|Year : 2016 | Volume
| Issue : 3 | Page : 149-152
Study of conduction blocks in acute myocardial infarction
Ratan Ram, Konsam Biona Devi, Keisham Jaya Chanu, Th Shanti Devi, Santa Naorem, Dhanaraj Singh Chongtham
Department of General Medicine, Tertiary Care Teaching Hospital, Imphal, Manipur, India
|Date of Web Publication||28-Sep-2016|
Department of General Medicine, Tertiary Care Teaching Hospital, Imphal, Manipur
Source of Support: None, Conflict of Interest: None
Context: Acute myocardial infarction (AMI) is a global epidemic. As a leading cause of morbidity and mortality, AMI is a major public health problem. Many of these deaths are attributed to the development of arrhythmias during the period of myocardial infarction (MI). Aims: To study various patterns of conduction blocks occurring in AMI and to determine the prognostic implications of conduction blocks in AMI. Settings and Design: Study was conducted at a Tertiary Care Teaching Hospital in Imphal. The study design was longitudinal study. Subjects and Methods: One hundred AMI patients from October 2013 to September 2015 were evaluated by detailed history, clinical examination, routine investigations, and observed for conduction defects. Statistical Analysis Used: Statistical Package for the Social Sciences (SPSS 16.0 version) and t-test, Chi-square test, and Fisher's exact were used for statistical analysis. P < 0.05 was considered statistically significant. Results: Atrioventricular (AV) blocks were more common in inferior wall MI and bundle branch blocks were more common in anterior wall MI (AWMI). AMI patients with conduction block had higher chance of mortality (41.2% vs. 16.8%) as compared to nonconduction block AMI patients. Conclusions: Most of the AMI patients were males. The most common block is being first-degree heart block. AV blocks were more common in inferior wall MI and bundle branch blocks were more in AWMI. Mortality was increased in MI patients with conduction block than that of nonconduction block.
Keywords: Acute myocardial infarction, arrhythmias, conduction blocks
|How to cite this article:|
Ram R, Devi KB, Chanu KJ, Devi T, Naorem S, Chongtham DS. Study of conduction blocks in acute myocardial infarction. J Med Soc 2016;30:149-52
|How to cite this URL:|
Ram R, Devi KB, Chanu KJ, Devi T, Naorem S, Chongtham DS. Study of conduction blocks in acute myocardial infarction. J Med Soc [serial online] 2016 [cited 2020 Oct 31];30:149-52. Available from: https://www.jmedsoc.org/text.asp?2016/30/3/149/191179
| Introduction|| |
Acute myocardial infarction (AMI) is a global epidemic. As a leading cause of morbidity and mortality, AMI is a major public health problem.  Many of these deaths are attributed to the development of arrhythmias during the period of myocardial infarction (MI). 
Various types of conduction blocks develop following AMI. In acute inferior MI, first-degree atrioventricular (AV) block is present in 2%-12%, second-degree AV block in 3%-10%, and complete AV block (CAVB) in 3%-7%. CAVB is more common in acute inferior wall MI (3.7%-15%) than acute anterior wall MI (AWMI) (1%-8%). 
Bundle branch block in AMI carries poor prognosis. This has been attributed both to the extent of myocardial damage and to the frequency of ventricular asystole.  Development of conduction blocks worsens the outcome of AMI. Knowledge about various types of conduction blocks occurring in AMI helps in the early recognition of conduction blocks at an early stage so that appropriate treatment including pacing can be instituted at an early stage. 
| Subjects and methods|| |
The study was carried out in the Intensive Cardiac Care Unit and Department of General Medicine ward at a Tertiary Teaching Care Hospital, Imphal. A total of 100 AMI patients were enrolled in this study from October 2013 to September 2015. Diagnosis of AMI was made by the World Health Organization criteria, and diagnosis of conduction block was made based on electrocardiogram (ECG).
Patients who were previously known case of conduction defects and patients who were on drugs causing conduction blocks were excluded from the study. All the patients admitted were evaluated by detailed history, clinical examination, and the required investigations using specific pro forma. The patients were observed for conduction defects during the hospital stay. A conventional 12 lead ECG with rhythm strip was recorded at the earliest on admission and repeated subsequently each day as well as when required following admission.
Data collected was analyzed using IBM Corp. Armonk, NY: IBM Corp. SPSS 16. Descriptive statistics such as percentages, mean, and standard deviation was used. Analytical statistics: t-test, Chi-square test, and Fisher's exact were used. P < 0.05 was considered statistically significant.
