The Determinants of Mortality and Morbidity after Multiple-Valve Operations

ORIGINAL ARTICLES

The Determinants of Mortality and Morbidity after Multiple-Valve Operations Kevin H. Teoh, M.D., George T. Christakis, M.D., Richard D. Weisel, M.D., Cathy P. Tong, M.R.L., Lynda L. Mickleborough, M.D., Hugh E. Scully, M.D., Bernard S. Goldman, M.D., and Ronald J. Baird, M.D. ABSTRACT The factors predictive of hospital mortality and morbidity after contemporary multiple-valve surgical procedures were identified to develop strategies to improve the results of such procedures. Preoperative, intraoperative, and postoperative information was collected prospectively on 90 consecutive patients undergoing surgical procedures between 1982 and 1984. The operative mortality was 5.6%, and the incidence of postoperative low-output syndrome was 16.7%. Multivariate logistic regression analysis identified tricuspid regurgitation ( p < .03, improvement-of-fit chi square) and the aortic valve lesion ( p < .03)as the independent predictors of postoperative complications (mortality or low-output syndrome). Patients with tricuspid regurgitation and right ventricular decompensation and those with aortic stenosis and left ventricular hypertrophy had limited ventricular functional reserve and faced an increased risk. Improved methods of myocardial protection may reduce the risk in these patients.

The operative risk of combined mitral valve and aortic valve replacement has improved, but it remains between 5% and 12% [l-31. Many reasons for the increased risk of surgery have been postulated [4, 51. However, there has been little statistical identification of predictive factors [6, 7. Identification of high-risk patients will allow surgeons to develop strategies to improve the results. Therefore, we analyzed the clinical and hemodynamic variables of 90 consecutive patients undergoing mitral valve and aortic valve replacement to identify those preoperative factors predictive of early postoperative mortality and morbidity.

Material and Methods Patient Population

We evaluated 90 consecutive patients who underwent mitral and aortic valve replacement between 1982 and 1984. Patients who had undergone concomitant coronary bypass surgical procedures, tricuspid annuloplasty, or tricuspid valve replacement were included. These 90 patients were 12% of the 734 patients who had

From the Division of Cardiovascular Surgery, Toronto General Hospital, and the University of Toronto, Toronto, Ontario, Canada. Accepted for publication Mar 31, 1986. Address reprint requests to Dr.Weisel, Cardiovascular Surgery, Toronto General Hospital, 200 Elizabeth St, Eaton North 13-224, Toronto, Ontario, Canada, M X 2C4.

353 Ann Thorac Surg 43:353-358, Apr 1987

valve replacements during this interval. The other procedures included aortic valve replacement in 334 patients, mitral valve replacement in 262, and aortic valve and ascending aortic procedures in 48.All of the 90 patients underwent cardiac catheterization preoperatively except for 4 who, based on two-dimensional echocardiographic findings, underwent urgent surgical procedures. Clinical and hemodynamic variables were prospectively collected and analyzed by univariate and multivariate statistics.

Clinical Data The sex, age, New York Heart Association (NYHA) Functional Class, presence of angina pectoris, presence of endocarditis, history of previous sternotomy, and urgency of the operation were recorded prospectively for each patient.

Catheterization Data Cardiac catheterization was performed to assess the valvar lesion, the ventricular function, and the extent of coronary disease. Right atrial, pulmonary arterial, pulmonary capillary wedge, and left ventricular enddiastolic pressure were measured. The cardiac index was calculated either by the thermodilution method or the Fick method. Pulmonary and systemic vascular resistance values were calculated from standard formulas [8]. The peak systolic aortic valve gradient was calculated either by simultaneous pressure measurements or by the pullback technique. Mitral and aortic valve areas were calculated from the cardiac output and the valve gradient measurements by the Gorlin formula [9]. The left ventricular ejection fraction was determined from a single-plane left anterior oblique contrast ventriculogram using planimetry. The severity of aortic and mitral regurgitation was estimated by the extent of left ventricular or left atrial opacification after aortic root or left ventricular contrast injection (minimal = 1+ , mild = 2 +, moderate = 3 + , severe = 4 + ) . The valvar lesions were divided into three categories: predominant stenosis, predominant regurgitation, and mixed disease. Predominant aortic stenosis was defined as a peak systolic gradient greater than 40 mm Hg, an aortic valve area less than 1cm2, and aortic regurgitation of 1+ or less. Predominant aortic regurgitation was defined as 3 or greater opacification of the left ventricle after aortic root injection and a pulse pressure equal to or greater than 60% of the systolic aortic pressure. Mixed aortic valve disease had characteristics of both

