Vol.48 - Número 3, Julio/Septiembre 2019 Imprimir sólo la columna central

Interatrial block in ECG after immediate electrical cardioversion
as a predictor of recurrence of atrial fibrillation

Instituto Cardiovascular de Buenos Aires (ICBA).
(1428) Buenos Aires, Argentina.
Recibido 14.MAR.2019 – ACEPTADO después de revisión el 06-MAYO-20119
There are no conflicts of interest to disclose.



Introduction: The association between the presence of interatrial block and supraventricular arrhythmias has been widely demonstrated in various clinical scenarios. The aim of the present study is to demonstrate that its presence in the ECG performed post immediate electrical cardioversion (ECV) of atrial fibrillation is a predictor of recurrence of this arrhythmia.
Methods: Between January and December 2015 there were 117 patients admitted for elective electrical cardioversion of paroxysmal or persistent atrial fibrillation (AF), 93 of which reverted to sinus rhythm and the presence of interatrial block (IAB) was analyzed through 12-lead ECG. The primary endpoint was recurrence of AF post-ECV at six months. The secondary endpoints were time to first recurrence in patients with and without interatrial block, time to first recurrence according to the subtype of IAB, and the correlation between IAB and dilation of the left atrium.
Results: From the 93 patients with successful ECV, clinical and electrocardiographic monitoring was performed on 91 of them for six months. Patients with interatrial block had a left atrium area in the echocardiogram higher than in patients without block (p=0.04). During follow-up, a statistically significant difference was found in the recurrence of AF among patients with and without interatrial block (p=0.04), with earlier recurrence in patients with block. No difference in recurrence of AF between interatrial block subtypes was observed (p=0.10).
Conclusion: The presence of interatrial block in the ECG post immediate electrical cardioversion of atrial fibrillation can be a useful and simple tool to predict recurrence.
Key words: Electrical cardioversion. Atrial fibrillation. Interatrial block.


Atrial fibrillation (AF) is the most frequent arrhythmia in clinical practice, affecting 1-2% of the general population, with a significant increase in cardiovascular morbidity and mortality [1,2].

Its treatment is based on anticoagulation accompanied by rhythm control (preferably) or frequency control by antiarrhythmic drugs, electrical cardioversion (ECV) and ablation [1,2].

ECV is a properly established treatment to reverse paroxysmal and persistent AF into sinus rhythm. However, failure of immediate or early ECV is estimated to occur approximately in 25% of cases [3], reaching between 50 and 80% per year [4,5]. The identification of subgroups in higher risk of recurrence could allow designing a more aggressive antiarrhythmic strategy after ECV [6].

Predictors of AF recurrence after ECV are: increase in the size of left atrium (LA), advanced age, underlying heart disease, increased heart rhythm variability and obesity, among others [7].

A delay in conduction between the atria may be identified in ECG with a longer duration of P wave. Currently, this is known as interatrial block (IAB). Previous studies showed that IAB could be a predictor of early and late AF recurrence in different clinical scenarios. In them, a presence of interatrial blocks was evident in very variable percentages, from 16 to 60% of patients analyzed [8-11]. There is evidence of intermittent IAB development immediately after EVC, with this being a predictor of AF recurrence [12]. However, no prospective analyses have been developed to estimate its implications.

The primary aim of our study is to determine prospectively if the presence of IAB in a post-ECV ECG is an independent predictor of AF recurrence, as this is a quick, simple and noninvasive method. The secondary aim is to determine whether the subtype of IAB differs in the rate of AF recurrence and if the time until recurrence is less in patients with IAB.


There were 117 patients admitted into our center in a scheduled manner for ECV of paroxysmal or persistent AF between January and December 2015. There were 93 patients included that were analyzed prospectively as they reverted to sinus rhythm in ECG certifying so. The remaining 24 patients were not included because of: failed electrical cardioversion (n=9), presence of left appendage thrombus evident in transesophageal echo (n=5), being in sinus rhythm in admission (n=4) and presenting non-AF supraventricular arrhythmia (atrial flutter/atrial tachycardia) (n=6).

Shocks of biphasic current of increasing energy were applied (100 J, 200 J) in anterior position and in the case of failure, 200 J in anteroposterior position under sedoanalgesia with propofol. A 12-lead ECG was conducted (150 Hz filter, 25 mm/sec, 10 mm/mV) after verifying in telemetry reversion to sinus rhythm to evaluate the presence of IAB.

IAB was classified into two groups: 1) partial (pIAB): duration of P waves ≥120 ms and bimodal morphology in DI, DII or DIII, that could be accompanied by a terminal negative component in V1; and 2) advanced (aIAB): P wave duration ≥120 ms with positive/negative  [±] morphology in DII, DIII and aVF [8-11].

Patients were divided into 4 groups: no IAB, with IAB, with pIAB and with aIAB. Basal characteristics were analyzed for each one: antiarrhythmic drugs, co-morbidities, body mass index (BMI), ejection fraction and left atrial area (measures made with color Doppler echocardiogram) and follow-up was conducted to assess AF recurrence.

