1. David Sanders Mini-Lecture 2017
SVT
David Sanders
Mini-Lecture
2017

2. Objectives Understand pathophysiology of types of SVT
Learn EKG features for AVNRT and AVRT
Review basic acute and long-term management strategies for the patient with AVNRT and AVRT

3. SVT: Overview
Definition: from Hurst’s the Heart: All tachyarrhythmias that either originate from or incorporate supraventricular tissue in a re-entrant circuit.
Paroxysmal SVT: Rapid, regular tachycardia with abrupt onset and termination
Definitions are listed above. The strip shows a regular narrow complex tachyarrhythmia represented of an SVT.

4. SVT Classification AV nodal reentrant tachycardia (AVNRT)
10% of the general population
Accounts for 2/3 of PSVT cases
AV reciprocating tachycardia (AVRT)
Second most common PSVT, ~1/3 of cases
Atrial Tachycardia
~5% of PSVT cases

5. AVNRT: Dual…or Duel?

6. AVNRT: Dual Pathways Pathphysiology: Dual Pathways through AV node
Fast and slow pathways with differing refractory periods
Electrical current can travel through two pathways within the AV node: A fast pathway and a slow pathway. The fast pathway conducts current more quickly and has a longer refractory period. The slow pathway conducts current more slowly and has a shorter refractory period. During sinus rhythm electrical impulses travel down both pathways simultaneously and the impulses cancel each other out. However, an PAC shortly after can travel down the slow pathway alone, while the fast pathway is still refractory. By the time the impulse reaches the end of slow pathway the fast pathway is no longer refractory and the current travels retrograde through the fast pathway and can create a circuit.

7. AVNRT: Dual Pathways
Typical AVNRT: Down the slow pathway and up the fast pathway
Atypical AVNRT: Down the fast pathway and up the slow pathway
There are two major types of AVNRT: In typical AVNRT the impulse travels anterograde through the slow pathway and retrograde through the fast pathway.
In atypical AVNRT the current travels anterograde through the fast pathway and retrograde through the slow pathway.

8. AVNRT: EKG Characteristics
Rate: 110 – 200
Typical AVNRT:
Short RP interval
P waves are hidden or obscured can result in:
Pseudo r’ wave in V1
Psuedo S wave in II, III, or aVF
Atypical AVNRT:
QRS-P-T complexes
P-waves may be more easily visible between QRS and T wave
RP interval is longer
ST depressions are often present
In Typical AVNRT: The short RP interval is the result of retrograde conducted p-waves coming from the AV node. Pseudo r waves and Pseudo S waves correspond to the retrograde p waves.
In Atypical AVNRT: Because the retrograde conduction is through the slow pathway there the RP interval is longer and p waves might be visible after QRS complex.

9. Typical AVNRT

10. Atypical AVNRT
Easier to see the p waves between QRS complex and t wave

11. AVNRT Management Benign rhythm: Treat to alleviate symptoms
Acute management
Vagal Maneuvers
Adenosine (nearly 100% effective at terminating AVNRT)
DC cardioversion if unstable
CCB and Beta blockers
Long term management
Catheter Ablation: If symptomatic
Medical therapy with BB, CCB, or antiarrhythmics

12. AVRT: Accessory Pathway
Accessory Pathway: Extranodal tract for electrical conduction
In WPW: Bundle of Kent
Pre-excitation: early activation of ventricles via AP (e.g. WPW)
AVRT: Re-entrant circuit
involving AP

13. AVRT: Orthodromic & Antidromic
Orthodromic: Retrograde conduction through accessory pathway
Antidromic: Retrograde conduction via the AV node
Orthodromic
Antidromic

14. Pre-excitation EKG Anterograde conduction via AP in sinus: Delta wave
Shorter PR interval (<120 ms)

15. Orthodromic AVRT EKG Rate 200 – 300 bpm
P- waves are retrograde and often buried
QRS is narrow
T wave inversion and ST segment depressions
Not necessarily indicative of ischemia
This is very often not distinguishable from AVNRT

16. Antidromic AVRT: EKG 200 – 300 bpm Wide QRS complex
Difficult to distinguish from VT

17. Acute Management of AVRT
Orthodromic:
Vagal maneuvers
Adenosine
CCB
If unstable then DC cardioversion
Antidromic
If uncertainty if VT or AVRT manage as VT
1st choice drug is: procainamide

18. Long Term Management of AVRT
Asymptomatic Pre-excitation
AHA/ACC/HRS Guidelines:
Observation or Electrophysiology Study & Ablation
Symptomatic
Electrophysiology Study & Catheter ablation
Oral beta blockers, diltiazem, and verapamil

19. MKSAP Question
A 31 year old man is evaluated for follow-up 2 days after emergency department visit for palpitations. He reports intermittent palpitations and occasional episodes of shortness of breath. These episodes have increased in frequency and are often accompanied by light headedness. He experienced loss of consciousness on one occasion. He does not have chest discomfort or jaw pain. His medical history is unremarkable except for a previous ED visit several years ago for palpitations. He has no significant family history.

20. MKSAP Question Continued
On physical examination, the patient is afebrile, blood pressure is 105/68 mm Hg, pulse rate is 67/min, and respiration rate is 12/min. BMI is 24. His neck veins are flat, and the point of maximal impulse is in the midclavicular line without heave or lift. He has no lower extremity edema.
Serum TSH is normal
TTE: no structural abnormalities
EKG…

21. MKSAP Cont.

22. MKSAP:Q & A
Which of the following is the most appropriate next step in management?
A) Antiarrhythmic drug therapy
B) Diltiazem
C) Electrophysiology study
D) Metoprolol

23. MKSAP:Q & A
Which of the following is the most appropriate next step in management?
A) Antiarrhythmic drug therapy
B) Diltiazem
C) Electrophysiology study
D) Metoprolol

24. MKSAP Answer Pre-excitation on EKG Symptoms suggesting WPW
Caused either by Orthodromic or Antidromic SVT or Afib with pre-excitation
Electrophysiology study can diagnose rhythm and ablation can be curative

25. Summary Three types of SVT: AVNRT: AVRT:
AVNRT, AVRT, and Atrial Tachycardia
AVNRT:
Fast and slow pathways in competition
Narrow complex tachycardia with buried p-waves
Treat with vagal maneuvers, and nodal blocking agents
AVRT:
Accessory pathway
Orthodromic: Narrow complex tachycardia
Antidromic: Wide complex tachycardia
When in doubt manage Antidromic like VT

26. Kent: The Duke, not the Bundle