Summary statistics for acute cardiac ischemia and chest pain visits to United States EDs, 1995–1996

Summary Statistics for Acute Cardiac Ischemia and Chest Pain Visits to United States EDs, 1995-1996 CATHARINE W. BURT, EdD In this article we describe characteristics of emergency encounters for patients with a diagnosis of acute cardiac ischemia (ACI) and for patients with chest pain complaints. Data are from the National Hospital Ambulatory Medical Care Survey, which includes abstracts from the medical records of a national probability sample of visits to emergency departments (ED). Analysis was limited to records of patients 25 years of age and older with a diagnosis of either confirmed or suspected acute myocardial infarction (AMI) or unstable angina pectoris and records with a nontraumatic chest pain complaint. There was an estimated annual average of 1.2 million visits to EDs by patients 25 years and over with a diagnosis of ACI in 1995-1996, an average annual rate of 7.2 visits per 1,000 persons. Visit rates varied by patient's age, race, and gender. Chest pain was a complaint in three-fourths of all ACl visits. There were an estimated 4.6 million annual ED visits where in patients aged 25 years and older had complaints of nontraumatic chest pain, an average annual rate of 27.7 visits per 1,000 persons. ACI accounted for 11% of all chest pain visits, but the probability of the chest pain visit having an ACl diagnosis varied by patient's age and race. There remains a large amount of variation in treatment for suspected and confirmed Aal, and for patients presenting with chest pain to EDs. (Am J Emerg ied 1999;17:552-559. Copyright © 1999 by W.B. Saunders Company) Early medical intervention is critical for prevention and recovery in acute cardiac ischemic (ACI) cases. Diagnostic procedures such as electrocardiograms have been a standard of care for suspected acute myocardial infarction (AMI). Therapeutic procedures such as thrombolytic therapy are important for reducing mortality from the condition. 1 Education efforts over the last few years have targeted emergency medical personnel on the advantageous use of various tests and technologies. 2 A general purpose medical survey such as the National Hospital Ambulatory Medical Care Survey (NHAMCS) can be used to describe the extent and characteristics of emergency medical utilization for acute cardiac ischemia and its leading symptom, chest pain. Chest pain complaints represent the second leading reason given by patients seeking care in the emergency department, exceeded only by abdominal pain. 3,4 In 1992, chest pain was the leading complaint given by patients 45 years and over. 5 The purpose of this report is to describe the frequency of emergency medical utilization and the patient, drug, and visit characteristics for ACI and chest pain visits in the From the National Center for Health Statistics, Centers for Disease Control and Prevention, Hyattsville, MD. Manuscript received July 23, 1998, returned August 17, 1998; revision received September 8, 1998, accepted September 20, 1998. Address reprint requests to Dr Burt, NCHS Room 952, 6525 Belcrest Rd, Hyattsville, MD 20782. Key Words: Chest pain, thrombolysis, acute cardiac ischemia, emergency department, NHAMCS, AMI. Copyright © 1999 by W.B. Saunders Company 0735-6757/99/1706-0012510.00/0 552

United States. This study also examines differences in utilization and treatment patterns over the last few years. The data presented here are important for public health, clinical, and academic purposes related to disease prevalence, emergency medicine research, and therapy guidelines and projections.

