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1.
Am Heart J ; 126(5): 1077-83, 1993 Nov.
Article in English | MEDLINE | ID: mdl-8237748

ABSTRACT

This study was designed to evaluate the effects of intravenous theophylline given before intravenous adenosine for thallium-201 imaging. Sixteen patients with known reversible thallium-201 defects were randomized to a double-blind crossover study of a 45-minute infusion of placebo or theophylline (given as the ethylenediamine salt, aminophylline, mean concentration 16.1 mg/L) before adenosine thallium-201 imaging. Adenosine was infused for 6 minutes at a rate of 140 micrograms/kg/min. Thallium-201 (2.5 to 3.0 mCi) was administered after 3 minutes of infusion. Blood pressure, heart rate, symptoms, and the electrocardiogram were monitored continuously. Planar thallium-201 imaging was obtained in three standard views and was interpreted using blinded segmental analysis and computerized quantitation. Systolic and diastolic blood pressure at baseline and during adenosine administration were similar following treatment with theophylline and placebo. The increase in heart rate observed during adenosine infusion was significantly reduced by theophylline pretreatment. Adenosine-induced symptoms (both cardiac and noncardiac) as well as ischemic electrocardiographic changes were significantly reduced after theophylline infusion (p < 0.05). In one patient, Mobitz type II heart block seen during adenosine infusion following placebo was absent with theophylline pretreatment. The size of adenosine-induced thallium-201 defects was unchanged by theophylline infusion using either segmental analysis (8 +/- 4 vs 9 +/- 5) or a computerized score (47 +/- 27 vs 45 +/- 21). Despite reduction in both symptoms and ischemic electrocardiographic changes, theophylline does not alter thallium-201 imaging following intravenous adenosine infusion.


Subject(s)
Adenosine , Coronary Disease/diagnostic imaging , Premedication , Thallium Radioisotopes , Theophylline/pharmacology , Adenosine/pharmacology , Aged , Blood Pressure/drug effects , Coronary Disease/physiopathology , Double-Blind Method , Electrocardiography/drug effects , Female , Heart/diagnostic imaging , Heart Rate/drug effects , Humans , Image Processing, Computer-Assisted , Male , Middle Aged , Radionuclide Imaging
2.
J Am Coll Cardiol ; 21(5): 1075-9, 1993 Apr.
Article in English | MEDLINE | ID: mdl-8459060

ABSTRACT

OBJECTIVES: Theophylline has been shown to delay the onset of myocardial ischemia and to prolong exercise duration. The present study was done to evaluate the mechanisms and actions of intravenous theophylline on the onset of ischemia and exercise duration. BACKGROUND: The ischemic threshold may be altered by the differential coronary vasodilation induced by endogenous adenosine. Theophylline is a competitive receptor antagonist of adenosine and may have a potential as an anti-ischemic medication. METHODS: A double-blind, placebo-controlled crossover trial using an infusion of intravenous theophylline (8.0 +/- 2.0 mg/liter) or placebo before exercise in 12 patients was done. Oxygen uptake, heart rate, blood pressure and heart rate-blood pressure product were determined at the onset of > or = 0.1-mV ST segment depression and angina pectoris, as well as at peak exercise. The extent of myocardial ischemia was evaluated by electrocardiographic criteria and quantitation of thallium-201 images at peak exercise. RESULTS: When compared with placebo, theophylline significantly delayed time to the onset of exercise-induced ischemia. Ischemia occurred at a higher heart rate-blood pressure product and oxygen uptake. Exercise duration was prolonged but was not associated with greater ischemia, as determined by oxygen uptake, ST segment depression, angina pectoris and size of thallium-201 defect. CONCLUSIONS: It is concluded that theophylline favorably alters myocardial ischemia not only by delaying its onset but also by enabling it to occur at a higher threshold without causing deleterious effects during exercise. The mechanism for the increased ischemic threshold may be through the inhibition of adenosine and the coronary steal phenomenon.


Subject(s)
Myocardial Ischemia/drug therapy , Theophylline/therapeutic use , Blood Pressure/drug effects , Double-Blind Method , Electrocardiography , Exercise , Heart/diagnostic imaging , Heart Rate/drug effects , Humans , Infusions, Intravenous , Male , Myocardial Ischemia/diagnosis , Myocardial Ischemia/etiology , Oxygen Consumption/drug effects , Radionuclide Imaging , Theophylline/administration & dosage , Theophylline/pharmacology , Treatment Outcome
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