Consecutive administration of atropine and isoproterenol for the evaluation of asymptomatic sinus bradycardia

Sinus node function is commonly evaluated by the atropine test. The isoproterenol test is less used. The aim of this study was to evaluate chronotropic reserve in patients with asymptomatic sinus bradycardia using the combined administration of atropine and isoproterenol.

A total of 100 patients were studied, 18–70 years old, with permanent, asymptomatic, sinus bradycardia and no detectable cardiac disease. The standard administration protocols for atropine and isoproterenol were used and successive heart rate recorded. Patients were stratified into three groups: Group A (control), showing normal response to atropine and isoproterenol; Group B, demonstrating abnormal response to atropine; Group C, with abnormal response to atropine and isoproterenol. No statistically significant difference was observed between Groups A and B ( P = 0.11), whereas Group C differed statistically from both Groups A ( P < 0.000001) and B ( P = 0.000003) to a significant extent. By the end of the 3-year follow-up period, 47% of the Group C patients had undergone permanent pacemaker implantation (DDDR)—Kaplan–Maier survival curves predict only 35% survival without pacing—whereas none did so in Groups A and B.

In patients with deficient chronotropic response to atropine administration, isoproterenol tests could differentiate those with inadequate chronotropic reserves, possibly requiring preventive pacemaker implantations.