METHODS Data from the 1995 and 1996 NHAMCS were combined to generate national estimates of emergency department visits for acute cardiac ischemias and chest pain. The NHAMCS is a multistage probability sample of visits to hospital emergency and outpatient departments conducted annually by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention. 6 Only the emergency department data were used for this study. The survey period was from December 25, 1994 through December 22, 1996. The NHAMCS uses a 4-stage survey design that involves probability samples of primary sampling units (PSUs), short-stay or general hospitals within PSUs, emergency service areas (ESA) within hospital EDs, and a systematic sample of approximately 50 visits from each emergency department within the ESAs. The first-stage sample consisted of 112 out of 1,900 geographically defined PSUs that covered the 50 states and the District of Columbia. The second-stage sample of hospitals was from the 1991 SMG Hospital Market Database. A sample of 600 hospitals was randomly divided among 16 subsets, 13 of which were used in any survey year. Each sampled hospital was inducted once every 15 months. Census Bureau Field Representatives inducted the hospitals and formed a list of the emergency ESAs under the direction of the hospital's emergency department. Up to five ESAs from each sampled hospital were included. There were only 2 hospitals that had more than 5 ESAs; in those cases a sample of 5 was selected. Only those hospitals with an emergency department were eligible to participate in the ED component. In the final stage of sampling, hospital personnel used the daily patient logs during the randomly assigned 4-week reporting period to identify the sampled cases and pull the appropriate medical records. Hospital staff abstracted the patient, drug, and visit data from emergency medical records onto the data collection instrument usually within 1 day of the visit. Because no patients were directly contacted and confidential identifying information was not collected, the NHAMCS is exempt from Institutional Review Board approval. Emergency department data were available from 494 hospitals over the 2 years which represented an overall response rate of 94%. Abstracted data included up to 3 physician diagnoses, up to 3 reasons for visit or complaints as stated in the patient's (or patient surrogate's) own words, up to 6 medications prescribed or provided, and various patient and visit characteristics, such as age, race, gender, diagnostic and therapeutic services, and visit disposition. Medications included all new or continued drugs ordered, supplied, or administered at the visit, immunization and desensitizing agents, and anesthetics. Diagnoses were classified and coded according to the International Classification of Diseases, 9th

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revision, Clinical Modification (ICD-9-CM). 7 Patient's complaints were coded to the Reason for Visit Classification (RVC) 8 and medications were assigned a therapeutic class from the National Drug Code Directory, 1995 Edition (NDC). 9 Because the NDC does not differentiate the drug class for anticoagulants and thrombolytics, drugs falling into that class were manually coded to either thrombolytic or anticoagulant agents for analysis. All classification and coding was performed centrally by NCHS. Missing data for patient's age, race, and gender were imputed using a hot-deck approach controlled by first-listed diagnosis, geographic region~ and urgency level. I° Quality control analysis was performed only on data classification and coding, not on the sampling or abstraction process. Medical classification error rates were less than 2% and data entry error rates for checkbox items were less than l%. Acute cardiac ischemia visits are based on records where any of the 3 physician diagnoses were coded 410 or 411, AMI, or other acute and subacute ischemic heart disease. This broad category of acute cardiac ischemia included both questionable and confirmed cases of AMI and unstable angina pectoris. Chest pain visits were based on records with any complaint of "chest pain" (code S050 in the RVC) and no indication of the visit being injury;related. This definition excludes about 8% of chest pain visits that were for traumatic reasons. For purposes of this study, visits by patients under the age of 25 were excluded. The sample records included 542 records considered ACI visits and 2,053 records considered nontraumatic chest pain visits. About two-thirds of the ACI records had a diagnosis of AMI (code 410). For comparative purposes, data from the 1992 and 1993 NHAMCS were combined to provide national annual averages of chest pain and ACI visits. The sampling and data collection methodology was similar to 1995-1996 NHAMCS, except that only 5 medication mentions were allowed as opposed to 6. The 1992-1993 data were based on 3,171 chest pain records and 914 ACI records. Sample weights were applied to yield national annual estimates of ACI visits and chest pain visits. National estimates of visits presented here are rounded to the nearest thousands. A large proportion of the ACI records are also included in the set of chest pain visits. Techniques for evaluating the precision of the estimates were based on approximations of the standard error using SUDAAN software and are published elsewhere. 11Population rates are based on the average of US Bureau of Census estimates of the civilian, noninstitutionalized population of the United States as of July 1, 1995 and 1996 and have been adjusted for net underenumeration.I° Age-adjustment of visit rates used the 1995-1996 white male population as the standard. Variations in frequency distributions within and across survey years for patient or visit characteristics were evaluated by Chi square analysis and logistic regression using S U D A A N software. 11 For within years, a model containing gender, age (25-54 years and 55 years and older), and race (white, black) was used. Analysis for trends compared the 1995-1996 NHAMCS data with the 1992-1993 data. The model contained gender, age, race, and year (1992-1993 and 1995-1996). The outcome variable was the presence or absence of the Variables of interest (chest pain, acute cardiac ischemia). For models involving trends in medication use, the independent variable was year and the outcome variable was medication use (eg, thrombolytics). To assess the significance of the variables in the models, the Likelihood Ratio Test (×2 statistic) was used.

