By Dr. Anthony C. Pearson, MD, FACC
Symptomatic Afib is quite common worldwide and is increasing in prevalence. A study in the Journal of Geriatric Cardiology estimated the global prevalence of clinically diagnosed Afib at 33.5 million in 2010, and research in the American Journal of Cardiology projects that it will reach 12.1 million in the United States by 2030.
The condition is associated with a marked increase in stroke risk and mortality. The majority of Afib patients, however, experience no Afib symptoms, and the best method for identifying those patients and reducing the global burden of disease related to Afib remains a subject of intense debate in cardiology.
Prevalence of Undiagnosed AF
A study in PLOS ONE estimated that 13.1% of the 5.3 million cases in the US in 2009 were undiagnosed. This undiagnosed population was noted to be at moderate to high risk of stroke.
The prevalence of previously undetected Afib has also been reported in a number of studies using long-term monitors in patients with no known Afib and without symptoms or arrhythmia. In the ASSERT-III trial published in the Journal of Electrocardiology, among patients 80 years of age and older, 1 in 7 experienced Afib ≥6 mins duration.
Clinical Significance
Stroke is generally considered the most important clinical outcome of undetected Afib, and it is the first symptom felt for some patients.
A 2017 study in Stroke looked at how often patients with undiagnosed Afib presented initially with stroke symptoms by examining the 1,809 participants in the Framingham Heart Study. The investigators noted 87 strokes that occurred ≤1 year prior to Afib detection. The stroke occurred on the same day in 1.7% of cases, and overall 4.8% occurred ≤1 year before Afib detection.
This study suggests strokes may present as the initial manifestation of Afib at a rate of 2 to 5 per 10,000 person-years in both men and women, making it quite rare.
There is also a substantial body of evidence to support this notion based on long-term monitoring of patients with cryptogenic stroke, which is now more frequently termed embolic stroke of undetermined source, or ESUS.
Risks Presented by Subclinical Afib
When Afib is asymptomatic but diagnosed either by a screening process or analysis of an implanted device, it has been termed subclinical Afib (SCAF), as a Medicina review notes. According to the ASSERT-III data, Afib can be detected in approximately 10% of asymptomatic individuals within three months if they undergo long term monitoring with implanted pacemakers or defibrillators, but it is not clear what to do with the information obtained.
Patients with SCAF can develop heart failure with cardiomyopathy typically tied to Afib-related tachycardia. They also have two to four times the annual stroke risk of similar CHADS2 score risk patients without SCAF but one-fourth to one-half the risk of clinic Afib patients, according to ASSERT trial data in the New England Journal of Medicine. The data shows that duration >24 hrs of device-detected SCAF confers a substantially higher risk of stroke compared to durations of 6 min to 6 hrs or 6 hrs to 24 hrs.
The Question of Screening
In order to prevent disabling stroke, widespread screening has been proposed using ECG, monitoring, or other modalities. However, it is not clear which method is optimal, what duration of clinically silent Afib is significant, and whether this is a cost-effective approach to public health management of Afib.
The European Society of Cardiology Afib guidelines from 2016 recommended opportunistic screening for Afib by pulse palpation or ECG screening for patients older than 65 years or with high stroke risk factors. On the other hand, the USPSTF does not believe there is enough evidence showing that the potential benefits outweigh the risk of ECG screening to warrant such an approach.
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Cost Burden of Undiagnosed Afib
Several studies have attempted to assess the true cost burden of undiagnosed Afib. Using a claims-based cohort, researchers published a study in the American Journal of Cardiology and found that the incremental annual cost of undiagnosed Afib was $3.1 billion. This cost burden was greater in the 18-to-64-year age range, compared to patients ≥65 years.
The ASSERT-III study examined the cost-effectiveness of using 30-day continuous outpatient ECG monitoring in patients. In one hundred subjects ≥80 years of age without prior history of Afib, the investigators found Afib ≥6 mins in 14% and Afib ≥24 hrs in 3%. The cost-effective analysis found that "one week of monitoring cost $50,000 per quality-adjusted life-year-gained, 30 days and 60 days of monitoring cost $70,000 and $84,000, respectively."
Best Practice for Undiagnosed Afib
According to the PLOS ONE data, more than 690,000 Americans have Afib that has not been diagnosed due to exhibiting no Afib symptoms. These patients are at substantial risk for stroke and death, but simple methods for identifying these patients are available, including opportunistic pulse palpation or 12-lead ECGs during annual physician visits.
Long-term ECG monitoring using ECG-patch-type devices can identify even more undiagnosed Afib. Effective medical therapies have been shown to lower the risk of stroke diagnosed Afib patients substantially, but strong mandates to utilize any of these approaches await randomized studies that show the beneficial effects of this early identification strategy on cardiovascular morbidity and mortality.
Dr. Anthony C. Pearson, MD, FACC is a Professor of Medicine at the St. Louis University School of Medicine Division of Cardiology and specializes in general and noninvasive cardiology.
The opinions, beliefs, and viewpoints expressed in this article are solely those of the author and do not necessarily reflect the opinions, beliefs, and viewpoints of GE Healthcare. The author is a paid consultant for GE Healthcare and was compensated for creation of this article.
