Electrical acitivty toward the positive pole is upright.

Activity heading toward the negative pole is upside down.

drug toxicity

conduction disturbances

electrolyte imbalances

ischemia

infarction

determining chamber size/axis orientation

Represents the generation of an electrical impulse and depolarization of the atria

**Important in determining if the electrical impulse started in the sinoatrial node.

Q wave- 1st negative deflection

Q wave widened may indicate cardiac death

Q wave should be >0.04 sec and > 1/3 height of R wave

First positive deflection in the QRS complex.

Usually large in leads (I, II, III, aVL, aVF, V5, V6) and small in the others

3 rd major deflection in the ECG

Repolarization of the ventricles

Inverted in ischemia/infarction

The time for the electrical impulse to spread fom the atrium to the atrioventricular (AV) node. Beginning of P wave to Beginning of QRS.

Normal 0.12-0.20

Time from complete depolarization of the ventricles to the beginning of repolarization of the ventricles.

Normal Flat or Isoelectric

Myocardial Injury- May be elevated

Ischemia- May be depressed

Total periods of time required for depolarization of the ventricles

Normal <0.40s but depends on HR, a QT interval corrected for heart rate is called the QT_c

Lead I: Lateral Wall

Lead II: Inferior Wall

Lead III: Inferior Wall

aVR: (Augmented Vector Right)

aVL: (Augmented Vector Left) Lat Wall

aVF: (Augmented Vector Foot)Inf Wall

V1: Ventricular Septum

V2: Anterior Wall

V3: Anterior Wall

V4: Anterior Wall

V5: Lateral Wall

V6: Lateral Wall

Indicates previous MI. Negative deflections in front of R waves. Significant if > 0.04s and >1/3 height of R wave.

Indicate cardiac muscle death

Take appx 24 hrs to form.

Anterior/Septal MI  :  Leads V1-V4

Lateral MI  :   I, aVL, V5, V6 

Inferior MI   :   II, III, aVF

Posterior MI   :    V1, V2

Right Ventricular MI   :   V₃R_, V₄R, V₅R, V₆R

Typically caused by obstruction of the R coronary artery

Frequently produce dysrhytmias such as second-degree heart block

Directed inferiorly and to the left.

Meaning: if all electrical activity in the heart were averaged the net direction of electrical impulses would be toward the area of largest muscle concentration

Left Axis: Anterior Hemiblock

Left Ventricular Hypertrophy, PVCs

Right Axis: Posterior hemiblock

Right Ventricular Hypertrophy

Extreme Right Axis: PVCs