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Electrocardiogram
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What is an ECG?
The electrocardiogram (ECG) is a representation of the electrical events of the cardiac cycle. Each event has a distinctive waveform, the study of which can lead to greater insight into a patients cardiac pathophysiology.
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What types of pathology can we identify and study from ECGs?
Arrhythmias Myocardial ischemia and infarction Pericarditis Chamber hypertrophy Electrolyte disturbances (i.e. hyperkalemia, hypokalemia) Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)
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Anatomy of Heart and ECG signal
Normal ECG signal Conducting System of Heart
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P wave PR segment
PR interval
QRS ST segment QT interval
Atrial depolarization Condition delay through AV node; used as baseline to evaluate ST segment elevation or depression Atrial depolarization + conduction delay through AV node Ventricular depolarization Isoelectric; ventricles still depolarized Ventricular depolarization + ventricular repolarization;
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ECG Leads
Leads are electrodes which measure the difference in electrical potential between either:
1. Two different points on the body (bipolar leads) 2. One point on the body and a virtual reference point with zero electrical potential, located in the center of the heart (unipolar leads)
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ECG Leads
The standard ECG has 12 leads: 3 Standard Limb Leads 3 Augmented Limb Leads 6 Precordial Leads
The axis of a particular lead represents the viewpoint from which it looks at the heart.
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Precordial Leads
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Precordial Leads
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Calculating Heart Rate
1. 1500
method divide 1500 by the number of small squares between two consecutive QRS complexes 2. R-R method find a QRS where the peak R wave
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Normal H.R. 60-100 bpm Bradycardia less than 60 bpm Tachycardia less than 100 bpm
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Normal cardiac rhythm parameters
Normal Sinus Rhythm Sinus Bradycardia Sinus Tachycardia QRS width P-R interval Q-T interval Atrial rate, inherent Junctional rate, inherent Ventricular rate, inherent 60 100 bpm < 60 bpm > 100 bpm 0.08 - 0.12 sec (3 small boxes) 0.12 0.20 sec 0.30 0.40 sec 60 100 bpm 40 60 bpm 20 40 bpm
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Rapid ECG Assessment and Identification Algorithm
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1. 2. 3.
Check Rhythm regular or irregular? Check Heart rate fast or slow? Check QRS wide (>0.12 secs) or narrow (<0.12 secs)? Check P waves present or absent? More Ps than QRSs?
4.
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Regular rhythm Heart rate HR > 100 bpm QRS > 0.12 secs HR < 60 bpm QRS>0.12 secs
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HR > 100 bpm
QRS > 0.12 secs Yes
P waves present? Yes More P waves Ventricular No Consider
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HR > 100 bpm
QRS > 0.12 secs No
P waves present? Yes Sinus Tachycardia Tachycardia No Junctional
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HR < 60 bpm
QRS > 0.12 secs Yes
P waves present? Yes AV block No Ventricular Escape
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HR < 60 bpm
QRS > 0.12 secs No P waves present? Yes No Consider Junctional Tachycardia
More P waves than QRSs
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Irregular rhythm Heart rate HR > 100 bpm QRS > 0.12 secs HR < 60 bpm QRS>0.12 secs
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HR > 100 bpm
QRS > 0.12 secs Yes
P waves present? Yes AV block No aberrantly conducted AF: R/O VT
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HR > 100 bpm
QRS > 0.12 secs No
P waves present? Yes Heart Block vs Atrial Flutter No Rapid AF
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HR < 60 bpm
QRS > 0.12 secs Yes
P waves present? Yes AV block No aberrantly conducted AF: R/O VT
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HR < 60 bpm
QRS > 0.12 secs No
P waves present? Yes Heart Block vs Atrial Flutter No Slow AF
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Sinus Rhythms
Normal Sinus Sinus
Sinus Rhythm (NSR)
Bradycardia Tachycardia
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Atrial Rhythms
SA
node fails to generate an impulse, the atrial tissue or areas in the internodal pathways may initiate an impulse. are called atrial dysrhythmias not considered life threatening or lethal careful and deliberate patient assessment must be continuous. life-
These
Generally
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Types of Atrial Rhythms
Atrial Atrial
Flutter Fibrillation Tachycardia
Supraventricular
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Ventricular Rhythms
SA
node or the AV junctional tissue fails to initiate an electrical impulse, the ventricles will shoulder the responsibility of pacing the heart. group of rhythms are called ventricular dysrhythmias electrical impulse can be instigated from any pacemaker cell in the ventricles, including the bundle branches or the fibers of the Purkinje
This An
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Types of Ventricular Rhythms
Premature Ventricular Torsades
Ventricular Complexes Tachycardia Fibrillation
de Pointes
Ventricular Asystole Pulseless
Electrical Activity (PEA)
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Torsades de Pointes
French May
term that signifies the twisting of the points. wax and wane in amplitude and may flip or twist on its electrical axes. to ventricular tachycardia by hypomagnesemia or by antiarrhythmic drugs
Similar Caused
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Pulseless Electrical Activity (PEA)
The
absence of a palpable pulse and myocardial muscle activity with the presence of organized electrical activity (excluding VT and VF) on cardiac monitor. is not an actual rhythm, it represents a clinical condition wherein the patient is clinically dead, despite the fact that some type of organized rhythm appears
It
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Electrolyte / drug ecg changes
Hypokalemia Hyperkalemia Digitalis
Toxicity de Pointes
Torsades
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hypokalemia
Increased Decrease
prominence of the U wave amplitude or flattening of the T wave depression of the ST segment amplitude and width of the P wave
Slight
Increased
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hyperkalemia
Increased
amplitude and peaking of the of the PR interval of the QRS interval
T-wave
Prolongation Prolongation Flattening
of the P wave
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Digitalis Toxicity
coved
ST segment depression T waves QTc interval
Flattened
Decreased
