Normal cardiac electrical and mechanical function

The ECG is a record of the average electrical potential generated in the heart muscle and graphed in terms of voltage against time during the different phases of the cardiac cycle

The sinoatrial node

The atrioventricular node

SA node --> right atrial muscle --> left atrial muscle --> AV node --> Bundle of his --> bundle branches --> endocardium --> purkinjie fibres --> epicardium

A negative and positive charge separated by a distance

Upward

• positive ions eg Na⁺
• The inside of the cell becomes positive (normally negative) and the outside becomes negative (normally positive)

The inside of the cell becomes negative and the outside of the cell becomes positive

P wave

Q wave

R wave

S wave

T wave

The time between atrial depolarisation and ventricular depolarisation

The length of time the ventricles remain depolarised

The time taken for ventricular depolarisation to occur once the wave of depolarisation has passed through the AV node from the atria

The time between atrial depolarisation

The time between ventricular depolarisation

The atria

The heart as a whole

• Right forelimb = red
• Left forelimb = yellow
• Right hindlimb (earth) = black
• Left hindlimb = green

the heart rate

Arrhythmia

Chamber enlargement

True, as electrical activity of the heart is dependent upon changes in ion concentration

An increased T wave ("more T more pots")

25mm/sec or 50mm/sec

Sinus arrhythmia

Physiological - due to a combination of inspiring and changes in intrathoracic pressure

• Systole - the period of ventricular contraction
• Diastole - the period of ventricular relaxation

• S1 = 'lub'.  This is associated with the mitral and tricuspid valves closing.
• S2 = 'dub'.  This is associated with the aortic and pulmonary semilunar valves shutting.
• S3 = 'whoosh'.  Associated with rapid ventricle relaxation.  
• S4 = 'dub'.  This is associated with turbulence during atria contraction.

A murmur