Each year in the United States, approximately 140,000 implantable cardioverter-defibrillators (ICDs) are implanted in cardiac patients. Physicians often face challenges when working with patients to decide whether it’s best to use a single- or dual-chamber device. Some patients have a clear indication for a dual-chamber device because they have an indication for a pacemaker. For patients without an indication for a pacemaker, the decision is much less clear. The potential benefits of dual-chamber devices remain to be proven, and they may have more complications. Clinical trial data to guide physicians on which option to choose have been lacking. Currently, nearly two-thirds of patients undergoing ICD implantation for primary prevention receive dual-chamber devices.

Variations in Dual-Chamber ICD Use

In a study published in the April 23, 2012 Archives of Internal Medicine, my colleagues and I set out to explore hospital-level variation in the use of dual-chamber ICDs across the U.S. Using the Medicare-mandated National Cardiovascular Data Registry (NCDR) ICD registry, we looked at 87,115 patients from 2006 to 2009 receiving an ICD as primary prevention without a documented indication for a pacemaker. We only wanted to analyze patients for whom it wasn’t clear whether a single- or dual-chamber ICD was the appropriate choice. Of these patients, about 58% received a dual-chamber ICD. More importantly, use of each ICD type varied significantly by hospital and by physician. In some hospitals and with some physicians, 100% of patients without a clear indication for a dual-chamber ICD received such a device. At other hospitals and with other physicians, 0% of these patients received a dual-chamber ICD.

“Differences in the local culture and practice norms in hospitals are causing variation.”

With the large amount of patient-level data in NCDR ICD registry, we were able to control for a host of patient characteristics in our model. Few patient characteristics influenced the decision. For example, patients with diabetes were slightly less likely to receive a dual-chamber ICD, while those with atrial fibrillation were slightly more likely to receive a dual-chamber ICD. In contrast, the region of the country where patients lived was a significant predictor. In New England, for example, 36% of patients received a dual-chamber ICD, compared with a 66% rate that was observed in the Pacific region.

Next Steps to Reduce Variations in ICD Use

Clearly, patient characteristics are not driving the variation in ICD use. Instead, our data support the hypothesis that differences in the local culture and practice norms in hospitals are causing variation. If opinion leaders in one area strongly believe that the data suggest only dual-chamber ICDs should be used, the hospital where they practice is likely going to implant patients with dual-chamber ICDs. To understand this variation more fully, research is needed that links procedure use to social science methods, including in-depth interviews.

The type of wide variation seen in our study tends to be more prominent in areas of medicine for which there’s no clear evidence. More data are needed from large, randomized trials of single- versus dual-chamber ICDs among patients with no indications for pacemakers to help clinicians with this choice. Such studies would be expensive, and it may be difficult to find a source for the funding of these investigations. Until such data emerge, our research should serve as a source of introspection into why physicians make the choices they make during patient care.


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