Transcript EKG no audiox

PRACTICAL ELECTROCARDIOGRAPHY
M. Catherine Hough Ph.D, RN
Kathy Robinson RN, Ph.D, CCRN
Spring Semester 2002
Electrocardiogram
EKG or ECG
Characteristics of EKG Paper
• Horizontal Axis is a function of time
• Vertical Axis indicates amplitude ONLY in a
calibrated recording
Calculating EKG Rate
Calculating EKG Rate
Components of the QRS Complex
P wave
• The P wave represents the depolarization of
the atria (atrial depolarization)
• The P wave contour is usually smooth
– entirely positive (Leads I, II, III, aVF, and V4 to V6)
– negative (aVR) (monophasic) in all leads except V1
P wave
• The P wave duration is normally less than 0.12
sec.
• The P wave amplitude is normally less than
0.25 mV in all leads
• The P wave normally appears entirely upright
PR Interval
• The PR interval measures the time required
for the impulse to travel from the atria
myocardium adjacent to the SA node to the
ventricular myocardium adjacent to the fibers
of the Purkinke network (atrial and
ventricular depolarization)
PR Interval
• The PR interval is measured from the
beginning of the P wave to the
beginning
of the QRS complex.
• Normal PR interval duration range is from 0.12
sec - 0.20 sec
QRS Complex
• represents depolarization of the ventricles
(ventricular depolarization)
• If the first deflection from the isoelectric line is
negative it is a Q wave (not always present)
• The first positive deflection from the isoelectric
line is an R wave
• The negative deflection following an R wave is an
S wave
QRS Complex
• Normal QRS interval range is from 0.04 sec
- 0.12 sec
• Measured from the first deflection from the
isoelectric line to the J-point
– (J-point is where the QRS complex ends and
the ST segment begins)
ST Segment
• represents the plateau (phase 2) of the action
potential (ventricles in active state following
depolarization, but NO electrical activity occurs at
this time.
• Is normally isoelectric - no difference exists in
electrical potential among the action potentials of
the heart
• No current flow occurs because all cells are at zero
potential
T wave
• represents phase 3 of the action potential, when
the ventricles are being rapidly repolarized
(ventricular repolarization)
• Is normally rounded, slightly asymmetric, and the
same polarity as the QRS complex
• The effective refractory period is present during
the beginning of the T wave.
QT interval
• represents the entire duration of ventricular
depolarization and repolarization (ventricular
refractory period is the time necessary for
the ventricle to depolarize, then repolarize)
• The normal QT varies with age, gender, and
heart rate
Cardiac Rhythms
Five Steps to Rhythm Interpretation
• Determine the rate
• Identify the P Waves
– are they present?
– How do they relate to the QRS
• Identify the QRS Complex
– How do they relate to the P Waves?
• Measure the P-R interval
• Measure the QRS interval
Specialized Conduction
System of
• SA Node (highest rate of automaticity)
– Located on POSTERIOR surface of Rt. Atria
• Internodal atrial pathways
– Anterior Tract (Bachman’s Tract)
– Middle Tract (Wenchebach)
– Posterior Tract (Thorel’s)
• Bachman’s BUNDLE - conducts impulse from SA node to Lt.. Atria
• AV NODE
– Delays impulses from atria before they go to ventricle
– Allows for ventricular filling
Intraventricular Conduction System
•
•
•
•
Bundle of His
RBBB
LBBB
Purkinje System
Electrical Activity of the Heart
The above is borrowed from the web site: http://www.heartsite.com
Cardiac Properties
The heart normally possesses four intrinsic functional
properties that are the result of electrical activity
occurring @ the myocardial cell membrane
1. Automaticity - intrinsic to the pacemaker cells of the
heart. These cells have the ability to discharge an
electrical impulse automatically without & outside
stimulus
Inherent rates of automaticity:
a. SA node
60-100 bpm
b. AV junction
40-60 bpm
c. His-Purkinje system 20-40 bpm
Cardiac Properties
2. Excitability - refers to the ability of cells to become
electrically charged in response to an outside electrical
stimulus
• The degree of excitability is directly related to how much
recovery time the heart has had before the next
electrical stimulus is received
Cardiac Properties
3. Contractility - refers to the ability of cardiac muscle fibers to
shorten or contract in response to an electrical stimulus
• This property is scientifically based on the Frank-Starling Law
which claims:
• “To a point, the longer the muscle fiber is stretched, the
greater its force of contraction. If however the muscle fiber is
overstretched, the contraction will be weak”
Cardiac Properties
4. Conductivity - refers to the propagation of an impulse from
cell-to-cell. Achieved by two methods:
• Interconnected muscle fibers with intercalated discs
• Specialized conduction system
SA node
Normal Sinus or Regular Sinus Rhythm
(NSR or RSR)
• P wave present and regular.
