title: Cardiac resynchronization therapy upregulates cardiac autonomic control.
abstract: OBJECTIVE
  To determine the effect of cardiac resynchronization therapy (CRT) on sympathetic nervous function in heart failure (HF).
  
  
  BACKGROUND
  Neurohormonal dysregulation and cardiac autonomic dysfunction are associated with HF and contribute to HF progression and its poor prognosis. We hypothesized that mechanical resynchronization improves cardiac sympathetic function in HF.
  
  
  METHODS
  Sixteen consecutive patients receiving CRT for advanced cardiomyopathy and 10 controls were included in this prospective study. NYHA class, 6-minute walk distance, echocardiographic parameters, plasma norepinephrine (NE) were assessed at baseline, 3-month and 6-month follow-up. Cardiac sympathetic function was determined by (123)iodine metaiodobenzylguanidine ((123)I-MIBG) scintigraphy and 24-hour ambulatory electrocardiography.
  
  
  RESULTS
  Along with improvement in NYHA class (3.1 +/- 0.3 to 2.1 +/- 0.4, P < 0.001) and LVEF (23 +/- 6% to 33 +/- 12%, P < 0.001), delayed heart/mediastinum (H/M) (123)I-MIBG ratio increased significantly (1.8 +/- 0.7 to 2.1 +/- 0.6, P = 0.04) while the H/M (123)I-MIBG washout rate decreased significantly (54 +/- 25% to 34 +/- 24%, P = 0.01) from baseline to 6-month follow-up. The heart rate variability (HRV) measured in SD of normal-to-normal intervals also increased significantly from baseline (82 +/- 30 ms) to follow-up (111 +/- 32 ms, P = 0.04). The improvement in NYHA after CRT was significantly associated with baseline (123)I-MIBG H/M washout rate (r = 0.65, P = 0.03). The improvement in LVESV index was associated with baseline (123)I-MIBG delayed H/M ratio (r =-0.67, P = 0.02) and H/M washout rate (r = 0.65, P = 0.03).
  
  
  CONCLUSIONS
  After CRT, improvements in cardiac symptoms and LV function were accompanied by rebalanced cardiac autonomic control as measured by (123)I-MIBG and HRV.
authors.affiliation: Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA. cha.yongmei@mayo.edu
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Cha
authors.forename: Jae
authors.initials: J
authors.lastname: Oh
authors.forename: Chinami
authors.initials: C
authors.lastname: Miyazaki
authors.forename: David L
authors.initials: DL
authors.lastname: Hayes
authors.forename: Robert F
authors.initials: RF
authors.lastname: Rea
authors.forename: Win-Kuang
authors.initials: WK
authors.lastname: Shen
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Asirvatham
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Kemp
authors.forename: David O
authors.initials: DO
authors.lastname: Hodge
authors.forename: Peng-Sheng
authors.initials: PS
authors.lastname: Chen
authors.forename: Panithaya
authors.initials: P
authors.lastname: Chareonthaitawee
mesh_terms: D019797:3-Iodobenzylguanidine; D000368:Aged; D001341:Autonomic Nervous System / Q000503:physiopathology*; D017147:Defibrillators, Implantable; D015716:Electrocardiography, Ambulatory; D005246:Feedback; D005260:Female; D006333:Heart Failure / Q000175:diagnosis / Q000503:physiopathology* / Q000517:prevention & control*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009638:Norepinephrine / Q000097:blood*; D019275:Radiopharmaceuticals; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology* / Q000517:prevention & control*
chemical_list: D019275:Radiopharmaceuticals; D019797:3-Iodobenzylguanidine; D009638:Norepinephrine