Atrial Fibrillation on ECG

Electrocardiography (ECG) is one of the most essential tools in modern cardiology, allowing clinicians to visualize the electrical activity of the heart in real-time. Understanding abnormal rhythms, especially atrial arrhythmias, is crucial for diagnosis, risk stratification, and management. Among the most common atrial arrhythmias are Atrial Fibrillation (AF), Atrial Flutter, and Supraventricular Tachycardias (SVTs). Each of these conditions has unique ECG characteristics and clinical implications. This post explores these arrhythmias in depth, focusing on their ECG manifestations, pathophysiology, clinical significance, and management.

1. Introduction to Atrial Arrhythmias

Atrial arrhythmias arise from abnormal electrical activity originating in the atria. They can be broadly classified into:

Atrial Fibrillation (AF): Chaotic, irregular atrial activity causing irregular ventricular response.
Atrial Flutter: Rapid, regular atrial depolarization typically due to a macroreentrant circuit.
Supraventricular Tachycardias (SVTs): Rapid rhythms originating above the ventricles, often from reentrant circuits or automatic foci.

These arrhythmias can be symptomatic, causing palpitations, dizziness, syncope, or shortness of breath, or asymptomatic, detected incidentally on ECG.

2. Basics of ECG Interpretation

Before discussing specific arrhythmias, it is essential to review basic ECG components:

P wave: Represents atrial depolarization. Normal P wave duration is <120 ms, and amplitude <2.5 mm in limb leads.
PR interval: Time from atrial depolarization to ventricular depolarization (120–200 ms).
QRS complex: Ventricular depolarization, normally <120 ms.
QT interval: Total time for ventricular depolarization and repolarization.
RR interval: Distance between two successive R waves, reflecting heart rate regularity.

Alterations in these components provide clues about atrial arrhythmias.

3. Atrial Fibrillation (AF)

3.1 Pathophysiology

Atrial fibrillation is characterized by disorganized atrial electrical activity, often due to multiple rapidly firing ectopic foci, commonly located in the pulmonary veins. Key features:

Loss of coordinated atrial contraction.
Irregular conduction through the atrioventricular (AV) node.
Risk of thrombus formation in the atria, especially the left atrial appendage, leading to stroke.

3.2 ECG Characteristics

Irregularly irregular rhythm: No predictable pattern in RR intervals.
Absence of discrete P waves: Instead, fibrillatory waves (f waves) are seen.
- Fine (0.5–1 mm) or coarse (>1 mm) oscillations.
Variable ventricular response: Rate may be slow (<60 bpm, “AF with slow ventricular response”) or fast (>100 bpm, “AF with rapid ventricular response”).
QRS complex: Usually narrow unless there is pre-existing bundle branch block or aberrant conduction.
ST-T changes: Non-specific, may appear due to rate-related ischemia.

3.3 Clinical Implications

Most common sustained arrhythmia in adults.
Symptoms: Palpitations, fatigue, dyspnea, dizziness.
Complications: Stroke, heart failure, tachycardia-induced cardiomyopathy.

3.4 Management Principles

Rate control: Beta-blockers, calcium channel blockers, or digoxin.
Rhythm control: Antiarrhythmic drugs or electrical cardioversion.
Anticoagulation: To prevent thromboembolic events, guided by CHA₂DS₂-VASc score.
Catheter ablation: Considered in refractory cases.

4. Atrial Flutter

4.1 Pathophysiology

Atrial flutter is usually caused by a macro-reentrant circuit, most commonly in the right atrium around the tricuspid annulus. The atrial rate is typically 250–350 bpm, with variable AV conduction.

Types of atrial flutter:

Typical (cavotricuspid isthmus-dependent) flutter: Counterclockwise or clockwise rotation around the tricuspid valve.
Atypical flutter: Non-isthmus dependent, often post-cardiac surgery or structural heart disease.

4.2 ECG Characteristics

Sawtooth “flutter waves” (F waves):
- Best seen in leads II, III, aVF.
- Typically 250–350 atrial beats per minute.
Regular ventricular response: Often 2:1, 3:1, or variable AV conduction.
QRS complex: Narrow unless pre-existing bundle branch block.
Rhythm: Usually regular (contrast to AF, which is irregularly irregular).

4.3 Clinical Implications

Symptoms: Palpitations, fatigue, mild dyspnea.
High risk of thromboembolism, though slightly lower than AF.
Can lead to tachycardia-induced cardiomyopathy if persistent.

4.4 Management Principles

Rate control: Beta-blockers or calcium channel blockers.
Rhythm control: Electrical cardioversion is highly effective.
Anticoagulation: Similar indications as AF.
Catheter ablation: Very effective for typical flutter; success rates >90%.

5. Supraventricular Tachycardias (SVTs)

SVTs are rapid heart rhythms originating above the ventricles, usually in the atria or AV node.

5.1 Common Types

Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
Atrioventricular Reentrant Tachycardia (AVRT)
- Often associated with Wolff-Parkinson-White (WPW) syndrome.
Atrial Tachycardia (AT)
- Focal ectopic atrial activity.

5.2 ECG Characteristics

5.2.1 AVNRT

Regular, narrow QRS tachycardia (unless aberrant conduction occurs).
Rate: 140–250 bpm.
P waves often hidden within or just after QRS.
Sudden onset and termination (“paroxysmal” pattern).

