Sinoventricular conduction is a rare form of cardiac conduction in which the sinoatrial node generates an impulse that is conducted to the atrioventricular node (AV node) in the absence of the right atrium contracting. This is the physiological proof for the presence of the internodal tracts, which have not been clearly demonstrated histologically. On electrocardiogram (ECG), there will be no P wave due to the inactivation of the atrial muscles.

Reference
Wiki: Atrial standstill