Asian Cardiovasc Thorac Ann 2004;12:324-329
© 2004 Asia Publishing EXchange Ltd
Impact of Age on The Results of Coronary Artery Bypass Grafting
Amir Mortasawi, MD,
Bert Arnrich1,
Jörg Walter, PhD1,
Inez Frerichs, PhD3,
Ulrich Rosendahl, MD2,
Jürgen Ennker, MD2
Department of Thoracic Surgery, Thoraxklinik, University of Heidelberg, Heidelberg, Germany
1 Technologic Faculty, Neuroinformatic Groups, University of Bielefeld, Bielefeld, Germany
2 Department of Cardiovascular and Thoracic Surgery, Heart Institute Lahr/Baden, Lahr/Schwarzwald, Germany
3 Department of Anesthesiological Research, University of Göttingen Göttingen, Germany
For reprint information contact: Amir Mortasawi, MD Tel: 49 6221 396 217 Fax: 49 6221 396 543 Email: amirmortasawi{at}yahoo.de Department of Thoracic Surgery, Thoraxklinik, University of Heidelberg, Amalienstr. 5, D-69126 Heidelberg, Germany.
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ABSTRACT
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As the average age of patients undergoing cardiac surgery is increasing, the effects of age on the incidence of postoperative complications and 30-day mortality after coronary artery bypass grafting were examined. The EuroSCORE and corresponding age-stripped EuroSCORE were calculated in 6,057 patients who underwent isolated coronary bypass between January 1996 and January 2002. Both EuroSCORE and age-stripped EuroSCORE exhibited a significant increase with age in the whole group of patients and in those who were alive 30 days after surgery. The 30-day mortality and the incidence of postoperative complications increased significantly with age. A significant age-dependent increase in EuroSCORE was found in patients who died within 30 days postoperatively, whereas no age dependence was observed in the age-stripped EuroSCORE. Univariate analysis showed diabetes mellitus and atrial fibrillation to be significant risk factors for 30-day mortality; atrial fibrillation was also found to significantly affect 30-day mortality on multivariate analysis. In view of the increasing co-morbidity and age-dependent organ changes in the elderly, specific preventive and therapeutic measures are needed in this group of patients undergoing cardiac surgery.
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INTRODUCTION
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An increasing number of elderly patients are being treated in cardiac surgery departments as a consequence of demographic changes and new developments in medical technology. In the year 1989, 3,673 patients aged 70 years and over underwent a cardiac surgical procedure in Germany, whereas in the year 2000, the number of cardiac surgical patients in this age group increased to 35,884. The proportion of such patients aged 
70 years rose from 11.2% to 36.7%.1 The EuroSCORE is one of the established risk evaluation scores applied in Europe (see http://www.euroscore.org/what_is_euroscore.htm). Besides other parameters, age > 60 years is regarded as an independent determinant of mortality in this scoring system, whereby the risk weight is increased in 5-year intervals (see http://www.euroscore.org/calc.html). We studied the effect of age on the mortality rate and occurrence of postoperative complications in a large group of patients who underwent isolated coronary artery bypass grafting (CABG) in our institutes.
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PATIENTS AND METHODS
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The EuroSCORE and the age-stripped EuroSCORE, calculated by subtraction of the age scoring point, were determined in 6,057 patients who underwent isolated first-time on-pump CABG between January 1996 and January 2002. The patients were divided into 5 age groups. Initially, the occurrence of postoperative complications and the 30-day mortality were determined in each age group. Thereafter, the effect of age was established by statistical analysis using Pearson’s chi-squared test and analysis of variance (ANOVA). Statistical significance was defined as p < 0.05. Along with the EuroSCORE parameters, the occurrence of arterial hypertension, diabetes mellitus, and atrial fibrillation (AF) was determined in all age groups studied. The relationship between 30-day mortality and these three variables was assessed by univariate and stepwise logistic regression analyses.
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RESULTS
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Table 1
shows the calculated EuroSCORE parameters and the occurrence of the three additionally determined accompanying diseases in all age groups studied. Significant age-dependent differences in the distribution of the following variables were found: female gender, chronic obstructive pulmonary disease (COPD), non-cardiac atherosclerosis, elevated serum creatinine values, unstable angina, left ventricular ejection fraction 30%–50%, arterial hypertension, diabetes mellitus, and AF. The postoperative course and complications are shown in Table 2. The duration of intensive care unit stay, transfusion of packed red blood cells, pneumonia, postoperative AF, neurological events, psychotic syndrome, re-intubation, renal insufficiency with hemofiltration, and 30-day mortality exhibited significant age-dependent differences.
Table 3 shows the EuroSCORE and the age-stripped EuroSCORE values determined in the group of all patients, those who died within 30 days after surgery, and those who survived. Both the EuroSCORE and the age-stripped EuroSCORE values increased significantly with age in the group of all patients and in the 30-day survivors. In the patients who died within 30 days, the EuroSCORE exhibited a significant age-dependent increase; however, the age-stripped EuroSCORE did not change significantly with age. The expected and observed 30-day mortality EuroSCORE values in all age groups studied are presented in Table 4. Univariate analysis revealed a significant relationship between 30-day mortality and diabetes mellitus ( p < 0.05) and AF ( p < 0.01). Stepwise logistic regression analysis showed a significant relationship between mortality and AF ( p < 0.05).
