Troels Niemann MD*, Torsten Toftegaard Nielsen MD, DR MED SCI **, Niels Thorsgaard MD, DR MED SCI*** and Jørgen Lous MD, DR MED SCI****

DEPARTMENTS AND INSTITUTIONS:

* The Medical Research Unit of Ringkjoebing County, Ringkjoebing, Denmark

** The Cardiologic Department, Aarhus University Hospital, Skejby, Denmark

*** Medical Department, Herning Central Hospital, Herning, Denmark

**** The Institute of General Practice and the Research Unit for General Practice, Aarhus University, Aarhus, Denmark.

Editorial correspondence and reprints to:

Troels Niemann, MD.
The Department of Medicine, Herning Central Hospital,
Gl. Landevej 61,
7400 Herning,
Denmark.
 

Phone: (45) 99 27 20 85
Fax: (45) 99 27 20 53

Objective: To analyse how exercise testing affects referral for invasive evaluation of patients with stable angina pectoris in a rural and an urban Danish county.

Design: Retrospective analysis based on regional hospital registers and case records.

Setting: All 10 hospitals and 6 private practising cardiac specialists within a well-defined rural and urban area.

Subjects: All patients who passed a bicycle exercise test during 1996.

Intervention: Referral for invasive evaluation of angina pectoris following pathological exercise test.

Main outcome measures: Age and sex distribution, morbidity of ischemic heart disease, pathological exercise test and referral for coronary angiography.

Results: A total of 2,934 exercise tests were performed. The age-adjusted number of tests were 3,246 (rural) and 3,493 (urban) per one million inhabitants (NS). Women accounted for 31%. The age and gender distribution did not differ between the two regions. Nor did the results. The age-adjusted referral rates following a pathological exercise test were as follows: rural women 31%, urban women 64% (RR=2.06 [95%CI:1.39-3.05]), rural men 50%, urban men 63% (RR=1.27 [95%CI:1.09-1.50]). The fraction of patients referred for angiography decreased from 0.79 to 0.33 with increasing distance (2-154 km) to the angiography centre (P=0.008).

Conclusions: The two counties did not differ in terms of exercise test activity and results, but referral following a pathological exercise test varied with the distance from the angiography centre. This would seem to indicate that medical consultants= triage may constitute a barrier to referral for coronary angiography.

This week in BMJ:

Differences in therapeutic consequences of exercise testing in a rural and an urban Danish county

Regional differences in coronary angiography activity are substantial. The impact of the exercise test on the decision making regarding patients suspected of angina pectoris and the barriers to their referral for coronary angiography is unknown. In their comparison of the bicycle exercise testing activity and therapeutic consequences in a rural and an urban county in 1996 Niemann et al (p ?) report that the two counties did not differ in terms of exercise test activity and results, but referral following a pathological exercise test varied with the distance from the angiography centre. It seems that medical consultants triage may constitute a barrier to referral for coronary angiography and methods to secure uniform diffusion of new technology may be considered.

Key words/brief points:

bicycle exercise test, coronary angiography, medical decision making, regional variation.

Bicycle exercise testing is one of the most common non-invasive cardiology tests performed to diagnose ischemic heart disease. Previous studies have settled its prognostic value among patients undergoing coronary angiographic evaluation ¹. Coronary angiography is the ultimate diagnostic test applied to decide upon referral for coronary revascularization, but resort to this procedure may vary significantly from one region to the other ^2-4. A recent study comparing two Danish counties ⁵ reported that in the rural county which had no coronary angiography centre, the coronary angiography activity was approximately half of that of the urban county hosting the centre serving both counties. A bicycle exercise test had been done as a part of the evaluation preceding coronary angiography in 79% of the rural and 73% of the urban patients and this test thus plays a central prognostic role in the evaluation of patients with symptoms of stable angina pectoris. However, the use of the bicycle exercise test and its impact on the coronary angiography activity has not yet been studied in population-based settings. The present study aims to fill this gap by investigating the impact of the exercise test on the decision making regarding patients suspected of angina pectoris and the barriers to their referral for coronary angiography.

Patients and methods

Denmark is divided into 15 counties. The counties involved in this study were the rural county of Ringkjoebing and the urban county of Aarhus. The counties were divided into hospital catchment areas attended by local hospital and practising specialists. Both counties involved in this study were served by the University Hospital in Aarhus for cardiac invasive examinations. The decision to refer a patient was taken either by a medical consultant at the local hospital (5 in each county) or by a practising cardiology specialist (3 in each county). A single team of cardiologists and heart surgeons at the Aarhus University Hospital decided upon pre-examination waiting times and therapeutic measures to be taken following coronary angiography for all patients included in the study.

