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  • Tachycardias are classically divided into narrow QRS and wide QRS complex
  • Narrow complex tachycardias (QRS <120 milliseconds) usually originate above the ventricle and are referred to as “supraventricular tachycardia” (SVT)

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SVT

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  • SVT differential includes sinus tachycardia, atrial tachycardia, multifocal atrial tachycardia, junctional tachycardia, atrial fibrillation, atrial flutter, AV nodal reentrant tachycardia (AVNRT), orthodromic reentrant tachycardia (ORT), or paroxysmal junctional reciprocating tachycardia (PJRT)
  • AVNRT (Figure 16-1) is a reentrant rhythm that utilizes dual AV nodal physiology or conduction via a slow and a fast pathway in the AV node. Typical AVNRT travels down the slow pathway node and up the fast pathway. Atypical AVNRT travels down the fast pathway and up the slow pathway
  • ORT is a reentrant arrhythmia that utilizes an accessory pathway for retrograde conduction
  • PJRT is also a reentrant arrhythmia that utilizes a slowly conducting retrograde pathway
  • Identification and characterization of atrial activity (P waves) is central to the diagnosis of SVT (Figure 16-2):
    • If there are no P waves but rather a fibrillatory baseline, then the rhythm is atrial fibrillation. A sawtooth baseline implies atrial flutter
    • If the P waves are regular and fast, then the “RP interval” or the relationship of the P wave to the preceding R wave is critical to the diagnosis
    • If the diagnosis is not clear based on surface EKG characteristics alone, an EP study needs to be done

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Figure 16-1. EKG of Typical AVNRT, the Most Common Type of SVT
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Reproduced from Fuster V, Walsh RA, Harrington RA. Hurst’s The Heart. 13th ed. Figure 41-3. Available at: www.accessmedicine.com. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.

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Figure 16-2. Algorithm for Determining the Etiology of Narrow Complex Tachycardia (QRS <120 Milliseconds)
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Table Graphic Jump Location
Table 16-1 EKG Appearance of Different Types of Tachycardias 
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Wide Complex Tachycardias

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  • Wide QRS because electrical impulses either originate or travel outside the normal conduction system
  • Differential for wide complex arrhythmias includes ventricular tachycardia, SVT with aberrancy, or conduction via an accessory pathway (antidromic reciprocating tachycardia)
    • SVT with aberrancy implies a rhythm that originates above the ventricle but is conducted aberrantly through the ventricle; usually this is secondary to bundle branch block
    • Antidromic reciprocating tachycardia is a ...

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