This engineer no longer has a bulbous monitoring device attached to his chest. He’s transitioned to a svelte successor, in the same location but this time placed subcutaneously.
Thanks to all of you who wrote in expressing concern and well wishes subsequent to the publication of my previous two posts in this series, focusing on my recent cardiac issues. I’m happy to report that I successfully made it through the 30-day regimen with a function-tailored smartphone in my pocket and a monitor stuck to my chest 
. I’m also happy to report that my cardiologist’s analysis of the collected data revealed no serious ongoing concerns. That said, I’m not yet completely “off the hook”, therefore the topic of today’s follow-up writeup.
What the 30-day results did reveal were a few brief episodes of tachycardia, i.e., elevated heart rate and intensity sequences, albeit with a still-regular cadence:
As my cardiologist explained (and I now paraphrase), my heart seemed to be trying to go back into irregular rhythm but (thankfully) didn’t succeed. As such, he was of the opinion that I still should proactively have a cardiac ablation, but I’ve declined that option, at least for now.
During my mid-November episode, while the bulk of my arrythmia rhythm was classified as atrial flutter, which has a near-100% success rate even after only a single ablation procedure:
my heart also occasionally transitioned into atrial fibrillation (AFib), whose single-procedure success rate is lower, due in part to the larger number of impulse sites that typically need to be severed (subsequent repeat procedures bolster the chances of a successful eventual outcome):
Instead, what I proposed (and he eventually agreed to) was a more conservative approach, at least initially. I’d remain on rhythm-stabilizing beta blockers. And he’d embed a miniature leadless cardiac monitor, with three-year operating life, subcutaneously in my chest to enable ongoing logging of any further heart rate abnormalities. He’d then automatically receive a report from the service provider each month. If there was no further detected AFib or atrial flutter after the monitor’s integrated battery eventually died, I could declare an “all clear”, with the now-inert monitor potentially remaining in me for the rest of my life. And if any recurrence of irregular arrythmia did occur, we could revisit the potential ablation scenario.
Tiny but mighty
The system I’m now artificially augmented with—just call me Steve Austin—is from Medtronic. Specifically, it’s the first-generation Reveal LINQ, which has been in widespread use for more than a decade at this point. At its nexus is the model LNQ11 ICM (insertable cardiac monitor), now in residence in my chest, which required only a local anesthetic (lidocaine) and sub-1 cm incision for installation, along with a couple of internal dissolvable stitches and some glue to temporarily hold the incision flaps together for the first two weeks while it healed.
The ICM has dimensions of approx. 44.8 x 7.2 x 4 mm, translating to (at ~1.3 cubic cm) roughly 1/3 the volume of a AAA battery, and weighs around 2.5 grams. Here are some stock shots:
Wireless diversity
The ICM communicates with a standalone AC-powered patient monitor which receives transmissions from the ICM and passes them along to a “cloud” server over a cellular data link:
Here are the meaningful perspectives of the outer packaging I received post-ICM installation:
Opening up the box, there was (obviously) no longer an ICM inside; it had already been relocated to my skin’s underside, at the left pectoral region of my chest, to be precise:
The patient monitor is variously described as needing to be no further than either 2 or 3 meters away (depending on the literature piece being referenced) from the ICM-toting patient in order to ensure reliable data transfers:
The system manual (PDF) accessible (along with other useful info) via the patient portal provides detailed information on the divers spectrum swaths used for various ICM-to-patient monitor and patient monitor-to-cloud functions, along with their associated modulation schemes. The companion ICM manual (PDF) translates these technical specifications into “for the masses” cautions and broader recommendations for cardiac monitor operation in EMI-rich environments (motors, arc welders, radio transmitters, etc.) along with the information you should share beforehand with MRI scanner operators as well as airport and other security personnel (I carry a Medtronic-supplied info card in my wallet for situations such as these).
Speaking of spectrum swaths, the FCC certification ID for the ICM is LF5MEDSIMPLANT1; I encourage you to check out the FCC site for more interesting information on the device, including a set of teardown images. Even more interesting info can be accessed by punching other FCC IDs, found on product labels both above and below this point in the writeup, into the independently developed and maintained FCC certification website search engine. And further to the spectrum swath topic, I’ll note that Medtronic has subsequently introduced the LINQ II ICM, similar in size (45.1 x 8 x 4.2 mm) and per my online research making several notable enhancements to the first-gen implementation:
- Like the 30-day cardiac monitor I described in my previous writeup, it communicates with the data receiver device over Bluetooth low energy (BLE), not the proprietary protocols leveraged with the first-generation ICM. As such, again as with the 30-day monitor I previously used, it can connect to a conventional smartphone versus requiring my dedicated bedside patient monitor device.
- Its BLE and smartphone intermediary foundations also enable it to be remotely reprogrammed by the cardiologist for settings fine-tuning purposes, versus necessitating an office visit for the patient.
- Estimated battery life is now 4.5 years.
- And the LINQ II is FDA-cleared for pediatric use with patients 2 years and older.
Selective storage and transmission
My previous cardiac monitoring device was bulky and required recharge every five days or so. How on earth, then, does this comparatively tiny ICM run for 3 years on a much smaller and non-rechargeable cell? Selectivity is one key differentiator; while the prior cardiac monitor was constantly logging heartbeat information, the ICM (automatically, at least; keep reading) only captures a data sequence when it senses there’s a potential arrhythmia event occurring, and cloud-based AI algorithms further weed out “false positives” before passing the information on to the cardiologist.
The ICM only houses enough onboard storage for 27 minutes’ worth of this auto-logged information. It’s what’s known as a “loop recorder”, overwriting old data with new, operating under the assumption that the old data has already been transferred to the patient monitor. Yes, this means that, as with my CPAP machine, I also need to travel with the patient monitor and its AC power adapter.
What happens if I’m symptomatic, suggestive of an in-process cardiac event; palpitations, dizziness, light-headedness, etc.? The answer to that question depends on whether my patient monitor is nearby. You may have already noticed in the earlier set of photos that the patient monitor appears to consist of two pieces, with the smaller portion sitting atop the larger base unit. Kudos on your insight: you’re right:
If the patient monitor is nearby when you find yourself in distress, you can detach the “reader” portion (which, perhaps obviously, contains an embedded rechargeable battery), place it on your chest directly above the implant area, and transfer the captured and “flagged” data for analysis by the cardiologist (who can also proactively reach out to you for an ad-hoc transmission of this same way, by the way, if he or she sees something awry in the auto-captured monthly report data).
And if you’re away from your patient monitor? That’s where the pocketable “patient assistant”, accompanied in the following photos by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes, comes into the picture:
Place it on your chest atop the ICM, punch the “record” button, LED light-confirm that the two devices are communicating and, later, that a successful sample has been captured, and the next time you’re nearby the patient monitor it’ll be priority-tagged and transmitted. The ICM contains additional storage sufficient for 30 minutes total (variously segmented) of patient-activated recordings, beyond the earlier-mentioned 27 minutes of auto-logged data.
I’ll pass along any other notable aspects of my “bionic augmentation” experience via this blog if/as I encounter them in the coming months (and years). For now, I welcome your thoughts in the comments on what I’ve shared so far!
—Brian Dipert is the associate editor, as well as a contributing editor, at EDN.
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