STEPUP Cardiovascular System: Tachyarrhythmias - Paroxysmal Supraventricular Tachycardia

Question 1

What is paroxysmal supraventricular tachycardia (PSVT) most often due to?

Answer 1

Reentry

Question 2

What is AV nodal reentrant tachycardia? How commonly does this cause supraventricular tachycardia (SVT)? How is it initiated or terminated?

Answer 2

1) Two pathways (one fast and the other slow) within the AV node, so the reentrant circuit is within the AV node
2) Most common cause of supraventricular tachyarrhythmia (SVT)
3) Initiated or terminated by PACs

Question 3

What does an ECG for AV nodal reentrant tachycardia show?

Answer 3

1) Narrow QRS complexes with no discernible P waves (P waves are buried within the QRS complex)
2) This is because the circuit is short and conduction is rapid, so impulses exit to activate atria and ventricles simultaneously

Question 4

What is orthodromic AV reentrant tachycardia? What is another name for it and what does it commonly cause? What can initiate or terminate orthodromic AV reentrant tachycardia?

Answer 4

1) An accessory pathway between the atria and ventricles that conducts retrogradely
2) Called a “concealed bypass tract,” and is a common cause of SVTs
3) Initiated or terminated by PACs or PVCs

Question 5

Describe the ECG for orthodromic AV reentrant tachycardia. Why does it look this way?

Answer 5

1) Narrow QRS complexes with P waves which may or may not be discernible, depending on the rate
2) This is because the accessory pathway is at some distance from the AV node (reentrant circuit is longer), and there is a difference in the timing of activation of the atria and ventricles

Question 6

What are causes of paroxysmal supraventricular tachycardia?

Answer 6

1) Ischemic heart disease
2) Digoxin toxicity - paroxysmal atrial tachycardia with 2:1 block is the most common arrhythmia associated with digoxin toxicity
3) AV node reentry
4) Atrial flutter with rapid ventricular response
5) AV reciprocating tachycardia (accessory pathway)
6) Excessive caffeine or alcohol consumption

Question 7

What are the three components of treatment for PSVT?

Answer 7

1) Maneuvers that stimulate the vagus nerve
2) Acute treatment
3) Prevention

Question 8

What are maneuvers that stimulate the vagus delay AV conduction and thus block the reentry mechanism for PSVT?

Answer 8

1) The Valsalva maneuver
2) Carotid sinus massage
3) Breath holding
4) Head immersion in cold water (or placing an ice bag to the face)

Question 9

What pharmacologic therapy is used in the acute treatment of PSVT?

Answer 9

1) IV adenosine - agent of choice due to short duration of action and effectiveness in terminating SVTs; works by decreasing sinoatrial and AV nodal activity
2) IV verapamil (calcium channel blocker) and IV esmolol (beta-blocker) or digoxin are alternatives in patients with preserved left ventricular function
3) DC cardioversion if drugs are not effective or if unstable; almost always successful

Question 10

What treatment is used in the prevention of PSVT?

Answer 10

1) Pharmacologic therapy: Verapamil or beta-blockers
2) Radiofrequency catheter ablation of either the AV node or the accessory tract (depending on which is the accessory pathway) is preferred if episodes are recurrent and symptomatic