Factors Influencing the Outcome of Thrombolysis in Acute Myocardial Infarction

INTRODUCTION: Coronary heart disease has been defined as "impairment of heart function due to inadequate blood flow to the heart compared to its needs, caused by obstructive changes in the coronary circulation to the heart". It is the cause of 25-30% of death is most of the industrialised countries. In India also it is a major public health problem. It is aptly called by WHO as the modern epidemic. The increasing incidence of coronary heart disease may be a reflection of increased longevity, adoption of high-fat diet based on meats, decreased exercise, modern life style, made possible by increasing affluence. It is not surprising to note that Sir William Osler devoted only a few pages in his text book of medicine, published in 1892, to the discussion of Acute Myocardial Infarction. It was the brilliant work of Herrick in 1912, who performed autopsy on Acute Myocardial Infarction patients that putforward the new concept of thrombotic occlusion of coronary artery as the cause of downstream necrosis of heart muscle. Definitive proof for the above said concept came from angiographic studies performed during the early hours of the acute coronary event. This prompted scientists to systematically test the thrombolytic strategies to treat Acute Myocardial Infarction, opening that new era of thrombolytic therapy in Acute Myocardial Infarction. Scientists have developed many effective thrombolytic drugs like, streptokinase, recombinant tissue plasminogen activator (rt PA), Reteplase (rPA), urokinase, APSAC (Anisoylated plasminogen streptokinase activator complex) etc. Evidence for the use of thrombolytic therapy came from large multi centre studies. GISSI and ISIS-2 confirmed reduction in mortality with the early use of streptokinase5. ISAM (intravenous streptokinase in Acute Myocardial Infarction study group) also stands as a proof of efficacy of thrombolytic drugs to reduce mortality. Success rate of thrombolysis and thus the overall reduction in mortality is different among different agents used6. The GUSTO-1 trial showed a 30 day mortality of 6.3% for accelerated t-PA versus 7.4% for streptokinase with intravenous heparin. But because of the prohibitive cost of tPA, streptokinase became the sheet anchor for thrombolytic therapy in Govt. General Hospital. Thrombolytic therapy has revolutionized the management of Acute Myocardial Infaction. GUSTO angiographic substudy showed a success rate of 54% at 90 minutes using IV streptokinase and Heparin. Thrombolytic therapy has been consistently proven to reduce the mortality and morbidity. Inspite of this it has been recognised that thrombolytic therapy has failed in a significant population. There is lot of room for improvement. We need to identify the factors that are responsible for failure of thrombolysis. In this background, we decided to look into our own patients who receive streptokinase for Acute Myocardial Infarction, in the coronary care unit of Govt. General Hospital. AIM OF THE STUDY: 1. To find out the overall success rate of thrombolysis in the coronary care unit of Govt. General Hospital. 2. To find out whether the following parameters influence the outcome of thrombolysis: a. Age, b. Sex, c. Time of Streptokinase administration, d. Pre-infarction angina, e. Alcohol intake, f. Smoking status, g. Pre existing systemic hypertension, h. Diabetes mellitus, i. Location of Myocardial infarction. MATERIALS AND METHODS: Place of Study: This study was conducted in the coronary care unit of Govt. General Hospital and Madras Medical College and Research Institute. Period of Study: From Jan 2005 to Feb 2006. Design: Observational prospective cohort study of patients receiving streptokinase for acute myocardial infarction. A total of 83 patients were included in the study. Methodology: Subject Selection: 1. Inclusion Criteria: a. Presence of typical chest pain suggestive of Acute myocardial infarction along with ECG evidence of Acute myocardial infarction who were thrombolysed. Criteria for thrombolysis being 2 mm or more ST elevation in two contiguous precordial leads or 1 mm or more ST elevation in two contiguous limb leads. ECGs were recorded using Hewlett Packard Page write 100 machine. b. Time window of 12 hrs from the onset of pain to the initiation of thrombolysis. 2. Exclusion Criteria: 1. Late thrombolysis (more than 12 hrs from the onset of pain). 2. Recurrent myocardial infarction. 3. Presence of bundle branch block. 4. Development of pericarditis CONCLUSION: In this study the overall success rate of thrombolysis was 54%. • Inferior wall myocardial infarctions had a better success rate than anterior wall myocardial infarctions and it was statistically significant. • Smokers had a lesser success rate than non smokers, but it did not reach statistical significance. • Alcohol intake was associated with a better success rate even though statistically not significant. • Hypertensives didn't show any difference in the success rate. • Diabetics donot differ from non diabetics with respect to the success rate of thrombolysis. • There was a trend towards a worse outcome in those aged more than 60 years. But it was not statistically significant. • Gender was not found to influence the success rate of thrombolysis. • Pre infarction angina had no effect on the success rate of thrombolysis. SUMMARY: The study was conducted to evaluate the success rate of thrombolysis in acute myocardial infarction and the various factors influencing its out come. It was done by observational prospective cohort study of patients receiving streptokinase for acute myocardial infarction in coronary care unit, Government General Hospital, Chennai. The overall success rate of thrombolysis was 54%. Patients with inferior wall myocardial infarction had a better out come than anterior wall myocardial infarction. Alcohol, smoking and age were factors which influenced the out come, but were not statistically significant. Early thrombolysis had a better out come when compared to other predictors. Success rate was 64% in those patients thrombolysed within 4 hrs. from the onset of symptoms. Time window was found to be the most powerful factor influencing the out come of thrombolysis in patients with acute myocardial infarction