Dr. Sundeep Mishra reviews the PRAETORIAN trial that compared sub-cutaneous ICD with transvenous ICD and how the former offers several advantages in current practice.

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Implantable cardioverter defibrillator (ICD) provides protection for a broad range of patients at risk for sudden cardiac death. However, conventional transvenous ICD (TV-ICD) is an invasive procedure associated with certain risks and complications. The new ICD system is designed to be implanted intra-muscularly outside the sternum, never touching the heart, using only anatomical landmarks. This may reduce the need for fluoroscopy during implant ensuring a simple, predictable and consistent implant procedure.

PRAETORIAN Trial

It was a non-inferiority trial in which patients with an indication for an ICD but no indication for pacing were assigned to receive a subcutaneous ICD or transvenous ICD. This trial which randomised 849 patients (426 in the subcutaneous ICD group and 423 in the transvenous ICD group) and followed them up for a median 49.1 months, revealed that subcutaneous ICD (SC-ICD) was non-inferior to the transvenous ICD with respect to device-related complications or inappropriate shocks in patients with an indication for defibrillator therapy but with no indication for pacing.

The results were consistent in several sensitivity analyses and subgroup analyses.

1. There were equal numbers of arrhythmic deaths in the two groups (although deaths from other causes were higher in the SC-ICD group; cancer and gastro-intestinal causes).
2. Fewer (~ 4 times lesser) lead-related complications (including infection [twice as many}, perforation, lead dislodgement, and lead dysfunction) and subsequent surgical re-interventions occurred in the SC-ICD group than in the TV- ICD group, but this effect was counterbalanced by more frequent pocket haematomas with the subcutaneous ICD.

While device-related complications are associated primarily with physical distress, ICD shocks can have profound psychological implications. The use of general anaesthesia and defibrillation testing was much greater with the SC-ICD than with the TV- ICD. However, an important issue in the ICD area is long-term outcomes.

While battery longevity is a limiting factor for the SC-ICD, device extraction is not only more frequent but is a bigger challenge for TV- ICDs. Data in >91,000 transvenous lead extractions found that those extracted for infection had a higher overall complication rate and a higher in-hospital mortality rate. Moreover, it also increased the cost of therapy.

Current practice

Theoretically, subcutaneous ICD has several advantages:

• Offers a less invasive alternative that’s predictable, safer, and simpler
• Works for patients of all ages
• Minimises serious complications
• Is more flexible and easier to extract

Optimised implant techniques (such as the intermuscular technique) and implant best practices have contributed to >79,000 SC-ICDs implantations worldwide.

The future

Advances in SC-ICD have lead to 68% reduction in the rate of in-appropriate shocks. Certainly, a sensing filter that attenuates oversensing can by itself result in a 50% reduction of first inappropriate shocks. In a more recent UNTOUCHED study, the 1-year IAS rate was 3.1%,which is comparable to or even lower than the rates observed with TV-ICDs in other studies, including the PRAETORIAN trial. In EMBLEM MRI study, the 1-year IAS rate was even lower (2.4%). Thus it seems that SC-ICD is likely to become standard-of-care in majority of patients requiring defibrillation.

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Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author, Dr. Sundeep Mishra is a Professor of Cardiology.