Cardio

Question 1

Describe the events in an ECG

Answer 1

1. Atrial depolarisation, initiated by SA node causes the P wave.
2. With atrial depolarisation complete, the impulse is delayed at the AV node.
3. Ventricular depolarisation begins at the apex causing QRS complex, atrial repolarisation occurs.
4. Ventricular depolarisation is complete.
5. Ventricular repolarisation begins at apex causing T wave.
6. Ventricular repolarisation is complete.

Question 2

1. Ventricular filling stage of cardiac cycle

Answer 2

• mid to late diastole
• pressure in the heart is low
• blood flows passively through the atria and the open AV valves into ventricles
• aortic and pulmonary valves are closed
• 80% of filling occurs during this period
• atrial contraction delivers last 20%
• at this point ventricles have maximum volume of blood know as end diastolic volume (EDV)

Question 3

2. Ventricular systole stage of cardiac cycle

Answer 3

• Atria in diastole
• As atria relax, ventricular wall start to contract
• Ventricular pressure rises
• Closing AV valves
• Isovolumetric contraction is the split second period where ventricles are contracting but blood volume stays the same
• Pressure exceeds pressure in aorta and pulmonary arteries.
• Pulmonary and Aortic valves open blood, rushes out

Question 4

3. Describe Isovolumetric relaxation stage of cardiac cycle

Answer 4

• early diastole
• following t-wave ventricles relax
• blood remaining in the ventricles (ESV) is no longer compressed so ventricular pressure drops
• SL valves close

Question 5

Factors affecting heart rate

Answer 5

• sympathetic pathway activated by physical or emotional stress
• heart rate: anxiety, exercise
• parasympathetic slows heart rate
• increased or decreased levels of CO2 in blood changes BP which involves reflexive controls of HR
• hormones in blood, adrenalin, noradrenalin, thyroid hormone
• levels of Ca+ and K+

Question 6

Factors affecting cardiac output

Answer 6

Cardiac Output = Heart Rate x Stroke Volume

Affected by changes in EDV AND ESV

• coronary atheroslerosis impairs O2 delivery to cardiac muscle, effects contractility
• hypertension
• succession of MI’s