Nuclear stress test can detect more than blockages

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Using a nuclear stress test to look at how fast blood flows into the heart's left ventricle can determine if a patient's left ventricle is having trouble, according to a study published in the May issue in the Journal of Nuclear Medicine.

"If someone has a slow fill rate, that means the left ventricle is not relaxed enough to get enough blood," said lead study author Dineshkumar Patel, MD, internal medicine resident from the Medical College of Georgia (MCG) in Augusta, Ga. “And if the left ventricle cannot receive enough blood, then it cannot collect enough blood to be pumped out to the rest of the body. There is a four-fold increase in morbidity and mortality when diastolic dysfunction is present in patients with coronary disease.”

Patel, collaborating with Vincent J.B. Robinson, MD, and a MCG team, examined 52 consecutive patients who underwent cardiac catheterization within 15 days of a nuclear stress test to test the efficacy of a nuclear stress test in diagnosing diastolic dysfunction.

During a nuclear stress test, radioactive thallium is injected into the bloodstream to show how well blood flows to the heart muscle. Scans are taken shortly after an exercise test to show blood flow when the heart is stressed and two or three hours later to show blood flow during rest.

“In addition to the blockages, we have demonstrated that it also shows the left ventricle filling pressure, thus giving us an excellent prognostic value in predicting diastolic dysfunction because when the filling pressure is too high, the left ventricle has a hard time receiving blood,” Patel said.

Patel and the MCG nuclear cardiology research team compared the diastolic filling pressure from the catheterization and from the nuclear stress test, and found that the latter had 94 percent specificity in detecting diastolic dysfunction.

The nuclear stress test plots out a heartbeat in 16 frames, and that represents the diastolic filling curve at 16 points, said study adviser Vincent J.B. Robinson, MD, nuclear cardiologist at MCG and the Charlie Norwood Veterans Affairs Medical Center in Augusta. The slope of the filling portion of the curve is a representation of the left ventricle filling pressure used as a marker of diastolic dysfunction.

"We have discovered that just looking at these markers can tell us whether a patient has diastolic dysfunction or not,” Robinson said. “Previously, the nuclear stress test was only detecting diastolic dysfunction in patients who were already sick, whose hearts were weak and barely pumping."

"In other words, the test only picked up patients who had diastolic and systolic dysfunction," he said. "But now, we can use the diastolic filling curve on a nuclear stress test to diagnose patients with diastolic dysfunction who have normally squeezing hearts."