1,328,000) and an annual average rate of 7.2 visits per 1,000 persons (95% CI = 6.3, 7.9). These visits represented 2.1 percent of all ED visits by people 25 and over. ACI visits accounted for 10% of all El) visits ending with admission to inpatient status for this age group. Approximately 30% of the admissions to the critical care units of the hospital from the ED were from patients with a diagnosis of ACI. The chief complaint of patients in 7 out of 10 ACI visits was "chest pain." While "chest pain" was the predominant chief complaint, "breathing difficulty" and "abdominal pain" accounted for another 10% of visits. Secondary complaints of "breathing difficulty, . . . . pain in arm, neck or shoulder," and "nausea or vomiting" were also common. A complaint of "pain in arm, neck or shoulder" was more common in ACI visits by patients under 55 years compared with ACI visits by older patients (11.0% and 5.1% respectively). The percent distribution of A C I visits by patient characteristics is shown in Table 1 along with population rates. The mean ages for patients in acute cardiac ischemia visits were 67.1 for women and 62.4 for men. While the population rate was less for persons aged 25-55 years compared to older persons, there were no significant differences in ageadjusted population rates by race and gender except that white men (8.9 visits per 1,000 persons, 95% CI = 7.4, 10.3) were more likely to have emergency ACI visits compared to white women (5.6 visits per 1,000 white women, 95% CI = 4.6, 6.7). The percent of all ED visits with a diagnosis of ACI was less for patients 25-55 years compared to older patients (X2 = 141.76, df = 1, P < .01) (.8% v 4.5% respectively). ED arrival time showed that the percent of ACI visits by men was highest between noon and 6 pm (38 percent), whereas women had fairly equivalent percentages of ACI visits between 6 am and noon, noon and 6pro, and 6pm and midnight (between 27% and 30%). Medication therapy was the predominant form of treatment for acute cardiac ischemia visits with 86.8% of visits receiving at least 1 medication. Thirteen percent of the visits had at least 6 medications mentioned. Patients in 1 out of 4 ACI visits received an anticoagulant such as heparin (Table 2). Patients in 63.1% of ACI visits were given antianginal agents such as nitroglycerin. Patients in one-third of ACI visits were given aspirin, and 12.1% were given oxygen, Patients in 8% of suspected or confirmed AMI visits received a thrombolytic such as alteplase (t-PA). Alteplase is a second-generation thrombolytic recombinant tissue plasminogen that targets coronary thrombi.a2 Data on selected therapeutic procedures and diagnostic services recorded in ACI visits show that 91.8% of visits had an electrocardiogram (ECG) recorded, 80.5% had intravenous fluids, and three-fourths had a cardiac monitor recorded (Table 3). Seventeen percent had no therapeutic services recorded. Very few patients in AMI visits were given cardiopulmonary resuscitation (CPR). Acute myocardial infarction was the principal diagnosis for only 6% of the ED patients who received CPR (N = 16,000). Most of the ED visits that had CPR (62 percent) were visits with a principal diagnosis of cardiac arrhythmia (ICD-9-CM code #427). The disposition data show that 86.4% of ACI visits ended with admission for inpatient care, 42% of which were admitted directly to the critical care units of the hospital from the ED. Six percent were transferred to other facilities.

RESULTS Acute Cardiac Ischemic Visits There were an estimated 2,378,000 visits for acute cardiac ischemia to hospital emergency departments in 1995 and 1996 made by persons 25 years and older, an annual average of 1,189,000 visits (95% confidence interval [CI] = 1,050,000,

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TABLE 1. Number, Percent Distribution and Annual Rate of ED Visits With a Diagnosis of Acute Cardiac Ischemia, Averaged Over a 2-year Period: United States, 1995-1996

Patient Characteristic All acute cardiac ischemia visits Age 25-54 years 55 years & over Gender and age Female 25-54 years 55 years & over Male 25-54 years 55 years & over Race and age White 25-54 years 55 years & over Black 25-54 years 55 years & over Race and gender White female White male Black female Black male

