The determinant role of arterial hypertension in cardiac rhythm disturbances, both induced by electrical stimulation of the midbrain reticular formation in the cat.

The arrhythmogenic and hypertensive effect of electric stimulation of the midbrain reticular formation (MRF) is known. The aim of the present paper is to demonstrate that the hypertensive effect potentiates the arrhythmogenic effect. Ten semiacute experiments were carried out on curarized cats, stimulating the MRF by stereotoxically implanted electrodes. After stimulation complex cardiac rhythm disturbances developed (consisting in their order of appearance of tachycardia, bradycardia, ventricular extrasystoles and idioventricular paroxysmal tachycardia--IPT), as well as an increase in arterial pressure. IPT always appeared after the increase in arterial pressure reached almost maximum values and disappeared after pressure values fell below this threshold. During the transition period from sinusal rhythm to arrhythmia fusion contractions were observed and in the course of IPT frequent capture phenomena. In all the cases, the frequency of IPT was inferior to that of the control. The correlation coefficient between latency in the onset of IPT and latency in the peak rise in arterial pressure was = +0.840, and between the duration of arrhythmia and the duration of the rise in arterial pressure was = +0.768. In conclusion the increase in arterial pressure produced by stimulation of the MRF represents a definite correlation to the genesis of rhythm disturbances: produced by the same stimulation.