5.2.2 AVRT (Orthodromic)

Narrow QRS tachycardia.
Retrograde P waves may appear after QRS.
Pre-excitation (delta wave) may be seen in sinus rhythm if WPW present.

5.2.3 Focal Atrial Tachycardia

P waves often abnormal in morphology.
Usually regular atrial and ventricular rhythm.
Rate: 100–250 bpm.

5.3 Clinical Implications

Symptoms: Palpitations, dizziness, chest discomfort, syncope in severe cases.
Often episodic with abrupt onset and termination.
Generally benign but can affect quality of life and occasionally lead to hemodynamic instability.

5.4 Management Principles

Acute termination:
- Vagal maneuvers (carotid massage, Valsalva maneuver).
- Adenosine: Rapid IV bolus for AVNRT or AVRT.
- Synchronized cardioversion if unstable.
Long-term therapy:
- Beta-blockers or calcium channel blockers.
- Catheter ablation: Definitive treatment for recurrent symptomatic SVT.

6. Distinguishing AF, Flutter, and SVTs on ECG

Feature	Atrial Fibrillation	Atrial Flutter	SVTs
Rhythm	Irregularly irregular	Usually regular	Regular
P waves	Absent; fibrillatory waves	Sawtooth F waves	Abnormal P waves or hidden
Rate (ventricular)	Variable	Usually 150 bpm (with 2:1 conduction)	140–250 bpm
QRS	Usually narrow	Usually narrow	Usually narrow
Onset	Gradual or sudden	Sudden	Sudden (paroxysmal)
AV conduction	Variable	Often fixed ratio	Reentrant or ectopic

7. Advanced ECG Concepts

7.1 Rate Control vs. Rhythm Control

Rate control: Slows ventricular response, letting atria fibrillate.
Rhythm control: Restores sinus rhythm.
Choice depends on symptoms, comorbidities, and risk of stroke.

7.2 Risk Stratification

CHA₂DS₂-VASc score: Assesses stroke risk in AF/flutter.
HAS-BLED score: Estimates bleeding risk with anticoagulation.

7.3 Recognizing Aberrant Conduction

Sometimes AF, flutter, or SVT may have wide QRS due to bundle branch block or pre-excitation.
Important for distinguishing from ventricular tachycardia.

8. Special Considerations

8.1 AF with Pre-Excitation (WPW)

Dangerous as rapid conduction through accessory pathway can lead to ventricular fibrillation.
ECG: Irregularly irregular wide-complex tachycardia, delta waves may appear.

8.2 Atrial Flutter with Variable Block

Ventricular response may appear irregular due to varying AV conduction (e.g., 2:1, 3:1, 4:1).
Careful analysis needed to differentiate from AF.

8.3 Tachycardia-Induced Cardiomyopathy

Persistent rapid atrial or supraventricular rhythms can reduce cardiac output.
ECG monitoring and early treatment prevent long-term damage.

9. Practical Tips for ECG Interpretation

Check rhythm first: Regular or irregular?
Look for P waves: Normal, absent, or abnormal morphology?
Measure intervals: PR, QRS, QT.
Assess ventricular rate: Fast, slow, or normal?
Search for underlying causes: Ischemia, structural heart disease, electrolyte imbalance.
Consider patient symptoms: Correlate with ECG findings for management urgency.

10. Case Examples

Case 1: Atrial Fibrillation

68-year-old male with palpitations.
ECG: Irregularly irregular rhythm, absent P waves, ventricular rate 110 bpm.
Diagnosis: AF with rapid ventricular response.
Management: Rate control with beta-blocker, anticoagulation initiated.

Case 2: Typical Atrial Flutter

55-year-old female with fatigue.
ECG: Regular sawtooth flutter waves in II, III, aVF, 2:1 AV conduction.
Diagnosis: Typical atrial flutter.
Management: Electrical cardioversion performed; started on anticoagulation.

Case 3: AVNRT

30-year-old male with sudden palpitations.
ECG: Narrow QRS tachycardia at 180 bpm, P waves hidden in QRS.
Diagnosis: AVNRT.
Management: Adenosine administered; rhythm restored to sinus.

11. Summary

Atrial fibrillation: Irregularly irregular rhythm, no P waves, variable ventricular rate.
Atrial flutter: Regular rhythm, sawtooth flutter waves, fixed or variable AV conduction.
Supraventricular tachycardias: Sudden onset, regular narrow QRS, may have hidden or abnormal P waves.

Key Points for Clinicians:

ECG is the cornerstone of diagnosis.
Correct identification guides management and reduces complications.
Rate vs. rhythm control and anticoagulation are central decisions in AF/flutter.
Catheter ablation offers curative potential for certain arrhythmias.
Early recognition prevents stroke, heart failure, and tachycardia-induced cardiomyopathy.

References (for further reading)

Zipes DP, Jalife J. Cardiac Electrophysiology: From Cell to Bedside. 8th Edition. Elsevier, 2020.
January CT, et al. 2019 AHA/ACC/HRS Guideline for the Management of Patients With Atrial Fibrillation. Circulation. 2019;140:e125–e151.
Knight BP. Clinical ECG Interpretation: A Textbook and Review. Elsevier, 2021.
Sharma AD, et al. Supraventricular Tachycardia. Circulation. 2016;134:1532–1548.
Kalman JM, et al. Atrial Flutter: Mechanisms and Management. Heart Rhythm. 2017;14:1890–1900.