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Ann Thorac Surg 2000;70:448-455
© 2000 The Society of Thoracic Surgeons

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Original articles: cardiovascular

Ten-year trends in heart valve replacement operations

^a Division of Cardiothoracic Surgery, Carlyle Fraser Heart Center, Department of Surgery, Emory University School of Medicine, Atlanta, Georgia, USA
^b Emory Center for Outcomes Research, Emory University School of Medicine, Atlanta, Georgia, USA
^c Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, USA

Address reprint requests to Dr Guyton, Division of Cardiothoracic Surgery, Emory Clinic, 1365 Clifton Rd, Atlanta, GA 30322
e-mail: rguyton{at}emory.edu

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. There has been increasing concern in recent years about the quality and cost of heart valvular replacement procedures. The purpose of this study is to examine the profile of patients undergoing valvular operations during the past decade, and to look at trends in outcome and resource utilization over that period.

Methods. Clinical and procedural data of 2,972 patients undergoing heart valve replacement at Emory University Hospitals between 1988 and 1997 were recorded prospectively on standardized forms by trained medical personnel and entered into a computerized database.

Results. There were 1,802 patients undergoing aortic valve replacement (AVR), 966 undergoing mitral valve replacement (MVR), and 204 undergoing combined aortic and mitral valve procedures (AVR + MVR). No patients were excluded. There was a statistically significant trend for patients undergoing AVR, MVR, or AVR + MVR over time to be older and sicker by multiple criteria. Nonetheless, procedural outcome and in-hospital mortality for patients undergoing AVR remained unchanged. Cost and length of stay increased from 1988 to 1992 when a concerted effort to decrease resource utilization began. Between 1992 and 1997 for AVR, length of stay decreased from 13.4 to 8.0 days and cost from $37,047 to $21,856. Similarly, between 1992 and 1997 for MVR, length of stay decreased from 15.6 to 8.1 days and cost from $45,072 to $21,747. The net result over the time period from 1988 to 1997 was an average decline in the cost of operation of $785 a year, adjusted for other factors.

Conclusions. This study reveals that outcome of valvular replacement during the period from 1988 to 1997 has remained constant despite the patients becoming older and sicker during the same period. This constant outcome has been accomplished, but length of stay has decreased significantly. Hospital costs increased during the first years of the study period, but then decreased to levels in 1997 that were equal to or significantly less than 1988 levels.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Within the past decade, advances in intraoperative myocardial protection and postoperative care, as well as other surgical and anesthetic techniques, have extended the range of patients who may be offered cardiac procedures. With these improvements in the medical and surgical care of the cardiac patient, the benefits of operation have been extended to patients who were previously deemed inoperable because of their high risk status. Correspondingly, there has been increasing concern about the quality and cost of cardiovascular surgical procedures, whether it be coronary artery bypass grafting (CABG) or valvular procedures.

For patients undergoing CABG, we [1–3] and others [4, 5] have shown a progressive trend toward older and sicker patients with more complex coronary disease and associated medical illnesses. Nevertheless, we have shown a decrease in in-hospital mortality rates for patients undergoing CABG within the past 3 to 5 years despite this increase in high-risk patients [1, 3]. Similarly, trends for patients undergoing heart valve procedures have reflected an increase in mean age and associated comorbid risk factors [6]. Despite this dynamic change in the characteristics of patients undergoing heart valve operations, reports documenting the changing patterns for large cohorts of patients undergoing valve operations are lacking. The independent predictors of mortality for patients undergoing isolated aortic or mitral valve replacement and combined aortic and mitral valve operation have been well described [7–11]. Furthermore, the indications for heart valve operation are well documented, and valvular replacement has been shown not only to prolong life, but also to improve the quality of life. Nevertheless, concerns by physicians, hospital administrators, insurance companies, and patients regarding the allocation of economic resources for patients undergoing these expensive heart valve operations remains highly debated.

