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| REVIEW ARTICLE |
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| Year : 2016 | Volume
: 1
| Issue : 1 | Page : 33-37 |
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Silent Atrial Fibrillation: Unknown Truths
Hakan Aksoy, Ali Oto
Department of Cardiology, Memorial Ankara Hospital, Ankara, Turkey
| Date of Web Publication | 30-Sep-2016 |
Correspondence Address:
Hakan Aksoy
Department of Cardiology, Memorial Ankara Hospital, P.O. 06520, Cankaya, Ankara
Turkey
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/2352-4197.191477
In recent years, silent atrial fibrillation (AF) has acquired broad interest in the neurologic and cardiovascular communities. Silent AF has been associated with similar morbidity and mortality as symptomatic AF and with similar rates of silent embolic events. In current clinical practice, AF remains mostly underdiagnosed, and 25% of patients with AF-associated cardioembolic stroke have not been previously diagnosed with AF. Silent AF detection methods include pulse palpation, ambulatory external electrocardiographic recordings, insertable cardiac monitors, and previously implanted cardiac devices with atrial lead. The increased interest is being directed toward detection of silent AF. Whether this will imply better outcomes for patients remains to be demonstrated. Keywords: Atrial fibrillation, atrial high-rate episodes, stroke and embolism
How to cite this article:
Aksoy H, Oto A. Silent Atrial Fibrillation: Unknown Truths. Int J Heart Rhythm 2016;1:33-7 |
| Introduction | |  |
Atrial fibrillation (AF) is the most common sustained arrhythmia in clinical practice. Prevalence and incidence of AF are increasing, especially in the elderly population.[1],[2]
AF has been associated with a 2-fold increase in the risk of death. The most important cause of morbidity and mortality in patients with AF is ischemic stroke [3],[4] and accounts for approximately 20% of strokes.[5] Subclinical AF has been associated with similar morbidity and mortality rates as symptomatic AF [6] and with similar rates of silent embolic events.[7] In about 25% of patients with ischemic strokes, no etiologic factor has been identified [8],[9] and asymptomatic or subclinical AF may be related to those episodes.[10] Most important consequences of AF are stroke and embolism, heart failure and early mortality. The risk of cerebrovascular events can be reduced by anticoagulant treatment. When compared with the CHADS2 score, the CHA2 DS2-VASc index better-discriminated stroke risk with an improved predictive ability.[11]
The prevalence and prognostic value of silent AF have been difficult to assess.[9],[10] Silent AF is diagnosed incidentally during routine physical examination, preoperative assessment, or population survey.[12] The real prevalence of silent AF is unknown. In recent years, data provided by implanted pacemakers and defibrillators have increased awareness about silent AF.[13],[14],[15] However, there is currently no consensus regarding the screening and management of silent AF. In this review, we discuss definition and risk factors of silent AF and detection methods for this arrhythmia.
| Definition | | |
The term silent AF was defined as occurrence and detection of subclinical asymptomatic episodes of paroxysmal AF. To quantity such episodes of asymptomatic silent AF the concept of “AF burden” has been suggested.[16] AF burden is defined as the amount of time spent in AF each day of a specific follow-up period. While patients with symptomatic AF are generally recognized by medical attention resulting from palpitations, dyspnea, chest discomfort, fatigue, dizziness, and syncope, silent AF may only present after the most serious of complications such as ischemic stroke. The specific threshold of AF burden associated with high stroke risk is still a matter of investigation and debate, but it is clear that a maximum daily AF burden of ≥1 h carries important negative prognostic implications and requires risk stratification for stroke.[17]
| Risk Factors | | |
Clinical risk factors to detect silent AF are summarized in [Table 1].[16] These clinical risk factors have a strong association to the various arrhythmic definitions described in the current literature.
| Arrhythmia Detection | | |
Early detection of silent AF even in an asymptomatic stage has potential advantages for several reasons [Table 2].[18] | Table 2: Potential benefits of detecting atrial fibrillation in an asymptomatic stage[18]
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Silent AF detection methods include physical examination, surface electrocardiography (ECG) recordings, and invasive ECG devices.
In physical examination, a physician examines the radial pulse for a minimum of 20 s, and then classifies the rhythm as regular or with occasional ectopic beats, or with frequent ectopic beats or continuously irregular.[19] According to this classification, pulse irregularity can be divided into three categories: Continuous irregularity, continuous, or frequent irregularity and any irregularity.[19] Previous studies have shown that pulse assessment of any pulse irregularity has high sensitivity (90%), but moderate specificity (70–80%).[19],[20] Conversely, pulse assessment of continuous irregularity has high specificity (98%), but low sensitivity (54%).[19]
Surface ECG recordings include ECG strips, Holter monitoring, and event recorders. Invasive ECG devices include dual chamber pacemakers and implantable cardioverter-defibrillator (ICDs) or insertable cardiac monitors (ICMs).
