Implanted cardiac monitors indicate incidence of undiagnosed AFib may be substantial in high-risk patients

Atrial fibrillation affects millions of people worldwide and increases with older age, hypertension, diabetes, and heart failure, conditions that are associated with increased stroke risk. Atrial fibrillation episodes may be symptomatic, asymptomatic (i.e., silent AF), or both. Heart failure or stroke can be the first clinical manifestation of AF. Recognition of previously undiagnosed AF and initiation of appropriate therapies is essential for stroke prevention.

Minimally invasive prolonged electrocardiographic monitoring with small, insertable cardiac monitors (ICMs) placed under the skin could assist with early AF diagnosis and earlier treatment. James A. Reiffel, M.D., of the Columbia University College of Physicians and Surgeons, New York, and colleagues conducted a study in which 385 patients received an insertable cardiac monitor. The patients were at high risk of both AF and stroke; approximately 90 percent had nonspecific symptoms potentially compatible with AF, such as fatigue, breathing difficulties, and/or palpitations, and had either three or more of heart failure, hypertension, age 75 or older, diabetes, prior stroke or transient ischemic attack (TIA), or two of the former plus at least one of the following additional AF risk factors: coronary artery disease, renal impairment, sleep apnea, or chronic obstructive pulmonary disease. Patients underwent monitoring for 18 to 30 months.

The researchers found that the detection rate of AF lasting six or more minutes at 18 months was 29 percent. Detection rates at 30 days and 6, 12, 24, and 30 months were 6 percent, 20 percent, 27 percent, 34 percent, and 40 percent, respectively. Median time from device insertion to first AF episode detection was 123 days. Of patients with AF lasting six or more minutes at 18 months, 10 percent had one or more episodes lasting 24 hours or longer, and oral anticoagulation therapy was prescribed for 72 patients (56 percent).

The study notes some limitations, including its modest size.

The authors write that as the AF incidence was still rising at 30 months, the ideal monitoring duration is unclear. "Further trials regarding the value of detecting subclinical AF and of prophylactic therapies are warranted."