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J Thorac Cardiovasc Surg 1998;116:440-444
© 1998 Mosby, Inc.
Surgery for Adult Cardiovascular Disease |
*Formerly Division of Cardiothoracic Surgery, University of Alabama at Birmingham, Ala.; currently Cleveland Clinic Foundation, Cleveland, Ohio.
Read at the Seventy-seventh Annual Meeting of The American Association for Thoracic Surgery, Washington, D.C., May 4-7, 1997.
Received for publication May 12, 1997. Revisions requested July 19, 1997; revisions received April 17, 1998. Accepted for publication April 29, 1998. Address for reprints: Prof. Dr. Paul Sergeant, Cardiac Surgery Department, Gasthuisberg University Hospital, Herestraat 49, 3000 Leuven, Belgium.
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Abstract |
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Introduction |
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1 and a previous study failed to identify a late benefit of even a single arterial graft on return of ischemic symptoms. 2 Therefore we have studied the return of angina symptoms after coronary artery bypass grafting (CABG) in a larger patient population in which both single and multiple arterial grafting has been performed with follow-up to 20 years to determine (1) whether return of angina is immutable, (2) the factors, including grafting technique, that might delay its onset, and (3) whether its return is predictive of subsequent adverse events. |
Methods |
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1
Surgical technique
The number of conduits used was 1 (12%), 2 (42%), 3 (38%), 4 (7%), and 5 (1%). The number of distal anastomoses was 1 (9%), 2 (24%), 3 (31%), 4 (23%), 5 (10%), 6 (3%), 7 (1%), 8 (0.2%), 9 (0.02%), and 10 (0.01%).
The first internal thoracic artery (ITA) anastomosis was constructed in 1972, and 6074 patients had at least 1 in situ ITA anastomosis. The first bilateral in situ ITA graft (N = 1192) was used in 1973, and the first in situ sequential ITA graft (N = 711) 3 was performed in 1978. Bilateral ITA grafts were connected to 2 different coronary systems in 985 patients and to only 1 single system in 207 patients. Free ITA grafting was used in 122 patients.
Follow-up
A regular stream of follow-up reports from referring specialists updates the Katholieke Universiteit Leuven Coronary Surgery Database. 4 These reports are sent after each event, suspicion of event, or regular visit. In addition, a formal cross-sectional follow-up of known surviving patients was undertaken between January 1, 1993, and July 1, 1994. 1 The common closing date for outcomes information was set at 1 Jan 1993. The follow-up was complete for 99.9% of patients. The median follow-up for the survivors was 6.4 years. Table I gives the number of patients at risk by year after the operation (alive without having experienced the return of angina after CABG) and by number of in situ thoracic artery distal anastomoses.
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Events
Return of angina
The object of the study was the event defined as return of angina of any degree of severity without death or infarct the same day. The intent was to identify patients with return of reversible ischemia in contrast to those experiencing an acute myocardial infarction. Patients not experiencing this event were censored at the common closing date, at the end of follow-up for those with incomplete follow-up, or at death, whichever occurred earliest. The diagnosis of angina was documented, at the discretion of the attending cardiologists, with cyclo-ergometric or radionucleide tests and coronary angiograms. When these were found to be normal and when the clinical history left doubt, the chest pain was not coded as return of angina.
Events after the return of angina
Events studied after the return of angina were death, myocardial infarction, and reintervention (cardiologic or cardiosurgical). The time interval from the return of angina (time-zero) to the occurrence of these events was analyzed.
Characterization of overall freedom from angina
Nonparametric estimates of overall non-risk–adjusted freedom rate from angina were obtained by the method of Kaplan and Meier. 5 A parametric method was used to resolve the number of hazard phases, to identify the form of the equation for each phase, and to estimate the parameters that characterized the distribution of times until first return of angina. 6
Depictions
In various figures, events are depicted by a symbol positioned along the horizontal axis at the time of the event and on the vertical axis according to the Kaplan-Meier life table estimate. They are enclosed at periodic intervals between confidence limits equivalent to 1 standard error. The numbers in parentheses represent the number of patients without the event and traced beyond that point. When parametric time-related depictions are shown, the solid line is the parametric estimate of freedom from the event enclosed within dashed 70% confidence limits equivalent to one standard error.
Multivariable analysis of return of angina
The general methods used to identify incremental risk factors for return of angina have been described previously for the event death, 1 including the variables and their organization for analysis and the exploratory analyses accompanying the multivariable analyses conducted in the parametric, multiphase hazard function domain.
In the directed stepwise entry of variables into the multivariable risk factor model, the P-value criterion for retention of variables in the final analysis was .05. Regression coefficients are presented ± 1 standard error.
