ECG: electrocardiogram; AV: atrioventricular; PVCs: premature ventricular complexes; PACs: premature atrial complexes. Refer to UpToDate content on distinguishing supraventricular from ventricular rhythms. https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 13/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate If no atrial activity is detected or the morphology of atrial activity is unclear, use ECG amplification (digital magnification or increase in gain for the entire ECG signal). The ventricular rhythm associated with Mobitz I or II second-degree AV block is not irregularly irregular since there is a pattern to the variation in ventricular rate, but this pattern may not be immediately recognized. Graphic 132103 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 14/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Normal sinus rhythm with artifact Normal sinus rhythm with artifact: 12-lead ECG showing sinus rhythm (best seen in lead V1) along with baseline artifact that resembles AF (most evident in leads II, III, and aVF). The best way to avoid misinterpretation of this AF mimic is to carefully review all leads of the 12-lead tracing, noting any leads with evidence of regular P waves, a consistent PR interval, and a one-to-one correspondence of P waves to QRS complexes (in this case, lead V1 along with the occasional concurrent P waves in lead II demonstrates sinus rhythm). ECG: electrocardiogram; AF: atrial fibrillation. Graphic 132168 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 15/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Normal sinus rhythm with tremor Normal sinus rhythm with tremor: Lead V1 and lead II rhythm strips show sinus rhythm, evident from typical sinus P waves in leads V1 and lead II, with superimposed 3 to 5 Hz oscillations consistent with tremor activity. Graphic 132169 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 16/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Value of increasing ECG gain with possible AF Value of increasing ECG gain with possible AF. (A) Lead V1 and lead II rhythm strips show an irregularly irregular rhythm. At first glance, the rhythm looks li with moderate ventricular response. (B) However, when the gain is increased twofold, it is now apparent that there are P waves preceding each QR th (*). Some P waves (eg, the 1 , 2 5 , 10 , 11 , 12 , and 13 P waves appear to be nonsinus, suggesting frequent atrial premature complex st nd th th th th th rd , 6 , 7 , 8 , 9 , and 14 ) appear to be sinus P waves, while the 3 , 4 th th th th th In this case, magnification of the ECG tracing facilitates recognition of a common AF mimic that could be associated with a preliminary ECG machine interpretation of AF. ECG: electrocardiogram; AF: atrial fibrillation. Graphic 132167 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 17/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate ECG atrial fibrillation Atrial fibrillation. 12-lead ECG shows an irregularly irregular rhythm. Discrete P waves are not seen, and there is fibrillatory atrial activity, best seen in lead V1. The average heart rate is 102 bpm, with a normal axis, QRS duration, and QTc interval, and with nonspecific ST-T changes. ECG: electrocardiogram; bpm: beats per minute. Graphic 132160 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 18/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial fibrillation with a slow, moderate, and rapid ventricular response Atrial fibrillation with a slow (A), moderate (B), and rapid (C) ventricular response. Lead V1 and lead II rhythm strips show irregularly irregular rhythms without discrete P waves and with fibrillatory atrial activity. Graphic 132159 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 19/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial fibrillation with left bundle branch block Atrial fibrillation with LBBB. Rhythm strip shows an irregularly irregular rhythm. Discrete P waves are not seen, and there is fibrillatory atrial activity. The QRS duration is approximately 120 ms, and a complete LBBB is seen with a QS complex in lead V1. LBBB: left bundle branch block. Graphic 132162 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 20/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial fibrillation with complete heart block AF with complete heart block. Lead V1 and lead II rhythm strips show AF with complete heart block with a na complex junctional escape rhythm (A) or with a wide complex ventricular escape rhythm (B). AF: atrial fibrillation. Graphic 132164 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 21/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial fibrillation with fully paced QRS complexes Atrial fibrillation with fully paced QRS complexes (beats 1 ,5, 6, 7, 8). Native ventricular conduction is present (beats 2, 3, 4), and there are complexes (beats 9, 10) where the pacer stimulus occurs while the native complex is being conducted, resulting in a complex that has the same morphology as the native QRS complex (pacemaker pseudofusion). Graphic 