Ambulatory external electrocardiographic monitoring (AEEM) technologies have been developed to increase the possibility of arrhythmia detection.[21] AEEM is based on the use of external ECG recorders that provide prolonged cardiac rhythm recordings and/or can be activated by the patient when symptoms emerge.[22]
Three categories of AEEM technologies are available: Continuous short-term (24–48 h) recorders; intermittent long-term recorders (patient-activated event and loop recorders); continuous long-term recorders (ambulatory telemetry monitoring and patch-type extended Holter monitoring).[21],[23]
AEEM may help detect AF episodes in patients who are either asymptomatic or with transient and unexplained symptoms. They may also be beneficial to evaluate AF burden, mean heart rate during AF, and pattern of initiation and termination of the arrhythmia.[21] AF burden is an expression of the frequency and duration of AF episodes, being an estimate of the severity of the disease.
Lowres et al.[24] performed a systematic review of studies screening for AF at a single time point in unselected patients in the community. Thirty studies, representing 122,571 patients, were included, and the overall prevalence of AF in the total population was 2.3%. If only patients aged at least 65 years were considered, the prevalence was 4.4%. Previously undiagnosed AF was found in 1% of the overall population and 1.4% of those aged at least 65 years. As with most ECG-based studies that evaluate the presence of AF at a single time point, the main limitation is the difficulty in detecting paroxysmal arrhythmias.[6],[7]
Deif et al.[25] reviewed the ECGs of 1459 ambulatory patients aged more than 65 years presenting for elective surgery and found previously undiagnosed AF in 10 (0.7%). Similarly, Salvatori et al.[26] reported that no patient had a new diagnosis of AF by 12-lead ECG in their study. In this study, 48-h Holter monitoring showed silent AF in about 10% of the screened subjects who were aged 65 years or more and were affected by systemic arterial hypertension. The role of Holter monitoring for screening of silent AF has been mainly assessed in patients with stroke of presumed cardioembolic origin. In these patients, the reported rate of AF varies between 3.8% and 24.3%.[27] Turakhia et al.[28] reported that outpatient extended ECG screening for asymptomatic AF is feasible, with AF identified in 1 in 20 subjects and sustained atrial tachycardia (AT)/AF identified in 1 in 9 subjects, respectively. They also found a high prevalence of asymptomatic AT and frequent supraventricular ectopic complexes, which may be relevant to the development of AF or stroke.
| Cardiac Implantable Devices and Atrial High-Rate Episodes | | |
Cardiac implantable devices diagnostics include system diagnostics revealing battery status, pacing threshold, lead impedance and algorithms for detecting and treating cardiac arrhythmias. Stored electrograms (EGMs) can help clinicians to confirm an arrhythmia detected by the device. Stored EGMs also provide the date and time of events and facilitate the clinician to correlate them with the patient symptoms. AF are potentially detectable from implantable arrhythmia management devices (pacemakers or defibrillators) that have an atrial lead and can be programmed to record the number, duration, and frequency of atrial rates that exceed a certain threshold (typically 170–220 beats/min). These devices typically report atrial high-rate events (AHRE). The diagnostic accuracy for AHRE detection is highly reliable when episodes >5 min in duration are considered, thus obtaining appropriate detection of 95% of AF episodes.[17]
Small cross-sectional studies demonstrated that patients with a pacemaker have a high prevalence of AHRE. The Automatic Interpretation for Diagnostic Assistance study found that 50.6% of patients had supraventricular arrhythmias detected by the pacemakers, 58% of these patients were completely asymptomatic.[29] However, this study has limitations such as short follow-up of only 28 days and particularly by the lack of device-stored EGMs to prove the presence of AF. Israel et al.[30] reported that in 46% of patients, AF was documented by the resting ECG during follow-up whereas device interrogation revealed episodes of AF in 88% of patients.
The patients with AF lasting >48 h are exposed to a 5–7% risk of clinical thromboembolism, whereas this risk appears to be much lower (<1%) for AF of <48; h duration. Likewise, AHRE of <48; h has been related to increased risk of thromboembolism and cardiovascular events. The ASSERT (Asymptomatic Atrial Fibrillation and Stroke Evaluation in Pacemaker Patients and the Atrial Fibrillation Reduction Atrial Pacing Trial) trial enrolled 2580 patients ≥65 years of age with hypertension and no history of AF in whom a pacemaker or defibrillator was recently implanted. During the first 3 months, 10% of subjects had atrial high-rate episodes of >190 bpm for >6 min.[13] These high-rate episodes were associated with a >5-fold increase in subsequent diagnosis of atrial arrhythmia on ECG and a 1.60%/year rate of stroke or systemic embolism compared with a 0.69%/year rate for those without high-rate episodes during the first 3 months. In a subgroup analysis of the MOST (Mode Selection Trial in Sinus Node Dysfunction) trial, patients with atrial high-rate episodes (rate >220 bpm for >10 beats detected by a pacemaker) were more than 2 times as likely to die or have a stroke and 6 times as likely to be subsequently diagnosed with AF with respect to patients without AHREs.[14] In a study of 560 patients with HF, the recording of AHREs lasting >3.8 h in 1 day was associated with a 9-fold increased thromboembolic event rate.[31]
TRENDS was a prospective, observational study enrolling patients with ≥1 stroke risk factor (heart failure, hypertension, age ≥65 years, diabetes, or prior thromboembolic event) receiving pacemakers or defibrillators that monitor AT/AF burden (defined as the longest total AT/AF duration on any given day during the prior 30-day period). An AT/AF burden ≥5.5 h on any given day during the antecedent 30 days appeared to confer a doubling of thromboembolic risk.[32] Although the incidence and thromboembolic risk estimates vary in different studies, they consistently prove the relation between the AHRE and thromboembolic events.
