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Survival in Acute Myocardial Infarction

Iraola, Marcos; Santana, Argelio;
Rodríguez, Belkys; Valladares, Francisco.

University Hospital "Dr. Gustavo Aldereguía Lima", Cienfuegos, Cuba

SUMMARY
Introduction: The problem in acute myocardial infarction (AMI) survival has some approaches. The delay to receive assistance in any of the AMI phases can play a significant role in the development of complications and the limitation to give of drugs that patients most receive immediately. Sex and age have been associated with these events.
Objective: To identify the one-year survival in patients with AMI following admission to the Intensive Care Unit (ICU).
Material and Methods: 108 patients with IMA admitted in the ICU of the University Hospital "Dr. Gustavo Aldereguía Lima" in Cienfuegos, Cuba between January 1st and September 30 of 1998. Retrospective, observational study. Survival was studied in relation to sex, age, localization of the infarction and the administration of thrombolytic therapy.
Results: The overall one-year survival was 74.1%. Differences in survival were found: sex (men 79.7% vs. women 61.8%, p<0.05), age (87.5% in <60 years vs. 63.3% in >60 years, p<0.005), localization of the AMI (anterior 62.9% vs. inferior 84.9%, p<0.005). No differences were found in the one-year survival related with the administration of thrombolytic therapy. Table 1.

Survival after AMI according to sex, age, localization and use of thrombolytic therapy.

Discussion: Deaths in ischemic heart disease in men have declined. Age, comorbidity and limitations in receive thrombolytic therapy can explain less survival in women than in men. Increase in age lead to increase mortality and it limits the use of thrombolysis. The in-hospital mortality was 22.2% and it remains high in reference to other reports.
Conclusion: The one-year survival rate found was low. Deficiencies in the pre-hospital, in-hospital and post-hospital phases of patients care can explain these findings.

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INTRODUCTION
   Cardiovascular diseases, and within them, Acute Myocardial Infarction (AMI), have been the greatest health problem and the main cause of death in many countries during several decades, nevertheless it has been observed that mortality due to this cause has been declining in the last two or three decades. During the 1969-1985 period, countries like The United States, Australia, New Zealand, Canada and Israel showed important decreases (1), but in spite of this, there are authors who consider that morbility and mortality by AMI is still elevated (2-3).

   The problem of survival for patients who undergo an AMI has various approaches, because this aspect is influenced upon by numerous factors. Time is a very important parameter. The patient's delay to recognize the symptoms and ask for medical attention, or the delay if the symptoms are not recognized by the doctor he goes to, or the one produced during transportation to the hospital can motivate the presence of immediate complications and even death (4). The type of treatment applied is another factor which has extreme importance in the results that will be obtained concerning survival. There are drugs of proven efficacy in AMI that should be prescribed immediately if there are not counter indications, as in the case of thrombolytic agents, beta-blockers and aspirin (ASA) (5,6). These drugs have demonstrated their short and long term usefulness, but even though they are indicated for this disease, they are not always prescribed (7,8).

   In our province there are no antecedents of designed studies which evaluate survival of AMI in patients discharged from hospital and which measure, at least as a final point, the impact of medical care.

OBJECTIVE
   To determine the survival of AMI patients during the year after admission to the ICU.

MATERIAL AND METHODS
   Patients: The 108 patients diagnosed with AMI who were admitted to the ICU at the "Dr. Gustavo Aldereguía Lima" University Hospital between January 1st to September 30th 1998.

   Study Design: Retrospective, descriptive, case-series type. A revision was made of the registration of AMI patients admitted to the ICU, and the following variables were taken from the clinical files: age, sex, infarction location, whether trombolysis was or was not performed and the moment when death occurred. The authors requested the Statistics Department of the Provincial Health Sector to supply the list of the deceased patients whose basic cause of death was AMI, their date of death and the place where death occurred were also specified. Within this list, we looked for the patients who were the subject of our study in order to determine whether they were alive or dead, and in the latter case, to know the time interval between death and admission. Survival was determined at 2, 7, 30, 180 and 365 days.

   Statistical analysis: The variables obtained were recorded in a data collection form, later they were related and analyzed in the Epi Info program, version 6.0. The results were expressed in absolute numbers, percentages, mean and standard deviation (SD). For the analysis of difference between proportions, the variance analysis was used (ANOVA). The results were interpreted as significant when the value of p was less than 0.01. For the graphic representation of survival Kaplan and Meier's curve was used.

RESULTS
   The average age of the patients was 62.9±14.4 years (Table 1). With regards to sex, the average age of women was greater compared to men (67.7±12.3 versus 60.7±14.8, p=0.01848). On the other hand, upon hospital discharge the deceased showed a higher average age compared to the living (69.54±15.18 versus 61.0±13.7, p=0.01001).

   The survival rate observed 2 days after occurrence of AMI was 85.1%, which was decreasing progressively to 74.1% a year (Table 2 and Graph 1). The survival rate observed in men was always larger in all the periods of time. In a year's time, 79.7% of the men and 61.8% of the women survived (p=0.04785).


