Complete Heart Block In Acute Myocardial Infarction Biology Essay

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It has been recognized that many patients with complete heart block suffer from a bilateral bundle branch block is due to ischaemic heart disease. Ischemic heart disease is the most common for of heart disease causing complete heart block (CHB) and sudden death. CHB is a condition in which no conduction of electrical impulses occurs from atria to ventricles lead to severe bradycardia and acute heart failure. Heart blocks may occur as complications of acute myocardial infarction (AMI) and are associated with increased mortality.

Study Setting:

Study was conducted in the department of Cardiology, Liaquat University of Medical and Health Sciences, Hyderabad.

Study Design:

Cross sectional and descriptive study

Duration of study:

Six months from 1st August 2009 to 31st January 2010.

Materials and Methods:

Eighty seven patients were taken to fill in a pre-formed questionnaire. ST segment elevation equal to or more than 1mm (0.1mv) in two of these leads II, III and aVf. Rise in serum creatinine kinase level (CPK Level) more than twice the normal Value along with CK-MB fraction more than 6% of CPK value.

All patients who came in the coronary care unit (CCU) or cardiac ward with history of chest pain, shortness of breath, nausea, vomiting and unconsciousness were evaluated and enrolled in the study. All the patients were examined for acute myocardial infarction by performing electrocardiogram (ECG). The cardiac enzymes Tropinin T was also performed at bed side by venous blood sample.

Temporary pacemaker was also considered.

Results:

Out of 87 patients, prevalence of heart blocks was 27.58% (24 patients), most of the cases (males & females) were found in the age group of 46 to 66 years. There was highly significant difference in the gender (P value < 0.0001).

Anterior Wall MI was present in 50(50.5%) patients. Of these, 13(54.2%) cases were found with complete heart block. Inferior wall MI was present in 37(42.5%) cases, amongst which, 11(45.8%) cases were found with complete heart block. There was no any significant difference or statistical correlation between Anterior Wall MI and Inferior Wall MI with complete heart block (P value > 0.05).

Overall mortality was determined in 2 (2.3%) patients with anterior wall MI. Three (3.4%) patients with inferior wall MI without complete heart block developed ventricular tachycardia, 2(3.2%) cases of inferior wall MI had Re-infarction and 1(1.1%) patient had post MI Angina. One (1.1%) patient who had complete heart block with anterior wall MI developed pericarditis and Stokes - Adams attacks respectively. Only 3(12.5%) patients with inferior wall MI were reverted to normal rhythm.

Conclusion:

Development of complete heart blocks has important prognostic significance. Complete heart block has frequent complication of myocardial infarction.

Keywords: Acute Myocardial infarction, complete heart block, Inferior wall MI, anterior wall MI

INTRODUCTION: Complete heart block (CHB) is major clinical complication in patients hospitalized with acute myocardial infarction (AMI), prior studies have suggested that approximately 4% to 7% of patients hospitalized with AMI will develop CHB.[1]

In pre-thrombolytic era, high (third degree) AV block was seen in approximately 5-7% of patients presenting with acute MI.[2] In setting of Inferior MI, this was even as high as 28%.[3]

Although, after the advent of thrombolytic therapy has substantially decreased the mortality associated with acute MI, the incidence of AV block, particularly in myocardial infarction[4], associated with high mortality in hospital, however, its effect on long-term mortality is uncertain.[5] The occurrence of high degree AV block is usually explained by the fact that the blood supply to the AV node depends in 90% of patients on the Right Coronary Artery (RCA).[6-8]

CHB may be inherited acquired, most important causes include myocardial infarction, drug intoxication, surgery, rheumatic disease, infiltrative heart disease, myocarditis, and hypertensive heart disease. Acquired CHB is usually accompanied by signs and symptoms of reduced (CO). The prognosis of CHB has improved greatly after the invention of the pacemaker. Before using pace maker, acquired CHB was associated with high mortality with sudden death, progressive heart failure[9], complete atrio-ventricular block is relatively frequent complication of myocardial infarction with early diagnosis and thrombolytic therapy, hospital mortality reduced. Complete AV block and syncope sometimes are the presenting signs of acute myocardial infarction. Among patients of acute inferior myocardial infarction, frequency of artio-ventricular block is high particularly complete heart block that complicates in hospital course.[10]

The incidence of CHB complicating AMI has declined appreciably over time, with the greatest decline in these incidence rates occurring during the most recent years (2.0% of patients hospitalized with AMI in 2005 vs. 5.1% in 1975).[11] Although Rathor and Gersh showed that the incidence of heart blocks is higher among those patients who had a history of thrombolytic therapy.[12]

