Friday April 25 2008
CT (Computed Tomography) Angiography. The purple areas are calcifications in the arteries.
The Daily Telegraph reports today that angina patients are being put at risk of heart attacks because seven out of 10 of them do not receive coronary angiography. It says that a study has found that women, people of south-Asian origin and the elderly are particularly unlikely to receive the test. Those who do not receive the test are more likely to die from heart disease.
The researchers, according to Channel 4 News, say, “there could be a number of possible explanations for the results, including different referral methods, or patients not wanting to undergo the procedure”.
These findings come from a well-conducted study that looked back at the records of over 10,000 people who attended six 'rapid access' chest pain clinics in England between 1996 and 2002. A panel of experts identified over 1,000 of these people as appropriate candidates for investigation by coronary angiography, and researchers then looked to see whether they had received an angiogram or not.
The findings of this study will probably lead to investigation of what is stopping people having coronary angiography and the feasibility of using standardised assessment measures to reduce the inequalities seen.
Where did the story come from?
Dr Neha Sekhri and colleagues from Barts and the London NHS Trust, and universities in London and Bristol carried out this research. The study was funded by the NHS service delivery and organisation research and development programme. It was published in the British Medical Journal, a peer-reviewed journal.
What kind of scientific study was this?
This was a cohort study looking at whether certain groups of patients were less likely to receive coronary angiography and whether this had an effect on their outcomes. Coronary angiography is a procedure where doctors inject a special dye, which shows up on X-rays, into the heart or the arteries that surround it. The dye reveals how well the heart is working and if the arteries leading to it are narrowed or blocked.
The procedure is performed when people are suspected of having stable angina, which is caused by a narrowing of the arteries around the heart. Angina causes people to have regular chest pains when they exert themselves, but not when they're at rest.
An independent panel of experts (cardiologists, cardiothoracic surgeons and family physicians) looked at electronic records from 10,634 people who attended six rapid-access chest-pain clinics in England between 1996 and 2002. They identified 1,375 patients in whom a coronary angiography would have been appropriate based on accepted criteria (modified Rand/UCLA criteria). The researchers then used data from the NHS-wide clearing system to identify which of these patients had received an angiography. They compared the characteristics of these participants with those of patients who were eligible for angiography but did not receive the test.
The researchers were specifically interested in factors that have been previously associated with inequalities in access to care for stable angina. These include age, gender, socioeconomic status (based on where the patients lived) and whether the patients were south Asian (defined as Indian, Pakistani, Sri Lankan or Bangladeshi). Other ethnic minorities were excluded from the study as there were too few cases among these groups for any analyses to be statistically robust.
The researchers then used data from the Office for National Statistics and the NHS-wide clearing system to identify the people who had coronary events. These events included death from coronary heart disease (CHD) and admission to hospital for acute coronary syndrome (ACS). ACS is a group of conditions, including heart attack, where there is complete or partial blockage of the coronary arteries leading to insufficient blood supply to the heart muscle and unrelieved chest pain at rest.
The patients were followed for an average of three years and a maximum of five years. The researchers then used complex statistical methods to compare outcomes between patients who received or did not receive angiography. In their analyses the researchers adjusted for factors that might affect their likelihood of receiving angiography and of having heart-related events, such as demographic factors, receipt of certain medications (aspirin, statins or beta blockers) and results of their exercise electrocardiogram (ECG).
What were the results of the study?
Most of the patients who the expert panel judged to be eligible for angiography (69%) did not receive it. The researchers found that patients who were aged over 64 years, were women and were of south-Asian origin were less likely to receive coronary angiography than those who were aged under 50 years, were men or were white.
People in the most deprived fifth of the population also tended to be less likely to receive angiography than those from more affluent areas. However, this difference was not large enough to reach statistical significance when analyses were adjusted for age, race and gender.
Of the 1,375 patients, 230 experienced a coronary event (ACS or death from CHD) during the five years of follow up (17%). People who had not had an angiography were more likely to have a coronary event than those who had.
What interpretations did the researchers draw from these results?
The researchers concluded that coronary angiography is underused among patients with suspected angina. This is especially evident in patients who are older, female, south Asian or from deprived areas.
The researchers also say that people who do not receive coronary angiography are more likely to have a coronary event. They suggest that standardising the way that people are judged suitable for having angiography, such as the Rand/UCLA method, might help to tackle these inequalities.
What does the NHS Knowledge Service make of this study?
This was a well-conducted study and its results seem reliable.
The Scottish Intercollegiate Guidelines Network recommends that coronary angiography should be performed if, following non-invasive testing (such as ECG, exercise tolerance tests or other forms of imaging using dyes, for example myocardial perfusion scintigraphy), the patient is identified as high risk or if the diagnosis remains uncertain.
There are some limitations to this study:
- Data on ethnicity was classified by the clinician seeing the patient, and may not have agreed with how the patient themselves would categorise their ethnicity.
- The measure of deprivation that was used was based on where a person lived, rather than on their personal circumstances (such as their employment status and salary). This could have resulted in mis-classifications.
- The study did not assess whether there were differences in the rates of referral to specialist services between different groups of patients. If there were inequalities in the use of referrals, this could also have contributed to the differences in coronary events seen.
- This type of study does not randomly assign people to groups. Therefore, the groups may be imbalanced for factors other than the ones studied and this may affect results. The researchers tried to take this into account in their analyses of the rate of coronary events, but there may have been unknown confounders that could not be adjusted for.
- The reasons why people did not receive angiography were not given and may have included the individual’s refusal of the procedure. The press have termed angiography an "X-ray", but it is a more invasive procedure. It typically involves patient sedation, local anaesthetic and insertion of a tube (catheter) into the artery of the groin or arm. The catheter is then advanced to the heart.
- The difference in subsequent coronary events between those who received the angiogram and those who did not is not because of the angiogram itself, but because identified problems are then treated. For example, patients who were found to have blockages or severe narrowing on angiogram could have had their condition treated, possibly at the same time, either by having a stent (tube) inserted into the artery or by having any narrowing expanded with a balloon (angioplasty).
The results of this study highlight an underuse of angiography for people with suspected stable angina and inequalities between different patient groups. Further research is needed to investigate the causes of these inequalities and to develop measures to target any barriers and improve outcomes.
Sir Muir Gray adds...
Ethnic, gender and age prejudice is a symptom of poor quality care and needs to be identified by studies such as this.