Most of health professional has little understanding about how to read easily electrocardiography especially those who are not dealing with the ECG in their work place.However, learning how to read ECG rhythms and to manage patients condition according to the ECG is absolutly needed. By learning ECG pattern we can interpret wich part of the heart are affected,and immediate action must be perform as soon as possible.
Now we will learn together how to read tipically ECG pattern and interpretation.
ELECTROCARDIOGRAM BASIC
An electrocardiogram reflects the electrical activity of cardiac cells and records electrical activity at a speed of 25mm/sec.
An electrocardiogram strip consist of horizontal square representing seconds and vertical representing voltage.
Each smaal square represents 0.04 second
Each large square represents 0.20 second.
P WAVE :represents as atrial depolarization
PR INTERVAL : represents the time it takes an impuls to travel from atrial through the
atrioventricular node bundle his and bundle branch of the purkinje
fibers.Normal PR interval duration from 0.12 to 0.2 second
QRS COMPLEX:represent as ventricular depolarization.QRS complex duration
from 0.04 to 0.1 second
Q WAVE :as the first negative deflection in the QRS COMPLEX and
reflects initial ventricular septal depolarization.
R WAVE :the first positive deflection in the QRS complex
S WAVE :appears as as the second negative deflection in the QRS complex.
ST SEGMENT :represents as ventricular repolarization.
T WAVE :represents as ventricular repolarization and ventricular diastole
U WAVE :follow the T wave ,prominent U wave hypokalemia.
QT INTERVAL :represents as ventricular refractory time or total time for
ventricular depolarization and repolarization. QT interval measured
from the beginning of the QRS complex to the end of the T wave.
ECG GRID
Left to right = Time and duration
Vertical = Measure of voltage < Amplitude >
P WAVE
>Depolarization of atrial muscle
>Low voltage (2-3mm in amplitude)
>Duration <0.11 second
Abnormal P WAVE
>P=Pulmonal
* tall peaked
* right atrial enlargment secondary to pulmonary HTN
>P=Mitrale
* broad notched
* Left Atrial enlargement secondary to mitral valve disease
QRS Complex
>Depolarization of ventricles
>Larger muscle mass
>As high as 25 mm
>Duration normal conduction <0.10
>Amplitude >25 mm can mean chamber enlargement as
in ventricular hypertrophy
QRS complex
* Low amplitude
- diffuse,severe coronary artery disease
- pericardial effusion
- hypothyroid
QRS Complex
* 1st Negative deflection=Q Wave
*1st Positive deflection =R Wave
*Negative deflection after R Wave= S Wave
*Positive deflection after R Wave =R Prime
*Negative deflection after S Wave = S Prime
ST Segment
>Time between completion of depolarization and onset of
repolarization.
- Normally isoelectric & gently blends into upslope of T Wave
- Point where ST take off from QRS = J Point
- Plays important role in diagnosis of Ischemic heart disease
ST Elevation
* HALLMARK OF MI
*Slight elevation across entire tracing is normal especially
in young male
ST Depression
* Indicative of Ischemia,Ventricular hypertrophy
T WAVE
>Repolarization of the ventricles
>Same direction as predominant QRS deflection
>Abnormalities-usually inversion with BBB,hypertrophy
or AMI
QT Interval
>Beginning QRS to the end of T Wave>Abnormalities :
*Prolonged-commonly from drugs like Procan and
Quinidine or electrolyte imbalance
*Increased opportunity for R on T.ventricular re-entry
rhythms and sudden death.
ECG RHYTHM
In this section you will find the most common ECG pattern.
Normal Sinus Rhythm
- Rhythm - Regular
- Rate - (60-100 bpm)
- QRS Duration - Normal
- P Wave - Visible before each QRS complex
- P-R Interval - Normal (<5 small Squares. Anything above and this would be 1st degree block)
- Indicates that the electrical signal is generated by the sinus node and travelling in a normal fashion in the heart.
- Clinical Tip :A normal ECG does not exclude heart disease
-
Sinus Tachycardia
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - More than 100 beats per minute
- QRS Duration - Normal
- P Wave - Visible before each QRS complex
- P-R Interval - Normal
- The impulse generating the heart beats are normal, but they are occurring at a faster pace than normal.
- Clinical Tip :Sinus tachycardia may be caused by exercise,anxiety,fever,hypoxemia.hypovolemia.or cardiac failure.
-
Sinus Bradycardia
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - less than 60 beats per minute
- QRS Duration - Normal
- P Wave - Visible before each QRS complex
- P-R Interval - Normal
- Usually benign and often caused by patients on beta blockers
- Clinical Tip :Sinus bradycardia is normal in athletes and during sleep.
-
Supraventricular Tachycardia (SVT) Abnormal
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - 150-250 beats per minute
- QRS Duration - Usually normal
- P Wave - Often buried in preceding T wave
- P-R Interval - Depends on site of supraventricular pacemaker
- Impulses stimulating the heart are not being generated by the sinus node, but instead are coming from a collection of tissue around and involving the atrioventricular (AV) node
- Clinical Tip :SVT may be related to caffeine intake,nicotine,stress,or anxiety in healthy adults.
