ECG I Flashcards by Salma Khan

What are leads?

visual representation of cardiac activity from a given perspective (coronal/horizontal plane)
different lead = different view of heart so change in ECG indicated location of damage

fixed cathode (+ve) and fixed anode (I,II,III) or virtual anode (avF, avL, avR, V1-6)

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What is a cardiac vector?

magnitude and direction of waves of depolarisation measured using ECG

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What does the isoelectric line represent?

no net V change, vector perpendicular to lead

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What does downward deflection (negative) mean?

toward anode (-)

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What does upward deflection (positive) mean?

toward cathode (+)

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What does the steepness of the line, width of deflection mean?

steepness of line - denote velocity of action potential

width of deflection - duration of event

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How to calculate the velocity of waveforms?

ECG amplitude/time

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What are the measurements on an ECG?

04s wide, 0.1mV high

0. 2s wide, 0.5mV high

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What is lateral?

left circumflex artery

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What is anterior/inferior?

right coronary artery

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What is septal?

left anterior descending

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What is Einthoven’s triangle?

3 limb leads

heart at centre represents 0 potential when voltages summed together

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What are leads 1, 2, 3 ?

1 - RA to LA
2 - RA to LL
3 - LA to LL

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Describe the placing of...
V1
V2
V3
V4
V5
V6

polarity?
plane?

1 - right sternal border, 4th intercostal space
2 - left sternal border, 4th intercostal space
3 - halfway between 2/4
4 - mid clavicular line, 5th intercostal space
5 - anterior axillary line (armpit crease), level of V4
6 - mid axillary line, level of V4

unipolar
horizontal

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What is the cathode and anode for V1-V6?

virtual anode (Wilson's Central Terminal) - composite pole of 1/3(RA + LA + LL)
cathode = chest lead

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Views of V1-6?

1-2 = septal
3-4 = anterior
5-6 = lateral
each measure activity of different region of heart

Describe leads 1-3?

bipolar
coronal plane
1 cathode = LA, anode = RA LATERAL
2 cathode = LF, anode = RA INFERIOR
3 cathode = LF, anode = LA INFERIOR

Describe leads avR, L and F?

unipolar (virtual anode)
coronal
avR cathode = RA, anode 1/2(LA+LF) - 
avL cathode = LA, anode 1/2(RA+LF) LATERAL
avF cathode = LF, 1/2(RA + LA) INFERIOR

P wave duration

80ms

PR interval duration

120-200ms

QRS duration

<120ms

QT interval duration

420ms

T wave duration

160ms

RR interval duration

0.6-1.2s

Why is QT interval corrected?

reported to correct interval according to breathing rate

How to calculate cardiac axis? if 2 cycles given

use 2 leads with 90 degree separate view of each other calculate value of angle relative to 0 find average angle of the two lead II most commonly used single leads

What is the cardiac axis?

net vector of R wave (largest electrical event because most muscle) range -30 to +90 degrees

Positive deflection?

towards positive electrode

Negative deflection ?

towards negative electrode

How do deflection rules change for repolarisation?

reverse process | positive deflection is away from positive electrode

Why does lead 3 show a negative deflection?

lead is oriented more normally to direction of depolarisation in the heart

What are augmented leads? Which show positive and negative deflections?

average voltage of 2 points on skin as -ve pole and 3rd reading from +ve electrode positive = avL/F negative = avR

What do the 6 chest and limb leads measure?

limb - depolarisation in frontal plane of heart | chest - measure depolarisation in horizontal plane of heart

How to determine if heart is on the correct side?

same deflection of avL up and down

Describe respiratory sinus arrhythmia

breathing cycle affects heart beat RR interval smaller during inspiration so HR increases and longer during expiration so HR decreases resting HR controlled by PNS and during inspiration inhibition removed so HR increases little between 70 --> 110bpm