Atropine testing prior to cardioneuroablation: what is a normal result?

Background Substantial acceleration of sinus rhythm after administration of atropine is required in candidates for cardioneuroablation (CNA). This is frequently expressed in the sinus rate (SR) percentage increase. Patients with a value of <25% may have an intrinsic sinus nodal disorder and should not be considered for CNA. However, there is limited data regarding the physiological sinus nodal response to atropine. Purpose We assessed the average response of SR to the atropine depending on baseline clinical factors in patients scheduled for CNA. Methods An atropine test before the CNA was performed in supine rest and consisted of intravenous bolus administration of 0.04 mg/kg atropine sulfate limited to a maximum dose of 2 mg. ECG was recorded immediately prior to and 5 minutes after the injection. Factors significantly associated with the post-atropine SR were investigated by univariate and multivariate linear regression analysis. Results The study included 255 patients aged 40±12 years, 56% men, with baseline SR of 64±14 bpm, post-atropine SR of 107±20 bpm, and relative post-atropine SR increase of +69 ± 30%. Age (P<0.0001), gender (P<0.01), and baseline SR (P<0.0001) were independently associated with post-atropine SR (Figure). A corresponding regression equation was as follows: post-atropine SR (bpm) = 67.5 + 4.5 [if female] – 0.37 * age (years) + 0.87 * baseline SR (bpm). With a realistic range of age and baseline SR, this equation provides a wide range (from +43% to + 107%) of average relative SR increase (examples in Table). Conclusions In suitable CNA candidates, the result of atropine testing is highly variable depending on their trivial clinical characteristics. This should be considered when indicating patients to a CNA.