ICD Shocks - A Blessing or a Curse?

It's all across the media: ICD shocks predict impending death!

Thanks. My patients appreciated these headlines, I'm sure.

But if we're going to tell the 234,000 people who have implantable cardiac defirillators (ICDs) that they're going to die in less than a year after their first shock, shouldn't the media attempt to exercise even a modicum of discernment before going public with these headlines?

First, these findings come from analysis of the Sudden Death in Heart Failure trial (SCD-HeFT) - a well-designed prospective multicenter randomized trial in adults over age 18 which randomized over two thousand patients between three therapeutic treatments for heart failure: (1) conventional medical therapy, (2) converntional medical therapy plus Amiodarone, and (3) conventional medical therapy plus a single chamber, shock-only ICD therapy. The main finding of the SCD-HeFT Trial, in its original form, was that medical therapy (be it with o without Amiodarone), mortality in this group of patients was 7.2% annually. In other words, our best antiarrhythmic at the time, Amiodarone, failed to effect patient mortality. The addition of an ICD for primary prevention of sudden death is this sick population, actually reduced mortality (to 5.5% per year in patients followed for 5 years - a 23% reduction in mortality compared to medical therapies).

So now, is it any wonder that patients who have received an ICD to prevent death on a preventative bases, might just get a shock as their condition deteriorates?

When you can take fairly sick individuals and implant an ICD in them as primary prevention (i.e., they never had an arrhythmia before) and then look at those who develop arrhythmias suddenly, it seems intuitive to me that those patients would be sicker or have had a change in their clinical situation.

The data from the study support this theory. Therefore, evaluating for the development of worsened heart failure or additional ischemic burden might be prudent in these patients, since these causes seemed to be the largest culprits resulting in ICD shocks. Additionally, the study found that patients with either appropriate (shocks for ventricular arrhythmias) or "inappropriate" (shocks for rapid heart rates from non-ventricular causes, like atrial fibrillation onset) have a poorer prognosis compared to those who did not receive shocks, but this also might be a way to risk-stratify the sicker patients of the overall implant population. Does this mean the patients should not receive devices to live longer? Of course not. But there has to be balance to recommending ICDs in the sickest patients, since recurrent shocks can impact the patient's quality of life if they occur frequently. Infrequent shocks, interestingly, did not seem to convey a worse quality of life in this same group as reported (ironically) in the same issue of the New England Journal of Medicine.

Remember that all mortality curves of different therapies that divert favorably from one therapy, will again meet with the alternate therapy some time in the future, since none of us are immortal. ICD's reduce mortality in sick patients with heart failure, but an ICD shock might suggest that, of the group implanted, those patients with shocks have a better indication for the device, since their mortality is higher. It is important, however, to keep in mind who was NOT studied in this paper:

The patient population studied did not include children.

The patients studied did not have cardiac resynchronization devices.

The devices were not programmed for antitachycardia pacing and did not have dual chamber devices which are better capable of detecting atrial arrhythmias.

So before our patients go out to buy funeral plots, let's keep the issues of the risks and benefits of ICD therapy, and the benefit or curse of their shocks, in perspective.

-Wes


Reference: Poole, JE et al, "Prognostic Importance of Defibrillator Shocks in Patients with Heart Failure," New England Journal of Medicine Sep 4, 2008 Vol 359(10):1009-1017.