Number of Visits in Thousands*

Percent Distribution

Rate per 1,000 Pop

SE for Rate

Percent of ED Visitst

Percent of Visits With Complaint of Chest Pain

1,189

100.0

7.1

0.42

2.1

76.4

318 870

26.8 73.2

2.8 16.5

0.31 1.12

0.8 4.5

84.6 73.3

530 123 407 658 195 463

44.6 10.4 34.2 55.4 16.4 39.0

6.0 2.1 13.8 8.3 3.5 20.0

0.49 0.38 1.13 0.64 0.49 1.92

1.7 0.6 3.7 2.5 1.1 5.7

78.0 85.7 75.7 75.0 84.0 71.3

1,063 259 804 112 55 57

89.5 21.8 67.6 9.4 4.6 4.8

7.5 2.7 17.3 3.0 4.0 12.0

0.49 0.34 1.23 0.98 0.86 2.50

2,4 0.9 5,0 1.0 0.7 2.2

76.8 89.1 72.8 72.0 67.6 76.3

459 605 64 48

38.6 50.9 5,3 4,1

6.2 8.9 6.1 5.9

0.54 0.75 1.31 1.12

1.9 3.0 1.0 1.0

77.5 76.2 82.9 57.7

NOTE:*Includes any visits with any diagnosis = 410 or 411, based on the ICD-9-CM; -j-based on the total number of ED visits for each demographic category.

There were no age, race, or gender differences related to likelihood of hospital admission. Approximately 2% of the ACI visits ended with the patient's death or death on arrival to the emergency department. It is possible that some of those patients admitted to inpatient status may have subsequently died. While the NHAMCS data do not measure inpatient status, unpublished data from the 1995 National

Hospital Discharge Survey show that 10% of discharges for AMI had a disposition of patient's death. Chest Pain Visits

There were almost 10 million nontraumatic chest pain visits to hospital emergency departments made by persons

TABLE 2. Number and Percent of Visits With the Leading Therapeutic Classes for Drugs Mentioned in ACI and Chest Pain Visits, Averaged Over a 2-year Period: United States, 1995-1996

Therapeutic Class* All visits Antianginal agents Analgesics, nonnarcotic Anticoagulants/thrombolytics Anticoagulants ThrombolyticslAnalgesics, narcotic Diuretics Adjuncts to anesthesia/analeptics Calcium channel blockers Disorders, acid/peptic NSAID:~

NDC Code 0503 1722 0409

1721 0507 0119 0510 0874 1727

Number of ACI Visits in Thousands

Percent of Visits

Number of Chest Pain Visits in Thousands

Percent of Visits

1,189 749 408 340 304 64 189 150 158 119 67 24

... 63,1 34.3 28,6 25.6 5.4 15.9 12.6 13.3 10.0 5.6 2.0

4,639 1,298 1,158 467 437 50 411 388 372 416 395 562

... 28,0 25.0 10.1 9.4 1.1 8.9 8.4 8.0 9.0 8.5 12.1

NOTE: . .. Category not applicable; *Based on the standard drug classification used in the National Drug Code Directory, 1995 Edition (NDC); tNDC code does not separate a drug class for thrombolytics and anticoagulants. Visits with thrombolytic drugs were classified separately. Approximately 8% of visits with a diagnosis of suspected or confirmed AMI (iCD-9-CM code 410) received a thrombolytic agent; :~NSAID is nonsteroidal antiinflammatory drug. Total exceeds total number of visits because more than one drug class can be reported per visit.

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TABLE 3. Percent of ED Visits by Selected Diagnostic Services, Therapeutic Procedures, and Visit Disposition, Averaged Over a 2-year Period: United States, 1995-1996

Procedure or Disposition

Percent of Acute Cardiac Ischemia Visits

Percent of Chest Pain Visits

Blood pressure Electrocardiogram Intravenous fluids Chest x ray Other blood test Cardiac monitor Pulse oximeter No therapeutic procedures Admit to hospital* Admit to ICU/CCU Other admit1 Transfer to other facility Return to ED, PRN Died, DOA

