The study took place in a semi-urban fourpartner group general practice in North Staffordshire, which has held computerised records of all practice contacts since 1990 and which conducts an annual review to ensure that the presence of all chronic conditions is updated each year. The practice is a recording practice for the Royal College of General Practitioners' (RCGPs') Weekly Returns Service which provides data for the national UK general practice morbidity database6
and, as a member of the North Staffordshire GP Research Network, undergoes regular audits of its recording quality.7
The software system used for the morbidity and medication recording was VAMP Vision (In Practice Health Systems Ltd). The morbidity recording utilises the Read code system, the most common method for assigning morbidity and treatment codes in UK clinical practice. A self-complete general health survey was mailed to a randomly selected 50% sample (n
= 4002) of the adult population aged 18–75 years registered with the study practice. In the UK virtually all the adult population is registered with a general practice, so practice registers provide a convenient frame for sampling a local population. As part of the survey, permission was sought from the mailed population sample to view their medical records for research purposes. Only those survey responders who gave this permission were considered in the current analysis. Demographic information in the questionnaire included age, sex, and current work status.
The Rose questionnaire for angina pectoris,8
a validated instrument for use in the general population,9
was included as part of the general health survey. The questionnaire asks first about any chest pain, and then specifically about chest pain brought on by exertion. To meet the definition of ‘definite angina’ according to the previously established ‘Rose’ criteria, there must be pain located over the sternum or in both the left chest and arm. This pain comes on with exertion and causes the person to stop or slow down and goes away within 10 minutes. Three groups were identified from the chest pain data in the questionnaire: (i) those with any chest pain, (ii) those with any exertional chest pain, and (iii) those with definite angina according to the Rose criteria. Group (iii) is a subgroup of group (ii), and group (ii) is a subgroup of group (i). Those who had no chest pain at all formed the other group for analysis.
How this fits in
Chest pain in adults is associated with a higher risk of future cardiovascular mortality. Many adults who report chest pain in population surveys have not been diagnosed with coronary heart disease (CHD). It has been shown that when such adults are followed-up over a 7-year period, although most still will not be diagnosed with CHD during this time, they are still at a higher risk of such a diagnosis throughout this period than people followed up for the same period of time who do not start off with chest pain. Men were shown to have a higher cardiovascular mortality. There may be potential in enquiring about chest pain as part of identifying those at higher risk in the general population who could be the target for preventive strategies.
A download from the general practice records of all consenting survey responders was carried out to obtain information concerning both their consultations and prescribed medication. The period of the download extended from January 1994 to December 2003. The postal survey was carried out in September 1996. Thus, the general practice records were used to determine the presence of a diagnosis of CHD in the 32 months prior to the survey (retrospective review). This information was used to identify the study population for the prospective cohort analysis. The records were then used to determine newly diagnosed CHD for this analysis, from the time of the survey up to the end of 2003 (prospective review). GPs in the participating practice were not informed of the survey results, and it is unlikely that the survey could have influenced subsequent GPs' coding.
Participants were assigned a GP diagnosis of CHD if either the G3 Read code (angina, myocardial infarction, other CHD) or the British National Formulary (BNF) code for nitrate use (02060100) was found in their records. This definition of CHD has been used previously in a UK study and was found to have a sensitivity of 73% and a positive predictive value of 79% when compared with diagnosis confirmed by objective diagnostic strategies, such as a positive coronary angiogram, exercise test, or raised cardiac enzyme activity.10
Deaths from all causes up to December 2003 among responders to the survey who were included in the prospective cohort, were ascertained from the records held at the practice.
As symptom frequency, consultation rates, and mortality related to CHD are reported to differ between males and females, all analyses were stratified by sex. Prospective analysis compared the survival of participants with and without chest pain at baseline, according to the three different classifications, from the time of the survey until the earliest of the following: firsttime GP diagnosis of angina; death (any cause); exit from the practice; or end of the study period. Results were then presented separately for angina diagnosis and death, and survival proportions were compared using the log-rank test, adjusted for age group. Kaplan–Meier curves were drawn for survival to angina diagnosis. To adjust the associations, between each of the three baseline chest pain groups and subsequent consultation for CHD, for other risk factors for CHD onset andmortality (age and employment status), a Cox regression analysis was performed. In this analysis, age at survey was categorised into two groups (above and below the ‘at risk’ population median) and employment status was recorded as working or not. Results for this analysis are presented as adjusted risk ratios and 95% confidence intervals. All analyses were carried out using Stata software (version 7.0.)