BOSTON — A sensing filter reduced inappropriate shocks from a subcutaneous implantable cardioverter defibrillator by nearly 70%, according to data presented at the Heart Rhythm Society Annual Scientific Sessions.
Previous studies showed that approximately 70% of inappropriate shocks from the subcutaneous ICD (Emblem S-ICD System, Boston Scientific) resulted from cardiac oversensing, Tom F. Brouwer, MD, from the department of clinical and experimental cardiology, Academic Medical Center, Amsterdam, said during a press conference.
“There is a new algorithm update that takes care of that specific phenomenon,” Brouwer told Cardiology Today. “In cardiac oversensing, the device sees some part of the QRS in the T-wave and misinterprets those signals. The new algorithm eliminates 70% of all inappropriate shocks.”
The algorithm controls a filter (Smart Pass, Boston Scientific) that removes or reduces T-waves and other low-frequency signals, he said.
Brouwer and colleagues analyzed 1,984 patients (mean age, 48 years) implanted with the ICD in 2015 and 2016, of whom 655 had the filter activated at implant.
Endpoints of interest were inappropriate shocks and appropriate shocks. The filter setting was modeled as a time-dependent variable.
At 1 year, 4.3% of patients with the filter had an inappropriate shock vs. 9.7% of those without the filter (HR after adjustment for age and programming = 0.5; P < .001), according to the researchers.
Over 1 year, there were 28 total inappropriate shocks in the group without the filter vs. seven in the group with the filter (HR after adjustment for age and programming = 0.32; P < .001), Brouwer said.
“When the algorithm is turned on, the number of patients with inappropriate shocks is reduced by 50%,” Brouwer told Cardiology Today. “If you look at how many shocks those patients with inappropriate shocks received, that number is reduced by 70%.”
Inappropriate shocks due to cardiac oversensing occurred in 6.4% of the patients without the filter and 1.6% of patients with the filter (P < .001), whereas inappropriate shocks due to noncardiac oversensing happened in 2.3% of patients without the filter and 0.5% of patients with the filter (P = .003), the researchers found.
Inappropriate shocks for reasons other than oversensing occurred in 1.1% of the nonfilter group and 2.3% of the filter group (P = .07).
Appropriate shocks at 1 year occurred in 6.6% of the nonfilter group and 5.2% of the filter group (P = .21).
Time to therapy was not affected by the use of the algorithm, Brouwer said.
The findings mean that “the rate for this type of inappropriate shock is now in the same range as that for standard transvenous ICDs,” Brouwer told Cardiology Today. “This is important for patients because experiencing inappropriate shocks is very uncomfortable, and for clinicians because patients are often readmitted when at first the reason for the shock is unknown.” – by Erik Swain
Brouwer TF, et al. LBCT03-06. Presented at: Heart Rhythm Society Annual Scientific Sessions; May 9-12, 2018; Boston.
Disclosure: The study was funded by Boston Scientific. Brouwer reports his institution receives research support from Boston Scientific.