+

354 The Annals of Thoracic Surgery Vol 43 No 4 April 1987

aortic stenosis and aortic regurgitation. A mitral valve area less than 1.5 cm2 and mitral regurgitation less than 1+ was considered as predominant mitral stenosis. Predominant mitral regurgitation was defined as 2 + or greater opacification of the left atrium and a mean mitral valve gradient less than 5 mm Hg. Mixed mitral valve disease had characteristics of both mitral stenosis and regurgitation. Patients whose clinical findings suggested tricuspid regurgitation underwent echocardiography with microbubble studies, Doppler evaluation, or both. Right heart catheterization was also performed to assess the degree of tricuspid regurgitation and to evaluate right ventricular function. A diagnosis of tricuspid regurgitation was made when moderate or severe regurgitation was found preoperatively and confirmed intraoperatively. In assessing the extent of coronary artery disease, the left ventricle was divided into three regions: left anterior descending, circumflex, and right coronary artery. A clinically significant stenosis to the major artery supplying one of these regions was defined as a narrowing equal to or greater than 50%.

Anesthetic Management and Operative Technique Anesthetic management and operative techniques were similar among the anesthetists and the five surgeons involved in this study. Fentanyl citrate (75 p g k g ) was used for induction and maintenance of anesthesia. Moderate hemodilution (hematocrit 20 to 25%) and systemic hypothermia (25OC) were maintained during cardiopulmonary bypass. A cooling pad provided topical hypothermic protection. Multidose cold crystalloid cardioplegia was used in the majority of the patients (87), and some patients (3) received blood cardioplegia. Cardioplegia was delivered by hand-held cannulas every 20 minutes during aortic occlusion to maintain myocardial temperatures below 15°C. Concomitant coronary artery bypass was performed with saphenous veins or internal mammary arteries. Distal anastomoses were performed before valve replacement to permit vein graft perfusion with cardioplegic solutions. The surgeon selected the prosthesis based on the patient’s age and history of thromboembolism or bleeding disorder. Mechanical valves were generally inserted in younger patients and in those with a history of thromboembolism requiring anticoagulation therapy. Bioprostheses were generally inserted in older patients and those who had a contraindication to anticoagulation therapy. However, the surgeon’s choice of prosthesis was also based on a discussion with the patient and the patient’s cardiologist. All valves were inserted using interrupted pledgeted sutures. The posterior leaflet of the mitral valve was preserved when a bioprosthesis was inserted for mitral regurgitation. Tricuspid regurgitation was corrected by annuloplasty if the tricuspid valve was normal. Tricuspid annuloplasties were performed by the DeVega technique or by using a Carpentier or Duran ring. The tricuspid valve was replaced if it was intrinsically diseased.

