Office of Educational Affairs, IU School of Medicine

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Browsing Office of Educational Affairs, IU School of Medicine by Author "Adams, David"

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    Skin Sympathetic Nerve Activity as a Biomarker for Syncopal Episodes during a Tilt Table Test
    (Elsevier, 2020-05) Kumar, Awaneesh; Wright, Keith; Uceda, Domingo E.; Vasallo, Peter A., III.; Rabin, Perry L.; Adams, David; Wong, Johnson; Das, Mithilesh; Lin, Shien-Fong; Chen, Peng-Sheng; Everett, Thomas H., IV.; Medicine, School of Medicine
    Background: Autonomic imbalance is the proposed mechanism of syncope during a tilt table test (TTT). We have recently demonstrated that skin sympathetic nerve activity (SKNA) can be noninvasively recorded using electrocardiographic electrodes. Objective: The purpose of this study was to test the hypothesis that increased SKNA activation precedes tilt-induced syncope. Methods: We studied 50 patients with a history of neurocardiogenic syncope undergoing a TTT. The recorded signals were band-pass filtered at 500-1000 Hz to analyze nerve activity. Results: The average SKNA (aSKNA) value at baseline was 1.38 ± 0.38 μV in patients without syncope and 1.42 ± 0.52 μV in patients with syncope (P = .77). On upright tilt, aSKNA was 1.34 ± 0.40 μV in patients who did not have syncope and 1.39 ± 0.43 μV in patients who had syncope (P = .65). In all 14 patients with syncope, there was a surge of SKNA before an initial increase in heart rate followed by bradycardia, hypotension, and syncope. The peak aSKNA immediately (<1 minute) before syncope was significantly higher than baseline aSKNA (2.63 ± 1.22 vs 1.39 ± 0.43 μV; P = .0005). After syncope, patients were immediately placed in the supine position and aSKNA dropped significantly to 1.26 ± 0.43 μV; (P = .0004). The heart rate variability during the TTT shows a significant increase in parasympathetic tone during syncope (low-frequency/high-frequency ratio: 7.15 vs 2.21; P = .04). Conclusion: Patients with syncope do not have elevated sympathetic tone at baseline or during the TTT except immediately before syncope when there is a transient surge of SKNA followed by sympathetic withdrawal along with parasympathetic surge.