(Chest. 2005;128:970-975.)
© 2005
American College of Chest Physicians
Interatrial Block*
Pandemic Prevalence, Significance, and Diagnosis
Vignendra Ariyarajah, MD;
Navrid Asad, MD;
Anwar Tandar, MD and
David H. Spodick, MD, DSc, FCCP
* From the Division of Cardiology, Department of Medicine, Saint Vincent Hospital, Worcester Medical Center, Worcester, MA.
Correspondence to: David H. Spodick, MD, DSc, FCCP, Professor of Medicine, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655; e-mail: spodickd{at}ummhc.org
Key Words: atrial fibrillation • atrial excitability • ECG • interatrial block • left atrium
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Introduction
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Interatrial block (IAB) [P-wave duration 
110 ms] is well described but poorly recognized since it was first noted experimentally in 1925 and clinically in 1965. Its high prevalence was demonstrated in two well-separated general hospital populations.12. IAB is important because it is associated with abnormal atrial excitability leading to atrial fibrillation and other arrhythmias,34567 significant electromechanical dysfunction of the left atrium (LA),78 LA thrombosis, and systemic embolism.378 However, both IAB and its consequences are widely overlooked, at least partly because many textbooks in general medicine91011 and even in cardiology121314 fail to discuss and, in most cases, even mention IAB and its ominous association with other clinical conditions, such as atrial fibrillation and flutter.34567 Moreover, even articles3 recognizing IAB and its diagnostic, functional, or arrhythmic associations underreport its prevalence by restricting investigations either to lead II alone or cite only one or two other leads. These omissions limit awareness, which is the key to timely detection and recognition of IAB, as well as anticipation and even prevention of sequelae. Our purposes are to define IAB, discuss investigations reporting its remarkable prevalence and its grave associations with other conditions, and propose a sound approach to its diagnosis as prolonged conduction between the right atrium (RA) and LA.15
Josephson and colleagues16 studied electrode catheter techniques to map out atrial endocardial activation, while others like Leier and colleagues17 and Bachmann18 measured interatrial conduction times. However, because discrete lesions produced experimentally in the Bachmann bundle (BB) cause delayed activation of the LA resulting in the typical P waves of IAB (Fig 1
),15 the main mechanism of IAB is thought to lie in BB abnormality. During sinus rhythm, this large bundle of collimated muscle fibers is the preferential route of impulse conduction from the RA to the LA.151617 Depending on the severity of the block, IAB can be partial or advanced and has been so classified by Bayés de Luna.15
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Figure 1.. Typical P waves of IAB. Wide P waves (IAB) are seen in many leads, and their duration is indicated by inverted brackets in representative leads such as V5, lead II, and lead III. The P waves are slightly notched in lead II, but definitely notched in V5. Especially marked is lead V3, which has the widest P waves. It is important to note that all 12 leads must be inspected because any lead can have the widest P wave, which, as with all ECG waves, determine the degree of block.
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Partial IAB
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Incomplete block is seen when impulses travel from the RA to the LA via the BB but conduction is delayed. This produces wide, usually bifid P waves (Fig 2
).215
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Figure 2.. Partial and "complete" (advanced) IAB. Top: With normal interatrial conduction, the impulse leaves the sinus node and crosses from the right to the LA in the BB and other connections (the atrioventricular node is shown at the crux of the heart, but is not involved in this diagram). Normal P-wave duration is established as < 110 ms. Middle: With the usual partial IAB, the impulse still crosses as it does in the normal, but is delayed (shown as cross-hatching), and P-wave duration is > 100 ms. Bottom: With (relatively uncommon) advanced (complete) IAB, the impulse is completely blocked for its usual manner of crossing from the right to the LA, but descends in the RA to the area of the atrioventricular node, after which it activates the LA in reverse, giving biphasic (+, –) P-waves in leads III, aVF, and usually also II. Thus, in advanced IAB, the RA is activated in orthograde (net inferior) direction and the LA is activated in a retrograde (net superior) direction.