92.5 91.8 80.5 76.2 76.2 74.9 62.9 17.4 86.4 36.5 52.4 6.4 1.6 1.9

89.3 77.9 45.4 67.7 63.4 50.6 48.7 52.4 39.6 12.4 28.0 2.6 22.3 0.1

which were suspected or confirmed AMI. Chest pain visits with a principal diagnosis of acute cardiac ischemia (ICD-9-CM codes #410 or 411) were more likely to result in hospitalization than were visits with other principal diagnoses. The percent distribution of chest pain visits is shown in Table 5 along with population rates. The mean ages for patients with chest pain visits were 54.7 for women and 53.7 for men. Population rates reveal that persons 25-55 years were less likely to have ED visits with a chest pain complaints compared to older persons. After adjusting for age distribution differences, black persons were more likely to present with chest pain compared with white persons, regardless of gender (56.1 visits per 1,000 black women, 95% CI = 47.4, 64.7; 41.7 visits per 1,000 black men, 95% CI = 32.8, 50.6; 24.1 visits per 1,000 white women, 95% CI = 21.2, 26.9; and 26.3 visits per 1,000 white men, 95% CI = 23.2, 29.4). The percent of ED visits that had a complaint of chest pain varied with patient's age (X2 = 90.57, df = 1, P < .0l), 11.3% for persons 55 years and over compared with 6.6% of persons 25-54 years. The percent of chest pain visits that had an ACI diagnosis varied by patient's age and race (X2 = 42.65, df = 1, P < .01). Chest pain visits by older persons were more likely to have an ACI diagnosis than younger persons, and within age, white patients had a higher probability than black patients that the visit resulted in an ACI diagnosis (Figure). For the figure, the NHAMCS data were combined over a 5-year period (19921996) to provide reliable estimates for chest pain visits by older black patients. The analysis of chest pain visits resulting in an ACI diagnosis was based on 1,253 records of black patients and 4,963 records of white patients contained in the 1992-1996 NHAMCS data sets. Medication therapy was the predominant form of treatment for chest pain visits with 81.1% of visits receiving at least 1 medication. Nine percent of the visits had at least 6 medications mentioned. Patients in 9.4% of chest pain visits received an anticoagulant such as heparin (Table 2). Twentyfive percent of the visits had a nonnarcotic analgesic such as aspirin mentioned. Patients in 28% of chest pain visits were

NOTE: *Admit to hospital if either admit to hospital or admit to ICU was marked; -j'other admit includes any records where admit to hospital was marked but admit to ICU was not marked.

aged 25 years and older in 1995 and 1996, an annual average of 4,639,000 ED visits (95% CI = 4,254,000; 5,024,000) with an annual average rate of 27.7 visits per 1,000 persons (95% CI = 25.4, 30.0). Chest pain visits represent 8.2% of all ED visits in this age group, of which one-fifth had a diagnosis of acute cardiac ischemia. About 18% of hospital admissions from the ED were for patients with "chest pain" complaints. Over one-third of the admissions to the critical care unit from the ED were from patients with visits for nontraumatic chest pain. While chest pain was the predominant chief complaint in AC1 visits, not all chest pain visits resulted in an ACI diagnosis (Table 4). Almost half of all chest pain visits had a principal diagnosis of symptoms involving the respiratory system and other chest symptoms (ICD-9-CM code # 786), implying that no definite diagnosis could be determined. ACI diagnoses represented the next most frequent diagnoses (11% of chest pain visits), half of

TABLE 4. Number and Percent Distribution of Visits With a Complaint of Chest Pain by Principal Diagnosis and Selected Visit Characteristics, Averaged Over a 2-year Period: United States, 1995-1996

Principal Diagnosis*

ICD-9-CM Code

All chest pain visits Symptoms involving the respiratory system and other chest symptoms

786

Other acute and subacute forms of ischemic heart disease

411 '

Acute myocardial infarction Congestive heart failure Bronchitis, not specified as acute or chronic Angina pectoris All other diagnoses NOTE: *Based on the ICD-9-CM.

410 428 490 413

Percent Distribution

Percent Distribution for Ages 25-54

Percent Distribution forAges 55 Years & Over

Percent Admitted to Hospital

4,639

100.0

100.0

100.0

39.6

1,888

45.3

43.1

38.0

40.1

324

5.8

3.1

11.4

85.3

223 154 146 145 1,903

5.2 2.5 2.4 2.0 41.0

2.5 0.9 4.3 1.7 46.1

7.4 6.1 1.8 4.8 35.2

88.4 75.2 5.6 56.1 21.2

Number of Visits in Thousands

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TABLE 5.