Ethical approval was taken from the Institute Ethics Committee, before starting of study. Informed consent was taken from all participants before enrolling them in the study. However, patient could stop participating any time. All details of participating individual were recorded. Professional confidentiality was maintained.
| Results|| |
Among the 100 patients enrolled in this study. In both males and females, the most common age group for MI is 51-60 years age group as shown in [Figure 1]. The mean difference observed (59.6 years vs. 55.2 years), i.e., males were older than females, is found to be statistically significant (P < 0.05).
[Figure 2] shows that hypertension, smoking, and ischemic heart disease (IHD) were more among males, but diabetes was more among females; however, the finding is statistically insignificant (P > 0.05).
|Figure 2: Bar diagram showing distribution of patients by risk factors stratified by sex|
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[Figure 3] shows that majority of the MI occurred was inferior wall MI followed by AWMI.
|Figure 3: Bar diagram showing distribution of patients by site of myocardial infarction|
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[Figure 4] shows that among 40 inferior wall MI patients, 9 developed conduction blocks; 4 first-degree AV blocks, 3 second-degree AV blocks, and 2 third-degree AV blocks. Among 26 cases of AWMI, 4 developed conduction block; a case each of first- and second-degree AV block, left anterior hemiblock (LAHB), and left bundle branch block (LBBB).
|Figure 4: Bar diagram showing relation between type of myocardial infarction and conduction block|
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[Figure 5] shows that conduction block MI patients had greater chance of mortality (41.2% vs. 16.8%) than nonconduction block MI. This finding is found to be statistically significant (P < 0.05).
|Figure 5: Bar diagram showing relation between type of conduction block and mortality|
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| Discussion|| |
In this study, MI was common in the age group of 51-60 years, and the mean age was 57.3 years with a standard deviation of 9.5 years. Similar findings were observed in Chavda et al.  where MI is common in sixth decades of life and many studies. , However, in some studies, maximum incidence was found over 60 years of age. ,, Males were significantly younger than females when they had MI in this study. This finding is similar with Bangalore et al. 
The incidence of MI was more in males than females. Many studies have similar findings. ,,,,, This can be explained by more prevalence of risk factors such as hypertension, IHD, and smoking among males in this study.
Various risk factors such as hypertension were present in 27% of cases, diabetes in 25% of cases, IHD in 13% of cases, and smoking in 30% of cases. A similar finding was observed in the study by Chavda et al.  where smoking (72.0%) was the most common risk factor followed by IHD in 14% of cases and 10% had DM. The prevalence of hypertension and diabetes mellitus in the study by Hreybe and Saba  was 22.3% and 20.2%, respectively. On comparing between males and females, hypertension, IHD, and smoking were more among males, but diabetes was more among females.
Inferior wall MI is the most common site of MI in this study followed by AWMI. This finding is consistent with the study by Hreybe and Saba  and Shah et al. 
In this study, out of 100 MI patients, 17 (17%) had conduction block. Moreover, out of this 17, 7 (7%) cases were first-degree AV block, 4 (4%) cases were second-degree AV block, 3 (3%) cases were complete heart block, and one case each of LAHB, right bundle branch block, and LBBB. Similar findings were observed in the study by Bhalli et al.,  Archbold et al.,  and Shirafkan et al.  where conduction block was present in 17.6%, 16.0%, and 15.8% of patients, respectively.
Males had more conduction block than females (18.0% vs. 14.7%) as observed in this study and in Escosteguy et al.  study. However, there is no statistical significant difference.
Although the prevalence of cigarette smoking, hypertension, and diabetes mellitus in patients with heart block was greater than in patients without, the differences were not statistically significant.
The mortality rate among MI patients in this study is 21%. There were 7 deaths among 17 conduction block patients accounting for 41.2%, and there were 14 deaths among 83 patients with no conduction block accounting for 16.8%. Hence, MI patients with conduction block had higher chance of mortality as compared to nonconduction block MI patients. This finding is found to be statistically significant (P < 0.05). This finding is consistent with various studies. ,,,,,
| Conclusions|| |
The study showed that most of the MI patients were males and most common age group was 50-60 years. The study found out that conduction block was present in one-fifth of the MI patients. The most common block being first-degree heart block and third-degree heart block was present in three cases. AV blocks were more common in inferior wall MI, and bundle branch blocks were more in AWMI. Associated comorbidities increased the risk of conduction blocks in MI. Mortality was increased in MI patients with conduction block than that of nonconduction block.
Since mortality is increased among MI patients with conduction blocks, special attention must be given to these patients to improve the mortality rate in MI patients.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]