SVT

Question 1

Supraventricular tachycardia includes a fib and macro reentrant atrial arrhythmias such as a flutter.

Name the 3 most common SVTs.

Answer 1

• AV node reentrant tachycardia (AVNRT)
• AV reentrant tachycardia (AVRT)
• Atrial tachycardia

Question 2

What is the most common presentation of patients with AVNRT or AVRT?

Answer 2

Palpitations and ECG showing narrow QRS complex tachycardia.

Usually palpitations are sudden onset and offset with no clear precipitating factor. Abrupt onset is often startling with regular thudding in the chest, neck or head.

LH, anginal-type chest pressure or uneasy neck sensation is seen in some.

Syncope is rare but can occur in elderly.

Patients often describe an urge to micturate soon after termination of the arrhythmia.

Question 3

What is the most common presentation of automatic AT?

Answer 3

Gradual onset palpitations and get more rapid over time (warm-up); offset may also be gradual.

Patients with AT may find that a maneuver or position provokes the syndrome.

Question 4

In contrast to patients with Afib or Aflutter, patients with AT, AVNRT, AVRT can often do what?

Answer 4

Tap out a very regular rhythm of their palpitations.

Question 5

What is one physical exam feature that may be helpful during episodes of AVNRT, AT and AVRT?

Answer 5

Regular cannon a waves with AVNRT and AVRT; may be irregular with AT (particularly with variable AV conduction)

Question 6

In regular narrow QRS tachycardia, assuming P waves can be visualized what are the 2 classic rhythms with short RP?

Answer 6

• AVNRT

- Orthodromic AVRT

Question 7

In regular narrow QRS tachycardia, assuming P waves can be visualized what rhythm is likely with a long RP?

Answer 7

-Atrial tachycardia

Question 8

In narrow complex regular QRS tachycardia, if the P wave is seen within or immediately after the QRS complex what is the most likely rhythm?

Answer 8

AVNRT

The VERY short RP interval is only possible with near simultaneous activation of atrium and ventricle which can happen with AV node conduction.

Question 9

In narrow complex regular QRS tachycardia, if it is short RP tachycardia BUT the P wave is seen 110 mS after the QRS what is the most likely rhythm?

Answer 9

Orthodromic AVRT

In orthodromic AVRT, a finite interval has to elapse between activation of the ventricle by way of the AV node and travel of the electrical wave front through the ventricle and back to the atrium through the accessor pathway – the interval is almost never less than 100 mS.

Question 10

What is a pseudo-R’?

Answer 10

In AVNRT with a very short RP interval, the P wave may give rise to a deflection at the end of the QRS complex which causes the complex to look like an incomplete RBBB in lead V1.

Question 11

Describe a common cause for incessant tachycardia-related cardiomyopathy through an orthodromic AVRT mechanism.

Answer 11

Very specific variant of slowly conducting retrograde pathway that usually occurs in the posterior surface of the heart. A permanent form of junctional reciprocating tachycardia is incessant because the long retrograde conduction times allow for enough recover of the atrial and ante grade AV nodal conduction to allow tachycardia to be initiated and sustained.

Question 12

Describe a mechanism that allows AT to present as a short RP tachycardia.

Answer 12

This occurs when antegrade AV nodal conduction is very slow (diseased or medication induced). Thus, depending on the cycle length of the tachycardia because of the long PR interval, the RP interval may be shorter than the PR interval.

Question 13

Which cause of SVT (almost) never terminates with a P wave?

Answer 13

AT

Question 14

What 2 SVT circumstances may present with a wide QRS complex?

Answer 14

• When a bundle branch block is present during tachycardia
• Due to antegrade conduction by way of an accessory bypass tract (antegrade preexcitation) which also occurs in 2 situations:
• -Opposite of orthodromic AVRT, called antidromic tachycardia. When the ante grade conduction is through an accessory pathway and retrograde conduction is through the AV conduction system. QRS vector is from base to apex because most accessory pathways insert into the base of the heart (typically causes positive QRS complexes in anterior chest leads).
• -When conduction occurs simultaneously through AV node and the accessory pathway

Question 15

Describe the path of the “fast” pathway of the sinus impulse.

Answer 15

Primarily travels superior to the fossa ovals and posterior to the eustachian ridge reaching the AV node.

Because of the 2 distinct pathways to the AV node a reentrant tachycardia becomes possible.

Question 16

Descrive the path of the “slow” pathway of the sinus impulse.

Answer 16

Anterior to the eustachian ridge from the region of the coronary sinus, probably utilizing the musculature of the coronary sinus to reach the AV node.

Because of the 2 distinct pathways to the AV node a reentrant tachycardia becomes possible.

Question 17

Describe conservative mgmt for AVNRT.

Answer 17

No therapy for infrequent palpitations. Patients taught to use valsalva-like maneuvers; if effective no further therapy required.

Question 18

Describe mgmt for AVNRT in patients with more frequent episodes (especially with recurrent episodes).

Answer 18

AV nodal blocking agents (B blockers, CCBs or sometimes digoxin alone). In the ER, if carotid massage not effective (or inadvisable) adenosine will invariably terminate AVNRT; if it doesn’t terminate check the IV or consider alternate diagnosis.

**RFA is 95% effective; 2% chance of serious complication; 2% chance of repeated ablation.