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Advanced IAB
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Advanced IAB is seen when conduction is completely blocked in the BB so that sinus impulses cannot cross it but must travel inferiorly in the RA toward the atrioventricular junction and thereafter superiorly through the LA. This conduction pathway is reflected in biphasic (+, –) P waves in the inferior leads (Fig 2).15
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Definitions
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Some investigators style IAB as LA enlargement or LA abnormality, as IAB has indeed been long associated with LA enlargement.781519 However, what is seen by ECG—prolonged P waves—is block23615 (on the ECG, time equals duration of conduction; excessive time equals block). Normal P-wave duration is considered to be < 110 ms.1011121415 IAB, prolonged interatrial conduction, is defined as P-wave prolongation 110 ms.15 To improve specificity, most investigators, like Goyal and Spodick,8 used P-wave durations of 120 ms; others, like Montreggi et al,20 used P-wave durations 130 ms. Jairath and Spodick1 and later Asad and Spodick2 found that the maximum duration of P waves in IAB was most often in leads II, aVF, and V5, but the widest P wave (defining the degree of block) could be found in any lead.215 Thus, a 12-lead search is always required.
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Prevalence
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Jairath and Spodick1 showed a 32.8% prevalence of IAB among patients in a general hospital population. In that population, the prevalence of IAB among patients in sinus rhythm was 41.1%. In a similar but more recent series where 1,000 consecutive ECGs were evaluated for IAB with P-wavedurations 120 ms, Asad and Spodick2 reported a 47% prevalence of IAB in patients in sinus rhythm among all ages in a general hospital population and a 59% IAB prevalence when an age-based comparison was made for patients 60 years old (Table 1
).
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IAB and LA Size
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Goyal and Spodick8 conducted a controlled echo-Doppler investigation of 24 patients with known IAB who were compared for LA dynamics with 16 carefully matched patients without IAB. They showed that although the two groups were matched for LA volumes and diameters and had abnormal LA function, the group with IAB proved to have longer left ventricular Doppler A-wave acceleration times and significantly lower LA stroke volumes (LASVs), LA ejection fractions (LAEFs), and LA kinetic energy (LAKE) [Table 2 ]. They concluded that IAB is associated with a sluggish, poorly contractile LA, and that the degree of dysfunction was related to the degree of conduction delay between the RA and LA (represented by maximum P-wave duration). Munaswamy et al21 reported that 88% of patients with P waves consistent with IAB had LA enlargement, but unlike Goyal and Spodick,8 who had used orthogonal two-dimensional echocardiography to measure actual LA volumes, they had used only M-mode echocardiography, which may often understate true LA size.
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IAB and Arrhythmias
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Leier and colleagues6 showed that prolonged atrial conduction was a predisposing factor for development of atrial flutter as early as 1978. Kumagai and colleagues22 used multisite mapping studies confirming findings of a previous study by Ogawa and colleagues.23 They concluded that the mechanism of atrial arrhythmias was indeed aberrant impulse conduction between the atria along interatrial pathways, mainly the BB. Duytschaever and colleagues24 then successfully reproduced this mechanism in animal studies. In another series, Giudici and colleagues25 investigated 21 patients with uncontrolled atrial fibrillation who underwent atrioventricular nodal ablation and permanent pacing. They showed that when the leads were placed in the BB, atrial conduction times were decreased.
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IAB and Left Ventricular Function
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Ramsaran and Spodick7 demonstrated a 37-ms mean delay in active left but not right ventricular atriogenic filling (LV A-wave vs RV A-wave onsets) with IAB. This was associated with a considerable late activation of the LA. Similarly, Goyal and Spodick8 also suggested an increased risk for congestive heart failure in IAB patients owing to a compromised atrial "kick" from a sluggish chamber and particularly, the greatly reduced LASV and LAKE (mean values of 19.8 kilodyne[kdyne]/cm/s vs 64.7 kdyne/cm/s, p < 0.0001) [Table 2] in association with a significantly reduced preload.
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IAB and Ischemia
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A few authors such as Dilaveris et al26 have suggested the association of IAB as an additional predictive marker in determining ischemic heart disease. However, most of such studies used solely P-wave dispersion and therefore are beyond the scope of this article. Myrianthefs and colleagues27 showed that including P-wave durations of 120 ms during exercise tolerance tests in addition to conventional criteria for diagnosing ischemia would increase sensitivity from 57 to 75% while decreasing specificity only from 85 to 77%.
