ECG LP 05

Question 1

ECG IN CONDUCTION ABNOR

Answer 1

Delaying/blocking the stimulus in a certain territory (situated in the specific conduction tissue or in the myocardial muscle).

Question 2

CLASSIFICATION OF THE CONDUCTION ABNORMALITIES (I) - LOCATION

Answer 2

Sino-atrial block = the stimulus is delayed/blocked between SAN and the atrial muscle.
Interatrial block = the stimulus conduction between the two atria is perturbed.
AV blocks = the stimulus is delayed/blocked between atria and ventricles, in AV node.
Intra-ventricular conduction abnormalities = the stimulus way is perturbed in one/more of the branches/fascicules/terminal ramifications of HIS bundle

Question 3

CLASSIFICATION OF THE CONDUCTION ABNORMALITIES (II) - SEVERITY

Answer 3

1. First degree blocks - just a delay of the stimulus.
2. Second degree blocks - intermittent blocking of the stimulus.
3. Third degree blocks - complete and permanent blocking of the stimulus

Question 4

ETIOLOGY OF THE CONDUCTION ABNORMALITIES

Answer 4

Ischemic heart disease
Endocarditis, myocarditis, collagen diseases,
Degenerative diseases of the conduction tissue (e.g. Lenegre disease)
Congenital defects of the conduction tissue (AVN agenesy)
Iatrogenic:
- coronarography
- cardiac surgery
- drugs that induce depression of conduction, especially in AV node: digoxin, beta (- sympathetic) blockers, calcium-blockers (verapamil), other anti-arrhythmic drugs

Question 5

ATRIO-VENTRICULAR BLOCKS (AVB)

Answer 5

A delay/ a blocking of transmission of the electrical stimulus between atria and ventricles.

The delaying/blockage may be situated in the AV node or in the His bundle.
There are 3 degrees of AVB:

Question 6

FIRST DEGREE AVB

Answer 6

 just a delay of the stimulus
all P waves are followed by QRS complex
PR interval is longer than 0.20 s

Question 7

SECOND DEGREE AV BLOCK

Answer 7

Intermittent blockage: some impulses from the atria go through to the ventricles, 
but some are blocked.
Some P waves are followed by a QRS complex and some are not.
There are 4 types of second degree AVB:
Mobitz I = Wenckebach 
Mobitz II
Advanced or high degree 
Second degree AVB 2/1 ratio

Question 8

MOBITZ I = WENCKEBACH

Answer 8

PR intervals are prolonged more and more until one atrial impulse is blocked. Then the cycle restarts.
PP interval is constant.
P/QRS ratio = n/n-1.
This cycle is called a ‘Wenckebac period’

Question 9

MOBITZ II

Answer 9

PR interval is constant in duration throughout the entire ECG tracing.
The PR interval may have a normal duration or it may be > 0.20 sec (association with
first degree AVB)
P/QRS ratio = n/n-1
Because not all P waves are followed by QRS complex, the ventricular rhythm is irregular in second degree AVB type Mobitz I and II (RR intervals are not constant)

Question 10

ADVANCED OR HIGH DEGREE

Answer 10

More P waves are blocked than transmitted.
PP interval is constant; RR interval is constant
P/QRS ratio = n/1

Question 11

SECOND DEGREE AVB WITH 2/1 RATIO

Answer 11

It can’t be classified as a Mobitz I or II type.
There are no two consecutive P that are transmitted.
PP interval is constant; RR interval is constant (and double the PP).
One P wave is transmitted, one P wave is blocked.

