practical 5- ECG & anatomy of the heart

how to convert sec to msec

times by 1000

where does the left ventricle pump blood

throughout the systemic circulation

where does the right ventricle pump blood

throughout pulmonary circulation

2 ways cardiac muscle & skeletal muscle are different

1. cardiac muscle cells = short, branched, uninucleate skeletal muscle = long, cylindrical, multinuclated

2. cardiac muscle has involuntary contraction, skeletal muscle has voluntary control for contraction (stimulation of somatic motor neurons)

what are pacemaker cells + function

• specialised myocytes

• produces action potential faster than other myocytes & contributes to automatic and rhythmic ability

• makes up the SA node

4 things for all ECG recordings

1. pair of electrodes is needed to measure difference in electrical potential

2. potential difference is recorded when a wave of depolarisation moves between 2 electrodes

3. multiple electrode placements are used to get a 3D view of cardiac activity

4. minimal electrode connections: right arm, left arm, left leg (right leg)

colours + location of electrodes needed for EMG

• black: left arm

• white: right arm

• green: right/left leg

why is a ground electrode needed

for electrical stability (prevents interference & provides a baseline)

6 stages of the cardiac cycle

• SA pacemaker fires and depolarisation spreads across atria

• activation of AV node and bundle of His

• depolarisation spreads through interventricular septum

• depolarisation spreads through ventricular walls

• depolarisation reaches basal points of the ventricle ring

• repolarisation of ventricles

what does the P wave represent

spread of depolarisation across the atria

what does the QRS complex represent

spread of depolarisation across the ventricles

Q wave of QRS complex

depolarisation of the interventricular septum

R wave of QRS complex

depolarisation of the main mass of the ventricles

S wave of QRS complex

last phase of the ventricular depolarisation at the base of the heart

what does the T wave represent

repolarisation of ventricles

why is atrial repolarisation not shown on the ECG

its hidden by the large surface potentials of the QRS complex

what does a QRS complex look like in a normal heart

tall R (highest peak) & deep S

2 groups of disorders ECG helps diagnose

abnormalities & ventricular

3 types of abnormalities ECG can detect

• cardiac rate (tachycardia/bradycardia)

• rhythm (arrythmia)

• conduction (heart block, arrythmias)

how are abnomalities detected by ECG

changes in frequency/timings of P & QRS waves

3 ventricular changes ECG can detect

• muscle damage

• depth

• overgrowth (hypertrophy)

how are ventricular changes detected

changes in size/shape of QRS & T waves

which phase of depolarisation is larger + why

• ventricular depolarisation

• ventricles have larger muscle mass than atria (to pump blood out of the heart)

• purkynje fibres are involved (found in ventricular wall)

which wave is the largest on ECG

QRS complex

when listening to the heart what 3 areas produce sound

• L2 pulmonary (pulmonary valve area)

• APEX mitral (where 1st heart sound is ‘lub’)

• R2 aortic (tricuspid valve area)