Chapter 49

atria
the two upper chambers of the heart
atrioventricular (AV) node
the part of the cardiac conduction system between the atria and the ventricles
bundle of his
specialized muscle fibers that conduct electrical impulses from the AV node to the ventricular myocardium
cardiac arrest
condition in which cardiac contraction stop completely
cardioversion
the use of electroshock to convert an abnormal cardiac rhythm to a normal one
defibrillator
a machine that delivers an electroshock to the heart through electrodes placed on the chest wall
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diastole
the relaxation of the chambers of the heart during which blood enters the heart from the vascular system and the lungs
ectopic
originating outside the normal tissue
infarction
an area of tissue that has died from lack of blood supply
ischemia
decreased blood flow to a body part or organ, caused by constriction or blockage of the supplying artery
myocardial
pertaining to the heart muscle
palpitations
a pounding or racing of the heart; may or may not indicate a serious heart disorder
sinoatrial (SA)node
the pacemaker of the heart; it is located in the right atrium
systole
the contraction of the heart
ventricles
the two lower chambers of the heart
precordial or chest leads
record the electrical activity between specific point on the chest wall and a point within the heart
patient who have difficulty breathing
can be placed in semi fowler’s position
patients should
breathe normally during the EKG procedure
smoking may
artificially alter the ECG
too much digitalis is
toxic and may alter the ECG
the three most common ECG changes are
elevated ST segments, inverted (upside down) T waves and abnormal (pathologic) Q waves
skin is
a poor electrical conductor; therefore, electrolyte gel must be applied to obtain in ECG tracing
ECG records
both amplitude and time
the SA node is
located in the upper back wall of the right atrium at the junction of the superior vena cava and the right atrium
the ventricles contract in a
twisting sort of action, forcing the blood out of the chambers and deoxygenated blood into the pulmonary artery on the right side of the heart
the SA node generates
an electrical impulse that travels in a wavelike pattern across the cardiac muscle of the atria, causing them to contract simultaneously
polarization is the
resting state of the myocardial wall; depolarization is the term for myocardial contraction
the P wave occurs
during the contraction of the atria and shows the beginning of the cardiac depolarization
multichannel ECG
tracings take seconds to perform and can be placed in the patient’s chart without mounting
the leads and lead wires carry
cardiac electrical impulses into the machine
lead 1
records tracings between the right arm and left arm; it records the electrical activity of the lateral part of the left ventricle
the typical standard speed for and ECG recording is
25mm/sec
the augmented leads are
unipolar leads with a single positive electrode that uses the fight leg for grounding
the QRS complex show as a
negative deflection in V1 and V2 views with each subsequent lead becoming more positive
an abrasive device should be used when
preparing a patient for a Holter monitor, but a routine ECG requires only that the area be clean and dry before electrodes are placed
normal sinus rhythm (NSR)refers to a
regular heart rate that falls within the average range of 60-80 beats per minute
sinus bradycardia is a
heart rate below 60 beats/mm
sinus tachycardia is a
heart rate above 100 beats/mm
an irregular cardiac rhythm is called
arrhythmia
in sinus arrhythmias, the pathway of the electrical change is
normal but the rate or rhythm of the heartbeat is altered
PACs occur
when the atrium contracts before it is supposed to in the normal cardiac cycle; this can be caused by stimulants
a patient in V fib
do not have a pulse
pacemakers are implanted in the
chest wall just above the heart location in a hospital siting under local anesthesia (a pacemaker keep the heart beating at a set rate)
an implanted cardioverter defibrillator (ICD)
monitors the heart rhythm and delivers a shock to the heart if it detects a dangerous tachycardia or fibrillation (also implanted in the patient chest just above the heart)
a cardiac event monitor must be
removed during bathing, so the patient must be taught how to remove and reapply the electrodes throughout the test period
ten sensors, called electrodes are placed on the
patient’s arms (two), legs (two), and chest (six) to pick up the electrical activity of the heart
a single lead records the
electrical activity of the heart between two different electrodes, one positive and one negative. the placement of the positive electrode determines the particular view of the heart recorded. if depolarization occurs toward the positive electrode, the deflection is upright; if it moves toward the negative electrode, the waveform is deflected downward. each lead records the average electrical flow at a specific time in a specific location of the heart. the ECG records views of the heart on both a frontal and a transverse plane
