Changes in profile of patients submitted to coronary bypass graft surgery

Introduction: The improvement in care and management of ischemic heart disease and the dissemination of percutaneous coronary intervention (PCI) changed the indications for coronary artery bypass grafting (CABG), regarding procedures for patientswith multivessel disease in bad clinical conditions. Objective: To compare surgical and clinical profiles between two groups of CABG patients at a 10 year interval observing the influence on hospital mortality rates. Method: Retrospective Cohort study, including 307 CABG patients operated on in 1991to 1992 (n=153) and 2001 to 2002 (n=154). Demographic characteristics, heart disease severity, comorbidities and pre-operative events were evaluated and compared between the groups. Results: Patients operated in 2001 and 2002 were older, more severely ill (in a worse NYHA classand had higher prevalence of heart failure, and multi-vessel involvement) and with more co-morbidities. Patients operated in 1991 and 1992 had more urgent procedures. The observed surgical mortality rates were similar (3.3% and 1.9%, respectively). Conclusion: Patients submitted to CABG currently are older and in worse clinical conditions than those operated 10 years ago, but hospital mortality has not altered significantly. Descriptors: Myocardial revascularization. Risk assessment. Heart diseases, surgery.


INTRODUCTION
The treatment of ischemic cardiopathy has passed through significant changes, with implications in the natural history of the disease and in the indication of surgical intervention [1][2][3][4][5]. Some pharmacological or invasive therapeutic interventions, such as percutaneous transluminal angioplasty (PTCA), prove the necessity of coronary artery bypass grafting (CABG) or delay it, by allowing a more favorable clinical evolution [6][7]. However, when surgery is delayed, there is the probability of a future surgery when the patient is older, after the appearance or aggravation of comorbidities, when the coronary disease has evolved (frequently accentuated by the use of the catheter) and when the left ventricular function of the patient is worse (especially if ischemic events occur), conditions that increase surgical risk [1,2,6].
Logically, aggravation of ischemic disease in surgical patients must increase the morbidity and mortality of CABG. However, the evolution of the preoperative management, through the identification of operative risk factors and the development of measures capable of neutralizing their deleterious influence, and the progress in the postoperative management are reflected in a current reduction in the surgical morbidity and mortality, an effect that has been observed over the last 20 years [1,2,4,8].
The objective of this study is to evaluate the profiles of patients submitted to CABG currently and ten years ago, trying to identify changes that can have influenced the surgical risk.

Patients
A retrospective cohort involving 307 patients submitted to CABG, isolated or together with left ventricular aneurysmectomy or endarterectomy of the carotid arteries, in the Institute of Cardiology in Rio Grande do Sul/ University Foundation of Cardiology was studied. The patients were allocated to two groups: Ten-year: 153 patients operated on between October 1991 and April 1992; Current: 154 consecutive patients who performed the same procedure between October 2001 and April 2002. Patients who performed CABG associated with valve replacement or valvuloplasties were excluded.

Risk factors of hospital mortality
Characteristics of patients recognized as possible factors capable of increasing the hospital risk [9][10][11][12][13][14][15], were classified as: Demographic characteristics: factors related to patients but independent of disease, such as age, gender, race, weight (obese), hematocrit and creatinine levels. Heart disease: determined by factors that identify the extent and repercussions of coronary disease or that can directly influence the performance of the heart, such as clinical symptoms (anginal state and functional class -New York Heart Association), left ventricular function, systemic arterial hypertension (SAH), dyslipidemia, cardiac insufficiency (CI), distribution of coronary lesions, previous events such as acute myocardial infarction (AMI) or percutaneous transluminal angioplasty (PTCA) with or without the implant of a stent. Comorbidities: preexistent diseases that are not directly related with the heart disease, such as smoking, diabetes mellitus (DM), peripheral vascular disease (PVD), cerebral vascular disease (CVD), renal insufficiency (RI), chronic obstructive pulmonary disease (COPD). Operative variables: surgical characteristics such as indication criteria (elective or urgency emergency), previous CABG (reoperation), cardiopulmonary bypass (CPB) time, aortic clamping time, number of grafts utilized, use of the internal thoracic artery. The use of intra-aortic balloon (IAB) or nitroglycerin (NTG) in the preoperative period was also evaluated.

