Complete Right Bundle Branch Block in Acute Coronary Syndrome with ST Segment Elevation: Epidemiological Features

: Background: Complete right bundle branch in acute coronary syndrome with ST segment elevation is common and may predict a poor clinical prognosis. Its incidence has been the subject of several international studies, as well as, its related mortality, but its epidemiological data is lacking in Algeria. Aims: The main objective of our study is the determination of the frequency of complete right bundle branch block in acute coronary syndrome with ST segment elevation, the secondary objective was the analysis of its predictive factors and related mortality. Methods and materials: In this prospective study, conducted in the cardiology department of Hussein Dey hospital (Algiers-Algeria), 467 patients with acute coronary syndrome with elevated ST segment (87 women and 380 men) were enrolled between 28 February 2014 and 16 July 2015. The average age is 60 ± 13 years; at admission, a Holter recorder was attached for continuous ECG monitoring during 48 hours. Kruskal’s ANNOVA or H tests were used for comparison of quantitative variables, χ2 test or Fisher’s exact test, were used for qualitative variables, all tests were performed with 1 st species risk of 5%. Results: The frequency of complete right bundle brunch block is 10.9 % (51 patients), CI 95%: [8.1%-13.7%], multivariate analysis identified the following independent predictors: anterior acute coronary syndrome, persistence of chest pain after thrombolysis, and diabetes type 2. The risk of mortality expressed by Hazard Ration (HR) is 3.4, CI95%: [1.07-11.35], p = 0.037; persistence of ST segment elevation after thrombolysis is the only predictive factor of mortality, identified in our study. Conclusion: Complete right bundle brunch block is frequent in acute coronary syndrome with elevated ST segment, its predictive factors according to our study are: anterior acute coronary syndrome, persistence of chest pain after thrombolysis, and type 2 diabetes. Its occurrence increases the risk of in-hospital mortality, and the predictor of this latter is the failure of thrombolysis.


Introduction
Complete right bundle branch block (RBBB) in acute coronary syndrome with ST segment elevation, represents the most frequent conductive disorder.It may reflect the importance of myocardial damage; predict hemodynamic instability with poor prognosis.After acute coronary artery occlusion, ischemia and necrosis are the principal mechanisms of complete RBBB.The right proximal branch is irrigated by the atrioventricular node artery, which frequently originates from the right coronary artery and also by the septal branch of the left anterior descending artery.Its incidence and prognostic value have been widely reported in the literature, but its epidemiological data is lacking in Algeria.The main objective of our study is to determine the frequency of complete right bundle branch block in acute coronary syndrome with ST segment elevation, during the first 48 hours of hospitalization, while the secondary objective is the analysis of its predictive factors and the related mortality.

Methods and materials
We prospectively studied a group of 467 consecutive patients (380 men and 87 women; mean age 60 ± 13 years) who presented acute coronary syndrome with ST segment elevation and admitted in cardiology department of Hussein-Dey hospital (Algiers, Algeria), between 28th February 2014 and 16th August 2015.At emergency department admission, an ECG Holter recorder was attached for continuous ECG monitoring during 48 hours, the 17-leads surface ECG recorded at admission and repeated during hospitalization, Doppler Echocardiography, coronary angiography, and biological assessment were performed in the majority of patients.The most important rhythm and conduction disorders were identified, the patients with the same type of disorder are grouped together, and the name assigned to each group is that of the disorder that characterizes it; there are overlaps between the groups, so that several disorders may exist in the same patient.The constitution of each group of the rhythm disorder implies the constitution of the opposite group without the corresponding disorder, the latter group is used for the comparative study; each group is therefore described and then compared to the corresponding opposite group.In this sub study, the group of patients with complete right bundle brunch block was compared to the rest of patients without complete right bundle brunch block

Statistical analysis
Data are presented as mean ± SD, median, or frequency (percentage) where appropriate.Continuous variables were compared using the ANNOVA test, or H Kruskal Wallis test.χ2 tests and Fisher's exact test were performed to distinguish differences between categorical variables.Statistical significance was defined as p < 0.05.In this first step, we used EPI-info version 6.0.A multivariate Binary regression was performed to determine the predictor factors of arrhythmias, and Cox regression was performed to identify the predictor factors of mortality.The magnitude of the relationship between complete RBBB and their predictive factors is estimated by the Cramer V coefficient, a coefficient lower than 0.2 is in favor of a weak link, between 0.2 and 0.5: moderate link, greater than 0.5: strong link.The statistical analysis was performed using SPSS Statistics (release 17).

