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Ann Thorac Surg 1998;65:1215-1219
© 1998 The Society of Thoracic Surgeons

Management of Patients With Mild Aortic Stenosis Undergoing Coronary Artery Bypass Grafting

James W. Tam, MDa, Roy G. Masters, MDa, Ian G. Burwash, MDa, Alain D. Mayhew, BSa, Kwan-Leung Chan, MDa

a University of Ottawa Heart Institute, Ottawa, Ontario, Canada

Accepted for publication October 31, 1997.

Address reprint requests to Dr Chan, University of Ottawa Heart Institute, 1053 Carling Ave, Ottawa, Ontario, Canada, K1Y 4E9
e-mail: (kchan{at}heartinst.on.ca)


   Abstract
Top
 Abstract
Introduction
 Patients and methods
 Results
 Comment
 References
 
Background. The management of mild aortic stenosis during coronary artery bypass grafting remains controversial.

Methods. We reviewed the medical records of consecutive patients between January 1, 1977, and December 31, 1994, to identify 51 patients with mild aortic stenosis who underwent isolated coronary artery bypass grafting (group A), and 19 patients with mild aortic stenosis who underwent combined coronary artery bypass grafting and aortic valve replacement (group B). Patients with more than moderate aortic regurgitation were excluded. Preoperative angiograms were reviewed to assess the severity of calcification and restricted mobility of the aortic cusps.

Results. In group A there were 11 deaths and 8 subsequent aortic valve replacements; in group B there were 5 deaths and 3 prosthetic valve-related complications. There was no difference in event-free survival between the two groups after adjusting for the difference in age. Among group A patients, the initial transvalvular gradient (p = 0.0005) and aortic valvular calcification (p = 0.06) identified patients who demonstrated progression to severe aortic stenosis during follow-up.

Conclusions. Our data suggest that routine aortic valve replacement during coronary artery bypass grafting in patients with mild aortic stenosis is not indicated, but concomitant aortic valve replacement may be appropriate in patients with higher transvalvular gradients and calcified valves.


   Introduction
Top
 Abstract
 Introduction
Patients and methods
 Results
 Comment
 References
 
It is controversial whether to perform aortic valve replacement (AVR) during coronary artery bypass grafting (CABG) in patients with symptomatic coronary artery disease and mild aortic stenosis (AS) [1–4]. Progression of AS may necessitate, within a fairly short time, subsequent AVR, which carries an increased perioperative risk [1–3, 5, 6]. However, many of these patients may not have significant progression of AS during follow-up, and it is not justifiable to expose them to the increased perioperative risk of combined AVR and CABG, or the short- and long-term complications of prosthetic heart valves. Recent studies have examined the timing and outcome of subsequent AVR in these patients [1–3], but little is known about the probability of progression of AS in the whole group of patients. We reviewed our experience with all patients with mild AS and symptomatic coronary artery disease who underwent CABG or combined CABG and AVR to determine the natural history of mild AS after CABG and to identify predictors of accelerated AS progression leading to the development of symptoms or AVR.


   Patients and methods
Top
 Abstract
 Introduction
 Patients and methods
Results
 Comment
 References
 
Patient population
In this study, we included all patients with symptomatic coronary artery disease and mild AS who went on to have isolated CABG or combined AVR and CABG between January 1, 1977, and December 31, 1994, at the University of Ottawa Heart Institute. The medical records on consecutive patients undergoing isolated CABG were reviewed to identify those with concomitant AS documented at cardiac catheterization. The diagnosis of AS was based on hemodynamic data and not on clinical findings. Aortic regurgitation was assessed using a four-grade system (mild, moderate, moderately severe, and severe) according to the degree of left ventricular opacification during aortography [7]. All patients had at the time of CABG mild AS with peak to peak gradients less than or equal to 25 mm Hg or valve areas of 1 cm2 or greater (group A). We also reviewed all patients who had combined CABG and AVR during the same period to identify those patients with mild AS by the same hemodynamic criteria (group B). We included patients with mild or moderate aortic regurgitation, but patients with more than moderate aortic regurgitation were excluded.

Cardiac catheterization
Cardiac catheterization was performed using standard percutaneous or brachial arterial cutdown techniques. Transvalvular gradients were measured by pulling the catheter back from the left ventricle to the aortic root before injection of contrast material. Calculated aortic valve areas were not available in all patients because transvalvular aortic gradients were generally low in these patients and cardiac output measurements were not routinely performed in the absence of significant left ventricular dysfunction. Significant coronary stenosis was defined as greater than or equal to 70% luminal diameter narrowing by visual inspection. Left ventricular function was assessed using a regional wall motion score system with grade 0 being normal, grade 1 abnormal contractile function involving less than or equal to 25% ventricular circumference at angiography (right anterior oblique projection), grade 2 26% to 50%, grade 3 51% to 75%, and grade 4 no normal contractile segments [8].