Sequential analyses
To better understand the nature and influence of the risk factors, the multivariable analysis was conducted in a sequential fashion. First, only patient variables were entered, then procedure variables that were likely to be known or estimated at the time of decision-making were added, including the use and method of use of arterial grafts, and finally experience variables were entered. Variables from the isolated and preceding analyses were allowed to leave the model.
Nature and influence of risk factors
Nomograms representing the solution of the patient, procedure, and experience parametric equation for specific supplied values of each factor were used to explore the influence of risk factors. In general, each figure represents the prediction for a specific but typical hypothetical patient (Table II) whose profile was the median for patients who underwent an operation in the last year of entry into the study. Point estimates are enclosed within confidence limits equivalent to ± 1 SE. However, for statistical consistency, the solid lines for comparative difference in predicted percent freedom from angina are enclosed within dashed 90% confidence limits.
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) was identified. It consisted of a small early hazard phase that was slowly declining and a prominent late hazard phase that was continuing to rise relentlessly after approximately 2 years for the extent of the follow-up. The implication is that if a patient lives long enough, angina will return (is immutable).
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Noncardiac nonvascular comorbidities were potent risk factors for late the return of angina after CABG. At 10 years after an operation, the freedom rate from angina was 35% for a median-risk patient (Table II) with insulin-treated diabetes, 44% for a patient with orally treated diabetes, and 45% for a hypertensive patient, compared with 51% for a patient without these comorbidities.
Events after the return of angina
Death
The parametric non-risk–adjusted 1-month and 10-year survival was 99% and 68% after the return of angina after CABG (Fig. 5, A). Uncorrected for patient and procedure variability, this survival rate was improved in the presence of an arterial graft (P = .0001). No additional reduction was identified by increasing the number of in situ thoracic artery anastomoses beyond a single one (P = .8) (Fig. 5, B). The more severe was the degree of angina at return, the worse was the subsequent survival rate (P = .0001). The 1-year survival rate was 80% when angina returned in the form of unstable angina and was 97% when the angina was mild (Fig. 5, C).
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) in the presence of an arterial graft. No additional reduction was identified in the presence of a larger number of in situ ITA anastomoses at the time of the original procedure (P = .17). The higher the severity grade of angina was at return, the more frequent (earlier) was the occurrence of an infarct (P = .0001) (Fig. 6, C).
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Discussion |
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Follow-up biases
Variable intensity of follow-up may have influenced the identification of the event. Medical care in Belgium is without financial consequences for the patient. It is possible that patients with considerable comorbidity have been subjected to more frequent follow-up. This is true for patients who are treated with dialysis or insulin. This difference in follow-up intensity could produce a biased association between these comorbidities and the event, certainly for mild grades of angina. A reverse bias is equally possible, where patients who have been symptom-free for years will visit their cardiologist at the first symptoms of chest pain, sometimes indistinguishable from muscular pains, even for experts.
Unavoidable under-reporting
Under-reporting of the event may have occurred from silent ischemia.
However, the combination of a continuous clinical event update system and periodic formal follow-up constitutes the potential power of this database for the analysis of a refined event such as the return of angina. Most returns of symptoms were already documented in the database before the formal follow-up and were based on the original documents of the attending cardiologists, documented a few days after the actual return. The additional cascade of letters further refined this information for the other patients. A follow-up study 7 that used alternative follow-up methods (anniversary method) of patients with CABG with only venous grafts reported a similar freedom from angina as this study for patients with only venous grafts.
Limitations of the analytic method
A multivariable analysis comes closest to adjusting for the deliberate or unconscious patient selection in the variability of surgical techniques used. The complexity of the variables induce complex analyses, but they can generate patient-specific estimates useful for predictions. The strengths and limitations of these predictions on independent patient samples 8 include: patients with new risks, variables unavailable for the analysis, variables with low numbers of patients at risk and therefore instability of the coefficients, and variables that have taken different meanings over time.
Deliberately imposed limitations
This study has been limited, by purpose, to the variables known before or at the time of surgery to permit prediction before the operation, even though the Katholieke Universiteit Leuven database contained time-related co-variables such as smoking habit and lipid values after the operation.
The impact of choice of procedure on the return of angina
The one completely controllable risk factor for the return of angina is the surgeon's choice of conduit for the operation. However, the benefit that can be anticipated in delaying the onset of angina by the use of extensive arterial grafting was found to be disappointingly small.
