Download Sinus Tachycardia

Dr. Ziad NOFAL
CARDIOLOGIST
DAMASCUS HOSPITAL
THE NORMAL CARDIAC
CONDUCTING SYSTEM
 The heart consists of variations of three types of
specialized tissue:
1) pacemaker cells that undergo spontaneous
depolarization and can initiate an electric impulse
(this property is called automaticity).
2) cells that conduct electrical waves more rapidly
than other cardiac cells, causing a very rapid
propagation of the electric impulse throughout the
heart.
3) contractile cells, which contract when electrically
depolarized.
Impulse conduction
Impulses originate
regularly at a
frequency of 60-100
beat/ min
SAN
AVN
0
-20
-40
-60
Cardiac Action
Potential
Phase 1
20
Depolarization
mv
Phase 2
(Plateau Phase)
Phase 3
Phase 0
-80
Phase 4
Resting membrane
Potential
+
Na
-100
Na
Na++++
Na
Na+
Na
m
Na+
h
++ ++
caca
ca++
K+
K+
+++
+K
KKK
ca++
ATPase
Na+
mv
-20
-40
-60
Depolarization
0
Cardiac Action
Potential
Phase 1
20
Phase 2
(Plateau Phase)
Phase 3
Phase 0
Phase 4
(only in
pacemaker cells
-80
Phase 4
R.M.P
-100
+
Na
Na
Na++++
Na
Na+
Na
m
Na+
h
++ ++
caca
ca++
K+
K+
+++
+K
KKK
ca++
ATPase
Na+
Rhythm Disorders
2 Categories of Rhythm Disorders
Disorders of
Impulse Formation
Impulse Conduction
Rhythm Disorders
Impulse Formation
Impulse Conduction
Underlying Mechanisms
• Abnormal
Automaticity
Abnormal Automaticity
Mechanisms of Rhythm Disorders
Abnormally Slow = Bradycardia
 Failure due to disease
Excessively Rapid = Tachycardia
 Due to sympathetic nervous system
Mechanisms of Cardiac Arrhythmias
Mechanisms of bradicardias:
Sinus bradycardia is a result of abnormally slow
automaticity while bradycardia due to AV block is
caused by abnormal conduction within the AV node or
the distal AV conduction system.
Mechanisms generating tachycardias include:
- Accelerated automaticity.
- Triggered activity
- Re-entry (or circus movements)
ACCELERATED AUYOMATICITY
 It occurs due to increasing the rate of diastolic
depolarization or changing the threshold potential.
 Abnormal automaticity can occur in virtually all
cardiac tissues and may initiate arrhythmias.
 Such changes are thought to produce:
sinus tachycardia,
escape rhythms and
accelerated AV nodal (junctional) rhythms.
Automatic tachycardias
 They are characterized by:
1)rate acceleration at the onset
(warming up) and deceleration before
termination (cooling down)
2) response to sympathomimetics and
to autonomic modulation
Automatic tachyarrhythmias
 Important automatic tachyarrhythmias include certain
types of :
atrial tachycardias,
 pulmonary vein potentials in atrial
fibrillation,
 acclerated junctional tachycardias,
idioventricular rhythms,
and inappropriate sinus tachycardias.

