Available online at www.sciencedirect.com

Journal of Electrocardiology 45 (2012) 445–451www.jecgonline.com

Interatrial blocks. A separate entity from left atrial enlargement:a consensus report☆

Antonio Bayés de Luna, MD, PhD, a,⁎ Pyotr Platonov, MD, PhD, b Francisco G. Cosio, MD, c

Iwona Cygankiewicz, MD, d Carlos Pastore, MD, PhD, e Rafa Baranowski, MD, f

Antoni Bayés-Genis, MD, PhD, g Josep Guindo, MD, h Xavier Viñolas, MD, i

Javier Garcia-Niebla, RN, j Raimundo Barbosa, MD, k Shlomo Stern, MD, l

David Spodick, MD, PhDm

aInstitut Català Ciències Cardiovasculars, Barcelona, SpainbLund University Hospital, Lund, SwedencHospital Unviersitario de Getafe, Spain

dThe Division of Electrocardiology, Medical University of Lodz, Lodz, PolandeHeart Institute (InCor) - HC- FMUSP, Sao Paulo, Brazil

fInstitute of Cardiology, Warsaw, PolandgCardiology Service, Hospital Germans Trias i Pujol, Badalona, Spain

hCardiology Department, Hospital Parc Taulí, Sabadell, SpainiArrhythmias Unit, Hospital Sant Pau, Barcelona, Spain

jServicios Sanitarios del Área de Salud de El Hierro, Valle del Golfo Health Center, Canary Islands, SpainkCoronary Center, Hospital de Messejana Dr. Carlos A. Studart, Fortaleza-Ceará, BrazillEmeritus Professor of Medicine, The Hebrew University of Jerusalem, Jerusalem, Isarel

mMedical Service, St Vincent Hospital, University of Massachusetts Medical School, Worcester, MA, USA

Received 19 March 2012

Abstract Impaired interatrial conduction or interatrial block is well documented but is not described as an

☆ Sponsored byElectrocardiology.

⁎ CorrespondingHospital Sant Pau. Ba

E-mail address: ab

0022-0736/$ – see frodoi:10.1016/j.jelectroc

individual electrocardiographic (ECG) pattern in most of ECG books, although the term atrialabnormalities to encompass both concepts, left atrial enlargement (LAE) and interatrial block, hasbeen coined. In fact, LAE and interatrial block are often associated, similarly to what happens withventricular enlargement and ventricular block. The interatrial blocks, that is, the presence of delay ofconduction between the right and left atria, are the most frequent atrial blocks. These may be of firstdegree (P-wave duration N120 milliseconds), third degree (longer P wave with biphasic [±]morphology in inferior leads), and second degree when these patterns appear transiently in the sameECG recording (atrial aberrancy). There are evidences that these electrocardiographic P-wavepatterns are due to a block because they may (a) appear transiently, (b) be without associated atrialenlargement, and (c) may be reproduced experimentally. The presence of interatrial blocks may beseen in the absence of atrial enlargement but often are present in case of LAE. The most importantclinical implications of interatrial block are the following: (a) the first degree interatrial blocks arevery common, and their relation with atrial fibrillation and an increased risk for global andcardiovascular mortality has been demonstrated; (b) the third degree interatrial blocks are lessfrequent but are strong markers of LAE and paroxysmal supraventricular tachyarrhythmias. Theirpresence has been considered a true arrhythmological syndrome.© 2012 Elsevier Inc. All rights reserved.

Keywords: Interatrial blocks; Left atrial enlargement; Atrial abnormalities

International Society for Holter and Noninvasive

author. Institut Català Ciències Cardiovasculars,rcelona, Spain.ayes@csic-icc.org

nt matter © 2012 Elsevier Inc. All rights reserved.ard.2012.06.029

Introduction

It has been considered that an interatrial block existswhen there is a delay of conduction in some part of theBachmann bundle zone.1-4 The interatrial blocks are themost frequent and well-known blocks at atrial level. These

446 A. Bayés de Luna et al. / Journal of Electrocardiology 45 (2012) 445–451

are expressed in the electrocardiogram (ECG) by thepresence of P-wave duration that equals or exceeds 120milliseconds and presents usually a bimodal morphology,especially in leads I, II, and VL and inferior leads.2-4 Sincethen, there are several reports describing the ECG charac-teristics of different types of interatrial blocks, and alsohave been described their clinical implications.5-16 Thesepublications considered that, in spite that the ECG patternsfound in left atrial enlargement (LAE) are often signifi-cantly influenced by the presence of impaired interatrialconduction, the same as that happens with ventricularenlargement and ventricular blocks, these 2 ECG patternsmay appear individually, in spite that the atrial blocks ingeneral and the ECG patterns of interatrial blocks inparticular are not described and even mentioned as an ECGpattern in most of books of ECG.17-22 On the contrary, theterm atrial abnormalities23-25 has been coined to encompassboth the terms LAE and interatrial block. This consensusreport emphasizes the concept that interatrial blocks andatrial enlargement are separate entities and that interatrialblocks, similarly to other types of blocks at sinoatrial, AVjunctional, and ventricular level, are a specific ECG patternthat may present first, second, and third degree types ofconduction block.