Results
Incidence: The characteristics of the 467 patients included in our study are shown in Table 1; fifty-one patients had presented complete RBBB at admission or during hospitalization, so its frequency in this present study is 10.9 % (51 patients), CI 95% [8.1%-13.7%].
This group of patients included nine women and forty-two men.The mean age was 61.43 ± 12 years; the extreme age was 29 and 85 years.Forty-two patients had presented complete RBBB at admission, (Figure1) (Figure 2) and nine patients had presented complete RBBB during their hospitalization.The complete RBBB was persistent in thirty-three patients, and transient in eighteen patients.1.The Surface ECG had shown, extensive anterior ACS in 29 patients, circumferential in 3 patients, anterior in 6 patients, antero-septal in 1 patient, antero-septo-apical in 1 patient, inferior in 4 patients, infero-basal in 6 patients, right ventricular in 27 patients.The mean heart rate at admission was 89.52 ± 18.73 beats/min, heart rate ≥ 80 beats/min in 34 patients, the mean PR interval was 144.89 ± 27.54 msec, the mean duration of the QRS complex was 109.80 ± 23.108 msec, complex QRS duration ≥ 100 msec in 40 patients, the mean amplitude of the ST segment elevation was 5.21 ± 2.68 mm, ST segment elevation ≥ 5 mm in 31 patients, the mean amplitude of the ST segment depression was 1.45 ± 1.17 mm, the mean amplitude of the T wave was 7.11 ± 3.50 mm and the mean corrected QT was 440.84 ± 51.69 msec, QTc interval ≥ 440 msec in 25 patients.Eight patients had persistence of the segment ST elevation during hospitalization.Treatment at admission and during hospitalization: Metalyse (Tenecteplase) as fibrinolytics treatment were administered in 46 patients (90.19 %), 42 patients had presented complete RBBB at admission before any therapy, 4 patients had presented complete RBBB after thrombolysis.(Figure 3) Holter ECG was performed in 47 patients; this exam had participated in the recording of complete RBBB, also showed its character (transient or persistent), and detected associated arrhythmias.(Figure 4)

Predictive factors
According But after the multivariate analysis using binary logistic regression, three predictive factors were identified: extensive anterior acute coronary syndrome, Persistence of chest pain after thrombolysis, and diabetes type 2. (Table 3) (Figure 5)  The magnitude of the relationship between complete RBBB and persistence of chest pain is moderate; the Cramer V coefficient exceeds 0.2, but this magnitude is low for the two others, the Cramer V coefficient doesn't exceed 0.2.(Table 4)

Mortality
Hospital mortality (first 48 hours), in the complete RBBB group is 7.84 % while it does not exceed 3.12 % in the group without complete RBBB, but this difference isn't significant (p=0.102),but when using Cox regression, this difference becomes significant and hospital mortality is high, with HR at 3.4, CI 95% [1.07-11.35],p = 0.037.(Figure 6) According to the univariate study, some factors have a statistically significant association with the occurrence of mortality in the complete RBBB group.(Table 5) The magnitude of the relationship between mortality and its predictive factor in the complete RBBB group was strong; the Cramer V coefficient exceeds 0.5.(Table 7) The right proximal branch is irrigated by the atrioventricular node artery, which frequently originates from the right coronary artery and also by the septal branch of the left anterior descending artery.[1] According to several studies conducted before thrombolysis era, the incidence of RBBB varied between 3 % and 29 %.This incidence has declined significantly in the reperfusion era, and varies between 2 and 11 % [7]; according to another study published in 2013, the incidence of the complete RBBB is about 9%.[8] The incidence of complete RBBB in our study was 11 % (51 patients), CI 95% [8.1%-13.7%].This incidence is within the range of that reported in the literature; the high incidence in our study was probably related to the more frequent extensive anterior localization of acute coronary syndrome, and also the failure of thrombolysis especially for patients who developed complete RBBB during hospitalization, in our study RBBB was persistent in 33 patients, which could be related to necrosis.Predictors of complete RBBB have not been reported in the literature.
According to our study three predictive factors were identified: extensive anterior acute coronary syndrome, persistence of chest pain after thrombolysis and diabetes type 2. The extensive anterior ACS, which reflects the importance of the lesions and their extension to the conduction pathways, is principally linked to the occlusion of the left anterior descending artery in its proximal portion, preventing the irrigation of the septal arteries thus inducing the suffering of the right branch brunch.The persistence of chest pain after thrombolysis reflects the failure of thrombolysis and therefore the persistence of myocardial damage (ischemia and necrosis), which induces hemodynamic and electro physiological consequences with conduction disruption in the right bundle brunch.Diabetes increases the risk of developing a complete right branch block, this risk related to the micro and macroangiopathy of diabetes, inducing ischemia and fibrosis.Several international studies have reported risk of mortality related to complete RBBB, Before thrombolytic era, complete RBBB was associated with high risk of mortality, which related to severe ventricular arrhythmias, left ventricular failure, and cardiogenic shock.In ACS, mortality related to left or right bundle brunch block is 23.6% without thrombolysis and 18.7% with thrombolysis.[9] According to Hindman et al, the rate of mortality related to RBBB is high (28 % in RBBB group versus 12 % in group without RBBB) [10]; Ricou et al (32% versus 8%) [11]; for Klein et al, the rate of mortality related to RBBB is about 35 % [12] According to another study published in 1997, occurrence of complete RBBB increases the risk of mortality (25.9 % with RBBB versus 9.9 % without RBBB).[7] According to another study, the rate mortality related to RBBB in inferior ACS is about 11.4 % (p=0.03), while the rate mortality related to RBBB in anterior ACS is about 31.6 % (p=0.001) if RBBB is present at admission, and 33 % (p= 0.001) if RBBB occurred 60 min after thrombolysis.
[13] In our study, the occurrence of complete RBBB increases the risk of in-hospital mortality (first 48 hours) with HR at 3.4.The persistence of chest pain after thrombolysis is the predictive factor of mortality, which reflects the extension of myocardial damage (ischemia and necrosis), which induces severe hemodynamic and electro physiological consequences.

