module 6 cardiac electrophysiology

Question 1

describe the cardiac conduction cycle

Answer 1

1. SA node generates impulse ⇒ 2. impulse travels

through muscle fibers of both atria ⇒3. atria begin to

contract. ⇒action potential enters the AV node from the

right atrium, its conduction slows to allow complete

contraction of both atrial chambers before impulse

reaches the ventricles. ⇒4. after the AV node, conduction

velocity increases as the impulse is relayed through

the AV bundle into the ventricles, stimulating them to

contract almost simultaneously.

Question 2

ECG

Answer 2

Electrocardiogram.

• graphic record of the heart’s electrical activitly, its conduction of impulses
• electrodes are attached
• changes in voltage are recorded that represent changes in the heart’s electrical activity
• the cardiac cycle

Question 3

What does a normal ECG show?

3

Answer 3

1. P wave - depolarization of the atria
2. QRS complex - depolarization of the ventricles and repolarization of the atria
3. T wave - repolarization of the ventricles

measurement of the intervals between P, QRS, and T waves can provide information about the rate of conduction of an action potential through the heart.

Question 4

The cardiac cycle

Answer 4

a complete heartbeat consisting of contraction (systole) and relaxation (diastole) of both atria and both ventricles

Question 5

atrial systole what happens, 5 points

Answer 5

1. contraction of atria completes emptying of blood out of the atria into the ventricles
2. AV valves are open
3. SL valves are closed
4. ventricles are relaxed and fill with blood
5. this cycle begins with the P wave of the ECG

Question 6

isovolumetric contraction

Answer 6

1. occurs between the start of ventricular systole and the opening of the SL valves
2. ventricular volume remains constant as the pressure increases rapidly
3. onset of ventricular systole coincides with the R wave of the ECG and the appearance of the first heart sound

Question 7

Ejection

Answer 7

1. SL valves open and blood is ejected from the heart when the pressure gradient in the ventricles exceeds the pressure in the pulmonary artery and aorta
2. rapid ejection, initial short phase characterized by a marked increase in ventricular and aortic pressure and in aortic blood flow
3. reduced ejection, characterized by a less- abrupt decrease in ventricular volume, coincides with the T wave of the ECG

Question 8

isovolumetric ventricular relaxation

Answer 8

1. ventricular diastole begins with this phase
2. occurs between closure of the SL valves and opening of the AV valves
3. a dramatic fall in intraventricular pressure but no change in volume
4. the second heart sound is heard during this period

Question 9

Passive ventricular filling

Answer 9

returning venous blood increases intra-atrial pressure until the AV valves are forced open and blood rushes into the relaxing ventricles

influx lasts approximately 0.1 second and results in a dramatic increase in ventricular volume

Question 10

Diastasis