Narrow Complex Tachycardia

  • Based on site of origin of Tachycardia, can be either, SVT or VT
  • But in clinical practice, duration of QRS is the first guide in identifying the nature of tachycardia 
    • Narrow Complex 
    • Wide Complex 
Understanding Tachycardia
  • Even before you look at any EKG, you need to understand the following to make sense of any EKG 
    • First: Be able to define narrow complex and wide complex tachycardia 
    • Then, understand the cardiac conduction pathway, and review the sequences of normal ventricular activation. Knowing this - 
    • Understand how does narrow complex and wide complex QRS occur. Knowing this - 
    • Locate the possible site of origin of cardiac conduction, and its propagation into the ventricle in the narrow complex tachycardia and in wide complex tachycardia 
      • Narrow and Wide Complex
      • PR segment present or absent (as in pre excitation)
      • Jump wave if seen 
    • Know the pathophysiology of tachycardia 
  • After this you are ready to look at an EKG 
    • In order to avoid misdiagnosis, few catch points, or not to miss points while reviewing EKG are 
      • Always use caliper or tool in computer. 
      • Always have a same sequence of reviewing EKG. 
      • And, review EKG in its entirety. 
      • Understand, normal looking p wave can occur in AT if the origin of atrial tachycardia is near SA Node 
      • In reviewing Narrow Complex tachycardia, 
        • Look for PR and RP relationship 
          • Short PR Tachycardias and Long PR tachycardias are different 
            • Short RP Tachycardia 
            • Long RP Tachycardia
              • Atrial tachycardia
              • Atypical AVNRT
              • ORtw with a slow decremental pathway (PJRT)
        • Understand AT typically does not exceed 200 atrial bpm
        • Look for Isoelectric line to differentiate AT from A flutter . 
          • Atrial flutter has no isolectric line that is representation of atrial depolarization
            • 2 exception
              • If prior history of cardiac surgery or ablation is present, it is atrial flutter even if isoelectric lines are present 
        • Look for uniformity of morphology. 
          • Flutter wave in atrial flutter is of same morphology. If different morphology is present, then it may actually be Atrial Fibrillation
      • 10-20 % of Atrial Tachycardia can respond to Adenosine. Just a response to Adenosine does not mean it is AV node involved tachycardia.

SVT:  symptomatic / asymptomatic - wide Complex or not -  Narrow Complex - regular or not - Heart Rate - Then Rapidity of onset - presence or absence of P-Wave - response to vagal maneuvers and adenosine (if given) - most likely etiology -- your plan

Diagnosis and management of supra ventricular tachycardia BMJ 2012
Evaluation and Initial Treatment of Supraventricular Tachycardia NEJM 2012

Bhargava - CCF: Expert Approach to SVT

Bhargava - CCF: Expert Approach to SVT

Bhargava - CCF: Expert Approach to SVT

Reference below is from uptodate

RP relationship — In patients with a retrograde P wave, the temporal relationship between the P wave and the R wave divides narrow complex tachycardias into two categories: short RP and long RP tachycardias.

Short RP tachycardias — If the RP interval is less than one-half of the RR interval, the tachycardia is considered a short RP tachycardia. The differential diagnosis of a short RP tachycardia is generated by considering the P wave morphology.

Abnormal P wave – The combination of abnormal P waves and a short RP interval is most often seen in the setting of an atrial tachycardia with AV nodal conduction delay. 

Retrograde P wave – The combination of retrograde P waves and a short RP interval is typical of the "common" form of AVNRT and of AVRT utilizing an accessory pathway. 

In the "common" form of AVNRT (which accounts for 90 percent of AVNRT), reentry occurs in the AV node and perinodal tissues. Antegrade conduction occurs down the slow pathway and retrograde conduction up the fast pathway. This slow-fast pattern gives rise to retrograde P waves that may be inapparent if obscured by the QRS complex 

AVRT utilizing an accessory pathway can be either orthodromic or antidromic. Orthodromic AVRT is more common, and in this form of the arrhythmia, antegrade conduction occurs through the AV node, producing a narrow QRS complex, and retrograde conduction to the atrium occurs over an AV bypass tract

In contrast, during antidromic AVRT, antegrade conduction occurs through the AV bypass tract and retrograde conduction occurs through the AV node or a second accessory pathway. This pattern of activation results in a wide QRS complex (thus, antidromic AVRT is not a narrow QRS complex tachycardia)

Long RP tachycardias — If the RP interval is more than one-half of the RR interval, the tachycardia is considered a long RP tachycardia. As with short RP tachycardias, the differential diagnosis is generated by combining the PR relationship with the P wave morphology.

