Andrew D. Krahn, MD, FHRS

The enrollment of the existing studies on the people we intuitively thought were most likely to benefit from the device. It is a younger population, patients with preserved heart function, etc. Transvenous systems have struggled with lead reliability, the major limitation of their design and technology.

The UNTOUCHED trial instead looked at the general primary and secondary prevention population. The researchers conducted a large trial showing the outcomes of a large series of patients who had subcutaneous ICDs who historically would predominantly or entirely have gotten the transvenous system.

There isn’t a control arm, and that is a limitation of the study. In a perfect world, it would be comparative, but the investigators are able to look at concurrent patients and evidence that supports what expected complications, shock rates and outcomes would be in patients with transvenous devices. They show that in that population, in general, the shock burden was quite acceptable, the complication rates for implants were very acceptable and the platform appears to perform comparably to the typical primary prevention advanced heart disease population, which has not been the focus of the randomized trials.

One of our policies locally is that ICDs and cardiac resynchronization therapy devices all go through a local consensus process and triage for approval for implantation. This has to do with the complexity and cost of the platform and to ensure that we are abiding by guideline-directed best therapies. That conversation has typically shied away from using subcutaneous ICDs such as in this UNTOUCHED population for a number of reasons, part of which was the lack of comparative evidence. One issue was the lack of systematic evidence and another is in our environment, there’s a cost differential. This now is informative to suggest that there is support for the idea that the outcomes are equivalent and very acceptable in this population. We should be considering this in patients, especially when there are elements of their characteristics that may be better suited to a subcutaneous as opposed to a transvenous system.

We need longer-term follow-up to look at the outcomes of the subcutaneous ICD because the scope and duration of the data is still much more limited than we have for the data from the index trials that proved the efficacy of the transvenous systems. That is one side of it.

The second side of it is there are many important details around how the evidence plays out. A good example is there are some conditions where antitachycardia pacing is more likely to be a useful intervention to reduce shocks and treat arrhythmias than others. In those populations, we don’t have sufficient evidence beyond an early description that the subcutaneous device performs well, comparably or arguably superior in some sectors.

There is still a lot of room for more comparative evidence in this area. There is a question about whether there is support to do all of that because physicians will take the existing data and use those as grounds to expand their subcutaneous ICD practice into areas where there are incomplete data. It would be very helpful to commit to more comparative evidence in this area to try to support the best platform for patient subgroups.

I know Dr. Gold (past president of the Heart Rhythm Society) and Lucas V. Boersma, MD, PhD, FESC, are very highly respected experts in this field who are to be commended for compiling a very good, robust dataset. I look forward to the due diligence around peer review as well as the inevitable substudies that will come out of these data.