Lecture 13+14 Flashcards by Trevor Losego

Waves, segments, and intervals

waves: are deflections
P, QRS, T, and U

segments: baseline between two waves
PR segment
ST segment
TP segment

intervals: include wave and segments 
PR interval 
QT interval 
RR interval (one heart beat)

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Phase 4 on the ECG?

TP segment

no dipole (RMP)

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Phase 2 on the ECG

ST segment

no dipole (completely depolarized)

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depolarization on the ECG?

depolarization on ECG if perpendicular?

the vector points toward the + electrode
positive deflection

perpendicular: no net deflection
QRS (up and down deflection)

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Repolarization on the ECG

The vector points away from the + electrode

positive deflection

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Eithoven’s triangle

Lead I: RA to LA ( - to +) positive deflection

Lead II: RA to LL ( - to +) positive deflection

Lead III: LA to LL ( - to +) no net deflection

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meaning of the different waves on the ECG

P-wave = arterial depolarization

PR segment = AV node and Bundle of His

QRS complex = ventricular depolarization

ST segment: ventricles are depolarized

T- wave = ventricular repolarization

TP segment = RMP

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P-wave time

0.08 to 0.10 seconds

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PR interval time

0.12 to 0.20 seconds

more than 0.20 seconds indicates AV block

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QRS complex time

0.06 to 0.10 seconds

more than 0.12s means a intraventricular block

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ST segment depression/ elevation means?

ischemia

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T-wave inversion?

ischemia or MI

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QT interval time

0.20 to 0.40s

greater than 0.44s may indicate high risk for arrhythmias

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acute ischemia (hours, 24 hours, days)

within hours: peaked T-waves and ST changes

24 hours: T-wave inversion and ST segment resolution

few days: pathologic Q waves
more than 0.40 s and less amplitude

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ECG leads (12)

bipolar limb leads: I, II, and III

augmented (unipolar) limb leads: aVL, aVR, and aVL

precordial chest leads: V1 to V6

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aVR

The mean QRS vector is in the opposite direction to lead aVR, thus QRS complex is largely negative

augmented, indifferent electrode
+ electrode is right arm

aVL

the vector goes towards the left arm
usually a positive deflection (QRS)

augmented and indifferent electrode
+ electrode is left arm

aVF

The vector goes down towards the feet
QRS is largely upward

augmented and indifferent electrode
+ electrode is left foot

precordial chest leads

V 1/2 = RV

V 3/4 = septum

V 5/6 = LV

QRS complex

V 1/2 = downward
V 3 = equiphasic
V 4/6 = upward

What leads to right and left axis deviation

RV hypertrophy = right axis deviation

LV hypertrophy = left axis deviation

bradyarrhythmia and tachyarrhythmia

abnormal heart rhythm

brady = slow abnormal heart rhythm

tach = fast abnormal heart rhythm

causes of arrhythmias?

altered automaticity (SA node, AV node, new pacemakers)

altered conduction (blocks)

sinus tachycardia

faster pace than normal (below 100)
increased depolarization of phase 4 of the SA node potential

occurs during exercise, stress, fright, fever

atrial fibrillation

rhythm irregular
P wave is not distinguishable
P-R interval is not measurable
QRS is normal

common in elderly
blood can pool in the atria causing clots

ventricular tachycardia

rate: 150-300bpm p wave is not seen QRS is wide, tall, and bizarre (prolonged) poor CO, this can be deadly

ventricular fibrillation

Rate: 300 or more beats per minute irregular and deadly rhythm does not generate a pulse QRS is disorganized all waves are fibrillary CO and MAP are decreased; most likely unconscious defibrillation and CPR is needed (emergency) may be due to MI

1st degree heart block (prolonged P-R interval)

rate is normal QRS normal PR is longer (AV conduction is slowed) causes: age, athletic training, surgery, electrolyte disturbance

2nd degree block (1+2)

Mobitz type 1 (wenckeback): ``` defect at the AV node PR interval gets progressively longer sometimes QRS and T waves dont occur benign condition (children, athletes, vagal tone increase) ``` ``` Mobitz type II: rate can be 30-100 bpm almost every P wave is followed by QRS no T wave sometimes it just the P wave Need a pacemaker ```

3rd degree heart block

QRS will look odd and wide dissociation of P and QRS relationship Need pacemaker! CO and BP is compromised

right and left bundle branch block

right- will see "bunny ears" wide QRS left: just a wide QRS and flatter top contractions of the heart are weaker