Intro To ECG Flashcards
What does an ECG provide information about?
Rate and rhythm
Chamber size
Electrical axis
What is an ECG the main test for?
Myocardial ischaemia and infarction
What causes current flow within tissue and surrounding tissue?
Electrical activity in and between (gap junctions) of myocytes
What generates potential differences on the body surface?
Extracellular current
Name of sensitive recording device
ElectrocardioGRAPH
How an ECG works
Action potentials spread through conducting system and heart muscles in sequence, causing potential differences in different regions and makes up an electrical dipole
Theses potential differences are detected by electrodes on skin, which are linked to an electrocardiograph and then printed on an ECG
What determines magnitude of electrical axis of heart?
Cardiac muscle mass (A+V dominate)
What determines direction of electrical axis of heart?
Overall activity of heart at any time, which varies throughout the cycle
ECG lead
Lead axis (imaginary line) between at least 2 electrodes ***not the wire
Line generated on ECG when depolarisation moves towards positive/ recording electrode
Upward deflection
Electrodes which lead I connects
RA-ve to LA+ve
Electrodes which lead II connects
RA-ve to LL+ve
Electrodes which lead III connects
LA-ve to LL+ve
From what position does lead II view the heart?
Inferior position
Which part of cardiac cycle does the P wave represent?
Atrial depolarisation, which spreads inferiority and left from SAN, thus moving towards electrode (upward deflection)
Which part of cardiac cycle does the QRS complex represent?
Ventricular activation and depolarisation
What direction is Q wave deflected? What causes this?
Downward deflection
Ventricular activation starts in intraventricular septum, moving to right thus depolarisation is moving away from recording electrode and results in downward deflection
What direction is R wave deflected? What causes this?
Upward deflection
Main free walls of ventricles depolarise towards recording electrode
What direction is T wave deflected? What causes this?
Upward deflection
Repolarising wave is spread away from recording device (think double negatives)
Which part of cycle does the PR interval reflect?
SAN impulse to reach ventricles, which is influences by delay in AVN
Why is elevation or depression in ST segment diagnostically important?
It is usually isoelectric (which means there should be no deflection)
What does the QT interval reflect?
Ventricular depolarisation and repolarisation
What comprises the 12 lead ECG?
3 standard limb leads
3 augment voltage (aV) leads
6 chest/ precordial leads
Which leads help create a vertical/ coronal picture of heart?
augmented voltage and standard limb leads
Which leads help create a horizontal/ transverse picture of heart?
precordial/ chest leads
Standard limb leads are unipolar. True/ false?
False
They are bipolar
aV leads are unipolar
Goldberger’s Method
1 +ve electrode (recording) and 2 -ve linked electrode, positing the reference electrode in centre of heart where the recording electrode looks
This is how augmented limb leads are linked
Electrodes which aVR connects
RA(+) to [LA & LF] (-)
Electrodes which aVL connects
LA(+) to [RA &LF] (-)
Electrodes which aVF connects
LF (+) to [RA & LA] (-)
Hexaxial reference system
View of heart in frontal/ coronal plane provided by the standard and augmented limb leads
What are lateral leads and which leads are lateral?
Lead I, aVL
The recording electrode is on the left arm and views heart from left
What are inferior leads and which leads are inferior?
Lead II, III and aVF
Recording electrode is on left for and views heart from inferior direction
aVR waves are negative. True/ false?
Depolarisation moving away from recording electrode is the predominant vector
Where is V1 placed?
4th intercostal space, right sternal border
Where is V2 placed?
4th intercostal space, left sternal border
Where is V3 placed?
Halfway between V2 and V4
Where is V4 placed?
5th intercostal space, left midclavicular line
Where is V5 placed?
Left anterior axillary line, on same horizontal plane as V4 and V6
Where is V6 placed?
Left midaxillary line, on same horizontal plane as V4 and V5
Which chest electrodes are looking at the interventricular septum?
V1 and V2
Which chest electrodes are looking at the anterior of the heart?
V3 and V4
Which chest electrodes are looking at the lateral aspect/ left ventricle of the heart?
V5 and V6
R wave progressively increases from V1 to V6 whereas S wave gradually decreases. True/ false?
True
How to calculate HR from ECG trace
300/ number of large squares between beats (if regular rhythm)
300/number of large squares between R-R interval
What is the rhythm strip and which lead usually shows this?
Prolonged reading of one lead which allows HR and cardiac rhythm to be identified
Lead II
What change is crucial for diagnosing chamber hypertrophy?
Voltage criteria changes
What change is crucial in diagnosing Ischaemic Heart Disease?
Any ST segment or T wave changes in specific regions of heart
Questions to consider when working out rate and rhythm using rhythm strip
- is electrical activity present?
- is the rhythm regular?
- what is the HR?
- is there a P-wave present?
- what is the PR interval?
- is each P-wave followed by a QRS-complex?
- is the QRS duration normal?
What is indicative of an MI in an ECG?
ST elevation MAY occur- doesn’t always show up and therefore cannot always be diagnosed via an ECG
Which significant heart diseases do not show up on a normal ECG?
MI may show up (ST elevation)
Intermittent Rhythm Disturbance- if suspected do AECG for 24hr or 7 days
Stable angina- if suspected, do exercise ECG
