Author + information
- Received April 23, 1997
- Revision received July 17, 1997
- Accepted July 21, 1997
- Published online November 1, 1997.
- Jaume Marrugat MDA,* (, )
- Ginés Sanz MDB,
- Rafel Masiá MDC,
- Vicente Valle MDD,
- Lluis Molina MDE,
- Maria Cardona MDB,
- Joan Sala MDC,
- Lluis Serés MDD,
- Lluis Szescielinski MDE,
- Xavier Albert MDC,
- Josep Lupón MDD,
- Jordi Alonso MDA,
- for the RESCATE Investigators1
- ↵*Dr. Jaume Marrugat, Departament d’Epidemiologia i Salut Pública, Institut Municipal d’Investigació Mèdica (IMIM), Carrer Doctor Aiguader 80, E-08003 Barcelona, Spain.
Objectives. The aim of the present study was to ascertain whether the degree of accessibility to coronary angiography and revascularization results in differing usages or outcomes, or both, in the setting of a high coverage national health system.
Background. The selective use of coronary angiography and revascularization procedures in the management of acute myocardial infarction (MI) remains controversial.
Methods. A cohort of 1,460 consecutive patients with a first MI admitted to four referral teaching hospitals (one with tertiary facilities) were followed up for 6 months after admission. Only patients initially admitted to each of the study hospitals were retained for analysis in the original hospital’s cohort. End points were 6-month mortality and readmission for reinfarction, unstable angina, heart failure or severe ventricular arrhythmia.
Results. Patients admitted to the tertiary hospital were more likely to undergo coronary angiography (adjusted relative risk 4.22, 95% confidence interval [CI] 3.37 to 5.45) than those admitted to the nontertiary sites (use rate: 22.1% for nontertiary care, 55.5% for tertiary care). Revascularization procedures were performed in 21.2% of patients in the tertiary hospital and in 8.3% in the nontertiary hospitals (p < 0.0001). Median delay for emergency coronary angiography was shorter in the tertiary hospital (within 1 vs. 2 days, p < 0.0001). Six-month mortality or readmission rates were similar (23.7% and 24.7% for tertiary and nontertiary care, respectively). After adjustment for comorbidity and disease severity, the relative risk of death or readmission for the tertiary hospital was 1.03 (95% CI 0.69 to 1.53) times that of the nontertiary hospitals.
Conclusions. Selective use of coronary angiography and revascularization procedures may be as effective as less restricted use in the management of acute MI.
The prognosis of patients admitted for acute myocardial infarction (MI) has progressively improved in the past 30 years, due mainly to the development of coronary care units and the use of thrombolytic therapy [2, 3]and other pharmacologic treatments [4, 5]. However, the optimal use rate of tertiary care procedures, such as coronary angiography, coronary artery bypass graft surgery (CABG) and percutaneous transluminal coronary angioplasty (PTCA) , has not been established. Marked geographic variations in use rate have been described [8, 9], and on-site availability is one of the strongest predictors of their use . It remains to be determined whether restricted use of such procedures results in worse patient outcome. Retrospective studies [11, 12]suggest that a high use rate of tertiary procedures does not result in better survival, although anginal symptoms may be reduced and quality of life and functional status at 1 or 2 years improved.
The Spanish National Health System covers >97% of the population ; thus, hospital treatment does not depend on the patient’s ability to pay.
The aims of the present study were to ascertain whether the variation in accessibility to coronary angiography, PTCA and CABG, depending on the in-hospital availability of these procedures, determines different use rates or delays in patients with MI and to assess whether these differences, if existent, are associated with differences in outcome.
1.1 Study Design
The study was designed as a 6-month follow-up study of patients admitted to one hospital with and three without angiography or coronary surgery facilities. All four participating hospitals were public teaching institutions. Patients admitted to the tertiary care hospital were referred to as group A and those admitted to the nontertiary hospitals as group B. The tertiary hospital included exclusively primarily admitted patients; thus, patients referred from group B hospitals were not included. Patients from group B hospitals were referred to several tertiary hospitals in Barcelona for angiographic procedures, and each patient outcome was attributed to the initial admitting hospital.
1.2 Inclusion Criteria
Between May 1992 and June 1994, all patients with a first MI up to the age of 80 years admitted to the four participating hospitals within 72 h of onset of symptoms of MI were included. MI was diagnosed when two of the following criteria were present: 1) abnormal new Q waves, 2) increase in cardiac enzyme levels (more than twice the upper normal value), and 3) typical chest pain >20 min in duration.