Contemporary AV block rarely complicates myocardial infraction with early revascularization strategy, the incidence of AV block decreased from 5.3 to 3.7%. Occlusion of each of the coronary arteries can result in development of conduction disease despite redundant vascular supply to the AV node from all coronary arteries. Most common the occlusion of the right coronary artery (RCA) is accompanied by AV block. In particular the proximal RCA occlusion has high incidence of AV bock (24%) since not only the AV nodal artery is involved but also right superior descending artery, which originates from the very proximal part of the RCA. [13]

In most cases, AV block resolves promptly after revascularization but sometimes the course is prolonged. Overall the prognosis is favorable. AV block in a setting of occlusion of the left anterior descending artery (particularly proximal to the first septal perforator) has more ominous prognosis and usually requires pacemaker implantation. Second degree AV block associated with bundle branch block and in particularly with alternating bundle branch block is an indication for permanent pacing. [14]

Mortality/Morbidity

Patients with complete heart block are frequently hemodynamically unstable, and as a result, they may experience syncope, hypotension, cardiovascular collapse, or death. Other patients can be relatively asymptomatic and have minimal symptoms other than dizziness, weakness, or malaise. 

MATERIALS AND METHODS

This Cross sectional and descriptive study was conducted in the departments of Cardiology and Medicine, Liaquat University of Medical and Health Sciences, Hyderabad for six months from 1st August 2009 to 31st January 2010.

Total 87 cases of myocardial Infarction were included, adult patients age ranged 25 to 65 years of either sex presenting with severe chest pain, shortness of breath and unconscious state and fulfill the following criteria:

ST segment elevation equal to or more than 1mm(0.1mv) in two of these leads II, III and aVf.

Rise in serum creatinine kinase level (CPK Level) more than twice the normal Value along with CK-MB fraction more than 6% of CPK value.

Inferior wall myocardial infarction with concomitant right ventricular infarction i.e. ST segment elevation equal or more than 1 mm in one or more right precordial lead V4R to V6R.

Exclusion criteria:

The patients with history of artificial pacemaker implantation.

The patients had previous history of myocardial infarction / old myocardial infarction and were already on maintenance therapy.

Data Collection Procedure:

The study was conducted on the basis inclusion and exclusion criteria. A written consent was taken from all patients who came in the coronary care unit (CCU) or cardiac ward with history of chest pain, shortness of breath, nausea, vomiting and unconsciousness were evaluated and enrolled in the study. All the patients were examined for acute myocardial infarction by performing electrocardiogram (ECG). The cardiac enzymes Tropinin T was also performed at bed side by venous blood sample.

Temporary pacemaker was also considered if any type of bardycardia(sinus or atrio-ventricular block) causing symptoms and signs of low perfusion. In these patients of acute myocardial infarction, the in-hospital complications were divided into major and minor. Among the major asystole, angina, reinfarction, altered consciousness, ventricular tachycardia, death congestive cardiac failure (CCF) and sinus bardycardia. Among the patients having atrioventricular blocks, the degree of block, duration and in case of complete heart block the stability of escape rhythm in view of ORS width, heart rate and associated other conduction defects (inraventicular) were also recorded. The diagnosis of MI and detection of complete heart block were made according to parameters. All the data were recorded through a structured proforma.

Ethical considerations:

Informed consent was taken from all patients participated in the study. All the expenses of this study were paid by the researcher himself

Statistical analysis

The data were evaluated in statistical program SPSS version 16.0. Qualitative data (frequency and percentage) such as complete heart block (with and without), Gender, age (in groups), myocardial infarction (inferior and anterior), complications and outcome were presented as n(%) and chi-square test was applied to compare the proportions among the groups with and without complete heart block. The numerical parameters such as age (in years), hospital stay(in days), heart rate etc. were expressed as Mean + Standard Deviation and student t test (2 tailed) was applied to compare the means among the group (with and without complete heart block). All the data were calculated on 95% confidence interval. A P value < 0.05 was considered as statistically significant level for all the comparisons.

RESULTS

Eighty seven patients of myocardial infarction were analyzed in this study based on inclusion criteria. Of these, 54(62.1%) were male and 33 (37.9%) female. The mean age + SD of the patients was 52.03 ± 8.58 years (range 25-66 years). The overall prevalence of heart blocks was 27.58 (24 patients).

Out of these 87 cases of MI, 54(62.1%) were males, out of them 14(58.3%) males had complete heart block. There were 33(37.9%) females, out of them 10(41.7%) were presented with complete heart block. No significant difference was noted regarding complete heart block in gender (P value 0.80).

Out of 87 subjects, 27(31.0%) were seen in the age group of 25 to 45 years and 60(69.0%) cases were found 46 to 66 years of age group. Majority of the patients with complete heart block was seen in older patients.