• Atrial rate (P waves) between 60 and 100
beats/min
• Each P wave is followed by a QRS complex
Sinus Bradycardia
•
•
•
•
P wave present and regular
Atrial rate (P waves) < 60 beats/min
Each P wave is followed by a QRS complex
RX:
– May require no treatment
– Atropine IV
– May require temporary pacemaker or permanent
pacemaker
Sinus Tachycardia
•
•
•
•
P wave present and regular
Atrial rate (P waves) > 100 beats/min
Each P wave is followed by a QRS complex
RX:
– treat underlying cause
Sinus Arrhythmia
• P wave present
• P-P interval - phasic shortening then
lengthening of P-P interval, usually with
respirations
• Impulse initiation by SA node
• RX:
– usually none
Common Arrhythmias
Originating from Atria:
Premature Atrial Contractions (PAC)
• initiated by ectopic focus in the atria
• premature P wave with a contour different from a
sinus P wave (location of ectopic focus
determines its shape)
• QRS may or may not be normal
• PAC is followed by a pause ~ equal to the sinus
cycle
• (measured R to R)
Premature Atrial Contractions (PAC)
• associated with use of caffeine, stress, or use of
tobacco
• may be a precursor to developing uncontrolled AF
• RX:
– may require no treatment
– sedation
– quinidine
Atrial Flutter
• rapid sawtooth P waves
• ventricular rate regular
• associated with CAD, pulmonary embolism, mitral
valve disease, and thoracic surgical procedures.
• atria depolarize at a rate of 250 to 350 beats/min
Atrial Flutter
• RX:
– cardioversion
– digitalis
– ibutilide
– IV diltiazem
Atrial Fibrillation
• rapid irregular P waves > 350/min
• ventricular rate irregularly irregular
• ventricular rate varies, may increase to greater
than 150 if untreated
• if rate > 100 beats/min referred to as uncontrolled
AF
• if rate < 100 beats/min referred to as controlled
AF
Atrial Fibrillation
• RX:
– digitalis
– cardioversion
– quinidine
– IV dilitiazem
Sick Sinus Syndrome (SSS)
• term to describe several disorders of the SA node
• tachycardia-bradycardia syndrome is the most
common type of SSS
• complication associated with SSS is CHF and CVA
resulting from thromboembolisms
• RX:
– stabilization of heart with perm pacemaker
Atrial Tachycardia
•
•
•
•
•
rate 150 to 250 beats/min
P wave present but may be hidden
QRS is generally normal
ventricular rate is regular
RX:
– usually none
– prolonged episodes may require carotid sinus pressure,
vagal stimulation, verapmil, digitalis, or beta blocks
Impulse Conduction Deficits
A-V Blocks
First Degree AV Block
– PR interval prolonged - > 0.20 sec
– RX:
• usually none
– May warn of impaired conduction
Second Degree AV Block
Mobitz I (Wenckebach)
– PR interval progressively lengthens until a P
wave is not followed by a QRS complex
– Ratio of P waves to QRS complexes varies, i.e.
can be 5:1, 4:1, 3:1, or 2:1
– more often is a transient event
– seen with patients post Inferior MI, Digitalis
toxicity, or postoperative
– RX:
• generally none unless symptoms occur because of
slow rate seen with 2:1 ratio
Mobitz II
• more serious that Mobitz I
• less common than Mobitz I
• characterized by nonconducted sinus impulses
despite constant PR intervals
• usually the QRS are widened because of a BBB,
the dropped beat represents a form of
intermittent blockage of both bundle branches
Mobitz II
• the defect is found in either the bundle branches or
the bundle of HIS
• occur more frequently with patients with acute
anterior septal wall MIs
• often progress to CHB
• RX:
– temporary pacemaker
– possible need for perm pacer
Third Degree AV Block (Complete Heart
Block)
•
•
•
•
atria and ventricles beat independently
P waves have no relation to QRS
ventricular rate may be as low as 20-40 beats/min
RX:
– temporary or permanent pacemakers
– Isoproterenol to increase HR
– Epinephreine if Isuprel ineffective
Bundle Branch Block (BBB)
• same as normal sinus except QRS complex is >
0.12 sec
• depending on site of defect is labeled RBBB or
LBBB - the LBBB has two main devision the
anterior and posterior fascicles
• seen with severe CAD, acute anterior wall MI,
hypertensive pts
Bundle Branch Block (BBB)
• RX:
– usually none
– if sufficient blockage is present may require
perm pacer
Ventricular Arrhythmias
Premature Ventricular Contractions
(PVCs)
•
•
•
•
arise from an ectopic focus in the ventricles
wide bizarre QRS greater than 0.12 sec
no associated P wave
T wave is in the opposite direction from the main
QRS deflection
– ~ 50% of PVCS are followed by a compensatory pause
(the interval from the beat preceding to the beat
following the PVC is equal to two sinus cycles)
Premature Ventricular Contractions
• the remaining 50% PVCs result in retrograde
conduction to the atria causing the next sinus P
wave to be early and a compensatory pause occurs
• associated with CHF, digitalis toxicity, electrolyte
imbalances, and
excessive
caffeine intake
• RX:
– intravenous lidocaine (bolus and drip)
– oral antiarrhythmic drugs:
– Norpace, Quinidine, oxygen, KCL
Ventricular Tachycardia
•
•
•
•
no P wave before QRS
QRS wide and bizarre
ventricular rate > 100 beats/min (usually 140-240)
RX:
– lidocaine
– procainamide
– cardioversion
Ventricular Fibrillation
• chaotic electrical activity
• no recognizable QRS complex
• associated with MI, drug toxicity, electrocution,
freshwater
drowning
• no CO
• absent pulse or respirations -- CARDIAC ARREST
Ventricular Fibrillation RX:
•
•
•
•
•
initiate CPR
defibrillation
epinephrine
sodium bicarbonate
lidocaine, bretylium
Miscellaneous EKG Examples
• Pacemakers