the frontal leads include
leads 1,2,3, aVr, aVL, and aVF horizontal plane leads include the six precordial (or chest leads) V1-V6
ECG has ten leads that produce
a 12 lead reading
the first three leads recording are called
standard or bipolar leads, because they each use two limb electrodes to record the heart’s electrical activity
the right arm electrode is the
negative pole and the left leg or left arm electrodes are the positive pole. roman numerals I,II,III are used to designate these leads
lead I records tracing between the
right arm and left arm; recording the electrical activity of the lateral part of the left ventricle
lead II tracing between the
right arm and left leg; recording the electrical activity of the inferior surface of the left ventricle
lead III tracing between the
left arm and leg which reflects the electrical activity of the inferior surface of the left ventricle
augmented leads (or combined leads)
the next three leads augmented voltage right arm (aVr) augmented voltage left arm (aVL) and augmented voltage left leg (aVF) these are all unipolar leads with a single positive electrode that uses the right leg for ground
aVr
records the electrical activity of the atria from the right shoulder; P waves and QRS complexes are deflected below the baseline
aVL
records the electrical activity of the lateral wall of the left ventricle from the left shoulder
aVF
records the electrical activity of the inferior surface of the left ventricle from the left leg
precordial leads
chest leads are unipolar and provide a transverse plane view of the heart. V1,V2,V3,V4,V5,V6
the V means
chest and each numbers represents a specific location on the chest
V1 place 4th intercostal space
just to the right of the sternum
V2 place 4th intercostal space
just to the left of the sternum
V3 placed midway between
V2 and V4
V4 place 5th intercostal space
at the left midclavicular line
V5 place horizontal to
V4 in the left anterior axillary line
V6 placed horizontal to
V4 in the left midaxillary line
RA
right arm
LA
left arm
RL
right leg
LL
left leg
telephone transmission
transmit a record over a telephone to an ECG data interpretation center. the recording is interpreted by a computer at the data center and verified by a cardiologist
artifacts
is an unwanted erratic movement of the stylus caused by outside interference
the main types of artifacts are
(1) wandering baseline accrue when pt. moving, (2) somatic tremor means muscle movement; (3) alternating current (AC) interference appears as a series of uniform small spikes/due to nearby electrical equipment or wiring/need to unplug appliances; (4) interrupted baseline occurs when the electrical connection has been interrupted
horizontal axis
represents time
vertical axis
represents amplitude
each small square measures
1mm on each side
every fifth line both vertically and horizontally is
darker than the other lines and creates a larger square measuring 5mm on each side
when the electrocardiograph runs at
normal speed, one small 1mm square passes the stylus (the writer) every 0.04 second which means that one large 5mm square passes the stylus every 0.02 second. continuing this logic, in 1 second, five large squares pass the stylus. therefore, five sequential large square show the record of what occurred in the heart during a time span of 1 second (5 large square 0.2 seconds=1 second) another way to say this that at normal speed
5 large boxes
1 second
15 large boxes
3 seconds
30 large boxes
6 seconds
ECG paper travels past the stylus at a rate of
25mm per second
the voltage or strength of the heart beat also is
recorded on the paper. can be positive or a negative deflection one millivolt (mV) of electricity moves the stylus upward over 10mm (two large squares) this is the standard used for obtaining an ECG and can be adjusted to match the strength of the electrical activity of the heart. the machine must be calibrated so that 1mV of electrical activity produces a deflection that is 10mm either above or below the baseline. ECG records both strength of the electrical activity of the heartbeat in millivolts and the speed of the heartbeat over time
holter monitor
portable system for recording cardiac accurate monitor heart function for a 24hr period; the entire time the monitor is worn the pt. must keep a journal of all stressful events and activities and also specific details about activities when any cardiac symptoms occur
an abrasive device should be used when
preparing a pt. for a holter monitor, but a routine ECG requires only that the area be clean and dry before electrodes are placed
the QRS complex shows as a
negative deflection in V1 and V2 views, with each subsequent lead becoming more positive
in sinus arrhythmias the pathway of the
