Electrophysiology

ELECTROPHYSIOLOGYOFTHE

HEART

EKGs

Chapter 2

DEPOLARIZATION & REPOLARIZATION

 Cardiac cells at rest

 Polarized – state of readiness, ready for electrical action

 Negatively charged

 Stimulation of the cell by an electrical impulse

 Large amounts of Na rushes into cell

 Small amount of K pushed out of cell

 Cell is now positively charged

 Depolarized

 Electrical wave courses from cell to cell spreading the
electrical charge

 Cell recovery

 Na and K are shifted back to their original position by way
of the sodium-potassium pump

 Cell is returned to original negative charge

 Repolarization

CELLDEPOLARIZATION & REPOLARIZATION

CONTINUED….

 Depolarization and repolarization are electrical
events

 Electrical always precedes mechanical function

 Contraction and relaxation of the heart are
mechanical events

 Depolarization – muscle contraction

 Repolarization – muscle relaxation

 Electrical and mechanical function must function
normally for optimal cardiac performance

 Electrical malfunctions show up on EKG

 Mechanical malfunction show up clinically

HEARTWAVES & COMPLEXES

 P wave

 Represents atrial depolarization

 Normal P

 Small, rounded, upright

 Should never be pointed or peaked

 P wave is the signal that electrical potential has left
the SA Node

 Initiates atrial contraction

QRSCOMPLEX

 QRS complex

 Represents ventricular depolarization

 Normal QRS

 Spiked, consisting of one or more deflections from the
baseline

 Q wave – negative deflection

 R wave – positive deflection from baseline

 S wave – negative deflection following R wave

T WAVE

 T wave

 Represents ventricular repolarization

 Normal T wave

 Broad and rounded

 If QRS is upright, T wave usually is also

 If there is a QRS, there MUST be a T wave after it

 Any tissue that depolarizes must repolarize

U WAVE

 U wave

 Represents late ventricular repolarization

 Not normally seen

 Normal U Wave

 Shallow and rounded

 Follows the T wave

 If T wave is upright, so should the U wave

 Usually seen only with slow HR

 Bradycardia

SEGMENTS

 Each P – QRS – T sequence is one heartbeat

 Flat line between waves

 Known as baseline or isoelectric line

 Represents electrical silence

 PR segment

 Flat wave between the beginning of the P wave and
QRS

 ST segment

 Flat line between the beginning of the S wave and
beginning of the T wave

EKGSEGMENTS

SUMMARY

 EKG waves tell us something electrical is
happening

 Flat lines indicate no electrical activity

 Atrial contraction

 Occurs during P wave and PR segment

 Atria depolarize and P wave is recorded on EKG
paper

 Atria contract filling the ventricles with blood

 Ventricular contraction

 Occurs during QRS and ST segment

 Ventricular depolarize and QRS complex is recorded
on EKG paper

 Ventricles contract