Out of 27(31.0%) patients who were found in the age group of 25 to 45 years, 7(29.2%) patients with mean age + SD, 41.2 + 7.31 developed complete heart block as compared those, 60(60.9%) patients of > 45 years, 17 (70.8%) with mean age + SD, 55.5 + 6.48 developed complete heart block, there was statistically significant difference of age group with and without complete heart block. (P value 0.0001). Most of the males were older and all the females were found in the age group of > 45 years. There was insignificant difference among the gender and age (P value 0.81)

Out of 62(71.3%) cases of hospital stay < 7 days, 19(79.2%) patients with complete heart block and 43(68.3%) without complete heart block whereas out of 25(28.7%) cases of hospital stay > 7 days, 5(20.8%) had complete heart block and 20(31.7%) patients did not develop the complete heart block.

All the patients had Myocardial Infarction in this study, out of 87 cases of Myocardial infarction, Anterior Wall MI was present in 50(50.5%) patients. Of these, 13(54.2%) cases were found with complete heart block. Inferior wall MI was present in 37(42.5%) cases, amongst which, 11(45.8%) cases were found with complete heart block. There was no any significant difference or statistical correlation between Anterior Wall MI and Inferior Wall MI with complete heart block.

In-hospital complications 87 patients of acute myocardial infarction between complete and without complete heart block are presented. These complications were recorded during their whole stay in CCU. Overall mortality during hospital stay in 87 patients of acute myocardial infarction with complete heart block was determined in 2 (2.3%) patients with anterior wall MI. Three (3.4%) patients with inferior wall MI without complete heart block developed ventricular tachycardia, 2(3.2%) cases of inferior wall MI had Re-infarction and 1(1.1%) patient had post MI Angina. One (1.1%) patient who had complete heart block with anterior wall MI developed pericarditis and Stokes - Adams attacks respectively.

Out of 87 cases of myocardial infarction, only 3(12.5%) patients with inferior wall MI were reverted to normal rhythm.

Table No. 1: Demographic characteristics (n = 87)

Parameters

With Complete Heart Block

n = 24

Without complete Heart Block

n = 63

P value

Age (in years)

Gender:

Male

Female

Age groups:

25 to 45

46 to 66

Hospital stay (in days)

Hospital stay (in groups)

<7 days

>7 days

Heart Rate (beats/min.)

51.4 +9.34

14(58.3%)

10(41.7%)

7(29.2%)

17(70.8%)

5.5 +1.86

19(79.2%)

5(20.8%)

36.2 +3.42

52.2 +8.35

40(63.5%)

23(36.5%)

20(31.7%)

43(68.3.0%)

6.4 +2.17

43(68.3%)

20(31.7%)

89.1 +9.47

NS

NS

NS

NS

NS

<0.001*

Results are expressed as Mean + Standard Deviation

NS = not significant

* P value is statistically highly significant

Table No. 2. Mean comparison of age in years with and without complete heart block (n = 87)

Age groups

N(%)

With Complete Heart Block

n = 24

P value

Without complete Heart Block

n = 63

N(%)

P value

25 to 45 years (Mean +SD)

>45 years (Mean +SD)

7(29.2%)

17(70.8%)

41.2 +7.31

55.5 +6.48

<0.0001**

42.5 +3.3

56.7 +5.6

20(31.7%)

43(68.3.0%)

<0.0001**

** P value is statistically highly significant

Table No. 3. Myocardial infarction with and without complete heart block (n = 87)

Myocardial Infarction

With Complete Heart Block

n = 24

Without complete Heart Block

n = 63

Total

P value

Anterior Wall MI

Inferior Wall MI

13(54.2%)

11(45.8%)

37(58.7%)

26(41.3%)

50(57.5%)

37(42.5%)

0.80*

0.79*

* P value is statistically not significant

Table No. 4. Complications of myocardial infarction with and without complete heart block (n = 87)

Complications

With Complete Heart Block

n = 24

Without complete Heart Block

n = 63

Total

Intermittent asystole

Re-infarction

Ventricular tachycardia

Post MI Angina

Death

Pericarditis

Stokes - Adams attacks

1(4.2%)

0

0

0

2(8.3%)

1(4.2%)

1(4.2%)

0

2(3.2%)

3(4.8%)

1(1.6%)

0

0

0

1(1.1%)

2(2.3%)

3(3.4%)

1(1.1%)

2(2.3%)

1(1.1%)

1(1.1%)

Table No. 5. Complications with inferior wall mi (n = 87)

Complications

Inferior Wall MI

Total

With inferior

n = 37

Without inferior

n = 50

Intermittent asystole

Re-infarction

Ventricular tachycardia

Post MI Angina

Death

Pericarditis

No complication

Stokes - Adams attacks

0

2(5.4%)

3(8.1%)

1(2.7%)

0

0

31(83.8%)

0

1(2.0%)

0

0

0

2(4.0%)

1(2.0%)

45(90.0%)

1(2.0%)

1(1.1%)

2(2.3%)

3(3.4%)

1(1.1%)