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IAB and Medical Therapy
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So far, study of this potentially very important relationship is still in its infancy. However, Engelstein and Lerman28 reported transient interatrial block with administration of 6 mg of adenosine IV during high atrial pacing. Newer investigations, tailored toward patients with atrial fibrillation, such as studies by Zaman et al,29 Vermes et al,30 and Madrid et al31 have suggested the use of angiotensin-converting enzyme inhibitors (ACEIs) as an adjunctive therapy in reducing the incidence of atrial fibrillation or maintaining sinus rhythm. Given the fact that IAB often progresses to atrial flutter or fibrillation,456715 this is indeed encouraging. However, without any current controlled drug trials with IAB, it is hard to ascertain concrete evidence-based benefits of ACEI or similar drugs as a preventive or maintenance therapy. No studies to date have shown the need for prophylactic anticoagulation therapy, but perhaps it is an aspect that deserves some investigation in view of the potential ill effects of untreated IAB. Other investigators323334353637 have repeatedly investigated atrial resynchronization techniques and pacing as a preventive therapy for atrial tachyarrhythmias due to IAB, but these investigations have yet to be tested conclusively in randomized trials. Furthermore, at this stage, it is unknown which degree (advanced or partial) of IAB is more likely to progress to an atrial tachyarrhythmia and which degree may benefit from these preventive techniques.
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IAB and Medical Disease
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There have been limited investigations of the associations between IAB and disease states that potentially affect P-wave morphology. Oreto et al38 reported artifactual effects of respiratory disease in ECG tracings that could mimic IAB. Montereggi et al20 described P-wave prolongation in patients with hyperthyroidism. Further investigation is needed to clarify these and other, possibly causal, associations and effects of such variables on P-wave morphology and the diagnosis of IAB.
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Proposed Guide for IAB Diagnosis
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P-wave duration 120 ms indicates IAB. Although even normal P waves may be bifid ("notched"), nearly all P waves 120 ms are,15 and the notch separating the RA and LA P-wave components may alert the ECG interpreter to IAB (Fig 1). Any lead may have the most prolonged P wave. Thus, for maximum P-wave measurements, it cannot be overemphasized that evaluation of full 12-lead ECGs is essential in detecting maximum P-wave duration and morphology as compared to single-lead tracings, as the sensitivity increases with the number of leads used.
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Summary
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IAB is remarkably prevalent among hospitalized patients.12 The association between IAB and arrhythmias, particularly atrial flutter and fibrillation,345615232539 is well established. Besides the risk of subsequent stroke as a result of atrial thrombosis and especially with such arrhythmias, both paroxysmal and chronic, many patients are probably also at risk of congestive heart failure78 from an ineffective "atrial kick." Hence, the importance of awareness and detection of IAB to anticipate and perhaps prevent its sequelae. Today, with advancing age, many if not most patients do not have merely isolated diseases but have multiple medical problems. As such, further investigation is needed to determine the effects of other medical conditions on interatrial conduction such as respiratory diseases38 and thyroid dysfunction.20 Although the clinical consequences of IAB may be grave, at present, absence of controlled clinical trials means that no guidelines can be constructed for managing IAB patients. Do these patients need immediate treatment (ie, ACEI, anticoagulation, or antiarrhythmic therapy), and if so, should it be prophylactic, anticipating atrial arrhythmias (ie, anticoagulation)? Would there be a role for pacing in the future,323334353637 given the potential risks already cited for IAB such as atrial fibrillation345615 and congestive heart failure78? It is well accepted that electrophysiologic studies can evaluate the propensity of the atria to initiate and perpetuate atrial arrhythmias. While such investigations are needed, electrophysiologic studies are inconvenient, costly, and unsuitable as a screening tool among the general population. Clinically, the ECG is an excellent diagnostic tool for demonstrating abnormal interatrial conduction (Fig 1).12347815 Therefore, ECGs should be carefully scrutinized by clinicians to better understand IAB and cultivate an awareness of its potentially dangerous consequences.
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Footnotes
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Abbreviations: ACEI = angiotensin-converting enzyme inhibitor; BB = Bachmann bundle; IAB = interatrial block; kdyne =kilodyne; LA = left atrium/atrial; LAEF = left atrial ejection fraction; LAKE = left atrial kinetic energy; LASV = left atrial stroke volume; RA = right atrium/atrial
Dr. Spodick has indicated to the ACCP that he has not received anything of value, either directly or indirectly, from a commercial or other party related directly or indirectly to the subject of this article submission. Dr. Spodick has also indicated that he will not be discussing any information about a product/procedure/technique that is considered research and is not yet approved for any purpose.
