Many cardiologists were no doubt surprised to read accounts of the recent U.S. Preventive Services Task Force (USPSTF) Evidence Report on ECG screening for atrial fibrillation, which included this headline from the American Academy of Family Physicians: “USPSTF: Evidence Lacking on Screening for AFib with ECG”. Without knowing the specifics of the study, it would be easy to misinterpret this to mean that ECG screening does not effectively detect incidents of atrial fibrillation (AF). In fact, the headline refers only to the researchers’ inability to find enough substantive, high-quality data to confidently answer three key questions about ECG testing:
Key Question 1. Does screening for AF with ECG improve health outcomes (e.g., reduce all-cause mortality or morbidity or mortality from stroke) in asymptomatic older adults?
Key Question 2. Does systematic screening for atrial fibrillation with ECG identify older adults with previously undiagnosed atrial fibrillation more effectively than usual care?
Key Question 3. What are the harms of screening for atrial fibrillation with ECG in older adults?
The USPSTF concluded that “the current evidence is insufficient to assess the balance of benefits and harms of screening for atrial fibrillation with ECG.” As the American College of Cardiology response to the report aptly notes, “This conclusion is not a recommendation against ECG screening for AF. ”
The scope of the task force’s investigation of ECG screening for AF was both ambitiously wide (KQs #1 and #3) and a bit narrow (KQ2), which explains why researchers found a paucity of substantive data. Here are five things cardiologists should know about the USPSTF report to better understand the limitations of its findings and relevance to their everyday ECG practices:
The researchers were unable to identify a clinical study that adequately addressed KQ1; findings for the entire ECG section were based on just four clinical trials
For KQ1, the study noted that “No eligible studies were identified that focused on this question and reported results.” The authors cited an ongoing randomized clinical trial, the STROKESTOP study, which is investigating whether intermittent ECG screening can lower the incidence of stroke over five years. The strength of evidence for the four ECG studies reviewed was either “insufficient or low.”
KQ2 focused on systematic ECG screening by general practitioners and did not include studies of adults who had experienced transient ischemic attacks
One of the primary reasons to order ECG tests is to assess whether AF was a contributing factor for ischemic stroke, whose cause is undetermined in 30% of cases. One American Heart Association (AHA) guideline states that cardiac monitoring “should be conducted routinely after an acute cerebrovascular event to screen for serious cardiac arrhythmias.”
While the benefits of systematic ECG screening warrant further study, the three clinical trials reviewed for KQ2 added little to advance this discussion.
The report does not cover key elements of ECG screening, especially diagnostic accuracy and monitoring duration, which affect the efficacy of detecting AF
Paroxysmal AF (PAF), which occurs intermittently and asymptomatically, is a major contributing factor in cryptogenic stroke and accounts for an estimated 25% - 60% of AF events. The ability to detect PAF will largely depend on 1) the accuracy and completeness of information from the ECG test, and 2) the monitoring duration time. Yet the report did not include any longer monitoring duration studies and its authors acknowledged, “We did not systematically review the evidence regarding the diagnostic accuracy of screening tests for AF.”
Today’s portable, patient-friendly ECG monitoring systems can be worn for extended periods of time to provide a continuous, full disclosure ECG signal. For example, the results from a study presented at the 2018 Heart Rhythm Society Annual Scientific Sessions found that continuous monitoring with the PocketECG mobile arrhythmia monitoring solution provided significantly higher diagnostic yield than two frequently used fixed duration offline methods – 24- and 48-hour Holter monitors and multi-day patches.
If not seen in the proper context, the USPSTF report’s conclusion could be dangerously misleading
The study’s conclusion stated that: “Although screening with ECG can detect previously unknown cases of atrial fibrillation, it has not been shown to detect more cases than screening focused on pulse palpation.” To put this in context, remember that:
- The strength of evidence supporting this conclusion was rated as “low”
- The researchers did not evaluate the ECG monitoring methods or the accuracy and completeness of their information
- The conclusion was based on three general practitioner studies in the UK, each with high error rates (i.e., missed more than 20% of AF cases on 12-lead ECGs)
Despite extensive research underpinning the report, the investigators only answer to all three questions posed about ECG screening can be summed up in three words: We don’t know.
Perhaps report authors should have considered asking one of the most important ECG questions facing cardiologists: Is my patient at too high a risk if I do not order an ECG test?
The answer to this question will depend on multiple patient-specific variables. Yet some facts should be always be top of mind when making these tough decisions:
- AF increases the risk of stroke up to fivefold.
- About 20% of patients with an AF-associated stroke are unaware of AF before the stroke
- Approximately 30% of patients with AF who have a stroke die within 1 year of the stroke, and up to 30% of survivors are permanently disabled
- Early detection of previously undiagnosed AF could lead to earlier stroke prevention via anticoagulation
- ECG monitoring systems have varying capabilities for detecting AF