Comparison of muscle sympathetic activity in ischemic and nonischemic heart failure.
BACKGROUND
The magnitude of sympathetic activation in chronic heart failure is assumed to be independent of its cause. However, because a higher sympathetic component of heart rate variability (HRV) in patients with ischemic cardiomyopathy (ICM) has been reported, we hypothesized that patients with ICM would have a higher resting muscle sympathetic nerve activity (MSNA) than patients with nonischemic dilated cardiomyopathy (DCM).


RESULTS
Resting MSNA was assessed by microneurography and HRV concurrently by coarse-graining spectral analysis in 30 treated normotensive patients with chronic heart failure (12 with ICM and 18 with DCM), matched for age and left ventricular ejection fraction, and 23 healthy normal control subjects, matched for age and blood pressure. Peak oxygen uptake was determined during graded cycling (17 W/min) to maximum effort. MSNA was significantly different between groups (P < .001; ICM 60 +/- 3; DCM 47 +/- 3; control subjects 35 +/- 3 bursts/min). Compared with control subjects, the total spectral power and the high-frequency component of HRV were lower in both ICM and DCM groups, but fractal and low-frequency power were lower only in the ICM group (P < .05). Peak oxygen uptake (milliliters per kilogram of body weight per minute) was significantly less in the ICM group than in the DCM group (P = .04) and lower in both groups than in the control subjects (P < .001).


CONCLUSIONS
These observations suggest an additional ischemic stimulus to sympathetic activation in heart failure, which may impair exercise capacity reflexively.
Notarius
Catherine F
CF
Toronto General Research Institute, Toronto, Ontario, Canada.
Spaak
Jonas
J
Morris
Beverley L
BL
Floras
John S
JS
D004558:Electric Stimulation; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D015637:Gated Blood-Pool Imaging; D006333:Heart Failure / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008839:Microelectrodes; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000378:metabolism / Q000503:physiopathology; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000503:physiopathology*; D010101:Oxygen Consumption; D010543:Peroneal Nerve / Q000503:physiopathology; D012720:Severity of Illness Index; D013147:Spirometry; D013318:Stroke Volume / Q000502:physiology; D017779:Sympathetic Fibers, Postganglionic / Q000503:physiopathology*; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology*