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An evaluation of the prognostic indices in acute myocardial infarction SJ Mishra, SC Sharma, SC Bandi, PK Periwal, BM Amin, NJ Shah, IJ PintoIntensive Coronary Care Unit, Medical Research Centre, Bombay Hospital Trust, Bombay Hospital, Marine Lines. Bombay-400 020, India
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 614423
A prospective study of hundred patients of acute myocardial infarction admitted in the Intensive Cardiac Care Unit was carried out. The prognosis of each patient, immediate and delayed mortality, were assessed on admission by the coronary prognostic indices (C.P.I.) formulated by Peel, Norris and Chapman. The merits and drawbacks of each coronary prognostic index system are discussed. It is felt that the coronary prognostic index would be more accurate if a higher score is given to precursor, life threatening arrhythmias, and conduction defects, and the prognostic index is calculated daily during the stay in the I.C.C.U.
Assessment of prognosis in acute myocardial infarction is of utmost importance to a treating clinician as it helps to determine the period of stay in an Intensive Coronary Care Unit, the period of immobilization after the attack and plan of rehabilitation. Patients with acute myocardial infarction are now observed continuously in Intensive Coronary Care Units and it has become possible to assess more acucurately the likely prognosis of an individual patient. The coronary prognostic indices commonly used are those reported by Peel et al [12] Norris et al [9] and Chapman et al [4] and many clinicians have combined their criteria to calculate the mortality and assess the prognosis of an attack of acute myocardial infarction. As the risk factors in acute myocardial infarction in India differ from those in Western countries [13] it is possible that the severity of the disease and clinical course and prognosis also differ. The purpose of this article is to compare the accuracy of the three commonly used coronary prognostic indices [4],[9],[12] in Indian patients with myocardial infarction.
One hundred consecutive patients with acute myocardial infarction admitted at the Intensive Coronary Care Unit of the Bombay Hospital were studied. There were 83 males and 17 females in the age range from 37 years to 76 years. A detailed medical history with special reference to age, symptomatology, precipitating factor, previous history of infarction, angina, hypertension or diabetes was enquired and their family history was noted. A detail physical examination was performed and pulse, systolic blood pressure, presence of shock, cardiac failure and other complications were recorded on admission. Electrocardiogram was taken to find out the extent of infarction, arrhythmias or conduction defect. A portable X-ray chest was taken routinely on each patient to assess the heart size and the condition of lung fields. Fasting venous blood was collected at the time of admission for routine examination and for serum glutamic oxaloacetic transminase, lactic dehydrogenase, sugar, urea and serum electrolytes. Enzyme studies were repeated after 24 hours and 48 hours. All the patients were observed under continuous E.C.G. monitoring for 2-3 days with the help of heart rate monitor, audiovisual alarm system and arrhythmia monitor at the Central Nursing Station. All patients were assessed on admission for their likely prognosis by recording the score according to the indices of Peel et al , [12] Norris et al [9] and Chapman et al, [4] in a special protocol. Patients were kept under observation during the intermediate coronary stay. The fatal cases were analysed for their cause of death and their prognostic index scores were correlated.
A hundred patients of proved acute myocardial infarction were studied. Their electrocardiographic diagnosis is stated in [Table 1]. Thirteen patients out of hundred included in this study expired (13%). The prognostic index scores of these 100 patients are tabulated in [Table 2]. For the convenience they were classified in 3 groups-mild, moderate and severe with the comparable scores of 3 prognostic indices. The mortality rate was higher in the more severe forms of the disease. Of the 13 cases which expired, cardiogenic shock was the causative factor for 6 of them accounting for 46.15%. 3 died of cardiac arrest, 2 following ventricular asystole and 1 due to ventricular fibrillation, thus accounting for 23.0717 . 3 (23.07%) cases succumbed to left ventricular failure and pulmonary oedema and 1 case (7.68%) died as a result of pulmonary embolism. Thus pump failure, (shock, left ventricular failure and pulmonary embolism) were responsible for 69.227c mortality. It was observed that 7 patients who had very high scores in one or all three coronary prognostic indices have survived.
