ECG Flashcards
What is an ECG?
ECG is a recording of the electrical activity of the heart from the skin
What does the P wave represent?
Atrial depolarisation
What does the QRS complex represent?
Ventricular depolarisation
What does the PQ interval represent?
Delay through the AV node
What does the St segment show?
Plateau phase of repolarisation
What does the T wave show?
Repolarisation of ventricle
What are the 2 types of lead-in ECG and what is the difference between the two?
Unipolar: measures the potential variation at a single point (single electrode)
Bipolar: measures the potential difference between two points
How many leads does a typical ECG have?
12
What is the name of the wiring you attach the actual skin?
Electrode
What are the unipolar leads?
Augmented Limb leads:
aVR (right shoulder), aVL (left shoulder), aVF (left Leg)
Chest leads: V1-V6
what are the bipolar leads?
Limb leads: I, II, III
I = Right Arm to Left Arm
II = Right Arm to Left Leg
III = Left Arm to Left Leg
all should make a triangle
What is a lead?
Lead = electrical vector: angle and direction of an electrical impulse
What planes do each of the leads work in:
Coronal plane: Limb leads
Transverse plane: Chest leads
Whats the rule for placing electrodes?
Either put them all on proximally or all on distally
e.g. either wrist and ankles or shoulder and thighs
What is the anterior heart surface assessed by?
V1-V4 e.g. damage to Anterior Left Descending Artery
What is the inferior heart surface assessed by?
Limb leads: II, III and aVF (foot lead)
What is the lateral heart surface assessed by?
V5, 6, Lead I, aVL
What gives a positive deflection on the ECG?
DEPOLARISATION OF THE HEART towards the positive electrode
What gives a negative deflection on the ECG?
Depolarisation of the heart away from the positive electrode
what effect does depolarisation of the heart parallel to the positive electrode have?
Positive deflection as it approaches and negative deflection as it moves away
outline a systemic approach to the interpretation of ECG
Get clinical context of patient Check patient details match (date, time) Assess technical quality if many artefacts then redo check paper speed Gain
Go to the rhythm strip (continuous across page) identify P/QRS/T measure heart rate check ECG intervals determine QRS axis
Looking at 12 leads:
Look at PQRST morphology
How do you calculate the HR from ECG?
count the number of squares between each QRS interval and then do 300 divided by the number
What is the normal QRS interval speed
120 ms
what is a normal QRS axis?
between +90 to - 30 degrees
What is bundle branch block and what effect will it have on QRS complex?
When one of the limbs of the conducting system is not working. QRS Complex is longer than 120 ms.
what effect does acute coronary occlusion have on ECG?
Elevated ST segment
