Single Tc99m Sestamibi injection, double acquisition gated SPECT after stress and during low-dose dobutamine infusion: a new suggested protocol for evaluation of myocardial perfusion.

BACKGROUND: The ability of low dose dobutamine (LDD) has been established in exploiting the reserved contractility of ischemic myocardium. This study was designed to assess the value of a new protocol, with an additional stress imaging during LDD infusion instead of the rest images, for evaluation of coronary artery disease (CAD) and perfusion reversibility.
METHODS: A total of 51 patients (42 men, 9 women; 57.2 +/- 11.3 years) were included in the study and underwent three sequential steps of imaging; the first step-stress gated SPECT with Tc-99m sestamibi, immediately followed by the second step-gated SPECT during constant infusion of 7.5 microg/kg/min dobutamine and finally the third step-rest phase scan following trinitroglycerine administration in the next day. The findings were interpreted using the images in three sets of display; first vs. second step-single injection-double acquisition gated SPECT before and during LDD (SIDAGS-LDD), first vs. third step-standard stress/rest protocol, and only first step-gated stress-only SPECT. In all cases, the Visual perfusion index of each protocols were calculated by summating the premeditated 5-point scale (5: normal, 4: completely reversible, 3: partially reversible, 2: nontransmural fixed and 1: transmural fixed defects) of 17 standard myocardial segments. The accuracy as well as the correlation and agreement of protocols for detecting perfusion abnormality and corresponding reversibility were statistically analyzed.
RESULTS: Calculated sensitivity, specificity, positive predictive value, negative predictive value and accuracy regarding the presence of CAD in both SIDAGS-LDD and standard protocols were 90.9% (40/44), 71.4% (5/7), 95.2% (40/42), 55.6% (5/9) and 88.2% (45/51), respectively. The extent and localization of perfusion abnormality with the new protocol were correlated well with standard method. The estimation of reversibility, however, was considerably improved by SIDAGS-LDD, especially in those with history of previous myocardial infarction (MI).
CONCLUSION: Our proposed protocol demonstrates good correlation and agreement with standard method and even is superior in some cases especially for estimation of viability after MI. Regarding no need for the rest phase radiotracer injection and imaging, this protocol can be more convenient (except the need for close monitoring of the patient during LDD infusion), less time-consuming, less expensive and moreover with less radiation burden to the patients and personnel.