Where the interatrial blocks are located

During sinus rhythm, interatrial conduction occurs viaanatomically distinct connections composed of workingmyocardium fibers already described in the beginning ofXX century by Bachmann, Wenckebach, and Thorel. Theprimary left atrium (LA) breakthrough is in the Bachmannbundle area in two thirds of cases, and the rest occursaround the fossa ovalis and rarely in the coronary sinus.15

It has been demonstrated16,26 that, in most of cases, P-wave morphology can be used to correctly identify the leftatrial breakthrough site and the corresponding atrialimpulse propagation route. It has to be also noted thatthe relative proximity of site of origin in the sinus originwithin the sinus node to the Bachmann bundle or posteriorconnections may affect P-wave morphology. Deteriorationof conduction between the right atrium and LA—theinteratrial blocks—is the most frequent and well-studiedtype of atrial conduction disturbance that is discussedbelow in detail.

When an ECG pattern may be considered as beingcaused by an interatrial block

There are 3 criteria that define an ECG pattern as beingcaused by a block or deterioration of conduction26:

(a) the ECG pattern may appear transiently, and thepattern may change abruptly and progressively tomore advanced forms;

(b) the ECG pattern may appear without associated otherprocesses such as cardiac chamber enlargement or

ischemia, although in many cases, 1 or more of theseconditions may coexist; and

(c) similar ECG pattern may be reproduced experimentally.

P-wave ECG patterns that meet criteria forinteratrial block

The P-wave ECG pattern of interatrial block maybe transient

Transient deterioration of interatrial conduction, that is,interatrial block, of first or third degree may appear in thesame ECG recording on a beat-by-beat basis (Fig. 5).These cases may be considered as an illustration of atrialaberrancy, a concept coined by Chung27 in 1972, similarlyto ventricular aberrancy.

The P-wave ECG pattern of interatrial block may appearwithout associated atrial enlargement9,28

The prolonged P-wave duration (P-wave duration ≥120milliseconds) may be present in the elderly and also as aconsequence of an acute illness as pericarditis or acutemyocardial infarction without atrial enlargement. In fact, inthese cases, the duration of P wave may be as long as that inLAE, but the P loop does not move so clearly backwards asin a figure 8 shape, which results in a much smaller nega-tive P-wave component in lead V1. However, the associa-tion of LAE and the presence of advanced interatrial block(wide P-wave ≥120 milliseconds and ± in leads II, III, andVF) are common.

The P-wave ECG pattern may be reproduced experimentally

Experimental studies29 have demonstrated that cuttingthe Bachmann bundle at either right or left atrial side resultsin a typical ECG pattern with wide P wave with biphasic ±morphology in inferior leads. It was also demonstrated30 thatan attenuation of interatrial conduction without affectingatrioventricular conduction may occur after ablation of inte-ratrial conduction zones along the right atrial septum. Thisintervention produces partial interatrial conduction blockwith an increase of P-wave duration.

How do we measure interatrial conduction time

We refer to the increased duration of P wave in surfaceECG and in VCG recordings. Other techniques that may offermore exact and/or precise measurements are signal averagingP wave, 2-bidimensional echocardiography with timeDoppler imaging, and intracardiac ECG measurement.31,32

May the interatrial blocks be of first, second, andthird degree

The interatrial blocks, by analogy with other types ofblock, (sinoatrial, atrioventricular, and/or bundle-brunchblock at the ventricular level), may be of first (partial),second (transient interatrial block, atrial aberrancy), or thirddegree (advanced) (see before) (Fig. 1).

Fig. 1. Diagram of atrial conduction under normal circumstances (A), first-degree interatrial block (B), and third-degree interatrial block with left atriaretrograde activation.

447A. Bayés de Luna et al. / Journal of Electrocardiology 45 (2012) 445–451

Electrocardiographic pattern of first-degree (partial)interatrial block

The P wave has a normal electrical axis. The electricalimpulse is conducted from the right to the LA through thenormal propagation route but with a delay (Fig. 1B). Theendocardial recording confirms that the coronary sinus acti-vation time is delayed.

∎ The ECG shows that (a) a P wave of 120 milli-seconds or more, usually bimodal that is especiallyvisible in leads I, II, or III, and (b) the P-wavemorphology in V1 often presents a P-wave negativemode that is less evident than in cases of LAEbecause in the absence of LAE, the P loop is directedin a less backward direction.

