Usefulness of isoproterenol during atrial fibrillation in evaluation of asymptomatic Wolff-Parkinson-White pattern.

The asymptomatic individual with a Wolff-Parkinson-White (WPW) pattern is considered at risk for ventricular fibrillation if a rapid ventricular response (shortest RR interval less than or equal to 250 ms) is observed during induced atrial fibrillation (AF) in the laboratory. It has been suggested that isoproterenol administration during AF may more accurately define the patient at risk. Consequently, the effect of isoproterenol on ventricular response during AF was studied in 21 asymptomatic individuals with WPW pattern to assess the potential of isoproterenol to identify patients at risk for sudden death. An electrophysiologic study that included elective induction of AF was performed. The shortest and mean RR intervals between 2 consecutive preexcited and normal QRS complexes, the average RR interval and the proportion of preexcited QRS complexes were measured in the control state and after bolus injections of isoproterenol (0.5, 1.0, 2.0 and 4.0 micrograms) during AF. Both atrioventricular nodal and accessory pathway conductions were enhanced proportional to isoproterenol dose. Isoproterenol had a greater effect on the atrioventricular node, as reflected by significantly greater changes in the shortest RR between normal complexes (339 +/- 70 vs 255 +/- 21 ms, mean +/- standard deviation, p less than 0.001) than the shortest RR between preexcited complexes (264 +/- 39 vs 219 +/- 34 ms, p less than 0.001) and a decrease in percentage of preexcited complexes (65 +/- 37 vs 50 +/- 33%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)