A Lexiscan is a drug used during a heart imaging test when you can’t exercise on a treadmill. It mimics what exercise does to your heart by widening your coronary arteries, allowing doctors to take pictures of blood flow and check for blockages or other problems. The generic name is regadenoson, and the test itself is often called a “Lexiscan stress test” or a pharmacologic stress test.
How a Lexiscan Stress Test Works
During a normal exercise stress test, physical activity forces your heart to pump harder, increasing blood flow through your coronary arteries. If an artery is partially blocked, blood flow to that area lags behind, and the difference shows up on imaging. Lexiscan creates the same effect chemically. It activates specific receptors on the walls of your coronary arteries, causing them to relax and widen. Healthy arteries dilate significantly, while narrowed or diseased arteries can’t open as much. That contrast is what makes blockages visible on the scan.
The imaging portion of the test uses a small amount of radioactive tracer injected into your bloodstream. The tracer travels to your heart muscle, and a special camera captures how it distributes across different regions. Areas receiving less blood flow appear darker, signaling a potential problem. This type of imaging is called myocardial perfusion imaging, or MPI.
Who Needs a Lexiscan Instead of a Treadmill Test
Lexiscan is specifically designed for people who can’t complete an adequate exercise stress test. That includes people with joint problems, mobility limitations, lung conditions, neurological issues, or simply an inability to reach the target heart rate on a treadmill. It’s also used for patients whose baseline heart rhythm on an EKG would make an exercise test hard to interpret, such as those with left bundle branch block, certain pre-excitation syndromes, or a permanent pacemaker.
Beyond routine screening for coronary artery disease, doctors use Lexiscan stress tests to evaluate patients who are clinically stable after a heart attack, to assess people who come to the emergency room with chest pain after other causes have been ruled out, and to monitor heart function after a heart transplant.
What Happens During the Test
The entire appointment typically takes a few hours, though much of that is waiting time. The active portion is surprisingly short. Here’s the general sequence:
- Before the test: You’ll need to avoid all caffeine for at least 12 hours beforehand. That means no coffee, tea, energy drinks, chocolate, or caffeine-containing medications. Caffeine directly blocks the receptors that Lexiscan activates, so even a small amount can compromise the results. Your doctor’s office will also give you instructions about specific medications to hold.
- The injection: A technician or nurse places an IV line. The Lexiscan dose is a single, fixed injection of 0.4 mg delivered over about 10 seconds. There’s no weight-based dosing or slow drip involved.
- Tracer injection: The radioactive tracer follows shortly after the Lexiscan injection. Research has shown that peak blood flow in the coronary arteries occurs roughly 90 seconds after the Lexiscan injection, which is when imaging captures the most useful information.
- Imaging: You’ll lie still under a gamma camera while it captures images of your heart. You may have two sets of images taken: one at rest and one after the Lexiscan injection, so the doctor can compare the two.
What It Feels Like
Most people feel something during a Lexiscan injection. The drug is designed to stress your heart, so the sensations can be uncomfortable but are usually brief, lasting only a few minutes. The most common effects include shortness of breath, headache, flushing or a feeling of warmth, and chest discomfort. Some people also report dizziness, nausea, or an odd sensation in the abdomen. These side effects tend to fade quickly because regadenoson has a short duration of action in the body.
If the side effects are severe, a reversal agent can be given through the IV to counteract the drug’s effects. This works because it directly competes with Lexiscan at the same receptors, essentially shutting down the reaction.
Who Should Not Have a Lexiscan Test
Lexiscan is contraindicated for people with certain heart rhythm problems, specifically second- or third-degree heart block or sinus node dysfunction, unless they have a functioning pacemaker in place. These conditions affect the electrical signaling in the heart, and because Lexiscan can temporarily slow conduction through the heart’s electrical pathways, it could cause dangerous rhythm disturbances in these patients.
People with severe asthma or active wheezing are also generally not candidates, since the drug can trigger bronchospasm (tightening of the airways). Your doctor will review your full medical history before scheduling the test to determine if Lexiscan is safe for you or if an alternative approach is needed.
What the Results Tell Your Doctor
The images from a Lexiscan stress test produce a map of blood flow across your heart muscle. If blood flow looks even and consistent during both the rest and stress phases, the result is considered normal, meaning significant blockages are unlikely. If a region of the heart receives noticeably less blood during the stress phase but looks normal at rest, that suggests a blockage is limiting flow when demand increases. If a region looks abnormal during both phases, it may indicate prior heart damage, such as scar tissue from a past heart attack.
These results help your doctor decide the next steps. A normal result is reassuring and often means no further cardiac testing is needed in the near term. An abnormal result may lead to additional testing, such as a cardiac catheterization, where a thin tube is threaded into the coronary arteries to directly visualize any blockages and potentially treat them.