-
-
Atrial Fibrillation
Many sites within the atria are generating their own electrical
impulses, leading to irregular conduction of impulses to the ventricles
that generate the heartbeat. This irregular rhythm can be felt when
palpating a pulse - Rhythm - Irregularly irregular
- Rate - usually 100-160 beats per minute but slower if on medication
- QRS Duration - Usually normal
- P Wave - Not distinguishable as the atria are firing off all over
- P-R Interval - Not measurable
- The atria fire electrical impulses in an irregular fashion causing irregular heart rhythm
- Clinical Tip: Atrial fibrillation is usually a chronic arrhythmia associated with underlying heart disease.
-
-
Atrial Flutter
Looking at the ECG you'll see that: - Rhythm - Regular
- Rate - Around 110 beats per minute
- QRS Duration - Usually normal
- P Wave - Replaced with multiple F (flutter) waves, usually at a ratio of 2:1 (2F - 1QRS) but sometimes 3:1
- P Wave rate - 300 beats per minute
- P-R Interval - Not measurable
- As with SVT the abnormal tissue generating the rapid heart rate is also in the atria, however, the atrioventricular node is not involved in this case.
- Clinical Tip : The presence of atrial flutter may be the first indication of cardiac disease.
-
-
1st Degree AV Block
Looking at the ECG you'll see that: - Rhythm - Regular
- Rate - Normal
- QRS Duration - Normal
- P Wave - Ratio 1:1
- P Wave rate - Normal
- P-R Interval - Prolonged (>5 small squares)
- Clinical Tip: Usually AV block is benign,but if associated with an acute MI it may lead to further AV defects.
-
-
2nd Degree Block Type 1 (Wenckebach)
Looking at the ECG you'll see that: - Rhythm - Regularly irregular
- Rate - Normal or Slow
- QRS Duration - Normal
- P Wave - Ratio 1:1 for 2,3 or 4 cycles then 1:0.
- P Wave rate - Normal but faster than QRS rate
- P-R Interval - Progressive lengthening of P-R interval until a QRS complex is dropped
- Clinical Tip : This rhythm may be caused by medications such as beta blockers,digoxin,and calcium channel blockers (see emergency medications).Ischemia involving the right coronary artery is another cause.
-
-
2nd Degree Block Type 2
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - Normal or Slow
- QRS Duration - Prolonged
- P Wave - Ratio 2:1, 3:1
- P Wave rate - Normal but faster than QRS rate
- P-R Interval - Normal or prolonged but constant
- Clinical Tip : Resulting bradycardia can compromise cardiac output and lead to complete AV block.This rhythm often occurs with cardiac ischemia or an MI.
-
-
3rd Degree Block
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - Slow
- QRS Duration - Prolonged
- P Wave - Unrelated
- P Wave rate - Normal but faster than QRS rate
- P-R Interval - Variation
- Complete AV block. No atrial impulses pass through the atrioventricular node and the ventricles generate their own rhythm.
-
-
Bundle Branch Block ( BBB )
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - Normal
- QRS Duration - Prolonged
- P Wave - Ratio 1:1
- P Wave rate - Normal and same as QRS rate
- P-R Interval - Normal
- Clinical Tip : Commonly ,BBB occurs in coronary artery disease.
-
-
Premature Ventricular Complexes
Looking at the ECG you'll see that:
- Rhythm - Regular
- Rate - Normal
- QRS Duration - Normal
- P Wave - Ratio 1:1
- P Wave rate - Normal and same as QRS rate
- P-R Interval - Normal
- Also you'll see 2 odd waveforms, these are the ventricles depolarising prematurely in response to a signal within the ventricles.(Above - unifocal PVC's as they look alike if they differed in appearance they would be called multifocal PVC's, as below)
-
Junctional Rhythms
- Rhythm - Regular
- Rate - 40-60 Beats per minute
- QRS Duration - Normal
- P Wave - Absent,inverted,burried,or retrograde.Ratio 1:1 if visible. Inverted in lead II
- P Wave rate - Same as QRS rate
- P-R Interval - Variable
-
Below - Accelerated Junctional Rhythm
* Clinical Tip :Monitor the patient ,not just the ECG,for clinical improvement .
Ventricular Tachycardia (VT) Abnormal
- Rhythm - Regular
- Rate - 180-190 Beats per minute
- QRS Duration - Prolonged
- P Wave - Not seen
- Results from abnormal tissues in the ventricles generating a rapid and irregular heart rhythm. Poor cardiac output is usually associated with this rhythm thus causing the pt to go into cardiac arrest. Shock this rhythm if the patient is unconscious and without a pulse.
- Clinical Tip :Consider electrolyte abnormalities as a possible etiology.
-
-
Ventricular Fibrillation (VF) Abnormal
Looking at the ECG you'll see that:
- Rhythm - Irregular
- Rate - 300+, disorganised
- QRS Duration - Not recognisable
- P Wave - Not seen
- Clinical Tip :This patient needs to be defibrillated!! QUICKLY
-
-
Asystole - Abnormal
- Rhythm - Flat
- Rate - 0 Beats per minute
- QRS Duration - None
- P Wave - None
- Carry out CPR!!
-
-
Myocardial Infarct (MI)
- Rhythm - Regular
- Rate - 80 Beats per minute
- QRS Duration - Normal
- P Wave - Normal
- S-T Element does not go isoelectric which indicates infarction
Looking at the ECG you'll see that:
Info
ECG Component | Time(sec) | Small Squares |
P Wave | 0.10 |
up to 2.5
|
PR Interval | 0.12 - 0.20 | 2.5-5.0 |
QRS | 0.10 |
1.5-2.5
|
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