Cardio - Supraventricular Tachycardias Treatment

Question 1

What signs are an indicative of unstable pt/peri arrest and that DC cardioversion needs to be given?

Answer 1

• Shock: hypotension (systolic BP <90 mmHg), pallor, sweating
• Cold, clammy extremities, confusion or impaired consciousness
• Syncope
• Myocardial ischaemia
• heart failure
• Provide synchronised DC shocks to these patients

Question 2

What do you do for regular broad complex tachycardia?

Answer 2

Regular

• Assume ventricular tachycardia unless you have previously confirmed SVT with bundle branch block (ie the current is taking aberrant pathway)
• Give loading dose of amiodarone followed by 24h amiodarone infusion

Question 3

What do you do for irregular broad complex tachycardia?

What are the causes of iregular broad complex tachy?

Answer 3

1. AF with bundle branch block: treat as narrow complex tachy (next flashcards)
2. Polymorphic VT: torsade de pointes - rx with IV magnesium and call for help

Question 4

What are the causes of regular narrow complex tachycardia? What is the treatment pathway?

Answer 4

-atrial tachy, orthodromic AVRT, atrial flutter, AVNRT (assume not BBB)

• Vagal manoeuvres: carotid sinus massage, Valhalla manoeuvre
• IV adenosine: 6mg bolus —> 12 mg bolus —> 12 mg bolus (C/I in asthmatic patients -verapamil is better for them)
• Electrical cardioversion

Question 5

What are preventative measures for episodes of regular narrow complex tachycardia?

Answer 5

• Beta blockers

- radio-frequency ablation

Question 6

What are the causes of irregular narrow complex tachy and what is the Mx?

Answer 6

• Most likely AF
• If onset is <48h, consider cardioversion with flecainide —> amiodarone —> DC cardioversion
• If onset >48 hours have to anticoagulate for >=3wks (heparin cover with warfarin), but them on rate-controlling Beta Blocker (bishop roll/atenolol or Dixogin if not mobile) and then bring them in for scheduled DC cardioversion

Question 7

Supraventricular tachy: what is the difference between an AVRT and a AVNRT? How does this affect treatment?

Answer 7

• AVRT: have an accessory pathway that is somewhere in the fibrous atrio-ventricular fibrous valvular ring
• AVNRT: have 2 pathways (1 slow and 1 fast) that are both within the R atrium, either in or right next to the AV node
• This means they have to be treated differently b/c if you give a AVN blocker in AVRT, the circuit will take the aberrant pathway and not have the slowing influence of AV node - thus taking the A-V conduction ratio to 1:1 and can result in Vfib.

Question 8

What is the Rx for AVRT?

Answer 8

• Procainamide (class 1a Na+ blocker - slows down velocity and increases refractory period - slowing maximal rate of depolarisation) —> cardioversion
• amiodarone used to be used but can cause v fib so no longer routinely used.

Question 9

What drugs should you avoid when trying to treat AVRT and you suspect it is WPW (which could turn into AF)? What is the definitive treatment for these supra ventricular tachycardias?

Answer 9

• Avoid AVN blockers: adenosine, diltiazem, verapamil (other CCBs), Beta blockers b/c can force current via aberrant pathway
• Ablation of abnormal pathway

Question 10

What is the Rx for AVNRT?

Answer 10

• Aim to slow down conduction at AVN
• Vagal manoeuvre
• Meds: adenosine, beta blockers, non dihydropyrine CCBs (verapamil/Diltiazem), flecainide, amiodarone
• Cardioverion
• Catheter ablation: definitive Rx

Question 11

What is the use and MOA of adenosine?

Answer 11

• Purine nucleoside used for re entrant arrhythmias that require AVN for re-entry.
• Will work for AVRT (but not Pre-excitatory AF/WPW) and AVNRT
• Will not work for AF/Aflutter or Ventricular tachy because these don’t require AVN for re-entry