Transcript document

Cardiac
dysrhythmia (arrhythmia and
irregular heartbeat) is a large and
heterogeneous group of conditions in
which there is abnormal electrical
activity in the heart.
The heart beat may be too fast or too
slow, and may be regular or irregular.
Each
heart beat originates as an
electrical impulse from a small area
of tissue in the right atrium of the
heart called the sinus node or sinoatrial node which generates a Sinus
Rhythm.
 The SA Node paces the heart in the
normal rate range of 60 to 100 per
minute.
 The
impulse initially causes both atria to
contract, then activates the
atrioventricular (or AV) node which is
normally the only electrical connection
between the atria and the ventricles
(main pumping chambers). The impulse
then spreads through both ventricles via
the Bundle of His and the Purkinje fibres
causing a synchronised contraction of
the heart muscle and, thus, the pulse. In
adults the normal resting heart rate
ranges from 60 to 80 beats per minute.
The resting heart rate in children is
much faster.
The causes of the cardiac arrhythmias are
usually one or a combination of the
following abnormalities in the
rhythmicity-conduction system of the
heart:
 Abnormal rhythmicity of the pacemaker
 Shift of the pacemaker from the sinus
node to another place in the heart
 Blocks at different points in the spread
of the impulse through the heart
 Abnormal pathways of impulse
transmission through the heart
 Spontaneous generation of spurious
impulses in almost any part of the heart
Cardiac dysrhythmias are often first detected by
simple but nonspecific means:
 auscultation of the heartbeat with a stethoscope, or
 feeling for peripheral pulses.
(cannot usually diagnose specific dysrhythmias, but
can give a general indication of the heart rate and
whether it is regular or irregular. Not all the
electrical impulses of the heart produce audible or
palpable beats; in many cardiac arrhythmias, the
premature or abnormal beats do not produce an
effective pumping action and are experienced as
"skipped" beats).
The simplest specific diagnostic test for assessment
of heart rhythm is the electrocardiogram. A Holter
monitor is an EKG recorded over a 24-hour period,
to detect dysrhythmias that may happen briefly
and unpredictably throughout the day.
Tachycardia means fast heart rate, usually
defined in an adult person as faster than
100 beats per minute.

This electrocardiogram is normal
except that the heart rate, as determined
from the time intervals between QRS
complexes, is about 150 per minute
instead of the normal 72 per minute.
 Bradycardia
means a slow heart rate,
usually defined as fewer than 60 beats
per minute. Bradycardia is shown by the
electrocardiogram.
 Any
circulatory reflex that stimulates the
vagus nerves causes release of acetylcholine
at the vagal endings in the heart, thus giving
a parasympathetic effect. Perhaps the most
striking example of this occurs in patients
with carotid sinus syndrome.
 In
these patients, the pressure receptors
(baroreceptors) in the carotid sinus region of
the carotid artery walls are excessively
sensitive. Therefore, even mild external
pressure on the neck elicits a strong
baroreceptor reflex, causing intense vagalacetylcholine effects on the heart, including
extreme bradycardia.
 During
atrial fibrillation the atria show
chaotic depolarisation with multiple foci.
Mechanically the atria stop contracting
after several days to weeks of atrial
fibrillation, the result of the ultra-rapid
depolarisations that occur in the atria,
typically around 400 bpm, but up to 600
bpm. At the AV node 'every now and then'
a beat is conducted to the ventricles,
resulting in an irregular ventricular rate,
which is the typical ECG characteristic of
atrial fibrillation.
 During
atrial flutter the atria depolarize
in an organized circular movement. This
is caused by re-entry. The atria contract
typically at around 300 bpm, which
results in a fast sequence of p-waves in a
saw-tooth pattern on the ECG. For most
AV-nodes this is way to fast to be able to
conduct the signal to the ventricles, so
typically there is a 2:1, 3:1 or 4:1 block,
resulting in a ventricular frequency of
150, 100 or 75 bpm respectively

