Focal Atrial Tachycardia (FAT) – ECG

01 · Definition and clinical context

What is focal atrial tachycardia?

Focal atrial tachycardia is an organized atrial rhythm arising from a discrete site outside the sinus node. Electrical activation spreads centrifugally from that focus through the atrial myocardium. The resulting P waves are usually monomorphic and differ from the patient's sinus P-wave morphology.

The mechanism may be enhanced automaticity, triggered activity or localized re-entry (micro-re-entry). Focal atrial tachycardia can be paroxysmal or incessant. Persistent or frequently recurring tachycardia can produce tachycardia-induced cardiomyopathy, making recognition and appropriate follow-up clinically important.

Core diagnostic concept: look for organized, repetitive atrial activation with a consistent non-sinus P-wave morphology. Then establish whether the atrial rhythm is independent of, or conducted through, the AV node.

Terminology matters

“Atrial tachycardia” is an umbrella term in broad usage. Focal atrial tachycardia should be distinguished from macro-re-entrant atrial tachycardias (including typical atrial flutter) and multifocal atrial tachycardia. These are not interchangeable ECG diagnoses and their management differs.

Typical presentationPalpitations, dyspnoea, chest discomfort, light-headedness or occasionally syncope. Some patients are asymptomatic.

Clinical courseEpisodes may start and stop abruptly, or show gradual acceleration (“warm-up”) and deceleration (“cool-down”), particularly with automaticity.

02 · Electrophysiology

Mechanisms and contributing conditions

Enhanced automaticityAn ectopic atrial focus develops an increased spontaneous phase-4 depolarization rate. Warm-up and cool-down may be observed.

Triggered activityAfterdepolarizations initiate repetitive atrial firing. Some triggered focal tachycardias may respond to adenosine.

Localized re-entryA small re-entrant circuit within atrial tissue can generate a focal-appearing activation pattern.

AV node is a separate part of the pathwayThe atrial focus may continue despite transient AV block; ventricular rate therefore need not equal atrial rate.

Potential associated factors

Digoxin toxicity, particularly when atrial tachycardia coexists with AV nodal suppression.
Atrial scar or structural substrate, including ischaemic heart disease and previous atrial procedures.
Catecholamine excess and stimulant exposure (including cocaine and high caffeine intake).
Alcohol, congenital cardiac abnormalities, and idiopathic cases.

Clinical correlation: review medications and possible toxicity, electrolytes, precipitating illness and structural heart disease. The ECG alone does not establish the underlying cause.

03 · Characteristic morphology

ECG features of focal atrial tachycardia

Interpret the atrial signal first. The P wave is the key surface ECG clue because its morphology reflects the direction of atrial activation from the ectopic site.

ECG feature	Typical finding	Interpretive value
Atrial rhythm	Organized, usually regular; monomorphic P waves	Supports a single dominant atrial focus.
Atrial rate	Conventionally ≥100 bpm for focal AT in the ESC definition	Count atrial depolarizations, not only QRS complexes.
P-wave morphology	Abnormal compared with sinus P waves; consistent beat-to-beat	Suggests an ectopic atrial activation origin.
Inferior leads	May be inverted when activation is directed superiorly from a caudal focus	Provides a clue to the direction of atrial activation; not a stand-alone localization diagnosis.
Baseline	Discrete P waves with an intervening isoelectric segment may be seen	Supports focal AT, but does not exclude scar-related macro-re-entry.
AV conduction	1:1 or variable; AV block can occur	Variable conduction may reveal atrial activity that would otherwise be obscured.
QRS	Usually narrow unless pre-existing or rate-related aberrancy, bundle branch block, or pre-excitation	QRS width describes ventricular activation, not the atrial origin.

Source ECG example 1 · 120 bpm

Original 12-lead ECG example 1 from the supplied Focal Atrial Tachycardia PDF, showing narrow-complex rhythm at approximately 120 beats per minute with consistent abnormal P waves. — Figure 1. Focal atrial tachycardia example 1. The supplied source describes a narrow-complex tachycardia at 120 bpm. Each QRS is preceded by an abnormal P wave, upright in V1 and inverted in leads II, III and aVF, with consistent morphology throughout. Source: *Focal Atrial Tachycardia (FAT)(1).pdf*, PDF page 3, Example 1. Image extracted from the supplied page; tracing morphology and lead labels retained.

How to read Figure 1: identify the repetitive P waves and compare their morphology across beats. The negative P waves in the inferior leads indicate an atrial activation vector directed away from the inferior leads. The upright P wave in V1 is part of this example's morphology; it should not be treated as a universal FAT pattern.

