How soon following pacemaker implantation can patients safely undergo elective cardioversion?

That is a good question. From a technical standpoint, a cardioversion can be done at any time after a pacemaker implantation. In the past, we often did defibrillation threshold testing on patients on the EP lab table after implanting an ICD and sometimes they would require a shock externally. This would not lead to issues or compromise of the leads or system. I think if you cardiovert someone, it would be prudent to avoid placing the pads or paddles on top of or in near proximity to the device. Also, the device should be interrogated after to make sure there are no issues or changes.

From a practical standpoint, if the elective cardioversion is being done for atrial fibrillation or flutter, the only issue I would foresee is that there is a need for uninterrupted anticoagulation. So I think the earliest one can do elective cardioversion is once the patient is back on anticoagulation and there are no issues or need for cessation. In this case, I would obtain a TEE as well due to the interruption of anticoagulation. I think that approach may vary depending on the patient and the implanting physician. In my practice, I implant devices on uninterrupted warfarin, so that would not affect timing. With respect to DOACs, I often hold for one night and often resume the following day. So I think if a patient is back on their DOAC for at least one day with no pocket issues, the patient can undergo elective cardioversion. If cardioversion is more urgent, I would just perform the pacemaker on uninterrupted DOAC.

In general and prior to 1 year ago, I would 100% agree with Dr. @Dr. First Last's response. As long as there are no bleeding (uncommon hematoma) or perforation (rare) complications, the likelihood of anticoagulation interruption should remain low. I tend to use an empiric pressure dressing more often in cases where I'd consider early cardioversion.

The new article that brings up concern is a big data study out of Denmark published in Heart Rhythm Sept 2023 (online in Mar 2023) by Elgaard et al - Long-term risk of cardiovascular implantable electronic device reinterventions following external cardioversion of atrial fibrillation and flutter: A nationwide cohort study. The review by Yoneda and Crossley is also a reasonable read that tempers the timing and biological plausibility.

Elgaard et al., PMID 36965653

Yoneda & Crossley, PMID 37169159

Essentially, in almost 2600 patients with CIED (half pacemakers, half ICDs) compared to almost 13K matched controls, in 2-year follow-up more external cardioversion systems had generator changes (8.1 vs 5.3%, ARR ~3%, NNH ~30) and lead reinterventions 5.6 vs 2.3% (also ARR ~3%, NNH ~30) with HR >1.5 and 2-3 respectively (depending on adjustments, timing of 1 or 2 years). In the results section of Reasons for reinterventions:

For lead reintervention, the indication “lead displacement” was more frequent in the first months after ECV: n = 21 (21/110 [19%]) for ECV-exposed after 6 months of follow-up and n = 24 (24/247 [9%]) after 2 years of follow-up. In one-seventh (n = 35) of the lead reinterventions, the reason was categorized as “other”, without additional entries.

The 19% figure in the first 6 months seems high and we don't know what type of lead (though they report no statistically significant difference on the manufacturer) and the unknown and elective/recall in Table 3 leave a lot to speculation... but it should cause pause for reflection.

Do I think we should wait 6 months after the device implant to DCCV electively? Almost assuredly not. Do I think (with this data) it should be mentioned/disclosed as part of the risks, benefits, and alternatives? Sure - especially if it can mean lead revision, higher risk of infection for early exploration, even higher mortality purported by the authors, etc. >80% of the time, they'll do okay. They also comment on the 7 lead reinterventions in 192 ECV/90 matched patients who underwent ablation if that contributed to dislodgment.

With regard to the older era of defibrillation threshold testing, does a 20-25J intracardiac coil to can DFT compare well to an anterior-posterior 200J or anterior-lateral/ventricular cardioversion? Not sure. Also, there were more right-sided lead interventions (absolute 2% difference) and gen changes (absolute 4% difference) so the difference was less prominent for leads and more prominent for a general change compared to entire cohort (3%) difference. Not sure what to make of it. I feel left with more questions than answers as did the reviewers.

In conclusion:

If urgent, they need their cardioversion and prophylactic pressure dressing if concerned. If truly elective, probably waiting longer until after more endothelialization and calling back to drop outputs at chronic stable threshold in 4-8 weeks may be a balance between POD1 and 6 months. It will be interesting to see follow-up studies and if this signal tempers practice in any way.