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Introduction
The SA node spontaneously depolarize to initiate an action impulse that is rapidly
propagated through the atria (causing atrial contract), then slowly through the AV node
and rapidly via the bundle branches and Purkinje system to the ventricles, causing
ventricular contraction.
The electrical activity of the heart can be recorded at the surface of the body using an
electrocardiogram. The electrocardiogram (ECG) is simply a voltmeter that uses up to 12
different leads (electrodes) placed on designated areas of the body.
The electrocardiogram is composed of waves and complexes. Waves and complexes in
the normal sinus rhythm are the P wave, PR Interval, PR Segment, QRS Complex, ST
Segment, QT Interval and T wave .
BREAKDOWN OF AN ECG
P-Wave
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SA node fires, sends the electrical impulse outward to stimulate both
atria and manifests as a P-wave.
Approximately 0.10 seconds in length.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
PR Interval (PRI)
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Time which impulse travels from the SA node to the atria and downward
to the ventricles
QRS Complex
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Impulse from the Bundle of HIS throughout the ventricular muscles
Measures less than 0.12 seconds or less than 3 small squares on the ECG
paper
T-Wave:
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Ventricular repolarization, meaning no associated activity of the
ventricular muscle
Resting phase of the cardiac cycle
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INTERPRETATION OF AN ECG STRIP
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Step 1: Heart Rate
Step 2: Heart Rhythm
Step 3: P P-Wave
Step 4: PRI
Step 5: QRS Complex
Heart Rate
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Heart rhythm are classified as regular or irregular.
Can calculate the heart rhythm involves establishing a pattern of QRS complexes
occurrence.
Measure ventricular rhythm by measuring the interval between R-to-R waves and
atrial rhythm by measuring the P-to-P waves.
Interval > than 0.06 seconds, irregular.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Determining Heart Rate and Rhythm
· The ECG paper is made of a grid of big boxes and small boxes. Each big box is
10 mm in length has five small boxes and is 0.20 sec. Each small box is 1 mm and
represents 0.04 sec. The ECG paper moves at a standard speed of 25 mm/sec. At
standard speed, the heart rate can be determined by either of the following
methods.
Method I
· Examine the distance between QRS complexes and determine if the peaks (RR
intervals) are regularly spaced.
· The ECG below shows regular RR intervals. If the RR distances are regular,
count the number of "small boxes" from the beginning of one QRS complex to the
beginning of the next QRS complex. Then d ivide 1500 by the number of "small
boxes" to obtain the heart rate in beats per minute.
Heart Rate =
1500
No. small boxes
· The ECG on the bottom right shows irregularly spaced RR intervals. If
the distances are irregular, count the number of QRS complexes within 30 large
boxes (which each represent 0.2 seconds) and multiply this number by 10 to
obtain the heart rate in beats/minute.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Method II
· If the peaks are regular, the heart rate can be estimated using the ECG grid. To do
this locate a QRS complex on a bold line. If the next QRS complex is separated
by:
i. One large box, the heart rate is 300 BPM (300/1)
ii. Two large boxes, the heart rate is 150 BPM (300/2)
iii. Three large boxes, the heart rate is 100 BPM (300/3)
iv. Four large boxes, the heart rate is 75 BPM (300/4)
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...and so on.
The ECG grid used to rapidly estimate the heart rate
The difference between Atrial and Ventricular Rates
· The heart rate calculated using the RR intervals is the ventricular rate. In sinus
rhythm, the ventricular rate corresponds to the atrial rate. The atrial rate can be
determined from the PP interval using either of the two methods above.
The P Wave
5 questions:
· Are P-Waves present?
· Are P-Waves occurring regularly?
· Is there a P-Wave for each QRS?
· Are the P-Waves smooth, rounded, and
· Upright in appearance, or are they inverted?
· Do all P-Waves look similar?
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
The PRI
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Normal length of the PRI is 0.12 to 0.20 second ( 3-5 small squares)
3 Questions to ask:
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1. Are PRI greater that 0.20 seconds?
2. Are PRI less than 0.12 seconds?
3. Are the PRI’s constant across the ECG strip?
The QRS Complex
3 questions to ask:
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1. Are QRS intervals greater than 0.12 second (wide)? If so, the complex may be
ventricular in origin
2. Are QRS intervals less than 0.12 seconds (narrow)? If so, the complex is most
likely supraventricular in origin.
