EKG and the Cardiac Cycle Study Guide

Question 1

3 portions of a cardiac action potential

Answer 1

• Depolarization: opens fast Na+ channels, extracellular Na+ enters (rising phase of action potential)
• Voltage change opens ca2+ channels, influx of extracellular ca2+ (plateau)
• repolarization : results from inactivated ca2+ channels; the opening of K+ channels – an efflux of K+ (ca2+ either pumped out of cell or into SR, resting potential is restored)

Question 2

significance of the plateau phase

Answer 2

Sustained contraction ensures efficient ejection of blood from ventricles, and the longer absolute refractory period avoids tetany

Question 3

3 waves/deflections on a typical EKG

Answer 3

P wave, QRS complex, T wave

Question 4

electrical event causes p wave to appear

Answer 4

movement of the depolarization wave from SA to AV node

Question 5

electrical event causes qrs complex to appear

Answer 5

ventricular depolarization, precedes ventricular contraction

Question 6

electrical event causes t wave to appear

Answer 6

results from ventricular repolarization

Question 7

Why is atrial repolarization not seen on a typical EKG?

Answer 7

Its occurs during ventricular depolarization – the resulting wave is obscured by the QRS complex

Question 8

interval

Answer 8

duration of time that includes 1 segment and 1+ wave

Question 9

Segment

Answer 9

a region between two waves

Question 10

What is the possible clinical significance of an elevated or depressed ST segment?

Answer 10

They can indicate cardiac ischemia (reduced blood flow to the heart)

Question 11

4 electrical events and the 4 correlating mechanical events of each cardiac cycle

Answer 11

Atrial depolarization = DIASTOLE
Ventricular depolarization = SYSTOLE
Atrial repolarization = SYSTOLE
Ventricular repolarization = DIASTOLE
* electrical events always precede mechanical events

Question 12

Systole

Answer 12

contraction – blood is forced out of the heart’s chambers

Question 13

Diastole

Answer 13

blood refills the heart’s chambers

Question 14

4 steps of the cardiac cycle

Answer 14

1. Ventricular filling
2. Isovolumetric contraction
3. Ventricular ejection
4. Isovolumetric relaxation

Question 15

cardiac steps when the ventricles are closed chambers

Answer 15

Isovolumetric contraction and Isovolumetric relaxation

Question 16

AV and SL valves are open or closed in each step of the cardiac cycle?

Answer 16

Ventricular filling – AV VALVES OPEN, SL VALVES CLOSED
Isovolumetric contraction – AV VALVES CLOSE, SL VALVES CLOSE
Ventricular ejection – AV VALVES CLOSE, SL VALVES OPEN
Isovolumetric relaxation – SL VALVES CLOSE, AV VALVES CLOSE

Question 17

EDV - end diastolic volume

Answer 17

the maximum volume of blood that the ventricles will contain in the cardiac cycle

Question 18

ESV

Answer 18

the un-ejected blood remaining in the ventricular chambers

Question 19

Dicrotic Notch

Answer 19

a brief rise in aortic pressure caused by blood rebounding off the newly closed aortic valve

Question 20

Which is a higher-pressure circuit: the pulmonary or the systemic?

Answer 20

Systemic circulation = higher pressure

Question 20

average pressure in the pulmonary trunk

Answer 20

24/10 mmHg

Question 21

average pressure in the aorta

Answer 21

120/80 mmHg

Question 22

How does pressure correlate with what you’ve learned about ventricular anatomy and workload?

Answer 22

the left side, with the aorta in the systemic circulation, has a much higher workload bc it is spreading blood to the whole body

Question 23

What causes the sounds heard during auscultation?

Answer 23

closure of valves

Question 24

Closure of the _____ Valves is the 1st Sound (“lub”).

Answer 24

av

Question 25

Closure of the __ Valves is the 2nd Sound (“dup”).

Answer 25

sl

Question 26

heart murmur

Answer 26

Abnormal heart sound due to turbulent blood flow

Question 27

How can a heart murmur eventually result in a weakened myocardium

Answer 27

Backflow of blood / turbulent flow of blood due to malfunctioning valves can weaken myocardium, as it will have to work harder (stenotic (narrow) valves cause a clicking sounds from reduced blood flow)