Postoperative Outcome Postoperative outcome was assessed prospectively by reviewing the charts and interviewing the patients before discharge. Operative mortality was defined as a death occurring within 30 days or during the hospital stay. Low-output syndrome was defined as hypotension (systolic blood pressure less than 90 mm Hg) and a cardiac index of less than 1.4 L/min/m2despite an adequate preload. In most patients Swan-Ganz catheters were inserted preoperatively for measurement of cardiac output and pulmonary capillary wedge pressure. A Swan-Ganz catheter was inserted in any patient suspected of hemodynamic instability postoperatively. Low output was initially managed by optimization of preload and afterload. Metabolic abnormalities were corrected, and myocardial ischemia was treated with intravenous nitroglycerin. Preload was optimized by volume loading, and afterload reduction was attempted before the institution of inotropes. Patients who continued to have inadequate perfusion received inotropes. Dopamine was used most frequently, but dobutamine, isoproterenol, or epinephrine were employed for specific indications. An intraaortic balloon was inserted in those patients who continued to have inadequate perfusion despite inotropes. In one patient who continued to have refractory low-output syndrome, a right ventricular assist device was inserted. Flow from the right atrium to the pulmonary artery was maintained with a Biomedicus centrifugal pump (Biopump, Biomedicus, Minnetonka, MN). Preoperative and postoperative electrocardiograms were reviewed by a cardiologist who was not involved in the clinical care of the patient. A postoperative myocardial infarction was defined as the appearance of new Q waves or an increase in creatine kinase-musclehain (CK-MB) hybrid isoenzyme to greater than 50 IUL if the CK-MB level was greater than 8% of the total CK when the electrocardiogram had a left bundle branch block or inadequate R wave progression. A postoperative stroke was diagnosed if a persistent neurologic deficit was present at the time of discharge or death. A wound infection was diagnosed if prolonged hospitalization was required because of antibiotic therapy or surgical procedures in patients from whom pathogenic organisms had been recovered from the wound. Statistical Analysis Statistical analysis was performed using programs of the Statistical Analysis Systems Institute (Cary, NC). Univariate analysis was performed on all discrete clinical data to determine the predictors of mortality or lowoutput syndrome; the chi-square test, Fisher’s exact test, or the Mann-Whitney U test were used, as appropriate. Continuous data were tested by t tests or an analysis of variance (ANOVA), and differences were specified by Duncan’s multiple-range t test when the ANOVA was significant ( p < .05). Stepwise logistic regression was performed by the BMDP program (BMDP Statistical Software, Los Angeles, CA), using all discrete and continuous variables. Step selection was based on the max-

355 Teoh, Christakis, Weisel, et al: Multiple-Valve Procedures

imum-likelihood ratio. A p value of less than .15 was required for entry, and a p value greater than .10 was required for removal. An improvement chi square was calculated for each variable entered. Variables were considered independently significant if the improvementof-fit chi square was significant ( p < .05). Interpretation and illustration of the logistic curves were based on the predicted probability for postoperative complications using the variables found to be significant.

Results

Clinical Data

The patient profile is presented in Table 1. The majority of the patients (60%) were women. Most of the patients were in NYHA Functional Class I11 or IV. Operations were usually performed on an elective basis, but 6 patients (6.7%) required urgent surgical procedures because of endocarditis or congestive heart failure. Twelve of the 90 patients (13%) had previously had a sternotomy for a cardiac procedure.

Catheteriza tion Data Thirteen patients had angiographically significant coronary artery disease, and 4 had angina. Seven patients underwent concomitant aortocoronary bypass procedures. The remaining 6 patients who had coronary artery disease but did not have bypass procedures were asymptomatic and had either single-vessel disease (4) or double-vessel disease (2). The majority of patients had aortic regurgitation (stenosis: 12 patients, or 13%;regurgitation: 42 patients, or 47%; and mixed: 36 patients, or 40%). The mitral valve lesion was more evenly distrib-

Table 1. Clinical Profile of 90 Patients Undergoing Mitral and Aortic Valve Operations No. of Patients With

Gender Male Female Age (yr)

Total (%)

Complicationsa

36 (40) 54 (60) 53.6 2 13.2b

7 (41) 10 (59) 57.3 ? 9.5b

New York Heart Association

Functional Class

1 I1 111

IV Timing of procedure

Elective Urgent Previous surgical procedure Angina pectoris Endocarditis

4 (4) 13 (14) 58 (65) 15 (17)

84 (93) 6 (7) 12 (13) 4 (4) 5 (6)

aMortality or low-output syndrome. bMean standard deviation.

