Clinical Outcome of Urgent Coronary Artery Bypass Grafting

Clinical outcomes of percutaneous coronary intervention (PCI) have dramatically improved due to the development of new stents. Thus, the age of the population of patients eligible for surgery has increased, and the possibility of belonging in the high risk group has increased as well. Despite this, the outcome of a coronary artery bypass graft (CABG) is excellent. This can be attributed in part to the use of off-pump CABG, the development of minimally invasive surgical techniques, surgery using a robot, and total arterial revascularization. CABG has become one of the safest forms of heart surgery. However, such a favorable clinical outcome can be expected only if the procedure is elective (1-4).

Medical conditions that may require urgent CABG include acute coronary syndrome (ACS). ACS may include clinical conditions such as ongoing myocardial infarction unresponsive to maximal medical treatments, failure of PCI, or cardiogenic shock due to coronary artery diseases. This may be one factor contributing to a high mortality rate.

The purpose of this study were to evaluate the predisposing risk factors prior to and after urgent CABG, to analyze clinical outcome and prognosis, and to characterize risk factors associated with mortality.

There were many studies on risk factors in urgent CABG in western countries. However, only several studies were found in Asia (1, 12-15, 19). Our study, is based on single-hospital experience involving a relatively large population. It is noteworthy to mention that our study was different from other reported studies in Asia.

The standard timeframe for urgent surgery varies depending on different reports. Treatment within 24 hr of patient decompensation or within six hours of an unfavorable coronary artery angiogram is considered as the standard (2, 8, 15, 19). In our study, surgery was performed within six hours in most cases (86%). Several cases (endocarditis, failed PCIs) were transferred from other medical institutions and surgery was able to be performed within 24 hr in most cases. Therefore, in our study, 24 hr was considered the standard timeframe.

In other studies, severe stenosis in the left main coronary artery has been reported to be the most common indication for surgery (13, 19). In such patients, the left main coronary artery demonstrated an average stenosis of 76.0%. However, in our study the left main coronary artery lesion was not a risk factor of surgical mortality (p=0.133).

Twenty-two cases (21.2%) required urgent CABG as a result of an acute coronary dissection or occlusion secondary to PCI failure. Recently, with the development of stents, the number of urgent CABG after failed PCI has declined. However, the incidence has been reported between 1.5% and 2% (5). Similarly, in our hospital during the study period, a total of 5,714 PCIs were performed; 84 of those cases (1.4%) proved unsuccessful. Among them only 22 patients (22/84, 26.2%) underwent urgent surgery. Among the failed PCIs, four patients died postoperatively (4/22, 22.2%); this is higher than the total operative mortality rate 17.3%. Although patients consider PCI to be safer than surgery, this is not always the case. When PCI fails, immediate urgent surgery could lower the mortality rate (6). In light of this, PCI intervention by cardiologist should be performed in a hospital where emergency surgery is available. In order to decrease morbidity and mortality, careful selection of patients is required and as a principle of performing PCI, surgical consideration should be made in all cases. In cases that develop complications, there should be immediate and aggressive surgical intervention.

According to the Worcester and Mass study on cardiogenic shock patients with accompanying AMI, it has been reported that, between the years of 1975 and 1988, the incidence was 7.5%, and in the cases treated with only medically, there was an 80% mortality rate (7, 8). This ratio did not change depending on yr evaluated. Despite advancements in cardiac surgery over the past 10 yr (i.e., the development of surgical techniques, improvement in the myocardial protection method and the development of mechanical assist device or equipment) there was no overall improvement in the mortality rate (Table 8). We divided the whole study period into three groups and compared the mortality, but there was no significant difference between groups (p=0.790).

Table 8
Surgical outcomes by year

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The purpose of the urgent CABG is to reperfuse the coronary artery blood flow rapidly, improve areas of myocardial ischemia, repair ventricular dysfunction, and prevent the spread of the infarction area (1, 3, 9-11). In our study, 58 cases (52.9%) had an AMI, 39 had unstable angina pectoris (37.5%), and 7 had stable angina pectoris (6.7%). Of those AMI patients, 16 patients (27.6%) died. Only two (5.1%) of the unstable angina pectoris patients died. In other studies involving urgent CABG in AMI patients, early mortality rates ranged from 8.5% to 39%, which was higher than other patient groups. Cardiogenic shock, left main coronary artery lesion, and advanced patient age have been reported to be prognostic risk factors (12, 13).

In cases involving patients older than 70 yr of age, ongoing AMI, the use of an IABP, the need for CPR, preoperative shock state and low ejection fraction, there was a statistically close association with an early mortality rate on univariate analyse. These risk factors have already been reported in other studies (3, 12-16). Among them advanced age (>70 yr), preoperative shock status, and low ejection fraction (<40%) were identified independent risk factors of mortality by multivariate logistic regression (Table 7). It is thought that these risk factors reflect the cardiac function of the patient prior to surgery. Indeed, among the eleven (61.1%) postoperative deaths, left ventricular failure due to the low cardiac output persisted postoperatively, and the patients eventually developed MOF. Due to prolonged respirator use and decreased immunity, sepsis developed in one patient resulting in death. This implies that the presurgical hemodynamic condition of a patient is very important. Therefore, it is thought that establishing hemodynamic stability in conjunction with the cardiologist prior to surgery significantly influences surgical outcome.

Gender ratio, the presence or absence of a left main coronary artery lesion, hypertension, diabetes or hyperlipidemia was not associated with the mortality rate.

Statistical significance regarding surgical methods or the choice of graft was not obtained. However, recently, with the development of IABP or percutaneous cardiopulmonary support system (PCPS), patients are stabilized preoperatively. Off-pump CABG is on the rise, as well as the use of arterial grafting.

The time required to harvest the internal mammary artery is longer than that required to harvest the great saphenous vein. The initial blood flow rate and reperfusion is higher in urgent CABG involving the saphenous vein. Hence, the use of the saphenous vein was preferred (17). However, it has been reported that the mortality rate did not differ according to the vessel used in urgent CABG (18, 19). Similarly, in our hospital, arterial grafts were not used prior to 1994. After this time period, arterial grafts were used aggressively, and are currently used in patients who are hemodynamically stable and undergoing off-pump CABG. In fact, in nine recent cases performed OPCAB, the mortality rate within 30 days of surgery was zero. However, since the number of cases was not sufficient, it could not be statistically compared with conventional CABG.

After urgent CABG, complications developed in 36 of the 86 cases (34.6%), excluding those patients who had expired. Such complications were considered to be unrelated to survival; however, they are important predictive factors in determining clinical outcomes. Twelve patients experienced renal failure due to the pre- and postoperative shock state (14.0%). Eleven patients developed a superficial wound infection in the area where the saphenous vein had been harvested (12.8%). Such complications might have developed as a result of insufficient evaluation before surgery; nonetheless, in many cases it could be prevented by the careful medical treatment. It is thought that in urgent cases, similarly to elective patients, the status of the patients' health before and after surgery may contribute to the quality of life of the patient. To obtain a good clinical outcome, collaboration with the cardiologists is necessary in order to stabilize preoperative hemodynamic condition via IABP or PCPS. However, in cases unresponsive to medical management, or in the failed PCI cases, it is important to perform emergent surgery, before the hemodynamic condition of the patient deteriorates irreversibly.

In conclusion, the present study demonstrated that independent risk factors of mortality included advanced age (>70 yr), preoperative shock status, and low ejection fraction (<40%). Despite the higher surgical mortality rate (17.3%) after the urgent CABG, a favorable long-term clinical outcome can be expected if the patients survive.