One out of five patients who receive a well-known cardiac implant don't need it and are at greater risk of dying of heart attacks because of the device, a US study said.
The survey of more than 100,000 patients who had received implantable cardioverter-defibrillators (ICDs) "found that about 20 percent did not meet evidence-based guidelines for receipt of an ICD," researchers said.
"These patients had a significantly higher risk of in-hospital death than individuals who met criteria for receiving an ICD," they added.
The study was carried out by doctors at Duke Clinical Research Institute and published in the Journal of the American Medical Association (JAMA).
Several clinical trials have shown that ICDs can save the lives of patients with advanced systolic heart failure by detecting irregular rhythms and delivering an electrical shock to the heart to make it beat normally.
But they are not recommended for patients recovering from a heart attack or bypass surgery, or for those with severe heart failure symptoms or a recent diagnosis of heart failure.
"The degree to which physicians in routine clinical practice follow these evidence-based recommendations is not clear," the authors of the study said.
Of the 111,707 initial primary prevention ICD implants that occurred during the study period, 25,145 (22.5 percent) were for a "non-evidence-based indication".
Of those, 9,257 (36.8 percent) were in patients within 40 days of a heart attack, and 15,604 (62.1 percent) were in patients with newly diagnosed heart failure.
The authors admitted that the absolute difference in complications between patients who needed the ICDs and those who did not was "modest" but warned against prescribing unnecessary implants.
"These complications resulted from procedures that were not clearly indicated in the first place," they said.
"While a small risk of complications is acceptable when a procedure has been shown to improve outcomes, no risk is acceptable if a procedure has no demonstrated benefit."