Caffeine Enhances Heart Rate Variability in Middle-Aged Healthy, But Not Heart Failure Subjects.
BACKGROUND
In chronic heart failure (CHF) due to left ventricular dysfunction, diminished heart rate variability (HRV) is an independent predictor of poor prognosis. Caffeine has been shown to increase HRV in young healthy subjects. Such an increase may be of potential benefit to patients with CHF.


OBJECTIVE
We hypothesized that intravenous infusion of caffeine would increase HRV in CHF, and in age-matched healthy control subjects.


METHODS
On two separate days, 11 patients (1F) with CHF (age=51.3±4.6 years; left ventricular ejection fraction=18.6±2.7%; mean±standard error) and 10 healthy control subjects (age=48.0±4.0) according to a double-blind randomization design, received either saline or caffeine (4 mg/kg) infusion. We assessed HRV over 7 minutes of supine rest (fast Fourier Transform analysis) to determine total spectral power as well as its high-frequency (HF) (0.15-0.50 Hz) and low-frequency (LF) (0.05-0.15 Hz) components, and recorded muscle sympathetic nerve activity (MSNA) directly from the peroneal nerve (microneurography).


RESULTS
In healthy control subjects, compared with saline, caffeine reduced both heart rate and sympathetic nerve traffic (p≤0.003) and increased the ratio of HF/total power (p≤0.05). Baseline LF power and the ratio LF/HF were significantly lower in CHF compared with controls (p=0.02), but caffeine had no effect on any element of HRV.


CONCLUSIONS
Caffeine increases cardiac vagal heart rate modulation and reduces MSNA in middle-aged healthy subjects, but not in those with CHF.
Division of Cardiology, University Health Network and Mount Sinai Hospital, University of Toronto , Toronto, ON, Canada .
Catherine F
CF
Notarius
Division of Cardiology, University Health Network and Mount Sinai Hospital, University of Toronto , Toronto, ON, Canada .
John S
JS
Floras