3. Are QRS complexes similar in appearance across the ECG strip?
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Artifact
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Four Common Causes:
1. Patient Movement
2. Loose or defective electrodes
3. Improper grounding
4. Faulty ECG apparatus
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Patient assessment is critical
Types of Rhythms
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Rate:
o Bradycardia = rate of <60 bpm
o Normal = rate of 60-100 bpm
o Tachycardia = rate of >100-160 bpm
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Where it’s coming from:
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Sinus; SA node
Atrial; SA node fails, impulse comes from the atria ( internodal or the AV node)
Ventricular; SA node or AV junction fails, ventricles will shoulder responsibility
of pacing the heart
SINUS RHYTHMS
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Normal Sinus Rhythm (NSR)
Sinus Bradycardia
Sinus Tachycardia
Normal Sinus Rhythm (NSR Rhythm)
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In a normal heart rhythm, the sinus node generates an electrical impulse which
travels through the right and left atrial muscles producing electrical changes
which is represented on the electrocardiogram (ECG) by the p-wave. The
electrical impulses then continue to travel through specialized tissue known as the
atrioventricular node, which conducts electricity at a slower pace. This will create
a pause (PR interval) before the ventricles are stimulated. This pause is helpful
since it allows blood to be emptied into the ventricles from the atria prior to
ventricular contraction to propel blood out into the body. The ventricular
contraction is represented electrically on the ECG by the QRS complex of waves.
This is followed by the T-wave which represents the electrical changes in the
ventricles as they are relaxing. The cardiac cycle after a short pause repeats itself,
and so on.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
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Therefore, on an ECG in normal sinus rhythm p-waves are followed after a brief
pause by a QRS complex, then a T-wave.
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Normal sinus rhythm not only indicate that the rhythm is normally generated by
the sinus node and traveling in a normal fashion in the heart, but also that the
heart rate, i.e. the rate at which the sinus node is generating impulses is within
normal limits. There is no one normal heart rate, but this varies by age. It is
normal for a newborn to have a heart rate up to 150 beats per minute, while a
child of five years of age may have a heart rate of 100 beats per minute. The
adult's heart rate is even slower at about 60-80 beats per minute.
Sinus Bradycardia (Brady - slow)
Sinus Bradycardia occurs when the hearts rate is slower than 60 beats per minute.
The sinus Bradycardia rhythm is similar to normal sinus rhythm, except that the
RR interval is longer. Each P wave is followed by a QRS complex in a ratio of
1:1. The PR interval is often slightly prolonged and occasionally, the P-waves
might be abnormally wide.
The ECG on the top shows normal sinus rhythm. The ECG at the bottom shows sinus
Bradycardia
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
The symptoms of sinus Bradycardia include dyspnea, dizziness, and extreme
fatigue. Bradycardia may be accompanied by an increase in stroke volume due to
greater end diastolic pressure (preload). The pulse volume may be greater due to a
greater stroke volume and an increased diastolic run-off time (longer time for
blood to flow away from the heart).
Sinus Bradycardia may occur due to any of the following:
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Increase in parasympathetic (vagal) tone, for instance, due to training in
athletes. This is a normal response. The heart rate increases with exercise
or atropine.
Parasympathetic (vagal) stimulation, for instance, with carotid sinus
stimulation. Stimulation of carotid sinus baroreceptors results in increased
parasympathetic stimulation that decreases the heart rate.
Sick sinus syndrome or sinoatrial (SA) node disease. These are rhythm
disorders that occur if the SA node loses its ability to initiate or increase
the heart rate. If the SA node is unable to properly function due to sick
sinus syndrome, the AV node (or ventricular tissue if the AV node is also
not functioning) take over the initiation of the heart beat, but at a rate that
is slower than the sinus rhythm.
Heart block which occurs when the signal from the SA node is slowed or
stopped at the AV node or in the ventricular conducting system. Heart
block is described as first, second, or third degree. The decrease in the
heart rate depends on the degree of heart block.
Acute myocardial infarctions.
Drugs like digitalis and beta-blockers.
Sinus Tachycardia (tachy - fast)
Sinus tachycardia occurs when the sinus rhythm is faster than 100 beats per
minute. The rhythm is similar to normal sinus rhythm with the exception that the
RR interval is shorter, less than 0.6 seconds. P waves are present and regular and
each P-wave is followed by a QRS complex in a ratio of 1:1. At very rapid rates,
the P-waves might become superimposed on the preceding T waves such that the
P waves are obscured by T waves.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
The ECG on the top shows normal sinus rhythm. The ECG at the bottom shows sinus
tachycardia
Sinus tachycardia may be accompanied by a decrease in stroke volume because
the ventricles do not have enough time to fill (after atrial systole) before
ventricular contraction.. The pulse pressure may decrease due to a lower stroke
volume and decreased time for diastolic run-off.
