Adverse consequences of high sympathetic nervous activity in the failing human heart

In view of previous experimental evidence relating sympathetic nervous overactivity in the heart to myocardial necrosis and ventricular arrhythmias, we prospectively examined the hypothesis that heightened cardiac sympathetic nervous activity is associated with an adverse outcome in patients with moderate to severe heart failure.

Despite recent therapeutic advances, patients with heart failure continue to have high mortality from progressive hemodynamic decompensation and lethal ventricular arrhythmias. It is believed that initially compensatory increases in sympathetic nervous system activity may ultimately be maladaptive, potentially contributing to subsequent adverse events.

Sixty patients with moderate to severe heart failure (left ventricular ejection fraction 18.9 +/- 0.9% [mean +/- SE]) were studied prospectively. In addition to the compilation of a hemodynamic, biochemical and electrocardiographic profile for each patient, whole-body and cardiac sympathetic activity were determined by isotope dilution. The relation of these variables to outcome was determined by Cox proportional hazards analysis.

The mean follow-up period of the study group was 7 +/- 1 months (range 1 to 24) with a 12-month actuarial survival of 75%. Deaths (14 in all) were accounted for either by sudden death or progressive heart failure in equal numbers. The rate of release of norepinephrine from the heart was significantly higher in patients with heart failure than in healthy subjects (402 +/- 37 vs. 105 +/- 19 pmol/min, p < 0.01), although the values for heart failure ranged widely from normal to 10 times normal. By univariate Cox proportional hazards analysis, pulmonary capillary wedge pressure (p < 0.01), mean pulmonary artery pressure (p < 0.001), serum sodium levels (p < 0.01) and cardiac norepinephrine spill-over rate (p < 0.001) were identified as significant prognostic markers. In a multivariate analysis, cardiac norepinephrine spillover rate was identified as the most powerful prognostic marker (p = 0.0006) of those evaluated in this study.

These results suggest that activation of the sympathetic nervous system in patients with heart failure, specifically the cardiac sympathetic nerves, may contribute to the poor prognosis associated with severe heart failure. The data therefore provide a rationale for the use of drugs such as beta-adrenergic blocking agents in the management of patients with heart failure.