Therefore, the purpose of this study was to examine the change in the profile of patients undergoing valvular procedures from 1988 to 1997 at Emory University Hospitals, and to look at trends in outcome and resource utilization during that period.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
From 1988 through 1997, 2,972 consecutive patients underwent heart valve replacement at Emory University Hospitals. The population was divided into 1,802 patients undergoing aortic valve replacement (AVR), 966 undergoing mitral valve replacement (MVR) and 204 undergoing combined aortic and mitral valve replacement (AVR + MVR). No patients were excluded from the 10-year period. Patients who underwent valve repair during the present study were not included. Clinical and procedural data were recorded prospectively on standardized forms by trained medical personnel and entered into a computerized database. All fields were defined in a data dictionary.

Definitions for variables studied are described. Single-vessel disease: presence of more than 50% diameter lumen narrowing in either the left anterior descending, left circumflex or right coronary artery or a major branch or branches; double-vessel disease: presence of more than 50% diameter lumen narrowing in two of the three major epicardial vessel systems; three-vessel disease: presence of more than 50% diameter lumen narrowing in all three major epicardial vessel systems or in the left anterior descending and proximal circumflex coronary artery in left-dominant patients; urgent procedure: a procedure judged by the surgeon to be required within 24 hours; emergent procedure: a procedure performed in the setting of acute ischemia, infarction, or hemodynamic compromise; postoperative myocardial infarction: development of significant new Q waves on electrocardiogram; discharged alive: includes in-hospital mortality for all patients, regardless if patients received concomitant CABG; related variables defined from the patient’s history and physical examination: hypertension, diabetes, severity of angina, and previous myocardial infarction. Because we do not discriminate between aortic regurgitation or aortic stenosis as the indication for AVR, hypertension as a variable for patients with aortic valve disease may be misleading. The Canadian Cardiovascular Society Classification was used to define angina and the New York Heart Association criteria (The Criteria Committee) to define congestive heart failure.

Hospital charges were obtained from the UB92 formulation of the hospital bill provided by the hospital finance department. Charges were reduced to costs using departmental cost to charge ratios obtained from the hospital cost report, which is provided yearly to the Health Care Financing Agency. All costs were inflated to 1997 costs using the Medicare cost inflation rate. The clinical and financial data were combined in a single computerized database with the Social Security number as the primary key.

Statistical analysis
Data are expressed as proportions or means. Trends in categorical variables over time were analyzed using the Mantel-Haenszel test for trend [12] and differences in continuous variables by analysis of variance with a test of linear trend. Correlates of hospital cost and length of stay were determined by stepwise linear regression. Both the original scale as well as the natural logarithm were used as dependent variables, to adjust for the fact that the underlying distribution of both cost and length of stay on the original scale was somewhat skewed. Goodness-of-fit of the final models was examined using the adjusted R². Age, ejection fraction, and year of procedure were modeled as continuous variables. Statistical modeling and testing were performed in S-Plus (Mathsoft Inc, Seattle, WA). Because the number of factors examined, results are considered significant if the value of p was less than 0.01 with a trend toward significance if 0.05 was greater than p was greater than 0.01.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Aortic valve replacement
The demographics and medical history of patients undergoing primary aortic valve replacement throughout the 10-year period are described in Table 1. The proportion of patients with hypertension, diabetes, heart failure, prior myocardial infarction, and prior CABG increased significantly during the period studied. There was a slight trend toward an increase in mean age and the proportion of patients with class III/IV angina.

View larger version (33K): [in this window] [in a new window]   Fig 1. The length of stay in days of patients undergoing heart valve replacement. (AVR = aortic valve replacement; MVR = mitral valve replacement; AVR + MVR = combined aortic and mitral valve replacement.)

View larger version (32K): [in this window] [in a new window]   Fig 2. The hospital cost in US dollars of patients undergoing heart valve replacement. (AVR = aortic valve replacement; MVR = mitral valve replacement; AVR + MVR = combined aortic and mitral valve replacement.)