Mortality in case of acute myocardial infarction treated in a hospital intensive coronary care unit, varies widely according to the individual risk factors. Peel et al [12] constructed a coronary prognostic index (CPI) by addition of these risk factors viz. age and sex, past history of infarction, angina or other cardiovascular disease, presence of shock or failure and electrocardiographic findings. The expected mortality in their indices was directly proportional to the scores. Their indices are based mostly on subjective criteria and have no consideration for the site of infarction. It has been observed by Beard et al [2] and Norris et al [9] that there is a significantly greater mortality from anterior wall infarction compared with posterior wall infarction. This has been observed in our series too [Table 1]. Failure to consider this factor may have caused a lower score in the fatal cases. Norris et al [9] formulated coronary prognostic indices based on a prospective study of 57 patients of myocardial infarction using mostly objective criteria consisting of age of the patient, site of infarction, systolic blood pressure on admission, heart size, lung fields and history of previous infarction. They claimed that theirs was an unbiased method of assessment of prognosis of acute myocardial infarction and was calculated immediately after admission. We have observe( in the present series that this index too does not correlate well with the mortality rate, as some patients having as love a score as 1.7 have died and those having as high a score as 4.8 have had an uneventful recovery [Table 2] and [Table 3] On closer analysis it was noticed that it our series the patients with low Norris (CPI) score mostly died of ventricular fibrillation, pulmonary embolism or hear' block which had not been given an adequate score while constructing Norris's, C.P.I. Analysis of most of the larger recorded series [5],[7],[10] has shown that during the first 2448 hours after acute myocardial infarction irritability is at its peak; 85. 90% of the patients in intensive coronary care unit developed one or more arrhythmias. These arrhythmias may be benign and short lasting but certain arrhythmias may be persistent and may lead to a fatal outcome. The recorded incidence shows that these fatal arrhythmias, especially ventricular tachycardia (13.4%), ventricular fibrillation (11% ) and complete heart block (6.4%) are not uncommon causes of death. Ventricular fibrillation is the commonest malignant arrhythmia accounting for about 60% of deaths that occur within 1-2 hours after acute myocardial infarction, mostly before the admission to intensive coronary care unit. [11] Although cardiac arrest due to ventricular fibrillation is relatively common during first 24-48 hours after acute myocardial infarction, it can also occur later in the course of the disease even after transfer of the patient from intensive coronary care unit. [1] Ventricular fibrillation is a major cause of death and the importance of precursor arrhythmias has been completely ignored while formulating the Norris's prognostic index and that might explain its inaccuracy. The assessment of likely prognosis of acute myocardial infarction when calculated and analysed by the coronary prognostic index scores constructed and reported by Chapman [4] shows that in mild cases (CPI scores 0-28) the mortality was 6.06% while in severe cases (CPI scores 57-83) the mortality was 58.33%. But it has been observed in our series that patients with scores as low as 4 had expired and on the other hand patients with scores as high as 80 had uneventful recovery. In Chapman's coronary prognostic index like in Norris's prognostic index, there is no score for arrhythmias as it is felt that in a well run intensive coronary care unit, all arrhythmias can be controlled. In addition, the known risk factors like previous history of infarction, age of patient, presence of heart failure have not been taken into account in constructing this coronary prognostic index. The occurrence of incipient left ventricular failure after acute myocardial infarction is relatively common and may not worsen the prognosis, but occasionally acute pulmonary oedema may develop after 48 hours, with rapid rise in left ventricular and diastolic pressure leading to rapid increase in pulmonary venous pressure. [8] If this occurs it will increase the mortality and this complication has accounted for three of the deaths in the present series. The score given to left ventricular failure is therefore considered low. The presence or absence of arrhythmia and heart block has not been taken into account while compiling Chapman's coronary prognostic index. Complete A-V block is particularly hazardous and it may precipitate cardiac arrest. In the present series 23.07% of the mortality was due to cardiac arrest (due to ventricular fibrillation or ventricular asystole). Complete heart block develops relatively late with inferior wall infarction and does not have much effect on the prognosis [9] On the other hand with anterior wall infarction, complete A-V block develops suddenly leading to high mortality. [3],[6] Prediction of the eventual outcome of acute myocardial infarction is difficult as re-infarction cannot be predicted and may occur in cases which at the beginning are mild; further although the incidence of fatal complications is higher in severe cases, a certain number of mild cases may also develop fatal complications later in the intermediate stage [14] as well as during the stay in intensive coronary care unit resulting in unpredictable deaths. It would appear that a higher score should be given to life threatening and precursor arrhythmias and conduction defects and the scores must be assessed every day during the stay in intensive coronary care unit. This would combat the drawback of low admission score and enable us to give a more accurate prognosis.
[Table 1], [Table 2], [Table 3]
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