Change of P-Q intervals of the electrocardiogram in the rat hearts sensitized with the killed group A streptococci.

Prolongation of P-Q interval in the anesthetized rat was observed by repeated injection of killed group A streptococci. The prolongation was clearly recognized at about the 11th week after the first injection, but afterwards P-Q interval recovered to the normal level in spite of continuous injection of killed streptococci. His bundle electrogram recorded from isolated heart revealed the prolongation of A-H interval in the treated rat. Moreover, the transmembrane action potential in the atrioventricular nodal region of treated rat was slightly deteriorated, but the action potentials in the other cardiac muscles were not changed. It was deduced from the above results that P-Q prolongation was transiently brought about by the injection of killed group A streptocci and that deterioration of muscle in the atrioventricular nodal region might take a main part in the P-Q prolongation.