Complete Sino Atrial Block in Acute Coronary Syndrome with ST Segment Elevation: Incidence, Predictive Factors and Related Mortality.

: Background: Sino atrial block in acute coronary syndrome with ST segment elevation is not rare and may be dangerous by causing severe bradycardia. Its incidence was reported in the literature, but no data about its predictive factors or related mortality, also its epidemiological data is lacking in Algeria. Aims: The main objective of our study is the determination of the frequency of Sino Atrial Block in acute coronary syndrome with ST segment elevation, the secondary objective was the analysis of predictive factors of this Brady arrhythmia, 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 Sino atrial block is 2.6 % (12 patients), CI 95%: [1.2%-4%], multivariate analysis identified the following independent predictors: right ventricular acute coronary syndrome, infero basal acute coronary syndrome, and large right atrium surface. The risk of mortality expressed by Hazard Ration (HR) is 5.4. (CI95%: [1.2-24], p = 0.024); right acute coronary syndrome is the only predictive factor of mortality identified in our study. Conclusion: Sino atrial block is not rare in acute coronary syndrome with elevated ST segment, its predictive factors according to our study are: right ventricular acute coronary syndrome, infero basal acute coronary syndrome, and large surface of right atrium, its occurrence increases the risk of hospital mortality.


Introduction
Sino atrial block (SAB) in acute coronary syndrome with ST segment elevation is not rare, but less frequent than Atrio ventricular block. Complete SAB may be dangerous by causing severe bradycardia and hemodynamic instability. Several mechanisms have been proposed to explain Sino atrial conduction disorders like ischemia, necrosis and neurologic reflexes. Its incidence was reported in the literature, but no data about its predictive factors or related mortality, also its epidemiological data is lacking in Algeria. The main objective of our study is to determine the frequency of Complete Sino atrial 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 www.cmhrj.com 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 Sino atrial block was compared to the rest of patients without Sino atrial 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 Sino atrial block 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; Twelve patients had presented complete Sino atrial block at admission or during hospitalization, so its frequency in this present study is 2.6 % (12 patients), CI 95% [1.2%-4%]. This group of patients included one woman and eleven men. The mean age was 63 ± 13 years; the extreme age was 37 and 89 years. Nine patients had presented complete SAB at admission, and three patients had complete SAB during their hospitalization. The complete SAB was persistent in five patients, and transient in seven patients. The average rate of junctionel escape rhythm was 59±14 beats/min, with the extreme rate was 34 beats/min and 86 beats/min.   Table 1. The Surface ECG had shown, anterior ACS in two patients, inferior in five patients, inferobasal in six patients, right ventricular in five patients. The mean heart rate at admission was 59.16 ± 14.03 beats/min, the mean PR interval after regression of complete SAB was 160 ± 56.56 msec, the mean duration of the QRS complex was 68.33 ± 13.37 msec, the mean amplitude of the ST segment elevation was 3.33 ± 1.23 mm, the mean amplitude of the ST segment depression was 1.08 ± 0.66 mm, the mean amplitude of the T wave was 5.50 ± 1.88 mm and the mean corrected QT was 411 ± 35.35 msec. Two patients had persistence of the segment ST elevation during hospitalization. Treatment at admission and during hospitalization: Metalyse (Tenecteplase) as fibrinolytics treatment were administered in 10 patients (83.33 %), 9 patients had presented complete SAB at admission before any therapy, 1 patient had presented complete SAB after thrombolysis. (Figure 3) www.cmhrj.com Thrombolysis failure: the persistence of chest pain and ST segment elevation after thrombolysis was observed in 1 patient. Doppler echocardiography was performed in 10 patients, the left ventricular fraction above than 40 % was found in 10 patients (100%), left ventricular hypertrophy in 3 patients (30 %), the mean area of the left atrium: 18.10 ± 4.20 cm², that of the right atrium: 14.80 ± 3.67 cm², surface of right atrium above or equal 14 cm² in 6 patients, the mean diastolic diameter of the left ventricle: 51.60 ± 7.48 mm, the mean diastolic diameter of the right ventricle was 29.77±5.91 mm, diastolic diameter of right ventricle above or equal 28 mm in 5 patients, the systolic pulmonary blood pressure: 23.66 ± 4.41 mm Hg, wall akinesia in 4 patients (40%) and significant mitral insufficiency in 2 patients (22.22%). Holter ECG was performed in 10 patients; this exam had participated in the recording of complete SAB, also showed its duration (transient or persistent), the rates of junctional escape rhythm, and detected associated arrhythmias. (Figure 4)

