Normal Findings and Variants

Question 1

What are the two types of cardiac muscle cells?

Answer 1

Myocardial conduction cell - 1%
Highly specialised cells that allow electricity to be conducted throughout the heart- Automaticity

Myocardial contraction cell 99%

Question 2

What is the resting membrane potential of a contraction cell when polarised?

Answer 2

-90mV

Question 3

What does adjacent cell simulation cause?

Answer 3

ion channels to open and close in pattern causing ionic flux termed depolarisation and repolarisation

Question 4

Where is the SA node located?

Answer 4

posterior wall of RA

Question 5

What are the characteristics of the SA node?

Answer 5

sized 20 by 4 mm
unstable membrane potential
blood supply -
right coronary artery 59%
circumflex 38%
both 3%

Question 6

What is the AV node?

Answer 6

mass of cells and connective tissue
located in lower posterior region of the inter-atrial septum
Blood supply-
RCA 90%
LCF 10%

Question 7

On average, how long is the delay at the AV node?

Answer 7

100ms

Question 8

Why is there a delay at the AV node?

Answer 8

Allow atria to contract fully before fventricular filling

Question 9

Why is there a delay at the AV node?

Answer 9

Allow atria to contract fully before ventricular filling

Protection mechanism- prevents ventricular rates exceeding 230bpm

Question 10

What is the bundle of his?

Answer 10

Bundle of fast active muscle fibres

Blood flow supplied by the Left anterior descending (LAD) and posterior
descending (PDA) arteries

Conveys the electrical impulse from the AV node to the upper part of the
interventricular septum and onto the left and right bundle branches

Question 11

What are the normal features of a P wave?

Answer 11

height should not exceed 0.25 mV (2 1/2 small squares)

duration should not exceed 120ms (3 squares)

Question 12

What are the features of a normal P wave in V1?

Answer 12

Biphasic

Question 13

What is a normal atrioventricular relationship?

Answer 13

Every P wave should be followed by a QRS

Relationship should be constant

PR interval should not vary

Question 14

What is a normal QRS duration?

Answer 14

80-100ms

Question 15

What is a normal PR interval?

Answer 15

120-200ms

Question 16

What classifies as abnormal ST depression?

Answer 16

0.5mm (half a square)

Question 17

Is ST elevation normal?

Answer 17

no

Question 18

Depolarisation occurs from e_____ to e______. Hence, the T wave is a depolarisation wave heading towards the exploring electrode.

Answer 18

Repolarisation occurs from endocardium to epicardium. Hence, the T wave is a depolarisation wave heading towards the exploring electrode.

Question 19

Repolarisation occurs from e______ to e_______ and is an opposite wave to depolarisation. A repolarisation wave travelling away from exploring electrode also gives a positive deflection. Therefore, the T wave should be in the same direction as the QRS.

Answer 19

Repolarisation occurs from the epicardium to the endocardium and is an opposite wave to depolarisation. A repolarisation wave travelling away from exploring electrode also gives a positive deflection. Therefore, the T wave should be in the same direction as the QRS.

Question 20

The T wave should be inverted in lead ___ and possibly V _ and V _.

Answer 20

The T wave should be inverted in lead AVR and possibly V1 and V2.

Question 21

Should the T wave be symmetrical? The __slope should be slower than the ____slope.

Answer 21

No
The upslope should be slower than the downslope.

Question 22

The T wave amplitude should not be any taller than _mm in leads __ , __, __. And no taller than __mm in precordial leads.

Answer 22

The T wave should not be any taller than 5mm in leads I, II, III. And no taller than 10mm in precordial leads.