±S.D.) | 29.3±19 | 22.5±18 | 14.7±13 | 58±0 | 29.5±20 | 23±33 | .29 |
| Triglyceride (mean±S.D.) | 122.7±120 | 82.3±82 | 74±67 | 466±0 | 84.5±67 | 48±68 | .04 |
| Ejection fraction (mean±S.D.) | 44.5±13 | 41±12 | 26±26 | 57±0 | 38.8±8 | 30±42 | .08 |
| Discharge medication | |||||||
| Aspirin (%) | 160 (90.9) | 10 (5.7) | 2 (1.1) | 1 (0.6) | 2 (1.1) | 1 (0.6) | <.01 |
| Clopidogrel (%) | 143 (90.5) | 9 (5.7) | 2 (1.3) | 1 (0.6) | 3 (1.9) | 0 (0) | <.01 |
| β-Blocker (%) | 154 (91.7) | 9 (5.4) | 1 (0.6) | 0 (0) | 3 (1.8) | 1 (0.6) | <.01 |
| ACEI/ARB (%) | 108 (94.7) | 2 (1.8) | 1 (0.9) | 0 (0) | 2 (1.8) | 1 (0.9) | <.01 |
| Statin (%) | 174 (91.1) | 11 (5.8) | 2 (1) | 1 (0.5) | 3 (1.6) | 0 (0) | <.01 |
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