Patient identification

At birth all Danish citizens are given a 10-digit civil personal registration number, the first six digits of which make up the date of birth. The central personal registration number is used for registration of all patient-related activities. We identified all patients who passed a bicycle exercise test during 1996 from regional hospital registers and from Public Health Authority registers.

Baseline characteristics

Case records were used to obtain information about history of previous myocardial infarction and result of the bicycle exercise tests. The test was considered pathological if one or more of the following evaluation points were met: Symptoms of angina pectoris, significant electrocardiographic ischemia and/or drop of blood pressure during the exercise test. Conclusions drawn on the basis of the exercise tests fell into four categories: Normal, pathological, inconclusive or no data on conclusion. The exercise tests occasioned institution of the following therapeutic measures: Conservative treatment (ie medical treatment or observation), referral for coronary angiography, further examination needed or no data on consequence.

Data of background population

During 1996 the populations did not change significantly, and population data from Statistics Denmark collected on 1 January in 1996 were used in this study. The Ringkjoebing and Aarhus County Public Health Authorities provided data on the number of admissions due to acute myocardial infarction in 1996 ⁶. The Danish National Board of Health ⁷ furnished data on mortality due to suspected ischemic heart disease in 1996 (Table 1). The data indicate a similar or slightly higher prevalence of ischemic heart disease in the rural county. The Ringkjoebing Public Health Authority and the Aarhus University Hospital delivered data on the total coronary angiography activity during 1996 (Tables 1 and 2).

Statistical analysis

Bivariate analysis were performed using the c² test. Relative risks and rate ratios were calculated and adjusted in stratified analyses using the Mantel-Haenzel model. Associations between the number of inhabitants in the hospital catchment area, distance from the local hospital to the coronary angiography centre and the fraction of pathological exercise tests that gave rise to referral for angiography were calculated in a linear regression model weighted by the inverse variance of the fraction. Associations between local coronary angiography and exercise test activity rates were calculated in a linear regression model weighted by the inverse number of angiographies. All significance tests were two-tailed with a P value below 0.05 being considered significant. All rates were age standardised directly pooling the total population characteristics of the two counties.

Results

During 1996 a total of 2,934 bicycle exercise tests was performed in patients from the two counties. The exercise test rates were 3,183 (rural) and 3,315 (urban) per one million inhabitants (rate ratio=0.96; 95%CI: 0.89-1.04). Women accounted for 31 percent of the examinations. Table 2 shows that the exercise test rates of the different hospital catchment areas varied 2.1 fold and the angiography rates varied 2.9 fold. Figure 1 shows that in the different age groups the activity rate patterns were the same for both genders and both counties, with the highest rate in the age group of 60-to-69-year-olds. A history of previous myocardial infarction was registered more often in men (38%) than in women (22%) (c²=69, df=1, P<0.001), but there was no regional difference.

Exercise test results

Table 3 shows that there were no differences in the distribution of results between the two counties. The interpretation of a pathological exercise test was rather similar in the two counties: 55% (rural) and 51% (urban) had angina pectoris (c²=0.83, df=1, P=0.34), 88% (rural) and 89% (urban) had significant ischemia (c²=0.72, df=1, P=0.34) and 12% (rural) and 7% (urban) experienced a blood pressure drop during the exercise (c²=3.1, df=1, P=0.08). A pathological bicycle exercise test was found more often in men (30%) than in women (22%) (c²=15.3, df=1, P<0.001). There was little inter-hospital area variation in the fraction of pathological exercise tests (Table 2).

Therapeutic consequences of a pathological exercise test

Table 3 shows that if the bicycle exercise test was considered pathological, there was a smaller risk of referral in the rural county than in the urban county. Stratified for age, the relative risk of referral was 2.06 (95%CI: 1.39-3.05) for women living in the urban county and 1.27 (95%CI: 1.09-1.50) for men.

Table 4 shows that if the exercise test was considered pathological, the relative risk of referral for coronary angiography decreased by age among those living in the rural county. Adjustment for the history of myocardial infarction did not influence the relative risk of referral to coronary angiography.

Predictors of therapeutic consequences

The fraction of patients with a positive bicycle exercise test referred for angiography (dependent variable) decreased from 0.79 to 0.33 with increasing distance (2-154 km) to the angiography centre (Figure 2) (b= -0.78, P=0.008). There was no association between the number of inhabitants in the hospital catchment areas (b=0.33, P=0.35) and the exercise test rate (b=0.46, P=0.18) and the fraction of patients with a positive bicycle exercise test referred for angiography (dependent variable). We found no association between the angiography rate (dependent variable) and the exercise test rate (b=0.45, P=0.19).