2(2.3%)

1(1.1%)

76(87.4%)

1(1.1%)

Table No. 6. Complications with anterior wall mi (n = 87)

Complications

Anterior Wall MI

Total

With anterior

n = 50

Without anterior

n = 37

Intermittent asystole

Re-infarction

Ventricular tachycardia

Post MI Angina

Death

Pericarditis

No complication

Stokes - Adams attacks

1(2.0%)

0

0

0

2(4.0%)

1(2.0%)

45(90.0%)

1(2.0%)

0

2(5.4%)

3(8.1%)

1(2.7%)

0

0

31(83.8%)

0

1(1.1%)

2(2.3%)

3(3.4%)

1(1.1%)

2(2.3%)

1(1.1%)

76(87.4%)

1(1.1%)

Table No. 7. Comparison of outcome between inferior and anterior wall mi in complete heart block (n = 24)

Outcome

Inferior Wall MI

Total

Inferior

n = 11

Anterior

n = 13

Reversion to normal rhythm

No reversion to normal rhythm

3(27.3%)

8(72.7%)

0

13(100.0%)

3(12.5%)

21(87.5%)

DISCUSSION

Heart block (atrio-ventricular block) is more common with inferior than anterior infarction[15]. The development of heart blocks is associated with more post-infarction hypokinesia of cardiac walls, a lower ejection fraction, and greater in-hospital mortality. These detectable abnormalities have important prognostic significance.[16]

The present study reveals that complete heart block may be due not only to inferior wall myocardial infarction but also to infarcts of the anteroseptal wall. It seems clear that the majority of patients with inferior wall myocardial infarction, in whom the right coronary artery had probably been obstructed, suffered from a block which was situated above the bifurcation. The right coronary artery gives off the posterior perforating arteries that supply the posterior third of the interventricular septum.

Patients of this study were divided into two groups depending on absence and presence of complete heart block.

This study shows, overall prevalence with AMI who developed complete heart block was 27.58% (24 patients) out of 87 subjects. A study of Nguyen et al. [17] found that overall incidence of patients with AMI who developed complete heart block is 4.1% whereas Abdul Majeed Pirzada et al.[18] noted that prevalence of AMI with complete heart block was 4.0% out of 220 cases which is similar to the study of Nguyen et al. but found not similar to this study.

Although in this study there was a highly significant difference between the patient's age and incidence of complete heart block. (P value <0.0001) Table No. 3.

This study revealed 2.3% mortality rate out of 87 patients while it was noted by Ben-Ameur Y et al.[19] and Meine TJ[20], the mortality rate in patients with inferior MI and high degree AV block varies from 12-23%. They also reported that these patients had high mortality only in the presence of heart complete heart block. Similarly, in the study of Nguyen et al.[17] also found that patients with AMI who developed complete heart block had greater in hospital mortality 43.2%. In these studies, the mortality rate is found different as compare to this study due to the relatively larger infarct area. Moreover, it should be noted that the in-hospital mortality rate in our infarcted population was considerably lower than that observed in developed countries.[20,22]

The frequency of inferior wall MI in this study was 42.52%. Many studies have shown that patients with inferior MI associated with complete heart block have larger infarctions.[23,24-26]

In this study, I found that patients with inferior and anterior myocardial infarction who developed complications with complete heart block such as Ventricular tachycardia 3.4%, Re-infarction 2.3%, Intermittent asystole 1.1%, Post MI Angina, death, Pericarditis and Stokes - Adams attacks were seen in 1.1% respectively out of 87 cases. In the study of Khalid Amin et al.[15] , in his study, patients developed complications i.e. Death was 9%, post MI angina was in 27%, reinfarction was in 10%, intermittent asystole was 5% and ventricular tachycardia was 4% out of 130 patients whereas Stokes - Adams attacks were not seen in his study. The prevalence of complications was different in the study of Khalid Amin et al.[15] due to increase of patients.

CONCLUSION

It seems that the morbidity, as evaluated by the presence and severity of a Stokes-Adams attack, and mortality are much lower in patients with inferior wall myocardial infarction with block above the bifurcation.

The use of temporary transvenous pacemakers may have been somewhat excessive in patients with inferior wall myocardial infarction.

They are definitely indicated in those patients with anteroseptal infarctions and Stokes-Adams attacks.

Among patients with inferior wall myocardial infarction, only for those with block above and below the bifurcation and for those with Stokes-Adams attacks may the pacemaker be definitely indicated.

It is also our impression that in a patient with an inferior wall myocardial infarction and block, with a slow ventricular rate, the cardiac output may be improved by ventricular pacing at a faster rate.

This would in all probability be advisable when the block persists for several days. Most patients with inferior wall myocardial infarction and block above the bifurcation may recover with the use of isoproterenol. However, a larger experience is necessary before a final opinion can be given.

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