Angiograms were reviewed in a blinded fashion to assess the degree of calcification of the aortic cusps or annulus with grade 0 being no calcification, grade 1 flecks of calcification, grade 2 larger areas, and grade 3 dense calcification in all cusps [9]. Mobility of the aortic cusps was graded based on the amount of aortic cusp excursion as grade 0 being normal, grade 1 mild restriction (>75% normal excursion), grade 2 moderate (50% to 75% normal excursion), and grade 3 severe (<50% normal excursion) [6].

Patient follow-up
Follow-up was performed by reviewing the medical records and by telephone interviews with the patients or their primary physicians. The outcome events were death or AVR for group A and death or prosthetic valve-related complications for group B. The functional class and symptomatic status of patients were determined. In patients who required subsequent AVR, the indication and timing of surgery were recorded. In patients who died, the cause of death was determined by the primary physicians or from autopsy reports when available. Deaths were attributed to AS only if progression to severe AS had been documented before death.

Follow-up hemodynamic information was obtained from repeat cardiac catheterization or from Doppler echocardiograms. Peak to peak gradients were used for comparison between catheterization studies. On follow-up Doppler echocardiograms, maximum instantaneous gradients and aortic valve area by continuity equation were obtained [10].

Statistical analysis
Data were expressed as mean values and standard deviations. Intergroup comparison was performed using Student’s t test for continuous variables and {chi}2 analysis for discrete variables. Analysis of variance was used to test the relationship between aortic valve calcification and AS gradient. A p value less than 0.05 was considered significant. Event-free survival was measured and compared between groups using Cox proportional hazards model [11]. Hazard ratio was calculated using maximum likelihood estimates with adjustment for age as a confounding covariate [11, 12].


   Results
Top
 Abstract
 Introduction
 Patients and methods
 Results
Comment
 References
 
During the study period there were 51 group A patients. Group B consisted of 19 of 520 consecutive patients who underwent combined AVR and CABG but had only mild AS at cardiac catheterization. Ten group B patients received bioprosthetic valves and 9 patients mechanical valves.

The clinical characteristics and hemodynamic measurements of these two groups of patients are shown in Table 1. In one group A patient, hemodynamic data were obtained by Doppler echocardiography because retrograde catheter crossing of the aortic valve was not achieved. Group B patients were older but had less severe angina. Despite similar gradients and left ventricular function, aortic valves in group B demonstrated denser calcification and more restricted mobility. As expected the perfusion time and pump time were longer in group B. Although survival to hospital discharge was similar between the two groups, outcome events occurred at a shorter time from initial surgery in group B patients.


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  		Table 1. Patient Characteristics in the Two Groups of Patients With Mild Aortic Stenosisa

 
Follow-up data
Four group A patients did not have follow-up data beyond hospital discharge and were excluded from further analysis although they were included in the survival estimate. The median length of follow-up was 59 months for group A and 33 months for group B. The event-free survival curves for the entire follow-up were not significantly different between the two groups (p = 0.32) (Fig 1). At 48 months, there was a trend favoring group A in event-free survival (p = 0.06), but this was no longer apparent after adjusting for age (p = 0.10).



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  		Fig 1. Cumulative event-free survival of patients with mild aortic stenosis who underwent isolated coronary artery bypass grafting (CABG) or combined coronary artery bypass grafting and aortic valve replacement (AVR). Hospital deaths are included.

 
In group A there were 19 events (11 deaths and 8 subsequent AVR). The median time of death after CABG was 12 months (range 0 to 161 months). The causes of death were perioperative complications in 4 patients, progressive AS with heart failure in two, sudden cardiac death in 1, stroke in 1, cancer in 1, and unknown causes in 2. Subsequent AVR was performed with no perioperative mortality in 8 patients at a median time of 71 months (range 18 to 137 months) after initial CABG. Three of these patients also had repeat CABG.

There were eight events (five deaths and three valve-related complications) in group B. The causes of death were perioperative complication in 1 patient, heart failure in 1, sudden death in 1, stroke in 1, and unknown in 1. Prosthetic valve-related complications included thromboembolism in 2 patients and endocarditis in 1 patient. In addition 1 patient had repeat CABG during follow-up.

Of the 28 event-free survivors in group A, 22 had follow-up echocardiographic assessment. The mean maximum instantaneous gradient was 40 ± 23 mm Hg, and the aortic valve area was 1.3 ± 07 cm2 at a mean follow-up of 65 ± 47 months.

