Results:
A total of 372 patients (69.5% male; 48.6 ± 14.4 years old) underwent
S-ICD implantation during the study period. The most common indications
for S-ICD implantation included primary prevention in patients with
heart failure with reduced ejection fraction (39.3%), secondary
prevention of ventricular tachyarrhythmias (31.1%), and primary
prevention in patients with hypertrophic cardiomyopathy with high-risk
features (17.2%). There were 22 (5.9%) patients (81.8% male; 52.1
±13.2 years old) who underwent S-ICD extraction during a median
follow-up period of 4.4 [2.0-6.5] years. The baseline
characteristics of the study population are listed in Table 1. For all
patients, no extraction tools were required to extract the S-ICD,
highlighting that S-ICD extraction, when indicated, is uncomplicated.
The median length of time between implantation and extraction was 39.6
[8.3-64.6] months. The most common indications for S-ICD extraction
were need for bradycardia pacing (frequency among extractions, 18.2%),
infection (22.7%), and inappropriate shocks due to oversensing (22.7%)
(Figure 1). Other common indications for S-ICD extraction included need
for cardiac resynchronization pacing (9.1%), failure to shock (4.6%),
heart transplantation (9.1%), and patient preference (13.6%). No
patients required S-ICD extraction for ATP. Programming changes were
unsuccessful in two of the five patients who presented with
inappropriate shocks due to oversensing. For the other three patients,
oversensing could not be overcome with changes in programming. One
patient had lead coiling and significant retraction of the lead body,
raising concern for Twiddler’s syndrome. For the second patient, the
S-ICD electrode causing excessive noise was under the Boston Scientific
advisory for premature electrode fracture; thus, the device was
extracted. The third patient had already undergone revision of her S-ICD
parasternal lead in years prior, but re-presented with inappropriate
shocks due to oversensing of noise that was reproducible with isometric
exercises in all three vectors. Univariate analysis demonstrated that a
history of smoking (P=0.01), lower left ventricular ejection fraction
(P=<0.001), and history of atrial fibrillation (P=0.02) were
associated with S-ICD extraction (Table 1).
A multivariate analysis was conducted of all factors with P<0.05
on univariate analysis as well as BMI, given its established increased
risk of shock failure in obese patients.16,17 This
analysis revealed that both a history of smoking (p=0.02) and BMI
(p=0.03) were independently associated with S-ICD extraction (Table 2).
Specifically, patients whose devices were extracted smoked, on average,
13.9 pack years more than those patients who did not undergo device
extraction (t (370)=3.99, P=0.0001). Patients whose devices were
extracted had BMIs, on average, 3.91 kg/m2 higher than
those patients who did not undergo device extraction
(t (370)=2.31, P=0.02).
Subgroup analyses by indication for extraction were performed. Only
variables with a priori clinical association with extraction for
a particular indication were assessed to avoid multiple testing. In
comparing those whose devices were extracted for all pacing needs (N=6)
with those whose devices were not extracted, no significant differences
in baseline PR interval (P=0.78) or QRS duration (P=0.39) were found on
univariate analysis. Patients who underwent S-ICD extraction for
inappropriate shocks (N=5) had higher BMIs than patients who did not
undergo extraction (P=0.01). Finally, compared to patients who did not
undergo device extraction, patients whose devices were extracted due to
infection (N=5) were more likely to have a history of smoking (P=0.03),
have a history of prior pocket infection (0.01), and have elevated BMIs
(P<0.001) (Table 3). The bacteria found to be responsible for
these new pocket infections included Stenotrophomonas maltophilia,
Streptococcus agalactiae, Streptococcus mitis, Staphylococcus aureus,
and Enterococcus.