*

0 (0) 3 (18)

9 (53) 5 (29)

16 (94) 1 (6) 1 (6) 2 (12) 0 (0)

Table 2. Hemodynamic Profile of 90 Patients Undergoing Mitral and Aortic Valve Operations All

Patients

Cardiac index (L/min/m2) 2.2 t 0.7 Left ventricular end-diastolic 14.9 2 6.6 pressure (mm Hg) Mean pulmonary artery pressure (mm Hg) 33.1 t 13.1 Mean right atrial pressure (mm Hg) 9.9 2 6.6 Ejection fraction 20-40% 11 (12) 4040% > 60%

~

19 (21) 60 (67)

Patients with Complications 1.8 t 0.7

17.7

2

7.6

37.7 t 10.3

12.8 2 7.8 3 (17) 4 (24) 10 (59)

~~~

Numbers are mean theses.

k

standard deviation; percents are given in paren-

uted (stenosis: 29 patients, or 32%; regurgitation: 25 patients, or 28%; mixed: 36 patients, or 40%). Fifteen patients (16%) had clinically significant tricuspid regurgitation. In these patients the right ventricle was enlarged and contracted poorly despite the presence of tricuspid regurgitation. No patient had tricuspid stenosis. In 60 patients (67%) the ejection fraction was greater than 60%, whereas in 19 (21%) it was between 40 and 60%, and in 11 (12%)it was between 20 and 40%. In no patient was the ejection fraction less than 20%. The hemodynamic profile is summarized in Table 2.

Prosthesis Selection In 37 patients (41%) mechanical prostheses were inserted in both aortic and mitral positions (36 BjorkShiley devices and 1 Medtronic-Hall device). Bioprostheses were inserted in both positions in 38 patients (42%)(27 Ionescu-Shiley pericardial devices, 6 Hancock pericardial devices, and 5 Carpentier-Edwards porcine devices). Two patients (2%)received a bioprosthesis in the aortic position and a mechanical prosthesis in the mitral position. Nine patients (10%) underwent aortic valve replacement and a mitral valve repair, and 3 (3%) patients underwent aortic valvuloplasty and a mitral valve replacement. In 1 patient (1%)both valves were repaired. A tricuspid annuloplasty was performed in 10 of the 15 patients whose preoperative diagnosis of moderate or severe tricuspid regurgitation was confirmed intraoperatively. One tricuspid valve replacement was performed. Four patients thought to have significant tricuspid regurgitation preoperatively did not undergo an annuloplasty because, intraoperatively, they had mild to moderate regurgitation that was believed to be reversible postoperatively.

Postoperative Complications Five patients (6%) died and in 15 patients (17%) lowoutput syndrome developed postoperatively. All pa-

356 The Annals of Thoracic Surgery Vol 43 No 4 April 1987

tients with low-output syndrome required inotropes, and 6 (7%)patients also required intraaortic balloon assistance. A right ventricular assist device was successfully used in a patient who could not be weaned from cardiopulmonary bypass because of right ventricular failure. Four patients (4%) died because of inadequate ventricular function, and 1 patient (1%)died intraoperatively of uncontrollable bleeding caused by atrioventricular separation. Two patients (2%)had a perioperative myocardial infarction, and 2 suffered strokes. Seven patients (8%)required reoperation for bleeding, and in 4 patients (4%)a sternal infection developed.

Determinants of Outcome The aortic valve lesion and tricuspid regurgitation were determinants of postoperative complications (mortality or postoperative low-output syndrome) (Fig 1). The mitral valve lesion was not predictive. Patients with aortic stenosis had the highest risk (45%), those with aortic regurgitation had an intermediate risk (21%), and those with combined aortic stenosis and regurgitation were at the lowest risk (8%)of postoperative complications. Patients with tricuspid regurgitation also had an increased risk of postoperative complications (40%in patients with tricuspid regurgitation; 15% in those without tricuspid regurgitation). Multivariate logistic regression analysis identified aortic valve lesion and tricuspid regurgitation as independent predictors of postoperative complications (Fig 2A). Tricuspid regurgitation increased the risk with any aortic valve lesion (Fig 2B). Annuloplasty did not influence the incidence of postoperative complications in the patients with tricuspid regurgitation. Five of the 11 patients with tricuspid regurgitation (45%)who underwent annuloplasty and 2 of the 4 patients with tricuspid regurgitation who did not undergo annuloplasty (50%)had a postoperative complica tion. Age was a univariate but not a multivariate predictor of postoperative complications. The mean age ( * stan-

