Interpretation And management of
the ECG
In
Bradyarrhythmias And Heart Blocks
DR.Tareq M.Al-Muflehi
INTERVENTIONAL CARDIOLOGIST
. Sinus Bradycardia.
. Junctional rhythm.
. Idioventricular rhythm.
. Sinus node dysfunction or (sick
sinus syndrom).
. AV-blocks.
. Heart block with acute MI.
. Intraventricular conduction
abnormalities(IVCAs).
. MI in the presence of BBB.
BLOOD SUPPLY OF THE CARDIAC
CONDUCTION SYSTEM
The blood supply to the sinoatrial node is from
the sinus node artery which arises from the
proximal RCA in 55% of the population and in
35% from the circumflex artery and in 10% from
both RCA and CX.
 The AV-node receives its blood supply from the
AV- nodal artery which arises from the PDA of
RCA in 80% of population and 10% from
circumflex artery and 10% from both arteries .

Collateral blood supply from the LAD artery
makes the AV- node somewhat less prone to
ischemic damage than the sinoatrial node .
 The AV- nodal artery and the first septal
perforator of the LAD artery offer dual blood
supply to the atrioventricular (His) bundle and
RBB .
 The anterior fascicle of the LBB receives blood
from the other septal perforating branchs of the
LAD .
 The posterior fascicle has a dual blood supply
from the septal perforating branchs of the LAD
and branchs of the PDA of RCA.

Cardinal features of normal sinus
rhythm
. The P wave is upright in leads 1,2,3
and AVF
. The P wave is negative in lead AVR
. Each P wave is followed by a QRS
complex
. The heart rate is 60-100 beat\ min
NSR Parameters
• Rate
60 - 100 bpm
• Regularity
regular
• P waves
normal
• PR interval
0.12 - 0.20 s
• QRS duration
0.04 - 0.12 s
Any deviation from above is sinus
tachycardia, sinus bradycardia or an
arrhythmia
Pacemakers of the Heart
• SA Node - Dominant pacemaker with an
intrinsic rate of 60 - 100 beats/minute.
• AV Node(Junctional) - Back-up
pacemaker with an intrinsic rate of 40 60 beats/minute.
• Ventricular cells - Back-up pacemaker
with an intrinsic rate of 20 - 45 bpm.
Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
Sinus
bradycardia
Normal resting heart rate has been
defined as 60-100 bpm.
 Bradicardia is defined as ventricular
rate less than 60 bpm.
 It should be noted some otherwise
healthy individuals have resting heart
rate less than 60 bpm. The greatest
variation is found in athletes primarily
from increase parasympathetic tone.

Sinus bradycardia exists when a P wave
precedes each QRS complex. this QRS
complex is usually narrow (less than 0.120
seconds ) because the impulse originates
from a supraventricular focus .
 There are specific incidences in which,
despite the supraventricular focus, the
QRS is widened (greater than 0.12
seconds ) an example of this is a BBB
(right or left ) in which the QRS is wide
but each QRS complex is still considered
by a P- wave .

Sinus Bradycardia

Etiology: SA node is depolarizing slower
than normal, impulse is conducted
normally (i.e. normal PR and QRS
interval).
Sinus bradycardia--etiologies
Normal aging
 15-25% Acute MI, esp. affecting inferior wall
 Hypothyroidism, infiltrative diseases
(sarcoid, amyloid)
 Hypothermia, hypokalemia
 SLE, collagen vasc diseases
 Situational: micturation, coughing
 Drugs: beta-blockers, digitalis, calcium channel
blockers, amiodarone, cimetidine, lithium


History:

Sinus bradycardia is most often asymptomatic.
However, symptoms may include the following:

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Syncope
Dizziness
Lightheadedness
Chest pain
Shortness of breath
Pertinent elements of the history include the following:

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Previous cardiac history (eg, myocardial infarction, congestive
heart failure, valvular failure)
Medications
Toxic exposures
Prior illnesses

Physical:

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Cardiac auscultation and palpation of peripheral
pulses reveal a slow, regular heart rate.
The physical examination is generally nonspecific,
although it may reveal the following signs:
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Decreased level of consciousness
Cyanosis
Peripheral edema
Pulmonary vascular congestion
Dyspnea
Poor perfusion
Syncope

Lab Studies:


Laboratory studies may be helpful if the cause of the bradycardia is
thought to be related to electrolytes, drug, or toxins.
Reasonable screening studies, especially if the patient is symptomatic
and this is the initial presentation, include the following:

