Resting muscle sympathetic nerve activity,cardiac metaiodobenzylguanidine uptake,and exercise tolerance in patients with left ventricular dysfunction

Background  Sympathetic nerve overactivity and reduced exercise tolerance are characteristic features of patients with heart failure. However, to what extent sympathetic nerve overactivity contributes to limiting exercise tolerance has not been clearly defined. Methods  Myocardial iodine 123-metaiodobenzylguanidine (MIBG) scintigraphy, muscle sympathetic nerve activity (MSNA), and cardiopulmonary exercise testing were performed within 3 days in 30 patients with left ventricular dysfunction (LVD). Cardiac sympathetic nerve activity was estimated using H/M ratio and washout rate (WR) of 123I-MIBG imaging. MSNA was recorded by microneurography. Results  The patients with peak VO₂ < 20 mL/minute/kg (group II, n = 15) had significantly higher MSNA and WR, and lower H/M ratio than those with peak VO₂ ≧ 20 mL/minute/kg (group I, n = 15) (P < .05). Peak VO₂ had negative correlations with MSNA and WR (r = 0.58, 0.56), and positive correlations with early H/M ratio and delayed H/M ratio (r = 0.71, 0.75) in group II. Moreover, MSNA had negative correlations with early H/M ratio and delayed H/M ratio (r = 0.78, 0.66), and a positive correlation with WR (r = 0.79) in group II. However, similar relations were not found in group I. Conclusions  A link between cardiac and peripheral sympathetic nerve activities contributed to limiting exercise tolerance in patients with LVD patients and reduced exercise tolerance. See related editorial, doi: