Long-term results after aortic valve replacement with four different prostheses

Long-term replacement

results with

after aortic four different

valve prostheses

Jon Dale, M.D. Olaf Levang, M.D. Ivar Enge, M.D. Oslo, Norway

The ideal prosthetic heart valve should combine excellent durability, a wide opening, laminar blood flow and minimal gradients; it should not traumatize blood cells or trigger thrombus formation. All these demands have so- far not been fulfilled by any prostheses, in spite of extensive research and development of new designs. In our hospital, four types of aortic valve prostheses have‘been implanted during the seven-year period from 1966 to 1973. First used was the StarrEdwards ball valve type 1200 (SE 1200) with silicone rubber balls and metal cage, which was later replaced by type- 2300, in which a Stellite hollow ball moved within a cloth-covered cage.’ The modifications were done primarily to avoid ball variation’. Z and escape,” but also to reduce the high incidence of arterial thromboembolic complications which had been reported to accompany the oldest type. The need for anticoagulation in patients with prosthetis heart valves had early been recognized’, “; it reduced the incidence of arterial thromboembolism, but only to some extent.“. i The incidence of thromboembolic episodes in our patients has previously been reported6; it was found to be significantly lower with the newer modification of the ball valve, but it still represented a serious problem in spite of adequate anticoagulation, cerebral embolism being the most frequent manifestation.” From Medical Department B. Surgical ment for Radiology, Rikshospitalet, Oslo, Norway. Received

for publication

June

Accepted

for publication

Sept.

Reprint requests: Oslo 1, Norway.

OOOZ-8703/80/020155

Dr. J. Dale,

Department National

A, and the DepartHospital of Norway,

Department

B, Rikshospitalet,

Materials

24, 1979.

+ 08$00.80/O

0 1980

The

C. V. Mosby

and

methods

Altogether 449 patients received isolated aortic valves during a seven-year period from 1967 and 1973. Until November, 1968, valve type SE 1200 was implanted in 80 patients; thereafter the modified valve SE 2300 was used in 173 patients,

12, 1979. Medical

Increased red cell breakdown was found to accompany implantation of the ball valves,” and especially the SE type 2300 induced a considerable iron loss and in several patients frank hemolytic anemia.8 From 1971 disc valve prostheses have been used at this hospital. Two types were implanted, the Bjork-Shiley (BS)s and Lillehei-Kaster (LK)” prostheses, both incorporating a free-floating disc in an annular housing. The cage is slightly different in the two types, the LK-prosthesis allows a wider opening, and the disc closes against the ring, while the BS disc has minimal contact with the housing and allows a very slight regurgitation The incidence of thromboembolic complications was, however, not lower after disc valve implantation than in patients with the SE 2300 prosthesis, and thrombosis on the valve represented a particularly dangerous complication,” as confirmed by others.“. l3 Red cell destruction was slight, especially in patients with the BS prosthesis, and hemolytic anemia did no longer represent a clinical problem.” The present investigation was done in order to study the long-term survival and clinical effect of valve replacement with the two types of StarrEdwards ball valves and with the disc valve prostheses, and to evaluate the influence of valve size on the clinical improvement.

Co.

American

Heart

Journal

155

Dale,

Levang,

Table

and

Enge

I. Comparison of preoperative characteristics of patients receiving the different. valve types

SE 1200 No. of patients No. of men No. of women No. in functional Group IV No. with arrhythmia Mean age at operation (years) Mean heart size (ml./M.‘)

11

.i2.6 661

53.3 650

25 14

13 18

19 18

19 10

55 14 65

37 9 20

34 5 23

9 20 10

4 6 1

3 14 2

16 2

10 2

12 3

Aortic incompetence

3 7

8 6 1

From 1971 the BS and LK disc valves were inserted according to randomization in 196 individuals. Before operation, a left-side catheterization was always done, in most patients by retrograde catheter introduction into the left ventricle, and in some by transseptal catheterization. Angiography included contrast injections into the ventricle and the aortic root, and pressures were recorded. Before 1970, selective coronary angiography was done in patients with angina, later also in patients older than 50 years. Thus, coronary angiography was done in a larger proportion of the patients with disc than with ball valves. The operative technique and postoperative care remained largely unchanged during this period of time, but some important changes were later introduced which have reduced the early mortal-

156

62 37 ,‘35 ,

29

16 6

29

99

76 21 310

14

Aortic stenosis

Aortic stenosis and incompetence Mitral stenosis Mitrul incompetence Mitral stenosis and incompetence Coronary heart disease Left c~entriculur aneurysm

9i

51.3 692

‘fl

Severe Less severe

BS

1 ;:?I 121

II. Preoperative hemodynamic findings in patients in the four groups

100 mm. Hg 50-99 mm. Hg

LK

80 60 20 17

Table

Gradient Gradient

SE 2300

52 42

7

54.6 604

ity rate considerably. This is the reason why patients operated later were not included in the study. Oxygenation was achieved by a bubble oxygenator until 1970; thereafter a disc oxygenator with filters has been employed. Light hypothermia, 32 to 34” C., was routinely used, and the left coronary artery was always perfused. The patients were heparinized with 300 I.U. of heparin per kilogram body weight, and after operation the heparin activity was neutralized with protamine sulfate. Oral anticoagulation was started after two to four days unless bleedings persisted. Follow-up

The follow-up examinations were performed at different times. The first examination of the patients with ball valves was done in the autumn of 1972, when all except six met up. Two years later, the surviving patients were examined, and only seven were unable to come. Similarly, the follow-up studies of the patients with disc valves were done early in 1975and in the autumn of 1976 six patients did not report for the first and 23 did not report for the last examination. A questionnaire was sent to all patients’ physicians asking for additional information after each of the follow-up examinations, and relatives were contacted when necessary. When patients had been admitted to other hospitals, requests for reports were sent. Thus, the data presented were obtained from three different sources: hospital records, examination of the patients, and information from doctors and relatives. None of the patients were lost for follow-up. At examination, an exact history with emphasis on symptomatology and clinical course, occurrence of arterial thromboembolic episodes or bleeding complications was obtained. A careful

February,

1980, Vol. 99, No. 2

Aortic

clinical examination was done, including ECG, x-ray of heart and lungs, and several blood tests regarding intravascular hemolysis and anemia, platelet function and coagulation, including control of anticoagulant therapy with the Thrombotest as previously reported.“. ll. I3 Heart size was calculated in milliliters per square meter of body surface area.“‘. ‘; Criteria for the diagnosis of arterial thromboembolism have been described earlier.“. ‘I. ” Results

The material is presented in Table I. More women received BS than LK valves, in spite of randomization. The proportion of patients in functional Group IV according to the New York Heart Associations (NYHA)lR classification differed only insignificantly between the patient groups, being slightly higher in the patients with disc valves. Only minor differences appeared in the incidence of continuous arrhythmias, mostly atria1 fibrillation, between the groups. The mean age at operation rose slightly throughout the period, mainly because some more individuals older than 70 years received disc valves than ball valves. The mean preoperative heart volumes were 88 ml./M.’ less in patients with BS than in those with the SE 1200 valve. The differences were, however, not accompanied by similar deviations in the functional group distribution. The preoperative hemodynamic findings are listed in Table II. No significant differences appeared in the distribution of severe stenosis with systolic peak gradients higher than 100 mm. Hg, or in severe aortic regurgitation with contrast reaching the apex of the left ventricle without being pumped out during the following systole, or in the proportion of patients with combined stenosis and insufficiency. Mitral incompetence not regarded serious enough to require mitral valve replacement was more frequent in the BS than the LK group of patients, while mitral stenosis was most common in patients with ball valves. Significant coronary artery stenosis or occlusion was found in approximately 10% of the patients. The type of operation performed is presented in Table III. Mitral commissurotomy was more often done in patients with ball valves. This reflects a gradual changes in policy regarding mitral valve operations, with the preference of valve replacement for commissurotomy. Aorto-

American

Heart

Journal

rnlve replacement

III. Type of operations four patient groups

Table

with four prostheses

performed

on the

Pafienfs u&z rlalue type

Valve replacement alone Valve + mitral commissurotomy Valve + aortocoronary

SE

SE

1200

2300

LK

BS

63 10

155 16

84 5

86 5

3

2

bypass Valve + aneurysmecto-

1

1

2

3

my Replacement Emergency

6

11

2 8

2 9

of old valve operations

IV. Time from operation and to the first and second follow-up studies in the four groups of patients

Table

Mean time to first examination (years) Mean time to second examination (years)

4.7

2.7

2.5

2.5

6.7

4.7

4.3

4.3

coronary bypass was introduced at the hospital in 1970, but was performed only in five patients who simultaneously received disc valves. Resection of a left ventricular aneurysm was done in seven patients, and in four previously implanted prostheses were replaced by disc valves. The mean time intervals from operation until the follow-up examinations are presented in Table IV, demonstrating that the patients with the oldest ball valve type were followed on an average more than six and a half years and the patients in the three other groups were followed approximately four and a half years. The long-time survival, calculated according to the actuarial method, is illustrated in Fig. 1. The early mortality rate (deaths within 30 days) remained fairly constant at 15% throughout the period, and did not differ between patients with disc and ball valves. The late mortality rate was remarkably similar in the four groups, the recorded or actuarial five-year survival rate being 65% in patients with ball valves and 68% in those with disc valve prostheses. No significant differences

157

Dale,

Levang,

and

Enge

.LK

l 8S . SE IZOO r SE2300

80

80

Hz

1

2

3

4

5

8

7

Time, years Fig. 1. Lang-term indicate surcival

survival estimated

after aortic valve replacement by the actuarial method.

V. Causes of late deaths after aortic valve replacement

Table

Patients

with

the

four

different

prostheses.

The

dotted

lines

Vi. Mean heart size before and after aortic valve replacment Table

with

Mean

heart

size (ml./M.‘)

I Ball salt-es Myocardial failure Arterial thromboembolism Sudden death Sepsis Myocardial infarction Intracranial bleeding Mitral incompetence Ventricular fibrillation Reoperation Rupture of aneurysm Paravalvular leak Cancer

19 6 6 5 4 4 1 2 2 1 1 2

Disc salves 7 3 3 1

2 1

2

26 9 9 6 4 4 3 3 2 1 1 4

appeared between any of the groups at any time. The most frequent causes of early death were in this order: myocardial failure, arrhythmia, sepsis, myocardial infarction, and arterial thromboem158

ISE I 2xIoSE I

To&I

1200

Before operation At first follow-up At second follow-up

679 584 619

637 586 615

Lx 642 617 597

I

BS 584 545 567

bolism. Myocardial failure was responsible for an even higher proportion of late deaths, and also frequent was sudden death, as well as death from thromboembohc complications,‘L ‘I. li mostly cerebral emboli in ball valve patients and valve thrombosis in the others (Table V). Myocardial infarction and intracranial bleeding caused some deaths in patients with prosthetic ball valves. The heart size reduction from the preoperative examination until the first postoperative examination was most marked in patients with valve type SE 1200, who had the largest hearts before February,

1980,

Vol.

9.9. No.

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Aortic

VII. Preoperative heart volumes in patients with isolated aortic valve disease who received smaller or larger valves

Table

Heart size (ml./M.‘) Smaller valves

SE 1200 SE 2300 LK BS

S.D.

Mean

545 588 593 530

143 139 139 108

719 730 699 624

p < 0.01 p < 0.001 p < 0.02 p < 0.01

operation, but a significant reduction also occurred in the other groups (Table VI). From the first to the second follow-up, however, no further over-all improvement was found. The change in heart size in the individual patient may, however, not be due only to the type of valve implanted. Thus, an increase in heart size was frequently seen in patients with coexisting valvular or coronary heart disease. In order to evaluate the effect of valve type and size, patients with isolated aortic valve dysfunction were studied. The ball valve termed smaller were of size 10 A or less, corresponding to an inner diameter of 15.5 mm. in type SE 1200 and to 14.3 mm. in series SE 2300, while the orifice diameter was 18 mm. or less in smaller disc valves of both types. The preoperative heart size of patients who had the smaller valves of the different types implanted was on an average approximately 100 ml. less than in those with larger valves (Table VII). At operation, valve size had been selected according to the size of the aortic ostium. Implantation of the smaller ball valves of both series, and especially type 2300, resulted in a very moderate reduction of heart size (Table VIII), and insertion of smaller disc valves also led to only a limited decrease in heart volumes. The disc valves did not represent an advantage over larger ball valves when reduction of heart enlargement is concerned. Indeed, the most marked reduction was obtained with the larger valves of the SE 1200 series, even if the

smaller

Heart

Journal

Reduction of heart size Mean orifice diameter (mm.) SE 1200 SE 2300 LK BS

16.4 14.7 18.2 18.4

45.0 37.4 56.0 57.9

74.8 149.5 120.3 70.2

162.5 119.3 124.4 108.0

182.6 211.5 163.9 138.4

IX. Mean functional group according to NYHA Classification before and after operation of patients who survived the follow-up period

Table

Mean functional group

Before dperation At first examination At second examination

SE

SE

I200

2300

BS

LK

3.18 2.29 2.34

3.18 2.28 2.31

3.31 2.01 2.29

3.36 2.33 2.42

X. Preoperative functional group patients with isolated aortic valve disease

Table

Functional

SE 1200 SE 2300 LK BS

in

group

Larger valves

Smaller valves

Mean

SD.

