Lecture 13+14 Flashcards
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)
Phase 4 on the ECG?
TP segment
no dipole (RMP)
Phase 2 on the ECG
ST segment
no dipole (completely depolarized)
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)
Repolarization on the ECG
The vector points away from the + electrode
positive deflection
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
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
P-wave time
0.08 to 0.10 seconds
PR interval time
0.12 to 0.20 seconds
more than 0.20 seconds indicates AV block
QRS complex time
0.06 to 0.10 seconds
more than 0.12s means a intraventricular block
ST segment depression/ elevation means?
ischemia
T-wave inversion?
ischemia or MI
QT interval time
0.20 to 0.40s
greater than 0.44s may indicate high risk for arrhythmias
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
ECG leads (12)
bipolar limb leads: I, II, and III
augmented (unipolar) limb leads: aVL, aVR, and aVL
precordial chest leads: V1 to V6
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
