ECG Flashcards
What leads are ECG changes in if anterior infarction?
V1-V4
ECG changes in leads V1-V4 show what type of infarction and what coronary artery is affected?
Anterior
Left anterior descending
What leads are ECG changes in if inferior infarction?
II, III, aVF
ECG changes in leads II, III, aVF show what type of infarction and what coronary artery is affected?
Inferior
Right coronary artery
What leads are ECG changes in if lateral infarction?
I, aVL, V5-6
ECG changes in leads I, V5-V6 show what type of infarction and what coronary artery is affected?
Left circumflex artery
What does P wave represent?
Atrial depolarisation
What does the PR interval (start of P to start of Q) represent?
Time for electrical activity to move between atria and ventricles
What does the QRS complex represent?
Depolarisation of ventricles
What does the ST segment (end of S to start of T) represent?
time between depolarisation and repolarisation of the ventricles (ventricular contraction)
What does the T wave represent?
Ventricular repolarisation
What is the RR interval?
One R wave to the end of the next R wave. Time between 2 QRS complexes
What is the QT interval?
Starts of QRS to end of T. Time taken for ventricles to depolarise and then repolarise.
Small square
0.04s
Large square
0.2s
How many squares is 1 second?
5 large squares
How many squares is 1 minute?
300 large squares
How many electrodes (conductive pad that records electrical activity) and how many leads (graphical representation of heart’s activity calculated by analysing the electrodes) are used in ECG?
12 leads so 12 separate graphs on 1 ECG paper.
10 electrodes that attach to pt to generate the 12 leads.
How many electrodes?
10
Name the chest electrodes?
V1-V6
V1 location?
4th intercostal space at the right sternal edge
V2 location?
4th intercostal space at the left sternal edge
V3 location?
Midway between the V2 and V4 electrodes
V4 location?
5th intercostal space in the midclavicular line
V5 location?
Left anterior axillary line at the same horizontal level as V4
V6 location?
Left mid-axillary line at the same horizontal level as V4 and V5
How many limb electrodes?
4
Name the limb electrodes
Red (RA)
Yellow (LA)
Green (LL)
Black (RL)
Red electrode location
Ulnar styloid process of the right arm
Yellow electrode location
Ulnar styloid process of the left arm
Green electrode location?
Medial or lateral malleolus of the left leg
Black electrode location?
Medial or lateral malleolus of the right leg
View of heart from V1 and V2?
Septal (Anteroseptal)
View of heart from V3 and V4?
Anterior
View of heart from V1, V2, V3, V4?
Anterior (anteroseptal)
View of heart from V5 and V6?
Lateral
What view of the heart does lead I show and how is it calculated?
Lateral (activity between RA and LA electrodes)
What view of the heart does lead II show and how is it calculated?
Inferior (activity between RA and LL)
What view of the heart does lead III show and how is it calculated?
Inferior (activity between LA and LL)
What view of the heart does aVL show and how is it calculated?
lateral (activity between RA+LL and LA)
What view of the heart does aVF show and how is it calculated?
Inferior (activity between RA+LA and LL)
One more lead that don’t really look at on ECG?
aVR (lateral view - activity between LA+LL and RA)
Why is each lead’s ECG recording slightly different in shape?
Each lead records heart’s activity from different direction (viewpoint)
When the electrical activity in the heart travels towards a lead, what do you get?
+ve deflection
When the electrical activity in the heart travels away from a lead, what do you get?
-ve deflection
What does each deflection (wave) on ECG represent?
Average direction of electrical travel (electrical activity in heart flows in many directions simultaneously)
What does the deflection height represent?
amount of electrical activity flowing in that direction (higher deflection, more activity towards the lead)
The lead with the most positive deflection is most aligned with what?
The direction the heart’s activity is travelling
R wave is greater than S wave?
Depolarisation is moving towards that lead
S wave greater than R?
Depolarisation is moving away from that lead
R wave and S wave equal size?
Depolarisation is exactly 90° to that lead
Electrical activity of the heart to cause ventricular contraction?
Electrical activity starts at sinoatrial node, spreads to the atrioventricular (AV) node. Then spreads down bundle of His and Purkinje fibres to cause ventricular contraction
What does the cardiac axis show?
Overall direction of electrical activity
In healthy individuals, where would you expect the cardiac axis to lie?
between -30°and +90º
If in healthy individuals, the cardiac axis lies between -30°and +90º, the overall direction of electrical activity is towards what leads?
I, II and III
(pointing towards 4&5 on a clock)
What lead shows the most positive deflection in healthy individuals whose cardiac axis lies between -30°and +90º?
Lead II as it is the most closely aligned to the overall direction of electrical spread (pointing towards 4&5 on a clock)
What lead shows the most negative deflection in healthy individuals whose cardiac axis lies between -30°and +90º?
aVR as it provides a viewpoint of the heart from the opposite direction
Cardiac axis leads in everyone?
horizontal= lead I
diagonal down to R= lead II (most + deflection)
diagonal down to L= lead III
vertical down= aVF
diagonal up to R= aVL
diagonal up to L= aVR (most -ve deflection)
What is right axis deviation (RAD)?
The direction of depolarisation is distored to the right (between +90º and +180º- like pointing to 7 on clock)
Most common cause of right axis deviation?
R ventricular hypertrophy- extra RV tissue generates stronger signal by R side of heart
Deflection in leads in right axis deviation?
Deflection in lead I becomes -ve and deflection in lead aVF/III to be more +ve
What is RAD associated with?
Pulmonary HTN as cause RV hypertrophy. Can be normal finding in very tall people.
What is left axis deviation?
Direction of depolarisation is distorted to the left (between -30° and -90°- like pointing towards 1 on a clock)
Deflection in leads in left axis deviation?
Deflection of lead III becomes -ve (only significant if deflection in lead II also becomes -ve)