It may sound like futuristic scientific fantasy, but this technology is already available. As yet it is only being offered to 15 per cent of heart patients who might benefit from it. Yet countless sufferers of heart disease could be given more appropriate treatment if only more specialists made use of it.
The diagnostic technique is called myocardial perfusion. It is a new method of photographing the heart in which safe radioactive chemicals are injected into the bloodstream and tracked with a special camera. The camera can take pictures of the heart and its blood supply while it is beating, giving doctors a precise view of how it is performing.
Consultant cardiologist Dr Avijit Lahiri, a researcher in nuclear cardiology and lecturer at Northwick Park Hospital in Middlesex, is convinced of its benefits.
Dr Lahiri says cardiologists increasingly recognise that what were once thought of as dead zones in diseased heart muscle are in fact "hibernating" - waiting for a new blood supply so that they can start working again. Some 75 per cent of heart failure patients have been found to have such viable tissue which can often be "rejuvenated" by minor surgery. But the difference between dead and hibernating heart muscle can only be detected using myocardial perfusion.
The technique involves injecting a radionuclide, or radioactive isotope, into the bloodstream during exercise to trace the activity of the heart. Two tests, one at stress and one at rest, are carried out and the results picked up by a gamma camera and recorded as photographs using a scanner. The difference between the two states tells the clinician how serious the patient's condition is.
The advantage of the technique, says Dr Lahiri, is that it reveals the actual blood flow, or lack of it. "You can also see it in three dimensions," he says. "Ultimately, the size of the deficiency is going to be the size of the heart attack." Thus, the bigger the difference in images between exercise and resting, the bigger the potential heart attack.
A patient who is found to have hibernating heart muscle may be spared an agonising and often fruitless wait for major surgery or a transplant. All he or she may need is a simple operation to get the blood flowing again.
One of Doctor Lahiri's patients is a man of 44 who was constantly in and out of hospital with heart failure following a heart attack when he was just 36 years old. Since the heart muscle was thought to be dead, he was put on a waiting list for a heart transplant.
Further investigation using myocardial perfusion showed that what was previously thought to be dead tissue was hibernating muscle. After bypass surgery, the patient was able to return to work within six months.
"My condition has improved considerably," he says. "My shortness of breath is almost gone, I take a minimal number of tablets and I'm able to do a full day's work without any problem, whereas I could hardly dress myself before."
In the UK, however, only 15 per cent of patients who could benefit from myocardial perfusion actually receive it. This is because many British cardiologists continue to rely on simple exercise tests to determine the extent of damage to the heart and its circulation. This test measures the electrical activity of the heart during exercise with an electrocardiogram (ECG) monitor. Its results are not always accurate and if used alone it can lead to unnecessary or inappropriate treatment.
Cardiologists in the rest of Europe, Japan and the United States have been quicker to exploit the advances in imaging techniques. Many of the leading medical centres in the US - such as Johns Hopkins, Massachusetts General and the medical schools at Virginia and Yale - have stopped using exercise tests unless they are performed in combination with myocardial perfusion.
So why do British doctors seem reluctant to take myocardial perfusion on board? Dr Duncan Dymond, former secretary of the British Cardiac Society and a consultant cardiologist at St Bartholomew's hospital in London, says: "It's easy to pop a patient on a treadmill because you only need a technician and basic resuscitation equipment; it's cheap and easy. But with myocardial perfusion you need a gamma camera, radioisotopes, an experienced nuclear technologist, and you need to follow protection guidelines very carefully."
Although cheap, the chief disadvantage of exercise testing, which is widely acknowledged within cardiology, is the one-in-five ratio of inaccurate results. ECG readings often incorrectly suggest patients have healthy hearts when in fact they have serious problems and vice-versa. Younger patients and women have a particularly high rate of false negative results.
A poor performance on the exercise test is usually followed by an X-ray of the heart, an angiogram, to provide more detailed information about the location of the abnormality. But conversely, those patients given a clean bill of health by the exercise test will receive no such follow- up, and for them this could be fatal. Equally, healthy patients have to be unnecessarily subjected to an invasive angiogram.
Greater use of myocardial perfusion could benefit heart patients and the whole of the NHS, says Dr Richard Underwood, director of nuclear medicine at the Royal Brompton hospital. "Resources for coronary angioplasty, bypass and transplant operations are limited, therefore it is essential to identify those patients who would most benefit from these interventions," he says. "With myocardial perfusion imaging, most of the necessary information on which to base these decisions can be obtained."
The most important benefit of myocardial perfusion is that it allows specialists to stratify patients according to future risks. As Dr Dymond explains, test results can predict "the likelihood of a patient to run into trouble in the future, even though their symptoms may appear to be well controlled at the moment".
These benefits have been widely acknowledged in the United States, where joint guidelines were issued by the American College of Cardiology and the American Heart Association earlier this year, detailing when and for whom myocardial perfusion should be used. In particular, they state that the most recently developed imaging agents should be used to test women for coronary heart disease to overcome poor results usually achieved by ECG and exercise testing.
Like many aspects of the UK healthcare market, however, the availability of myocardial perfusion is something of a lottery and there are no similar guidelines available here.
Although most district hospitals have the kind of gamma camera needed to produce the images, Dr Dymond says, cardiologists are reluctant to hand patients over to nuclear medicine specialists to perform tests they themselves do not understand. The Royal College of Surgeons says every registrar in cardiology should be trained in nuclear cardiology, but who, asks Dr Lahiri, is going to train them? "There is a lack of education among consultants so they can't teach junior staff. Cardiovascular medicine has changed enormously in the last two decades. It is important to have more cardiologists who are trained in non-invasive cardiology as they have in the US."
Although it is not yet possible to put a figure on how many lives could be saved or improved if myocardial perfusion was more widely available, particularly to distinguish between dead and sleeping heart tissue, the answer could be available soon. Dr Lahiri, with colleagues from some major specialist centres, is hoping to spearhead a study looking precisely at this issue.
Nuclear imaging is easy to learn, says Dr Lahiri. "You can teach someone in three months. If cardiologists don't use this technique they will be doing their patients a disservice."Reuse content