How the Heart Works.Electrical activity in the heart.

Blood flow through the heart

http://www.youtube.com/watch?v=Ww2OAsAUIT0

Right Side- Deoxygenated blood

enters the right atrium through 2 large veins - Superior vena cava:

upper half of the body- Inferior vena cava:

below the diaphragm

Left Side- Oxygenated

blood (from the lungs) enters the left atrium through the pulmonary vein

Heat BeatsStep 1: Enter Atrium

Heat BeatsStep 2: Contract Atrium

• Blood flows from the atrium into the ventricle

• The atrioventricular (AV) valve allows for a one-directional flow

• The AV valve closes once the ventricle is full

Heat BeatsStep 3: Contract Ventricle

Right Side•Right ventricle contracts•Blood flows through the pulmonary valve into the pulmonary arteries •Blood flows towards the lungs

Left Side•Left ventricle contracts•Blood flows through the aortic valve into the aorta (largest artery)•Blood flows out towards the body

2 parts of the heart beat

• Two parts of Heart Beat– LUB: closure of the AV valves (beginning of

ventricular contraction - systole)

– DUB: closure of the pulmonary & cardiac valves (end of ventricular systole – diastole)

Electrical structures of the heart

Electrical activity through the heart

Starts from SA node in the Right Atrium (top R)Causes Atria to contract (ventricles fill with blood)Impulse sent to the AV node (bottom R of RA)Impulse travels down bundle branches & Purkinje fibresVentricles contract!

Electrocardiogram - ECG

• P wave: SA node fires and the atria contract

• QRS complex: AV node stimulates the ventricles to contract (AV valves close)

• T wave: ventricles relax (the pulmonary valve and aortic valve close)

Normal sinus rhythm

ECG is used to measure:

- heart rate & regularity of heartbeats

- the size and position of the chambers

- any damage to the heart

- the effects of drugs or devices used to regulate the heart

Atrial Fibrillation

• Visible: lack of P wave

• Cause: hypertension

• Result: chest pain, heart palpitations, fainting, heart failure, higher risk of stroke

• Treatment: blood thinners, medication to slow heart rate

Ventricular Fibrillation

• Visible: no clear rhythm

• Cause: heart attack

• Result: chest pain, NO heart beat

• Treatment: defibrillation (Shock)

AV Block

• Visible: delay between S wave & P wave

• Cause: many... decrease O2 in blood

• Result: depends on severity

• Treatment: pacemaker

Asystole

• Visible: no waves

• Cause: lack of electrical activity

• Result: no blood flow, no contractions

• Treatment: none