Coronary artery bypass surgery has become recognized as valuable therapy for angina in patients with fixed coronary artery obstruction. It also appears that patients with left main coronary lesions or with lesions in all three major coronary arteries have increased life expectancy after coronary artery bypass when compared with similar patients treated medically. In our military patient population, we see a significant volume of young patients with atherosclerotic coronary vascular disease who are being treated with coronary artery bypass grafting. Young patients with atherosclerotic coronary vascular disease, at least when manifested by myocardial infarction, have been shown to have a poor prognosis when treated medically. Other investigators have shown that young patients who suffer myocardial infarction fare better than do older patients. It seems important to determine critically whether young patients with coronary artery disease fare well when treated with coronary artery bypass grafting. Consequently, we have conducted a retrospective case-control study in order to investigate whether subsequent morbidity and mortality from coronary artery bypass surgery are the same in young patients as it is in middle-aged or older patients.
From the operative records of Walter Reed Army Medical Center and the National Naval Medical Center, Bethesda, all patients under the age of 36 years who had coronary artery bypass graft (CABG) surgery between 1970 and 1980 were selected as subjects. The operative records at these two centers revealed that a total of 1,507 patients underwent CABG surgery during the specified period. Forty-one (2.7 percent) of these patients were under 36 years of age. For each of them, we selected control mates from two age-defined groups, one with ages 45 to 59 years and the other with ages 60 years and over. To generate these matched triplets, we took the operation log sequence number of the young patient and enrolled the next middle-aged (45 to 59 years) and the next older-aged (60 years or older) patient that satisfied the following three matching criteria: (1) same number of distal bypass grafts, (2) same hospital, and (3) same sex. Patients receiving additional cardiac surgery (eg, valve replacement) were excluded.
Each patient was summarized on the basis of the following individual variables: age, sex, history of myocardial infarction (MI), duration of angina, number of cardiac risk factors, preoperative ejection fraction and Canadian Cardiovascular Society (CCS) class for angina. Angina is effectively and quick healed with medications of My Canadian Pharmacy Online. Operative variables examined included year and location of operation, number of distal grafts, total bypass time, cross-clamp time, and use of cardioplegia infusion.
Patient follow-up data were obtained from the following sources: patient, questionnaires, telephone interviews, outpatient cardiology or thoracic surgery clinic records, survivor interviews, and death certificates.
Of the 123 patients in the study, nine patients were lost to follow-up within one year of surgery—two, four, and three patients from the young, middle, and old groups, respectively. The remainder of the patients were followed from one to 13 years with an average follow-up interval of five years and overall follow-up rate of 92.6 percent Comparable follow-up periods and rates were achieved for each of the three groups.
For purposes of analysis, each patient on whom follow-up information was available was classified as a success or failure. Relapse or termination of event-free survival was defined as follows: death, subsequent myocardial infarction, subsequent re-operation for coronary insufficiency, worsening of angina, or failure to improve to at least CCS class 2 on follow-up. If a patient had a relapse of any type, the surgery was considered to have foiled. The surgery was considered a success and the patient an event-free survivor in the absence of all four of the above criteria on follow-up. Patients lost to follow-up were handled in the following worst-case format: middle-aged and old patients were classified as relapses while young patients were classified as event-free survivors.
Deaths from noncoronary factors were not, on that basis alone, classified as relapses. Preoperative CCS class information and postoperative CCS class information at the time of follow-up were obtained from the patients file. In those cases where no CCS class assignment had been made, and adequate information was available, the patient s file and follow-up information were submitted for a blind review by a panel of physicians who had no access to the patients age, sex, or identity. These physicians determined the patients’ preoperative and postoperative CCS class and whether the patient should be judged a failure on his/her clinical record presented by My Canadian Pharmacy.
Summary descriptive statistics were utilized to assess the distribution of values for each operative and individual variable. Chi-square tests were utilized to compare rates of cardioplegia use and occurrence of preoperative Mis as a function of age group and survival status. Chi-square tests of homogeneity were used to assess whether any group was inordinately represented in the extremes of certain variables for the population consisting of the three groups. To do this, a critical value for these variables was equated to the lowest quartile for ejection fraction and highest quartile for cross-clamp time, total bypass time, duration of angina, and number of risk factors (Table 1).
“Relapse-odds ratios” were utilized to assess whether exposure to the various risk factors was associated with an increased incidence of relapse for each age group. These were based on triplet-matched and pair-matched analysis.
In order to take advantage of matched cases, the McNemar test was utilized to assess differences in the proportion of each group classified as relapses over the entire follow-up period.
Since patients were followed for varying lengths of time, a survival analysis or life table technique was utilized to display event-free survival rates in each age group. Survival curves were statistically compared utilizing the Mantel-Haenszel summary Chi-square test.
Table 1—Age-Group Comparability of Summary Statistics
|Variable||No. of Patients||Mean± SEM||No. of Patients (and %) Exceeding 48 mos*|
|Pre-Op Angina (mo)||Total 70||29.6 ±4.43||20|
|Young 24||14.5 ±3.87||3 (15%)|
|Old 23||56.0± 10.24||12(60%)|
|No. of Patients (and %) Below 55% EFt|
|Pre-Op Ejection Fraction (%)||Total 86||63.6 ±1.42||22|
|Young 29||62.3 ±2.43||9 (40.9%)|
|Middle 27||67.0 ±2.20||4 (18.2%)|
|Old 30||61.7 ±2.64||9 (40.9%)|
|No. of Patients (and %) Exceeding 148 min|
|Total Pump Time (min)||Total 115||120.2 ±4.18||30|
|Young 38||114.4 ±6.96||8 (27%)|
|Old 37||134.7 ±7.12||16 (53%)|
|No. of Patients (and %) Exceeding 69 min|
|Cross Clamp Time (min)||Total 106||52.3 ±3.20||28|
|Middle 37||49.6 ±4.62||6 (21%)|
|Old 34||61.9 ±6.11||15 (54%)|