Progression of silent AFib tied to heart failure

Patients who progressed to having longer episodes of subclinical atrial fibrillation (SCAF) were more than four times as likely to be hospitalized for heart failure in a one-year span, according to a study published June 4 in the Journal of the American College of Cardiology.

“Most of our knowledge of the relationship between atrial fibrillation (AFib) and HF (heart failure) are based on studies of overt clinical AF, and limited data exist on the association between asymptomatic, subclinical atrial fibrillation and HF,” wrote lead researcher Jorge A. Wong, MD, MPH, and colleagues.

The authors studied 415 hypertensive patients 65 or older who had no clinical history of AFib but who had incidents of SCAF detected by implantable defibrillators or pacemakers in the year prior to the analysis. SCAF was defined as an episode between six minutes and 24 hours in which the atrial rate was greater than 190 beats per minute.

Over an average follow-up of two years, 15.7 percent of patients progressed to having SCAF episodes longer than 24 hours or being diagnosed with clinical AFib. In addition, those who experienced this disease progression were found to be 4.58 times as likely to be hospitalized for heart failure—at a rate of 8.9 percent per year—after adjustment for other risk factors.

Other independent factors of heart failure hospitalization included older age, higher body mass index and longer durations of SCAF prior to the follow-up evaluation period.

“This study is the first to demonstrate that progression of AFib, even at its asymptomatic, subclinical stage can be associated with adverse outcomes,” Wong and colleagues wrote. “As prior studies using implanted cardiac devices suggest that up to 85 percent of AFib is not clinically recognized, the current analysis of SCAF adds significantly to our understanding of the relationship between AF and HF, identifying a subgroup of patients who might benefit from preventive strategies.”

Wong et al. said the connecting factors between AFib episode duration and heart failure are unclear. However, they ventured some guesses.

“Patients predisposed to HF may not tolerate prolonged, rapid ventricular rates during SCAF, leading to the clinical unmasking of HF,” the researchers wrote. “Furthermore, tachycardia-induced cardiomyopathy due to prolonged episodes of SCAF may be an important factor in some patients. Atrial systole can contribute a considerable proportion of the cardiac output in patients pre-disposed to HF, and its loss during episodes of SCAF might also account for some of the observed increase in HF risk.”

The authors noted their findings may not apply to patients who aren’t indicated for implantable cardiac devices, although the incidence of SCAF was similar to that reported in patients who didn’t require implantable devices.

“Randomized studies are needed to assess whether strategies aimed at reducing the progression of AFib will avoid the need for HF hospitalization and potentially decrease mortality,” they wrote.

In a related editorial, Taya V. Glotzer, MD, pointed out other studies have linked heart failure to AF, but this is the first one that implicated SCAF, or “silent AFib,” in the equation. She said it doesn’t really matter which conditions comes first because both need to be treated to reverse progression and improve a patient’s prognosis.

Glotzer added that detection of SCAF should spur clinicians to act, even as the research community is still “(homing) in on the burden level that warrants treatment with anticoagulation.”

“Detecting SCAF on an implanted device is akin to having x-ray vision into a patients’ protoplasm, knowing that health is likely not going in the right direction,” wrote Glotzer, with  Rutgers New Jersey Medical School and Hackensack University Medical School.

“Therefore, at a minimum, when SCAF is detected, lifestyle modifications should be made wherever possible: weight should be lost to modify obesity; therapies to treat sleep apnea should be implemented and used consistently; alcohol excess should be curtailed; smoking should be stopped; glucose levels in diabetics should be carefully controlled; and medications for coexisting conditions such as hypertension should be optimized to prevent disease progression. That, in itself, should lead to decreases in hospitalizations and morbidity for both AFib and (congestive heart failure).”