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Imaging Studies:

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Electrolytes
Glucose
Calcium
Magnesium
Thyroid function tests
Toxicologic screen
Routine imaging studies are rarely of value in the absence of specific
indications.
Other Tests:

12-lead ECG may be performed to confirm the diagnosis.
Sinus Bradycardia
HR< 60 bpm; every QRS narrow, preceded by p wave
 Can be normal in well-conditioned athletes
 HR can be<30 bpm in children, young adults during
sleep, with up to 2 sec pauses

Sinus bradycardia--treatment
No treatment if asymptomatic
Office: Evaluate medicine regimen—stop all
drugs that may cause
 Bradycardia associated with MI will often resolve
as MI is resolving; will not be the sole sxs of MI
 ER: Atropine if hemodynamic compromise,
syncope, chest pain
 Pacing


Junctional
rhythm

Junctional rhythm is another example of a
supraventricular rhythm in which the QRS
complex is usually narrow (less than 0.12
seconds ) and regular this is distinguished
from sinus bradycardia on ECG because
it is not associated with preceding Pwave, a junctional escape rate is usually
40- 60 bpm a junctional rhythm with a
rate slower than 40 bpm is termed a
junctional bradycardia and a rate faster
than 60 bpm is termed an accelerated
junctional rhythm or a junctional
tachicardia .

There are times when there are p waves evident
on the ECG of patients who have a junctional
rhythm but unlike normal sinus rhythm or sinus
bradycardia thes P waves are not conducted in
an anterograde fashion these are termed P
waves and may appear before during or after
the QRS complex depending on when the atrium
is captured by the impules emanating from the
AV junction As in sinus bradycardia, there are
also times in which the QRS is widened because
of right or left BBB.
Junctional bradycardia
Junctional bradycardia is treated in the same
way as sinus bradycardia .
 Junctional bradyardia is a frequent
accompaniment of reperfusion and indeed can
be used as a marker of successful reperfusion.
 Therapy of junctional rhythm secondary to
sinoatrial node, failure of AV-block is as the
treatment of atrioventricular conduction
disturbances.

Accelerated Junctional Rhythm
Etiology

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Accelerated junctional rhythm is seen in approximately
10% of patiens with MI more than half these patients
have inferior MI and about on- third have anterior MI.
Digitalis toxicity by itself does not seen to cause
accelerated junctional rhythm, as evidence in persons
with normal hearts who take accidental overdoses of
digoxin.
Concomitant heart disease is required to develop
accelerated junctional rhythm.
other causes of accelerated junctional
rhythm are valve surgery, acute rheumatic
fever, direct current cardioversion, cardiac
cath, COPD, Amyliodosis and uremia with
hyperkalemia.
 The distinguishing characteristic of
accelerated junctional rhythm is the
atrioventricular dissociation and changing
PR interval.

.
The difference between accelerated Junctional rhythm
and third- degree AV- block is the fact that the ventricular
rate is faster than the atrial rate in accelerated junctioal
rhythm and slower than the atrial rate in third- degree AVblock .
Treatment
Patients with accelerated junctional rhythm do
not usually require therapy for the arrhythmia,
although mangement of the underlying cause is
indicated.
 Suppression of accelerated junctional rhythm
maybe achieved by increasing the atrial rate
with drugs (eg, Atropin, Adrenergics) or pacing.
 Digoxin - induced accelerated junctional rhythm
is an indication to stop digoxin but does not
usually require administration of digoxin _
specific fab fragments.