Retrograde P waves – The combination of retrograde P waves and a long RP interval is usually caused by either "atypical" AVNRT or by AVRT with a slowly conducting accessory pathway; this combination can also be seen in atrial tachycardia with a focus that is close to the AV node 

Abnormal P waves – The combination of abnormal P wave morphology and a long RP interval usually suggests some form of atrial tachycardia. However, this pattern can also occur in the atypical or uncommon form of AVNRT and in AVRT with a slowly conducting accessory pathway (also called "permanent junctional reciprocating tachycardia" or PJRT)

The atypical form of AVNRT, which accounts for 10 percent of AVNRT, is characterized by antegrade conduction down a fast pathway and retrograde conduction through a slow pathway. As a result, the P wave occurs very late in the cardiac cycle (positioning it near to the next QRS complex)

In AVRT with a slowly conducting accessory pathway (also called "permanent junctional reciprocating tachycardia" or PJRT), antegrade conduction probably occurs through the AV node, and retrograde conduction through a slowly conducting accessory pathway  Because of slow conduction through the retrograde limb of the circuit, the retrograde P wave occurs late in the cardiac cycle. 

Reference above is from uptodate

  • Ventricular activation via His-purkinje system with 
  • Site of origin or maintainance of cardiac conduction is at or above the His-bundle. Ventricular activation occurs only down the AV Node, and his-purkinje fiber cardiac conduction is normal. 
    • SA Node
      • ST
      • Inappropriate ST 
      • SANRT (Sinoatrial nodal reentrant tachycardia)
    • Atrium
      • AT
      • Intraatrial Reenterant Tachycardia (IART)
      • Atrial Flutter (type of IART - macroreenterant)
      • A Fib (type of IART - microreenterant)
    • AV Node
      • AVNRT 
        • It is at AV Node, where the reentrant circuit is established and maintained
      • AVRT (reentrant or reciprocating tachycardia) 
        • In AVRT reentrant pathway involves AV Node, but itself is not a site of origin.
    • His-bundle 
      • Junctional ectopic tachycardia
      • Nonparoxsymal junctional tachycardia

Pathophysiological Classification. Understanding this is Important in selecting treatment mechanism
  • Focal (AT)
    • Ablate a focal point
      • Focal tachycardia coming close to Sinus Node can give a false impression of Sinus Tachycardia 
  • Macro-reenterant (A Flutter)
    • Need to ablate the critical isthmus 
  • Decremental conduction property of the fast conducting fibers of the AV node 
    • AVNRT (Note: AV Node has two tract. Fast tract and the slow tract)
      • Typical:
        • Down the slow AV tract
        • P wave closer to QRS means it is typical AVNRT 
      • Atypical: Down the fast AV tract 
        • P wave further out from QRS 
Commonly seen Narrow Complex Tachycardia 
Involving SA Node 
  • ST
  • Syndrome of Inappropriate Sinus Tachycardia
    • Definition HR 2015
    • sinus heart rate >100 bpm at rest (with a mean 24-hour heart rate > 90 bpm not due to primary causes) and is associated with distressing symptoms of palpitations.
Involving Atrium 
  • MAT
    • Pulmonary Disease
    • Dig toxicity 
  • Atrial Fibrillation: See under A fib and A FL 
Involving AV Node 
  • AVNRT 
  • Accessary Pathway
    • ART 
      • Are non-decremental
      • 5 % are multiple pathways
      • Shorter refractory period
      • Persistent or Intermittent 
      • Closer the pathway, more is the ventricular pre excitation 
      • Concealed Pathway
        • More often is due to retrograde conduction from these pathway. Not top to down. 
Involving His-bundle