Number, Percent Distribution and Annual Rate of ED Visits With a Complaint of Chest Pain, Averaged Over a 2-year Period: United States, 1995-1996

Patient Characteristic All chest pain visits Age 25-54 years 55 years & over Gender and age Female 25-54 years 55 years & over Male 25-54 years 55 years & over Race and age White 25-54 years 55 years & over Black 25-54 years 55 years & over Race and gender White female White male Black female Black male

Number of Visits in Thousands

Percent Distribution

Rate per 1,000 Pop

SE for Rate

Percent of ED Visits*

Percent of Visits with Diagnosis of Acute Cardiac Ischemiat

4,639

100.0

27.7

1.17

8.2

19.6

2,471 2,168

53.3 46.7

21.5 41.2

1.07 2.13

6.6 11.3

10.9 29.4

2,474 1,295 1,178 2,165 1,176 989

53.3 27.9 25.4 46.7 25.3 21.3

28.2 22.2 40.1 27.2 20.9 42.6

1.32 1.25 2.43 1.38 1.32 2.85

8.1 6.6 10.7 8.4 6.6 12.1

16.7 8.2 26.1 22.8 13.9 33.4

3,638 1,759 1,879 916 660 257

78.4 37.9 40.5 19,8 14.2 5.5

25.6 16.4 40.5 49.3 47.5 54.7

1.33 1.16 2.35 3.46 3.95 6.12

8.2 6.2 11.6 8.4 7.9 10.0

22.5 13.2 31.2 8.8 5.7 16.8

1,848 1,790 580 336

39.8 38.6 12.5 7.2

25.1 26.3 55.9 41.0

1.46 1.58 4.41 4.53

7.7 8.7 9.4 7.0

19.2 25.8 9.1 8.3

NOTE: *Based on total number of ED visits for each demographic category; fincludes any visits with any diagnosis = 410 or 411, based on the ICD-9-CM.

given antianginal agents such as nitroglycerin. Seventyeight percent of visits had an ECG recorded, 45.4% had intravenous fluids, and half had a cardiac monitor recorded (Table 3). Over half the visits (52.4%) had no therapeutic services recorded. About 4 out of 10 visits ended with admission for inpatient care, the minority of which were admitted directly to the critical care units of the hospital from the ED (Table 3). Less than 3% were transferred to other facilities. Patients at 22.3% of the visits were discharged and told to return if necessary. Of the patients that were admitted to the hospital from the ED with chest pain, 46% had an ED diagnosis of respiratory or chest symptoms (ICD-9-CM code # 786), 0.4 White 0.3

0.2-

Black 0.1

25-44years Shownwith 95% confidenceintervals

45-64 years

65 years & over

Patient's age

FIGURE. Probability of a nontraumatic chest pain visit ending in an acute cardiac ischemia diagnosis by patient's age and race, 1992-1996.

45% had acute ischemic heart disease (half of which were suspected or confirmed AMI), 9% had stable angina pectoris, and another 9% had congestive heart failure. Patients 25-55 years with chest pain visits were less likely to be admitted to the hospital than were patients in the older age group (X2 = 108.64, df = 1, P < .01), 24.1% and 57.4% respectively. There were no significant differences in admission rates by patient's race or gender.

Trend Data There were no significant differences in age-specific population rates between 1992-1993 and 1995-1996 for either ACI visits or chest pain visits to hospital emergency departments. Use of medication therapy in general increased from 81% to 87% of ACI visits. While general thrombolytic use did not increase significantly, use of alteplase (t-PA) in suspected, and confirmed AMI visits increased 236% from 2% in 1992-1993 to 7% in 1995-1996 (Table 6). General thrombolytic use increased from 4.3% to 7.6% but not significantly (P > .05) (OR = 1.96, 95% CI = .96, 4.0). In addition to alteplase (t-PA), general thrombolytic use includes agents such as streptokinase and a nonspecific entry of "thrombolytic agent" used in several records in 1992. Because only the term "thrombolytic agent" was recorded on these records, it is impossible to know which agent was actually used. The use of aspirin in AMI visits also increased from 15.7% to 34.3%. Heparin and nitroglycerin had modest increases. The use of other leading medications for suspected or confirmed AMI patients did not change from

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TABLE6. Comparisons in Percent of Visits With Leading Medications for AMI Visits, 1992-1993 and 1995-1996

