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 administration of 0.04 mg/kg atropine 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<0.02), and baseline SR (P<0.0001) were independently associated (multivariate R = 0.65) with post-atropine SR change (Figure). A corresponding regression equation was as follows: post-atropine SR change (%) = 179 + 7 [if female] – 0.65*age (years) – 1.35*baseline SR (bpm). With a realistic range of age and baseline SR, this equation provides a wide range (from +39% to + 106%) of average relative SR increase (examples in Table).

Conclusions:  In suitable CNA candidates, the results of atropine testing are highly variable, depending on their trivial clinical characteristics. This should be considered when indicating patients to a CNA. The >25% SR increase after atropine is not a universally applicable criterion of normality.