ICD use in primary prevention: Do we really know enough?

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The potential improper utilization of implantable cardioverter-defibrillators (ICDs) for primary prevention has recently come to the forefront, as some data have associated this practice with a greater risk of mortality. While many providers may be stretching the guideline recommendations in an effort to treat very sick patients with no alternatives, others are calling for a better understanding of how the therapy affects various populations.

A study in this week’s Journal of the American Medical Association found that, based on NCDR data, 22.5 percent of patients who received ICDs did not meet evidence-based guidelines for the devices, putting them at a higher risk of in-hospital death than individuals who met criteria for the implants. Out of more than 111,000 initial primary prevention ICD implants that occurred during the study period, more than 25,000 were for a non-evidence-based indication. The risk of in-hospital death for those who received a non-evidence-based device was 0.57 percent, compared with 0.18 percent for those who received an evidence-based device.

Alan H. Kadish, MD, of Northwestern University Feinberg School of Medicine in Chicago, who wrote the JAMA editorial, along with Jeffrey J. Goldberger, MD, of Northwestern, told Cardiovascular Business News that while “many of the 22.5 percent of patients shouldn’t have received defibrillators because they were not indicated, that statistic might be slightly higher than in reality due to various reasons.”

First, Kadish questioned the “reliability of the data,” as it may not be representative of real-life clinical practice due to lack of a proper documentation. “A more careful look at the data may indicate that some of the patients did meet indications,” he said.

“In most cases, ICD registry data are retrospectively abstracted from the medical record by nurses or other healthcare professionals,” wrote Kadish and Goldberger. “The precise onset of CHF [congestive heart failure] may not be well documented in the medical record because unlike the date of MI, evaluating the date of diagnosis of CHF may require a history that is targeted to this variable.”

Also, Kadish pointed out that there are a certain percentage of the patients who fall into a “gray area of the guidelines—where there is some data to indicate an ICD would be helpful, but not quite enough to make it a firm guideline.”

Of the more than 25,000 patients in the JAMA study who received an ICD with non-evidence-based indication, 36 percent were in patients within 40 days of an MI and 62 percent were in patients with newly diagnosed heart failure. Additional recent data have raised concerns about using ICDs as means of primary prevention, especially in such high-risk patients as those who recently experienced an MI or those who were recently diagnosed with heart failure.

The DINAMIT study, published online Dec. 6, 2010, in Circulation, found that the reduction in sudden death in ICD patients was completely offset by increased non-arrhythmic deaths, which were greatest in patients receiving ICD shock therapy. The researchers randomized outpatients with recent (six to 40 days) acute MI, left ventricular dysfunction (ejection fraction less than 35 percent) and low heart rate variability to ICD (311 patients) or standard medical therapy (342 patients). 

Michael O. Sweeney, MD, who wrote the DINAMIT editorial, told Cardiovascular Business News, that more than 35 years of investigation in animals and humans indicate that high-voltage shocks cause cardiac tissues damage, though the translation of these effects to adverse clinical outcomes is uncertain.

“Collectively, we need to face the possibility that mortality risk could be changed immediately following a mortality dividend from a high-voltage shock. The shock itself, interacting with the abnormal heart rhythm that triggered the shock, could contribute to the increased risk of death in some patients with advanced heart failure,” says Sweeney, who is from the cardiac arrhythmia services department at Brigham and Women's Hospital in Boston. “This is a very disruptive concept for physicians because it is difficult to confront the possibility that  a powerful therapy that is perceived as highly effective—especially one with no alternative—is potentially consequential to patient outcomes.”

Kadish also acknowledges that some physicians are practicing defensive medicine, in desiring to treat very sick patients. However, he also recommends a wearable defibrillator for these patients in the “gray area” or for those who have had an MI within the previous 40 days.

According to Sweeney, there was initially an intense debate about the potential adverse effects in delivering high voltage shocks directly into the failing heart during the early years of ICD therapy development. However, that discussion was curbed in the late 1990s, when it was revealed how effective defibrillators were at saving lives. 

“Recently, the topic has been reinvigorated by these consistent observations in primary prevention trials that link ICD therapies, mostly in the form of shocks, with an immediate increase in death,” he says. “Obviously, not every patient is harmed by shocks, which prolong life in many patients, but we need to better identify which patients are at highest risk for being harmed from shocks and develop alternative therapeutic strategies.”

Sweeney acknowledged that there are a great many patients who would benefit from an ICD, even peri-infarct patients, but providers simply need to have a better understanding of those patients who are not benefiting, in order to utilize ICD therapy more appropriately without accentuating mortality risk of the life-threatening arrhythmia episodes themselves. He adds that the results from DINAMIT and IRIS could have been widely different, if the investigators had applied contemporary shock-reduction strategies.

Sweeney is calling for new clinical trials to investigate these issues, which may also contribute to understanding differences in outcomes among guideline-compliant and out-of-guideline ICD patients.

While the potential adverse outcomes with utilizing ICDs in primary prevention will undoubtedly continue to be debated, there are recommendations to improving current implantation techniques. In fact, Kadish suggested that physician education is integral to knowing and following the guidelines, and the editorial suggested the decision is best undertaken by an electrophysiologist. “[I]ntensive training may improve both the preoperative evaluation of patients, as well as the operative and immediate post-operative care of patients undergoing ICD implantation,” Kadish and Goldberger commented.

The recent data have “uncovered important problems,” according to Kadish, adding that a larger problem is the great many patients for whom the guidelines recommend ICD therapy who aren’t receiving it. “We need to ensure the right patients are receiving the right therapies,” he concluded.