The effectiveness of oral anticoagulation for stroke prevention in AF is well documented, but no data on similar strategies in patients with cardiac implantable devices are available. Patients at low risk (i.e. CHADS2 =0) likely would not derive benefit, consistent with published data in AF. Conversely, high-risk patients (i.e. CHADS2> 2) likely will have benefit from anticoagulation. In the study by Botto et al.,[15] the authors observed an annual thromboembolic event rate of 17.6% in patients with CHADS2> 2, although the sample size was small. For patients at moderate risk (CHADS2 =1–2), the data are less clear. In the report by Botto et al.,[15] the combination of AF >5 min and CHADS2 =2, or AF >24 h and CHADS2 =1, yielded an annual thromboembolic rate of 4.0%.
The IMPACT (Randomized Trial of Anticoagulation Guided by Remote Rhythm Monitoring in Patients with ICD and Resynchronization Devices) trial is perhaps the only randomized trial that has attempted to address the question of management of device-detected AF.[33] This trial was designed to investigate the use of remote monitoring combined with a predefined anticoagulation plan compared with conventional device evaluation and physician-directed anticoagulation in patients with dual-chamber ICDs or cardiac resynchronization therapy devices. There was no significant difference between groups in the primary outcome, and the trial was terminated early because of inefficacy.
It seems evident that silent AF has the same prognostic effect as symptomatic AF. The symptomatic and silent AF have same electrophysiological and mechanical effects, and it is likely that progression from paroxysmal to persistent or permanent AF might be more rapid in patients with long-term unrecognized and untreated silent AF. In patients with device detected AHRE's usage of anticoagulation therapy is as yet uncertain in the absence of randomized studies. Until randomized studies are available, in patients with a CHADS2 score of 0, no anticoagulant therapy is recommended in most cases regardless of the burden of AF. In patients with a CHADS2 score of 1–2, anticoagulation would be considered if a single episode of AF exceeds 24 h. In patients with a CHADS2 score >2, the use of anticoagulation is recommended for AF episodes >6 min.[34] Further studies are needed to determine the role of anticoagulation in these patients.
Pacemaker with remote monitoring may also be useful for silent AF detection. Lima et al.[35] found that AF monitoring by means of the pacemaker is a valuable tool for silent AF detection and continuous remote monitoring allows early AF recurrence detection and reduces the number of days with AF.
| Insertable Cardiac Monitors | | |
ICMs are subcutaneous devices that record the heart rhythm over a period of 3 years and are aimed at patients experiencing undocumented palpitations or in whom the arrhythmia has a poor correlation with symptoms. Stroke guidelines recommend at least 24 h of continuous cardiac monitoring to rule out AF in patients with ischemic stroke.[36] However, for patients with infrequent symptoms, AF is unlikely to be detected during AEEM, and long-term monitoring might be needed.[37],[38],[39],[40]
CRYSTAL-AF, a randomized controlled trial, reported the use of ICMs for long-term monitoring of patients with cryptogenic stroke (CS). By 6 months, AF had been detected in 8.9% of patients in the ICM group versus 1.4% of patients in the control group. By 12 months, AF had been detected in 12.4% of patients in the ICM group versus 2.0% of patients in the control group. By 36 months, AF had been detected in 30% of patients in ICM group versus 3.0% of patients in the control group. The median time from randomization to detection of AF was 84 days in the ICM group and 53 days in the control group. Usage of oral anticoagulants was more than doubled in the ICM group, as compared with the control group, at both 6 and 12 months. Patients with recurrent stroke or transient ischemic attack were fewer in the ICM group than in the control group.[41] Furthermore, Diamantopoulos et al.[42] reported that ICMs are a cost-effective diagnostic tool for the prevention of recurrent stroke in patients with CS.
| Conclusion | | |
There is an increasing data showing that significant morbidity is associated with silent AF. Recent studies have shown us which populations carry a high burden of this disease, and advancing technology is giving us new tools to detect it. It is still not clear which patients with brief episodes of AF deserve anticoagulation and clinical trials in this area are readily expected. Until further studies are available, anticoagulation should be individualized and promoted attending to the CHADS2 and CHA2 DS2 VACs scores.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]
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