BASIC INTERPRETATION OF ONE MORE KIND OF ABNORMAL ECG: CONDUCTION DIFFICULTY

1. Conduction Difficulty
In ECG
SHILPASREE SAHA
ASSISTANT PROFESSOR, NIHS

2. INTRODUCTION
• Conduction blocks are another type of ECG abnormality.
• The propagation of a cardiac impulse may be inhibited or terminated along the
conduction pathway. Blockage can occur at the sinus node, between the atria and
ventricles, Or within the ventricular conduction system.
• Sinus block occurs if the impulse cannot propagate beyond the sinus node. In this
case, the AV junction usually takes over as the pacemaker, and a junctional
rhythm is seen with the absence of P-waves.

3. • More common are the A V blocks. They are ranked as first, second, or third-
degree, depending on the extent of delay or obstruction of the cardiac impulse
between the atria and ventricles.

4. FIRST-DEGREE A V BLOCK
• First-degree A V block is
characterized by a prolongation of
the P-R interval beyond its normal
0.2 seconds.
• Each impulse is delayed between the
atria and ventricles but each
eventually reaches the ventricular
conduction system resulting in a
normal QRS complex. Thus for each
P wave, there is a QRS complex;
therefore the conduction ratio is 1:
1.

5. SECOND-DEGREE A V BLOCK
• In second degree block Mobitz type I,
also known as Wenckebach, the P-R
interval lengthens progressively until
a P-wave fails to conduct to the
ventricles.
• The first three P-R intervals lengthen
until, after the fourth P-wave, a QRS
complex fails to appear. The cycle
then repeats itself.

6. • Second degree block Mobitz type 2 is
characterized by a fixed P-R interval
with a "dropped“ QRS following
every second, third, or fourth P-wave.
The conduction ratio in is 3: I, or
three P-waves for each QRS complex.
Both first and second-degree A V
blocks are considered to be
incomplete heart blocks.

7. • Third degree A V block or complete heart
block is also known as A V dissociation. In
this rhythm, P-waves are present, but there
is no relationship between P-waves or QRS
complexes.
• P-waves may be superimposed on QRS
complexes, but none of the sinus impulses
are conducted to the ventricles; the atria
and ventricles are contracting
independently of each other. In the absence
of clinical intervention such as artificial
pacing, ventricular depolarization is initiated
by a junctional or ventricular pacemaker.

8. MYOCARDIAL ISCHEMIA OR INFARCTION
• S-T segment shift has significant
diagnostic value. For exampIe, S-T
segment elevation is associated with
transmural Ml. whereas S-T segment
depression is associated with nOn
transmural or subendocardial MI.

9. • S-T segment depression is associated
with nOn transmural or
subendocardial MI.