Learning Objectives: 1. Identify the A P-wave duration associated with interatrial block. 2. Recognize that interatrial block is associated with significant cardiac morbidity, including atrial arrhythmias and stroke, and is frequently overlooked. 3. Recognize that prolonged conduction between right and left atria is a commonly unrecognized condition with a high prevalence in general hospital populations.
Received for publication August 31, 2004.
Accepted for publication December 22, 2004.
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References
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- Jairath, UC, Spodick, DH (2001) Exceptional prevalence of interatrial block in a general hospital population. Clin Cardiol 24,548-550[Medline]
- Asad, N, Spodick, DH Prevalence of interatrial block in a general hospital population. Am J Cardiol 2003;91,609-610[Medline]
- Agarwal, YK, Aronow, WS, Levy, JA, et al Association of interatrial block with the development of atrial fibrillation. Am J Cardiol 2003;91,882[CrossRef][ISI][Medline]
- Dilaveris, PE, Gialafos, EJ, Sideris, SK, et al Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation. Am Heart J 1998;135,733-738[CrossRef][ISI][Medline]
- Rugenius, II, Zhvironaite, VA, Rudis, AA Relation between intra-atrial conduction and disorder of sinoatrial atrioventricular and intraventricular conduction according to selectively intensified electrocardiographic findings. Kardiologiia 1984;24,44-48[Medline]
- Leier, CV, Meacham, JA, Schaal, SF Prolonged atrial conduction: a major predisposing factor for the development of atrial flutter. Circulation 1978;57,213-216[Abstract/Free Full Text]
- Ramsaran, EK, Spodick, DH Electromechanical delay in the left atrium as a consequence of interatrial block. Am J Cardiol 1994;50,1132-1134
- Goyal, SB, Spodick, DH Electromechanical dysfunction of the left atrium associated with interatrial block. Am Heart J 2001;142,823-827[CrossRef][Medline]
- Fauci, AS, Braunwald, E, et al Harrison’s principles of internal medicine 15th ed. 1998 McGraw-Hill. New York, NY:
- Weatherall, DJ, Leadingham, JGG, Warrell, DH Section 15. Cardiovascular disease. Oxford textbook of medicine 3rd ed. 1996 Oxford Medical Publications. New York, NY:
- Humes, HD Cardiovascular diseases. Kelley’s textbook of internal medicine 2000 Lippincott, Williams and Wilkins. Philadelphia, PA:
- Rosendorff, C Chapter 4. Disorders of rhythm and conduction. Essential cardiology: principles and practice 2001 W.B. Saunders Company. Philadelphia, PA:
- Alexander, RW, Schlant, RC, Fuster, V Part 4. Rhythm and conduction disorders. Hurst’s the heart 9th ed. 1998 McGraw-Hill Companies. New York, NY:
- Chatterjee, K, Cheitin, MD, et al Section 6. Electrophysiology. Cardiology: an illustrated text/reference 1991 Gower Medical Publishing. New York, NY:
- Bayés de Luna, A Electrocardiographic alterations due to atrial pathology. Clinical electrocardiography: a textbook 1998,69 Futura Company. New York, NY:
- Josephson, ME, Scherf, DL, Kastor, JA, et al Atrial endocardial activation in man: electrode catheter technique for endocardial mapping. Am J Cardiol 1977;39,972-981[Medline]
- Leier, CV, Jewell, GM, Magorien, RD, et al Interatrial conduction (activation) times. Am J Cardiol 1979;44,442-446[CrossRef][ISI][Medline]
- Bachmann, G The inter-auricular time interval. Am J Physiol 1916;41,309-320[Free Full Text]
- Josephson, ME, Kastor, JA, Morganroth, J Electrocardiographic left atrial enlargement: electrophysiologic, echocardiographic and hemodynamic correlates. Am J Cardiol 1977;39,967-971[ISI][Medline]
- Montereggi, A, Marconi, P, Olivotto, I, et al Signal-averaged P-wave duration and risk of paroxysmal atrial fibrillation in hyperthyroidism. Am J Cardiol 1996;77,266-269[CrossRef][ISI][Medline]
- Munuswamy, K, Alpert, MA, Martin, RH, et al Sensitivity and specificity of commonly used criteria for left atrial enlargement determined by M-mode echocardiography. Am J Cardiol 1984;53,829-832[Medline]