Outcomes
The demographic and operative characteristics, as well as the characteristics that defined the severity of the heart disease and the comorbidities were expressed in terms of absence or presence (dichotomous variables) or intensity (continuous variables) in both the Ten-year and Current Groups. With this, the study aimed at characterizing the two populations and attempted to identify significant differences in the distribution of variables between the studied groups, to assess possible changes in the clinical profile of the two populations who underwent CABG over a 10-year interval.
Surgical mortality was the outcome utilized to define the quality of the result of CABG, with the rate observed in each group compared with the expected rate.

Ethical considerations
The study was registered in the Research Unit of the Cardiology Institute of RGS/ Fundação Universitária de Cardiologia and it was approved by the Ethics Research Committee of the Institution. As it was a retrospective study with investigations of patient records, no risk or harm to the patients was predicted; secrecy of the medical information was observed throughout.

Data collection and statistical analysis
Information about patients was collected from the patient records and registered in tables for statistical analysis using the SPSS computer program. Numerical data are expressed as means and standard deviations. The comparative tests used the Student t-test and the chi-square and variance analysis tests. A critical α level of 5% was considered significant, giving a P-value < 0.05, although lower values for p are reported. (Table 1) Comparing the demographic characteristics the members of the Current Group were older than those of the Ten-year Group (62.71 years versus 58.86 years, respectively -pvalue = 0.01) and had a lower prevalence of obesity (9.7%, versus 20.9% p-value = 0.05). In the preoperative evaluation of the laboratory results, patients of the Current Group when compared to the Ten-year Group had lower hematocrit levels (38.05% versus 40.61%, respectively -p-value = 0.01) and higher creatinine levels (1.14 mg/dL versus 1.01 mg/dL, respectively -p-value < 0.05). b) Heart disease ( Table 2) In relation to the symptomatology, the patients in the Current Group had a higher prevalence of unstable angina than those in the Ten-year Group (88.7% versus 66.2%, respectively) and a lower rate of stable angina (7.2% versus 24.7%) giving a significant difference (p-value = 0.001). Patients of the Current Group had more severe heart conditions, with a predominance of functional classes II and III (NYHA) than patients in the Ten-year Group (15.6% versus 3.3% respectively for class II and 13% versus 2% for class III, pvalue = 0.01). The greater incidences of CI, SAH and dyslipidemia were in the Current group.

Profile of the groups a) Demographic characteristics
In respect to previous adverse events, we found a significant difference only in relation to the use of coronary stents implanted by PTCA, which was more common in the Current Group.
There was a statistical difference between the groups in respect to the number of vessels with severe lesions (> 70%) with preponderance in the Current Group when compared to the Ten-year Group (2.76 vessels versus 2.42 vessels, p-value = 0.01) as seen by coronary cineangiography. The ejection fraction of the patients in the Current Group was higher when compared to the Tenyear Group (68.3% versus 60.4%, p-value = 0.01), but ejection fractions under 30% also prevailed in the Current Group (1.9%) compared to the Ten-year Group (1.3%).  (Table 3) In respect to comorbidities, there was a significant preponderance in the Current Group in comparison with Ten-year Group for DM (36.4% versus 21.6%, respectively; p-value = 0.003), PVD (16.2% versus 5.2%; pvalue = 0.001), CVD (10.4% versus 4.6%; pvalue = 0.04) and RI (8.4% versus 0%, p-value < 0.001). Only COPD prevailed in the Tenyear Group in comparison with the Current Group, though the difference was not statistically significant (11.8% versus 6.5%; p-value = 0.08). d) Operative variables (Table 4) A higher frequency of urgent surgery was observed in the Ten-year as opposed to the Current Group (30.7% versus 9.1%, respectively; p-value = 0.01). Of the patients from the Ten-year Group, 4.6% had performed previous CABG and of the Current group, 4.5% (no significant difference). Preoperative IAB were used in five patients, all belonging to the Current Group (p-value < 0.05).
Trans-operative data such as CPB time, ischemia time and number of grafts utilized were not significantly distinct between the groups. Only the use of the internal mammary artery graft prevailed in the Current Group with relation to the Ten-year Group (74% versus 39.9%, p-value = 0.01).