.

a

5

p 005 Different by

ch, Square

I

40

40

30

30

30

zn

zn

20

10

10

10

AS

AR

AX

40

MS

MR

MX

TR

NoTR

Fig 1 . Postoperative complications in 90 patients undergoing multiple-valve procedures. The aortic valve lesion and tricuspid regurgitation were univariate (by chi-square analysis) determinants of these postoperative complications (mortality or low-output syndrome). (AS = aortic stenosis; AR = aortic regurgitation; AX = combined aortic stenosis and aortic regurgitation; MS = mitral stenosis; MR = mitral regurgitation; MX = combined mitral stenosis and mitral regurgitation; TR = tricuspid regurgitation.)

B Fig 2 . Probability of complications in 90 patients undergoing multiple-valve procedures. ( A )Aortic valve lesion and tricuspid regurgitation were independent predictors of postoperative complications, by logistic regression analysis. (B)The presence of tricuspid regurgitation when combined with any aortic valve lesion increased the risk of postoperative complications. (AX = combined aortic stenosis and aortic regurgitation; AR = aortic regurgitation; AS = aortic stenosis; TR = tricuspid regurgitation.) A

dard deviation) of the patients with aortic stenosis was 60.1 ? 9.8 years, compared with a mean of 52.7 13.4 years for those without aortic stenosis ( p = .08). Patients with concomitant tricuspid regurgitation also tended to be older (58.9 ? 10 years) than those without concomitant tricuspid regurgitation (52.6 ? 14 years, p = .09). Patients with tricuspid regurgitation had reduced cardiac indexes (1.7 0.5 L/min/m2vs. 2.3 0.7 L/min/m2,p = .006), elevated right atrial pressures (15.3 7.6 mm Hg vs. 8.8 5.7 mm Hg, p = .0003), and 11.3 mm elevated pulmonary artery pressures (42.0 12.5 mm Hg, p = .03) compared with Hg vs. 32.6 those patients without tricuspid regurgitation; this suggests right ventricular decompensation. Gender, NYHA Functional Class, timing of operation, incidence of reoperation, and coronary artery disease were not predictive of postoperative complications.

*

*

*

*

*

*

*

Comment Risk factors of postoperative complications for contemporary multiple-valve procedures were identified in this prospective study. Tricuspid regurgitation and the aortic valve lesion were found to be independent predictors of postoperative complications. Other factors may have influenced the outcome of multiple-valve procedures, but they were not identified by this limited study of 90 patients. Patients with aortic stenosis were found to be at higher risk of complications than patients with aortic regurgitation or mixed valvar disease. The aortic valve lesion has not previously been reported as a predictor of postoperative outcome after multiple-valve surgical procedures. However, a review [lo] of 277 patients undergoing isolated aortic valve surgical procedures in this institution revealed aortic stenosis and the peak systolic aortic valve gradient as independent predictors of postoperative ventricular dysfunction. Patients with aortic stenosis had left ventricular hypertrophy, and current methods of myocardial protection may not adequately

357 Teoh, Christakis, Weisel, et al: Multiple-Valve Procedures

protect the hypertrophied ventricle. Schaff and colleagues [ll]were able to correlate the extent of perioperative ischemic injury with the degree of ventricular hypertrophy in patients undergoing aortic valve replacement. Patients with clinically significant hypertrophy have abnormal metabolism, diminished high-energy phosphates, and ventricular dysfunction after aortic valve replacement [ 111. In previous studies aortic regurgitation was predictive of perioperative complications. More recently most patients with aortic regurgitation have undergone valve replacement when noninvasive studies have revealed mild ventricular decompensation. This earlier timing of surgical intervention has reduced the risk of aortic valve replacement for aortic regurgitation. Tricuspid regurgitation was found to be a powerful predictor of postoperative outcome in our study and in previous reports [7, 12, 131. Functional tricuspid regurgitation may result from right ventricular dilation or right ventricular decompensation, usually caused by increased impedance to right ventricular ejection. Patients with tricuspid regurgitation were older, had lower cardiac indexes, higher right atrial pressures, and poor right ventricular function at the time of right ventriculography. Baughman and associates (71 found that a history of either pulmonary edema or elevated pulmonary artery pressures was an independent predictor of mortality. Other reports [4, 5, 71 also showed that symptomatology was predictive of postoperative complications. Tricuspid regurgitation may identify those patients with the most advanced valvar disease and the most severe right ventricular decompensation. Tricuspid annuloplasty did not alter the incidence of early postoperative complications. Annuloplasty did not increase the risk of early postoperative right ventricular dysfunction, and it may have improved the late results of multiple-valve procedures [ 141. In this study, older patients were at higher risk of complications because those with aortic stenosis or tricuspid regurgitation were older. Age has been identified as a risk factor for aortic [lo, 15-17] and mitral [18231 valve procedures. Older patients may have more ventricular dysfunction. In patients undergoing aortic valve procedures [lo], we identified a negative correlation between age and cardiac index. Several approaches may be employed to reduce the risk of multiple-valve procedures in patients with aortic stenosis and left ventricular hypertrophy and in those with tricuspid regurgitation secondary to right ventricular decompensation. Earlier surgical intervention, improved perioperative myocardial protection, improved techniques of valve repair or replacement, and alternatives to management of postoperative ventricular dysfunction may improve the results in these highrisk patients. Surgical intervention before ventricular hypertrophy or decompensation may improve the results. Nuclear ventriculography [24, 251 and echocardiography [26] provide noninvasive methods to assess ventricular function serially and permit earlier surgical

intervention. Adequate myocardial protection may be critical to the preservation of the hypertrophied or decompensated ventricle. The use of a blood vehicle [27, 281, calcium antagonists [29, 301, or metabolic substrates [31] may improve the protection afforded by potassium cardioplegia and may improve postoperative ventricular function and metabolic reserve. The compromised right ventricle has limited reserves and may not be adequately protected by current techniques of cardioplegia delivery [32]. Better protection of the right ventricle may be provided by topical hypothermia 133, 341 or the retrograde delivery of cardioplegia into the right atrium or coronary sinus [35, 361. Postoperative ventricular dysfunction may be influenced by the technique of valve replacement. Excision of the posterior leaflet of the mitral valve and its papillary muscle attachments during mitral valve replacement may be detrimental to postoperative ventricular function. Preservation of the mitral valve apparatus may improve postoperative ventricular function as suggested by Lillihei and associates [37] and David and co-workers (38, 391. Valvar repair rather than replacement may have a similar beneficial effect [40, 411. The use of inotropic agents and the intraaortic balloon pump may provide inadequate hemodynamic support for critically ill patients after multiple-valve procedures. Left or right ventricular assist devices may permit recovery of ventricular function in the early postoperative period. A right ventricular assist device was successfully employed for 1 patient in this study. Biventricular assistance may be required after multiple-valve replacement because, as suggested by Pennington and associates [42], left ventricular assist devices have limited application in patients with right ventricular dysfunction. The results of multiple-valve procedures may be improved by better protection of high-risk patients. ~

~

~~~

~~

Supported by the Canadian Heart Foundation and the Heart and Stroke Foundation of Ontario.

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