ECG Flashcards
what are upward deflections?
depolarisation moving towards leads
what are downward deflections?
depolarisation moving away from leads
how do you get lead I?
left arm positive - right arm negative
how do you get lead II?
left leg positive - right arm negative
how do you get lead III?
left leg positive - left arm positive
what does V1-2 show?
right ventricle electrical activity
what does V3-4 show?
septum and anterior wall of left ventricle electrical activity
what does V5-6 show?
anterior and lateral walls of left ventricle electrical activity
what are the factors to remember while recording an ECG?
- Standard settings of machine (amplitude normally 10mm/mV), (speed – 25mm/s)
- Accurate placing of leads
- Electrode contact with skin – no oily moisturisers, clean and dry etc
- Patient relaxed – no tensing (other electrical signal interference)
- Slightly abrase skin – helps get ride of dead cells – better for conduction
what do you generally look for within an abnormal ECG?
- Wave height
- Wave duration
- Curves – straight/ gradual/ steep
- No rogue notches
- Normal order
what does the P wave show?
depolarisation of the atria - right side first
how is the P wave unique in comparison to the others?
its quite wide - goes across the atria
how long is the P wave duration?
0.12s
what is the PR interval in terms of electrical activity?
time for conduction from SAN through to AVN, bundle of His, Purkinje fibres
onset of atrial depolarisation to ventricular depolarisation
what is the duration of the PR interval?
0.12-0.3s
what does a shorter PR interval show?
either depolarisation occurred near AVN (hence no pause) or abnormally fast conduction from atria
what is the QRS complex showing?
ventricular depolarisation
septum depolarises left to right
what is the normal duration of QRS complex?
<120ms
where can Q waves be seen on the ECG leads?
leads facing left - I, II, AVL, V5, V6
what is the ST segement?
end of ventricular depolarisation to beginning of repolarisation
where does the ST segment usually lie?
on baseline on isoelectric point
what does the QT interval show?
total time for depolarisation and repolarisation of ventricles
what is the U wave?
small deflection after t wave
barely seen
potentially repolarisation of papillary muscles
what is the repolarisation of ventricles on the ECG?
T waves
what is prolonged QT interval a risk of?
pointes de tourades
which leads show QRS?
AVL, AVF, leads I, II, III
what is cQT used for?
more accurate and helps see ventricular tachycardia
what is the equation for cQT?
cQT= (QT (ms)/ √RR(s))
what do pathological Q waves suggest?
previous mild infarction
what is the RR interval?
between two R peaks
what is the RR interval useful for?
determining heart rate
* Hr= 300/RR
* Hr= (how many QRS in 30 big squares) x 10
on standard ECG, how many seconds is a big square?
0.2s or 200ms
on a standard setting ecg what is a little square in ms?
40ms
on a standard ecg what are 5 big squares worth in seconds?
1s
which leads show left lateral surface?
leads I, II and AVL
which leads show inferior surface?
leads II, III, AVf
which leads show right atrium?
AVR
what does V1-6 leads show?
chest leads - heart from horizontal plane from front to left side
what is the cardiac axis?
average direction of spread of depolarisation wave through ventricles as seen from the front
what is the normal heart axis?
-30 degrees to 90 degrees
what angle is left axis deviation?
<-30
what angle is right axis deviation?
> 90
what are the causes of left axis pathophysiology?
- Left ventricular hypertrophy (increase cell growth)
- Left bundle branch block
- Left anterior fasicular block
- Inferior MI
- Ventricular pacing
- Wollf-parkinson white – heart beats abnormally fast for a period time
Conduction abnormalities
what is seen on the ECG with left axis deviation?
QRS becomes negative in lead III
what are the causes of right axis deviation?
- Right ventricular hypertrophy
- Acute RV strain (PE)
- Lateral MI
- Chronic lung disease
- Dextrocardia (heart on right side not left)
- Variant of normal – children / thin adults
where is V1 placed?
4th intercostal space to the right sternal edge
where is v2?
4th intercostal space to the left
where is V3?
midway between V2 and v4
where is V4 placed?
5th intercostal space in midclavicular line
where is V5?
left axillary line at same horizontal level as v4
where is v6 placed?
left mid-axillary line at same horizontal line as V4 and V5
what colour electrode is RA negative?
red
what colour is left arm positive?
yellow
what colour is left leg (positive)
green
what colour is right leg (neutral)
black
where is overall direction of electrical activity in terms of leads?
leads I, II, III - positive deflection
which lead ha the most positive deflection and most closely aligned to the overall direction of the electrical spread?
lead II
what is the most significant cause of left axis deviation?
conduction abnormalities
what is the most common cause of right deviation?
right ventricular hypertrophy
what would indicate IE on an ECG?
prolonging PR (first degree heart block), p mitrale, dysthymia
what is P mitrale on ECG?
left atrial enlargement producing bifid p waves
what area does LCA cover?
anterolateral
what are the anterolateral leads (LCA)?
I, aVL, V3-6
what area of the heart is covered by LAD?
anterior
what leads show anterior part of the heart (LAD)?
V1-4
what area does the circumflex serve?
lateral
what are the lateral leads? (circumflex)
I, aVL, V5-6
what does the RCA serve?
inferior heart
what leads show RCA? (inferior)
I, II, aVF
