Download 4c HOW TO READ AN EKG

HOW TO READ AN EKG
http://jan.ucc.nau.edu/~daa/heartlung/lectures/ekg2.html
Heart rate estimation from the ECG
Identify the QRS complex; count the number of large squares between one QRS wave and the next;
divide that number by 300 to determine the rate. Each second of time is represented by 5 large squares.
So if the number of large squares between each QRS complex (the tall peaks) is:
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5 - the HR is 60 beats per minute.
3 - the HR is 100 per minute.
2 - the HR is 150 per minute.
Tachycardia is a heart rate that is faster than normal.
Bradycardia is a heart rate that is slower than normal
Rhythm
The presence of P waves immediately before every QRS complex indicates sinus rhythm. If there are
no P waves, note whether the QRS complexes are wide or narrow, regular or irregular.
Irregular heart rate
No P waves and irregular narrow QRS complexes
This is the hallmark of atrial fibrillation. Sometimes the baseline appears "noisy" and sometimes it
appears entirely flat. However, if there are no P waves and the QRS complexes appear at randomly
irregular intervals, the diagnosis is atrial fibrillation.
Sawtooth P waves
A sawtooth waveform signifies atrial flutter.
Long PR interval
A distance of more than five small squares from the start of the P wave to the start of the R wave (or Q
wave if there is one) constitutes first-degree heart block. It rarely requires action, but in the presence of
other abnormalities might be a sign of hyperkalemia, digoxin toxicity, or cardiomyopathy.
Q waves
A normal ECG has only very small Q waves. A downward deflection immediately following a P wave
that is wider than two small squares or greater in height than a third of the subsequent R wave is
significant: such Q waves can represent previous infarction
Large QRS complexes
Left ventricular hypertrophy (LVH)
Broad QRS complexes
A wide QRS complex despite sinus rhythm is the hallmark of bundle branch block.
ST Elevation or depression
Look for ST segment being elevated or depressed from the baseline. ST elevation indicates
Myocardial Infarction. ST depression is diagnostic of ischemia.
Review Your EKG: Write your results here:
HR: ______________
ST: ______________
PR: ______________
QRS: _____________
QT: ______________
P wave: Atrial Depolarization (contraction). Normal duration is 60 - 110 miliseconds.
The P wave results from atria contraction. P wave is generally about 1 box wide or 1
box tall. P wave that exceeds these might indicate atria hypertrophy, i.e., enlargement.
The P wave is the signal that the electrical potential has left the SA node, swept across the atria, and has initiated atrial
contraction. A normal P wave has a duration of 2.0 - 2.5 mm (.04 - .1 sec). If it is greater than 2.75 mm (.11 sec) it is
abnormal. Normal amplitude for a P wave is 2-3 mm. The P wave should always be gently rounded - never pointed or
peaked. Abnormal amplitude for the P wave is often seen in cor pulmonale, A-V valve disease, hypertension and in patients
with congenital heart disease. P waves within the same lead that are multiform (having different shapes) indicate the
presence of possibly multiple ectopic pacemakers in the right atrium. In the six limb leads, you will generally see P waves
that are positively deflected above the isoelectric line except in aVR where the P wave usually is upside down.
