ECG Flashcards
what is the ECG?
recording of potential changes, detected by electrodes positioned on the body surfaces
= allowing electrical activity of the heart to be monitored
how do potentials at the body surfaces arise?
arise from currents that flow when the membrane potential of myocardial tissue is changing (re-polarisation or depolarisation)
can all sizes of cardiac tissue generate sufficient current to be detected at body surface as potential changes?
Yes/no
NO.
- only large masses generate sufficient current to be detest at body surfaces
what ventricle has a notably larger mass?
left ventricle
what is an electrical dipole?
an electrical VECTOR, with components of magnitude and direction, that separates charges
what are the 2 components of the vector electrical dipole?
1) magnitude
2) direction
what is the magnitude determined by?
mass of cardiac muscle
what is the direction determined by?
overall activity of the heart
what is the ECG lead?
= the electrical picture obtained, the imaginary line, the lead axis, between two electrodes.
= NOT the wire that connects the electrodes to the recording device
In a lead, one electrode acts as the recording (positive) electrode.
What is the deflection on the ECG if the depolarisation is moving towards the recording electrode?
upwards deflection
what is the deflection on the ECG if the depolarisation is moving away from the recording electrode?
downwards deflection
what is an iso-potential?
there is no movement of current towers or away from the electrode, therefore. no deflection is seen
what are the 3 components of the 12 lead ECG?
1) 3 standard limb leads
2) 3 augmented voltage leads
3) 6 chest leads
what comprises the 3 standard limb leads?
what are these termed?
I
II
III
= Bipolar
what comprises the 3 augmented ted voltage leads?
what are these termed?
aVR = right aVL = left aVF = foor
= Unipolar
what comprises the 6 chest leads?
what can these leads also be called?
V1 - V6
Pre-cordial leads
what leads provide a vertical picture of the heart?
Leads I, II & III
Leads aVR, aVL & aVF
what lead provides a horizontal picture of the heart?
Leads V1 - V6
describe where the movement occurs in Lead I.
From RA-ve
To LA+ve
describe where the movement occurs in Lead II.
From RA-ve
To LL+ve
describe where the movement occurs in Lead III
From LA-ve
To LL+ve
what tis the right legs role in an ECG?
its earthed
from what direction does Lead II see the heart?
from an INFERIOR direction
describe the direction of atrial depolarisation during the P wave on an ECG.
Spreads from SA node inferiorly to left
= moving TOWARDS recording electrode producing an upward deflection
what does the P wave duration normally reflect in an ECG?
the time for the depolarisation of atrial muscle to be complete
what is the normal duration for a P wave in an ECG?
0.120s
120ms
describe the direction of depolarisation during the Q wave on an ECG as seen via lead 2.
- left to right depolarisation of the INTRA-VENTRICULAR SEPTUM
- moving slightly away from recording electrode
describe the direction of depolarisation during the R wave on an ECG.
depolarisation of main ventricular mass moving TOWARDS the recording electrode.
the main free walls of the ventricles depolarise causing a tall, narrow wave.
describe the direction of depolarisation during the S wave on an ECG.
depolarisation of ventricles at THE BASE OF THE HEART moving away from the recording electrode.
= produces a small narrow wave
describe the direction of depolarisation during the T wave one an ECG.
ventricular re-polarisation moving in a direction OPPOSITE to that of depolarisation accounts for usually observed upward deflection
what does a T wave represent?
ventricular re-polarisation
what is a Q wave.
downward (negative) deflection preceding an R wave
what is a R wave.
a deflection upward (positive), irrespective or not it is proceeded by a Q wave
what is an S wave.
a downward (negatiive) deflection following an R wave
what does the QRS complex represent?
ventricular activation, or depolarisation.
how long does QRS normally last?
- 1s
(100ms) or less
where does the PR interval start and end?
starts = P wave ends = start of the QRS complex
what does the PR interval reflect?
it reflects the time for SA node impulse to reach the ventricles
what is the PR interval normally?
0.12-0.2s
what is the PR interval strongly influenced by?
by AV node delay
where does the ST segment start & end?
From the end of QRS complex to the start of the T wave.
describe the ST segment?
it is normally iso-electric
where does the QT interval start & end?
from the start of QRS complex to the end of the T wave.
what does the QT interval reflect?
reflects the time for ventricular depolarisation & re-polarisation
what is the normal duration for the QT interval in makes & females?
Males = 0.44s Females = 0.46s
what does prolongation of QT interval predispose to?
predisposes to disturbances of cardiac rhythm
describe Goldberger’s method?
One +ve electrode (recording)
Two other linked as -ve
effectively positions the reference electrode in the centre of the heart
describe aVR waves
RA (+) to LA & LF (-)
describe aVL waves
LA (+) to RA & LF (-)
describe aVF waves
LF (+) to RA & LA (-)
what is the hex axial reference system?
six views of the heart in Toal
what are Leads I and aVL leads called?
LATERAL leads
what do lateral leads measure?
each has the recording electrode on the left arm and views heart from the left.
what are leads II, III and aVF called?
INFERIOR leads
what do inferior leads measure?
each has the recording o the left foot and views heart from an inferior direction
what term describes the chest leads?
unipolar
describe the view of the heart provided by the chest leads?
in the HORIZONTAL plane
where do leads V1 and V2 come from and where do they look at?
Come from;
= the right
Looking at;
= the inter ventricular septum
what do leads V3 and V4 look at?
they look at the anterior of the heart
what do leads V5 and V6 look at?
they look at the lateral aspect (left ventricle) of the heart
in V1, what is the first positive defection in the QRS complex?
an R wave
in V1, after the first positive defection in the QRS complex, what is the negative deflection that immediately follows?
the S wave
what happens to the R wave as you progress from V1-V6?
R wave = increases
what happens to the S wave as you progress from V1-V6?
S wave = decreases
what happens to the ventricles during the ST segment?
ventricles contract
= systole
what happens to the ventricles during the TP segment?
ventricles relax
=diastole
how do you calculate heart fate from an ECG?
300/number of large squares between bears
what time does a large box represent?
0.2seconds
what time does a small box represent?
0.4seconds
what is the ECG rhythm strip?
prolonged recording of one lead, usually lead 2
= allows you to determined heart rate and cardiac rhythm
what 3 reasons show the need for 12 leads?
1) determine axis of the heart in thorax
2) look for ST segments or T wave changes in relation to specific regions of the heart
= crucial for diagnosing ischaemic heart disease
3) look for voltage criteria changes
= crucial in diagnosing chamber hypertrophy
what 3 heart disease have a normal resting ECG?
1) myocardial infarction = heart attack 2) intermittent rhythm disturbance 3) stable angina = if suspected do exercise ECG, look for ST changes during/after exercise. = absent during rest
