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