Only half of the patients suffering with a risk for an irregular heart rhythm are receiving implanted devices throughout the US, a study says.

The study published in the December 2009 issue of the journal HeartRhythm found that there are unexplained variations in the use of the devices, known as implantable cardioverter defibrillators (ICDs).

Researchers reviewed the medical records of 15,381 patients in 167 community-based and academic-affiliated outpatient cardiology practices geographically dispersed throughout the US.

According to study findings, 7,532 patients were eligible for ICD implantation; 311 of those had documented medical contraindications or other reasons for not receiving an ICD and among the remaining 7,221 eligible patients, 3,659 had devices implanted.

The IMPROVE-HF (Improve the Use of Evidence-Based Heart Failure Therapies in the Outpatient Setting) study is sponsored by Medtronic, Minneapolis, Minnesota, a maker of ICD devices.