Silent A-fib After Acute MI Portends Poor Outcome

Patients who experience silent A-fib after acute MI have increased rates of cardiovascular (CV) death and heart failure-related hospitalization at 1 year compared with their counterparts without any A-fib, according to a study published online April 22, 2015, ahead of print in Heart.

“Whether the onset of silent [A-fib] in the course of MI is a simple marker of or an active contributor to a worse prognosis 1 year after the index episode remains to be elucidated,” write Marianne Zeller, PhD, of the University of Burgundy (Dijon, France), and colleagues. “However, the association between silent [A-fib], impaired LVEF, a greater infarct size, and more [heart failure] episodes is the most probable underlying mechanism.”

The researchers studied 737 consecutive acute MI patients at their institution who were assessed by continuous ECG monitoring within 48 hours after hospital admission and survived through discharge. Patients were enrolled between May 2011 and January 2013. Silent A-fib—defined as any asymptomatic episodes lasting at least 30 seconds—was identified in 106 patients (14.3%), and symptomatic A-fib within 48 hours of admission was seen in 32 (4.3%).

Compared with patients without A-fib, those with silent A-fib were markedly older, more frequently hypertensive, less likely to be smokers, and more likely to have impaired LVEF (P < .001 for all). Silent A-fib patients were acutely undertreated, with fewer having been prescribed beta-blockers or ACE inhibitors or treated with PCI. However, they received more diuretics and vitamin K antagonists than non–A-fib patients.

Comparing the silent and symptomatic A-fib groups, those with silent A-fib were more likely to smoke and less likely to have a history of stroke and prior A-fib. Silent A-fib patients were less likely to receive acute diuretics, but the rates of other therapies and PCI were similar.

CV Death Tripled With Silent vs No A-fib

At 1 year, CV mortality was 3.2% overall, with higher risks seen in patients with silent or symptomatic A-fib. These patients were also more likely to be hospitalized for heart failure, and of the 5 patients who had strokes, 3 were in the A-fib groups (table 1).

In a sensitivity analysis, mortality was higher for patients with known prior A-fib compared with patients lacking that history (18.8% vs 2.6%; P < .001). However, there were no associations between prior A-fib and stroke or heart failure–related hospitalization.

Another subgroup analysis excluding patients with a history of A-fib found that silent A-fib after acute MI remained linked to an increased risk of 1-year cardiovascular death compared with no A-fib and symptomatic A-fib (5.3% vs 1.9% and1.0%, respectively; P for trend = .019).

On multivariate analysis, silent A-fib was associated with the combined outcome of CV death or hospitalization for heart failure (OR 2.24; 95% CI 1.02-4.93; P = .046). “The association was only borderline significant… probably due to the lack of statistical power, and should be confirmed in larger populations,” Dr. Zeller and colleagues write.

Routine Screening Strategy Needed

The dramatically higher risk of mortality at 1 year with silent A-fib shows that the condition “may severely impair the prognosis,” according to the authors, although they admit that the findings are not definitive. “Given the similar rates of hospitalization for acute [heart failure] in the 2 groups with [A-fib], our work supports the hypothesis that silent [A-fib] in the acute phase of [MI] may lead to the subsequent development of symptomatic [A-fib] occurring within the first year after [acute MI],” they observe.

Moreover, that A-fib is so prevalent suggests “the need for a screening strategy in routine clinical practice,” the authors add.

The study’s biggest limitations, Dr. Zeller and colleagues say, are its reliance on the European Society of Cardiology definitions of A-fib, “which may overdiagnose asymptomatic arrhythmia, and the lack of data on the duration of the silent [A-fib] episodes.”

Further research is “urgently needed to identify diagnostic strategies and therapeutic opportunities in silent [A-fib] complicating [acute MI]. Whether the prognosis may be improved by specific management of [A-fib] should also be investigated,” the authors conclude.

New Technologies May Improve Monitoring

Sorin J. Brener, MD, of New York Methodist Hospital (New York, NY), told TCTMD in an email that silent A-fib is not something clinicians are usually on the lookout for. It “has not been studied in depth and continuous ECG monitoring is not practical,” he said, adding that he sees it in less than 10% of patients “because monitoring is not so intense.”

Further research will likely not focus directly on silent A-fib, Dr. Brener said, because it “is a marker of more adverse baseline characteristics and larger MI or more systolic and diastolic dysfunction.”

However, in an email with TCTMD, Jeff Healey, MD, MSc, of the Population Health Research Institute (Hamilton, Canada), said it is common for clinicians to monitor for silent A-fib following MI because of the condition’s adverse influence on prognosis. But, he noted, “there are no guidelines regarding monitoring for this after patients leave the hospital following MI.”

Dr. Healey said he prefers the term “subclinical” to “silent” A-fib because it “captures not only [A-fib] that does not produce any recognizable symptoms but also symptomatic [A-fib] that is so brief that it evades ECG documentation.”

Although no randomized studies have been performed to “demonstrate the value of any particular therapy for silent [A-fib after MI],” he said, the ongoing randomized ARTESiA trial is examining the use of oral anticoagulation in patients with subclinical A-fib and stroke risk factors.

“Other possible interventions for subclinical [A-fib include] blood pressure–lowering agents, statin medications, and lifestyle interventions,” he continued.

As to whether monitoring is best done using surface ECG or external or implantable devices, Dr. Healey noted: “Research is needed to determine their relative merits with regard to detection rate, false-positive rate, costs, etc and to determine the cost-effectiveness of screening for subclinical [A-fib] in different populations.”

Source:
Stamboul K, Zeller M, Fauchier L, et al. Prognosis of silent atrial fibrillation after acute myocardial infarction at 1-year follow-up. Heart. 2015;Epub ahead of print.

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