It's the first step in screening for heart disease New MOH guidelines say most people do not need to do extra screening tests for cardiovascular disease. Lea Wee reports.
The value of a popular screening tool for heart disease – the CT (coronary tomography) angiogram – has been questioned by the Ministry of Health’s new clinical practice guidelines on the screening of heart disease.
The recently released guidelines say it has an uncertain value as a screening test, especially in people with no obvious symptoms of heart disease such as chest pain.
The CT angiogram takes X-ray pictures of the heart to show if there are any blockages in the blood vessels. It costs at least $900 at restructured hospitals.
It is unclear how commonly the CT angiogram is used here as a primary screening tool. The practice may vary from doctor to doctor.
It used to be thought that screening would pick up heart disease early, before the symptoms show up, so that the patients can be given prophylactic treatment such as a balloon angioplasty to open up narrowed blood vessels and prevent future heart attacks.
But these theoretical benefits are difficult to prove and balloon angioplasty has not been shown to prevent heart attacks in asymptomatic people, said Associate Professor Terrance Chua, the deputy medical director from the National Heart Centre Singapore.
Prof Chua, who is also part of the guidelines’ workgroup, said routine screening using CT angiogram appears to benefit only a small number of people with heart disease, but it exposes all the people screened to a small radiation risk.
Some may need further tests if the results of their scans are not conclusive.
The ministry’s guidelines are similar to those in the United States and Europe. They came in the wake of several important publications and greater public awareness about the radiation hazards linked to medical imaging in general and CT angiogram in particular, noted senior consultant cardiologist Chai Ping from the National University Heart Centre Singapore (NUHCS).
While he was unable to speak for doctors in private practice, Dr Chai said most cardiologists in restructured hospitals and national centres are already following international guidelines for heart disease screening.
Already, the NUHCS is seeing a drop in the number of patients going for CT angiogram, from 350 in 2007 to 130 last year.
Most people who underwent the procedure have symptoms such as chest pain or cardiac abnormalities in other tests such as the exercise electrocardiogram (ECG), he said. The test measures the electrical activity of the heart during different intensities of exercise.
But whether symptoms are present or not, the guidelines say the first step in any screening for heart disease, or cardiovascular disease in general, is to do a global cardiovascular risk score.
Also known as the Framingham Risk Score, this calculates a person’s risk of cardiovascular disease based on well-known risk factors such as age and gender. A person’s score will indicate whether he should have further tests or not.
The Framingham Risk Score was developed by the Americans and adapted for local use about 10years ago. But Associate Professor Goh Lee Gan, the chairman of the guidelines’ workgroup, said it is not widely used here maybe because not enough patients and doctors recognise its value as a cost-effective screening tool.
He added that it is useful not just for people with no symptoms of heart disease but also for those who wish to find out whether they are at risk.
“Even people with symptoms of heart disease will benefit from doing the Score so that they will have a baseline to work with,” he said.
The guidelines state that those with a low--risk score do not need to go for further screening tests, though they should consider making changes if they have other lifestyle-related risk factors, such as a diet high in animal fat and protein, physical inactivity, obesity and diabetes.
These risk factors are not covered under the Framingham Risk Score. But the ones included, such as cholesterol, blood pressure and smoking status, are good enough to calculate a person’s risk of a heart event in the next 10 years, said ProfGoh.
Obesity and diabetes, together with high cholesterol and blood pressure, are the deadly quartet of high-risk diseases, which if left unchecked, can lead to cardiovascular disease.
But it does not mean that a person should just choose any heart screening package or one that comes with more tests.
Screening should be customised to a person’s risk profile, said Prof Goh.
The coronary angiogram, in which a dye is injected into blood vessels in the heart so that they show up on an X-ray, is the gold standard used to find out if blood vessels are narrowed or blocked. But this invasive test is done only if the benefits outweigh the risks, said Prof Goh.
For instance, a person with a positive exercise ECG may be recommended an angiogram if he is also obese and has high blood pressure.
Most of the other tests available have varying accuracies and they are only done in certain patients after weighing the pros and cons, he said.
For instance, a blood test called C-reactive protein, which measures inflammation in blood vessels and other parts of the body, may be useful for those in the intermediate risk group when doctors are not sure if they should start the patients on lipid-lowering medication, said Associate Professor Tai E Shyong, head of endocrinology at the National University Hospital.
This is especially so if their cholesterol is close to the boundary for treatment, he said.
The current guidelines update an earlier version in 2003, which looked at health screening for all diseases.
The former version did not include the Framingham Risk Score for heart disease screening, which was relatively new then, nor did it include newer heart screening tests such as the CT angiogram and the carotid intima-media thickness (CIMT), as they had not been developed yet. The CIMT, an ultrasound which measures the thickness of the carotid artery in the neck, is also not recommended for heart screening.
Unlike the old guidelines, the new ones also recommend that people complete a screening questionnaire before they take up competitive or strenuous sports such as tennis and badminton.
Said Prof Goh: “More people are taking up rigorous exercise and pre-exercise screening is a safety step which ensures they have enough heart reserve to handle the stress of exercise.”