Sinus tachycardia results from increased automaticity of the SA node, for
instance, due to increased sympathetic stimulation of the heart, fever or cardiac
toxicity.
ATRIAL RHYTHMS
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SA node fails to generate an impulse, the atrial tissue or areas in the internodal
pathways may initiate an impulse.
These are called atrial dysrhythmias
Generally not considered life threatening or lethal careful and deliberate patient
assessment must be continuous.
Types of Atrial Rhythms
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Atrial Flutter
Atrial Fibrillation
Supraventricular Tachycardia
Supraventricular Tachycardia
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SVT attacks are often only temporary and frequently go away on their own
without treatment. They often happen in young, healthy people, with attacks
Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
becoming less frequent as you get older. Attacks can last from a few seconds,
minutes to several hours.
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SVT occurs when there is an extra electrical pathway in the heart, between the
atria and the ventricles. This allows electrical signals to 'short-circuit' and re-enter
the atria. The signals end up travelling around the heart in a circle. These types of
SVT are often referred to as re-entrant tachycardias or paroxysmal SVT. This
means symptoms come on suddenly and are temporary.
Atrial Flutter
Atrial flutter occurs when the atria are stimulated to contract at 200-350 beats per
minute usually because electrical impulses are traveling in a circular fashion
around and around the atria. Often the impulses are traveling around an obstacle
like the mitral valve, tricuspid valve or the openings of the superior or inferior
vena cavae.
The atrial flutter waves, known as F waves, are observed. F waves are larger than
normal P waves and they have a saw-toothed waveform. Not every atrial flutter
wave results in a QRS complex (ventricular depolarization) because the AV node
acts as a filter. Some flutter waves reach the AV node when it is refractory and
thus are not propagated to the ventricles. The ventricular rate is usually regular
but slower than the atrial rate. A whole number fixed ratio of flutter waves to
QRS complexes can be observed, for instance 2:1, 3:1 or 4:1.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
The ECG on the top shows normal sinus rhythm. The ECG at the bottom shows atrial
flutter
Atrial flutter is usually associated with mitral valve disease, pulmonary embolism,
thoracic surgery, hypoxia, electrolyte disturbances and hypercalcemia. Atrial
flutter results in poor atrial pumping since some parts of the atria are relaxing
while other parts are contracting. Cardiac output decreases because the ventricles
do sufficiently fill (as they would normally) before ventricular contraction.
Ablation of some of the heart tissue to stop impulses from travelling around can
be used to treat this condition
Atrial Fibrillation
Atrial fibrillation occurs when the atria depolarize repeatedly and in an irregular
uncontrolled manner usually at atrial rate greater than 350 beats per minute. As a
result, there is no concerted contraction of the atria. No P-waves are observed in
the ECG due to the chaotic atrial depolarization. The chaotic atrial depolarization
waves penetrate the AV node in an irregular manner, resulting in irregular
ventricular contractions. The QRS complexes have normal shape, due to normal
ventricular conduction. However the RR intervals vary from beat to beat. The
ventricular rate may increase to greater than 150 beats per minute if uncontrolled.
The ECG on the top shows normal sinus rhythm. The ECG at the bottom shows atrial
fibrillation
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
The irregular ventricular contractions cause the systolic arterial pressure to vary
from beat to beat as ventricular filling time changes. The pulse pressure also may
vary from beat to beat because the diastolic runoff time varies from beat to beat.
Atrial fibrillation often involves microreentry. Atrial fibrillation is most common
in individuals with atrial enlargement, often associated with valve diseases, sick
sinus syndrome, pericarditis, lung disease and congenital heart defects. The
incidents of atrial fibrillation increase with age and are slightly more frequent in
men than women.
VENTRICULAR RHYTHMS
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SA node or the AV junctional tissue fails to initiate an electrical impulse, the
ventricles will shoulder the responsibility of pacing the heart.
This group of rhythms are called ventricular dysrhythmias
An electrical impulse can be instigated from any pacemaker cell in the ventricles,
including the bundle branches or the fibers of the Purkinje fibers.
Types of Ventricular Rhythms
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Premature Ventricular Complexes
Ventricular Tachycardia
Torsades de Pointes
Ventricular Fibrillation
Asystole
Pulseless Electrical Activity (PEA)
Ventricular Tachycardia (VT)
Ventricular tachycardia occurs when electrical impulses originating either from
the ventricles cause rapid ventricular depolarization (140-250 beats per minute).
