ECG Flashcards
ECG
Voltage against time graph
Typical settings
Speed = 25 mm/sec
Voltage=10 mm/mV
y axis: 2 big squares= 1mV
x axis: 5 big squares= 1s
Methods of rate calculations
Rate (bpm) = 300/no. of large squares between cardiac cycles
Rate (bpm) = (cycles in 10 secs) x 6
Fatstest depolarizing part of heart
Sinoatrial node
ECG Waves
P wave – atrial depolarization
QRS complex– ventricular depolarization and atrial repolarisation
T wave – ventricular repolarisation
Positive deflection= net current flow towards lead
Negative deflection= net current flow away from lead
Atrial flutter
Organised atrial activity ~300/min
Ventricular capture at ratio to atrial rate (usually 2:1 so 150 bpm)
Usually regular
Can be irregular if ratio varies
Atrial fibrillation
Random atrial activity
Random ventricular capture
Irregularly irregular rhythm
PR Interval- P to start of QRS
Normal values
120 – 200 ms
(3 to 5 small squares)
Normal QRS<120ms
QRS> 120ms
Bundle branch block most common cause
QT Interval
Measure of time to ventricular repolarization
Time from onset of QRS to end of T
Normal values
Men 350-440 ms
Women 350-460 ms
3 lead ECG
Looks at rhythm but not particularly anything else
Electrode
Physical connection to patient in order to measure potential at that point
10 electrodes to record a 12 lead ECG
Lead
Graphical representation of electrical activity in a particular ‘vector’
Calculated by the machine from electrode signals
12 leads for a 12 lead ECG (I-III, aVL, aVF, aVR, V1-6)
Negative
Current flowing away from the electrode
POSITIVE- current flowing towards the electrode
Bipolar lead
Measures the potential difference (voltage) between two electrodes
One electrode designated positive, the other negative
3 bipolar limb leads – I, II, III
Unipolar lead
Measures the potential difference (voltage) between an electrode (positive) and a combined reference electrode (negative)
Sometimes known as augmented leads
3 unipolar limb leads – aVL, aVF, aVR
Right leg
Neutral electrode
- Reduces artefact – not directly involved in ECG measurement
Left leg= positive
Right arm
Negative
Left arm
Positive
Unipolar limb leads
Measure potential from a single electrode (designated as positive) using a combined reference electrode as negative
Use same electrodes as the bipolar limb leads
Rules of thumb – Leads I + II
Lead I + II positive -> normal axis
Rules of thumb – Leads I + II
Lead I positive, lead II negative -> Left axis deviation
Leaving each other = Left axis deviation
Rules of thumb – Leads I + II
Lead I negative, lead II positive -> right axis deviation
Reaching towards each other = Right axis deviation
What you need to know for exam?
ECGs record voltage over time
Show us magnitude of collective electrical impulse in specified directions
Standard set up parameters
P-QRS-T corresponds to electrical (and therefore mechanical) cardiac cycle
12 lead ECG = 10 electrodes
3 bipolar limb leads – I, II, III
3 unipolar limb leads – aVL, aVF, aVR
6 unipolar chest leads (V1-6)
Provide information on rate, rhythm, axis, conduction, myocardial health
More about abnormalities in later phases but it’s important to grasp the basics first