Aortic and mitral valve replacement
The demographics and medical history of the patients who underwent combined AVR and MVR are listed in Table 5. There was a slight but not statistically significant trend toward increasing mean age, as well as the proportion of women, patients with hypertension, and patients who had undergone previous CABG. The proportion of patients with diabetes mellitus, heart failure, class III/IV angina, and prior myocardial infarction varied throughout the 10-year period with no clear trend.

Hospital cost and length of stay
Linear regression models using the natural logarithm of hospital costs were similar to those using hospital costs in their original scale in terms of the factors found to have a significant association and there was no increase in adjusted R². Therefore, results are presented for the models using hospital costs as the dependent variable. Clinical and procedural correlates of cost are shown in Table 7. The ability to account for variability in cost was low with an adjusted R² of 0.11. Increasing age, male gender, diabetes, heart failure, emergent or urgent procedures, and concurrent CABG were all associated with significant increases in hospital cost. Type of valve procedure was modeled using AVR as the reference category, and the model results describe the significant increase in cost associated with both MVR and MVR + AVR relative to AVR alone. Although costs increased initially from 1988 to 1992 and then declined from 1992 to 1997, the net result over the time period from 1988 to 1997 was a significant average decrease in the cost of the hospital stay of $785 a year, adjusted for the other factors.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

 
In the present study, we have shown that during the past decade, an increasing number of high-risk patients, especially those with coronary artery disease, are presenting to the Emory University Hospitals for heart valve operations. The number of valve replacements during the past 10 years has remained relatively constant. For patients undergoing AVR in 1997 as compared to 1988, there was a statistically significant increase in older patients, and more patients had a history of hypertension, diabetes, congestive heart failure, and class III–IV angina. There was also an increase during the decade toward an increasing number of patients with a history of previous myocardial infarction and coronary artery bypass operations. Furthermore, in 1997 more patients undergoing AVR had catheterization-proven coronary artery disease, necessitating CABG in conjunction with AVR. Similar to patients undergoing AVR, patients with MVR had increasing age and a history of hypertension, class III–IV angina, and prior myocardial infarction. Patients undergoing MVR in 1997 were also more likely to have catheterization-proven coronary artery disease and concomitant CABG with their MVR. Although the number of patients are considerably smaller, trends in demographics for patients undergoing AVR + MVR suggest that sicker patients are also presenting for double valve operations. Despite the sicker patients, outcomes in regard to postoperative Q-wave myocardial infarction, stroke, and in-hospital mortality were unchanged throughout the study period for patients undergoing AVR, MVR, or AVR + MVR. Length of stay and hospital cost gradually increased from 1988 to 1992, after which length of stay in 1997 for all patients was significantly reduced as compared to length of stay in 1988; whereas total hospital cost in 1997 for AVR and MVR patients was significantly reduced as compared to 1988, and was the same in AVR + MVR patients as compared to 1988. Therefore, the present study reveals that outcome of valvular replacement during the period from 1988 to 1997 has remained constant despite changes in multiple factors during the same period.

In the modern era, an increasing number of patients with valvular heart disease often have coexisting coronary artery disease. In the present study, 54%, 43%, and 44% of the patients in 1997 who underwent AVR, MVR, or AVR + MVR, respectively, had cardiac catheterization-proven coronary artery disease, representing a significant increase in patients with coronary artery disease from that of 1988. In contrast, Rao and colleagues [6] have shown that the incidence of coronary artery disease in patients undergoing AVR and MVR at the Toronto Hospital have decreased significantly over time, despite a significant increase in older patients undergoing heart valvular operations. Various studies have revealed the profound effect of coronary artery disease on perioperative survival after heart valve replacement. For patients undergoing AVR combined with CABG, in-hospital mortality rates vary from 5.8% to 13.5%, [13–15] whereas for patients undergoing MVR combined with CABG, in-hospital mortality rates may range from 7.3% to 13.9% [16–18]. Furthermore, Christakis and associates [7] have shown in a multivariate statistical model that the presence of coronary artery disease is an independent risk factor for either AVR or MVR. In addition, Mueller and colleagues [11] have shown that the presence of coronary artery disease for patients undergoing combined AVR and MVR is also an independent determinant of all valve-related events. Therefore, increases in the incidence of coronary artery disease for patients undergoing valvular heart procedures significantly impacts on eventual patient outcome.

