Supra spinal influence on ventricular fibrillation threshold and cardiac stores of norepinephrine in the cat.
The relationship between ventricular fibrillation threshold (VFT) as measured by voltage required to evoke ventricular fibrillation and the concentration of norepinephrine (NE) in different parts of the myocardium under experimental interventions has been studied in anaesthetized cats. A selective increase in VFT and a marked reduction in NE content have been observed after spinal transection, removal of spinal cord from cervical 6 to thoracic 6 or carotid sinus denervation. Reserpine pretreatment significantly reduces NE content of myocardium but fails to affect VFT. The fibrillating left ventricle shows a marked decline in NE content from the control level of 1.55 +/- 0.32 to 0.82 +/- 0.09 micrograms/g and there is also a similar concomitant reduction in NE content of the entire heart. Defibrillation brings back normal rhythm, but does not restore the NE content immediately. The results suggest that a marked reduction in cardiac stores of norepinephrine significantly affect VFT and that the central nervous system plays an important role in the genesis of sustained ventricular arrhythmia.