1 E & 2A : Electrocardiogram (ECG) & Cardiac Cycle

Question 0

What is the Lead I of the ECG?

Answer 0

The potential difference recorded between the electrodes on the persons left arm (LA) and right arm (RA )

Question 1

What is the Basic (3 Lead) ECG?

Answer 1

4 electrodes are placed on both the patient’s arms and the left leg

Question 2

Does a lead equals a electrode?

What is a lead?

Answer 2

No!

a lead is a particular view of electrical actiivity of the heart

Question 3

What is lead II and III?

Answer 3

Lim leads recorded between the right arm and left leg LEAD II
and left arm and left leg LEAD III

Question 4

How many electrodes are used?
What are the 6 precordial(chest) electrodes?
What are the 4 limb electrodes?

Answer 4

10 used.
V1, V2, V3, V4, V5, V6
RA, LA, RL, and LL–> Give 6 views (I, II, III, aVL, aVF, and aVR)

Question 5

What is the P wave?

What is the T wave?

Answer 5

P–>depolarization of the atria

T–> repolarization of the ventricles

Question 6

What is the QRS complex?

Answer 6

• depolarization of the ventricles

- triggers main pumping contractions

Question 7

What is the PQ segment ?

Answer 7

-Time when the impulse is traveling through the AV node, bundle of His, and bundle branches

Question 8

What is the QT interval?

Answer 8

**Onset of QRS complex to end of T wave

Question 9

What is the ST segment?

Answer 9

End of the QRS complex to onset of T wave

Question 10

What is the ST interval?

Answer 10

End of QRS complex to end of T wave

Question 11

What is a normal sinus rhythm (NSR)

Answer 11

Rate- within normal limits for age; in adults 60-100 bpm
Rhythm- Regular
P waves- uniform, positive (upright) in lead II, one precedes each QRS complex
PR interval- within normal limits for age & constant from beat to beat;ln adults 0.12-0.20 sec
QRS duration- 0.10 sec or less

Question 12

What is the PR interval?

Answer 12

Onset of P wave to middle of QRS complex

Question 13

What is overdrive suppression?

Answer 13

The AV Node and the Purkinje fibers are LATENT PACEMAKERS that my exhibit automaticity & override the SA node if it is suppresed.
- The intrinsic rate of phase 4 depolarization ( & HR ) is FASTEST in the SA node and SLOWEST in the Purkinje fibers.

***SA NODE–> AV NODE–> Purkinje fibers

Question 14

What is a cardiac cycle?

Answer 14

• coordinated sequence of mechanical and electrical events that repeats with every heartbeat
• At a HR of 75 bets/min, each cardiac cycle last 0.8 seconds

Question 15

What is systole?

Answer 15

• Period of contraction and emptying

- Atrial systole and ventricular systole

Question 16

What is Diastole?

Answer 16

• Period of relaxation and filling

- Atrial diastole and ventricular diastole

Question 17

What is Stroke Volume (SV)?

Answer 17

• Quantity of blood pumped out either ventricle per beat

- @ REST - 70 ml/beat\; max 120 ml/ beat

Question 18

What is HR?

Answer 18

• # of times the HR bats per minute

- @ REST - 72 bats/min; Max = 230 beats/min

Question 19

What is Cardiac Output? (CO)

Answer 19

• Quantity of blood pumped by either ventricle per minuet
• @ rest= 5L/min; Max 20-25 L/min

**HR X SV = CO

Question 20

What is Venous Return (VR) ?

Answer 20

• Quantity of blood returned to the heart per minute

- Normally, venous returns = CO

Question 21

What is End Diastolic Volume? (EDV)

Answer 21

-Quantity of blood remaining in either ventricle at the end of ventricular diastole

***AVG = 130 ml

Question 22

What is End Systolic Volume (ESV)?

Answer 22

-Quantity of blood remaining in either ventricle at the end of ventricular systole

Question 23

In the Wigger’s Diagram, What happens at the end of isovolumetric ventricular relaxation?

Answer 23

L. Atrial (LAP) exceeds L. ventricular pressure (LVP)

Result: opening of the mitral valve

***Ventricular filling occurs

Question 24

What are the 3 distinct phases of ventricular filling?

Answer 24

1) Rapid passive filling 2) Slow passive filling (diastasis) 3) Atrial Systole

Question 25

What occurs in Rapid passive filling during ventricular filling?

Answer 25

Blood flows quickly thru the mitral valve & into the relaxed ventricle ; Ventricular volume INCREASES * *No muscle contraction occurs * 3rd HEART SOUND PRODUCED

Question 26

What occurs during Slow Passive Filling?

Answer 26

Blood flows slowly thru the mitral valve & into the relaxed ventricle; * ** Ventricular volume continues to increase (majority of ventricular filling!!) * No muscle contraction

Question 27

What occurs during Atrial Systole?

Answer 27

- The L. Atrium must FIRST depolarize - Atria contract---> 4th heart sound produced ** Contribution of atrial contraction to ventricular filling his usually SMALL( 10-15 % of the total ventricular volume)

Question 28

What occurs after Atrial Systole, LVP > LAP and the mitral valve shuts?

Answer 28

The 1st heart sound is produced *** The volume of blood in the left ventricle at this point is the EDV ( increases the pre-load--> increases amount of blood ejected during systole)

Question 29

What occurs during isovolumetric ventricular contraction?

Answer 29

-The L. ventricle must FIRST be depolarized - Ventricles contract, & LVP rises - NO EJECTION of BLOOD OCCURS as the L. ventricular volume remains constant

Question 30

What occurs during RAPID ventricular ejection?

Answer 30

The L. ventricular develops enough pressure such that LVP exceeds aortic pressure -Aortic semilunar valve OPENS and BLOOD is EJECTED; Aortic pressure rises & L. Ventricular pressure

Question 31

What occurs when entering back into isovolumetric ventricular relaxation?

Answer 31

-Once blood is ejected, LVP falls below Aortic pressure & the Aortic Semilunar valve SHUTS; 2nd heart sound produced - Volume of blood remaining in the L. Ventricle after ejection is the ESV - Aortic pressure falls as blood runs off to arteries * **T wave produced

Question 32

During Isovolumetric ventricular relaxation what occurs when all 4 chambers are relaxed and all of tis valves are CLOSED?

Answer 32

- Ventricular volume is constant; Ventricular pressure is decreasing - The L. atrium is filling w/ blood that has returned to it via pulmonary veins; atrial pressure is rising

Question 33

What occurs during the Dichrotic Notch?

Answer 33

-CLOSURE of the AORTIC VALVE causes a brief rise in aortic pressure as back-flowing blood rebound off the closed valve cusps Note: significant in relation to coronary blood flow !