Sympathetic Outflow And Exercise Capacity Vary According To Etiology In Heart Failure

Abstract

We previously found that muscle sympathetic nerve activity (MSNA) is inversely related to peak oxygen uptake (VO2peak) in heart failure patients (HF). However, HF patients of ischemic etiology (ICM), who are reported to have a lower VO2peak(Clarke et. al. 1997), have similar MSNA as those with non-ischemic dilated cardiomyopathy patients (DCM) (Grassi et. al. 2001). Nevertheless, the sympathetic component of heart rate variability (HRV) is increased in ICM compared with DCM (Malfatto et.al.2001). PURPOSE We examined whether exercise capacity and sympathetic outflow in HF patients would differ according to etiology. METHODS We studied 29 treated heart failure patients, 12 of ischemic (mean age 54±SE 2 years) and 17 of non-ischemic dilated etiology (47±4) and 23 age-matched healthy normal subjects (N)(47±3 years). Left ventricular systolic dysfunction was similar in both HF etiology groups (LV ejection fraction of 22±3 % for ICM vs 24±3 % for DCM). VO2peakwas determined by open circuit spirometry during continuously ramped graded cycling (15 W/min) to peak effort. On a separate day, MSNA in the peroneal nerve was assessed by microneurography and HRV was measured concurrently using coarse-graining spectral analysis. RESULTS All groups had significantly different absolute VO2peak(p < 0.001) with ICM lower than DCM (p < 0.05) and both lower than N (p < 0.05). MSNA burst frequency and incidence were significantly different between groups (p < 0.001) with ICM higher (59±4 burst/min)) than DCM (47±3 burst/min) (p < 0.05) and both higher than N (35±3 burst/min) (p < 0.05). HRV parameters did not differ significantly between ICM and DCM. Total spectral power in both HF groups were lower than N (p < 0.05) as expected and the low frequency component was lower in DCM only compared with N (p < 0.05). CONCLUSION In contrast to previous work, sympathetic outflow to skeletal muscle is indeed augmented in ICM compared with DCM, which may contribute to their reduced exercise tolerance and presumed increased response to exercise training. Etiology of heart failure should be considered when examining sympathetic response and exercise intolerance in heart failure. Supported by the Heart and Stroke Foundation of Ontario.