Without a doubt, the implantable cardiac defibrillator (ICD) saves lives. Surgically placed under the skin of the chest, it detects abnormal heart rhythms and delivers a shock to the heart that restores its normal rhythm. But: Many patients today are getting a type of ICD that increases their risk for dangerous complications without providing clear benefits, a new study shows. Here’s what you need to know to keep that from happening to you…

Broadly speaking, there are two kinds of ICDs. A single-chamber ICD has one lead (wire) that runs from the device’s generator to one of the heart’s lower chambers…a dual-chamber ICD has that same lead plus a second lead that connects to one of the heart’s upper chambers. Problems with pacing, in which the heart beats too slowly, usually originate in the sinus node, which is in an upper chamber. That’s why people with pacing problems typically require a dual-chamber device.

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Yet even among ICD patients without problems requiring this pacemaker function, many are getting the dual-chamber device. Why? Perhaps their doctors believe that the extra lead helps the ICD distinguish normal from abnormal rhythms, theoretically reducing the risk that the device would mistakenly deliver an unneeded shock, which can be painful and potentially dangerous. The problem is that the dual-chamber device also carries additional risks. Because of the extra lead, the surgery is more complex, time-consuming and costly…patients are more prone to infection, which can be deadly…and there is a greater chance that a lead will eventually become dislodged and need to be surgically replaced.

Because most clinical studies have looked only at single-chamber ICDs, researchers set out to compare the two types of devices by looking at data on more than 32,000 patients who had received their first ICDs. Though none of these patients had the type of pacing problems that required the second lead, only 38% had been given single-chamber devices…the other 62% received dual-chamber ICDs. To make the comparison between the two groups as meaningful as possible, the researchers “matched” more than 11,600 pairs of patients—one with a single-chamber ICD and one with a dual-chamber ICD—whose overall health was otherwise quite similar.

What the researchers found: In the three months after surgery, the complication rate was 34% higher among patients who had received dual-chamber devices than among those who got single-chamber devices. Some of those complications required an additional operation to fix.

What’s more, in the year after the initial surgery, the rates of hospitalization or death from any cause were virtually the same for both groups—meaning that, among the study participants, the dual-chamber ICDs did not provide measurable benefits over the single-chamber devices. As for the rationale behind using dual-chamber ICDs to better detect abnormal rhythms and thus reduce unnecessary shocks, this hypothesis remains unproven.

Bottom line: For heart-rhythm patients without the need for the pacemaker function, dual-chamber ICDs offer no benefits over single-chamber devices—but they do increase the risks. If your doctor recommends a dual-chamber ICD even though your heart pacing is OK, talk to him/her about the information in this article…and if he doesn’t change his mind, seek a second opinion. After all, heart surgery is risky and costly enough already. You certainly don’t want anything to increase your odds of having to go through it a second time.