“By comparing the redistribution results of technetium-99m sestamibi at five minutes and 60 minutes post stress after a single injection, we can come up with an accurate picture of how much heart disease is present, and with a reduced radiation exposure,” said Richard M. Fleming, MD, in an interview.
Fleming, a cardiologist at the Cardiovascular Institute of Southern Missouri in Poplar Bluffs, Mo., and at the Sierra Nevada Cardiology Associates in Reno, Nev., is the lead author of a study of 120 men and women (between the ages 25-82 years) suspected of having ischemic heart disease, using both the rest/stress image comparisons approach and a one-day redistribution "stress/stress" approach published in the June issue of Federal Practitioner.
Fleming and colleagues noted that rest/stress comparisons are flawed. "The resting image more correctly can be used to determine if myocardial injury has occurred previously, but cannot be utilized to determine if ischemia is present.... Therefore, matching rest/stress images define ischemia present at the site of injury/infarction and not a simplistic absence of ischemia."
They have previously studied the redistribution property of sestamibi, correlating it with the extent of actual coronary artery disease seen in the angiography suite. In this study, they compared sequential stress studies to rest/stress and coronary angiography.
For this study, Fleming and colleagues acquired resting images after IV injection of 9 to 11 mCi (333 to 407 MBq) of sestamibi per protocol. Patients returned to the lab per institution protocol to undergo the stress component of the study where they underwent either treadmill exercise (25 patients) or pharmacologic stress: regadenoson (61 patients), adenosine (30 patients) or dobutamine (four patients).
Patients then received an IV bolus of sestamibi (28 to 32 mCi, 1036 to 1184 MBq) followed by a bolus of normal saline to ensure adequate delivery of the radioactive isotope into the venous system. Five minutes post-stress, a SPECT camera was used to obtain a five-minute image (anterior slice, single-head camera) or images (anterior and lateral slices, multiplehead camera). Fifty-five minutes later (60 minutes post-stress), participants returned to the lab for final images. No additional isotope was used for the final images.
Because sestamibi redistributes, comparison of five- and 60-minute stress images allows the physician to detect ischemia that otherwise would have been missed. "We can compare images either qualitatively or quantitatively using FHRWW [Fleming Harrington Redistribution Washin Washout] to calculate what will be seen in the cardiac cath lab," said Fleming.
"The use of FHRWW can reduce the need to cath people without significant coronary artery disease while correctly sending people to the cath lab who have the most critical (washin) need for intervention. In addition, it requires only a single dose of sestamibi, thereby reducing radiation exposure to the patient," added Fleming.
"FHRWW determination of sestamibi redistribution takes us from asking 'Does the patient have disease?' to 'How much disease does the patient have and how should we treat it?' This is analogous to the questions 'Does the patient have high cholesterol?' to "How high is the patient's cholesterol and how should I treat it?'" he said.
In the study, researchers found no difference in rest/stress image comparisons and FHRWW redistribution between exercise and pharmacologic stress, nor did they find any differences between the various stress agents. "Therefore, institutions with a preference for exercise or pharmacologic stress (regardless of which agent is used) can continue to utilize their preferred approach with the FHRWW method for detecting ischemia," they wrote.
Fleming plans to hold discussions with nuclear camera companies over software development to install FHRWW into computer programs in the future. He also noted that other centers are currently studying FHRWW as the new standard of care.