ECG basics Flashcards
What is an ECG?
ECG = electrocardiogram
Shows the electrical activity of the heart
How many seconds is 1 small box?
0.04
How many seconds is 1 large box?
0.2
How many large boxes make up 1 seconds?
5
How many large boxes make up 1 min?
300
What does a P wave show?
Depolarisation of the atria
What does QRS complex show?
Ventricular depolarisation
What does the T wave show?
Ventricular repolarisation
What are the parameters of the PR interval?
Start = beginning of P wave
End = beginning of Q wave
What does the PR interval show?
The length of time taken for electrical activity to move from the atria to the ventricles
i,e., the length of time between the depolarisation of the atrial and the start of ventricular depolarisation
What are the parameters of the ST segment?
Beginning = end of S wave
End = beginning of T wave
What does the ST segment show?
The time between ventricular depolarisation and ventricular repolarisation
What are the parameters of the RR interval?
Beginning = peak of one R wave
End = peak of the next R wave
What does the RR interval show?
The length of time between each ventricular depolarisation
What are the parameters of the QT interval?
Beginning = start of QRS complex
End = end of T wave
What does the QT interval show?
The length of time between the depolarisation and repolarisation of the ventricles
What are the chest electrodes and where are they placed?
V1 - 4th intercostal space right sternal edge
V2 - 4th intercostal space left sternal edge
V3 - midway between V2 and V4
V4 - left 5th intercostal mid-clavicular line
V5 - left anterior axillary line on same plane as V4
V6 - left mid-axillary line on same plane as V4 + 5
What are the limb leads and where are they placed?
Red - right arm on ulnar styloid process
Yellow - left arm on ulnar styloid process
Green - medial/lateral malleolus of left leg
Black - medial/lateral malleolus of right leg
TIP : mnemonic = Ride Your Green Bike (start from the patient’s right arm and move clockwise. Remember you need to face the patient for this to work)
What view of the heart does V1 show?
Septal
What view of the heart does V2 show?
Septal
What view of the heart does V3 show?
Anterior
What view of the heart does V4 show?
Anterior
What view of the heart does V5 show?
Lateral
What view of the heart does V6 show?
Lateral
What view of the heart does Lead I show?
Lateral
What view of the heart does Lead II show?
Inferior
What view of the heart does Lead III show?
Inferior
What view of the heart does aVR show?
Lateral
What view of the heart does aVL show?
Lateral
What view of the heart does aVF show?
Inferior
Name all the leads that provide an inferior view of the heart
Lead II
Lead III
Lead aVF
Name all the leads that provide a lateral view of the heart
V5
V6
Lead I
aVL
aVR
Name all the leads that provide a septal view of the heart
V1
V2
Name all the leads that provide an anterior view of the heart
V3
V4
What is the cardiac axis?
An overview of the heart’s electrical activity
What is positive deflection?
Movement of electrical activity towards that lead
What is negative deflection?
Movement of electrical activity away from that lead
What is the normal cardiac axis? Which leads does this lie between?
-30 to 90
Between aVL to aVR
In a normal cardiac axis where is the overall direction of electrical activity?
Towards leads I, II & III which all show positive deflections (the most positive deflection is in lead II)
Most negative deflection in the aVR as it looks at the heart in the opposite direction
What is a right axis deviation?
Depolarisation is deviated/distorted towards the right - between +90 to +180
Name some causes of right axis deviation
Right ventricular hypertrophy (RVD) (most common cause) - often associated with pulmonary HTN
RVD causes the deflection in lead I to be more -ve and that of lead aVF/III to be more +ve
What is a left axis deviation?
Depolarisation is deviated/distorted towards the left - between -30 to -90
Name some causes of left axis deviation
Conduction abnormalities
Which artery supplies the anterior and septal areas?
Left anterior descending (LAD)
Which artery supplies the inferior area?
RCA (in 70% of people)
Left circumflex (in 30% of people)
Which artery supplies the lateral area?
Left circumflex
Diagonal of LAD