Since the impulse originates from the ventricles, the QRS complexes are wide and
bizarre. Ventricular impulses can be sometimes conducted backwards to the atria.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
In which case, P-waves may be inverted. Otherwise, regular normal P waves (60100 beats per minute) may be present but not associated with QRS complexes
(AV dissociation). The RR intervals are usually regular.
The ECG on the top shows normal sinus rhythm. The two ECGs at the bottom show
ventricular tachycardia
Ventricular tachycardia is often due to some form of heart disease. Ventricular
tachycardia can occur rarely in response to exercise or anxiety. In this case, the
electrical impulses and rhythmic beats is similar is a normal beat but at a much
faster rate.
During ventricular tachycardia pumping blood is less efficient because the rapid
ventricular contractions prevent the ventricles from filling adequately with blood.
As a result, less blood is pumped to the body. The reduced blood flow to the body
causes weakness, dizziness, and fainting. If left untreated, ventricular tachycardia
may lead to a more life-threatening condition. Note, because of the decreased
diastolic time, coronary blood flow is decreased, increasing the chances of a
myocardial infarction.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Ventricular Fibrillation
Ventricular fibrillation occurs when parts of the ventricles depolarize repeatedly
in an erratic, uncoordinated manner. The ECG in ventricular fibrillation shows
random, apparently unrelated waves. Usually, there is no recognizable QRS
complex.
The ECG on the top shows normal sinus rhythm. The ECG at the bottom shows
ventricular fibrillation
Ventricular fibrillation is almost invariably fatal because the uncoordinated
contractions of ventricular myocardium result in ineffective pumping and little or
no blood flow to the body. There is lack of a pulse and pulse pressure and the
patients lose unconsciousness rapidly. When the patient has no pulse and
respiration the patient is said to be in cardiac arrest. A person in cardiac arrest
must receive CPR immediately.
Electrical defibrillation, by passage of current at high voltage, may be successful
in restoration of a normal regular rhythm. The electrical current stimulates each
myocardial cell to depolarize simultaneously. Following synchronous
repolarization of all ventricular cells, the SA node assumes the role of pacemaker
and the ventricular myocardial cells can resume the essentially simultaneous
depolarization of normal sinus rhythm.
Ventricular fibrillation is associated with drug toxicity, electrocution, drowning
and myocardial infarction.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Asystole
Is the complete absence of heart electrical activity. This is often a terminal
arrhythmia usually causing death. That is other arrhythmias, such as ventricular
fibrillation, progress to asystole if not treated. The heart does not pump or even
quiver.
Pulseless Electrical Activity (PEA)
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The absence of a palpable pulse and myocardial muscle activity with the presence
of organized electrical activity (excluding VT and VF) on cardiac monitor.
It is not an actual rhythm, it represents a clinical condition wherein the patient is
clinically dead, despite the fact that some type of organized rhythm appears on the
monitor.
Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
HEART BLOCKS
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Heart block is a condition in which the electrical signal cannot travel normally
down the special pathways to the ventricles. It doesn't mean the blood flow is
blocked; it means that the flow of the electrical signal within the heart is blocked.
For example, the signal from the atria to the ventricle may be (1) delayed, but
each one conducted; (2) delayed with only some getting through; or (3)
completely interrupted. If there is no conduction, the beat generally originates
from the ventricles and is very slow.
Types of Heart Blocks
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First Degree AV Block
Second-Degree AV Block (Mobitz Type I) or Wenckebach
Second-Degree AV Block (Mobitz Type II)
Third Degree AV Block (Complete)
First-Degree Heart Block
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In first-degree heart block, the heart's electrical signals are slowed as they move
from the atria to the ventricles (the heart's upper and lower chambers,
respectively). This results in a longer, flatter line between the P and the R waves
on the EKG(electrocardiogram).
First-degree heart block rarely causes any symptoms, and it usually doesn't
require treatment.
Second-Degree Heart Block
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In this type of heart block, electrical signals between the atria and ventricles are
slowed to a large degree. Some signals don't reach the ventricles. On an EKG, the
pattern of QRS waves doesn't follow each P wave as it normally would.
If an electrical signal is blocked before it reaches the ventricles, they won't
contract and pump blood to the lungs and the rest of the body.
Second-degree heart block is divided into two types: Mobitz type I and Mobitz
type II.
Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
Mobitz Type I
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In this type (also known as Wenckebach's block), the electrical signals are
delayed more and more with each heartbeat, until the heart skips a beat. On the
EKG, the delay is shown as a line (called the PR interval) between the P and QRS
waves. The line gets longer and longer until the QRS waves don't follow the next
P wave.
