Cardioversion of AT

Recently responded to a 76 y/o F c/o dizziness and rapid HR.  Pt hx A-fib w/ablasion procedure x 4 mos.  w/sucessful termination of A-fib.  Pt. status upon arrival:  seated at desk, AAOx3, - dysp (O2 NC admin.), - chest pain/discomfort, + radial rapid approx. 210 BPM, CRT<2, pt. c/o severe dizziness, BBS = clear bilat, patient transferred to floor, EKG showing narrow complex tach.  Irreg/irreg.  Initial interpretation poss uncontrolled A-fib or AT.  O2 NRB intiated as pt stated she "felt strange," but denied CP.  INT initiated and pt. coached through vagal manuver w/transient termination of rhythm. Pt. returned to tach. and 6 mg Adenosine administered w/transient interruption of tachycardia.  On scene awaiting ambulance for transport, we were considering sedation and external sync cardioversion.  Pt. BP, LOC and SpO2 remained WNL throughout episode.  I considered the cardioversion due to no other pharmacological appropriate interventions on the scene (no calcium channel blockers, et al, though we could have tried the additional 12, 12 of Adenosine).  We had some debate about this after the call.  The patient came in two weeks later and thanked us for our care.  She stated that her cardiologist had treated her in the ED and that the rhythm was not a recurrent A-fib, but an AT, and she was eventually cardioverted in the ED to terminate the rhythm.  Since then, there has been no return of the tachy rhythm.

My questions:

1.  The ends seem to justify my means, but was I premature with wanting to cardiovert (I know the concerns about thromboembolism, but I was going to contact medical control prior to the electrical intervention)?

2.  How long is it prudent to pursue pharmocological therapies as opposed to electrical therapy to terminate the rhythm?  Do you wait until the patient begins to decline or chest pain/altered LOC?  What is the risk for myocardial ischemia?

3. As a matter of statistics, do the additional doses of adenosine generally work?

[Michael J. McWilliams, M.D.]

1.  The ends seem to justify my means, but was I premature with wanting to cardiovert (I know the concerns about thromboembolism, but I was going to contact medical control prior to the electrical intervention)?

I would avoid cardioversion unless you have to for the reasons you state.  Strokes are relatively rare, but you don't want someone second guessing your decision in  retro spect.  It is always easy to criticize the care given if you aren't the one there on the spot.

2.  How long is it prudent to pursue pharmocological therapies as opposed to electrical therapy to terminate the rhythm?  Do you wait until the patient begins to decline or chest pain/altered LOC?  What is the risk for myocardial ischemia?

If they aren't having chest pains you are probably ok from an ichemia stand point.  

Reasons to cardiovert immediately include:
1. active chest pain from arrhythmia
2. loss of conciousness or unstable vital signs
3. others depending on the circumstances

Adenosine is a pretty safe medication but you have to stay with in limits of  your established protocols to protect yourself.  Adenosine can give you problems if the patient is on dipyridamole or they are a heart transplant recipient because they are super sensitive to the medication.

I will try 6 mg first, 12 mg second and 18 mg third.  If it is low right atrial tachycardia, it might break with adenosine, otherwise it is typically the AVNRTs and AVRTs that break with adenosine.

If the arrhythmia is less than 48 hours old, the risk of stroke from cardioversion is very low and it is generally accepted that they are safe for cardioversion.  From a risk perspective, you don't want to be the one giving the shock unless you have to.

3. As a matter of statistics, do the additional doses of adenosine generally work?

If it is AVNRT or AVRT, increasing doses will likely work.  If it is an irregular rate as with atrial tachycardia with irregular conduction or atrial fibrillation, additional dosing of adenosine is unlikely to work.

I hope this helps.  Thanks for posting and keep up the good work.  It is always good to question the way you handled something so that the next time you are in the same situation you are more prepared.  I applaud that.