PR Interval: Atrial and AV node depolarization. Regular duration is 0.12 - 0.20
seconds. The PR interval is measured from the start of the P wave to the start of Q
wave. It represents the duration of atria depolarization. Normal duration is from 0.12
to 0.20 seconds. If the PR interval is greater than 200 milliseconds, then an AV block
might be present. After the P wave, there is a "silent period" where nothing is happening in the EKG tracing. This
quiescent period is called the PR interval. The PR interval represents a refractory period in which the AV node captures the
SA node signal and holds it for a short time. The PR interval allows the atria to contract and "top off" the ventricles with
blood - an event called atrial kick. If there was no time lag after the P wave, the ventricles would pump prematurely before
being adequately filled by atrial systole. The PR interval is measured on the EKG tracing from the beginning of the P wave
to the beginning of the Q wave or the beginning of the R wave if the Q wave is absent. The PR interval represents the time
period encompassing atrial depolarization up to but not including the start of ventricular depolarization. The normal
duration of the PR interval is between 3-5 mm or .12 - .20 seconds in duration. In adults, if the PR interval is longer than 5
mm, then it is considered a prolonged PR interval and may be diagnostic for the presence of atrioventricular blocks (AV
blocks). The PR interval does shorten during exercise as a means of allowing the heart rate to accelerate. The PR interval
continues to shorten with heart rates up 140-150 bpm. With higher heart rates, the PR interval does not get noticeably
shorter. In young children, the PR interval is shorter than in adults. In very young children ages 1-2 years, the PR interval
may be as short as .11 seconds (2.75 mm). At the age of 6 years, the PR interval has lengthened out to .13 seconds (3.25
mm) and by the time the child is 12 years of age, the PR interval is .14 seconds (3.5 mm). Very short PR intervals are seen
in patients with pheochromocytoma and in patients with Wolfe-Parkinson-White Syndrome. Occasionally, individuals with
normal hearts will have very short PR intervals as a normal variant. Prolonged PR intervals are seen in individuals with 1st
degree AV block, 2nd degree AV block (Mobitz I), and in patients with rheumatic heart disease
QRS Duration: Ventricular depolarization. Regular duration is no longer than 120
milliseconds. The QRS duration is measured from the start of Q wave to the end of S
wave. It represents the duration of ventricle depolarization. Normal duration is from
80 ~ 120 milliseconds. If duration is longer than 300ms, it might indicate presence of
bundle branch blocks.
The QRS Complex
The QRS complex is the electrical wave that signals the depolarization of the myocardial cells of the ventricles. The
duration for a normal QRS is no greater than 3 mm or about .06 - .12 seconds (1.5 - 3.0 mm). If the duration is greater than
3 mm (.12 seconds), then you have to suspect an abnormal intraventricular conduction velocity.
The Q Wave
The Q wave is defined as the first downward deflection after the P wave. It may be present and it can be absent in a normal
EKG. The Q wave represents the depolarization of the intraventricular septum. It is never considered to be abnormal if it is
missing from any particular lead. However, it is considered very significant if it is greater than 1 mm wide and 25% - 33%
of the total amplitude of the R wave. If its amplitude is 25% - 33% of the R wave, it is diagnostic for a myocardial
infarction in the lead that it is found. If a significant Q wave appears in aVF or Lead II or III, then there has been an
infarction in the inferior portion of the left ventricular wall. If a significant Q wave appears in aVL or Lead I, then an
infarction has occurred in the lateral wall of the left ventricle. Q waves are therefore only significant if they are present and
have large amplitudes.
The R wave
The R wave is the first upward deflection after the P wave. It represents part of the ventricular depolarization cycle. The R
wave takes on a life of its own when seen in the precordial chest leads. Normally the R wave is very small to non-existent
in V1. In successive chest leads, the R wave amplitude continues to grow until it reaches its greatest amplitude in V5. This
increasing R wave amplitude that is seen in the precordial chest leads is called R wave progression. As the R wave gets
larger, the S wave gets smaller. If the R wave progression is reversed or greatly disturbed, it frequently suggests the
presence of a bundle branch block. Usually when the R wave is disturbed, there are also bizarre reciprocal changes in the S
wave.
The S Wave
The S wave is defined as the first downward deflection after the R wave. It represents the remaining time period for
ventricular depolarization. S waves are disturbed and have bizarre shapes in the presence of bundle branch blocks.
QT Interval: Ventricular refractory time. The QT is measured from the start of the Q
wave to the end of T wave. It represents the duration of activation and recovery of the
ventricular muscle. This duration varies inversely with the heart rate. To correct (QTC)
for variable heart rates among patients, the following calculation must be made:
QTC = QT / RR
RR is interval between R to R peak
The normal QT for a person whose heart rate is 70 bpm is approximately 410
milliseconds. Higher than 450 (males) or 470 (females) is abnormal. Lower than
430 (males) or 450 (females) is abnormal. As an alternative for doing the calculation
for corrected QT (QTc): start with QT. Then, for every 10 bpm above 70, subtract 20
miliseconds. If QT or QTc is abnormally prolonged or shortened, there is a risk of
developing ventricular arrhythmias. Prolonged QT may indicate hypothyroidism or
hypocalcemia. A short QT may indicate hypercalcemia.
