Four- versus 6-minute infusion protocol for adenosine thallium-201 single photon emission computed tomography imaging

Intravenous adenosine infusion results in immediate maximal coronary arteriolar vasodilatation. Side effects occur in most patients who receive adenosine. For these reasons, a shorter infusion for pharmacologic stress thallium-201 testing may improve patient tolerability without compromising diagnostic accuracy. In a retrospective, unblinded evaluation, we compared side effects and accuracy of a standard 6-minute adenosine infusion single photon emission computed tomography (SPECT) study with a 4-minute protocol in 730 and 621 patients, respectively. Adenosine was infused at 140 μg/kg/minute in both groups; thallium-201 was injected at the 3-minute mark oof the 4-minute protocol and at the 4-minute mark of the 6-minute protocol. Angiographic follow-up (mean 8 days) after thallium-201 testing was available in 233 (32%) of the patients in the 6-minute protocol and in 174 (28%) of the patients in the 4-minute protocol (p not significant (NS). Side effects occurred in 90% of the patients in the 6-minute protocol and in 91% of the patients in the 4-minute protocol (p = NS). Premature termination of the infusion was required in 4% of the patients in the 6-minute protocol and 2% of the patients in the 4-minute protocol (p = 0.02). Second- or third-degree atrioventricular block was noted in 4.5% and 3.0% of the 6- and 4=minute groups, respectively (p = NS). The duration of symptoms averaged 2.9 ± 4.4 minutes in the patients in the 6-min protocol and 2.1 ± 1.6 minutes in the patients in the 4-minute protocol (p < 0.05). Diagnostic accuracies of the two protocols were virtually identical: 93% for the 6-minute versus 92% for the 4-minute protocol (p = NS). Correct localization of disease in the three major epicardial coronary distributions was equivalent with the two protocols. In conclusion, the four-minute adenosine SPECT protocola was as accurate as and was better tolerated and safer than the traditional 6-minute protocol.