• Supraventricular Tachycardia (SVT)
• Paroxysmal SVT
• Prevalence of Paroxysmal SVT
• Irregular SVT (Differential Diagnosis)
• Regular SVT (Differential Diagnosis)
• RP and PR Intervals
• SVT with Short RP Interval (RP < PR)
• SVT with Long RP Interval (RP > PR)
• Carotid Sinus Massage
• Adenosine
• Adenosine Test and WPW Syndrome
• Termination of Regular SVT (with P Wave, QRS?)
• Complete SVT Diagnosis Algorithm

Supraventricular Tachycardia (SVT)

• SVT is a tachycardia (heart rate > 100/min.) with narrow QRS complexes (<0.12s)
• Impulses originate in supraventricular areas (above the bifurcation of the His bundle)
• Impulses can originate via 3 mechanisms:
• Increased automaticity
• Triggering activity
• Re-entry
  
  
• The key feature of SVT is narrow QRS complexes (<0.12s)
• The key feature of ventricular tachycardia is wide QRS complexes (≥0.12s)
• Because impulses originate in the ventricles
• Exceptions include 2 narrow-complex ventricular tachycardias (VT):
• VT from the ventricular septum area
• Fascicular VT

Paroxysmal SVT

• Paroxysmal SVT is one that starts suddenly and ends suddenly
• The most common trigger is atrial extrasystole
• It lasts for a few seconds to hours
• The patient experiences palpitations (heart pounding) during the SVT episode
• Paroxysm of SVT can be terminated by:
• Massage of the carotid sinus
• Valsalva maneuver

Paroxysmal SVT

• At the beginning there is a sinus rhythm with a frequency of 65/min.
• Atrial extrasystole (red arrow)
• Triggered SVT with f: 150/min.
• This is a typical (Slow-Fast) AVNRT
• In V1, there is a pseudo R wave (dashed arrow)

Irregular SVT (Differential Diagnosis)

• Supraventricular tachycardia (SVT) is divided into
• Irregular SVT (simple EKG diagnosis)
• Regular SVT (complex EKG diagnosis)
• Differential diagnosis of SVT uses diagnostic algorithms
• Diagnostic algorithms are also used for diagnosing wide-complex tachycardia

Atrial Fibrillation

• Irregular SVT (QRS complexes are irregular)
• P waves are NOT present (fibrillatory waves are present instead)
• Impulses originate from foci in the atria with a frequency: 350-600/min.
• The AV junction acts as a filter (not every impulse reaches the ventricles)
• Impulses do not generate P waves, impulses that reach the ventricles create QRS
• Mechanism is micro-reentry (most common)
• Atrial Fibrillation
• On EKG, P waves are absent and QRS complexes are irregularly irregular

Atrial Flutter

• Irregular SVT
• Sawtooth waves with a frequency of 300/min (>240/min.)
• The impulse circles in the right atrium (Usually around the isthmus with a frequency of 300/min)
• Each rotation in the atrium creates a "sawtooth" impulse
• AV junction acts as a filter (not every impulse passes to the ventricles)
• Impulses pass to the ventricles every second, third, etc.
• Mechanism is macro re-entry (most common)
• Atrial Flutter
• On EKG, atrial impulses create characteristic sawtooth waves
• Not every impulse passes through the AV junction to the ventricles
• (On EKG, atrial flutter with varying AV block 2:1 and 4:1)

Regular SVT (Differential Diagnosis)

• Diagnosing regular SVT is more complex
• Often, definitive diagnosis requires electrophysiological study
• For diagnosing regular SVT, it is ideal to:
• Have older EKGs with sinus rhythm (without SVT)
• During sinus rhythm, look for delta waves (delta waves are associated with AVRT)
• Have the EKG capture the beginning and end of SVT
• Determine if the SVT is paroxysmal
• Observe the response of regular SVT to carotid sinus massage and Adenosine

RP and PR Intervals

• Assessed when conduction to the ventricles is 1:1 (P:QRS)
• RP interval (Start of QRS - Start of P wave)
• PR interval (Start of P wave - Start of QRS)
  
  
• Intervals are used for differential diagnosis of regular SVT
• SVT with a short RP interval (RP < PR)
• SVT with a long RP interval (RP > PR)

Without P wave

• Typical AVNRT (Slow-Fast)
• Atrial tachycardia with AV block I

RP > 90ms

• Rare AVNRT (Slow-Slow)
• Orthodromic AVRT
• Atrial tachycardia

Carotid Sinus Massage

• Slows down automaticity of the atria (not reentry in the atria)
• Slows down the frequency of P waves (and QRS) in
• Sinus Tachycardia
• Atrial Tachycardia
• Slows down impulse conduction through the AV junction
• Causes AV block (Increases conduction to the ventricles: 2:1, 3:1, 4:1...)
• Unmasks atrial activity (P waves, Flutter waves) that is hidden in the QRS complexes
• Terminates SVT with a reentry mechanism
• Prolongs conduction through the AV junction (refractory period) and the reentry circuit is interrupted
• Terminates regular reentry SVT:
• AVRT
• AVNRT
  
  
• Response of SVT to carotid sinus massage is only 10%
• (Incorrect massage technique, obese patients, physician experience...)
• Similar effects to sinus massage have adenosine
• Response of SVT to adenosine is 90%

