Abstract 19783: The Impact of Cardiac Sympathetic Nerve Activity Evaluated by Cardiac I-123 Metaiodobenzylguanidine Scintigraphy on the Chronotropic Incompetence

Introduction: Chronotropic incompetence (CI), defined as the inability of the heart to increase its rate commensurate with increased activity, produces exercise intolerance, and is an independent predictor of overall mortality. Cardiac sympathetic nerve (SNS) activity has been suggested to have a relation to CI. However, the mechanisms for CI have not been fully elucidated. Thus, we investigated the cardiac SNS activity in patients with CI using cardiac I-123 metaiodobenzylguanidine (MIBG) scintigraphy. Methods: Sixteen patients with CI and 17 subjects who served as controls were enrolled in this study (age 77.5±9.2years; male 57.6%). Patients with CI were defined as who were implanted with pacemaker due to sick sinus syndrome. Results: There were no significant differences in age, sex, or left ventricular ejection fraction (66.3±14.3 vs 58.3±22.2%, ns) between patients with CI and controls. Plasma BNP level was also similar between two groups (79.0[IQR, 41.0-175.3] vs 90.9[IQR, 35.5-185.3]pg/mL, ns). The delayed heart/mediastinum (H/M) ratio was significantly higher in patients with CI than in controls (2.3±0.3 vs 2.0±0.4%, p=0.04). The early H/M ratio did not differ between two groups. The washout rate (WR) was significantly lower in patients with CI compared with that in controls (20.2±11.2 vs 33.3±14.1%, p=0.006). Conclusions: Decreased cardiac sympathetic nerve activity was associated with CI, and I-123 MIBG scintigraphy may be a useful modality for understanding the mechanism for CI.