During the stress stage of myocardial perfusion scan, a technologist will ask you to fill out a form containing questions regarding your demographics, risk factors for heart disease and your heart disease history. Electrodes will be placed on your chest and intravenous line be started. You will either have to walk on a treadmill or be given a pharmacologic stress with one of 2 types of medication - Adenosine or Dobutamine. In both cases at peak stress, a little amount of radioactive tracer will be administered, and 10-60 minutes after the injection the post stress images will be taken with help of a special instrument (called Gamma Camera).

During the resting part, the tracer will be injected through an intravenous line and the pictures taken within 30-60 minutes.

Myocardial perfusion scan has a long track record of safety in large number of patients with major side effects occurring very rarely. However, with pharmacologic stress test (either Adenosine or Dobutamine) side effects are more frequent and include chest pains, shortness of breath, warm feeling, dizziness and arrhythmias. The administering of radioactive tracer may cause a short funny taste for a few seconds after injection. The radioactive material is given in such a small dose, that there can be no side effects Nevertheless, in order to avoid a potential risk to a fetus, a pregnancy exam is performed on women with a capacity to become pregnant.

Your scan results will be notified to your doctor within 24 hours of termination of the scans after which he will discuss them with you.

More about Myocardial Perfusion

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Myocardial perfusion scan is a nuclear medicine procedure through which function of the heart muscle (myocardium) can be studied. It evaluates several heart conditions like coronary artery disease (CAD), hypertropic cardiomyopathy, myocardial wall motion abnormalities and so on. The function of the myocardium is also assessed by calculating the left ventricular ejection fraction (LVEF) of the heart. Myocardial perfusion scan is done in along with a cardiac stress test. Following are indications that this test should be taken:

• Diagnosis of CAD and other cardiac abnormalities.
• Identifying location and acuteness of coronary artery disease (CAD) in patients with a history of CAD.
• Risk stratification and evaluation of patients who are at risk of having a myocardial or coronary incident.
• Evaluation of heart after intervention revascularivation (angioplasty).

Myocardial perfusion imaging may have risks of cancer from the high radiation doses.In research with patient exposure to low-dose ionizing radiation, myocardial perfusion imaging had the highest average effective dose (15.6 millisieverts) and the highest percentage (22.1%) of all effective doses to the entire patient population from all major radiological procedures. Exposure to low-dose ionizing radiation has long been linked with up to 2% of solid cancers and leukemia.

However, Myocardial perfusion imaging scans are indispensable predictors of future clinical events, and in theory may spot the patients for whom aggressive therapies should improve outcome.

Exercise electrocardiography and thallium scanning (myocardial perfusion scan) were performed a mean of 24 days after uncomplicated acute myocardial infarction in 103 patients.  The patients aged 36 to 60 years, who also underwent coronary angiography. The purpose of the study was to determine the ability of the noninvasive tests to predict multivessel coronary artery disease (CAD). The patients were followed up to document medical complications (incidence 12%: 3 deaths, 1 resuscitated cardiac arrest, 4 recurrent infarctions, 4 admissions with unstable angina) and combined events (medical events or bypass surgery, incidence 23%). The sensitivity, specificity, predictive accuracy for predicting multivessel CAD were 64%, 77% and 64% for a positive exercise electrocardiographic (ECG) response, 64%, 88% and 80% for a remote thallium defect, and 42%, 96% and 88% for a combination of the two tests. With two tests yielding negative findings the probability of multivessel CAD was 13%. No variable (positive exercise ECG response, remote thallium defect and presence of multivessel CAD) predicted medical events, although there were non-significant trends to more events in patients with any of those findings. The relative risk of combined events was 2.5 (p less than 0.05) for a positive exercise ECG response; 1.8 (NS) for a remote thallium defect; 2.6 (p less than 0.05) for multivessel CAD; and 3.1 (p less than 0.025) for both positive ECG response and remote defect. A combination of exercise electrocardiography and thallium scanning (myocardial perfusion scan) early after acute myocardial infarction helps to identify subsets of patients with high and low probabilities of multivessel CAD and combined medical or surgical events.

Thallium-201 myocardial perfusion imaging; Comparative sensitivity to electrocardiography in coronary artery disease

The sensitivity of myocardial perfusion imaging (MPI) with help of thallium- 201 injected both at rest and during peak exercise was compared to simultaneously recorded 12 lead electrocardiography (ECG) for the purpose of detection of transient ischemia in 20 normal subjects and 63 patients with coronary artery disease (CAD). No perfusion defects or ECG changes were seen as such on either the rest or exercise studies  in any of the normal subjects. Fifty-six percent of patients with CAD developed new perfusion defects with exercise compared to 38% who showed signs of ischemic ST-segment depression (P less than 0.02).

However, when chest pain and/or ST depression were regarded indices of ischemia, the sensitivity of exercise testing and thallium - 201 MPI was similar. The increased sensitivity of MPI compared to ST-segment depression on the ECG was as a result of patients with baseline ECG  abnormalities and those who never achieved 85% of predicted maximum heart rate with exercise. Analysis of the exercise results according to the extent of coronary artery disease revealed a rapid increase in both positive ECGs and MPI with the number of vessels involved. In the patients with only one vessel disease, the MPI was more sensitive than the ECG (P less than 0.02).

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