Sensing filter cuts inappropriate shocks for S-ICDs by more than 50%

A sensing filter added to Boston Scientific’s Emblem subcutaneous implantable cardioverter defibrillators (S-ICDs) more than halved the number of inappropriate shocks given to patients over a one-year period, according to a real-world European study presented May 11 at the Heart Rhythm Society’s annual scientific sessions in Boston.

The results were published simultaneously in the HeartRhythm journal.

S-ICDs were developed to reduce complications related to transvenous leads, presenting study author Tom F. Brouwer, MD, told Cardiovascular Business. But S-ICDs have also been associated with a relatively high number of inappropriate shocks, mostly from oversensing.

To address this issue, Boston Scientific developed the SMART Pass filter, which is essentially an algorithm designed to reduce shocks from the device being overly sensitive.

In this study of about 2,000 patients, the percentage of patients who received an inappropriate shock over the one-year follow-up was 9.7 percent among those without the SMART Pass filter and 4.3 percent among those with the filter. After adjustment for age and device programming, that represented a 50 percent relative reduction in the number of patients who experienced at least one inappropriate shock.

In addition, there was a 68 percent adjusted reduction in the total number of inappropriate shocks because certain patients may have received multiple shocks during follow-up. The incidence of inappropriate shocks was 28 per 100 patient years in the no-filter group and seven per 100 years in the SMART Pass group. Brouwer said the latter figure is in line with previous studies of transvenous ICDs.

“One of the major limitations of the S-ICD in the eyes of many physicians was the somewhat higher inappropriate shock rates and all you now have to do is turn the algorithm on in the second-generation device (the Emblem S-ICD),” said Brouwer, of the Academic Medical Center at the University of Amsterdam.

“In the newer generation (Emblem MRI S-ICD) and the next generations the algorithm will be turned on at implant in every single patient, meaning there’s very little you have to do as a clinician to actually get the benefits of this algorithm. On the other hand, what you will get in return is many fewer patients with inappropriate shocks and often our clinical reality is that those patients will be admitted to a hospital.”

Brouwer noted clinicians can turn off the filter if they want to never miss a case of ventricular arrhythmia, although the number of appropriate shocks weren’t significantly different between the two study groups. About one-third of the patients had the SMART Pass turned on, while the other two-thirds didn’t.

Even though the study was conducted in Europe, the device and algorithm are available in the U.S.

Limitations of the study include that it wasn’t randomized and there were no mortality outcomes available. It was also sponsored by Boston Scientific, the device maker.

However, Brouwer believes the real-world data validate what was expected after a pretrial simulation. The take-home message for clinicians is simple, he said.

“I think this will be a no-brainer for everybody to turn the filter on and make it a better device for patients,” Brouwer said.