872: Intro to EKG Interpretation

Cardiac conduction system begins with the

Sinoatrial (SA) node

SA node

Located in the right atrium

Spontaneously and repeatedly depolarizes

After leaving the SA node the action potential will

Spread throughout the right and left atria

AV node

Depolarization is delayed which allows enough time for the ventricles to fill with blood before they are stimulated to contract

After leaving the AV node the action potential will

Bundle of HIS, right and left bundle branches, and finally the Purkinje fibers

Three main waves in a normal EKG

1. P wave

2. QRS complex

3. T wave

P wave

Represents atrial depolarization (action potential spreading through the atria)

QRS complex

Represents ventricular repolarization (action potential spreading through the ventricles)

T wave

Represents ventricular repolarization (point at which the ventricular cardiac muscles return to their resting electrical state)

The 6 second method

Count to the nearest half the number of R-R intervals in 6 seconds and multiply the number by 10

Sinus bradycardia

HR less than 60 bpm

Causes of sinus bradycardia

• exercise training adaptation

• Medications

• Decreased automaticity of the SA node

• TBI

• Increased vagal stimulation

Sinus tachycardia

HR is above 100 bpm

Causes of sinus tachycardia

• usually benign

• Increased sympathetic stimulation (fear, exercise, emotion, stimulants)

• Fever

• CHF

• Infection

• Anemia

• Hemorrhage

• Myocardial injury

• Hyperthyroidism

Sinus pause

SA node fails to initiate an impulse

Usually only for one cardiac cycle

Causes of sinus pause

• sudden increase in parasympathetic activity

• Sick sinus syndrome

• Infection

• Rheumatic disease

• Severe ischemia or infarction of the SA node

Premature atrial complex, PAC

Early, premature beat

This impulse arises from somewhere above the ventricles but not the SA node

Causes of premature atrial complex

• emotional stress

• Nicotine

• Caffeine

• Alcohol

• Hypoxemia

• Infection

• Ischemia

• Rheumatic disease

• Atrial damage

Atrial flutter

Rapid succession of atrial depolarization caused by one ectopic focus in the atria that depolarizes at a rate of 250-350 times per minute

Causes of atrial flutter

• rheumatic heart disease

• Mitral valve disease

• CAD

• Stress

• Drugs

• Renal failure

• Hypoxemia

• Pericarditis

Atrial fibrillation

• Erratic quivering or twitching of the atrial muscle caused by multiple ectopic foci in the atria that emit electrical impulses constantly

• No true p waves found

• Atria do not contract

Causes of atrial fibrillation

• advanced age

• CHF

• Ischemia or infarction

• Cardiomyopathy

• Digoxin toxicity

• Drug use

• Stress or pain

• Rheumatic heart disease

• Renal failure

Premature ventricular complexes

• an ectopic focus causes an impulse from one of the ventricles

• Occurs early before the SA node actually fires

• Wide QRS without a p wave

Causes of premature ventricular complexes

• caffeine, nicotine

• Stress/anxiety

• Over exertion

• Electrolyte imbalances

• Ischemia

• Cardiac disease

• Overdistension of the ventricle

• Irritation of the myocardium

• Lung disease

• Hypoxemia

• Medications

Ventricular tachycardia

Three or more PVCs in a row

Causes of ventricular tachycardia

• ischemia or acute infarction

• Hypertensive heart disease

• Reaction to meds

• Electrolyte imbalance in athletes during exercise

Ventricular fibrillation

An erratic quivering of the ventricular muscle resulting in no cardiac output

Multiple ectopic foci are firing

Causes for ventricular fibrillation

Same as those for v tach

V tach can progress into v fib