   Those over 60 years of age predominated, and it was significant that for all the periods of time analyzed, they reached less survival. In a year's time, 63.3% of those over 60 years and 87.5% of those under 60 years were alive (p=0.00440).

   There was practically an equal number of patients with anterior and lower location of the infarction, however, survival was greater for the second ones in all time intervals. In a year's time, 84.9% of the patients with lower location infarctions managed to survive, and so did 62.9% of those who had anterior location (p=0.00982). In our series there was only 1 case of acute left branch block as electrocardiographic criteria for AMI and this one survived in a year.

   Thrombolytic treatment was given to 69 patients out of 108 (63,8%). These patients showed a higher survival rate during all the time periods. Within a year, 78.3% of the thrombolyzed patients survived and only 66.7% of the not-thrombolyzed (p=NS).

DISCUSSION
   Since the mid 60's, men have shown a decrease in the deaths caused by coronary disease as compared to women. Age, the presence of comorbilities such as hypertension and diabetes, and the limitation in receiving thrombolytic treatment have explained, among other factors, the lower survival in women (8,10). Hochman found among women a larger number of complications during hospitalization with a lower survival rate within 30 days (11). In our study, there was a lower survival rate for women during all the time intervals, which we can relate to the higher average age they showed. Other factors were not related.

   Around 75% of the patients who undergo an AMI are over 70 years old (12). our study comprised patients with AMI that were hospitalized, and the largest number were over 60 years of age. Other studies performed with patients hospitalized because of an AMI point to average ages of 67 years (3) and 61 years (9). For the different times in which survival was evaluated, it was lower in those over 60 years. It has been observed that the older the age, the higher the mortality, specially after 70 years (9,13). Some have found that old age is a factor that limits the use of thrombolysis with a higher risk to die when its benefits are not received (8). Other authors have also referred to this fact and state that elderly patients, specially after 70 years of age, are treated less vigorously than the young ones, and they delay longer in receiving medical care, for which reason they have less possibilities to receive thrombolytic treatment (18). In our study we do not measure the use of thrombolysis according to age, therefore the influence of its use in relation to this variable was not determined. Age is considered an important risk factor when the AMI patients are stratified, because it is a marker of the depression of the left ventricular function, besides the elderly are more predisposed to develoving cardiac insufficiency and shock after an infarction (14,15). Survival in anterior location was lower compared to survival in lower location. Infarction location is one of the parameters which is taken into account when the risk is stratified and it is known that those with anterior location have twice the probability to die than those who have a lower infarction (15). A study performed in Israel found that there was practically an equal percentage of anterior and lower infarctions, however the presence of complications such as cardiac failure and arrhythmias was greater for the former, with a higher mortality rate within 1 year and 5 years (16).

   More than 30 years ago, the value of thombolysis was acknowledged, however it was not used as primary treatment until the central role of thrombosis was not established as a cause of AMI with Q wave, and its impact on mortality was proved. The efficacy of this procedure depends on the shorter time in which it is applied and of course, the fact of deciding for its application will bring about innumerable advantages in saving myocardio after the initiation of the ischaemia. An "open artery" is related to: improvement of the ventricular function and of the collateral blood flow, decrease of the infarct expansion, reduction of the possibility of the formation of ventricular aneurysm, it improves the ventricle remodeling, influences upon the achievement of a smaller ventricular dilatation, reduces ventricular arrhythmias and, in the long run, improves survival (17). Different studies have referred to the significant reduction of mortality within 35 days and it is known that these benefits can be maintained for 6 months (6). Recent studies show that they are extended beyond that (1). In a study about the benefit time of thrombolysis, Fox states that these benefits were observed 8 years after its application (18). Another study found that, when it is administered during the first 4 hours of the initiation of symptoms, survival is improved even to a period of 12 years (19). The benefits of its use are enhanced when it is associated with the administration of ASA and beta blockers and above all with its early and sustained administration during the years following hospital discharge (6,20). Survival was always greater in thrombolyzed patients. At the end of the study, 78.3% of the patients who received thrombolytic treatment survived, value that was slightly larger than general survival itself, which was 74.1%.

   Early mortality by AMI has decreased in the last 3 decades. Before the creation of Coronary Care Units it was 30%. Defibrillation, protection of ischemic myocardio and early coronary recanalization diminished it even more (22). During the last years numerous research papers on this topic have been carried out, and intra-hospital lethality rates of 18% (3) 16.7% (9) and even 10% (21) have been found. In a multivarious analysis, the predicting factors of intrahospital death were age, re-infarction and a new cardiac failure, with a third of the deaths on the first day and nearly two thirds on the third day (21). In our study, intra-hospital lethality was 22.2%, an elevated figure compared to the reference studies (3,9,19,20). Two days after occurrence of the event, survival was 85.1%. Many authors refer to the fact that this is the period of higher risk of complications and death (15). The survival observed within 30 days was the same as the one observed after discharge, that is, the patients who survived their hospital stay lived until the 30 days. After the 30 days, practically all the patients who were living at that time survived to the year. In a three-year study where the survival of AMI patients was studied in two periods of time (1983-1984 and 1991-1992) it was 86% and 92%, respectively (22). Even though it was evaluated in a larger time interval, there was a higher survival rate than in our study of only one year, but they only took into account the living discharged patients after an AMI with ages between 25 and 64 years, whereas in our study we considered patients of all ages and from the moment of their admission to the ICU.