Question 12

THIRD DEGREE AVB OR ‘COMPLETE’ AVB

Answer 12

No stimulus from the atria is transmitted to the ventricles.
The atria have their pace (PP is interval constant) while the ventricles have theirs.
This is an ‘atrio-ventricular dissociation’.
The ventricles are controlled by a ventricular pace-maker situated after the blockage: in the inferior portion of AV node, in the His bundle, in a branch or in the Purkinje network.
In this situation, on ECG tracing, the relationship between the P waves and the QRS complexes is totally random.
The ventricular rhythm is usually a regular rhythm = the RR interval is constant

Question 13

NODO-HISIAN RHYTHM

Answer 13

The ventricular pace-maker is situated in the inferior portion of AV node or in the  Hiss bundle.
The frequency is 50 – 40 bpm
The QRS complex is narrow (normal).
(red arrows = P wave)
IDIO-VENTRICULAR RHYTH

Question 14

IDIO-VENTRICULAR RHYTHM

Answer 14

The pace-maker is situated in one of the His bundle branches or in the Purkinje network.
The ventricular rate (and the heart rate) = 35 – 25 bpm.
The QRS complex is wide and it has a modified morphology (mimicking LBBB or RBBB)

Question 15

BUNDLE BRANCH BLOCKS

Answer 15

Intraventricular conduction abnormalities: the impulse is delayed/ blocked in one of the branches/ fascicle.
The impulse is transmitted through nonspecific myocardial cells, with a slower speed = the activation is delayed in that territory.
Secondary repolarization anomalies (ST/T changes) are present.
On ECG we can evaluate intraventricular blocks only if there is a supra-ventricular rhythm (= a rhythm that is generated by an atrial or junctional pace-maker).

Question 16

RIGHT BUNDLE BRANCH BLOCK

Answer 16

Complete blockage of the stimulus in the RBB.
Ventricular depolarization is made just with the help of LBB.
Septum depolarization is normal and it is followed by the left ventricle depolarization.
Then, the impulse is transmitted slowly toward the right ventricle (which, in the absence of a viable right branch, has not yet been depolarized).
RBBB ON ECG
QRS complex duration ≥ 0.12 sec.(‘wide’ QRS)
Frontal leads – the aspect may vary with the axis deviatio

Question 17

RBBB ON ECG

Answer 17

QRS complex duration ≥ 0.12 sec.(‘wide’ QRS)
Frontal leads – the aspect may vary with the axis deviation
right axis deviation (120 -150 degree)
DIII, aVF: positive QRS : RsR’, RR’, indented R
DI, aVL: negative QRS : rS , wide S wave
Horizontal leads
V1, V2: the most important aspect
- positive QRS : RsR’, RR’, indented R,  depressed ST and negative T
- R pick time > 0.07 sec.
- V5, V6: normal R followed by wide, deep S wave

Question 18

LEFT BUNDLE BRANCH BLOCK (LBBB)

Answer 18

Ventricular depolarization:
 The septal depolarization is abnormal, from right to left, followed the right ventricle depolarization, and then the left ventricular activation takes place (slowly).
The repolarization is also modified: the right ventricle that was first and normally activated will be the first to repolarize. So the repolarization vector is oriented towards right, down and anterior.

Question 19

LBBB ON ECG

Answer 19

QRS complex duration ≥ 0.12 sec.(‘wide’ QRS)
Frontal leads
left axis deviation (- 30 degree).
DI, aVL: positive QRS : wide R wave with plateau
DIII, aVF: negative QRS : rS , wide S wave
Horizontal leads
V5, V6: the most important aspect  positive QRS : wide R wave with plateau  depressed ST and negative T  R peak time > 0.07 sec.
V1, V2: small r followed by wide, deep S wave; sometimes QS wave

Question 20

LEFT ANTERIOR FASCICULAR BLOCK (LAFB)

Answer 20

The left ventricle is activated only through the posterior fascicle: the postero-inferior part of the LV is rapidly depolarized and becomes electro (-) and the antero-superior part is depolarized later (through nonspecific myocardial cells), remaining more time electro (+).
The depolarization vector is oriented from inferior to superior in the frontal plane
The electrical axis of the ventricular complex is left deviated, between -60° and -90°.

Question 21

LEFT POSTERIOR FASCICULAR (LPFB)

Answer 21

LV depolarization is slow in the postero-inferior part and this region remains longer electro (+) during ventricular depolarization.
The resultant ventricular depolarization vector is oriented towards inferior and right in the frontal plane
Right axis deviation, usually between +120° and +160°