electrical charge is normal but the rate or rhythm of the heartbeat is altered
PACs (premature atrial contraction)
occur when the atrium contracts before it is supposed to in the normal cardiac cycle; this can be caused by stimulants
PVC (premature ventricular contractions)
occur when the ventricle contract before they should for the next cardiac cycle; a QRS complex appears before a P wave
tachycardia is a
heart rate over 100 bpm
bradycardia is a
heart rate less than 60 bpm
an interrupted baseline typically is
caused by a disconnection between the leads and the machine
both arms and chest electrodes are
applied with the tabs pointing downward toward the center of the body
5 sequential large squares show the record of what
occurred with the heart during a time span of 1 second (5 large squares 0.2 second= 1second) the ventricular contraction rate can be determined by counting the number of complete QRS complexes that occur within 6 seconds and multiplying that number by 10; this gives the number of ventricular contraction in 1 minute
small uniform spikes in the baseline are
an AC interference artifact which is caused by electrical interference remember check and unplug nearby electric appliances
a wandering baseline (rising and falling) usually is
caused by slight movement by the pt. during the tracing or poor electrode attachment
the most common causes of somatic tremor artifacts are
pt. discomfort, apprehension, movement, or talking or a condition that causes uncontrollable body tremors. you need to help the pt. relax stay warm
the ventricles are larger chambers and have thicker myocardial walls
therefore, the electrical charge released when they contract is significant greatest deflection from the baseline on the ECG is the QRS complex
the T wave reflects the
effort of the ventricles to reach a relaxed state
the P wave is the first part of the
ECG and reflects atrial contraction
diastole is the
relaxation phase of the heart, during which the chambers refill with blood
the SA node controls the
rat of heart contraction by initiating electrical impulses 60-100 times a minute
a normal sinus rhythm is
a regular heart rate, the electrical flow of the heart is a normal pattern, and the heart rate is 60-80 bpm
the ST segment reflects the
time between the end of ventricular contraction and the beginning of ventricular recovery
the tracing paper is
heat and light sensitive, and every fifth line measures 5mm on each side
ECG paper has horizontal and vertical lines at
1mm intervals
when a machine is in standard mode or set
at 1 STD (standardization) 1mV of electricity causes the stylus to move vertically 10mm or two large squares. the stylus should deflect exactly 10mm when the standardization button is depressed with a quick pecking motion
conduction is
impaired if electrodes are placed over bony prominences; AC artifacts may occur if the bed is against the wall; the ground is on the right leg
uncontrollable muscular movement cause
somatic tremor artifacts
the pt. exercises during a
cardiac stress test so that the myocardium’s response to a lack of oxygen if present can be assessed
ectopic artrial beats cause
the atria to continue to fire randomly and do not allow the electrical charge to be collected and passed through to the AV node
cardioversion with a defibrillator is
necessary to restore normal function of electrical conduction system (that is in V-fib/can lead to death if not treated (asystole)/ can precede by V-tach)
the three most common ECG changes with an
MI are elevated ST segments, inverted (upside down) T waves and abnormal (pathologic) Q waves
the electron beam tomography heart scan is
a screening tool that allows physicians to see the amount of plaque in the coronary arteries by showing the calcium deposits. calcium make up approximately 20% of arterial plaque deposits
the P wave is
the first deflection from the baseline; depolarization of the atria
PR segment is
the return to baseline after atrial contraction
PR interval is
the time from the beginning of atrial contraction to the beginning of ventricular contraction
QRS complex
show the contraction of both ventricles/reflects the completion of cardiac depolarization (repolarization of the atria also occurs during this time, but cannot be seen)
ST segment
reflects the time between the end of ventricular contraction/beginning of ventricular recovery
QT interval
is the time between the beginning of the QRS complex
T wave
represents ventricular recovery (repolarization)
U wave
occasionally can be seen as a small waveform just after T wave in pt. with a low serum potassium level or other metabolic disorders
polarization
resting state of the myocardial wall; no electrical activity occurs in the heart during this phase which is recorded on the ECG strip as a flat line
depolarization
when the electrical system of the heart stimulates a myocardial cell, resulting in contraction (systole)
repolarization
resting state (diastole)