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DISCUSSION
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One of the consequences of the demographic changes in the population is the continuously increasing number of elderly patients undergoing cardiac surgery.2,3 In Germany, there is no nationwide database of the incidence of the associated diseases that were studied in our patient group. Therefore, it is not possible to compare our patients with an age-matched group to determine any possible biological selection. If we consider the age-stripped EuroSCORE as a measure of co-morbidity, then our data show an increase in co-morbidity with age in patients undergoing cardiac surgery. A detailed analysis of the individual EuroSCORE variables and the additional evaluation of other parameters confirm that the number of associated diseases in patients undergoing CABG increases with age. A large study published in 2000 revealed the following significant differences between 60,161 patients aged < 80 years undergoing isolated CABG and 4,306 patients 80 years undergoing the same type of surgery: female gender 28.2% vs. 44.1%, COPD 16.0% vs. 14.1%, diabetes mellitus 29.5% vs. 23.0%, renal insufficiency 4.8% vs. 8.0%, chronic cardiac failure 11.7% vs. 19.4%, cerebrovascular disease 10.4% vs. 18.7%, peripheral vascular disease 13.7% vs. 16.4%, and triple-vessel disease 64.3% vs. 70.4%.4 In view of the known increased co-morbidity in the elderly, the increased 30-day mortality and frequency of most postoperative complications with age as identified in our patient population, are not unexpected. These findings are in agreement with the results of other groups.4–7
The EuroSCORE rose significantly with age in the patients who died within 30 days postoperatively, whereas the age-stripped score did not exhibit such age dependence. This finding confirms the basic EuroSCORE information that age is an independent determinant of mortality in cardiac surgery. Therefore, the question arises as to which factors are concealed behind the common variable of age. Four points have to be mentioned with respect to this issue. Firstly, concomitant diseases, e.g., COPD, peripheral atherosclerosis, or renal insufficiency, are considered in the EuroSCORE analysis; however, the stage of disease and intensity of symptoms, both of which are influenced by the time factor, are not taken into account and may be hidden in the EuroSCORE parameter of age. Secondly, the EuroSCORE system has been developed using data from 19,030 cardiac surgery patients.8 Some diseases were not identified as being relevant with respect to mortality by multivariate analysis in this large population, and thus were not considered in the list of risk factors. We studied the effect on mortality of arterial hypertension, diabetes, and AF: three factors not included in the EuroSCORE system. All of these factors exhibit significant age-related distributions. Diabetes and AF significantly affected 30-day mortality in our study; such factors, which are not considered as independent variables in the EuroSCORE analysis, may contribute to the parameter of age. Thirdly, factors taken into account by the EuroSCORE system to assess cardiac status are unstable angina, left ventricular ejection fraction 30%–50% or < 30%, myocardial infarction within 90 days preoperatively, and systolic pulmonary artery pressure > 60 mm Hg. These data, which can be acquired easily and objectively, even in hospitals with differing personnel and technology backgrounds, guarantee good comparability of the findings and adequately describe certain aspects of the cardiac status. It would not be realistic to expect the EuroSCORE, which has been designed for a broad use, to consider in detail all the characteristic and complex features of the cardiovascular system. However, one of the cardiac factors that is not considered is diastolic function, and this might be expected to possess a high degree of diagnostic and therapeutic relevance, especially in the elderly.9 In a 1998 study, it was found that 43% of patients with a primary diagnosis of cardiac failure exhibited normal systolic function.10 Other groups have established that diastolic failure is found in approximately 50% of older patients with congestive heart failure.11,12 This aspect may also be hidden in the EuroSCORE parameter of age. Finally, functional and structural changes occur in various organ systems with increasing age, which may influence perioperative outcome and require specific preventive and therapeutic measures.
Reported age-dependent changes in the cardiovascular system include: dilation of large vessels; thickening of vessel walls, initially affecting the intimal layer; loss of vessel elasticity; increased left ventricular afterload with increasing systolic pressure; thickening of the left ventricular wall; cardiac myocyte cell loss and increased myocardial collagen; reduced number of pacemaker cells in the sinus node; decline in early diastolic left ventricular filling rate; increased atrial contribution to ventricular filling and larger atrial diameter; reduced adaptability of the cardiac response to different workloads resulting from modified ventricular filling volumes and changes in heart rate; increasing deficits in sympathetic modulation; and changes in myocardial calcium homeostasis affecting myocardial contractility and the tendency to arrhythmias.1,13 The consequences of all these changes are the reduced cardiac adaptability to workload and the higher incidence of disturbances of cardiac rhythm observed in the elderly.13,14 Therefore, the following issues should be considered in the postoperative care of older patients: use of a pulmonary artery catheter in the peri-operative phase; cautious administration of antihypertensive drugs, especially those with a long half-life; sufficient fluid administration with the aim of achieving relatively high filling pressures; use of temporary epicardial pacemaker wires; and frequent checks of electrolyte homeostasis, mainly regarding the determination of potassium and magnesium values.
