ecg

what are pacemaker cells collectively known as

sino atrial node

where are the pacemaker cells/sinoatrial node located

right atrium

how do cardiac muscle cells differ from skeletal muscle cells

• longer action potential - 200ms

• not multinucleated

• both striated

• cells are joined by intercalated discs

electrical conduction pathway

1) sino atrial node pacemaker cells fire and depolarisation spreads across atria

2) activation of AV node and Bundle of His

3) depolarisation of septum

4) depolarisation spreads though venticle walls through purkinje fibres

5) repolarisation of the ventricles

PR interval on ECG

• delay between atrial and ventricle contraction

• approximately 0.1 second

purpose of ground electrode

• subtract interference

• safety reference

• placed on right leg

why are the 3 limbs used

• 3 points of equilateral triangle

• equal distance from heart

colours for each wire

• right arm white

• left arm black

• left leg green (ground electrode)

what is a lead

pair of electrodes

bipolar lead

• pair of electrodes

• read potential difference between two limbs

• influenced by position of leads

waves on ECG

• P wave - spread of depolarisation across atria

• QRS complex - spread of depolarisation across ventricles

• T wave - repolarisation of ventricles

what two types of disorders can ecg identify

• abnormalities

• ventricular problems

examples of ecg disorders

• tachycardia, bradycardia

• arhythmias

• conduction problems - heart block

• ventricular muscle damage, death, hypertrophy

how can abnormalities in ecg be detected

• change in frequency and timings of P and QRS complex

how can ventricular muscle damage, death and hypertrophy be detected

• changes in shapes and sizes of QRST waves

effect of exercise on ECG

• intervals shorten - RR interval (peaks of waves) because faster conduction through AV node

• st segment depression

• heart rate increases