ECG basics Flashcards
Electrodes
Conductive pad attached to the skin to record electrical activity.
Leads
Graphical view of the hearts electrical activity calculated by analysing data collected from the electrodes.
Limb leads placement
3 electrodes give 6 leads of the heart
Red - right arm
Yellow - left arm
Green - Left foot
Black/earth electrode - right foot
Limb leads 1,2,3
1= Horizontally across heart red to yellow
2 = Diagonally across heart red to green (best lead as same direction as majority of electrical activity)
3 = Down heart yellow to green
Augmented Leads 4,5,6
Augmented view is an additional view of the heart calculated from an analysis of the electrical activity form the average of two electrodes (non positive) and one positive.
5 = augmented view right arm
6 = augmented view left arm
7 =augmented view left foot
precordial electrodes placement
V1 = 4th intercoastal space right sternal border
V2 = 4th intercoastal space left sternal border
V3 = in-between V2 and V4
V4 = 5th intercoastal space mid clavicular line
V5 = anterior axillary line on same horizontal line as V4
V6 = axillary line on same horizontal level as V5
Wilsons central terminal
Negative electrode of chest leads formed by averaging the three average limb electrode voltages requiring on the contract of at least 4 electrodes.
Direction of electrical activity and wave formation
Vector of electrical activity towards an electrode produces positive inflection
Vector of electrical activity away from an electrode produces negative inflection.
P wave
Atrial depolarisation
QRS wave
Ventricular depolarisation
T wave
Ventricular repolarisation
PR interval
start of P wave to start of start of Q wave
QRS interval
Start of Q wave to end of S wave
RR interval
Peak of R wave of one complex to Peak of R wave on next complex
J point
S wave returning to Isoelectronic line
PR segment
End of P wave to start of QRS complex
ST segment
J point to start of T wave
QT interval
start of QRS to end of T wave
PR interval limits
3-5 small boxes = 0.12-0.20 seconds
QRS interval limits
less than 0.12 seconds (3boxes)
QT interval limits
females - 0.46 seconds
males - 0.44 seconds
Systematic interpretation
1) glance and consider immediate concern
2) measure heart rate, PR interval and QRS interval
3) look at the rhythm
- regular/irregular
-regularly irregular or irregularly irregular
Method for working out heart rate on ECGs
1 big box = 0.2 seconds
count 30 big boxes
0.2 x 30 = 6 seconds
count number of QRS complexes in 6 seconds
multiply by 10
