Atrial Fibrillation

Atrial fibrillation, AFib, or AF, is chaotic and irregular atrial electrical activity and contraction. The atria beat out of sync with the lower heart chambers called ventricles. AFib may have no symptoms for some people. But for some, it may cause a fast, pounding heartbeat, shortness of breath, or light-headedness. An ECG is an important tool in diagnosing AFib.

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AF is increasing in incidence and prevalence. The lifetime risk for over 40 years is approximately 25%. Hemodynamic instability- Cardiomyopathy, Cardiac failure, and embolic events such as stroke are its complications. Distinguishing Afib from a normal heartbeat on the ECG can be challenging even for experienced clinicians. This article will explore key differences between an atrial fibrillation ECG and a normal ECG.

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Here, we will discuss the features of AFib on ECG, including irregular rhythm, absent P waves, and fibrillatory waves. By understanding distinct patterns of a fib on an ECG, healthcare professionals can improve diagnosis and manage this standard potential life-threatening condition.

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Symptoms

• Palpitations-Feeling of fast fluttering or pounding heartbeat

• Chest pain

• Dizziness

• Fatigue

• Lightheadedness

• Reduced ability to exercise

• Shortness of breath

• Weakness

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Causes of atrial fibrillation

• Ischemic heart disease.

• Hypertension.

• Valvular heart disease

• Acute infections.

• Electrolyte imbalance
• Thyrotoxicosis

• Drugs.

• Alcohol

• Pulmonary embolism

• Pericardial disease

• Acid-base imbalance

• Create excitation syndrome

• Cardiomyopathies

• Pheochromocytoma

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Risk factors of AF

• Age over 65 years

• Family history and genetics

• Consumption of alcohol

• Drugs

• Physical activity, those participating in endurance sports and doing heavy work are more predisposed to it. Moderate physical activity has a protective role and lowers the risk of atrial fibrillation and other heart diseases.

• Smoking increases the risk. Exposure to secondhand smoke increases the risk, especially to the unborn child.

• Stressful situations, panic disorders, and other type of emotional distress.

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Mechanism of atrial fibrillation

The initiating factor is an impulse release from atrial ectopic focus (Premature atrial contraction). Atrial fibrillation is sustained by impulses from several ectopic foci within the atria in a disorganized manner; hence, AF tends to be fast and irregular.

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The ectopic focus of conduction in the heart releases electrical stimuli outside normal conduction pathways. Stimulus release from ectopic focus disturbs the normal conduction and even takes control of the pacemaker role of the SA node.

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• Focal activation mechanism: It starts from a specific spot in the heart due to overactive electrical signals or tiny re-entry circuits. They are often found in pulmonary veins that carry blood from the lungs to the heart.

• Multiple focus activation: In the multiple wavelet mechanism, several small wondering electrical waves are formed in the heart, creating re-entry circuits that help to sustain irregular heartbeat. If the left atrium is enlarged, it provides a greater surface for waves to keep moving and causing fibrillation.

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Classification of atrial fibrillation based on the duration of arrhythmia

• First diagnosed atrial fibrillation: It has never been diagnosed before, irrespective of duration and symptoms.

• Paroxysmal atrial fibrillation: with a duration of fewer than 7 days, and the arrhythmia is self-terminating in most cases, lasting less than 48 hours.

• Persistent atrial fibrillation: It lasts more than 7 days and requires intervention.

• Long-standing: persistent atrial fibrillation is continuous, lasting more than a year.

• Permanent atrial fibrillation is when both the patient and clinician have agreed to accept the condition. The numerous attempts to induce cardioversion and restore sinus rhythm have been discontinued.

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Atrial fibrillation in Wolff Parkinson -White syndrome

• AF occurs in 20% of patients with Wolff Parkinson White syndrome.

• The accessory pathway allows for rapid conduction to the ventricles, directly bypassing the AV node.

• Rapid ventricular rate results in degeneration to VT or VF.

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Other features of AF

• Ashman Phenomenon: conduction abnormalities seen in AF.

• Ventricular response in AF: The heart rate in atrial fibrillation depends on factors like AV node, vagal tone, and medications.