132165 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 22/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial fibrillation with ventricular tachycardia AF with ventricular tachycardia. Lead V1 and lead II rhythm strips show AF with rapid ventricular response and the onset of monomorphic ventricular tachycardia at approximately 170 bpm. AF: atrial fibrillation; bpm: beats per minute. Graphic 132166 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 23/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial flutter Atrial flutter. (A) Lead V1 and lead II ECG tracings show AFL with a moderate ventricular response and variable AV conduct with flutter waves discernable in lead II. They are uniform, and occur at a rate of 300/min. Inferiorly directed flutter waves that are positive in V1 are suggestive of typical (cavotricuspid isthmus-dependent), countercloc AFL. (B) Lead V1 and lead II ECG tracings show AFL with moderate ventricular response and variable AV conductio with flutter waves in lead II at a rate of 272 bpm, consistent with typical AFL. ECG: electrocardiogram; AFL: atrial flutter; AV: atrioventricular; bpm: beats per minute. Graphic 132170 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 24/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Sinus rhythm with sinus arrhythmia Sinus rhythm with sinus arrhythmia. Lead V1 and lead II rhythm strips show an irregular rhythm with a ventricular rate that gradually increases, and with each QRS preceded by a sinus P wave, indicating sinus rhythm with sinus arrhythmia. This can mimic AF, especially if the P wave amplitude is low. AF: atrial fibrillation. Graphic 132171 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 25/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate ECG: Sinus arrhythmia and a junctional escape rhythm Sinus arrhythmia and a junctional escape rhythm. Lead V1 and lead II rhythm strips show an irregular rhythm that initiates with sinus rhythm with sinus arrhythmia and a gradual slowing of heart rate. When the heart rate slows below a rate of approximately 35 bpm, a junctional escape beat appears followed by an atrial premature complex (note the different P wave morphology in lead V1 compared with initial sinus beats). The variation in rate and the presence of some QRS complexes not preceded by a P wave contribute to this rhythm being incorrectly labeled as atrial fibrillation by a preliminary ECG machine interpretation. ECG: electrocardiogram; bpm: beats per minute. Graphic 132172 Version 3.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 26/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Normal sinus rhythm with Mobitz I second-degree AV block Normal sinus rhythm with Mobitz I second-degree AV block. Lead V1 and lead II rhythm strips show a regularly irregular rhythm with group beat. There are distinct P waves before each QRS as well as during the relative pauses. The P-P interval is constant, consistent with a sinus rhythm at a rate of 80 bpm. There is progressive prolongation of the PR interval followed by a dropped beat (nonconducted sinus P wave), reflective of Mobitz I second-degree AV block. AV: atrioventricular; bpm: beats per minute. Graphic 132173 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 27/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Normal sinus rhythm with an ectopic atrial rhythm Normal sinus rhythm with an ectopic atrial rhythm. Lead V1 and lead II rhythm strips show a somewhat irregular narrow QRS complex rhythm that starts off (first 3 beats) with sinus P waves, which then shift to a different (nonsinus) focus, evident by the change in P wave morphology in subsequent beats. Graphic 132174 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 28/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Atrial tachycardia with block Atrial tachycardia with block. Lead V1 and lead II rhythm strips show regular atrial activity at a rate of 160 bpm with variable AV block, consistent with atrial tachycardia with AV block. bpm: beats per minute; AV: atrioventricular. Graphic 132175 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 29/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Wandering atrial pacemaker Wandering atrial pacemaker. Lead V1 and lead II rhythm strips show an irregularly irregular rhythm. On close examination there are more than 3 different P wave morphologies preceding each QRS complex. As the rate is <100 beats per minute, the rhythm is wandering atrial pacemaker (rather than multifocal atrial tachycardia). Graphic 132176 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 30/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Multifocal atrial tachycardia Multifocal atrial tachycardia. Lead V1 and lead II rhythm strips show an irregularly irregular narrow QRS complex rhythm that, on first glance, looks like AF with rapid ventricular response. On closer examination, there are P waves preceding each QRS complex, and, overall, there are more than 3 different P wave morphologies, consistent with the diagnosis