An earlier analysis 2 on a smaller data-set (n = 5880) with a shorter follow-up did not identify a beneficial effect on return of clinical ischemia of extensive arterial grafting over and above that afforded by a single arterial anastomosis. We speculated 9 that, were the data-set larger and the follow-up longer, a progressive benefit of more extensive arterial grafting in reducing the early return of angina might be identified but that it was unlikely to reduce the clinically more important late return of angina.
Table V, a univariate and non-time–related presentation, suggests a benefit of the extensiveness of the arterial reconstruction, but this is before a correction for patient variability and method of use of this arterial grafting over time. Thus, in the present study with risk-adjustment, we found a progressive benefit on prevention of the early return of angina by more extensive arterial grafting, but the magnitude of this advantage was so small that the clinical benefit is trivial. Arterial grafting effected a small reduction in the late return of angina, but no incremental benefit of more extensive arterial grafting.
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This disappointing finding follows on the heels of a similar disappointing 1 benefit of extensive arterial revascularization on early, late, and very late survival after CABG. Although that analysis identified neither increased nor decreased early risk with the use of either single or extensive thoracic artery grafting, it failed to identify reduced late risk by extensive arterial grafting. Even the benefit of single arterial in situ grafting was modest and vanished when severe comorbidity was present. This demonstrated that extensive data exploration is needed before statements can be made in situations where patient-mix can influence the results of operative strategy.
In addition to the choice of procedure, the other controllable factors are the surgeon and the environment. In our study, institutional variables identified as risk factors for the return of angina included the identification of 2 surgeons and variables describing their experience or their surgical protocols. These differences appeared only early. The magnitude of the differences at 1 month and 10 years after surgery between the 2 extremes of surgeons after normalization for patient and procedure variables are limited to 0.2% and 2%, respectively, and therefore not clinically important.
The impact of demography and comorbidity on the return of angina
The therapeutic environment of the patient with coronary disease is constantly changing. The patient-mix of the larger cardiac operation centers includes patients with impressive accumulations of cardiac and noncardiac co-morbidities. Immutable demography and co-morbidity were associated with the earlier return of angina. Improved cardiac drugs and interventional techniques are rightfully challenging coronary operations in parts of the coronary patient-spectrum and for some of the follow-up events. The optimization of medical decision making in patient-specific situations 10 and for different follow-up events requires updates of the scientific bases and optimal correction for the patient variability.
In addition to the vascular co-morbidity variables (calcified aorta, vascular disease, and vascular surgery), expressing the extent of the atherosclerotic process, a large late impact was identified in the variables related to the initiation and progress of this atherosclerotic process (hypertension, 11 diabetic grade, renal failure, triglyceride value). Preoperative triglyceride values were already previously identified as incremental risk factors for several outcome events after CABG: survival, 1 return of angina, 2,12 first infarct, 2 any first ischemic event. 2 These variables demonstrate the progressive nature of the atherosclerotic process that cannot be expected to be stopped at the time of operation. Aggressive medical treatment 13,14 and dietary regimens may interfere with these negative influences.
Clinical relevance of the return of angina after CABG for the patient
If the return of angina after a coronary operation is largely immutable, the choice of operative technique will delay its onset only mildly, and it is yet uncertain whether risk-factor intervention will be effective, it is fortunate that the return of angina appears to have limited consequence on survival. It is also only a modest predictor of impending infarct because only 3% of the patients will have an infarct the first month after the return of angina. The surgical or cardiologic reintervention rate after the return of angina was only 4% the first month, increasing within the first year to approximately 20%, then stabilizing after that interval. We have previously shown that survival after the return of angina is no different from that expected had angina not returned. 2 Whether a biologic or iatrogenic factor, reintervention is less common after the return of angina when multiple arterial grafting has been performed. The return of angina is therefore an event with possibly high emotional impact on the until-then symptom-free patient, but its clinical consequences seem limited.
Inferences relevant to minimally invasive direct coronary artery bypass surgery
Minimally invasive direct coronary artery bypass (MIDCAB) surgery results refer nearly always to aggregate results of groups of patients treated with more conventional CABG techniques. The extreme patient selection for these lesser invasive techniques requires more precise standards for comparison. A patient-specific prediction was made for the return of angina in a typical patient with a median-risk profile who has undergone MIDCAB; the prediction is further refined with minimal co-morbidity, stable angina, single vessel disease, and an ITA anastomosis to the LAD. The 1-month, 5-year, and 10-year freedom rate from angina for this typical patient who has undergone MIDCAB was 99.8%, 86%, and 59%, respectively. We believe this should be the standard of comparison for such procedures.