• There is a connection between Sick Sinus Syndrome and Sinus Node dysfunction.

• AF rate

           Typical AF Rate: is 110-160 bpm

                       RVR (Rapid Ventricular Response): AF rate is > 100bpm

                       Slow AF: AF with a rate <60 bpm, caused by hypothermia, digoxin toxicity, and     

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Normal ECG

Normal ECG has a  P wave, QRS complex, and T wave. The P wave represents atrial depolarization. QRS complex represents ventricular depolarization, and the T wave shows ventricular repolarization. The heart rate ranges between 60 and 100 beats per minute.

P Wave

• It is the first small upward wave.

• It indicates atrial depolarization (systole), during which excitation spreads from the SA node to all over the atrium.

• About 0.1 seconds after the P-wave begins, atria contracts. So, the P wave represents atrial systole.

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QRS complex

• The second wave begins as a little downward wave, continues as a large upright triangular wave, and ends as a downward wave.

• It represents ventricular depolarization systole.

• After the QRS wave begins, ventricles begin to contract. Hence, the QRS wave represents ventricular systole.

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T waves

• It is a 3rd small wave in the form of a Dome shape. And shows an upward deflection.

• It indicates ventricular repolarization diastole.

• It also represents the beginning of ventricular diastole.

• Atrial diastole merges with the QRS wave.

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P-R Interval

It represents the time required for an impulse to travel through the atria, AV node, and a bundle of His to reach the ventricles.

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S-T segment

• It is measured from the end of S to the beginning of the T wave.

• It represents the time when ventricle fibers are fully depolarised.

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Atrial Fibrillation ECG 

Atrial fibrillation electrocardiogram is completely arrhythmic. The R-R intervals are irregular and follow no pattern. Because of the chaotic atrial stimuli, the P-waves do not form; instead small atrial waves called F waves have different morphologies form.

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The conduction to the ventricles is through the normal conduction system. So, the QRS complex is narrow except for alterations in bundle branch block or aberrant conduction (Ashman Phenomenon).

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Heart rate.

The heart rate in atrial fibrillation is very variable. In patients having no anti-arrhythmic treatment, the heart rate is very high. Within adjusted treatment, AF presents has heart rates on the normal or even lower side.

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ECG features of Atrial fibrillation

• Irregularly irregular rhythm

• P waves absent

• The isoelectric baseline is absent

• The ventricular rate is variable

• QRS complexes usually < 120ms unless pre-existing bundle branch block, accessory pathway, or rate-related aberrant conduction

• Fibrillatory waves present are either fine (amplitude < 0.5mm) or coarse (amplitude > 0.5mm)

• Fibrillatory waves may mimic P waves, leading to misdiagnosis

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Key Differences between AF ECG and Normal ECG

Normal ECG shows a regular rhythm. The atrial and ventricular contractions are coordinated. And each distinct P wave. A QRS complex follows it. The PR interval is between 120 to 200 MS, and the QRS duration is 80-100 MS. Conversely, atrial fibrillation lacks distinct P waves and has erratic fibrillatory waves.

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The rhythm is irregularly irregular. R-R intervals vary, and there is an absence of consistent P-R intervals. The QRS complexes in AF are regular in shape, occurring at irregular intervals, indicating disorganized atrial activity and irregular ventricular response.

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Rhythm

It refers to the regularity and origin of heartbeats. A normal rhythm is called a sinus rhythm. It originates from the Sinoatrial node and is consistent. And varies between 60 to 100 beats per minute.

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• Normal ECG: Has a regular rhythmic pattern and a consistent R-R interval.

• AF ECG: Irregularly irregular rhythm with the variable R-R interval.

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Heart Rate

It is the number of heartbeats per minute. It reflects the heart's ability to pump blood efficiently.

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• Normal ECG: heart rate is typically between 60 to 100 beats per minute.

• AF ECG: Heart rate is rapid and exceeds 100 beats per minute.‍

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P Wave

• Normal ECG: P wave is present, upright, and uniform in leads I, II, V5, and V6.

• AF ECG: P wave is absent or appears as a series of small irregular fibrillatory waves.  