of multifocal atrial tachycardia. AF: atrial fibrillation. Graphic 132177 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 31/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Sinus rhythm with frequent PACs with aberrant conduction Sinus rhythm with frequent PACs with aberrant conduction. st rd th th th th (A) Lead V1 and lead II rhythm strips show sinus rhythm with the 1 , 3 , 5 , 7 , 9 , and 11 beats preced t by normal sinus P waves. The 2 nd th th th th th th , 4 , 6 , 8 , 10 , and 12 beats are all PACs. However, while the 4 , 10 th nd th th th and 12 beats conduct normally, the 2 aberrant conduction with a RBBB morphology evident in lead V1. In lead II, the aberrantly conducted PACs ha similar appearance to normally conducted PACs except for a deep terminal S wave and some QRS widening d to the rate-related RBBB. , 6 , 8 , and 12 beats conduct with a wide QRS complex due to rd (B) Lead V1 and lead II rhythm strips show sinus rhythm with a PAC with aberrant conduction (3 beat) and w an interpolated PVC (8 beat). th PACs: premature atrial complexes; RBBB: right bundle branch block; PVC: premature ventricular complex. Graphic 132178 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 32/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate AF with aberrant conduction and concealed conduction AF with aberrant conduction and concealed conduction. Lead V1 and lead II rhythm strips show AF with th rapid ventricular response. Note that the 5 and 6 QRS complexes, as well as the 18 and the 20 to th th th th the 30 QRS complexes, are wide with a right bundle branch pattern apparent in lead V1, while the QRS complexes for these beats in lead II are similar to native AF beats. These are all aberrantly conducted beats. th While the initial or isolated aberrant beats (5 , 18 , and 20 ) occur after a relative long-short interval th th th st th (Ashman phenomenon), the subsequent beats (6 and 21 to 30 ) occur with a short-short sequence but are aberrant due to concealed conduction. For more detail, refer to UpToDate content on the electrocardiogram in atrial fibrillation. AF: Atrial fibrillation. Graphic 132179 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 33/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate AF with Wolff-Parkinson-White syndrome AF with Wolff-Parkinson-White syndrome. 12-lead ECG showing AF with preexcitation. There is an irregular, wide-complex tachycardia, with many QRS complexes showing a slurred upstroke (delta wave). At times, the ventricular rate can be as high as 300 bpm. AF: atrial fibrillation; ECG: electrocardiogram; bpm: beats per minute. Reproduced with permission from: Nathanson LA, McClennen S, Safran C, Goldberger AL. ECG Wave-Maven: Self-Assessment Program for Students and Clinicians. Copyright 2021 Beth Israel Deaconess Medical Center. Available at: http://ecg.bidmc.harvard.edu (Accessed on August 2, 2021). Graphic 132180 Version 1.0 https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 34/35 7/5/23, 10:47 AM The electrocardiogram in atrial fibrillation - UpToDate Contributor Disclosures Brian Olshansky, MD Other Financial Interest: AstraZeneca [Member of the DSMB for the DIALYZE trial]; Medtelligence [Cardiovascular disease]. All of the relevant financial relationships listed have been mitigated. Zachary D Goldberger, MD, FACC, FHRS Other Financial Interest: Elsevier [Book royalties from Goldberger s Clinical Electrocardiography]. All of the relevant financial relationships listed have been mitigated. Steven M Pogwizd, MD No relevant financial relationship(s) with ineligible companies to disclose. Bradley P Knight, MD, FACC Grant/Research/Clinical Trial Support: Abbott [Electrophysiology]; Atricure [Electrophysiology]; Biosense Webster [Electrophysiology]; Biotronik [Electrophysiology]; Boston Scientific [Electrophysiology]; BSCI [Electrophysiology]; MDT [Electrophysiology]; Philips [Electrophysiology]. Consultant/Advisory Boards: Abbott [Electrophysiology]; Atricure [Electrophysiology]; Biosense Webster [Electrophysiology]; Biotronik [Electrophysiology]; Boston Scientific [Electrophysiology]; BSCI [Electrophysiology]; CVRx [Heart failure]; MDT [Electrophysiology]; Philips [Electrophysiology]; Sanofi [Arrhythmias]. Speaker's Bureau: Abbott [Electrophysiology]; Biosense Webster [Electrophysiology]; Biotronik [Electrophysiology]; Boston Scientific [Transeptal catheterization]; BSCI [Electrophysiology]; MDT [Electrophysiology]. All of the relevant financial relationships listed have been mitigated. Nisha Parikh, MD, MPH No relevant financial relationship(s) with ineligible companies to disclose. Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these are addressed by vetting through a multi-level review process, and through requirements for references to be provided to support the content. Appropriately referenced content is required of all authors and must conform to UpToDate standards of evidence. Conflict of interest policy https://www.uptodate.com/contents/the-electrocardiogram-in-atrial-fibrillation/print 35/35