- Kumagai, K, Khrestian, C, Waldo, AL Simultaneous multisite mapping studies during induced atrial fibrillation in the sterile pericarditis model: insights into the mechanism of its maintenance. Circulation 1997;95,511-521[Abstract/Free Full Text]
- Ogawa, S, Dreifus, LS, Osmick, MJ Longitudinal dissociation of Bachmann’s bundle as a mechanism of paroxysmal supraventricular tachycardia. Am J Cardiol 1977;40,915-922[Medline]
- Duytschaever, MF, Wijffels, M, Kirchhof, CJ, et al Development of chronic atrial fibrillation in the goat is dependent on the intra-atrial conduction velocity measured along Bachmann’s bundle [abstract]. Circulation 1997;96,705
- Giudici, M, Bailin, SJ, Adler, S Prevention of chronic atrial fibrillation by pacing in the region of Bachmann’s bundle: results of a multicenter randomized trial. J Cardiovasc Electrophysiol 2001;12,912-917[CrossRef][ISI][Medline]
- Dilaveris, PE, Andrikopoulos, GK, Metaxas, G, et al Effects of ischemia on P-wave dispersion and maximum P-wave duration during spontaneous anginal episodes. Pacing Clin Electrophysiol 1999;22,1640-1647[Medline]
- Myrianthefs, MM, Ellestad, MH, Startt-Selvester, RH, et al Significance of signal-averaged P-wave changes during exercise in patients with coronary artery disease and correlation with angiographic findings. Am J Cardiol 1991;68,1619-1624[CrossRef][ISI][Medline]
- Engelstein, E, Lerman, BB Adenosine induced intra-atrial block. Pacing Clin Electrophysiol 1993;16,89-94[CrossRef][Medline]
- Zaman, AG, Kearney, MT, Schecter, C, et al Angiotensin-converting enzyme inhibitors as adjunctive therapy in patients with persistent atrial fibrillation. Am Heart J 2004;147,823-827[CrossRef][ISI][Medline]
- Vermes, E, Tardif, JC, Bourassa, MG, et al Enalapril decreases the incidence of atrial fibrillation in patients with left ventricular dysfunction: insight from the studies of left ventricular dysfunction (SOLVD) trials. Circulation 2003;107,2926-2931[Abstract/Free Full Text]
- Madrid, AH, Bueno, MG, Rebollo, JMG, et al Use of irbesartan to maintain sinus rhythm in patients with long-lasting persistent atrial fibrillation. Circulation 2002;106,331-336[Abstract/Free Full Text]
- Daubert, JC, Mabo, P, Berder, V, et al Atrial flutter and interatrial conduction block: preventive role of biatrial synchronous pacing? Waldo, AL Touboul, P eds. Atrial flutter: advances in mechanisms and management 1996,331-346 Futura Publishing. Armonk, NY:
- Daubert, C, Mabo, P, Berder, V, et al Atrial tachyarrhythmias associated with high degree interatrial conduction block; prevention by permanent atrial resynchronisation. Eur J Card Pacing Electrophysiol 1994;1,35-44
- Daubert, C, Gras, D, Berder, V, et al Resynchronisation atriale permanente par la stimulation biatriale synchrone pour le traitment preventif du flutter auriculaire associe a un bloc interauriculaire de haut degree. Arch Mal Couer 1994;87,1535-1546
- Daubert, JC, Leclercq, C, Pavin, D, et al Biatrial synchronous pacing: a new approach to prevent arrhythmias in patients with atrial conduction block. Prevention of tachyarrhythmias with cardiac pacing 1997,99-119 Futura Publishing. Armonk, NY:
- Padelleti, L, Pieragnoli, P, Ciapetti, C, et al Randomized crossover comparison of right atrial appendage pacing versus interatrial septum pacing for prevention of paroxysmal atrial fibrillation in patients with sinus bradycardia. Am Heart J 2001;142,1047-1055[CrossRef][ISI][Medline]
- Katsivas, A, Manolis, AG, Lazaris, E, et al Atrial septal pacing to synchronize atrial depolarization in patients with delayed interatrial conduction. Pacing Clin Electrophysiol 1998;21,2220-2225[CrossRef][Medline]
- Oreto, G, Consolo, S, Magazzu, G, et al Atrial dissociation simulated by respiratory artifact: case report [in Italian]. J Ital Cardiol 1980;10,926-932
- Stafford, PJ, Turner, I, Vincent, R Quantitative analysis of signal-averaged P waves in idiopathic paroxysmal atrial fibrillation. Am J Cardiol 1991;68,751-755[CrossRef][ISI][Medline]
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Introduction
Partial IAB
