The<unk> is a summation wave generated by the depolarization front as it transits the atria. Normally the right atrium depolarizes slightly earlier than left atrium since the depolarization wave originates in the sinoatrial node, in the high right atrium and then travels to and through the left atrium. The depolarization front is carried through the atria along semi-specialized conduction<unk> athways including Bachmann's bundle resulting in uniform shaped waves. Depolarization originating elsewhere in the atria (atrial ectopics) result in<unk>  with a different morphology from normal.
P wave 
J wave
QRS complex
U wave
Delta wave
T wave
ST segment
PR interval