1.3 Exclusion Criteria
Residence outside the study areas or any of the following conditions: 1) life-threatening diseases other than the index event; 2) previous CABG or PTCA; 3) or coronary angiography in the past 6 months. Patients enrolled in ongoing clinical trials were not excluded to reproduce actual care scenarios more faithfully.
1.4 Primary End Points
The composite primary end point included mortality or readmission within 6 months of the onset of MI for any of the following reasons: 1) reinfarction, 2) congestive heart failure, 3) ventricular fibrillation or tachycardia, or 4) unstable angina. Reinfarctionwas defined as a new infarction occurring at least 28 days after the onset of the initial event. Congestive heart failurewas diagnosed clinically according to standard diagnostic criteria [14, 15]. Ventricular tachycardiawas considered an end point only when sustained and leading to hospital admission. Progressive and rest angina were considered unstable angina, therefore requiring hospital admission according to Braunwald criteria .
1.5 Sample Size
Sample size was chosen to obtain a statistical power of 0.80 in a two-tailed test with an alpha risk of 0.05 if a difference ≥10 percentage points in the 6-month event rate was observed between the tertiary and the nontertiary hospitals (20% and 30% of primary end points, respectively). A 10% increase in the intended sample was applied to compensate for patients lost to follow-up; thus, 1,300 patients were required, of whom at least 325 had to be admitted to Hospital A. This sample size would permit a relative risk ≥1.5 to be statistically significant (p < 0.05).
1.6 Management of MI
Each participating hospital was allowed to follow its own routine, and no attempt was made to standardize patient management. However, all four hospitals had written MI protocols in accordance with international guidelines [17–19].
1.7 Appropriateness of Procedures
Emergency indications for coronary angiography, PTCA and CABG were standardized in advance to assess the need for their urgent use. These criteria were adapted from specific international treatment guidelines [17–19]. Emergency coronary angiographywas considered appropriate in the presence of 1) recurrent episodes of angina, particularly if accompanied by ST-T wave changes, not controlled after 48 h of appropriate treatment; or 2) mechanical complications, including severe mitral regurgitation due to papillary muscle dysfunction or ventricular septal rupture.
Emergency revascularizationwas considered appropriate in either of the aforementioned circumstances when coronary anatomy was deemed suitable. CABG was preferred to PTCA in patients with left main coronary artery stenosis or diffuse coronary disease (two to three vessels) or when cardiac repair was necessary. Patients with one- or two-vessel discrete lesions were judged to be candidates for PTCA.
The need for elective angiographywas assessed in detail in a random subsample half the total sample size. This procedure was considered necessary if at least one of the following occurred: 1) postinfarction angina, 2) mechanical complications, 3) positive exercise test results, or 4) reinfarction within 28 days.
1.8 Study Variables in Acute Phase of MI
The following variables were prospectively recorded by a trained investigator at each center: demographic data; history of hypertension; diabetes; chronic obstructive pulmonary disease; peripheral vascular disease; smoking status; MI location; Killip class; presence of severe arrhythmia (defined as the occurrence of at least one episode of ventricular fibrillation or sustained ventricular tachycardia requiring immediate medical intervention) within the first 72 h; delay from onset of symptoms to first monitoring in an emergency room, coronary care unit or general intensive care unit; and hospital stay, use of thrombolysis, exercise test, coronary angiography, PTCA and CABG and the complications associated with diagnostic and therapeutic procedures.
1.9 Analysis and Statistical Methods
Groups A and B were assessed for differences in categoric variables by the chi-square or Fisher exact test when appropriate and by the Student tor Mann-Whitney Utest when necessary for differences in continuous variables. The level of significance used was 5%.
Survival curves were estimated by the Kaplan-Meier method. Adjusted relative risks for 6-month mortality and morbidity were estimated using unconditional logistic regression . Severity or prognosis-related variables showing interhospital differences were adjusted for in the models to control for case mix. All two-level interactions between pairs of these variables were assessed in all models. The SPSS and EGRET (Statistics and Epidemiology Research Corporation) statistical packages were used.
