title: Cardiac iodine-123-metaiodobenzylguanidine scintigraphy may be useful to identify pathologic from physiologic sinus bradycardia.
abstract: BACKGROUND
  Sinus bradycardia includes pathologic sick sinus syndrome (SSS) and physiologic bradycardia such as athletes' heart. Pacemaker implantation is indicated for patients with symptomatic SSS; however, the indication remains difficult to determine in those with mild and/or unspecific symptoms. The sympathetic tone is increased in response to reduced cardiac output in SSS, whereas excessive vagal tone has been seen in physiological bradycardia. We sought to determine if cardiac iodine-123-metaiodobenzylguanidine scintigraphy (123I-MIBG) was useful in differentiating pathologic from physiologic sinus bradycardia.
  
  
  METHODS
  Twenty consecutive patients presenting with continuous sinus bradycardia (heart rate of <50 beats/min) in our outpatient clinic (male, eight patients; age, 70 ± 12 years old) were enrolled. The indication for a pacemaker implantation was determined by an experienced electrophysiologist in compliance with the international guidelines. The sympathetic nervous tone was assessed by cardiac123I-MIBG.
  
  
  RESULTS
  Eight patients (40%) were clinically diagnosed as SSS (type I) including four suffering from obvious symptoms (syncope or dizziness) and four suffering from mild symptoms (fatigue), and had an indication for a pacemaker implantation. The patients with SSS indicated for a pacemaker implantation had a lower early heart-to-mediastinum ratio (2.0 ± 0.6 vs 2.5 ± 0.2, P = 0.043), lower delayed heart to mediastinum ratio (2.0 ± 0.8 vs 2.8 ± 0.3, P = 0.026), and higher washout rate (34 ± 6.0 vs 26 ± 6.0, P = 0.008) than those without.
  
  
  CONCLUSIONS
  Excessive sympathetic tone detected by123I-MIBG may serve as an adjunct to determine the indication for a pacemaker implantation in sinus bradycardia.
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Akihiro
authors.identifier: http://orcid.org/0000-0003-2590-6696
authors.initials: A
authors.lastname: Sunaga
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Masaharu
authors.identifier: http://orcid.org/0000-0002-5566-466X
authors.initials: M
authors.lastname: Masuda
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Fujita
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Iida
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Kanda
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Matsuda
authors.affiliation: Ohara Internal medicine and cardiology Clinic, Hyogo, Japan.
authors.forename: Takakazu
authors.initials: T
authors.lastname: Morozumi
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Mano
authors.affiliation: Kansai Rosai Hospital Cardiovascular Center, Hyogo, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Uematsu
mesh_terms: D019797:3-Iodobenzylguanidine; D000368:Aged; D001919:Bradycardia / Q000175:diagnosis* / Q000517:prevention & control*; D057791:Cardiac Imaging Techniques / Q000379:methods*; D000066491:Clinical Decision-Making / Q000379:methods*; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D010138:Pacemaker, Artificial; D011300:Preoperative Care / Q000379:methods; D011877:Radionuclide Imaging / Q000379:methods*; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine
keywords: bradycardia; cardiac scintigraphy; iode-123-metaiodobenzylguanidine; sick sinus syndrome