Sometimes people who have Mobitz type I feel dizzy or have other symptoms.
This type of second-degree heart block is less serious than Mobitz type II.
Mobitz Type II
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In second-degree Mobitz type II heart block, some of the electrical signals don't
reach the ventricles. However, the pattern is less regular than it is in Mobitz type
I. Some signals move between the atria and ventricles normally, while others are
blocked.
On an EKG, the QRS wave follows the P wave at a normal speed. Sometimes,
though, the QRS wave is missing (when a signal is blocked).
Mobitz type II is less common than type I, but it's usually more severe. Some
people who have type II need medical devices called pacemakers to maintain their
heart rates.
Third-Degree Heart Block
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In this type of heart block, none of the electrical signals reach the ventricles. This
type also is called complete heart block or complete AV block.
When complete heart block occurs, special areas in the ventricles may create
electrical signals to cause the ventricles to contract. This natural backup system is
slower than the normal heart rate and isn't coordinated with the contraction of the
Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
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atria. On an EKG, the normal pattern is disrupted. The P waves occur at a faster
rate that isn't coordinated with the QRS waves.
Complete heart block can result in sudden cardiac arrest and death. This type of
heart block often requires emergency treatment. A temporary pacemaker may be
used to keep the heart beating until you get a long-term pacemaker.
HOW ARE ARRHYTHMIAS TREATED?
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Many arrhythmias require no treatment . Serious arrhythmias are treated in
several ways depending on what is causing the arrhythmia. Sometimes the heart
disease is treated to control the arrhythmia. Or, the arrhythmia itself may be
treated using one or more of the following treatments.
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Drugs
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There are several kinds of drugs used to treat arrhythmias. One or more drugs
may be used. Drugs are carefully chosen because they can cause side effects. In
some cases, they can cause arrhythmias or make arrhythmias worse. For this
reason, the benefits of the drug are carefully weighed against any risks associated
with taking it. It is important not to change the dose or type of your medication
unless you check with your doctor first.
If you are taking drugs for an arrhythmia, one of the following tests will probably
be used to see whether treatment is working: a 24-hour electrocardiogram (ECG)
while you are on drug therapy, an exercise ECG, or a special technique to see how
easily the arrhythmia can be caused. Blood levels of antiarrhythmic drugs may
also be checked.
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Cardioversion
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To quickly restore a heart to its normal rhythm, the doctor may apply an electrical
shock to the chest wall. Called cardioversion, this treatment is most often used in
emergency situations involving potentially life threatening problems, such as very
low blood pressure or decreased level of consciousness, or in patients who have
repeatedly failed to respond to medication. After cardioversion, drugs are usually
prescribed to prevent the arrhythmia from recurring.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL
·
Automatic implantable defibrillators
These devices are used to correct serious ventricular arrhythmias that can lead to
sudden death. The defibrillator is surgically placed inside the patient's chest.
There, it monitors the heart's rhythm and quickly identifies serious arrhythmias.
With an electrical shock, it immediately disrupts a deadly arrhythmia.
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Artificial pacemaker
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An artificial pacemaker can take charge of sending electrical signals to make the
heart beat if the heart's natural pacemaker is not working properly or its electrical
pathway is blocked. It works by sending small, painless amounts of electricity to
the heart to make it beat. During a simple operation, this small electrical device is
placed under the skin. A lead extends from the device to the right side of the
heart, where it is permanently anchored.
A variety of rhythm disorders can be successfully controlled with an artificial
pacemaker. Slow heart rates, such as heart block, are the most common reason to
use a pacemaker. However, new technology now let’s doctors treat some fast
heart rates with a pacemaker.
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Radiofrequency Catheter Ablation and Surgery
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Some tachycardia’s are life threatening or significantly interfere with normal
activities. Permanent treatment is often needed for these problems.
One procedure, called radiofrequency catheter ablation, is done with several
catheters in the heart. This is called an electrical physiologic study (EPS testing)
and requires a cardiologist with specialized training as well as special equipment.
This therapy involves threading an electrode into the heart through a large central
vein and electrically locating the abnormal conduction tract. Once the location of
the bypass tract is known another catheter is positioned directly over the area
that's causing the tachycardia. Its tip is heated and that small area of the heart is
altered so that electrical current won't pass through the tissue.
Surgery that interrupts the abnormal connection in the heart is another treatment.
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Cardiac Emergency. Lecturer: Abdel Rahman Nasr. | UNIVERSITY OF HAIL