Can we get some pictures of atrial fibrillation and atrioventricular blocks?

ECG Characteristics of Atrial Fibrillation and Atrioventricular Blocks

Atrial Fibrillation ECG Features

Atrial fibrillation displays three cardinal ECG features: absolutely irregular RR intervals without any repetitive pattern, absence of distinct P waves replaced by fibrillatory waves, and an atrial cycle length (when visible) that is variable and less than 200 ms. 1

Key Diagnostic Criteria

• The RR intervals are completely irregular (termed "arrhythmia absoluta"), meaning they follow no predictable pattern whatsoever 1
• P waves are entirely absent on the surface ECG, replaced by rapid fibrillatory waves of variable amplitude, shape, and timing 2
• Some apparently regular atrial electrical activity may be visible in certain ECG leads, most commonly in lead V1, but these are not true organized P waves 1
• The ventricular response is completely irregular when AV conduction is intact 1

Visual Appearance

• Fibrillatory waves replace normal P waves and appear as irregular undulations on the baseline 1
• The baseline shows continuous irregular atrial activity without distinct waves 1
• Figure 1 from the ACC/AHA/ESC guidelines demonstrates AF with controlled ventricular response, showing the characteristic absence of P waves and irregular ventricular rhythm 1

Rate Characteristics

• The atrial rate when visible is typically greater than or equal to 300 bpm (cycle length less than 200 ms) 1
• The ventricular rate varies widely depending on AV nodal conduction and autonomic tone 1
• Patients on antiarrhythmic drugs may demonstrate slower atrial cycle lengths during AF 1

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Atrial Flutter ECG Features

Atrial flutter exhibits a characteristic saw-tooth pattern of regular flutter (F) waves without an isoelectric baseline between deflections, most prominent in leads II, III, aVF, and V1. 1, 3

Classic Pattern Recognition

• The saw-tooth pattern consists of regular atrial activation at rates of 240-320 bpm in the untreated state 1, 3
• Flutter waves are inverted in ECG leads II, III, and aVF and upright in lead V1 in typical atrial flutter 1
• There is no isoelectric baseline between the flutter wave deflections, distinguishing it from focal atrial tachycardia 1
• Figure 2 from the ACC/AHA/ESC guidelines shows typical atrial flutter with variable AV conduction and the characteristic saw-tooth F wave pattern 1

Atrial Flutter with 2:1 AV Block

Atrial flutter commonly presents with 2:1 AV block, resulting in a regular ventricular rate most characteristically around 150 beats per minute. 1, 3

• The atrial rate remains 240-320 bpm, but only every other atrial impulse conducts to the ventricles 3
• The resulting ventricular rate is 120-160 bpm, with 150 bpm being the most typical rate 1, 3
• The 2:1 block can obscure flutter waves because every other flutter wave may be buried in the QRS complex or T wave 3

Critical Diagnostic Pitfall

When you encounter a regular narrow-complex tachycardia at approximately 150 bpm, always suspect atrial flutter with 2:1 block until proven otherwise. 3

• To unmask hidden flutter waves, perform vagal maneuvers or administer adenosine to transiently increase AV block, which slows the ventricular rate and reveals the underlying flutter waves more clearly 3
• Examine leads II, III, aVF, and V1 most carefully, as flutter waves are typically most visible in these leads 1, 3

Distinguishing Flutter from Fibrillation

• Atrial flutter is usually readily distinguished from AF, but when atrial activity is prominent in multiple ECG leads, AF may be misdiagnosed as atrial flutter 1
• The ECG pattern may fluctuate between atrial flutter and AF in the same patient, reflecting changing atrial activation patterns 1

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Atrioventricular Blocks

First-Degree AV Block

First-degree AV block is defined by PR interval prolongation greater than 200 ms, which can result from either AV nodal/His conduction delay or right intra-atrial conduction delay. 4

• In patients with AF and atrial flutter, first-degree AV block is significantly more prevalent (21-41%) compared to reference populations (8%) 4
• Right intra-atrial conduction delay accounts for 39-63% of first-degree AV block cases in patients with AF or atrial flutter, meaning the AH and HV intervals are normal despite PR prolongation 4

Second-Degree AV Block (2:1 Block)

In 2:1 AV block, every other atrial impulse fails to conduct to the ventricles, and the location of block can be inferred from PR interval and QRS duration. 5

• A normal PR interval with wide QRS suggests infranodal disease (His-Purkinje system) 5
• A prolonged PR interval with narrow QRS is more suggestive of AV nodal disease 5
• Block within the His bundle is suspected when 2:1 AV block occurs with both normal PR and normal QRS intervals 5

Complete (Third-Degree) AV Block

Complete heart block occurs when the atrial rhythm is totally independent of a junctional or lower escape rhythm, with no relationship between P waves and QRS complexes. 5

Complete AV Block Coexisting with Atrial Fibrillation

When AF coexists with complete AV block, the ECG shows absence of P waves (replaced by fibrillatory waves) with a regular ventricular rhythm—a paradoxical finding that is often misinterpreted. 6

• The regular ventricular rhythm in the setting of AF indicates complete AV dissociation with an escape rhythm 6
• This combination carries risk of sudden cardiac death and requires prompt recognition 6
• Before permanent pacing, exclude reversible causes including rate-limiting medications and electrolyte disturbances 6

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Practical Diagnostic Approach

Unmasking Atrial Activity

When the ventricular rate is rapid and obscures atrial activity, use vagal maneuvers, carotid massage, or intravenous adenosine to transiently increase AV block and reveal the underlying atrial rhythm. 1

• Ventricular pacing during electrophysiological study can remove QRS complexes superimposed on atrial activity 1
• A 12-lead ECG of sufficient duration and quality is necessary to properly evaluate atrial activity 1

Focal Atrial Tachycardia vs. Flutter

Focal atrial tachycardia typically shows discrete P waves with a clearly defined isoelectric baseline between P waves in all leads, distinguishing it from atrial flutter. 1

• The atrial rate in focal atrial tachycardia is typically 130-240 bpm, though it can range from 100-300 bpm 1
• At rapid rates or with intra-atrial conduction disturbances, focal atrial tachycardia can exhibit an atrial flutter pattern without isoelectric baseline 1
• P wave morphology helps localize the focus of origin before electrophysiological study 1