DSA: Abnormal ECGs

Question 1

What happens when the SA node fires?

Answer 1

1. AP is distributed throughout the atria
2. Sent to the AV node via the internodal pathway, where conduction is delayed–> ventricles are depolarized–> AP stops due to the cartilaginous rings.
3. Repolarization occurs backwards

Question 2

What is the purpose of the AV nodal delay?

Answer 2

Allows the atria to contract and pump all of the blood into the ventricles, before it begins to contract

Question 3

In the ventricles, what is the first and last to depolarize?

Answer 3

1st to depolarize–> septum

Last to depolarize–> posterior aspect of the L heart

Question 4

Why is the first ventricular myocyte to depolarize the last to repolarize?

Answer 4

The durations of the plateu phases of the AP are different.

The first ventricular myocyte has the longest plateau.

Question 5

What lead gives us a good view of what is going on from L–> R in the heart, but a poor view of events moving up or down?

Answer 5

Lead 1

Question 6

One of the limitations of either the augmented unipolar leads or the standard limb leads is that?

Answer 6

They all look at the heart from the same plane (the coronal, to use the anatomist’s term).

In order to view the heart from another plane (the transverse or horizontal plane), we use the six chest leads.

Question 7

What occurs during the P wave?

Answer 7

SA nodal depolarization

Atrial depolarization

Question 8

What occurs during the PR interval?

Answer 8

Depolarization from the SA node THROUGH the AV node via the internodal pathway.

Question 9

What is the QT interval?

Answer 9

Total time the ventricles are contracted

Question 10

What phase is QRS of ventricular AP?

Answer 10

Phase 0

Question 11

What refractory period occurs during the ST segment?

Answer 11

Absolute refractory period.

Question 12

At the end of the QRS complex, all ventricle myocytes are depolarized in phase ___ of the AP.

Answer 12

2

Question 13

What should we remember about how the T-wave relates to the QRS complex?

Answer 13

They often head in the same direction within 1 lead, despite their electrical events being opposite of one another.

Question 14

QT interval time

Answer 14

.35 seconds

Question 15

R-R interval time

Answer 15

Use to find HR

-0.6seconds to 1 second

Question 16

time in 1 little square

1 box

Answer 16

times in 1 little square= 0.04s

1 box= 0.2s

Question 17

The mean electrical axis tells us what?

Answer 17

the net direction the depolarization or repolarization is heading.

Question 18

______ degrees - meaning that the net depolarization is heading almost straight down towards the apex of the heart

Answer 18

Around 85 degrees

Question 19

Pt has a L ventricular hypertrophy but a normal conduction pathway. What will this do to the ECG?

Answer 19

Increase the amplitude (height) of the QRS

Question 20

What does normal sinus rhythm mean?

Answer 20

SA node is driving the heart

Question 21

What is sinus tachycardia?

How will this affect the ECG?

Answer 21

SA node is driving the heart, but at a faster rate than normal (>100 bp/min).

-PR interval may be shorter than normal

-QRS interval may be shorter than normal

Question 22

Sinus Bradycardia is the result of a what?

What do we see on the ECG?

Answer 22

Long phase 4 in the pacemaker cells of the SA node.

Prolonged PR interval and QT interval.

Question 23

In sinus bradycardia, the heart rate may get so slow, that what may happen?

Answer 23

Another pacemaker takes over.

Question 24

What is a flutter?

Fibrillation?

Answer 24

Flutter- depolarization tavels around the around, but does not stop; producing a high-rate weaker than normal contraction.

If we see chaos (same path is not taken every time), we see fibrillation. Heart cannot pump even though it is still depolarizing.

Question 25

What is this?

Answer 25

A fib - No P waves - QRS and T waves are normal - QRS complex are irregularly irregular

Question 26

What prevents a A-fib from becoming a V-fib?

Answer 26

**Slow conduction time of the AV node**

Question 27

What is this?

Answer 27

**V-fib** ## Footnote Ventricular flutter becomes v-fib.

Question 28

In V-fib, the most dangerous PVC occurs where on ECG? Why?

Answer 28

T wave - During the T wave, part of the ventricular myocardium is depolarized (in absolute refractory period) while the other parts are repolarized (not in absolute refractory period). By the time the depolarization travels around the heart, the muscle that was refractory has now repolarized and is ready to conduct the depolarization - so the depolarization just keeps going around the heart.

Question 29

SA nodal block is defined as a failure of the cardiac action potential to emerge from the SA node. How ? How will this look on the ECG?

Answer 29

-Pacemaker cells of the SA node work, but the AP cannot be spread from the SA node. ## Footnote -A flat line (whole thing is flat). Luckily, SA nodal block is intermittent and lasts only a beat or two. IF perm, you need a pacemaker

Question 30

What is this?

Answer 30

First degree AV blockà AV nodal depolarization is slower than normal, but that _every impulse generated by the SA node does get through to the ventricles_. Only differences: **Rate and rhythm are normal, but the PR interval is prolonged beyond the normal upper limit of 0.21 seconds.**

Question 31

What is this?

Answer 31

AV node is damaged so it remains refractory and unable to conduct an action potential for a much longer time than normal. 1. Thus, ventricular depolarization occurs intermittingly, causing losses of QRS waves in the reading. So, not every P wave is followed by a QRS complex.

Question 32

**What are the two types of 2nd degree AV nodal block?**

Answer 32

**1. Mobitz I block (Wenckebach)** **2. Mobitz II block**

Question 33

Mobitz II block?

Answer 33

AV node refractory period is so long that AV node cannot conduct on a regular bassis. AV nodal depolarization fails intermittingly, causing losses of QRS waves in the reading. **AV block is that not every P wave is followed by a QRS complex.**

Question 34

Mobitz I block?

Answer 34

PR interval gradually increases until the QRS segment is dropped. Cycle resumes on next beat.

Question 35

QRS complex of the 2nd AV nodal blocks are a result of what?

Answer 35

QRS complexes that occur are the result of the **depolarization initiated by the SA node.**

Question 36

What is this?

Answer 36

**Third degree AV block-** AV node does not conduct depolarization from the atria--\> ventricles. SA node will fire and depolarize atria,But the AV node does not conduct the AP at all. Thus, the ventricles are not depolarized. However, our backup pacemakers such as bundle branches or BoH will depolarize them - complete dissociation of P and QRS wave - atrial rate of 120 b/min and a ventricular rate of 45 b/min) - P waves occur virtually on top of QRS complex

Question 37

If bundle of His takes over in third degree AV nodal block, what happens to the QRS complex?

Answer 37

look normal - rate of 30-40 min--\> j**unctional rhythm**