Source ECG example 2 · source-labelled rate 95 bpm

Original 12-lead ECG example 2 from the supplied Focal Atrial Tachycardia PDF, showing a narrow-complex rhythm with biphasic P waves in V1 and inverted P waves in inferior leads and V3 to V6. — Figure 2. Focal atrial tachycardia example 2 (as labelled by the source). The source describes a narrow-complex rhythm at 95 bpm, with biphasic P waves in V1, inverted P waves in II, III and aVF, and inverted P waves in V3–V6. Source: *Focal Atrial Tachycardia (FAT)(1).pdf*, PDF page 3, Example 2. Image extracted from the supplied page; tracing morphology and lead labels retained.

Rate-definition caveat: the 2019 ESC guideline defines focal AT as an organized atrial rhythm ≥100 bpm. The supplied PDF labels its second example as FAT despite reporting a rate of 95 bpm. The source does not clarify whether 95 bpm refers to the atrial rate, ventricular rate, or a borderline rhythm. Therefore, this example is retained faithfully but should not be used to redefine the conventional rate threshold. Confirm the atrial rate directly on the tracing and consider the full clinical context.

What P-wave polarity can—and cannot—tell you

Negative P waves in II, III and aVF suggest activation moving superiorly, often associated with a low atrial origin.
P-wave polarity in V1 and the lateral precordial leads can help distinguish right- from left-sided or septal origins, but localization rules are imperfect.
Compare tachycardia P waves with the patient's sinus P waves whenever a sinus-rhythm ECG is available.
Do not assign a precise anatomic focus from one or two leads alone; electrophysiology mapping is needed for definitive localization.

04 · Practical approach

Systematic ECG interpretation: step by step

Check the recording. Confirm patient identity, lead placement, calibration (usually 25 mm/s and 10 mm/mV) and artefact. Review the full 12-lead tracing and a rhythm strip.
Determine ventricular rate and regularity. Measure RR intervals. A regular narrow-complex tachycardia narrows the differential but does not identify the mechanism.
Find the P waves. Inspect inferior leads and V1 carefully. Look before, within and after QRS complexes and T waves. Use a long rhythm strip when necessary.
Measure the atrial rate separately. Use PP intervals. Do not assume the ventricular rate equals the atrial rate, especially when AV block or variable conduction is present.
Compare P-wave morphology. Determine whether P waves are monomorphic and whether their axis and shape differ from sinus rhythm. Consistent abnormal P waves support a focal source.
Assess the P:QRS relationship. Establish 1:1 conduction, a fixed conduction ratio, variable AV block, or AV dissociation. Atrial activity continuing through AV block is an important clue to an atrial tachycardia.
Measure PR, RP and QRS intervals. Determine whether atrial activation precedes or follows ventricular activation. A short RP interval with retrograde P waves raises AVNRT or junctional tachycardia as alternatives.
Inspect the baseline and atrial pattern. Discrete P waves with intervening isoelectric segments favour focal AT; continuous flutter activity raises macro-re-entrant atrial tachycardia. An isoelectric interval alone is not definitive.
Look for onset/offset behaviour. Gradual acceleration or deceleration can support enhanced automaticity. Abrupt onset and termination can occur with re-entrant mechanisms, but neither feature is diagnostic in isolation.
Integrate the clinical context. Assess symptoms, haemodynamic status, medications (especially digoxin), structural heart disease, electrolytes and possible triggers. State uncertainty when the surface ECG cannot distinguish mechanisms.

Practical rule: in a regular narrow-complex tachycardia, do not stop after measuring the ventricular rate. The decisive step is often careful identification of atrial activity and its relationship to the QRS complexes.

05 · Diagnostic framework

Diagnostic criteria and supporting clues

There is no single P-wave axis or surface morphology that identifies every focal atrial tachycardia. The diagnosis is based on the combined rhythm pattern, atrial activity and clinical/electrophysiological context.

Core patternOrganized atrial rhythm from a discrete non-sinus origin, conventionally ≥100 bpm, with centrifugal atrial activation.

Supportive surface ECGMonomorphic P waves with morphology different from sinus rhythm; stable PP intervals; discrete P waves and often an isoelectric interval.

Conduction clueAV block or variable AV conduction may expose atrial activity and demonstrate that the atrial rhythm is not dependent on each ventricular response.

LimitationsSurface ECG may not reliably distinguish focal AT from some scar-related macro-re-entrant atrial tachycardias or other SVTs.

Rate definition follows the 2019 ESC SVT guideline. The supplied source's 95-bpm example is explicitly identified as a source inconsistency/caveat above.