Discussion

The salient findings of the present study were that the bicycle exercise test activities and results were the same in the two counties, but the therapeutic consequences of a pathological bicycle exercise test were significantly different, especially for the women and the oldest patients. There was a strong association between the fraction of patients with pathological exercise tests referred to angiography and the distance from the local hospital to the angiography centre.

This population-based study compares all patients from a rural and an urban Danish county examined with a bicycle exercise test in 1996. The total study population consisted of approximately 900,000 inhabitants, or 1/6 of the Danish population and is fairly representative of the Danish population. The strength of the study lies in the comprehensive nature of the material which has been gathered from registers on the basis of central personal registration numbers. All bicycle exercise tests were interpreted by cardiology specialists. Data were collected retrospectively to avoid bias in the specialists= interpretation and choices about therapeutic consequence of the tests. The two counties were quite similar in relation to population age and gender and use of the general practitioner ⁵, and there were no or only minor differences in relation to morbidity and mortality from coronary heart disease. There were no economic restrictions upon referral of patients from any of the hospital catchment areas to the coronary angiography centre; nor were there any principal or political difference between the two counties in their management of health care problems.

The coronary angiography rate of the rural county was approximately half the rate in the urban county, and we therefore expected to find the same difference in bicycle exercise test rates as a token of a generally low diagnostic activity concerning heart diseases in the rural county. But we did not. Nor did we find any association between bicycle exercise activity and angiography activity at the hospital catchment area level. The absence of regional differences in bicycle exercise test rates, history of myocardial infarction and results of the bicycle exercise tests, support the background data of identical morbidity from ischemic heart disease within the two counties. The absence of any difference between the two counties in the occurrence of angina pectoris and electrocardiographic ischemia as diagnosed by a pathological bicycle exercise test indicates a homogenous interpretation of this test between physicians.

The observation of a bicycle exercise test rate in women of less than half the size of that in men is in line with previous investigations of gender differences in diagnostic activities of heart diseases^8-11. The age and gender profile of the examined patients in the two counties was nearly identical, with the highest number of examinations performed in the age group between 60 and 69 years. Given the normal age and gender distribution of ischemic heart disease, we expected to find the female profile to show a 10-year delay, eg women between 60 and 69 years were expected to be comparable with men between 50 and 59 years. This was not the case (Figure 1) and may explain why fewer women than men had a positive bicycle exercise test.

Barriers to angiography

The fraction of patients with a pathological exercise test referred for angiography varied between the centres (from 0.33 to 0.79). The only reason for this seems to be differences in clinical decision making, since no other identifiable variables could explain the differences. This strongly suggests that the barrier to referral for coronary angiography is the medical specialist. This is in line with other studies showing that differences in the interpretation of an examination and of the indications for treatment are the main reasons for regional variation in health care activities ^{8; 12; 13}. Our finding of a conservative (non-invasive) therapeutic consequence of a pathological bicycle exercise test especially for the women and the oldest patients is in agreement with the findings observed in other studies ^{9-11; 14-18}.

The clear association between the distance to the coronary angiography service and the doctor`s decision to refer the patient for coronary angiography presumably reflects different local medical cultures rather than problems with the transportation of patients. The medical approach to invasive therapy is probably strongly influenced by local traditions and the behaviour of colleagues. In the urban area house officers often shift tenure between regional and university hospitals. Such shifts become less frequent the greater the distance from the university hospital. In September 1998 the Ringkjoebing County established a satellite unit for coronary angiography. The overall angiography activity rates of 1998 rose to the same level as in the urban county¹⁹. The fact that the activity rate in the rural county more than doubled within a 2-year period is attributed to the greater prominence given to invasive cardiology and the necessary training of medical consultants.

The observed differences in practice between centres have implications for the organisation of the coronary angiography service, the diffusion of new technology, the use of guidelines and for continued medical education. It remains an open question whether the observed differences in 1996 reflect appropriate or inappropriate use of medical resources; a question that clearly deserves further investigation.

Acknowledgements:

Thanks to Henrik Toft Sørensen for epidemiological support.

This study was supported by a research grant from the Ringkjoebing County.

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* RRa=rate ratio of rural:urban

* two hospitals with bicycle exercise test activity in Aarhus University Hospital, serving the same hospital area population.

Table 3 Relative risk for results and consequences of bicycle exercise tests in the rural and urban Danish county, 1996.
 

* RR=relative risk of rural:urban
 

Table 4 Number (percentage) of patients and relative risk of referral for coronary angiography by pathological bicycle exercise test.
 

* RR = relative risk of rural:urban