How to read ECG: September 2011

   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

Looking at the ECG you'll see that:

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

An excessive heart rate above 100 beats per minute (BPM) which originates from the SA node. Causes include stress, fright, illness and exercise. Not usually a surprise if it is triggered in response to regulatory changes e.g. shock. But if their is no apparent trigger then medications may be required to suppress the rhythm
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

A heart rate less than 60 beats per minute (BPM). This in a healthy athletic person may be 'normal', but other causes may be due to increased vagal tone from drug abuse, hypoglycaemia and brain injury with increase intracranial pressure (ICP) as examples
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

A narrow complex tachycardia or atrial tachycardia which originates in the 'atria' but is not under direct control from the SA node. SVT can occur in all age groups
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

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

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

1st Degree AV block is caused by a conduction delay through the AV node but all electrical signals reach the ventricles. This rarely causes any problems by itself and often trained athletes can be seen to have it. The normal P-R interval is between 0.12s to 0.20s in length, or 3-5 small squares on the ECG.

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)

Another condition whereby a conduction block of some, but not all atrial beats getting through to the ventricles. There is progressive lengthening of the PR interval and then failure of conduction of an atrial beat, this is seen by a dropped QRS complex.

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

When electrical excitation sometimes fails to pass through the A-V node or bundle of His, this intermittent occurance is said to be called second degree heart block. Electrical conduction usually has a constant P-R interval, in the case of type 2 block atrial contractions are not regularly followed by ventricular contraction
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

3rd degree block or complete heart block occurs when atrial contractions are 'normal' but no electrical conduction is conveyed to the ventricles. The ventricles then generate their own signal through an 'escape mechanism' from a focus somewhere within the ventricle. The ventricular escape beats are usually 'slow'
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 )

Abnormal conduction through the bundle branches will cause a depolarization delay through the ventricular muscle, this delay shows as a widening of the QRS complex. Right Bundle Branch Block (RBBB) indicates problems in the right side of the heart. Whereas Left Bundle Branch Block (LBBB) is an indication of heart disease. If LBBB is present then further interpretation of the ECG cannot be carried out.
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

Due to a part of the heart depolarizing earlier than it should
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

Looking at the ECG you'll see that:
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

Looking at the ECG you'll see that:
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

Disorganised electrical signals cause the ventricles to quiver instead of contract in a rhythmic fashion. A patient will be unconscious as blood is not pumped to the brain. Immediate treatment by defibrillation is indicated. This condition may occur during or after a myocardial infarct.
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

Looking at the ECG you'll see that:
Rhythm - Flat
Rate - 0 Beats per minute
QRS Duration - None
P Wave - None
Carry out CPR!!
Myocardial Infarct (MI)

Looking at the ECG you'll see that:
Rhythm - Regular
Rate - 80 Beats per minute
QRS Duration - Normal
P Wave - Normal
S-T Element does not go isoelectric which indicates infarction