P wave: Atrial depolarization. 0.08-0.10sec (8-10 miliseconds)

QRS complex: Ventricular depolarization. 0.06-0.10sec.

T wave: Ventricular repolarization. not measured

P-R interval: Atrial depolarization plus AV node delay. 0.12-0.20sec

ST segment: isoelectric period of depolarized ventricles.

Q-T interval: Length of depolarization plus length of repolarizatio.(Action Potential) 0.20-0.40sec. High heart rates can reduce action potential duration.

12 total

Limbs(standard) leads:

-Three bipolar

-Three augmented unipolar

Chest leads:

6

Record the same electrical activity of the heart, but from different angles. (Horizontal plane)

• Depolarization towards (+) node results in (+) deflextion.
• Repolarization towards (+) node results in (-) deflextion
• Away from (+) node, both are reversed.

I= 0^o

II= 60^o

III= 120^o

59^o(0-90)

Mean ventricular axis goes past 90^o.

Common causes:

-Right ventricular Hypertrophy

-Left Posterior fascicular block

-Acute right heart strain e.g. massive pulmonary embolism.

Mean electrical axis falls below 0^o

Common causes:

-Left ventricular hypertrophy

-Left anterior fascicular block

-Inferior wall of myocardial infarction

Cardiac abnormalities that cause part of the heart to remain partially or totally depolarized all the time.

Causes:

-Mechanical trauma

-Infectious process

-Ischemia due to local coronary occlusion(most common) disturb normal membrane polarization due to lack of nutrients.

•  J point on ECG: whole heart is depolarized at the end of QRS.
• ST stegment: above or below baseline after QRS.

heart rate>100 beats/min

otherwise normal ECG

Causes:

-Increase body temp.

-Increase sympathetic stimulation

-toxic conditions of the heart.

heart rate<60beats/min

otherwise normal ECG

Causes:

-athletic heart

-increased parasympathetic activity

• Sudden increase in heart beats (150-250 beats/min) goes away on it's own.
• Originates from Atrial or AV ectopic foci
• Occurs in young healthy individuals and they grow out of it after adolescence.

• Sudden fast heart beats (150-250 beats/min) goeas away on it's own.
• Originate from ectopic ventricular foci
• Serious condition most likely result from considerable ventricular ischemia.

• Delay of the AV bundle conduction from atria to the ventrical. Not actual blockage of conduction.
• Prolonged P-R interval > 0.2 sec

• AV bundle conduction slow down that results in missed ventricle beat.
• Prolonged PR interval 0.25 to 0.45sec and "dropped beat". Atrial P but no QRS or T waves.
• Rythms of 2:1, 3:1, or 3:2 can be seen

• Complete block of impulse from atria to ventricle.
• Ventrical establiches it's own signal (from AV node or bundle)
• P wave become disassociated with QRS-T waves

• Sudden atrial beat from an ectopic origin results in an earlier abnormal P wave.
• PR interval is shorter(ectpic origin is near AV node)
• Interval between premature beat and next one is slightly longer.

Causes:

-Sometimes none

-mild toxic conditions such as lack of sleep.

-too much coffee or alcohol.

-smoking

• Sudden ventricular beat from ectopic region results in a big abnormal QRS complex. Usually prolonged in time and has higher voltage.
• Can be followed by inverted T-wave.
• More serious than premature atrial sytstole.

• Multiple atrial beats originate from ectopic foci discharging rapidly. (350-450 discharges/min)
• Either small very fast P waves or straight line due to opposite direction of the waves that electrically neutralize each other. Normal QRS complexes but irregular in timing.
• Caused by atrial enlargment due to valve diseases

• Most serious of all cardiac arrhythmias.
• Death if not stopped within 1-3min
• Cardiac impulses go crazy. No coordination of muscle contraction
• No caridiac output.

Causes:

-Electrical cardiac shock

-Ischemia of the heart muscle or conductive system.