Clinical inferences
The study demonstrates that most patients, if they live long enough, will experience the return of angina, most frequently of a minor grade, within 15 to 20 years after their CABG. Thus the return of angina appears to be immutable after a coronary artery operation. Patients should not expect that use of multiple arterial grafts will lead to dramatic reduction in the occurrence of this event beyond the modest benefit afforded by a single arterial graft to the diseased LAD. Demographic variables are immutable, and coronary atherosclerosis is a chronic disease that has been in evolution in these patients for many years and has reached the level of hemodynamic and clinical significance. Coronary operations will not stop this process. However progression of disease can be delayed, theoretically, by the control of noncardiac comorbidity. Finally, the tendency, for whatever reasons, to avoid reintervention when arterial grafting is extensive appears to be prudent.
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Appendix: Discussion |
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These data have been subjected to sophisticated and multi-directional statistical analyses. I am not going to ask any questions about Dr. Blackstone's methods because it is unlikely that I am capable of understanding the answers. But I do think that we need to examine the endpoint.
Most studies of bypass operations focus on death and reoperation, because these events are not subjective and they have obvious clinical importance. My understanding is that first return of angina was a clinical diagnosis made by a referring cardiologist. Not only was it a subjective diagnosis, but the angina that occurred could have been an isolated event followed by a relatively benign clinical course. Do you have any data or any feelings about the data about the importance of a first-return-of-angina event in terms of predicting subsequent bad outcomes for the patient, death, reoperation, or disabling angina?
A second line of inquiry has to do with the business about arterial grafting. It does not appear that the strategy of complex arterial grafting had a major impact on the late return of angina, or whatever this event is. Now, we do need to realize that despite the 20-year extent of the study, the median follow-up was about 6 years, and only 128 patients with more than 1 internal thoracic artery anastomosis were followed for more than 10 years. So in reference to complex arterial grafting, this is really a study of the first decade after bypass operation.
I think the sensitivity of the event also has to be considered, because any time there are events that are extremely sensitive, they tend to blur the distinction among methods of treatment.
Furthermore, I would bet there was a very close covariance between young age, which is a very strong predictor of the recurrence of angina, and complex arterial grafting. Do you think you are able to perfectly isolate the effect of those very closely related variables even with multivariate techniques?
What implications do you think this study has in terms of your own practice in regard to the strategies of complex arterial grafting?
Lastly, interpreting the overall results, we can take solace from the sensitive nature of this endpoint. The fact that at the end of 20 years over 20% of the surviving patients had not had even a single event that some cardiologists might think was angina is, I think, remarkable.
Dr. Sergeant. First return of angina, is it a good outcome marker? First return of angina is a very sensitive marker. One day of angina, as you have pointed out, will have the event-flag go down and stay down forever.
This event was identified by the attending cardiologists or by the 2 senior researchers involved and mentioned as authors. A lot of effort was invested in the identification and refinement of the actual first return of angina.
Is it an important marker? We think it is an important marker. Even though it is sensitive, it is an important marker because it is the prime marker on the quality of life after coronary bypass operation. The uncertainty for the patient of the first return of angina is very destabilizing.
Is it an important marker for the late outcome? This is beyond the scope of this actual presentation, but we have explored this domain already in a previous analysis of the same event for a smaller dataset. This exploration indicated that the patients with return of angina, without infarct or death the same day, have a similar survival rate to the patients without this event.
There are 2 possible explanations: either the first return of angina is not a good outcome marker, or we have been treating these patients perfectly, no overtreatment nor undertreatment. I would doubt this last possibility very much. I would therefore propose that it does not seem to be a good outcome marker.
Dr. Lytle is referring to Table I in the article when he mentions arterial grafting and the extent of follow-up, and it has to be noted that this is just a listing of each individual use of arterial grafts. Please note that the late-hazard phase starts to rise by 2 years. At 5 years in follow-up, there are 2269 patients with a single thoracic artery, and there are 609 patients with a double thoracic artery. These are only the in situ thoracic artery reconstructions; free and other arterial grafts need to be added to get a complete overview of extensive arterial grafting in this dataset.
The median follow-up duration is very much related to the entry of patients into the study. A completely uniform entry of patients over 20 years would optimize this median follow-up to 10 years maximum. The only possible inference of the median follow-up is that it reflects nonuniform entry of patients and the growth of our cardiac surgical program.
Younger age very strongly influences the return of angina. But as you have seen on the depictions, younger age does not interact significantly with arterial grafting. Extensive analysis was done into this relationship, and no additional interaction could be identified.
In the presentation in Prague 1
(EACTS 96), the benefit of extensive arterial grafting on survival was studied.
