PAINFREE SST: Longer ICD detection intervals safe for secondary prevention patients

SAN FRANCISCO — Extending the detection time of an implantable cardioverter defibrillator was safe in patients with ICDs for secondary prevention, according to study results presented at the Heart Rhythm Society Annual Scientific Sessions.

Perspective from Theofanie Mela, MD

Researchers conducted an analysis to determine whether extending detection times for ventricular tachycardia (VT) or ventricular fibrillation (VF), which has been shown to decrease inappropriate therapies and mortality in patients with ICDs for primary prevention, could be performed safely in patients with ICDs for secondary prevention.

Laurence D. Sterns, MD, of the Royal Jubilee Hospital in Victoria, British Columbia, and colleagues enrolled 2,790 patients receiving Protecta ICDs with SmartShock Technology (Medtronic) in the PAINFREE SST study. In a substudy presented by Sterns, the researchers evaluated 705 patients from the study who had an ICD for secondary prevention and consented to interval detection randomization.

Laurence D. Sterns

Patients were randomly assigned on a 1:1 basis to a standard-interval (number of intervals to detect=18/24) or prolonged-interval (number of intervals to detect=30/40) detection of VT/VF ≥188 bpm.

The primary endpoint was freedom from arrhythmic syncope at 1 year. Secondary endpoints included time to first all-cause syncope, appropriate therapy and inappropriate shock. Mean follow-up was 20 months.

Sterns and colleagues found no difference between the groups in freedom from arrhythmic syncope at 1 year (standard group, 97.7%; prolonged group, 96.9%; P for noninferiority<.01).

The groups also did not differ in freedom from all-cause syncope at 1 year (standard group, 96%; prolonged group, 96%; P for noninferiority<.01), appropriate VF zone therapies (standard group, 13.3%; prolonged group, 12.3%; P for noninferiority<.01), or inappropriate shocks (standard group, 1%; prolonged group, 1.3%; P=.93).

There was a trend toward reduced mortality for the prolonged-interval group compared with the standard group at 1 year (standard group, 5.6%; prolonged group, 3.8%; P=.07).

“The results of this study are important for secondary prevention patients, who often are treated with more aggressive ICD programming to address arrhythmic events as quickly as possible,” Sterns said in a Medtronic press release. “Previous studies have demonstrated that devices programmed to wait longer to deliver therapy do not increase the risk of fainting episodes among primary prevention patients, and now we know the same strategy can be used in more patients, even patients at increased risk based on their disease progression.” – by Erik Swain

For more information:

Sterns LD. LB03-01. Presented at: Heart Rhythm Society Annual Scientific Sessions; May 7-10, 2014; San Francisco.

Disclosure: Sterns reports serving on the speakers’ bureau for Medtronic.

Perspective

Theofanie Mela, MD

The effort to avoid inappropriate ICD shocks has been intensified over the past few years. The results of MADIT-RIT are now widely applied in primary prevention patients with ICDs. This substudy of the PAINFREE SST trial comes to offer the information that was missing up to this point. How about the secondary prevention patients? Do they benefit from the MADIT-RIT-like programming?

In this study, sponsored by Medtronic, 705 patients who received a Medtronic ICD for secondary prevention were enrolled and randomly assigned 1:1 to two different detection patterns: the standard numbers of intervals to detect (NID) 18/24 or the prolonged NID 30/40. VT/VF detection was >188 beats per minute (bpm). The patients were followed for an average of 20 months. The rates of arrhythmic and all-cause syncope were similar in the two groups at 1 year; the arrhythmic syncope-free rate was 97.7% with standard detection vs. 96.9% with prolonged detection (P<.01 for noninferiority). However, although the prolonged detection was safe, it did not make a difference in the appropriateness of the shocks (at 1 year, 13.3% with standard detectopm vs. 12.3% with prolonged detection; P=.79) or the number of inappropriate shocks (at 1 year, 1% with standard detection vs. 1.3% with prolonged detection, P=.93). There was no mortality difference between the two groups, but there was a trend toward mortality benefit in the prolonged group (5.6% with standard detection vs. 3.8% with prolonged detection, P=.07).

There is undoubtedly a difference between primary and secondary prevention patients, but one would have not suspected that it would have made such a difference in the results of the trial. These results are quite surprising, given how strongly positive MADIT-RIT was.

Possible confounders include the smaller size of this study and the shorter follow-up. Also, the more-advanced arrhythmia discrimination technology with more recent devices may be playing a role in the significant reduction of inappropriate shocks. The low incidence of inappropriate shocks remained even with the detection rate for VF set slightly lower than MADIT-RIT (188 bpm vs. 200 bpm). While longer detection was deemed safe for such patients, for the future, a larger study with longer follow-up may be able to shed more light in the question of ideal programming for patients with ICDs for secondary prevention.

Theofanie Mela, MD

Director, Pacer and ICD Lab

Massachusetts General Hospital Institute for Heart, Vascular and Stroke Care

Disclosures: Mela reports receiving speaker’s honoraria from Biotronik, Boston Scientific, Medtronic and St. Jude Medical.