Ectopic atrial rhythm arises from an atrial focus outside the sinus node. It is a common finding on the resting ECG and Holter monitoring, especially during sleep, in athletes, and in children, and most of the time it has no consequence.1-4

Criteria

  • P wave: morphology different from sinus and, usually, an axis outside the sinus range (0° to +90°, with a positive P wave in leads I, II, and aVF); a focus close to the sinus node produces a P wave almost identical to the sinus P wave.1,5-7
  • P–QRS relationship: one P wave before each QRS complex.1,8
  • PR interval: usually ≥ 120 ms.1,4,5,8,9
  • Heart rate: 50 to 99 bpm.1,4,5,8,9
RhythmHRP wavePR interval
Ectopic atrial rhythm50–99 bpmOne morphology, different from sinus; one P wave per QRS complexUsually ≥ 120 ms
Atrial escape rhythm (ectopic atrial bradycardia)< 50 bpmSame as aboveUsually ≥ 120 ms
Wandering atrial pacemaker< 100 bpm≥ 3 different morphologies; one P wave per QRS complex≥ 3 different values
Atrial tachycardia (focal or multifocal)≥ 100 bpmOne or several morphologiesVariable
Table 1. Nonsinus atrial rhythms according to rate and P wave. HR: heart rate.1,4,5,8,9
12-lead ECG with a long lead II rhythm strip, with a negative P wave in leads II, III, and aVF before each narrow QRS complex
Figure 1. Low ectopic atrial rhythm: negative P wave in leads II, III, and aVF, one before each QRS complex, with a PR interval of about 120 ms. Rate of about 85 bpm, narrow QRS.

Mechanism

  • Passive form (escape): the sinus node slows, because of vagal tone or disease, and a latent atrial pacemaker takes control.1,8,10
  • Active form: the atrial focus fires faster than the sinus node and overrides it.1,8,10
  • Course: usually transient, and easiest to recognize when the same tracing shows the sinus P wave for comparison.1,8

Wandering Atrial Pacemaker

  • Criteria: at least 3 P-wave morphologies and 3 different PR intervals, changing gradually over several beats; variable PP and RR intervals, usually one P wave per QRS complex, HR below 100 bpm.5,8,9
  • With HR ≥ 100 bpm: the same pattern is multifocal atrial tachycardia.5,9,10
  • Significance: usually a physiologic variant related to vagal tone; it also occurs in sinus node dysfunction, drug toxicity, and structural heart disease.7,9,10
Lead II strip with ten beats in which the P wave changes from positive to flattened and negative and back to positive, with the PR interval shortening and lengthening again
Figure 2. Wandering atrial pacemaker in lead II. Ten beats with narrow QRS complexes; the P wave changes gradually from positive (beats 1 to 3) to flattened (4 and 5) and negative (6 to 8) and returns to positive (9 and 10); the PR interval shortens from 180 ms to 130 ms and returns to 180 ms; RR slightly variable, with an HR of about 60 bpm. Arrows over the P waves.

Differential Diagnosis

  • Sinus rhythm and sinus arrhythmia: positive P wave in leads I, II, and aVF; in sinus arrhythmia, the P wave changes little and follows respiration.1,5,7,10,11
  • Junctional rhythm: negative P wave in the inferior leads with PR < 120 ms, or P wave within or after the QRS complex.1,5,7,10,11
  • Focal atrial tachycardia: same nonsinus P wave, with HR ≥ 100 bpm.1,5,7,10,11
  • Premature atrial complexes: premature, isolated P waves over an underlying sinus rhythm.1,5,7,10,11
  • Arm electrode reversal and dextrocardia: negative P wave and QRS complex in lead I; with reversal, normal precordial leads; with dextrocardia, poor R-wave progression.1,5,7,10,11
  • Right arm–left leg electrode reversal: negative P wave, QRS complex, and T wave in leads I, II, III, and aVF and positive in aVR; in an atrial focus, only the P wave changes.1,5,7,10,11

