Diagnosis

12-Lead Electrocardiogram

The 12-lead ECG remains the gold standard of diagnosing AF.8 The ECG will be positive for lack of a p-wave, an oscillatory baseline wave with varying amplitudes, irregular rhythm, and the classic irregularly irregular ventricular waves. Sensitivity and specificity of AF detection with a 12-lead ECG when interpreted by general practitioners is 80% and 92%, respectively.17 Detection of AF may require additional work-up if clinical suspicion of AF is high, yet initial 12-lead ECG is nonspecific.


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Holter Monitors

The 24-hour Holter monitor allows for early detection of arrhythmias in patients with a high clinical suspicion for AF but whose initial 12-lead ECG finding are inconclusive..18 A Holter monitor is a 5- to 7-lead battery-powered cardiac device hung around the neck or secured on the waist. Continuous monitoring for 24 hours is performed and recorded. Use of the Holter monitor is often covered by insurance and is recognized as an effective tool in detecting arrhythmias before complications occur. Use of the 24-hour Holter monitor in a clinical study has demonstrated a 96.3% sensitivity and 96.8% specificity for detecting AF.19 Despite its high sensitivity and specificity, the Holter monitor may still be insufficient in the detection of asymptomatic or paroxysmal AF, as they are less likely to be detected within a 24-hour period.14,18

Patch Monitors

Technological has contributed to the development of more convenient methods of outpatient continuous cardiac recording. The Zio patch, manufactured by iRhythm Technologies, Inc, is an FDA-approved, 14-day continuous monitoring system. The device is a low-profile, self-adhesive, water-resistant patch that is adheres to the left chest wall; no leads or wires are required. This simple design allows for convenient use without interfering with daily activities.

Compared with other monitoring devices, patients preferred the patch monitors: 93.7% of users found the patch comfortable to wear compared with 51.7% who wore the Holter monitor.20 The Holter monitor still outperforms the Zio patch in detecting arrhythmias within a 24-hour window, but the Zio patch has demonstrated benefits in detecting arrhythmias outside the 24- to-48-hour window.20 With a mean wear time of 10.9 days and a median wear time of 13.0 days, the Zio patch is a convenient option for detecting intermittent arrhythmias within a 14-day period.21

Cardiac Event Monitors

Cardiac event monitors are capable of monitoring heart activity from a couple of weeks to just over a month. This device is useful when patients report AF symptoms that occur more than 1 week apart from each other. Cardiac event monitors come in 2 forms: external loop memory recorder and handheld event recorder. The looping memory recorder begins recording and stores information from a few minutes before and after abnormal input from the chest leads. The handheld event recorder allows a patient to manually capture a recording when symptoms occur.22 Because of the design of the cardiac event monitors, which rely on symptomatic stimuli or manual activation of the patient, the sensitivity ranges from 31.3% to 71.0%.23 For those individuals with more intermittent symptomatic arrhythmias, however, these devices are a good option.

Implantable Loop Recorders

Implantable loop recorders (ILRs) are small devices that are implanted subcutaneously in the chest. Continuous heart monitoring can be performed with an IRL for up to 3 years. It is a powerful tool used to discover undetected paroxysmal AF.24 An IRL is indicated when short-term monitors fail to identify arrythmias and there remains a high suspicion of AF. New generations of ILRs incorporate P-wave detection algorithms, raising sensitivity and specificity for AF detection both to 97%.25 The ILR may also be used to monitor the long-term efficacy of radiofrequency ablation, cryoballoon ablation, and anticoagulation therapy.26 An advantage of the ILR is its self-sufficiency. It requires no maintenance by the patient. Individuals do not need to carry a device around with them like the Holter and event recorders, which require human maintenance. Tools similar to the ILR are helpful in achieving accurate and precise diagnosis of AF and its subtypes.

Transthoracic and Transesophageal Echocardiograms

A transthoracic echocardiogram is indicated in the initial evaluation in all patients with AF and looks at heart size, chamber size, and valvular function, and directs further work-up and treatment modalities. A transesophageal echocardiogram (TEE) more accurately determines pressures and flow of the heart chambers and wall motion abnormalities, and detects thrombus formation in the left atrium.27,28 Indications for the use of TEE are to guide treatment of direct current cardioversion for AF. Direct current cardioversion may pose a risk for a thromboembolic event if thrombus formation was present in the left atrium or left atrial appendage, and may require prior anticoagulation.29 The use of TEE is beneficial in detecting 5% to 15% of thrombus before direct current cardioversion.6 After the indicated AF work-up, TEE helps identify risks associated with AF, in addition to other possible conditions..

Additional WorkUp

When making a diagnosis of AF, additional studies are indicated to identify underlying causes, rule out other pathologies, and assess baseline disease severity. In addition to the diagnostic workup, initial studies include a complete blood count, complete metabolic panel, and thyroid-stimulating hormone.Initial studies help to identify comorbid or exacerbating conditions, such as infection, anemia, and hyperthyroidism, as well as abnormalities in renal function, hepatic function, electrolytes, and glucose levels. A chest radiograph should be performed and is useful in recognizing potential pulmonary disease or comorbid heart failure.

Detecting Subtypes of Atrial Fibrillation

Establishing the AF subtype helps tailor treatment and better understand the condition. Classifications of AF is based on the duration of symptoms and concurrent cardiac conditions (Table).6,30 AF is considered symptomatic in the presence of an irregular pulse, jugular venous flutter, palpitations, fatigue, dizziness, dyspnea, tachycardia, murmurs, or neurologic deficits, in addition to positive risk factors for AF.

Differential Diagnosis

A number of conditions can mimic AF and need to be ruled out, including atrial flutter, premature atrial contractions (PACs), and multifocal atrial tachycardia.31 Atrial flutter should be considered alongside AF when ECG findings are consistent with the absence of P waves and atrial tachycardia.32 Atrial flutter is characterized by a regular ventricular rhythm and a “sawtooth” pattern seen in the atrial leads II, III, and augmented limb lead aVF. PACs are caused by ectopic foci that fire before the next sinus impulse. ECG findings indicative of PAC include isolated interruptions of P-wave morphology with a regular rhythm. Patients with PACs can be differentiated from those with AF, as the PAC usually disappears when the heart rate is accelerated and is generally asymptomatic. Multifocal atrial tachycardia is considered as a differential with AF, as patients present with palpitations in both arrhythmias. The ECG displays 3 or more varying P-wave morphologies with an irregular P-P interval and increased rate of 100 to 140 beats per minute in patients with multifocal atrial tachycardia, which is not characteristic of AF.33

Differentiation may be obscure, which is why close attention to clinical symptoms, proper diagnostic workup, and use of the 12-lead ECG and indicated monitors are necessary for accurate distinction.

Related Articles

James Zapata, PA-C, is an emergency medicine physican assistant (EMPA) fellow at Arrowhead Regional Medical Center, in Colton, CA; Drew Zimmer, PA-C, is an EMPA at JFK Memorial Hospital, Indio, CA; Benjamin Rinard, PA-C, is an EMPA intern at St. Bernardine Medical Center in San Bernardino, CA; Amir Abdou, PA-C, is a PA at Western University of Health Sciences, Pomona, CA; Arielle Paamoni, PA-C, is a cardiology PA at Sherev Heart and Vascular Clinic, La Mesa, CA; and Catherine Chang Letherer, PA-C, is an assistant professor of Physician Assistant Education, Western University of Health Science, Pomona, CA.

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This article originally appeared on Clinical Advisor