Of the 2,397 patients registered in the four hospitals, 1,460 (60.8%) (1,035 initially admitted to nontertiary hospitals, 425 to tertiary hospital) met the inclusion criteria. Previous MI (18.4%) and age >80 years (9.6%) were the most frequent reasons for exclusion. Other causes included patients residing outside the hospital catchment area, which made follow-up impractical (4.5%); previous revascularization (1.0%); and angiography in the previous 6 months (0.3%). An additional 5.8% were excluded for miscellaneous reasons, such as administrative; terminal, severe noncoronary disease; and referral from participant hospitals.
Patients admitted to the three group B hospitals did not differ clinically or statistically in any relevant characteristic (results not shown).
Differences in some demographic and clinical variables were found between groups A and B (Table 1). The group A hospital (the only tertiary site) more frequently admitted patients with comorbidity (i.e., diabetes and hypertension), non-Q wave MI or previous angina than did the group B hospitals. Conversely, patients in group B were more often in Killip class III or IV than patients in group A.
Median delays to first cardiac monitoring were similar in groups A and B. More than 50% of patients performed an exercise test. Thrombolytic therapy was administered in 545 patients (37.4%) (Table 2), with a median time from symptom onset to administration of 3 h. Streptokinase was the drug of choice in 77.8% of occasions.
Coronary angiography was performed in 463 patients (31.8%), PTCA in 93 (6.5%) and CABG in 83 (5.7%) within 6 months of admission. By the end of the follow-up period, the tertiary hospital had performed more coronary angiography than the nontertiary hospitals (55.5% vs. 22.1%, p < 0.0001), and the use rate of elective angiography was higher in the tertiary hospital (50.1% vs. 14.9%, p < 0.0001) (Table 2). In the random subsample, these procedures were deemed necessary in 40.7% of patients in the tertiary hospital and 39.6% in the nontertiary hospitals (p = NS). The proportion of patients who underwent revascularization was higher in group A than in group B (PTCA: 12.0% vs. 4.1%, respectively, p < 0.0001; CABG: 9.2% vs. 4.3%, respectively, p = 0.0002; PTCA or CABG: 21.0% vs. 8.3%, respectively, p < 0.0001) (Table 2).
In a model adjusted for age, Killip class, gender, diabetes, hypertension, MI location, Q wave MI and previous angina, the relative risk for coronary angiography use among patients in group A versus group B was 4.22 (95% confidence interval [CI] 3.27 to 5.45). Use rate of angiography in patients with a non-Q wave MI was 1.34 (95% CI 0.97 to 1.99) times that of patients with a Q wave MI.
Complications occurring during the 6-month period were death (one patient [0.3%]), MI (four patients), stroke (two patients) and surgical femoral artery repair (six patients) for coronary angiography; death (one patient) (1.4%) and surgical repair (one patient) for PTCA; and death (three patients [4.7%]), MI (one patient) and stroke (one patient) for CABG.
2.3 Appropriateness and Delay in Urgent Procedure Use
Rates of emergency coronary angiography and revascularization techniques according to hospital type are shown in Table 3. Ninety-six patients (6.4%) met objective criteria for emergency coronary angiography, which was eventually performed in 77 (80.8%).
No differences between groups were observed in the proportion of patients in whom PTCA was indicated or performed. In 19 patients, emergency coronary angiography was indicated but not performed: In 2 of these 19 it was not requested by the attending physician (both patients were alive at the end of the 6-month follow-up period). Of the remaining 17 patients, 12 rapidly deteriorated and died before the procedure could be performed. In five patients referred by nontertiary hospitals, coronary angiography was not performed by the receiving tertiary hospital (four patients were alive at end of the 6-month follow-up).
Among the 76 patients with emergency indication for coronary angiography, the proportion of patients meeting emergency criteria for PTCA or CABG and the proportion of patients who finally underwent these procedures was similar in both groups. The median delay in performing emergency catheterization was shorter in the tertiary hospital than in the nontertiary hospitals (within 1 vs. 2 days, respectively, p < 0.001) (Table 3).
Both 28-day and 6-month mortality and readmission rates for both groups are shown in Table 4. Only two patients were lost to follow-up. Overall intergroup differences in mortality or readmission rate were not statistically significant. Survival curves in both groups were similar and not statistically significant (Fig. 1).
Logistic regression models adjusted for differences between groups A and B (Table 5) show that hospital type was not an independent risk factor for 6-month mortality or readmission. The relative risk in group B was 0.97 (95% CI 0.68 to 1.55). No statistically significant interaction terms were identified. No differences between groups were found when only 6-month mortality was considered as a dependent variable. The relative risk for group B was 1.12 (95% CI 0.83 to 1.51). No statistically significant interaction terms were identified (Table 5).
