Kristen Cerio
At rest a myocyte has a negative charge and is called “polarized.” This is represented by the
isoelectric line, or baseline, on the EKG. When the SA node in the right atrium sends an
electrical signal through the right atrium and into the left atrium, the myocytes become positively
charged, or depolarized, causing the atria to contract and pump blood into the ventricles. This is
represented by the P wave on the EKG. The wave briefly returns to baseline after the P wave,
and it represents the electrical signal slowing down at the AV node to give the ventricles time to
fill. The signal travels through the AV node, Bundle of His, bundle branches, and Purkinje fibers
and depolarizes the ventricular myocytes causing them to contract and create the QRS complex
on the EKG. The EKG then returns to the isoelectric line after the QRS complex because the
ventricular myocytes are starting to recover from the contraction and begin regaining their
negative charge. This recovery phase is called repolarization. The atrial repolarization occurs
during ventricular depolarization, so it is masked by the QRS complex on the EKG. The T wave
represents the ventricles rapid phase of repolarization. Sometimes another wave will be seen
after the T wave and that is called a U wave. A U wave represents additional ventricular
repolarization.