Predictors of as progression
Severe AS developed in 10 group A patients, resulting in subsequent AVR in 8. Death occurred in both patients who were not surgical candidates and therefore did not have AVR. The clinical and baseline hemodynamic parameters of the 28 event-free survivors were compared with the 10 patients who demonstrated progression to severe AS (Table 2). Although left ventricular grade and coronary artery involvement were similar, those who demonstrated progression to severe AS had a higher baseline peak to peak gradient (p = 0.0005) and a trend to a higher aortic cusp calcification score (p = 0.06). There was a strong positive association between AS gradient and valvular calcification for the entire cohort (linear trend by analysis of variance p = 0.0001) (Table 3). Among patients in group A those who progressed to severe AS, but not the event-free survivors, were similar to group B patients in terms of AS gradient and calcium score (Table 4).


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  		Table 2. Patient Characteristics in Event-Free Survivors and Patients Who Progressed to Severe Aortic Stenosis in Group A

 

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  		Table 3. Relationship Between Aortic Transvalvular Gradient and Severity of Valvular Calcificationa

 

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  		Table 4. Comparison of Pressure Gradient and Aortic Valvular Morphology Between the Two Subgroups in Group A With Patients in Group B

 
The impact of AS gradient was further analyzed by dividing group A into two subgroups on the basis of the median AS gradient (that is, >=12 and <12 mm Hg) (Fig 2). Patients with gradient >=12 mm Hg had a worse outcome with a hazard ratio adjusted for age of 3.74 (95% confidence limits, 1.16 and 11.96; p = 0.02).



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  		Fig 2. Cumulative event-free survival of patients with mild aortic stenosis (AS) who underwent isolated coronary artery bypass grafting. Patients with peak to peak gradient less than 12 mm Hg and greater than or equal to 12 mm Hg are compared. Hospital deaths are included.

 

   Comment
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
References
 
It is not uncommon to encounter mild AS in patients with symptomatic coronary artery disease, but whether concomitant AVR should be performed at the time of CABG remains uncertain [1–5]. It has become increasingly clear that some of these patients will go on to require subsequent AVR as a result of progression to severe AS [1–3]. There is an increased perioperative risk of AVR in patients with prior CABG, and the operative mortality has been reported to be as high as 23.5% [3]. The high perioperative morbidity and mortality may be related to the advanced age of these patients, the need for repeat CABG in some of these patients, and the technical complexities resulting from mobilization and handling of vein grafts and internal thoracic arteries [5, 13–15]. This has led to the suggestion that AVR be prophylactically performed in these patients to avoid the substantial morbidity and mortality associated with subsequent AVR [3]. This approach, however, fails to consider that some patients may be needlessly exposed to the increased operative risk of the combined procedure, as well as the morbidity and mortality associated with prosthetic valves and chronic anticoagulation [15, 16]. For consecutive patients operated on in our hospital in 1996, the perioperative mortality is 2.0% for isolated CABG, and that for combined CABG and AVR is 7.8%. Prosthetic valve-related complications, including thromboembolism, infective endocarditis, perivalvular leak, hemolytic anemia, and anticoagulant-related hemorrhage, are estimated to occur at a rate of about 5% per year [16, 17]. The magnitude of this dilemma will likely increase in the coming years as patients referred for CABG have become older and thus the incidence of concomitant mild AS is certain to increase [18, 19].

Previous studies have focused solely on patients requiring subsequent AVR [1–3], and the conclusions based on these studies may be misleading because the likelihood of subsequent AVR in patients with mild AS and isolated CABG cannot be assessed by such analysis. These studies also do not allow for the determination of patient characteristics that may be helpful in identifying patients requiring subsequent AVR. In the present study we identified all patients with symptomatic coronary artery disease and mild AS who had isolated CABG or combined AVR and CABG. Patients with combined AVR and CABG had more events during early follow-up to 48 months, accounting partly for the apparently shorter follow-up of these patients. However, both the early and overall event-free survivals were similar between the two groups after adjusting for the difference in age. Thus concomitant AVR during CABG in these patients with mild AS did not adversely affect outcome, but it also did not confer significant benefit on event-free survival.

It is interesting to note that despite similar AS gradients the aortic valves were more calcified and less mobile in patients who underwent concomitant AVR. Indeed these morphologic features might be the reason for AVR in these patients at the time of CABG. The importance of these morphologic features was also seen when the subgroups of group A patients were compared with patients in group B. Group A patients who progressed to severe AS were more akin to group B patients, and these morphologic features could have identified them for concomitant AVR during CABG. Intraoperative transesophageal echocardiography or visual inspection of the aortic valve may be useful to the final decision whether to perform AVR, but neither strategy has been prospectively tested.