Medication

Nitroglycerin Aspirin Heparin Morphine Furosemide Oxygen Alteplase

Percent of Visits* 1992-1993

1995-1996

47,2 15.7 13.4 12.7 12.7 14.5 2.1

58.1 34.3 21.5 !1.9 10.5 11.1 7.1

Percent Increase

Odds Rat!ol-

95% CI for Odds Ratio

P-value

23.1 118.4 60.0 -6.3 - 17.3 -23.4 235.8

1.55 2.80 1.80 0.93 0.81 0.74 3.54

(1.01,2.37) (1.75, 4.49) (1.06, 3.06) (.41, 2.10) (.37, 1.74) (.36, 1.50) (1.24, 10.13)

.043 .000 .031 .856 .579 .388 .019

NOTE:*Visits with any diagnosis = 410 based on the ICD-9-CM; includes suspected and confirmed AMI cases; 1odds ratios and confidence limits were computed using Proc Logistic in SUDAAN which takes into account the complex nature of the NHAMCS sampling design. Bolded percentage increases are significant at .05 level.

1992-1993. It should be noted that the 1995-1996 NHAMCS allowed for up to 6 medication entries whereas the 19921993 NHAMCS allowed for up to 5 entries. Comparisons in Table 6 use only the first 5 medications listed for 1995 and 1996 to be more comparable to 1992-1993. There were no differences in the use of ECGs or blood tests between 1992-1993 and 1995-1996 for either acute cardiac ischemia or chest pain visits. The percent admitted for inpatient care also did not vary across the years.

DISCUSSION There has been little difference in the frequency or patient characteristics of people presenting to hospital emergency departments in the United States between 1992-1993 and 1995-1996 with a diagnosis of acute cardiac ischemia or a complaint of nontraumatic chest pain. However, medication practices within the emergency departments have altered with increased usage of the thrombolytic agent alteplase and nonnarcotic analgesic medications (aspirin). Use of heparin and nitroglycerin also increased. It was discouraging to find that an overall increase in the general class of thrombolytics was not observed over the last 5 years for AMI patients despite increased efforts to train emergency physicians about the advantages of timely therapeutic procedures. Not withstanding the small increase, data from the NHAMCS suggest that only 8% of AMI patients received a thrombolytic in the emergency department in 1995-1996. This figure is an underestimate of thrombolytic usage for patients with confirmed AMI in the ED because the denominator includes cases of both confirmed and suspected AMI. NHAMCS data prior to 1997 were unable to differentiate between the 2 types of cases. Preliminary data from the 1997 NHAMCS, which included a flag for suspected diagnoses, revealed that approximately half of visits with a diagnosis classified as 410 are suspected or "rule-out" AMI cases. 13 Further analysis revealed that as expected, suspected AMI cases were not treated with thrombolytics. When the 1997 data were analyzed for thrombolyfic therapy usage, the percentage increased from 9.5% to 20.9% when suspected AMI cases were first included, then excluded from the denominator. The percent of cases with heparin also increased from 17.8% to 44.3%. This would be expected because heparin is probably a beneficial cotreatment with alteplase, 14 the predominant thrombolyfic agent used in 1997. No increases in

aspinn or nitroglycerin were observed between suspected and confirmed cases of AMI. Early data from the National Registry of Myocardial Infarction (NRMI) (1990-1993) indicate that patients receiving thrombolytic therapy represent 35.1% of those enrolled, although one-quarter of these received treatment in the coronary care unit (CCU) rather than the ED. 15 Registry hospitals tend to be larger than national average and are more likely to have a CCU. The registry includes patients with confirmed AMI from over 1,000 hospitals spread throughout the US. The advantage of the registry is that the data collection form is designed specifically for AMI treatment, so checkboxes are included for medications such as aspirin and heparin. The NHAMCS form, which is a broad data collection tool, requires write-in mentions of up to 6 medications. There is probably underreporting for common medication usage such as aspirin in the NHAMCS. Protocol suggests that every MI or suspected MI patient should be given aspirin. 16 The NRMI data indicated that aspirin was administered to 84% of patients receiving thrombolytic therapy, whereas the NHAMCS data found only half the visits included mention of aspirin. Approximately 12% of AMI visits had as many as 6 medications listed on the form in 1995/1996. It is possible that aspirin may have been the seventh drug in the medical record which did not make it onto the data collection form. While aspirin was occasionally found as the sixth drug mention, thrombolytic agents were usually listed among the first 3 drug mentions. The NHAMCS data do not allow researchers to evaluate which patients are eligible to receive thrombolysis. A hospital inpatient study using the 1992-1993 Medicare records from Connecticut showed that of all patients 65 years and older with a discharge diagnosis of AMI, approximately 11% had received thrombolyfic therapy. Only onequarter of the AMI patients were eligible to receive the thrombolytic therapy. Most of the patients did not present to the emergency room within 6 hours of chest pain onset, had contraindications for thrombolytic therapy, or had bypass surgery. 17 It may be possible that a large percentage of patients presenting to the emergency department with AMI symptoms are still not arriving within 6 hours of the symptom onset. Public education materials are being developed to highlight the need for people with AMI symptoms to