In normal tissue, if a single Purkinje fiber
forms two branches (1 & 2), the action
potential will travel down each branch.
An electrode in a side branch off of
branch 1 would record single, normal
action potentials as they are conducted
down branch 1 and into the side branch.
If branches 1 & 2 are connected together
by a common, connecting pathway
(branch 3), the action potentials that
travel into branch 3 will cancel each
other out.
 Reentry
(bottom panel) can occur if
branch 2, for example, has a
unidirectional block. In such a block,
impulses can travel retrograde (from
branch 3 into branch 2) but not
orthograde. When this condition exists,
an action potential will travel down the
branch 1, into the common distal path
(branch 3), and then travel retrograde
through the unidirectional block in
branch 2 (blue line). Within the block
(gray area), the conduction velocity is
reduced because of depolarization.
 Ventricular
tachycardia is defined as a
sequence of three or more ventricular
beats. The frequency must by higher than
100 bpm, mostly it is 110-250 bpm.
Ventricular tachycardias often origin
around old scar tissue in the heart, e.g.
after myocardial infarction.
 Ventricular
fibrillation (VF or V-fib) is
chaotic depolarisation of the ventricles.
Mechanically this results in an arrested
cardiac pump function and immediate
death. VF can only be treated by
immediate defibrillation. If you consider
ventricular fibrillation in a conscious
patient, than you should look for a
technical problem with the ECG, eg.
movement or electrical interference.
 Ventricular
Flutter is mostly caused by
re-entry with a frequency of 300 bpm.
The ECG shows a typical sinusoidal
pattern. During ventricular flutter the
ventricles depolarize in a circular
pattern, which prevents good function.
 Conduction
disturbances can occur at the
level of the sinoatrial (SA) node, the
atrioventricular (AV) node and the bundle
branch system. In atrioventricular block the
conduction between atria and ventricles is
disturbed, leading to an increased PQ
interval or to P waves that are not followed
by QRS complexes: atrial activity that is not
followed by ventricular activity. Three
degrees of block can be distinguished.
First degree AV block
 In
first degree AV block there is a
prolongation of PQ duration (PQ time > 0.20
sec). Still every P wave is being followed by a
QRS complex. First degree AV block is
present in 16% of >90-year olds and is mostly
caused by a degeneration of the conduction
system. First degree AV block is relatively
harmless. Although the PQ interval is
prolonged, all P waves are followed by QRS
complexes: there is no dropout of complexes.
Second degree AV block
 In second degree AV block not all pwaves are being followed by QRS
complexes: beat dropout occurs.
 Second degree AV block can be
categorized in 3 types:
Second degree AV block type I (Wenckebach)
 the PQ interval prolongs from beat to beat up until
the drop-out of one QRS complex
 QRS complexes cluster (e.g. a 5:4 block or 4:3 block)
 The PQ interval prolongs every consecutive beat
 The PQ interval that follows upon a dropped beat is
the shortest.
 The RR interval shortens (!) every consecutive beat.
The amount of block decreases during exercise (e.g. a
4:3 block improves into a 6:5 block)
The conduction disturbance in a type I block originates
in the AV node. Isolated second degree AV block
type I is relatively benign and not a pacemaker
indication.
Second degree AV block type II (Mobitz)
 beats are dropped irregularly without
PQ interval prolongation
 no clustering of QRS complexes can be
seen as in second degree block type
 marks the starting of trouble and is a
class I pacemaker indication.
c) High grade AV block
 High grade AV block is defined as two or
more p-waves not followed by QRS
complexes
3. Third degree AV block is synonymous to
total block: absence of atrioventricular
conduction. The P-waves and QRS
complexes have no temporal
relationship, which is called to AV
dissociation.
The ventricular rhythm can be nodal,
idioventricular or absent. Absent
ventricular rhythm results in asystole
and death. During third degree AV block
the blood supply to the brain can
insufficient, leading to loss of
consciousness
If the conduction system is dysfunctional,
the QRS widens beyond 0.12 seconds. If
the QRS complex is wider than 0.12
seconds this is mostly caused by a delay
in the conduction tissue of one of the
bundle branches:
 Left Bundle Branch Block (LBBB))
 Right Bundle Branch Block(RBBB)
 Intraventricular conduction delay
A
bundle branch block causes a delay in the
depolarization of the right (RBBB) or left
(LBBB) ventricle.
 In RBBB the QRS complex shows a second
peak or R' in V1. Check V1 when QRS > 0.12
sec. When the "terminal force“(2nd half of
QRS) of the QRS in V1 is below the baseline
(i.e. QS wave), a LBBB is the most likely
diagnosis. When the "terminal force" of the
QRS in V1 is above the baseline (i.e. RSR'
wave), it's a RBBB. If the QRS > 0.12 sec. but
the morphological criteria of LBBB or RBBB
do not apply, it is called 'intraventriculair
conduction delay', a general term.
Criteria for left bundle branch block
(LBBB)
 QRS >0,12 sec
 Broad monomorphic R waves in I and V6
with no Q waves
 Broad monomorphic S waves in V1, may
have a small r wave
Criteria for right bundle branch block
(RBBB)
 QRS >0,12 sec
 Slurred S wave in lead I and V6
 RSR'-pattern in V1 where R' > R