Inappropriate Shock Rates Driven Lower With "Smart" Programming: Very Good News in ICD Therapy

John M. Mandrola


June 26, 2013

"It's time to revisit the therapy of sudden cardiac death"

Dr John Camm, EUROPACE 2013

Implantable cardioverter-defibrillator (ICD) therapy for the treatment of sudden cardiac death has undergone major improvements in the past year. This is welcome news for both patients and caregivers. I am happy to report a late-breaking clinical trial from EUROPACE 2013 that delivers really good news about ICD therapy.

First the Background:

Despite major advances in cardiology in the past decade, sudden cardiac death remains the number-one cause of death. Estimates vary, but it's likely that more than 200 000 humans die suddenly each year from ventricular tachyarrhythmia.

The ICD remains the only reliable way to treat this disease. Once ventricular fibrillation occurs, the likelihood of meaningful survival without an ICD remains very low.

The problem with ICD therapy has always been the benefit-to-burden ratio. In another era of medicine (a decade ago), clinical trials showed that selected patients at high risk for sudden death gained small but statistically significant mortality advantages with an ICD. For every 100 patients implanted with an ICD, only five to seven patients experience a life-saving shock. The rest are exposed to the risks but get no benefit.

Such small gains would not be an issue if the burdens weren't so great. One of the most devastating burdens of an ICD is inappropriate shocks. High-voltage internal shocks delivered in a fully awake patient are a huge problem. You just can't shock a person and expect no consequences. Shocks have been associated with anxiety, increased healthcare use, decreased quality of life, and even higher mortality. Until recently, the rate of inappropriate shocks has ranged between 5% and 15%. That's too high.

The Good News: Shock Reduction is Possible—and It Matters

Dr Jay Schloss (Christ Hospital, Cincinnati, OH) presented the PainFree SST study as a late-breaking clinical trial at EUROPACE 2013. The study evaluated the inappropriate-shock rate in patients implanted with single-chamber ICDs using a set of novel detection algorithms. It was a worldwide study that included a broad group of ICD/CRT-eligible patients. The primary end point of the trial was the rate of inappropriate shocks at one year postimplant. At HRS 2013, the PainFree SST investigators reported an inappropriate-shock–free rate of 98.2% in patients implanted with dual-chamber ICDs and CRT-D devices.

This presentation of the PainFree SST included a cohort of 757 patients implanted with single-chamber ICDs. The proprietary Medtronic detection algorithms address the three main causes of inappropriate ICD shocks—any supraventricular tachycardia (primarily AF), oversensing due to either T-wave oversensing or electrical noise, and nonsustained VT. Notable aspects of the programming features include wavelet morphology analysis, discriminating T-waves, assessment of lead integrity or noise, and improved recognition of when a nonsustained episode terminates. This suite of algorithms comes programmed "on" nominally.

Medtronic engineers estimated these algorithms would yield a 2% rate of inappropriate shocks. The PainFree SST trial aimed to test that theory.

PainFree SST investigators allowed physician discretion in ICD programming. A VT zone was programmable at any rate cutoff and any time to detection. Adjudication of episodes was rigorous; all events were assessed independently by two reviewers as well as a third if necessary.

Results: Baseline characteristics of patients were representative of a single-chamber ICD patient population. Notable features of the patients are as follows:

  • Average age—62 years.

  • 81% male.

  • 34% implanted for secondary prevention.

  • 20% were device replacements.

  • 22% had a history of AF.

  • Average LVEF—33%.

  • 7% had AV block.

The primary result was a 97.6% inappropriate-shock–free rate at one year. There were 19 inappropriate-shock episodes in 15 patients. No patient experienced more than two shock episodes. Programming a VT zone (at any rate cutoff) did not increase the risk of an inappropriate shock. The overall shock-free rate (including appropriate plus inappropriate shocks) was 91.6%, and the overall mortality was 2.4%, with 16 deaths.

Conclusions: In a representative sample of real-world patients from across the world, single-chamber ICDs equipped with novel detection algorithms provide a very low inappropriate-shock rate while allowing flexibility in programming.


The PainFree investigators have clearly shown that "smart" programming of ICDs results in very low rates of inappropriate shocks. Although this was a nonrandomized industry-sponsored trial, there are a number of features that deserve emphasis.

First, PainFree enrolled a real-world cohort of patients and evaluated all types of ICDs. In comparison, the MADIT-RIT trial used only dual-chamber devices, and patients with permanent AF, heart block, and those with generator changes were excluded. PainFree SST enrolled all comers; patients simply had to have an indication for an ICD. Trials that include real-world patients provide useful information to clinicians. It's often tough to apply the results of highly selected clinical trials to the patient who sits before you.

Second, information on shock rates for single-chamber ICDs has been sparse. Although recent trials show little clinical advantage with dual-chamber devices, there remains concern about inappropriate detection and shocks when only one lead is implanted. PainFree SST confirms that very low inappropriate-shock rates are possible with single-lead systems. That's important information for clinicians. Hopefully, these findings will underscore the message that less-is-more when it comes to ICD hardware.

Third, PainFree has lowered the bar of what should be expected for inappropriate-shock rates. Without compromising flexibility of programming or requiring waiting 60 seconds for VT detection, the PainFree trial proves it's possible to achieve ultralow rates of inappropriate shocks. This changes the ICD discussion with patients. In the past, quoted rates of inappropriate shocks ranged from 10% to 20%. This trial, combined with MADIT-RIT and ADVANCE III , should change the expectation of inappropriate shocks to below 5%.


This is important stuff. It goes to the core of ICD therapy. MADIT-RIT established that a strategy of shock reduction improves mortality. ADVANCE III confirmed that programming longer detection times decreases ICD interventions without compromising outcomes. PainFree shows that reducing inappropriate-shock rates below 3% for any device is possible.

Taken together, these data confirm that if we are really careful about device programming and selection, good outcomes will follow. In the difficult decision to recommend an ICD, the ratio of benefit to burden turns more favorable. If you lower the burden of having an ICD, net clinical benefit improves. That's a major development.

Finally, isn't it remarkable how good science exposes the weaknesses of expert opinion? We were all so convinced that ventricular tachyarrhythmia required fast and aggressive action, like what is done in a CCU. Science now shows it's the opposite: the best way to approach ventricular arrhythmia with an ICD is with patience and nuance. I will admit to you that that makes me smile.



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