In addition to CABG, multivariate analyses have shown that advanced age, preoperative New York Heart Association functional class III–IV, urgent or emergent operation with or without endocarditis, reoperative valve procedure, are also independent predictors of mortality in patients undergoing AVR [6–8, 19–21]. For patients undergoing MVR, independent predictors of mortality in addition to CABG include advanced age, female sex, preoperative New York Heart Association functional class III–IV, urgent operation, endocarditis, ischemic etiology of the mitral valve, and preoperative ventricular ejection fraction less than 40% [6, 7, 9, 18, 22]. For patients who undergo AVR + MVR, independent predictors of mortality include advanced age, urgent operation, coronary artery disease, preoperative low ventricular ejection fraction less than 50%, and tricuspid valve disease [7, 11]. Taken together, the well-established independent predictors of mortality for AVR, MVR and AVR + MVR with the increasing trend toward older age and a higher percentage of patients with coronary artery disease in the present study, one would expect mortality to be increased for patients undergoing heart valve procedures. Nevertheless, outcome analysis for patients undergoing heart valve operations in the present study and in an eloquent study by Rao and colleagues [6] has shown no significant change in mortality. It is possible that recent advances in intraoperative myocardial protection, along with improved postoperative pharmacologic management has neutralized mortality for valvular heart operations despite sicker patients.

Reasons for higher risk surgical patients presenting for valvular heart operations in this modern era may be multifactorial. It is possible that the recent popularization of valve repair by some investigators [23–26], especially in younger, low-risk patients, has resulted in patients with more extensive valvular dysfunction undergoing heart valve replacement. Despite the advent of valvular repair, the number of AVR, MVR, and AVR + MVR performed by our institution has remained relatively constant during the past decade. Also, the improvement in medical management, including valvuloplasty, for alleviating symptoms related to valvular heart disease potentially delays referral of these patients to the cardiac surgeon. Therefore, patients present for valvular replacement later in the course of their disease process and are more functionally compromised.

One would also expect that in the modern era of technologic advances, costs for performing heart valve operations, especially in these higher risk patients, would have continued to increase throughout the study period. Before 1992, the cardiac surgery services did not use patient care maps and there was minimal regulation of superfluous tests or cost containment. Therefore, from 1988 to 1992, costs for all patients undergoing heart valve replacement did indeed increase. However, in 1992, patient care maps and clinical pathways were introduced to the Emory Hospitals for all patients undergoing heart valve operations. These pathways targeted intense preoperative teaching, aggressive early extubation, reduction of superfluous tests, and early transfer from the intensive care unit. We believe that a combination of these factors, along with a careful scrutiny of hospital costs and a conscientious effort by the cardiac surgery health care employees to curtail cost without compromising quality health care, has decreased the overall cost of patients undergoing heart valve replacement. Consequently, in 1997 the costs associated with individual AVR and MVR were equal to 1988 levels despite a sicker operative patient population.

In the present study, we have shown that despite a trend during the past decade for patients undergoing valvular heart operations to be older and sicker by many criteria, procedural outcome, including Q-wave myocardial infarction and stroke, as well as in-hospital mortality changed little; although there were considerable decreases in cost and length of stay, particularly after 1992. We should continue to expect changes in the profile of patients undergoing heart valve operations. Although the indications for heart valve procedures are well documented, and valvular replacement has been shown not only to prolong life, but also to improve the quality of life, these operations remain expensive. By continuing to analyze critically the dynamic changes not only in the patient population undergoing AVR and MVR, but also in the new technologic advances in surgical valve conduits, we should be better capable of predicting future needs and trends of our health care resources.

	Acknowledgments

 
We are grateful to Gail Nechtman for assistance in preparation of the manuscript. Vinod H. Thourani, MD, was awarded a Fellowship from the Thoracic Surgery Research Foundation (1998 to 1999).

	References

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