BSI: EKG Interpretation I

• Rate
• Rhythm
• Axis
• Hypertrophy
• Infarction

• 1) Find R wave that falls on heavy black line.
• 2) Count off 300, 150, 100...75, 60, 50 for each consecutive heavy line.
• 3) Where the next R wave falls determines the rate.

Just below 75 beats per minute.

• Normal Sinus Rhythm: 60-100 beats/min
• Sinus Bradycardia: < 60 beats/min
• Sinus Tachycardia: > 100 beats/min

Examine the EKG and determine if there are normal distances between similar waves.

• Premature beats
• Rapid ectopic rhythms
• Heart blocks

A premature beat happens when an ectopic focus discharges and spontaneously produces a beat which appears earlier than expected in the rhythm.

• Premature atrial contraction (PAC)
• Originates suddenly in an atrial ectopic focus and produces an abnormal P wave earlier than expected.

• Premature ventricular contraction (PVC)
• Originates suddenly in a ventricular ectopic focus in a ventricle producing a giant ventricular complex.
• - Occurs before a P wave can begin a new cycle
• - Note: QRS complex is very wide and tall/deep. It is wider than normal because depolarization originates in the myocardium (instead of conduction system) and therefore depolarization impulse is conducted very slowly across both ventricles.

During normal ventricular conduction, the left and right ventricles depolarize simultaneously. As a result, depolarization going toward the left ventricle is somewhat opposed by simultaneous depolarization going toward right ventricle. Therefore, under normal conditions, the QRS is relatively small.

A PVC originates in one ventricle which depolarizes before the other ventricle, and therefore there is no simultaneous opposing depolarization from opposite sides. Therefore, QRS is very large.

• Flutter (rate between 250-350 beats/min)
• Fibrillation (rate between 350-450 beats/min)

Flutter (rate between 250-350 beats/min)

• Atrial flutter
• originates in an atrial ectopic focus
• - P waves occur in rapid succession and each is identical to the next
• - P waves look identical because they arise from the same ectopic focus
• - Only occasionally will the atrial stimulus penetrate the AV node and produce a QRS complex

Flutter (rate between 250-350 beats/min)

• Ventricular flutter
• produced by a single ventricular ectopic focus firing at an extremely rapid rate
• - Forms a smooth sine wave
• - No P waves or T waves

Fibrillation (rate between 350-450 beats/min)

• Atrial fibrillation
• caused by many atrial ectopic foci firing at rapid rates causing an exceedingly rapid, erratic atrial rhythm
• - No true P wave—just spikes appear

Fibrillation (rate between 350-450 beats/min)

• Ventricular fibrillation
• caused by rapid-rate discharges from many ventricular ectopic foci producing erratic, rapid twitching of the ventricles
• - looks like a bunch of random scribbles
• - Because so many foci are firing at once, each only depolarized a small area of ventricle and produces “twitching” of ventricle instead of full contraction of ventricle
• - No effective pumping!!!
• 

Heart blocks are electrical blocks which retard or prevent the passage of electrical (depolarization) stimuli.

• Sinus Block
• AV Block
• Bundle Branch Block

The SA node stops its pacing activity for at least one cycle.

The P waves are identical because the same SA node pacemaker is functioning before and after the pause (missed cycle).

Delay in transmission of the impulse through the AV node.

• 1° AV Block
• results in a longer pause before stimulating the ventricles
• - P-R interval prolonged (> 0.20 seconds).

Caused by block of depolarization in the right or in the left bundle branch.

Normally, the impulse spreads through right and left bundle branches simultaneously and therefore ventricles contract simultaneously.

• A block to either of the bundle branches creates a delay of the electrical impulse to that side and causes one ventricle to depolarize later than the other.
• 

• Results in widened QRS complex often with “rabbit ears” (> 0.12 seconds).
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