Idioventricular
rhythm

Idioventricular rhythms are regular but
unlike sinus bradycardia or junctional
rhythm, they are always characterized by
a wide QRS complex because their origin
lies some where within the ventricles on
ECG the rate is usually 20- 40 bpm except
for accelerated idioventricular rhythm (rate
greater than 40 bpm ).
Idioventricular rhythm (IVR)
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IVR is usually too slow to maintain adequate
cardiac output and treatment is more frequently
needed.
The patient depends on these complexes for
survival.
Suppressive treatment (e.g. lidocaine) may
therefore lead to asystole .
Atropine and pacing are usually required, as
well as correction of the underlying cause (AMI ,
complete heart block , cardiac , tamponade ,
hemorrhage ) .
CPR may be needed as well.
Accelerated Idioventricular
rhythm (AIVR)
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AIVR is a form of VT and occurs as a rule in patients
with cardiac disease ( almost in IHD ).
AMI and digitalis toxicity are the common precipitating
events. (It is common 48h after MI).
This rhythm is also commonly seen when thrombolytics
are given for an AMI, and if it occurs, thrombolytics
should be continued. (It usually means successful
reperfusion).
The mechanism is believed to be secondary to an
ectopic ventricular focus (usually in the reperfusion
zone) that accelerates beyond the intrinsic sinus rate.
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The P- wave may come closer and closer to the
QRS complex at the same time the shape of the
QRS complex changes to its wide ventricular
contour, and then disappears into it .
It is usually regular, has a rate of 60- 120 bpm,
and is of little clinical significance.
Treatment for AIVR is rarly necessary.
With severe symptoms or hemodynamic
compromise, Atropine or a trial pacing can be
used to stimulate the sinus rhythm to overdrive
the ectopic focus.
Treatment can also be considerd when AIVR
occurs with VT. Suppression of the dysrhythmia
can also be undertaken with the same drugs
used to treat VT.
. Sinus Bradycardia.
. Junctional rhythm.
. Idioventricular rhythm.
. Sinus node dysfunction or (sick
sinus syndrom).
. AV-blocks.
. Heart block with acute MI.
. Intraventricular conduction
abnormalities(IVCAs).
. MI in the presence of BBB.
SINUS NODE
DYSFUNNCTION OR
"SICK SINUS
SYNDROME"

sick sinus syndrom is a collective
term that includes a range of SA node
dysfunction that manifests in various
different ways on ECG including :
. Persistent inappropriate sinus
bradycardia .
. Intermittent sinus pause/ arrest.
. sinoatrial exit block.
. AV junctional (escape ) rhythm.
. Tachy - brady syndrome.
Sick Sinus Syndrome
 Patients
are usually elderly and
present with lightheadedness
and/or syncope, but it can also
manifest as angina, dyspnea, and
palpitations.
 About
50% of people with SSS
also display some degree of
dysfunction of the AV node

Sinus pause and sinus arrest are characterized by the
failure of the SA node to form an impulse although sinus
pause refers to a brief failure and sinus arrest refers to a
more prolonged failure of the SA node, there are no
universally accepted definitions to differentiate the two.
Because of this, they are often used interchangeably to
describe the same cardiac event.
On ECG there is an absence of the P-QRS-T complex
resulting in a pause of indeterminate length. The sinus
node most often resumes pacemaker activity and a
normal sinus rhythm is seen. In cases in witch it fails,
however the escape rhythm seen is usually from the AV
node. If the AV node fails, the next pacemaker to take
would result in an idioventricular rhythm. If all of these
fail to generate an ascape rhythm, the result is asystole .
Mechanism of sinus node dysfunction
includes decreased automaticity of sinus
nodal tissue and sinatrial (SA) exit block.
 In SA exit block, rhythmic depolarization
continues to occur , but the impulse is
delayed or blocked in the perinodal tissue.
 Diagnosis by surface ECG is difficult
because external leads do not directly
record activity within the sinus node.

Sinus bradycardia associated with sinus
node dysfunction is a marked, persistent
sinus bradycardia , with sinus rate less
than 40 bpm and pauses of greater than
2s.
 A sinoatrial pause greater than 3s
following carotid massage may indicate
sick sinus syndrome.

Sick Sinus Syndrome
Sinus bradycardia (rate of ~43 bpm) with a sinus pause
Sinoatrial (SA) blocks result when there is
an abnormality between the conduction of
the impulse from hearts normal
pacemaker (SA node) to the surrounding
atrium.
 AS with AV- block SA block is
characterized as first, second and thirddegree, with second- degree blocks
subclassified as type I and type II.

Tachycardia-Bradycardia Syndrome

Common variant of sick sinus syndrome
severe bradycardia alternates with
paroxysmal tachycardias, most often atrial
fibrillation.

There is usually a prolonged pause in the
cardiac rhythm following cessation of the
tachyarrhythmia.
Tachycardia-Bradycardia Syndrome
Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 7th ed., 2005.
Abrupt termination of atrial flutter with variable AV block,
followed by sinus arrest with a junctional escape beat.
Etiologies of Sick Sinus Syndrome
More Common
Sinus node firbosis
Atherosclerosis of the SA
artery
Congenital heart disease
Excessive vagal tone
Drugs
Less Common
Familial SSS (due to
mutations in SCN5A)
Infiltrative diseases
Pericarditis
Lyme disease
Hypothyroidism
Rheumatic fever
Sick sinus syndrome--treatment
Address and treat cardiac conditions
 Review med list, TSH
 Pacemaker for most is required

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