Predictive factors
According to the univariate study, several variables had a statistically significant association with the occurrence of complete SAB: Right ventricular heart failure, low systolic blood pressure, atrial tachycardia, right atrium surface ≥ 14 cm², right acute coronary syndrome, inferior acute coronary syndrome, and infero-basal acute coronary syndrome. (Table 2) But after the multivariate analysis using binary logistic regression, three predictive factors were identified: right acute coronary syndrome, infero-basal acute coronary syndrome, right atrium surface above or equal 14 cm². (Table 3) ( Figure 5)

Figure 5: Predictive factors of complete Sino atrial block
The magnitude of the relationship between complete SAB and its predictive factors is low; the Cramer V coefficient does not exceed 0.2. (Table 4)  Cox regression was used for univariate and multivariate studies of mortality predictors. According to the univariate study, some factors have a statistically significant association with the occurrence of mortality in the complete SAB group. (Table 5) According to multivariate analysis, right acute coronary syndrome was identified as predictive factor of mortality. (Table 6) The magnitude of the relationship between mortality and its predictive factor was not significant in the complete SAB group. (Table 7)

Discussion
Sino atrial block (SAB) in acute coronary syndrome with ST segment elevation is not rare, but less frequent than Atrio ventricular block (AVB), according to the literature, its incidence in acute coronary syndrome with ST segment elevation is between 0.5 and 4 %. [1] [2] SAB is due to failed propagation of pacemaker impulses beyond the SA node, complete (third degree) is characterized by complete absence of P waves, and may produce long sinus pauses, but the rhythm may be maintained by a junctional escape rhythm. Complete SAB may be dangerous by causing severe symptomatic bradycardia, and leading to hemodynamic www.cmhrj.com instability. The diagnosis of persistent Complete SAB is usually obvious, but for intermittent and short term episodes the diagnosis may be difficult, so Holter ECG may be useful in those cases. The sinus node is irrigated by the right coronary artery in 63%, and by branch of the left coronary artery or one of its branches, in 37%. [3] Several mechanisms have been proposed to explain Sino atrial conduction disorders during acute coronary syndrome, including ischemia or necrosis of sinus atial node, just after occlusion of sinus node artery, electrophysiological and morphological disorders were observed but generally reversible, this observation suggests sinus node resistance to infarction. [4] [5] Because of the high density of cholinergic ganglia in the right atrium, reflexes causes are common, and the vagus nerve may play a significant role. [2] The incidence of complete SAB in our study was 2.6 % (12 patients), CI 95% [1.2%-4%].This incidence is within the range of that reported in the literature. According to our study three predictive factors were identified: right acute coronary syndrome, infero-basal acute coronary syndrome, right atrium surface above or equal 14 cm². The right or the infero-basal acute coronary syndrome, involve right or circumflex coronary artery occlusion, and consequently occlusion of the artery supplies blood to Sino atrial region. The large right atrium could be related to right atrium wall necrosis and also bradycardia which contribute to chamber dilation.
Only one study reported hospital mortality rate in patients with myocardial infarction complicated of sino atrial dysfunction, in this study, 9 patients died out of 32 patients, so the percentage is about 28.12 %. [6] In our study, hospital mortality (first 48 hours), in the complete SAB group is about 16.66 %, with HR at 5.4, so occurrence of complete SAB increases mortality. The right acute coronary syndrome is the predictive factor of mortality, which could be related to hemodynamic instability, acute right ventricular failure, and severe bradycardia.

Conclusion
Complete Sino atrial block (SAB) in acute coronary syndrome with ST segment elevation is not rare, but less frequent than Atrio ventricular block. Its incidence was reported in the literature, but no data available about its predictive factors. In our study we reported incidence of complete SAB and also its predictive factors of and related mortality. Its predictive factors according to our study are: right acute coronary syndrome, infero-basal acute coronary syndrome, and large right atrium. The occurrence of complete SAB increases the risk of hospital mortality, related to hemodynamic instability, acute right ventricular failure, and severe bradycardia. To our knowledge, predictive factors of complete SAB were reported for the first time.