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Arrhythmias and EKGs
Normal Sinus Rhythm
Implies normal sequence of conduction, originating in the sinus node and proceeding to the ventricles via the AV node and His-Purkinje system.
EKG Characteristics: Regular narrow-complex rhythm
Rate 60-100 bpm
Each QRS complex is proceeded by a P wave
P wave is upright in lead II & downgoing in lead aVR
Mechanisms of Arrhythmogenesis
Recognizing altered automaticity on EKG
Gradual onset and termination of the arrhythmia.
The P wave of the first beat of the arrhythmia is typically the same as the remaining beats of the arrhythmia (if a P wave is present at all).
Decreased Automaticity
Increased/Abnormal Automaticity
Mechanism of Reentry
Reentrant Rhythms
AV nodal reentrant tachycardia (AVNRT)
AV reentrant tachycardia (AVRT)
– Orthodromic
– Antidromic
Atrial flutter
Atrial fibrillation
Ventricular tachycardia
Recognizing reentry on EKG
Abrupt onset and termination of the arrhythmia.
The P wave of the first beat of the arrhythmia is different as the remaining beats of the arrhythmia (if a P wave is present at all).
Example of AVNRT
Mechanism of AVNRT
Atrial Flutter
Most cases of atrial flutter are caused by a large reentrant circuit in the wall of the right atrium
EKG Characteristics: Biphasic “sawtooth” flutter waves at a rate of ~ 300 bpm
Flutter waves have constant amplitude, duration, and morphology through the cardiac cycle
There is usually either a 2:1 or 4:1 block at the AV node, resulting in ventricular rates of either 150 or 75 bpm
Unmasking of Flutter Waves
In the presence of 2:1 AV block, the flutter waves may not be immediately apparent. These can be brought out by administration of adenosine
Atrial Fibrillation
Atrial fibrillation is caused by numerous wavelets of depolarization spreading throughout the atria simultaneously, leading to an absence of coordinated atrial contraction.
Atrial fibrillation is important because it can lead to:
Hemodynamic compromise
Systemic embolization
Symptoms
EKG Characteristics: Absent P waves
Presence of fine “fibrillatory” waves which vary in amplitude and morphology
Irregularly irregular ventricular response
What is this arrhythmia?
Ventricular tachycardia
Ventricular tachycardia is usually caused by reentry, and most commonly seen in patients following myocardial infarction.
Rhythms Produced by Conduction Block
AV Block (relatively common)
– 1st degree AV block
– Type 1 2nd degree AV block
– Type 2 2nd degree AV block
– 3rd degree AV block
– SA Block (relatively rare)