06 · Differential diagnosis

Distinguishing FAT from other supraventricular rhythms

Rhythm	P-wave / atrial pattern	Useful distinguishing clues
Sinus tachycardia	Sinus P-wave axis and morphology; usually 1:1 AV conduction	Gradual rate change and an identifiable physiological driver are common. Compare with baseline sinus P waves.
Typical atrial flutter	Continuous organized atrial activity, often saw-tooth in inferior leads; atrial rate often around 250–350 bpm	Look for flutter waves and fixed or variable AV conduction. Atypical flutter may not show a classic saw-tooth pattern.
Multifocal atrial tachycardia	Irregular atrial rhythm with at least three distinct P-wave morphologies, variable PP/PR/RR intervals	Three or more P-wave morphologies and an irregular rhythm distinguish MAT from a single focal source.
AVNRT	P waves often hidden in or immediately adjacent to QRS; retrograde atrial activation may be present	Often regular, abrupt-onset narrow-complex tachycardia with short RP; pseudo-r' in V1 or pseudo-S in inferior leads may occur.
Orthodromic AVRT	Retrograde P waves commonly follow the QRS	Assess RP interval and evidence of an accessory pathway in sinus rhythm (pre-excitation may be absent in some patients).
Junctional tachycardia	Retrograde P waves may be before, within or after QRS; AV dissociation can occur	Consider a junctional origin when P waves are retrograde and closely coupled to QRS, while integrating age, context and EP features.

Important limitation: a discrete P wave and isoelectric baseline support focal AT but do not exclude macro-re-entrant atrial tachycardia, particularly in patients with atrial scar or previous atrial surgery/ablation. If the mechanism remains uncertain, document the differential rather than overstate certainty.

07 · Clinical significance

Clinical presentation, complications and assessment

Symptoms range from none to palpitations, dyspnoea, chest discomfort, presyncope or syncope. Clinical impact depends on ventricular response, duration, underlying cardiac disease and haemodynamic reserve.

Haemodynamic compromise: hypotension, altered mental status, ischaemic chest pain, acute heart failure or shock requires urgent assessment and treatment according to the patient's condition.
Tachycardia-induced cardiomyopathy: incessant or recurrent sustained tachycardia can impair LV systolic function; assess ventricular function when clinically indicated.
Potential causes: review medication exposure, digoxin level when relevant, electrolytes, thyroid status when indicated, and structural heart disease.
Further rhythm assessment: ambulatory monitoring may clarify onset/termination, atrial rate, intermittent AV block and burden of tachycardia.

08 · Management principles

Management overview

Management depends on haemodynamic status, symptoms, mechanism, underlying substrate and whether the tachycardia is recurrent or incessant. The following is an educational overview, not a patient-specific treatment protocol.

Acute assessment

Assess airway, breathing, circulation, blood pressure, perfusion, mental status and evidence of acute heart failure or ischaemia.
If unstable, follow the local emergency tachyarrhythmia pathway and consider synchronized electrical cardioversion. In incessant automatic focal AT, recurrence after cardioversion may occur.
In stable patients, obtain a 12-lead ECG during the rhythm, identify the atrial mechanism, address reversible triggers and seek specialist input as appropriate.

Pharmacological considerations

For selected stable patients, beta-blockers or non-dihydropyridine calcium-channel blockers (diltiazem or verapamil) may slow AV conduction and/or terminate some focal ATs. Intravenous adenosine may terminate selected triggered focal ATs, but it may instead produce transient AV block and reveal continuing atrial activity. Response to adenosine is not by itself proof of a specific mechanism.

Safety considerations: intravenous verapamil/diltiazem are contraindicated in hypotension or HFrEF; intravenous beta-blockers are contraindicated in decompensated heart failure. Drug choice requires assessment of ventricular function, blood pressure, pre-excitation, comorbidities and local protocols. Avoid treating a rhythm label without confirming the clinical context.

Long-term strategy

Address the underlying cause and document arrhythmia burden. Beta-blockers or calcium-channel blockers may be considered for ongoing symptom/rate control in appropriate patients. Catheter ablation is an important definitive option for recurrent focal AT, particularly when incessant tachycardia causes tachycardia-induced cardiomyopathy or symptoms persist despite medical therapy. Electrophysiology study and mapping identify the earliest activation site.

09 · Pitfalls and pearls

Common diagnostic pitfalls

Calling every regular narrow-complex tachycardia AVNRT without actively searching for P waves.
Assuming a ventricular rate below 100 bpm excludes atrial tachycardia without measuring the atrial rate and checking AV conduction.
Using inferior-lead P-wave inversion as a definitive diagnosis or exact focus-localization marker.
Assuming an isoelectric baseline excludes atrial flutter or other macro-re-entrant tachycardia.
Confusing a single consistent ectopic P-wave morphology with MAT, which requires at least three distinct P-wave morphologies and an irregular rhythm.
Interpreting transient AV block after adenosine as termination of the atrial arrhythmia when atrial activity continues.
Over-relying on automated ECG interpretation or a short rhythm strip when a full 12-lead ECG or ambulatory recording is available.

