Comparison of Subcutaneous and Transvenous ICDs

Study Questions:

How do clinical outcomes and complication rates compare between recipients of the subcutaneous implantable cardioverter-defibrillator (S-ICD) versus conventional transvenous ICD (TV-ICD)?


The authors performed a meta-analysis of studies in PubMed, Embase, and secondary referencing sources. Baseline characteristics and outcome data of both S-ICD and TV-ICD groups were appraised and analyzed. A random-effects model was used to derive odds ratio (OR) with 95% confidence interval (CI).


There were no randomized studies of S-ICD versus TV-ICD, but five case-control and retrospective studies met the inclusion criteria. Baseline characteristics were similar between the S-ICD and TV-ICD groups. Lead complications were less in the S-ICD group compared to the TV-ICD group (OR, 0.13; 95% CI, 0.05-0.38). The infection rate was similar between the S-ICD and TV-ICD group (OR, 0.75; 95% CI, 0.30-1.89). There were no differences in system or device failures between groups (OR, 1.13; 95% CI, 0.43-3.02). Overall, inappropriate therapy (T-wave oversensing, supraventricular tachycardia [SVT], and episodes of inappropriate sensing) was similar between the two groups (OR, 0.87; 95% CI, 0.51-1.49). Both devices appeared to perform equally well with respect to appropriate shocks.


S-ICD reduced lead-related complications, but was similar compared to TV-ICD in nonlead-related complications including inappropriate therapy.


TV-ICD leads have been called the ‘Achilles’ heel’ of the ICD therapy. Mechanical lead failures can result in inappropriate shocks as well as an inability to deliver appropriate therapy. TV leads are vulnerable to fracture in part due to the unceasing motion of the heart over years and decades. It is not surprising then that the lead failure rate is substantially less in S-ICD. It is important to note, however, that the follow-up times in this meta-analysis were <3 years for most studies, which seems not sufficiently long for the evaluation of lead longevity. The prevalence of inappropriate therapy was similar between the S-ICD and TV-ICD, which is reassuring. However, the nature of inappropriate therapy was different. Inappropriate therapies in the TV-ICD group were primarily due to SVT, whereas inappropriate shocks in S-ICD were mostly episodes of oversensing (sensing of noise, T-wave oversensing, etc.). Of note, the first randomized controlled trial comparing the outcomes of S-ICD versus TV-ICD (PRAETORIAN) is ongoing. It is scheduled to finish enrollment in 2019.

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