Evidence of a selective increase in cardiac sympathetic activity in patients with sustained ventricular arrhythmias

Ventricular tachyarrhythmia (erratic beating of the left ventricle, the heart chamber that pumps blood to the body) is a common cause of sudden cardiac death. Although the cause of sudden cardiac death is not clear, most affected patients also have coronary artery disease and poor left ventricular function. Patients with impaired left ventricles and ischemic heart disease (reduced heart circulation) often show abnormal ventricular rhythms on ambulatory electrocardiograms, and they are more likely to die of sudden cardiac death. One of the functions of the sympathetic nervous system is to regulate the heart, and it is suggested that there is a relationship between cardiac sympathetic activity and ventricular arrhythmia. To quantify sympathetic nervous activity in the hearts of high-risk patients, 10 men and 2 women who had an episode of life-threatening heart rhythm disturbance during the previous seven weeks were studied. Radiotracer kinetic techniques (methods of measuring a substance in the blood using radioactive isotopes) were used to trace norepinephrine, an adrenal hormone that regulates the sympathetic nervous system. An almost five-fold increase in cardiac norepinephrine spillover into the bloodstream was found, providing evidence of long-lasting activation of the sympathetic nervous system in these patients. Whether such a measurement will be useful in predicting which patients are at greatest risk has not been determined. (Consumer Summary produced by Reliance Medical Information, Inc.)