“Hey John, I hear there is a new ICD out…without any wires,” came the question in the doctor’s lounge.
That’s cool, they are reading the NEJM, I thought.
It is true that a very preliminary report on a subcutaneous-only ICD was published in the print version of the NEJM this week. The print version of anything these days is so yesterday, and those that get there medical news online, or on twitter, or the blogosphere knew about this device much earlier. In fact, my colleague Dr Wes first reported on this device in 2006. (way before I knew what a blog was) And a nice summary, including an interview with one of the lead authors is here.
This newly reported on ICD is not completely wireless, rather there are no wires inside the blood vessels or heart. The shocking coil sits underneath the skin parallel to the sternum, and is tunneled inferior to the breast, to the pulse generator along the lateral ribcage.
Here is a picture from the NEJM report.
Being devoid of any intravascular wires is at the same time both the major advantage and disadvantage of the device.
Advantages of not having wires in the heart or blood vessels:
- No risk of damage to the heart or blood vessels during the implant, like perforation.
- No risk of damage to the heart valves, anytime.
- No risk of occluded veins.
- Minimal risk of blood-born bacterial infections. (Big)
- Never needing extraction of chronic indwelling leads, which can be a high-risk procedure.
- Preservation of vascular access for future needs, like IV ports for chemotherapy, or shunts for dialysis.
Disadvantages of not having wires in the heart:
- Sensing an arrhythmia is more challenging, although in the report there were no inappropriate shocks in the carefully followed 78 patients.
- Patient’s with arrhythmias often require pacing. All present-day ICDs have back-up pacing delivered through wires in the heart. This device has no real pacing capabilities. If the heart slows, or stops, you are out of luck.
- Not all sudden death causing arrhythmias require shocks. Painless anti-tachycardia pacing–which comes standard in current ICDs–very often terminates these dangerous tachycardias without shocks. This device is shock only.
- Discomfort from a bulky pulse generator along the lateral aspect of the rib cage was not mentioned in the 78 patient report. As a colleague pointed out to me today, most Americans in whom an ICD is deemed beneficial have ample subcutaneous fat.
Is this not-even-close-to-FDA-approved device better or worse than a standard ICD. Interestingly, that it has less, is touted as its advantage. The authors of the report say it best…
Our studies are preliminary, early-phase trials that were primarily intended to show the feasibility of an entirely subcutaneous ICD. They provide limited information regarding the detection and conversion of ventricular tachyarrhythmia in the clinical setting, despite the demonstration of consistent detection and termination of ventricular fibrillation at the time of implantation. These studies cannot show whether subcutaneous ICDs are superior to conventional transvenous ICDs with respect to such characteristics as lead stability or failure.
We will see.
As has been the case in my previous 15 years of electrophysiology, devices like these will require doctors to be life-long learners, and herein lies one of doctoring’s greatest joys.