∎ In the presence of P wave 120 milliseconds or more,LAE is common. In fact, it has been considered thatthe wide and bimodal P wave of LAE is explainedmore because of underlying interatrial block ratherthan the longer distance that the impulse has to goacross.28

∎ The presence of isolated cases of partial interatrialblock may explain that, in some series, the specificityof the 120-millisecond cutoff for diagnosis of LAEmay be low (around 50%). However, when weconsider the association of P-wave prolongation witha P-wave negative terminal mode more than 40 milli-seconds in lead V1, the specificity is much higher.26

∎ Sometimes, it is possible to record the progressiveappearance of the ECG pattern of first-degree and laterthird-degree interatrial block (Fig. 2).

∎ It is often found in the elderly9,10 in the absence ofassociated LAE. Recently, it has been shown to be amarker of atrial fibrillation and cardiovascular and all-cause mortality.33

l

Electrocardiographic pattern of third-degree (advanced)interatrial block7,8,34

• It is an infrequent (≈1% of patients with valve heartdisease)7 but a very easily recognizable ECG pattern(Figs. 1C, 3-5).

• The electrical impulse is blocked in the upper andmiddle part of the interatrial septum, in the Bachmannbundle zone, and/or in the upper part of LA so thatretrograde left atrial activation occurs via muscularconnections in the vicinity of coronary sinus.7,8,16 Inrare occasions, right atrium and LA can demonstratedissociated electrical activity.26

• The ECG shows that (a) P-wave duration 120milliseconds or more and (b) the morphology of Pwave are usually bimodal in lead I and VL and biphasic[±] in leads II, III, and VF because of caudocranialactivation of the LA and also often in V1 and V2.

• The electrophysiologic mechanism underlying thisECG pattern has been explained using deductive ECG-VCG data correlated with recordings obtained fromthe high and low right atrium, coronary sinus, rightpulmonary artery, and esophagus and also with elec-troanatomic mapping.25,34

• It has been also demonstrated that the block may belocated in the LA not affecting conduction through theproximal Bachmann bundle. However, this does notmodify the terminal inferosuperior activation of theLA that explains the typical morphology ± in II, III,and VF. In fact, the same ± morphology appears aftercutting the Bachmann bundle in dogs at the right andleft sides of the septum.29

• Bayés de Luna et al7 defined the ECG-VCG criteria(Figs. 1C, 3 and 5) and demonstrated that this type ofblock is a very specific (90%) but insensitive marker ofLAE. The duration of P wave is 120 milliseconds or

Fig. 2. A, A 65-year-old patient with previous anterior myocardial infarction and left superoanterior hemiblock plus long and bimodal P wave in many leadwith plus minus morphology in V1 suggestive of LAE plus first-degree interatrial lock. B, One year later (left), there is a left bundle-brunch block pattern, andthe P wave is negative in II, III, and VF. However, this is not AV junctional rhythm because (a) the heart rate changes clearly along the day and with exercise ais well seen (see I and II of B), (b) the first part of P wave in II, III, and VF is isodiphasic (see II), (c) after premature atrial beat (III), a pattern of first-degreeinteratrial block appears, followed again by the pattern of third-degree interatrial block and (d) the PR interval is the same as before (160 ms).

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more (120-170 milliseconds in this series of 83 cases).7

However, it is the morphology of the P wave (± ininferior leads) that pinpoints that there is a retrogradeactivation of the LA. The positive mode of P waves inleads II, III, and VF is at times not well seen probablybecause of fibrosis, and the diagnosis of junctional

s

s

rhythm due to an apparently negative P wave in II, III,and VF may be made.It was demonstrated that this type of block is veryfrequently accompanied by paroxysmal atrial arrhyth-mia, especially atypical atrial flutter8,34,35 in patientswith valvular heart diseases and cardiomyopathies.

Fig. 3. Above: P wave ± morphology in I, II, and III typical of third-degree interatrial block with retrograde conduction to the LA in a patient with double aorticand mitral valve disease. Observe how the AP and the angle between the direction of the activation in the first and second parts of the P wave are measured. To theright, high esophageal ECG (HE) and endocavitary registrations (high right atrium and low right atrium) demonstrate that the electrical stimulus moves firsdownwards (high right atrium to low right atrium) and then upwards (low right atrium to HE). Below: P loop morphology in the 3 planes with the inscription othe second part moving upwards. HRA indicates high right atrium; LRA, low right atrium.

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Therefore, this association is considered an ECGclinical syndrome.34,36,37

• During long-term follow-up, especially in patientswith mitral valve disease or cardiomyopathy, thesuccessive appearance of first-degree and later third-degree interatrial block may be seen (Fig. 2).

