Myocardial Perfusion Scan

A myocardial perfusion scan is a nuclear medicine imaging test that shows how well blood flows through the heart muscle, both at rest and under stress.

A small amount of a radioactive tracer is injected into a vein. The tracer travels through the bloodstream and is absorbed by heart muscle cells in proportion to how much blood they receive. A special camera called a gamma camera then detects the radiation and produces detailed images. Areas that receive good blood flow appear bright, while areas with reduced or blocked flow appear darker. This lets doctors see whether any part of the heart muscle is not getting enough blood — a condition called ischemia (poor blood supply to the heart) — or whether there is scarring from a past heart attack.

Doctors use a myocardial perfusion scan to investigate symptoms or test results that suggest the heart muscle is not receiving enough blood. It is also used to guide treatment decisions and to check how well earlier treatment has worked.

• Chest pain or chest tightness that may be caused by narrowed coronary arteries (the vessels that supply blood to the heart muscle)
• Shortness of breath on exertion with no clear cause
• Suspected coronary artery disease (CAD) — a build-up of fatty deposits inside the heart's blood vessels
• Assessing the extent of damage after a confirmed heart attack
• Evaluating how well the heart is recovering after a procedure such as a coronary stent (a small tube placed inside an artery to keep it open) or bypass surgery
• Abnormal results on an exercise stress test or electrocardiogram (ECG — a recording of the heart's electrical activity)
• Risk assessment before major non-cardiac surgery in patients with known or suspected heart disease

This scan may not be the right choice in every situation. Your doctor will decide whether another test is more appropriate if any of the following apply.

• Pregnancy, because radiation exposure carries risk to the developing baby
• Breastfeeding women (a pause in breastfeeding is usually required — your doctor and the nuclear medicine team will advise on timing)
• Severe allergy to the radioactive tracer used
• Inability to undergo either physical or pharmacological (medication-induced) stress, in cases where a stress scan is planned

A myocardial perfusion scan is a well-established diagnostic test with a generally low risk profile; the radiation dose used is small and comparable to that of several other routine imaging tests.

• Radiation exposure: the tracer delivers a low dose of radiation to the body, which is considered acceptable for diagnostic purposes but is kept as low as reasonably possible
• Allergic reaction to the tracer: usually mild (skin redness, itching, or nausea) and rarely severe
• Discomfort or bruising at the injection site
• During the stress part of the test — if physical exercise is used: temporary chest tightness, dizziness, or palpitations (a sensation of the heart beating fast or irregularly), which typically pass quickly
• During pharmacological (medication-induced) stress — if drugs are used instead of exercise: flushing (a warm, red feeling in the face), headache, shortness of breath, or a brief drop in blood pressure; medical staff are present throughout and these effects are short-lived
• In very rare cases, a more serious heart event during the stress phase; this is why the test is always performed with monitoring equipment and trained staff present

Preparing well for a myocardial perfusion scan helps ensure the images are clear and the results are accurate. The nuclear medicine team will give specific instructions in advance; what follows describes what is commonly required.

Fasting and diet: patients are usually asked to avoid eating and drinking (except water) for several hours before the scan. Caffeine — found in coffee, tea, energy drinks, and some sodas — must typically be avoided for at least 24 hours beforehand, because it interferes with the stress part of the test. Chocolate also contains caffeine and is usually on the avoidance list.

Medications: some heart medications, particularly certain ones used to control heart rate, may need to be paused before the test, because they can blunt the heart's response to stress. The referring doctor or nuclear medicine team will advise which medications to continue and which to pause. Patients should never stop a medication on their own without this guidance.

Smoking and alcohol: smoking should be avoided on the day of the test. Alcohol is best avoided in the 24 hours before the scan. Comfortable, loose clothing and flat, closed-toe shoes suitable for walking on a treadmill are recommended if physical exercise stress is planned.

Preliminary tests: before or on the day of the scan, the following are commonly checked:

• A baseline ECG (electrocardiogram) to record the heart's electrical activity
• Blood pressure measurement
• A brief review of symptoms and current medications
• In some centres, a blood test to check kidney function, since the tracer is cleared by the kidneys

What happens during the procedure: the exact steps and timing vary between hospitals, but the general sequence is as follows.

• 1. A small intravenous (IV) line is placed in a vein, usually in the arm, for injecting the tracer.
• 2. Resting images are taken first: the tracer is injected, and after a waiting period — usually around 30–60 minutes to allow it to reach the heart — the patient lies still under the gamma camera while images are recorded. This part typically takes 15–30 minutes.
• 3. The stress phase follows, either on a treadmill or, if the patient cannot exercise, by injection of a medication that mimics the effect of exercise on the heart. Heart rate, blood pressure, and ECG are monitored throughout.
• 4. A second dose of tracer is injected at peak stress, and stress images are taken after another short waiting period using the gamma camera.
• 5. The two sets of images — rest and stress — are compared by the nuclear medicine physician (doctor specialising in nuclear medicine imaging) to identify any areas of reduced blood flow.
• 6. The IV line is removed once imaging is complete. Most patients can leave the department the same day.

A myocardial perfusion scan is a non-surgical, outpatient procedure, so recovery is straightforward for most people. There is no wound to care for and no anaesthetic (medication to make you unconscious) to recover from. However, a few simple steps help the body clear the tracer and keep follow-up on track.

• Monitoring: patients are observed briefly after the stress phase to ensure the heart rate and blood pressure return to normal before leaving; most people feel ready to go home within an hour of the scan finishing
• Hydration: drinking plenty of water for the rest of the day helps the kidneys flush the radioactive tracer from the body more quickly
• Radiation precautions: the radiation level is low and poses no danger to the patient themselves, but as a courtesy measure some centres advise briefly limiting very close contact with pregnant women and young children for the remainder of the day of the scan
• Driving: if pharmacological stress (medication-induced stress) was used, patients are usually advised not to drive immediately afterwards; the team will confirm when it is safe to do so
• Normal activities: most people can resume their usual daily activities the same day or the next day, unless their heart condition requires other restrictions
• Medications: any medications that were paused before the test are usually restarted according to the guidance given by the doctor — the nuclear medicine team will confirm this at discharge
• Follow-up appointment: the images are reviewed and a report is sent to the referring doctor, who will discuss the results and any next steps — this appointment is important and should not be skipped
• When to seek urgent attention: if chest pain, severe shortness of breath, dizziness, or palpitations (a sensation of a fast or irregular heartbeat) develop after leaving, the patient should seek medical care promptly