The results of the present study show that the use of tertiary procedures in patients with a first acute MI varies according to the type of admitting hospital. Although no differences were found in the proportion of patients undergoing emergency diagnostic or therapeutic procedures, longer delays were encountered in patients admitted to nontertiary hospitals. Furthermore, admission to an institution with on-site cardiac catheterization facilities was strongly associated with the use of coronary angiography. However, no differences were found in the 6-month mortality or readmission rate between the tertiary and the three nontertiary hospitals, even after adjustment for severity and comorbidity variables.
These results raise the question of whether differences in use reflect an excess in the number of procedures performed in the tertiary hospital. Several attempts have been made to assess the consequences of differences in acute coronary syndrome management, with inconclusive results [21–23]. Large geographic variations in procedure use rate have also been described, which indicates that some use may be inappropriate [8, 24, 25]. One study suggests that 30% of CABG may be performed for equivocal reasons and that 14% are inappropriate and another that low risk patients are selected for angiography and revascularization . Interestingly, in our study the proportion of patients with objective indications for emergency coronary angiography, PTCA and CABG was similar in both hospital types, although longer delays were observed in the nontertiaries. Therefore, the differences observed in utilization rates were due to the larger number of elective procedures carried out in the tertiary hospital. Again, the proportion of elective angiograms deemed necessary was similar in both types of hospitals when it was investigated in a random subsample. Patients admitted to hospitals with on-site cardiac catheterization facilities are more likely to undergo coronary angiography than patients admitted to other hospitals . The results of our study concur with that finding, also confirmed by others [27, 28]. The greater number of patients with non-Q wave MI admitted to the tertiary hospital may in part account for the higher use of elective angiography.
In addition to availability, financial incentives and patient demand have been suggested as factors influencing variations in the use of tertiary procedures in patients with coronary disease . Hospitals in the Spanish National Health System do not provide financial incentives for physicians to perform procedures. It is therefore highly unlikely that financial reasons accounted for the differences observed in our study.
3.1 Study Characteristics and Limitations
The finding that outcome was similar in both hospital types and was unrelated to the use of invasive procedures is in accordance with previously reported results . The present study was specifically designed and powered to detect differences in event rates between tertiary and nontertiary hospitals. The observation period was extended to 6 months, when most of the events related to the acute phase of MI would already have occurred. However, according to the results of previous studies [11, 12], a longer observation period might reveal differences in anginal symptoms or functional status.
The present study did not address other issues related to on-site unavailability of tertiary care procedures, such as inconvenience and distress for patients transferred between hospitals and their relatives.
The following measures were taken to ensure efficient case mix control: Only patients with a first MI were included; exclusions and their causes had to be justified; and statistical adjustment for case mix (i.e., differences in disease severity and comorbidity between the two hospital types) was used. To prevent physician-dependent outcomes, PTCA or CABG after discharge was not used as an end point.
Our results suggest that despite longer delays and probably more inconvenience to patients, the selective use of coronary angiography and revascularization procedures applied in nontertiary centers is as effective as the less restricted use observed in tertiary hospitals.
We appreciate the English revision of the manuscript made by Christine O’Hara.
A.1 Participating Institutions and Investigators for the Recursos Empleados en el Sı́ndrome Coronario Agudo y Tiempos de Espera (RESCATE) Study
G. Sanz, M. Cardona, Hospital Clinic i Provincial de Barcelona; R. Masiá, J. Sala, X. Albert, Hospital Josep Trueta de Girona; L. Molina, L. Szescielinski, Hospital del Mar de Barcelona; V. Valle, A. Curós, L. Serés, J. Lupón, J. Serra, D. Pereferrer, Hospital Germans Trias i Pujol de Badalona; J. Marrugat, J. Alonso, J. Vila, M. Pavesi, Institut Municipal d’Investigació Mèdica de Barcelona.
↵fn1 This project was funded by Grant 92/0009 from the Fondo de Investigación Sanitaria, Madrid and by Grant CIRIT/SGR 9500167 from the Generalitat de Catalunya, Barcelona, Spain.
- coronary artery bypass graft surgery
- confidence interval
- myocardial infarction
- percutaneous transluminal coronary angioplasty
- Received April 23, 1997.
- Revision received July 17, 1997.
- Accepted July 21, 1997.
- The American College of Cardiology
- The Beta Blocker Pooling Project Research Group
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