SPECT imaging boosts flow: Here’s how to use it
March 1, 2000 4 minutes read
SPECT imaging boosts flow: Here’s how to use it
According to a published study, new technology can identify myocardial infarction in chest pain patients in just minutes, says Stephen Stowers, MD of SouthPoint Cardiology in Jacksonville, FL. Single photon emission computed tomography (SPECT) imaging, combined with early exercise stress testing, might lead to reduced in-hospital costs and decreased lengths of stay, he adds.1
SPECT imaging is a diagnostic test used for patients not initially classified at high risk, in addition to echocardiography, exercise stress testing, and cardiac markers. It is similar to a computerized axial tomography scan of the heart, says Stowers. The patient is injected intravenously in the ED with an isotope that goes right into the heart muscle.
"This freezes’ whatever is happening at the time of the injection, even though the patient may be imaged 15 or 30 minutes later," he explains. After the patient is injected, a gamma camera takes X-rays to determine the blood flow in the heart.
The study found that SPECT imaging, combined with early exercise stress testing for assessing intermediate risk patients with chest pain and no electrocardiographic evidence of acute ischemia, leads to earlier discharges, says Eric Eisenstein, DBA, assistant research professor in the department of medicine at Duke Clinical Research Institute, Duke University Medical Center in Durham, NC. "It resolves the physician’s diagnostic dilemma and leads to more discriminate use of coronary angiography," he says.
Currently, the unit dose cost for the injection to perform a SPECT scan is about $60, Stowers says. There is an overall reduction in average costs of care with no adverse clinical outcomes, he maintains. Because length of stay was reduced, median in-hospital costs for patients in the conventional diagnostic strategy were $3,747, compared with $1,254 in the SPECT imaging, he reports.
The costs of implementing the technology depend on whether your facility currently has nuclear imaging, Eisenstein explains. "If so, the additional costs associated with implementing an acute imaging strategy would involve the availability of the imaging agent, training ED physicians, and providing nuclear imaging and exercise stress testing during off hours."
Currently, there is a dependence on cardiac enzymes for determining the presence of myocardial infarction in chest pain patients, says Stowers, principal investigator of a study that showed the benefits of SPECT imaging.
These biochemical markers take up to 10 to 12 hours from onset of symptoms before they become positive, he notes. "It takes time for them to be elevated in the blood. So you have people sitting around waiting for biochemical markers to become positive, which clogs up your ED."
That delays treatment, which can be life-threatening, says Stowers. "People who are having an having an acute MI will be sitting there with an occluded artery. Their enzymes will come back positive from six to eight hours after they present. By that time, it’s usually too late to get any effective relief of their MI."
With a perfusion scan, you can look at what’s actually going on in the patient’s heart, he says. "This is not an indirect marker of damage that we draw from the blood, and it’s not an electrical wave form."
Instead, you are actually looking at the myocardial blood flow at the time you are imaging the patient, Stowers explains. "If there is interruption of the blood flow, you are going to see it."
This technology is a tremendous advance in the diagnosis of acute coronary syndromes because it allows you to pick up the problem immediately, he emphasizes. "The scan is much more sensitive than an electrocardiogram. Because you are getting a direct look at the heart and blood flow at the time you are doing the scan, that allows us to be able to be confident that it’s safe to do an exercise test on that patient immediately and not have to wait."
If the test is positive, then it’s clear that intervention is needed to improve the disrupted blood flow or open up the arteries, he explains. "The scan will allow MI patients to be treated faster. In our study, we only had nine MI patients, but a larger study might be able to demonstrate that early intervention can save lives."
With the SPECT imaging, chest pain patients with a negative scan are discharged from the ED much more quickly, says Stowers, who refers to that as the "4S" approach: see, scan, stress, and street.
The technology will have a significant impact on ED patient flow, he says. "It will free up overcrowding caused by having five or six people waiting around for cardiac enzymes. Those people would be gone."
"If the initial scan is negative, patients would go directly to the treadmill and then home, which could be done in a couple of hours, Stowers says. "If the ED is jammed, this would remove the logjam, by not having these people clog up the ED and also not having to admit all these chest pain patients. You quickly identify the 10% to 15% who would be admitted."
However, for the system to work, your staff need to be committed, he notes. Every hospital has a gamma cam that can perform these scans, but the problem has been a lack of committed staff to come in and read them, he says. "You need staff who are willing to read these scans in the middle of the night and off hours. If you just do this from 9 to 5, it’ s not going to be effective. You need to have the service available for as many hours as possible."
A tech, nurse practitioner, or physician’s assistant can be cross-trained to perform the treadmill test under the supervision of the ED physician, says Stowers. "Then based on a treadmill score, decide whether patient is admitted or not."
Reference
1. Stowers SA, Eisenstein EL, Wackers FJ, et al. An economic analysis of an aggressive diagnostic strategy with single photon emission computed tomography myocardial perfusion imaging and early exercise stress testing in emergency department patients who present with chest pain but nondiagnostic electrocardiograms: Results from a randomized trial. Ann Emerg Med 2000; 35:17-25.
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