This is a substudy of the ASSUAGE trial ( NCT01250496 ) ; a double-blinded , randomized , placebo-controlled clinical trial which investigated the attenuation of regadenoson-related adverse effects using 75 mg of intravenous aminophylline vs placebo , administered 90 seconds following ( 99m ) Tc-tetrofosmin injection in patients undergoing regadenoson stress SPECT-MPI .