• SVT response to carotid sinus massage is only 10%
• Therefore, in some SVTs, it often does not cause any changes
• (Incorrect massage technique, obese patients, physician experience, etc.)
• Adenosine has similar effects to sinus massage
• SVT response to adenosine is 90%

Carotid Sinus Massage and No Decrease in Heart Rate

• Carotid sinus massage (CSM)
• Does not affect reentry in the atria
• Stops reentry only in the AV junction
• No decrease in heart rate after CSM
• This indicates sinoatrial nodal reentry tachycardia (In the SA node, there is reentry)
• On the ECG, it looks exactly like sinus tachycardia
• The difference is that it does not respond to CSM

Carotid Sinus Massage and Increased AV Block

• Carotid sinus massage (CSM) increases AV block in SVT:
• Atrial fibrillation (usually irregular SVT)
• However, with high frequency, atrial fibrillation is "almost" regular SVT
• Atrial flutter (is regular SVT if it has the same conduction to the ventricles)
• Atrial tachycardia
• Multifocal atrial tachycardia (is usually irregular SVT)
• However, with high frequency, it may be "almost" regular SVT
• After CSM, AV block increased
• Atrial flutter with (2:1) conduction changed to (4:1)
• Flutter waves were unmasked

Adenosine

• Affects the heart similarly to carotid sinus massage
• The difference lies in the SVT response
• SVT response to
• Carotid sinus massage is only 10%
• Adenosine is 90%
  
  
• Dosing of adenosine
• Administer rapidly (within 2 seconds) into a peripheral vein (i.v.)
• Effects last only 10 seconds (short half-life)
• Dosing regimen (6mg -> 1 minute -> 12mg):
• Initial 1st dose is 6mg i.v.
• If SVT does not respond, administer 2nd dose: 12mg i.v. after 1 minute
• If SVT still does not respond, then adenosine is not administered
• Administration of a 3rd dose: 18mg i.v. is controversial
  
  
• Contraindicated in Atrial fibrillation with WPW syndrome
• Adenosine blocks the AV junction
• All impulses from the atria then pass to the ventricles
• through an accessory pathway (with a frequency of 350 - 600/min.)
• Results in ventricular fibrillation

Adenosine Test and Delta Wave

• Initially, there is sinus rhythm without delta wave
• 12mg of Adenosine i.v. blocks the AV junction for several seconds
• The impulse starts to propagate through the accessory pathway to the atria
• A delta wave appears on the EKG (black arrow) - WPW syndrome
• The patient has a hidden (inactive) accessory pathway during sinus rhythm
• If they have regular SVT
• Then it is almost certainly Orthodromic AVRT

Regular SVT

• QRS Alternans (variation in the height of QRS complexes)
• RP interval > 90ms (the width of the RP interval is estimated from QRS width, without EKG squares)
• What suggests (Rare AVNRT, AVRT, Atrial Tachycardia)?
• After sinus massage, tachycardia was terminated with a P wave
• What suggests AVRT
• Patient had a hidden accessory pathway (WPW syndrome) during electrophysiological study
• EKG shows Orthodromic AVRT

Complete SVT Diagnosis Algorithm

• Complete algorithm for differential diagnosis of SVT (both irregular and regular SVT)
• The algorithm diagnoses SVT based on EKG during SVT
• Does not assess SVT response: to sinus massage, adenosine, termination of SVT (with P wave, QRS?)
  
  
• The algorithm is often insufficient and differential diagnosis requires
• EKG with sinus rhythm (presence of delta wave)
• SVT responses to sinus massage (Adenosine)
• Electrophysiological examination

SVT with Short RP Interval (Without P Waves)

• P waves are absent
• According to the algorithm, it is Typical AVNRT (Slow-Fast)
• (Tachycardia with a short RP interval)
• Typical AVNRT creates
• Pseudo r' wave (V1) after QRS (arrow)
• Pseudo s wave (II, III, aVF)

Pseudo r' (V1) in AVNRT

• Indicates typical AVNRT (Slow-Fast)
• Occurs due to retrograde P wave (P')
• Retrograde P wave creates
• Pseudo s' wave in the inferior leads

SVT with Long RP Interval (RP > PR)

• The patient is a 30-year-old woman who presented with palpitations
• According to the algorithm, this is an SVT with a long RP interval (RP > PR):
• Atypical AVNRT (Fast-Slow)
• PJRT
• Atrial Tachycardia (with an ectopic focus in the septal area)
• After administration of adenosine 6mg i.v., conversion to sinus rhythm occurred
• Sinus rhythm persisted
  
  
• It is not PJRT
• PJRT typically occurs in children under 1 year old
• And recurs after conversion to sinus rhythm
• It is not Atrial Tachycardia
• Atrial Tachycardia does not terminate after adenosine administration
• It is atypical AVNRT (Fast-Slow)
• Retrograde P wave after QRS (II, III, aVF)
• P wave after QRS (aVR)

SVT with Long RP Interval (RP > PR)

• According to the algorithm, SVT with a long RP interval (RP > PR) includes:
• Atypical AVNRT (Fast-Slow)
• PJRT
• Atrial Tachycardia
• SVT did not respond to adenosine
• This excludes reentry mechanisms through the AV junction (AVNRT, PJRT)
• Additionally, the mentioned SVTs most commonly have a heart rate > 150/min.
• This is atrial tachycardia