Electrocardiography Flashcards
What does the SAN do?
Spontaneously active cells
Conducts current down atria & internodal pathways
P-wave of ECG
What happens at the AVN?
Current slows down -> atrial muscle contraction
What happens at the septum and his-Purkinje fibres?
Current travels through septum -> His-Purkinje system
Rapid conduction through left & right bundle -> Purkinje fibres -> ventricular contraction
= QRS complex of ECG
Cardiac muscle relaxes & membrane potential
recovers/repolarises
= T-wave of ECG
how many leads in a normal ECG and what 2 areas are their placement split into?
10 electrodes-> 12 lead recording
Limb leads (coronal view)
Chest leads (axial view)
Where are limb leads placed?
Where are Chest leads placed?
V1: 4th intercostal space (ICS), right margin of the
sternum
V2: 4th ICS along the left margin of the sternum
V4: 5th ICS, midclavicular line
V3: midway between V2 and V4
V5: 5th ICS, anterior axillary line
V6: 5th ICS, mid-axillary line
What causes right axial and left axial deviation?
Gravity
what angles are Right axial and left axial deviation?
LAD= 0 to -90
RAD= 90 to 180
What does the biggest QRS complex show?
The deviation of the heart
What does atrial fibrillation lead to in terms of the ECG?
loss of p wave
What does atrial flutter lead to in terms of the ECG?
saw tooth pattern
What is rhythm?
movement of current, between P and QRS
What are the types of heart blocks?
1st, 2nd, 3rd
What affects the P-R interval?
conduction from atria to ventricles
- e.g., heart blocks
What does a 1st degree heart block do?
delay in conduction
What does 2nd degree heart block do?
loss of conduction
What is a 3rd degree heart block?
a medical emergency
What can happen to an ST segment in an ECG?
elevation or depression
How do you calculate rate from an ECG?
300/ number of large squares between 2 QRS complex
(like the rox of squares)
How do you calculate PR interval from an ECG and what is a normal PR?
5 x small squares
normal PR is 120-200ms
How do you calculate QRS duration from an ECG?
2.5 x small squares
What does an elevated ST segment?
ST elevated myocardial infarction
What does a saw tooth pattern suggest?
atrial flutter
What does a long PR interval suggest?
480ms
What does a slow and regular heart rate, and P wave is only occasionally associated with QRS (2:1)?
second degree heart block
What does a slightly depressed ST segment, and right axis deviation (120-150 degrees) suggest?
Right axis deviation (right ventricular hypertrophy/ pulmonary artery hypertension)
How do you know there’s a RAD?
If the QRS is predominantly negative in lead I and positive in lead aVF, then the axis is rightward (right axis deviation).
How do you know there is a LAD?
If the QRS is upright in lead I and downward (negative) in lead aVF, then the axis is between 0 and -90 degrees, likely left axis deviation.
