Question: What is a nuclear stress test (Myocardial Perfusion Imaging), and how does it differ from either a medicine or exercise stress Test?
Answer: A nuclear stress test, what we call myocardial perfusion imaging is a test that looks at the blood flow to your heart muscle. We do that while you're resting and also with some form of stress, either exercise or sometimes we give a medicine to simulate the effects of exercise.
The analogy here would essentially be looking at the blood flow to your heart the way that gas flows to a car engine. You know, you could have a totally healthy engine, but if you have a narrowed fuel line, you may not be able to step on the gas and get the car to accelerate properly. You have enough gas getting to the engine under resting conditions, but when you step on the gas and accelerate, if you have a narrow fuel line, you don't have enough stuff to make the engine go at a faster clip.
So the analogy works quite well for your heart; you may have a narrower artery that's supplying enough blood when you're resting, but when you exercise, that narrowed artery can't increase the flow to the heart muscle. And we can see that through the nuclear stress test because that's measuring the blood flow to the heart; you can see where the flow increases normally, compared to those areas where it doesn't increase. We can do that in one of two ways. We can have you exercise on a treadmill, to see how your heart responds to exercise.
In about 40 percent of patients, we don't do that because you can't exercise optimally to a high enough level to really make your heart work; you can't step on the gas enough. And therefore in the people who can't exercise adequately, we give them medicine that simulates the effects of exercise. The analogy of the car engine would be: we're not stepping on the gas, what we're doing is something else to increase the flow to the valves in the engine to make the flow occur more, at an increased clip.
So that's what the nuclear stress test does. And it's very helpful, not only in diagnosing individuals who may have coronary disease, but also in patients who have known coronary disease at giving us information regarding how severe it is and what the prognosis is as well. It's a very good way of identifying people at low risk and high risk.
If you're at low risk, or you're just doing this for a diagnostic test, sometimes we do an exercise test without the imaging. It's just called a standard exercise test. And that's quite helpful in people who are pretty healthy or just being sure that they're healthy without a high likelihood of having underlying coronary disease. That's a very good test in those people, without the imaging.