Stress testing can also be performed in conjunction with perfusion imaging. A perfusion scan is an indirect method of tracking blood flow to the myocardium or heart muscle both at rest and during exercise.
To perform the scan a radioactive tracer is injected into an arm vein. The tracer travels through the blood and into the heart muscle. As the tracer courses through the coronary circulation, the amount of the tracer absorbed by the myocardium is proportional to the amount of blood it receives and the amount of myocardium that is undamaged or viable. Areas of the myocardium that may not be getting enough blood or may have been damaged by a heart attack do not absorb the tracer and thus appear darker.
Two sets of images may be taken as part of a cardiac perfusion scan. One set is taken after exercise or after having been given a medication that increases blood flow through the coronary arteries.  The other set is taken while at rest.  Both sets of images are then compared with one another.
This test is frequently performed to determine whether CAD maybe causing chest pain. In patients known to have CAD, it can be done to monitor treatment, identify which arteries are involved, and determine the extent of the myocardium affected and resulting risk to the patient.  It may also be done after a heart attack to see if areas of the heart are not getting enough blood or to find out how much myocardium has been irreversibly damaged.
How Is It Done
The test is done by a doctor and technologist trained in nuclear cardiology.  The scanning itself is painless except for stinging or burning sensation discomfort when a needle is inserted into the vein. Lying still for an extended period of time on the table during the scans may also be uncomfortable.
Abraham Salacata, MD, FACC