Inclusion criteria were: older than 18 years, admission for scheduled ECV for paroxysmal/persistent AF, 12-lead ECG in sinus rhythm immediately after ECV, follow-up available in the next 6 months after ECV.

Exclusion criteria were: initial ECV for arrhythmia other than AF, 12-lead ECG in SR not available after immediate ECV, loss of follow-up in the first 6 months, unsuccessful ECV, impossibility of ECV by thrombus in left appendage and sinus rhythm in admission.

The primary endpoint was post-ECV AF recurrence in six months. Secondary endpoints were: time to the first recurrence in patients with and without IAB, time to the first recurrence according to IAB subtype, and correlation between IAB and left atrial dilatation by color Doppler echocardiogram.

Continuous variables were expressed as mean and standard deviation (SD) or means with interquartile intervals as it may correspond and categorical variables as ratios. Student’s t test or Mann Whitney U test were used to compare continuous variables and Chi square test for ratios with Fisher correction when necessary. A two-tailed p less than 0.05 was defined as statistically significant. Time to AF recurrence was compared between groups by Kaplan-Meier curves and Log-rank test.

The protocol was reviewed and approved by the Committee on Education and Investigation of the Institution as well as the Committee on Ethics, and the principles of the Declaration of Helsinki were followed.


Two of the 93 patients that reverted to sinus rhythm were lost in follow-up, performing an analysis of AF recurrence in 91 patients (97.8%).

From the patients that reverted to sinus rhythm, in 68 (73%), the presence of interatrial block was evident in immediate post-ECV ECG.

Patients with interatrial block presented a left atrial area in color Doppler echocardiogram greater than patients with no block (p=0.04), not observing another significant difference in the baseline characteristics of both groups (Table 1).

Table 1. Basal characteristics of patients
    Characteristics With IAB (n=68) W/o IAB (n=25) p
  Mean age (SD) 67 (10) 68 (9)  
  Female gender – n (%) 12 (17.6) 6 (24) 0.49
  Risk factors – n (%)      
  Hypertension 57 (83.8) 17 (68) 0.09
  Diabetes 11 (16.2) 3 (12) 0.61
  Dyslipidemia 28 (41.2) 13 (52) 0.35
  Previous medication – n (%)      
  Beta blockers 44 (64.7) 12 (48) 0.14
  Amiodarone 43 (63.2) 12 (48) 0.18
  Propafenone 4 (5.9) 5 (20) 0.04
  Flecainide 2 (2.9) 0 (0) 0.38
  Previous ablation – n (%) 12 (17.6) 5 (20) 0.79
  Body mass index – mean (SD) 28 (5) 28 (5) 0.75
  Left atrial area – mean (SD) 30 (8) 26 (5) 0.04
  Ejection fraction – mean (SD) 55 (11) 53 (10) 0.35


In the analysis of atrial fibrillation recurrence, a statistically significant difference was evident between patients with and without interatrial block (p=0.04), with an earlier recurrence in patients with block (Figure 1). However, when analyzing subgroups of patients with partial and advanced interatrial block, no significant differences were observed (p=0.10).

Figure 1.


As proven on numerous occasions and in different clinical scenarios, interatrial block proved to be an independent predictor of atrial fibrillation recurrence [8-11].

This study had as its aim to show that this finding in immediate post-electrical cardioversion electrocardiogram, with the latter being a method easy to access, simple, noninvasive and not requiring the patient to bring previous tests to the procedure, would also allow predicting patients in higher risk of atrial fibrillation recurrence, in order to apply a proper antiarrhythmic treatment in the selection of drugs, duration of it, and need to ablate by radiofrequency or cryoballoon after cardioversion.

The important percentage of patients with evidence of interatrial block (73%) is probably related to the search for it in ECG immediately after cardioversion, with the atrium being at the time, in the well-known state of stunning generated by reversion to sinus rhythm, manifesting both electrically and mechanically and consequently generating transient changes in the P wave of ECG [13]. The presence of interatrial block after electrical cardioversion of atrial fibrillation is a relatively usual observation, occasionally being a transient finding [12].

In spite of what was described above, and with the chance of the electrocardiographic changes observed that led us to identify interatrial block in 68 of the 93 patients studied, being transient and unable to predict atrial fibrillation recurrence, the results obtained were satisfactory, with a statistically significant difference in relation to patients with block that recurred in said arrhythmia (p=0.04).

In regard to the left atrial area, patients with block presented a more extensive area than patients without block, not being able to differentiate whether recurrence is related to a factor or another as, as it is well known, the larger the atrial area, the greater the risk of recurrence [7].

The limitations of this study were the size of the sample and the duration of follow-up. The statistical significance of our results was not as important as in previous studies in relation to block and its value as predictor of recurrence. Probably, this is the consequence of our small sample and a 6-month follow-up.

Prospective studies should be made with a greater number of patients and more extensive follow-ups to evaluate whether results match those obtained in this study.


The presence of interatrial block in 12-lead electrocardiogram immediately after cardioversion of atrial fibrillation is a factor predictor of recurrence of said arrhythmia, with this diagnosis being fast and simple, to determine risk groups to optimize their antiarrhythmic treatment.



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Publication: September 2019


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