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go immediately to hospital emergency facilities. Hopefully, such education campaigns will help reduce the interval between symptom onset and medical evaluation and treatment. Unpublished data from the National Hospital Discharge Survey (NHDS) show that the rate of hospital discharges with a first-listed diagnosis of acute cardiac ischemia (ICD-9 codes 410 and 411) has decreased from 57 to 41 discharges per 10,000 persons between 1992 and 1995. US Mortality data show that deaths from AMI and other acute ischemic heart disease have decreased from 9.1 deaths per 10,000 persons in 1992 is to 8.4 deaths per 10,000 persons in 199519 (the latest year for which data are available). The hospitalization and mortality rates for AMI have been declining since the 1980s. Unfortunately, the NHAMCS data do not go back further than 1992, so longer trends of thrombolytic therapy use in the ED can not be obtained from this survey. Increased use of timely thrombolytic therapy in emergency situations should result in reduced fatality from AMI. 1,2°-23 While US mortality rates in general are decreasing, the fatality rates in the inpatient setting have not changed significantly between 1992 and 1995 (10.8 and 9.9 fatalities per 100 discharges respectively from unpublished NHDS data). This lack of decrease in hospital fatality rates is consistent with the lack of increase in use of thrombolytic agents in the emergency department. The frequency distribution for chest pain visits was found to be positively skewed with the majority of chest pain visits made by patients 25-55 years of age. Yet these are the patients who are least likely to have a diagnosis of acute cardiac ischemia. The distribution of chest pain visits revealed that only those patients who are aged 55 and older have increased probabilities that their chest pain may be related to acute cardiac ischemia. Even though half of the chest pain visits were for patients who are under age 55, it is nonetheless important that all patients presenting in the ED with a chief complaint of chest pain receive a triage strategy that takes age into account along with comorbid conditions. 2° And patients who axe over age 40 should receive a diagnostic protocol to rule out AMI. The NHAMCS data showed that between 86% of nontraumatic chest pain visits by patients aged 55 and over had an ECG administered in the ED. About 70% of chest pain visits by patients 25-55 years also had an ECG recorded. In addition to the obvious medical benefits from using techniques to rule out AMIs, patient satisfaction with rapid diagnostic care received in a chest pain observation unit is higher than for patients who are admitted for acute chest pain, 24 and the cost is lowerY The NHAMCS data show that compared with other ACI symptoms, chest pain, either alone or in combination with other symptoms (eg, breathing difficulty, pain, nausea) 26 continues to be the leading symptom predictor for acute cardiac ischemia. Limitations of using NHAMCS data to describe acute cardiac ischemia visits and chest pain visits include that the NHAMCS does not permit evaluation of the need for medication based on clinical characteristics such as the results of the ECGs or blood tests, or the time between onset of pain and treatment sought or provided in the ED. In addition, there may be underreporting of medications or other tests performed in the ED that are so routine that they

are not recorded, such as blood pressure, electrocardiogram (ECG), or administration of aspirin. As stated above, inability to distinguish between suspected and confirmed AMI diagnoses limits the validity of AMI treatment estimates for survey years before 1997. The NHAMCS does not include federal hospitals within the scope of the survey, so the number of emergency visits in the United States for ACI and chest pains will be higher if visits to veteran administration and military hospitals are considered. The small sample of hospitals (494 nationally) precludes an equally small standard error for national estimates for black patients compared to white patients, and for older patients compared to younger patients. Combining data from multiple years helps but does not solve this problem. There may be coding error as well, the quality control procedure allows for up to a 5% error rate on diagnostic and reason for visit classification, although the observed coding error rate was less than 2% overall. Despite the limitations presented here, these factors do not affect the trend data because the same limitations apply for all years of NHAMCS data. The data may also serve as a baseline for examining trends in thrombolytic use in future years.

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