CONCLUSION
   A survival rate of 74.1% within a year is low and highlights, in an indirect way, deficiencies in the medical care received by the patients with an infarction during the pre-hospital, in-hospital and post-hospital phases.

REFERENCES

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2. Cantor WJ, Ohman EM. Results of recent large myocardial infarction trials, adjunctive therapies, and acute myocardial infarction: improving outcomes. Cardiol Rev 1999; 7: 232-44.

3. Mahon NG, O´rorke C, Codd MB, et al. Hospital mortality of acute myocardial infarction in the thrombolytic era. Heart 1999; 81: 478-82.

4. Cannon CP. Time to treatment of acute myocardial infarction revisited. Curr Opin Cardiol 1998; 13: 254-66.

5. Gassler JP, Topol EJ. Reperfusion revisited: beyond TIMI 3 flow. Clin Cardiol 1999; 22(8 Suppl): IV20-9.

6. Ryan TJ, Anderson JL, Antman EM, et al. ACC/AHA guidelines for the management of patients with acute myocardial infarction. A report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. J Am Coll Cardiol 1996;28:1328-428.

7. The Clinical Quality Improvement Network (CQIN) Investigators. Influence of a Critical Path Management Tool in the Treatment of Acute Myocardial Infarction. Am J Man Care 1998; 4: 1243-51.

8. Barron HV, Rundle A, Gurwitz J, et al. Reperfusion therapy for acute myocardial infarction: observations from the National Registry of Myocardial Infarction 2. Cardiol Rev 1999; 7: 156-60.

9. Jenkins JS, Flaker GC, Nolte B, et al. Causes of higher in-hospital mortality in women than in men after acute myocardial infarction. Am J Cardiol 1994; 73: 319-22.

10. Becker RC, Terrin M, Ross R, et al. Comparison of clinical outcomes for women and men after acute myocardial infarction. The Thrombolysis in Myocardial Infarction Investigators. Ann Intern Med 1994; 120: 638-45.

11. Hochman JS, Tamis JE, Thompson TD, et al. Sex, clinical presentation, and outcome in patients with acute coronary syndromes. Global Use of Strategies to Open Occluded Coronary Arteries in Acute Coronary Syndromes IIb Investigators. N Engl J Med 1999; 341: 226-32.

12. Barakat K, Wilkinson P, Deaner K, et al. How should age affect management of acute myocardial infarction?. A prospective cohort study. Lancet 1999; 353: 955-9.

13. Tsuyuki RT, Teo KK, Ikuta RM, et al. Mortality risk and patterns of practice in 2070 patients with acute myocardial infarction, 1987-92. Relative importance of age, sex and medical therapy. Chest 1994; 105: 1687-92.

14. Gurwitz JH, Gore JM, Goldberg RJ, et al. Recent age-related trends in the use of thrombolytic therapy in patients who have had acute myocardial infarction. National Registry of Myocardial Infarction. Ann Intern Med 1996; 124: 283-91.

15. Peterson ED, Shaw LJ, Califf RM. Risk stratification after myocardial infarction. Ann Intern Med 1997; 126: 556-60.

16. Behar S, Rabinowitz B, Zion M, et al. Inmediate and long-term prognostic significance of a first anterior versus first inferior wall Q-wave acute myocardial infarction. Secondary Prevention Reinfarction Israeli Nifedipine Trial (SPRINT) Study Group. Am J Cardiol 1993; 72: 1366-70.

17. Burton ES. Infarto agudo del miocardio. En: Wyngaarden JB, Smith LlH, Bennet JC, editores. Cecil Tratado de Medicina Interna. 19na ed. México: Interamericana; 1994. p. 349-65.

18. Fox KA. Have we reached the limit with thrombolytic therapy?. Cardiovasc Drugs Ther 1999; 13: 211-6.

19. French JK, Hyde TA, Patel H, et al. Survival 12 years after randomization to streptokinase: the influence of thrombolysis in myocardial infarction flow at three to four weeks. J Am Coll Cardiol 1999; 34: 62-9.

20. Kristjansson JM, Andersen K. Improved one-years survival after acute myocardial infarction in Iceland between 1986 and 1996. Cardiology 1999; 91: 210-4.

21. Mynard C, Weaver WD, Litwin PE. Hospital mortality in acute myocardial infarction in the era of reperfusion therapy (the Myocardial Infarction Triage and Intervention Project). Am J Cardiol 1993; 72: 877-82.

22. Stewart AW, Beaglehole R, Jackson R, et al. Trends in three years survival following acute myocardial infarction, 1983-1992. Eur Heart J 1999; 20: 803-7.

 

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2nd Virtual Congress of Cardiology

Dr. Florencio Garófalo
Steering Committee
President
Dr. Raúl Bretal
Scientific Committee
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Dr. Armando Pacher
Technical Committee - CETIFAC
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