Clinical pearls

Count P waves and QRS complexes separately.
Compare ectopic P waves with sinus P waves from the same patient whenever possible.
Variable AV block can be diagnostically useful because it unmasks atrial activity.
Warm-up/cool-down supports enhanced automaticity but is not exclusive to it.
Incessant focal AT warrants consideration of LV function and tachycardia-induced cardiomyopathy.

10 · Source-based ECG practice

Interpretation practice: two supplied ECG examples

These are educational interpretations of the two tracings reproduced from the supplied PDF. No additional patient history or clinical measurements have been invented.

Example 1 — 120 bpm

The source describes a narrow-complex rhythm at 120 bpm.
Each QRS is preceded by an abnormal P wave.
P waves are upright in V1 and inverted in II, III and aVF.
P-wave morphology is consistent throughout.
The source interpretation is focal atrial tachycardia.

Example 2 — 95 bpm

The source describes a narrow-complex rhythm at 95 bpm.
P waves are biphasic in V1 and inverted in II, III, aVF and V3–V6.
P-wave morphology is consistent throughout.
The source labels this focal atrial tachycardia; however, the stated rate is below the ≥100 bpm ESC definition. Verify the atrial rate and consider the source's rate-label ambiguity before using it as a definitive teaching criterion.

11 · Knowledge check

Test your ECG interpretation

A regular narrow-complex rhythm shows identical abnormal P waves, with P waves continuing at a regular rate during transient AV block. Which diagnosis is most strongly supported?

Typical AVNRT Multifocal atrial tachycardia Focal atrial tachycardia Sinus tachycardia

Which feature most strongly supports multifocal atrial tachycardia rather than a single focal atrial tachycardia?

One consistent abnormal P-wave morphology At least three distinct P-wave morphologies with an irregular rhythm A narrow QRS complex Negative P waves in the inferior leads alone

According to the 2019 ESC definition, what is the conventional minimum atrial rate for focal atrial tachycardia?

≥100 bpm ≥60 bpm ≥150 bpm ≥250 bpm

12 · Quick reference

Focal atrial tachycardia: key takeaways

Question	Key point
Where does it arise?	A discrete atrial focus outside the sinus node.
What is the hallmark?	Organized atrial rhythm with consistent abnormal (non-sinus) P-wave morphology.
Rate threshold?	Focal AT is conventionally defined as an atrial rate ≥100 bpm in the 2019 ESC guideline.
What is the QRS?	Usually narrow unless aberrancy, bundle branch block or pre-excitation is present.
What helps reveal it?	Careful P-wave analysis, PP measurement, AV relationship assessment and sometimes transient AV block.
What must be excluded?	Flutter/macro-re-entry, MAT, sinus tachycardia, AVNRT, AVRT and junctional tachycardia.
Why does it matter?	Persistent/incessant tachycardia can cause tachycardia-induced cardiomyopathy.

13 · References and further reading

References

Brugada J, Katritsis DG, Arbelo E, et al. 2019 ESC Guidelines for the management of patients with supraventricular tachycardia. European Heart Journal. 2020;41(5):655–720. doi: 10.1093/eurheartj/ehz467. Primary guideline reference for definition, ECG diagnosis and management principles.

Page RL, Joglar JA, Caldwell MA, et al. 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients With Supraventricular Tachycardia. Circulation. 2016;133:e506–e574. doi: 10.1161/CIR.0000000000000311.

Buttà C, Tuttolomondo A, Giarrusso L, Pinto A. Electrocardiographic diagnosis of atrial tachycardia: classification, P-wave morphology, and differential diagnosis with other supraventricular tachycardias. Annals of Noninvasive Electrocardiology. 2015;20(4):314–327. doi: 10.1111/anec.12246.

Poutiainen AM, Koistinen MJ, Airaksinen KEJ, et al. Prevalence and natural course of ectopic atrial tachycardia. European Heart Journal. 1999;20(9):694–700.

Burns E, Buttner R. Focal Atrial Tachycardia (FAT). Life in the Fast Lane (LITFL) ECG Library. 1 August 2020. Supplied PDF source used for the two ECG examples and source-described morphology. LITFL ECG Library.

Image licensing note: the supplied LITFL PDF states that its content is licensed under Creative Commons Attribution–NonCommercial–ShareAlike 4.0 (CC BY-NC-SA 4.0), based on work at litfl.com. This page preserves attribution and does not alter the ECG tracings. The NonCommercial condition may restrict use on a monetized/commercial Appcardio website; obtain permission or legal/licensing review before public deployment. User-supplied access to a PDF does not itself grant redistribution rights.