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QRS complex

It represents ventricular depolarization. Indicating. Electrical impulses spread through the ventricles, leading to their contraction. It lasts 80-100 milliseconds. And appears as a sharp, tall waveform following the P wave on ECG.

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• Normal ECG: QRS complex has standard duration and amplitude.

• AF ECG: The standard wave is affected by rapid heart rate and irregular rhythm.

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ST segment and T wave

Following the QRS complex, the ST segment represents the period of ventricular repolarization and should be flat. The T wave reflects the final phase of ventricular repolarization and appears as a smooth upward deflection.

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• Normal ECG: ST segment and T waves are regular.

• AF ECG: Rapid heart rate and irregular rhythm may affect the S-T segment and T wave. But usually, it is normal.

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Fibrillatory waves

Fibrillatory waves are irregular and rapid. They replace the P waves and appear as erratic small patterns on ECG reflecting chaotic atrial electrical activity.

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• Normal ECG: no fibrillatory waves present.

• AF ECG: Fibrillatory waves are present; they replace the normal P waves.

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Challenges in Afib ECG interpretation

• Distinguishing Afib from other arrhythmias: Conditions like atrial flutter and multifocal atrial tachycardia mimic Afib.

• Artifact interference: Poor electrode placement or patient movement can distort the ECG.

• Variable heart rate: Slow and rapid ventricular rate make interpretation challenging.

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ECG Interpretation in AF

ECG interpretation involves identifying key characteristics. Accurate interpretation is crucial for the diagnosis and effective management of AF.

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• Irregularly irregular rhythm.

• Absence of P waves.

• Presence of fibrillatory waves. Replacing the regular P waves.

• Irregularly placed QRS complexes.

• Varying R-R intervals indicate irregular ventricular rhythm response.

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Common pitfalls in atrial fibrillation ECG interpretation

Mistaking irregular rhythms or other arrhythmias, failing to recognize fibrillatory waves due to poor lead placement, and misinterpreting transient normal rhythms as AF are some of the common challenges in interpreting AF ECG.

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Inadequate electrode contact or movement artifacts are some more. Accurate analysis requires careful attention to the following details.

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Misdiagnosis or other arrhythmias

• Sinus rhythm and premature beats: Observe the regular P waves before each QRS complex.

• Atrial flutter: Has a regular atrial rhythm with the saw tooth pattern.

• Multifocal atrial tachycardia: Has multiple P-wave morphologies.

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Overlooking changes

• Intermittent AF: This may be sporadic, so multiple ECG needs to be taken for diagnosis.

• Slow AF: The irregular rhythm is less apparent.

• Ignoring underlying heart conditions.

• Structural heart disease: AF is often associated with underlying heart conditions such as coronary artery disease and hypertension‍

• Medication Effects: Certain medications affect heart rhythm and mimic AFib.

• Misinterpretation of artifacts

• Muscle artifact: It is differentiated by irregular shape and lack of association with heart rhythm

• Electrode noise: Identified by high-frequency oscillations.

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Artificial intelligence in AF ECG interpretation

Artificial Intelligence, AI, in atrial fibrillation, ECG interpretation enhances accuracy by quickly detecting irregularities in heart rhythms. AI algorithms identify AF earlier than the manual methods, reducing misdiagnosis.

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• Automated AF detection: AII algorithms identify AF-identifying patterns in ECG recordings and reduce errors due to human interpretations.

• Risk stratification: AI helps to assess AF-related complications such as stroke.

• Personalized treatment recommendations: A. I can assist in tailoring treatment plants based on individual patient characteristics and ECG findings.

• Early warning system: AI allows timely intervention and prevention of adverse events.

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Examples of AF in ECG

Let us see a few more examples

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Conclusion

Interpreting AF on an ECG strip is a fundamental skill for healthcare professionals. Irregular rhythm, absent P waves, and fibrillatory waves are the key features that help to diagnose it. Staying ahead with the latest tools and trends enhances ECG interpretation skills and improves patient outcomes. We at Gauze provide you with support for interpreting, treating, and managing Atrial Fibrillation.