ST Segment: represents the period from the end of ventricular depolarization to the
beginning of ventricular repolarization. The ST segment is measured from end of S
wave, J point, to the start of T wave. Normal is 80 -120 msec (2-3mm). This segment is
important in identifying pathology such as myocardial infarction (elevation) and
ischemia (depression). 40 ms = 1mm. The ST segment is the portion of the EKG tracing that begins from
the J point to the beginning of the T wave. It is a pause after the QRS complex. It is essentially a period of diastole for the
heart and represent the period from the end of systole to the beginning of repolarization of the ventricles. It may appear as a
flat line between the QRS and the T wave or it may be upsloping from the J point from 1-2 mm in its amplitude and may be
2-3 mm in its duration. The ST segment is a crucial part of the EKG tracing. The appearance of the ST segment changes
dramatically in the presence of ischemia or during a myocardial infarction. During ischemia, the ST segment will become
depressed and have a long duration and a large amplitude before it joins the T wave. The ST segment is elevated during an
acute myocardial infarction. The ST segment is, therefore, a diagnostic segment of the EKG strip that is very important in
the diagnoses of heart problems.
T Wave
Ventricular Repolarization. Usually 0.5mV or less
The T wave represents the repolarization of the ventricles after systole is completed. Repolarization begins in the apex of
the heart and moves up through the heart muscle to the base of the heart. The normal duration for the T wave is .04 - .08
seconds (1 - 2 mm). Amplitudes vary. Unusually tall T waves sometimes appear in patients with potassium intoxication and
in psychotic patients (probably due to the medications they are on). T waves can be deranged (flipped or inverted) during
an acute myocardial infarction. The classic signs of a myocardial infarction in progress are ST segment elevation, T wave
inversion and the presence of significant Q waves.
Normal Sinus Rhythm
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Descriptions: All complexes normal and frequency is between 60 to 100 beats per minute.
Sinus Bradycardia
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Descriptions: A sinus rhythm of less than 60 beats per minute.
Supraventricular Tachycardia (SVT)
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Descriptions: Usually caused by reentry currents within the atria or between ventricles and atria
producing higher heart rates of 140~250. (Sinus rhythm at 160 BPM.)
Atrial Fibrillation
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Descriptions: Rapid irregular atrial signal with no real P-waves. Irregular ventricular rate.
Atrial Flutter
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Descriptions: Large regular P-waves (sinus rate of 250~350BPM). Ventricular response varies.
Ventricular Rhythm
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Descriptions: (Extremely Serious-near death conditions) Similar to left focus PVCs at 120 BPM
Ventricular Tachycardia
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Descriptions: (Extremely Serious-near death conditions) Similar to left focus PVCs at 180BPM
Ventricular Fibrillation
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Descriptions: (Extremely Serious-near death conditions) Irregular ventricular waveform
Sinus Arrhythmia
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Descriptions: Normal beats, but triggered at an irregular interval from 60 to 100 BPM, causing
varying R-R interval.
Missed beat
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Descriptions: Missed beat at 80 BPM. Normal sinus rhythm, but every 10 beat is missing
Paroxysmal Atrial Tachycardia (PAT)
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Descriptions: A repeated periods of very fast heartbeat which begin and ends suddenly. 160 BPM
for 5 seconds alternating with normal sinus rhythm at 80 BPM.
Left Ventricular Hypertrophy
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Descriptions: Tall R wave caused by possible thickening of heart muscle wall.
Right Bundle Branch Block (RBBB)
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Descriptions: Wide QRS, usually more than 120ms or 3 small squares, and wide S wave, caused by
partial or complete blockage of signal along the right branch below the bundle of HIS.
Premature Atrial Contraction (PAC)
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Descriptions: A beat occurs early in the atria causing the heart to beat before the next regular beat.
3.23 Premature Ventricular Contraction (PVC)
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Descriptions: Ventricles contract before signals reached AV node. Time interval between normal R
peaks is a multiple of R-R intervals.