Multifocal Atrial T.
 Is due to enchanced automaticity within the atria,
resulting in abnormal discharges from several ectopic
foci
 Most often occurs in the setting of severe pulmonary
disease and hypoxemia.
 EKG: irregular rhythm with multiple (at leats 3) P
waves morphologies
Underlying Mechanisms
Mechanisms of Rhythm Disorders
Impulse Formation
• Abnormal
Automaticity
• Triggered Activity
Impulse Conduction
• Slow or Blocked
Conduction
TRIGGERED ACTIVITY
 Myocardial damage can result in oscillations of the
transmembrane potential at the end of the action
potential. These oscillations, which are called 'after
depolarizations', may reach threshold potential and
produce an arrhythmia.
 The abnormal oscillations can be exaggerated by
pacing, catecholamines, electrolyte disturbances, and
some medications.
 Examples as atrial tachycardias produced by digoxin
toxicity and the initiation of ventricular arrhythmia in
the long QT syndrome.
Action Potential of a Cardiac Cell
Refractory Periods
 ERP - Effective
Refractory Period
Phases 0, 1, 2 and early
Phase 3
A depolarization cannot
be initiated by an impulse
of any strength
Action Potential of a Cardiac Cell
Refractory Periods
 RRP - Relative Refractory
Period
Late Phase 3 and early
Phase 4
A strong impulse can
cause depolarization,
possibly with aberrancy
Triggered Activity
Mechanisms of Rhythm Disorders
• Afterpotentials occurring in
Phase 3 (early) or 4 (late) of
action potential
• Can trigger arrhythmias
Triggered Activity
Mechanisms of Rhythm Disorders
Early Afterdepolarization
Late Afterdepolarization
 Potential Causes:
 Potential Causes:
- Low potassium blood levels
- Slow heart rate
- Drug toxicity (ex. Quinidine
causing Torsades de Pointes)
 Premature beats
 Increased calcium
blood levels
 Increased adrenaline
levels
 Digitalis toxicity
QT interval corresponds to Ventricular AP duration
R
T
P
Q S
APD
Ventricular AP
Q-T
ECG
Action Potential
of
a
Cardiac
Cell
Effective & Relative Refractory Periods
Re-entry (or circus movement)
 The mechanism of re-entry occurs when a 'ring' of cardiac
tissue surrounds an inexcitable core (e.g. in a region of
scarred myocardium). Tachycardia is initiated if an ectopic
beat finds one limb refractory (α) resulting in unidirectional
block and the other limb excitable. Provided conduction
through the excitable limb (β) is slow enough, the other limb
(α) will have recovered and will allow retrograde activation to
complete the re-entry loop. If the time to conduct around the
ring is longer than the recovery times (refractory periods) of
the tissue within the ring, circus movement will be
maintained, producing a run of tachycardia.
 The majority of regular paroxysmal tachycardias are
produced by this mechanism.
Reentry Arrhythmias
Normal
Re-enterant
Tachycardia
Reentry tachyarrhythmias
 Reentry tachyarrhythmias usually exhibit
the following properties:
1) they are inducible by programmed
electrical stimulation
2) they have abrupt onset and offset.
3) during reentrant tachycardia,the RR
intervals are regular.
Bradyarrhythmias
 Impulse formation:
– Decreased automaticity: Sinus bradycardia
 Impulse conduction:
– Conduction blocks: 1º, 2º, 3º AV blocks
Tachyarrythmias
 Impulse formation
– Enhanced automaticity:
 Sinus node: sinus tachycardia
 Ectopic focus: Ectopic atrial tachycardia
– Triggered activity
 Early afterdepolarization: torsades de pointes
 Digitalis-induced SVT
 Impulse conduction
– Reentry: Paroxysmal SVT, atrial flutter and fibrilation,
ventricular tachycardia and fibrillation.
Q1
What is the most common mechanism involved in
clinically important cardiac arrhythmias?
 a.Triggered activity
 b.Abnormal automaticity
 c.Reentry
 d.Early afterdepolarizations
 e.Parasystole
Q2
In which of the following tissues is the upstroke of the
action potential generated by ingoing calcium currents?
 a.Atrial
 b.AV node
 c.His-Purkinje
 d.Ventricular
Q3
Repolarization of the myocardial cells is determined
mostly by which current?
 a.Outgoing sodium
 b.Ingoing calcium
 c.Outgoing potassium
 d.Ingoing chloride
 e.Ingoing sodium
Q4
Prerequisite conditions of the reentrant arrhythmia
include all of the following except:
 a.Two functionally distinct conducting pathways
 b.An anatomical obstacle around which the impulse
reenters
 c.Unidirectional block in one pathway
 d.Slow conduction via one pathway with return via the
second
Q5
 The most likely diagnosis based upon the clinical





symptoms and ECG is:
a.AVNRT
b.AV RT
c.Atrial tachycardia
d.PAF
e.Paroxysmal atrial flutter
Tachyarrhythmia Classifications
Classification Based on Disorder
Impulse Formation
Disorders
Impulse Conduction
Disorders
• Sinus Tachycardia
• Atrial Tachycardia
• Premature Contractions
• Accelerated IdioJunctional Rhythm
• Accelerated
Idioventricular
Rhythm (AIVR)
• Atrial Flutter
• Atrial Fibrillation
Atrial Fibrillation (AF)
*
Animation
• Origin:
Right and/or left atrium
• Mechanism:
Multiple wavelets of reentry
• Rate
400 BPM
• Characteristics:
Random, chaotic rhythm;
atria quiver; associated with
irregular ventricular rhythm
Atrial Fibrillation (AF)
AF Mechanism
Why AF begets AF
• Frequent or long AF episodes may cause chronic or
permanent AF by:
– Producing progressively shorter refractory periods
allowing reentry waves to self-propagate & spread
Other AF Mechanisms
Single Focus Firing
• Mechanism:
Abnormal Automaticity (singlefocus, usually in the Posterior
Left Atrium)
• Characteristics: Rapid discharge; single ectopic site
Tachyarrhythmia Classifications
Classification Based on Disorder
Impulse Formation
Disorders
Impulse Conduction
Disorders
• Sinus Tachycardia
• Atrial Tachycardia
• Premature Contractions
• Accelerated IdioJunctional Rhythm
• Accelerated
Idioventricular
Rhythm (AIVR)
• Atrial Flutter
• Atrial Fibrillation
• AVRT
THANK
YOU