Surgical mortality
The observed surgical mortality was not different between the groups, in the Ten-year Group it was 3.3% and in the Current Group it was 1.9% (p=0.358).

COMMENTS
In agreement with the literature [1], this study demonstrates that the patients who were submitted to CABG more recently are older. This seems to be consequent to a reduction in the surgical mortality of older patients and by the evolution of the management of patients considered to be high risk, which includes most elderly patients [14,16]. The worst current clinical condition of operated patients, represented by more comorbidities (such as MD, SAH and CVD), of CI, of increased functional class (class III -NYHA) and of multiple arterial disease, can be explained by referring lower-risk patients for PTCA, preferably with stent implantation [9,10]. It was observed that no patients in the Ten-year Group had implanted stents previous to the surgery as the technique was not developed at that time; however we did not find significant differences between groups in respect to previous percutaneous transluminal angioplasty using balloon-catheters (Table 2).
It is recognized that the risk of new procedures after a primary PTCA has been reduced and that the patients who underwent primary angioplasty have a low risk of requiring new revascularization procedures, estimated at 33.6% over two years after intervention in the 1990s, and 12.4% in the 2000s [7]. It is inferred that many patients, excluding those more serious ones in respect to atherosclerotic disease (coronary and systemic diseases), who performed angioplasty did not require CABG later and were excluded from the Current Group.
In spite of the worse clinical conditions presented by the operated patients in 2001/02, a greater number of patients with ejection fractions of less than 30% was not found in this group. On the contrary, patients showed in the heart catheterism examination a higher average ejection fraction than those patients operated on in 1991/92. This finding can not be clearly explained.
Although a lower mortality was seen in the Current Group, this rate was not statistically different from the Ten-year Group. These findings are in agreement with published results [2,4]. Some factors can have contributed to the increased mortality of patients in the Ten-year Group, such as the prevalence of unstable angina, a lower mean EF evidenced in the heart catheterism examination (even though it was close to the normal) and the higher prevalence of urgent surgeries which was considered preponderant. No attempt to identify direct effects of percutaneous coronary interventions was made, but it is possible that an increase in the number of these procedures has favored the current surgical results, reducing the number of urgent surgeries performed more recently. This is because possible candidates for emergency or urgent CABG may have had the severity of the coronary lesions minimized by percutaneous angioplasty and not require surgery in a period of acute ischemia (whether unstable angina or during the evolution of or recovery from acute myocardial infarction). Major thrombolytic diffusion, statins use and the nonsuspension of beta-blockers in the preoperative period could have also contributed.
This study was performed retrospectively, based on information from patient report cards, especially when considering patients operated on one decade ago, when computerized registers did not exist. For this, the work may be affected by a significant bias in relation to the Ten-year Group; similarly more recent progress related to the perioperative management of patients was not considered which may have contributed to the reduction in the mortality rate observed. But aiming at better characterizing the populations studied and excluding (negative) effects on the observed mortality rate, patients with valvar disease, requiring concomitant surgical intervention, were not considered [17].
Considering the Current Group, with very exact data collection, the results observed allow us to identify characteristics of the patients who underwent CABG associated with increased hospital mortality and, if correctly analysed this will include recognized operative risk factors [18]. This is an open perspective of the present study, to be concretized within the current methodology [19].

CONCLUSION
Patients who were recently submitted to CABG are older and in worse clinical conditions (heart and systemic conditions) than those operated on ten years ago, but the mortality related to the surgery is comparable between both populations, although slightly lower in the more recent operations. This seems to be justified by the greater prevalence of urgent surgeries among patients operated on one decade ago and by the evolution of the identification and neutralization of some risk factors in CABG.