Conclusion
Complete right bundle branch block in acute coronary syndrome with ST segment elevation is frequent, its predictive factors according to our study are: extensive anterior acute coronary syndrome, persistence of chest pain after thrombolysis, and diabetes type 2.
The occurrence of complete RBBB increases the risk of inhospital mortality, related to reperfusion failure, and extensive myocardial damage.
To our knowledge, predictive factors of complete RBBB were reported for the first time.

Figure 1 :Figure 2 :
Figure 1: Surface ECG showed complete right bundle branch block in extensive anterior acute coronary syndrome with ST segment elevation

Figure 3 :
Figure 3: Complete Right bundle branch block onset delay as a Function of Fibrinolytics treatment Aspirin, Clopidogrel and Anticoagulants were administered in 51 patients (100 %), beta blockers in 19 patients (37.25 %), ACE inhibitors in 24 patients (47.05 %), sympathomimetic agents in 3 patients (6 %), diuretics in 8 patients (15.08 %), external electric shock in 10 patients (19.60 %), Amiodarone in 7 patients (13.37 %), Magnesium and Potassium supplementation at admission in 27 patients (52.94 %), Insulin in 23 patients (45.09 %).Thrombolysis failure: the persistence of chest pain and ST segment elevation after thrombolysis was observed in 10 patients and persistence of ST segment elevation in 8 patients.Doppler echocardiography was performed in 47 patients, the left ventricular fraction less than 40 % was found in 12 patients

Figure 4 :
Figure 4: Holter ECG showed complete right bundle branch block and initiation of fast ventricular tachycardia in patient with anterior acute coronary syndrome with ST segment elevation Several arrhythmias were associated with complete RBBB, ventricular fibrillation (VF) in 8 patients, sustained ventricular tachycardia (SVT) in 3 patients, non-sustained ventricular tachycardia (NSVT) in 8 patients, atrial fibrillation (AF) in 6 patients, complete atrioventricular block (AVB) in 1 patient, bursts of ventricular premature beats in 13 patients, accelerated idioventricular rhythm in 5 patients, polymorphic ventricular

Figure 5 :
Figure 5: Predictive factors of complete right bundle branch block ACS: Acute coronary syndrome

Figure 6 :
Figure 6: Hospital mortality curve (48h) in complete right bundle brunch block (RBBB) group versus group without complete RBBB Cox regression was used for univariate and multivariate studies of mortality predictors.

Table 2 : Univariate study: variables associated with complete right bundle brunch block (RBBB)
to the univariate study, several variables had a statistically significant association with the occurrence of complete RBBB: diabetes type 2, persistence of chest pain, extensive anterior acute coronary syndrome, St segment elevation above or equal 5 mm, persistence of ST segment elevation, heart rate above or equal 80 beats/min, left ventricular ejection fraction less than 40 %, left atrium surface ≥ 20 cm², Diameter of left ventricle ≥ 56 mm, presence of akinetic segment, presence of apical thrombus, persistence of chest pain after thrombolysis, and persistence of ST segment elevation after thrombolysis.(Table2)

Table 7 : The magnitude of the relationship between mortality and its predictive factors
Complete right bundle branch block (RBBB) in acute coronary syndrome with ST segment elevation, represents the most frequent conductive disorder.It may reflect the importance of myocardial damage; predict hemodynamic instability with poor prognosis.After acute coronary artery occlusion, ischemia and necrosis are the principal mechanisms of complete RBBB.