The progressive nature of AS is well recognized [6, 9, 20–23]. Although there is considerable variability in the rate of progression from individual to individual, patients with mild AS generally have a slower rate of progression compared with patients with more severe AS [23]. Our results showed that patients with very low gradients, such as peak to peak gradient less than or equal to 12 mm Hg, may demonstrate less progression than those with higher gradients although still in the mild AS range. Davies and colleagues [9] showed that the mean rate of AS progression in patients with no initial gradient was 3.9 mm Hg per year, whereas that of patients with a mean initial gradient of 25 mm Hg was 7.1 mm Hg per year, although this difference did not reach statistical significance. In predicting the rate of AS progression, patients with mild AS may be further stratified by the severity of valvular calcification and transvalvular gradient. Valves with these two features are more likely to undergo further calcification leading to progressive AS in the short to medium term, although their transvalvular gradients are still relatively minor.

Limitations
The retrospective nature of this study does not allow the determination of why certain patients with mild AS underwent AVR and others did not. Our data suggest that the primary physicians might be influenced by the presence of calcification and restricted mobility, but this remains a conjecture. Aortic valve area measurements were not obtained in all patients. However the transvalvular pressure gradient is a reliable measure of AS severity with normal left ventricular function, and valve area was calculated in patients with impaired systolic function. We were unable to determine whether congenital bicuspid or tricuspid aortic valves had a high propensity for progression, because baseline echocardiography was performed in only a minority of patients.

Conclusion
Our data suggest that routine prophylactic AVR at the time of CABG in patients with mild AS and symptomatic coronary artery disease is unnecessary, as combined AVR and CABG does not favorably affect event-free survival. However, a higher transvalvular pressure gradient and more heavily calcified aortic cusps appear to identify those who may require subsequent AVR. Until the results of a prospective, randomized trial become available, the decision to perform concomitant AVR in these patients should be based on a comprehensive assessment taking into account the "severity" of mild AS and valvular calcification.


   References
Top
 Abstract
 Introduction
 Patients and methods
 Results
 Comment
 References
 

  1. Fiore A.C., Swartz M.T., Naunheim K.S., et al. Management of asymptomatic mild aortic stenosis during coronary artery operations. Ann Thorac Surg 1996;61:1693-1698.[Abstract/Free Full Text]
  2. Wong P.S., Davies S.W., Youhana A., Wright J.E., Magee P.G. Coronary artery bypass surgery and minor aortic stenosis—to replace or not to replace?. J Heart Valve Dis 1993;2:649-652.[Medline]
  3. Collins J.J., Jr, Aranki S.F. Management of mild aortic stenosis during coronary artery bypass graft surgery. J Cardiac Surg 1994;9(Suppl):145-147.[Medline]
  4. Antunes M.J. Coronary artery bypass surgery and minor aortic stenosis. To replace or not to replace? An alternative: to repair. J Heart Valve Dis 1994;3:235.[Medline]
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  6. Ng A.S., Holmes D.R., Jr, Smith H.C., et al. Hemodynamic progression of adult valvular aortic stenosis. Cathet Cardiovasc Diagn 1986;12:145-150.[Medline]
  7. In: Baim D.S., Grossman W., eds. Cardiac catheterization, angiography, and interventions, 5th ed. Baltimore: Williams and Wilkins, 1995:750.
  8. Morton B.C., Brais M.P., Beanlands D.S., et al. Do symptoms reflect a change in left ventricular function after aortocoronary bypass grafting in patients with depressed left ventricular function?. Can J Surg 1987;30:269-271.[Medline]
  9. Davies S.W., Gershlick A.H., Balcon R. Progression of valvar aortic stenosis: a long-term retrospective study. Eur Heart J 1991;12:10-14.[Abstract/Free Full Text]
  10. Skjaerpe T., Hegrenaes L., Hatle L. Noninvasive estimation of valve area in patients with aortic stenosis by Doppler ultrasound and two-dimensional echocardiography. Circulation 1985;72:810-818.[Abstract/Free Full Text]
  11. Norman GR, Streiner DL. Biostatistics, the bare essentials. St. Louis: Mosby Year Book, 1994:182–95.
  12. SAS Proprietary Software Release 6.11. Cary, NC: SAS Institute Inc, TS021.
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  14. Grondin C.M., Pomar J.L., Hebert Y., et al. Reoperation in patients with patent atherosclerotic coronary vein grafts: a different approach to a different disease. J Thorac Cardiovasc Surg 1984;87:379-385.[Abstract]
  15. Sindhi R., Belisle J., Cleveland R.J., Diehl J.T. Patch aortotomy for aortic valve replacement after previous coronary artery bypass grafting. Ann Thorac Surg 1991;51:676-677.[Abstract]
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  21. Cheitlin M.D., Gertz E.W., Brundage B.H., Carlson C.J., Quosh J.A., Bode R.S. Rate of progression of severity of valvular aortic stenosis in the adult. Am Heart J 1979;98:689-700.[Medline]
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