PET, SPECT measures of LVEF have superior predictive value

ATLANTA - PET and SPECT measurements of left ventricular ejection fraction (LVEF) appear to be a better predictor of mortality than other measures in stress myocardial perfusion imaging (MPI), according to two studies presented at the American College of Cardiology (ACC) meeting.

In the first study, LVEF predicted a 2.5-fold higher one-year mortality than normal stress MPI despite a normal rubidium-82 PET myocardial perfusion study with pharmacologic stress.

Although PET is increasingly used for stress MPI, little data is available regarding specific prognostic factors in PET MPI, said lead author Dr. Bret Rogers, a fellow at the Cleveland Clinic in Ohio.

Rogers and colleagues reviewed more than 4,500 studies of consecutive initial PET scans conducted at their institution, and identified 380 perfusion tests in which a normal result was rendered on PET. They then followed up these normal patients over the next year with mortality data from the U.S. Social Security database for 339 of the patients and LVEF data from the clinic's medical records. All LVEFs were measured by echocardiography or gated stress MPI within six months of the PET scan.

For patients who had a normal PET myocardial perfusion test, the one-year mortality rate was 10 times higher than the rate for patients who had a normal SPECT myocardial perfusion test, Rogers said. The results indicate that a normal PET result might not be that reassuring for physicians managing patients, he said.

Next, the researchers analyzed the diagnostic factors that might predict which normal PET studies might benefit from additional monitoring. They found that impaired LVEF, defined as less than 55% of normal, was associated with a 2.5-fold increase in mortality risk. This more closely mirrored the actual 7.4% mortality at one year found from Social Security records.

"Any LVEF reduction incrementally predicts an increased one-year mortality risk despite normal MPI," Rogers said.

In the second study, researchers led by Dr. Athanasios Kapetanopoulos at the University of Connecticut - Hartford Hospital in Hartford, CT, used technetium-99m exercise and pharmacologic gated SPECT to see if LVEF could be a predictor of future cardiac events. They analyzed records of 8,381 patients in a prospectively gathered database.

Forty-eight percent underwent exercise stress and 52% pharmacologic stress. Of these, 14.5% had a vasodilator with exercise while 27.4% had a vasodilator without exercise and 9.6% had dobutamine stress testing.

Test interpreters were blinded. LV function was classified as preserved if at least 45%, mildly to moderately impaired if between 30% and 44%, and severely impaired if less than 30%.

LV cavity size at stress and rest, as well as the difference between the two, were significantly higher in patients who had a pharmacologic gated SPECT versus exercise gated SPECT. LVEF was significantly lower at 56.6% for pharmacologic compared to 59.8% for exercise SPECT. The annual cardiac death rate was 0.28% for the exercise stress group compared to 1.92% for the pharmacologic stress group.

Both regional and global LV function categories measured by gated SPECT predicted higher annualized cardiac death rate.

"Visual assessment of regional wall motion from gated SPECT is highly effective in risk stratification for cardiac death, even in the subgroup of patients undergoing pharmacologic stress," Kapetanopoulos said.

By Crystal Phend contributing writer
March 13, 2006

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