Age-related changes in the pulmonary system include structural lung tissue changes associated with an increasing amount of connective tissue, progressive rigidity of the chest wall, bone transformation of rib cartilage, weakness of the expiratory muscles, and malfunction of the airway epithelium with disturbed mucus clearance, which result in an increase in functional residual capacity, residual volume, and dead space volume, reduced efficiency of cough, increased mucus production, increased tendency to develop atelectasis, and increased ventilation-perfusion mismatch with a consequent increase in right-to-left shunting. In addition, the central nervous system response to hypoxia and hypercapnia deteriorates in the elderly.15,16 To prevent pulmonary complications in older patients, it is necessary to examine lung function and initiate chest physiotherapy with breathing exercises during the preoperative period. Postoperatively, early extubation, mobilization, and pharmacologically supported bronchial clearance should be performed, and dehydration of the patient must be avoided.
Changes in renal structure can be observed in the elderly: reduced renal mass by approximately 10%–20%; glomerular sclerosis and reduced number of the glomeruli by approximately 50%; tubular hypertrophy; and vascular involution. These changes start to develop at the age of 40 years and result in a reduction of renal plasma flow, which falls by approximately 10% per decade, and is reduced by approximately 50% at the age of 90. There is also a diminished glomerular filtration rate and reduced tubular secretion and resorption capacity, as well as a limited response to antidiuretic hormone and reduced urine concentration ability. Therefore, dehydration and electrolyte loss occur more frequently in elderly patients. Furthermore, there are considerable changes in the distribution of body compartments that develop with age, e.g., an increasing proportion of body fat with reduced plasma, total body fluid, and extracellular fluid volume.15 These changes influence the pharmacokinetics of both hydrophilic and lyophilic pharmaceutical agents due to the significant alteration of their compartmental distribution. Therefore, it is extremely important to avoid hypotonic phases in the perioperative period, to frequently check electrolyte and fluid homeostasis, to perform daily body weight measurements, and to adjust the doses of pharmaceutical drugs in the elderly.
Advanced age is a risk factor for the development of neurological complications in patients undergoing cardiac surgery. The risk of stroke is increased due to atherosclerotic processes in the aorta and neck arteries. Therefore, intraoperative manipulation of the ascending aorta should be minimized. The nervous system exhibits multiple age-dependent changes. Brain mass is reduced by approximately 20% by the age of 80 years. The synthesis and breakdown of neurogenic transmitters as well as the density of receptors decreases with age. This process also affects the opiate receptors; consequently, a higher opiate sensitivity is typically observed in elderly patients. Other age-dependent changes encountered are attenuated protective laryngeal reflexes and limited maintenance of proper thermoregulation. These changes are particularly relevant in the early postoperative period. Visual and auditory perception is limited by approximately 30% in the elderly. These sensory deficits compromise communication and also play a role in the multifactorial pathogenesis of deliriant states. Finally, depression and sleep disorders, which also occur more frequently in the elderly, should be taken into account if perioperative complications in this patient group are to be prevented.15,16
Metabolic functions exhibit age-dependent changes including reduced muscle mass, hepatic metabolic activity, and responsiveness and density of insulin receptors, which contribute to the limited glucose tolerance in the elderly despite generally preserved insulin secretion. Diabetes mellitus, which is accompanied by several microscopic and macroscopic vascular complications, is the most frequent endocrine disorder in those aged 65 years, with a prevalence of more than 10%. It has a significant impact on the results of cardiac surgery.15,17 Frequent estimations of blood glucose levels and preferential administration of short-acting drugs are necessary. Beginning at the age of 30 years, changes in bone metabolism can be detected. This is accompanied by a loss of bone mass of approximately 1% per year of age and results in progressive demineralization. A reduction of bone flexibility by 15%–20% and compressibility by approximately 50% is evidenced by the age of 70.15 These factors may be of relevance in the case of otherwise trivial traumas and fractures occurring during perioperative reanimation. Age-dependent gastrointestinal vascular changes increase the risk of ischemic complications.
Reduced gastrointestinal motility in the elderly causes constipation and esophageal reflux. Avoidance of hypotonic circulatory phases, early onset of enteral nutrition, if possible, sufficient fluid administration, a diet rich in fiber, administration of laxatives, and control of gastric acid production by drug administration have to be considered in this group of patients.15,18
It can be concluded that mortality and the incidence of perioperative complications after cardiac surgery are significantly influenced by age. Consequently, the increasing co-morbidity with age and occurrence of age-dependent organ changes should be specifically considered in the therapy of elderly patients undergoing heart surgery.
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TOP
ABSTRACT
INTRODUCTION