Key Points

  • Rate ranges: with HR < 50 bpm, it is atrial escape (ectopic atrial bradycardia); with HR ≥ 100 bpm, atrial tachycardia.1,4,5,8,9
  • Benign in most cases: with a normal HR and no symptoms, it is almost always benign; it is a normal finding during sleep, in athletes, and in children.2,3,9
  • Athletes: junctional escape rhythm or wandering pacemaker appears in up to 8% at rest, and sinus rhythm returns with exertion.2,3,9,10

Pitfalls

  • Calling a low atrial focus junctional rhythm. Both produce a negative P wave in the inferior leads; the PR interval separates them: usually ≥ 120 ms in the atrial focus, < 120 ms or P wave within or after the QRS complex in junctional rhythm.1,5,6,8
  • Calling electrode reversal an ectopic rhythm. If the P wave, QRS complex, and T wave change together in the limb leads, think of reversal; in an atrial focus, only the P wave changes.1,5,7,10,11
  • Missing sinus node dysfunction. Below 50 bpm while awake, ectopic atrial rhythm may be the manifestation of a subsidiary pacemaker taking control.4
  • Mistaking wandering pacemaker for atrial fibrillation. The rhythm is irregular, but the P waves are distinct and separated by an isoelectric baseline.8,9

Test Yourself

An ECG shows distinct P waves of four different morphologies, separated by an isoelectric baseline, one before each QRS complex, with three different PR intervals, an irregular RR, a narrow QRS complex, and a heart rate of 112 bpm. What is the rhythm diagnosis?

Choose an answer to see the explanation.

References

  1. Surawicz B, Knilans TK. Chou's Electrocardiography in Clinical Practice. 6ª ed. Philadelphia: Elsevier; 2008.
  2. Drezner JA, Sharma S, Baggish A, Papadakis M, Wilson MG, Prutkin JM, et al. International criteria for electrocardiographic interpretation in athletes: Consensus statement. Br J Sports Med. 2017;51(9):704-731.
  3. Drago F, Battipaglia I, Di Mambro C. Neonatal and Pediatric Arrhythmias: Clinical and Electrocardiographic Aspects. Card Electrophysiol Clin. 2018;10(2):397-412.
  4. Kusumoto FM, Schoenfeld MH, Barrett C, Edgerton JR, Ellenbogen KA, Gold MR, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2019;74(7):e51-e156.
  5. Samesima N, God EG, Kruse JCL, Leal MG, Pinho C, França FFAC, et al. Brazilian Society of Cardiology Guidelines on the Analysis and Issuance of Electrocardiographic Reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680.
  6. Pastore CA, Samesima N, Tobias NMMO, Pereira Filho HG. Eletrocardiografia Atual: Curso do Serviço de Eletrocardiografia do InCor. 3a ed. São Paulo: Atheneu; 2016.
  7. Das MK, Zipes DP. Electrocardiography of Arrhythmias: A Comprehensive Review (A Companion to Cardiac Electrophysiology: From Cell to Bedside). 2a ed. Philadelphia: Elsevier; 2022.
  8. Scheffer MK, De Marchi MFN, Alencar Neto JN, Felicioni SP, editores. Eletrocardiograma de A a Z. 1a ed. Barueri (SP): Manole; 2024.
  9. Issa ZF, Miller JM, Zipes DP. Clinical Arrhythmology and Electrophysiology: A Companion to Braunwald's Heart Disease. 3ª ed. Philadelphia: Elsevier; 2019.
  10. Goldberger AL, Goldberger ZD, Shvilkin A. Goldberger's Clinical Electrocardiography: A Simplified Approach. 9a ed. Philadelphia: Elsevier; 2018.
  11. Paul A, Jacob JR. Electrocardiographic lead reversals. Indian Pacing Electrophysiol J. 2023;23(6):205-213.