Electrocardiographic pattern of second-degreeinteratrial block

∎ Similarly to the conduction block at the level of AVjunction, SA junction, or the ventricles, the interatrialblock may occur transiently on a beat-to-beat basis.

• In a typical case, the morphology of the P wave ischanging in the same recording from normal to

Fig. 4. Virtual anatomic rendering of the LA in the other patient with typical biphasic (±) P wave in leads II, III, and aVF suggestive of Bachmann bundle blockNote that early left atrial activation (white) occurs at the high septal wall, as expected for Bachmann bundle conduction. Activation does not progress through theleft atrial roof because of the presence of a large zone of low voltage (gray) that diverts activation toward the low septal (orange-yellow) then the low posterio(green) and finally the high posterior (violet) left atrial wall.

tf

interatrial block pattern or from first-degree interatrialblock to third-degree interatrial block pattern or viceversa, with or without relation to the precedingpremature beats, and may be considered as atrialaberrancy, similarly to ventricular aberrancy27 (Fig. 2).

Clinical implications of interatrial blocks

• Although the diagnosis of interatrial blocks isfrequently associated to LAE, there are cases,especially of first-degree interatrial blocks, withoutassociated LAE.

• The diagnosis of partial interatrial block by itself hasmany clinical implications that have been closely

.

r

Fig. 5. Typical ECG of third-degree interatrial block (P± in II, III, and VF and duration N120 milliseconds) in a patient with ischemic cardiomyopathy. Whenamplified, we can see the beginning of P in the 3 leads.

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studied by the Spodick group9,10,38 and others.15,33,34

It was demonstrated that the presence of first-degreeinteratrial block (prolonged interatrial conduction time[IACT]) is associated with abnormal left atrial function.Furthermore, IACT is related not only to anincreased P-wave duration but also to a prolongedPR interval.33,39 We know now that the prevalence offirst-degree interatrial block in the general population isvery high9,10 and that this condition has recently beenshown to be associated with cardiovascular and all-cause mortality.33

• The presence of third-degree interatrial block is veryfrequently associated with supraventricular arrhythmias.In fact, this type of interatrial block constitutes for someauthors a clear arrhythmological syndrome.34,36,37 Itspresence in patients with valvular heart disease orcardiomyopathy advices to study the risk of supraven-tricular arrhythmias (Holter ECG) to decide whether aprophylactic antiarrhythmic treatment and/or anticoagu-lation is needed. Bayés de Luna et al35 suggested thatantiarrhythmic treatment prevents recurrences of atrialtachycarrhythmia in these cases. D'Allonnes et al40

demonstrated the importance of synchronous biatrialpacing to prevent of recurrences of atrial fibrillation.

• It was also demonstrated that, in patients with sinusnode disease and intra-atrial conduction delay at theposterior triangle of Koch, low interatrial septumpacing was superior to right atrial appendage pacing inpreventing progression to persistent or permanentatrial fibrillation41 and is associated with the shortestatrial activation time compared with other atrial septalpacing sites in patients with prolonged P waves.42

• On the other hand, the presence of increased P-waveduration has been described as an important parameterwhen programming the optimal AV delay in patientswho require atrial pacing. In fact, it has been dem-

onstrated that the adverse effect of interatrial delay inbiventricular pacing may be avoided with interatrialseptum pacing.32

• In some studies, it has been shown that interatrialconduction time (IACT) measured by tissue Dopplerechocardiography was more closely related to the PRinterval than to the duration of the P wave.Furthermore, in patients with heart failure and wideQRS, IACT is frequently prolonged. Before cardiacresynchronization therapy (CRT), an IACT measuredby tissue Doppler imaging more than 100 millisecondscan affect LA remodeling and function after CRT atearly follow-up but does not influence the response inLV end-systolic volume or ejection fraction.43

Conclusions

• After all the arguments that we have presented, it isclear that interatrial blocks are an entity separate fromatrial enlargement. However, the 2 are often associatedespecially in the case of interatrial block of thirddegree, as often happens with ventricular enlargementand ventricular blocks.

• Interatrial blocks are located in the zone of the high/middle septum especially close to the Bachman bundlebut may also be located beyond the interatrial septumin the LA.

• In case of first-degree interatrial block, the ECG showsa P-wave duration 120 milliseconds or more. If theinteratrial block is of third degree, also, the P wave isprolonged, but the second part of the P wave in inferiorleads becomes negative because of the retrogradeactivation of the LA (P± in II, III, and VF).

• There are clear and important implications related withthe presence of interatrial blocks. They are frequently

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associated to LAE that, in the case of third-degreeinteratrial blocks, have a specificity of 90% and tosupraventricular arrhythmias that are also, much morefrequent in third-degree interatrial blocks.

• The prevalence of first-degree interatrial block in thegeneral population is very high, whereas third-degreeinteratrial blocks are rarely seen.

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