• Supraventricular Impulse
• Narrow QRS Complex
• Basic Classification of Tachycardias
• Supraventricular Tachycardia (SVT)
• Most Common SVTs
• Supraventricular Tachycardias

Supraventricular Impulse

• Supraventricular area is defined in electrophysiology as
• Part of the heart above the bifurcation of the His bundle
• Anatomically includes the entire atria and AV junction (above the bifurcation)
• Overdrive suppression
• Is a electrophysiological mechanism
• Focus with the highest frequency (physiologically, this is the SA node)
• Deactivates foci with lower frequency
  (AV junction, Ventricular Purkinje fibers)
• The heart thus beats according to the focus with the highest frequency
• Supraventricular impulse
• Is an impulse originating in the supraventricular area
• Physiologically originates in the SA node (sinus rhythm)
• Depolarizes the atria (P wave) and then travels to the ventricles
• AV junction is an electrical connection between the atria and ventricles
• During ventricular depolarization, a QRS complex is formed

Basic Classification of Tachycardias

Basic Classification of Tachycardias

• Tachycardia is defined as a ventricular frequency > 100/min.
• Tachycardias are divided into 3 groups:
• Supraventricular Tachycardia
• Atrial Tachycardias (Impulses originate in the atria)
• Nodal Tachycardias (Impulses originate in the AV junction)
• Ventricular Tachycardias (Impulses originate in the ventricles)

Narrow Complex Tachycardia

• Frequency: 136/min.
• Narrow QRS complexes (<0.12s)
• Indicate that impulses are supraventricular
• and then activate the ventricles through the AV junction (QRS)
• A characteristic feature of ventricular tachycardia is wide QRS complexes (≥0.12s)
• Because impulses originate in the ventricles
• Exceptions are 2 narrow complex ventricular tachycardias (VT):
• VT from the ventricular septum
• Fascicular VT
• On the ECG, there is atrial flutter
• Supraventricular impulse circulates in the atrium (reentry)
• and creates characteristic sawtooth waves (instead of P waves)

Supraventricular Tachycardias

• Sinus Tachycardia
• Inappropriate Sinus Tachycardia
• Sinoatrial Nodal Reentry Tachycardia
• Atrial Tachycardia
• Intraatrial Reentry Tachycardia
• Multifocal Atrial Tachycardia
• Atrial Fibrillation
• Atrial Flutter
• Junctional Tachycardia
• Accelerated Junctional Rhythm
• AV Nodal Reentry Tachycardia (AVNRT)
• AV Reentry Tachycardia (AVRT)
• Permanent Junctional Reciprocal Tachycardia (PJRT)

Inappropriate Sinus Tachycardia

• Impulses originate in the SA node
• Each impulse creates a P wave, then passes to the ventricles (QRS)
• Mechanism is increased automaticity
• Is pathological sinus tachycardia (without a known cause)
• The SA node is "reprogrammed" to tachycardia
• Inappropriate Sinus Tachycardia
• Has the same ECG pattern as sinus tachycardia
• Because impulses originate from the same location (SA node)

Atrial Tachycardia

• Impulses originate from an ectopic single focus in the atrium (outside the SA node)
• Each impulse creates a P wave, then passes to the ventricles (QRS)
• P wave from the focus is different from the P wave of the SA node (has a different vector)
• Mechanism is enhanced automaticity (most common)
• Atrial Tachycardia
• On ECG, there are P waves (different from sinus P waves)

Multifocal Atrial Tachycardia

• Impulses originate from at least 3 ectopic foci in the atria
• Each impulse creates a P wave, then passes to the ventricles (QRS)
• Each focus (impulse) produces a different P wave (different vector)
• Mechanism is enhanced automaticity (most commonly)
• Multifocal Atrial Tachycardia
• On ECG, there are 3 P waves of different shapes

Atrial Flutter

• Impulse circulates in the right atrium (most commonly around the isthmus with a frequency of: 300/min.)
• With each revolution in the atrium, the impulse creates a "sawtooth"
• AV junction acts as a filter (not every impulse from each revolution reaches the ventricles)
• Only impulses from every second, third, etc., revolution reach the ventricles
• Mechanism is macro reentry (most commonly)
• Atrial Flutter
• On ECG, atrial impulses create characteristic sawtooth waves
• Not every impulse passes through the AV junction to the ventricles
• (On ECG, it appears as atrial flutter with 4:1 AV block)

Nonparoxysmal Junctional Tachycardia

• More commonly referred to as accelerated junctional rhythm
• Impulses originate in the AV junction (exactly like in junctional tachycardia)
• Mechanism is enhanced automaticity
• Occurs in severe AV junction damage, in digoxin toxicity, myocardial infarction
• Nonparoxysmal junctional tachycardia has a frequency of 70-130/min.
  (though a frequency of < 100/min. is not considered tachycardia)
• On ECG, retrograde (negative) P waves are seen just before the QRS
• P waves may be before, in, or after the QRS complex
• It is nonparoxysmal (does not have a sudden onset and sudden end)

AV Reentry Tachycardia (AVRT)

• The patient has WPW syndrome (congenital accessory pathway)
• Atria and ventricles are electrically connected through 2 sites:
• Accessory pathway and AV junction
• The impulse circulates from the atria to the ventricles (through the AV junction and accessory pathway)
• The impulse activates the ventricles through the AV junction (QRS)
• and then retrogradely through the accessory pathway to the atria (P wave)
• The opposite direction of the impulse is wide-complex tachycardia (Antidromic AVRT)
• Mechanism is macro reentry
• AV Reentry Tachycardia (Orthodromic AVRT)
• Retrograde (negative) P wave is after the QRS (it is hidden in the T wave)