There was no overwhelming benefit, even of the use of a single thoracic artery,
and absolutely no benefit (once the patient variables were completely corrected
for) in extending the use of arterial grafting.
We are therefore at this moment in time still using more extensive arterial revascularization but not going toward the extreme. The possible benefit on any event of radial and gastroepiploic artery grafting seems very distant if not unreachable, if the second thoracic artery benefit is so parsimonious. If there is no contraindication for the second thoracic artery, there seems to be no reason not to use it.
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Appendixes |
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Early phase: d = 0; r = 1.053;
n = 0; M = 1
Late phase: t = 1; g = 2.089; a =
1; h = 1
Appendix 2. The selected variables, their coefficients, their standard error and their mathematic transformations for the final model (patient, procedure, and institutional variables):
Early phase: intercept = –3.980
Younger age ([age (years)/50]2,squared transformation) = –0.5386 ± 0.122; female gender = 0.7586 ± 0.103; longer duration of angina history (ln[duration (months) natural logarithmic transformation] = 0.1524 ± 0.033; unstable ST-segment at surgery = 0.5267 ± 0.086; clinically positive exercise test = 0.3942 ± 0.166, and electrocardiogram negative exercise test = 9.5794 ± 9.180 (subgroup of patients experiencing onset of angina during exercise testing before electrocardiographic changes are evident); greater stenosis of left main coronary artery ([% stenosis/100]2, squared transformation) = –9.8522 ± 9.27; history of peripheral vascular disease = 0.6062 ± 0.116; use of vein grafts only = –0.5739 ± 0.24; use of patch grafts = 0.1.325 ± 0.28; proportion of total distal anastomoses to vessels of size 1 mm or less = 0.6602 ± 0.2; grafting to the LAD system = –0.3436 ± 0.133; lower ratio of the number of arterial anastomoses to total number of distal anastomoses (1/[ratio + 0.5] inverse transformation) = 0.9393 ± 0.26; incomplete revascularisation = 0.4976 ± 0.108 and use of internal thoracic grafts only = 0.74 ± 0.3 (subset of patients who were incompletely revascularized, and only internal thoracic arterial grafts were used); number of coronary endarterectomies = 0.4937 ± 0.14; high risk for angina return surgeon = 0.3485 ± 0.106; low risk for angina return surgeon = –0.3052 ± 0.113
Late phase: intercept = –6.550
Younger age (ln (years) logarithmic transformation) = –0.9071 ± 0.2; female gender = 0.3304 ± 0.072; longer duration of angina history (ln[duration (months) natural logarithmic transformation] = 0.3304 ± 0.072; higher angina class (ln[(angina class) + 1] natural logarithmic transformation) = 0.3414 ± 0.062; preoperative anterior or septal infarct = –0.2570 ± 0.102; greater stenosis of left main coronary artery ([% stenosis/100] scaling transformation) = –0.2364 ± 0.099; multi-system coronary artery disease (2 or more systems diseased by 70% diameter reduction criterion) = 0.2291 ± 0.083; mild aortic valve stenosis = 0.4595 ± 0.2; left ventricular hypertrophy (by electrocardiographic criteria) = 0.2144 ± 0.085; history of non-carotid vascular surgery = 0.5204 ± 0.155; calcified ascending aorta = 0.7202 ± 0.3; overweight now or previously (more than 10 kg over ideal weight: for male patients, ideal weight is [height (cm)-100], and for female patients, ideal weight is [height (cm)-110]) = –0.8918 ± 0.34 and older age (product of age [years] and obesity indicator variable [interaction term])= 0.01818 ± 0.0062; hypertensive (defined as a systolic blood pressure greater than 160 mm Hg, a diastolic blood pressure greater than 100 mm Hg, or being medicated for hypertension by history) = 0.01748 ± 0.052; higher diabetic grade (grade 0, no diabetes; grade 1, abnormal glucose tolerance test with dietary treatment; grade 2, diabetic, receiving oral hypoglycemic treatment; grade 3, insulin-treated diabetes. The squared transform of diabetic grade is used.) = 0.05179 ± 0.0146; higher preoperative triglyceride level (ln[triglyceride level(mg/dl)] logarithmic transformation) = 0.1818 ± 0.054; history of renal failure (patients receiving dialysis therapy or having received renal transplantation) = 1.218 ± 0.31; use of vein grafts to the LAD system = 0.1517 ± 0.051; later date of operation ([date/13]2 squared, scaled transformation of date of operation expressed as the number of years between January 1, 1971, and the calendar date of the operation) = 0.3458 ± 0.067
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Acknowledgments |
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2] = .001)