PRETREATMENT WITH THEOPHYLLINE DOES NOT AFFECT ADENOSINE-INDUCED TL-201 MYOCARDIAL IMAGING

This study was designed to evaluate the effects of intravenous theophy lline given before intravenous adenosine for thallium-201 imaging. Six teen patients with known reversible thallium-201 defects were randomiz ed to a double-blind crossover study of a 45-minute infusion of placeb o or theophylline (given as the ethylenediamine salt, aminophylline, m ean concentration 16.1 mg/L) before adenosine thallium-201 imaging. Ad enosine was infused for 6 minutes at a rate of 140 mug/kg/min. Thalliu m-201 (2.5 to 3.0 mCi) was administered after 3 minutes of infusion. B lood pressure, heart rate, symptoms, and the electrocardiogram were mo nitored continuously. Planar thallium-201 imaging was obtained in thre e standard views and was interpreted using blinded segmental analysis and computerized quantitation. Systolic and diastolic blood pressure a t baseline and during adenosine administration were similar following treatment with theophylline and placebo. The increase in heart rate ob served during adenosine infusion was significantly reduced by theophyl line pretreatment. Adenosine-induced symptoms (both cardiac and noncar diac) as well as ischemic electrocardiographic changes were significan tly reduced after theophylline infusion (p < 0.05). In one patient, Mo bitz type II heart block seen during adenosine infusion following plac ebo was absent with theophylline pretreatment. The size of adenosine-i nduced thallium-201 defects was unchanged by theophylline infusion usi ng either segmental analysis (8 +/- 4 vs 9 +/- 5) or a computerized sc ore (47 +/- 27 vs 45 +/- 21). Despite reduction in both symptoms and i schemic electrocardiographic changes, theophylline does not alter thal lium-201 imaging following intravenous adenosine infusion.