Single-chamber ICDs with novel detection algorithms show low inappropriate shock rate

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Primary results from the PainFree SST study have shown that 97.6% of patients were free from inappropriate shocks with single-chamber implantable cardioverter defibrillators (ICDs) at one year of implantation.

Data were presented by Edward J Schloss, director of Cardiac Electrophysiology, The Christ Hospital Health Network, USA, at a late-breaking trial session at the European Heart Rhythm Association (EHRA) Europace congress (23–26 June 2013, Athens, Greece).

Schloss told delegates that ICD shocks are associated with anxiety, decrease in quality of life and mortality. “Modern ICD trials show inappropriate shock rates of 2–10%,” he noted. Specifically, single-chamber devices have been excluded in prior trials focused on shock reduction (eg. MADIT-RIT and EMPIRIC). The PainFree SST study, according to Schloss, is the first trial that evaluates the performance of SmartShock discrimination algorithms-a set of novel detection algorithms developed by Medtronic-designed to reduce inappropriate shocks with single-chamber, dual-chamber ICDs and cardiac resynchronisation therapy defibrillator (CRT-D) devices. “These algorithms were developed to address the three most common causes of inappropriate shocks including supraventricular tachycardia, oversensing and non-sustained ventricular arrhythmias,” said Schloss. At the Heart Rhythm Society (HRS) congress, the PainFree SST investigators reported the results with dual-chamber ICDs and CRT-D devices showing that 98.2% of patients were free from inappropriate shocks.

For this subset analysis of PainFree SST, 709 patients (61.9 mean age, 81% male) from Europe, Canada, USA, Middle-East and Japan were implanted with single-chamber devices. After one year, 97.6% of patients were free from inappropriate shocks. In total 252 shocked episodes were reported, 175 (41 patients) of those shocked episodes were appropriate and 19 (15 patients) were inappropriate. Three hundred and seventy five patients had ventricular tachycardia therapies enabled and the overall mortality rate was 2.4%, with 16 deaths.


To conclude, Schloss said: “Single-chamber ICDs with SmartShock algorithms provide a low inappropriate shock rate while allowing for flexibility in rate detection interval programming.”