Mean

3.07 3.08 3.29 3.35

0.47 0.47 0.51 0.54

3.22 3.26 3.12 3.29

S.D. 0.42 0.57 0.53 0.53

N.S. N.S. N.S. N.S.

Xl. Relation between the orifice diameter of the implanted valves and clinical improvement expressed by NYHA group reduction Table

than in the larger

The mean functional group value was recorded according to the NYHA classification before and after valve replacement (Table IX). Most patients were in Functional Class 3. Individuals with disc valves were on an average in a slightly poorer clinical condition than the ball valve patients at the time of implantation. A considerAmerican

VIII. Relation between the orifice diameter of the implanted valve and the reduction of heart size from before operation to the second follow-up examination

S.D. 168 165 194 150

with four prostheses

Table

Larger valves

Mean

orifice is considerably disc valves.

valve replacement

NYHA group reduction I Smaller valves

SE 1200 SE 2300 LK BS

Larger valves

Mean

S.D.

Mean

0.67 0.65 1.13 1.22

0.88 0.59 0.54 0.80

1.09 0.93 1.11 1.13

S.D. 0.33 0.62 0.80 0.68

N.S. N.S. N.S. N.S.

159

Dale, Levang,

and Enge

able functional improvement occurred in all groups, especially in patients with BS valves until the first follow-up examination. The improvement seemed, however, to reach a maximum after a few years, whereafter the condition remained constant or det,eriorated slightly. The preoperative functional impairment did not differ significantly between patients who received smaller or larger valves (Table X ). The effect of valve size was evaluated in patients without other valvular defects or CHD (Table XI). Significant differences in the improvement which occurred in all eight groups did not appear, although a slightly lessmarked positive development was recorded in patients with the smaller ball valves than with other types. Discussion

The early mortality rate after aortic valve replacement was similar in patients with the different valves, indicating that prosthesis design was of little importance. The early death rate was comparble with’. ,i, I!’ or higher than’. 20-J2that found by others, and the most common causes of death were largely the same.’ :. i. ‘” The majority of early deaths were due to complications unrelated to the prosthesis, such as myocardial failure and arrhythmia, indicating that the preoperative condition of the myocardium is of great importance for early survival. The early mortality rate has later been reduced considerably in our hospital, chiefly because of improved techniques, such as the introduction of extreme hemodilution during extracorporeal circulation, local cooling without cannulation of the coronary arteries, and better prophylaxis against ventricular arrhythmias. Surprisingly, even the late mortality rate appeared to be independent of valve type. Deaths caused by thrombus formation on the prosthetic valve, such as cerebral embolism,“- IT valve dysfunction,“- ’ i. I” and sometimes myocardial infarction,‘,> might to some extent be related to valve type and function. One would anticipate that the lesser orifice and higher peak systolic gradients across the ball valves, especially the 2300 prosthesis,“. “j would represent an extra load on the left. ventricle, and thereby carry a slightly worse prognosis than the disc valves. Again, the importance of an adequate myocardial function for long-term survival is evident, as also reported by othersw’- 1: 21; An exact estimation of the mortality rate after aortic disc valve implanta160

tion can not be made, since only nineteen late deaths occurred during the observation period, which was shorter than in t,he groups of patients with ball valves, where fifty-three late deaths were recorded. Although a larger material could have provided a better basis for a comparison of late death rates, our results allow the conclusion that the introduction of disc valves has not considerably reduced t.he late mortality rate after aortic valve replacement. The importance of myocardial function indicates that late survival can be better increased by earlier operations”’ 24t than by improved design. Valve-related causes of death such as arterial embolism or valve thrombosis might be reduced with combined antithrombotic therapy where drugs affecting platelet function, such as acetylsalicylic acid,” or dipyridamole” are added to anticoagulants. The moderate effect of aortic valve replacement on heart size is in accordance with the findings of others.‘-;- 2\i :!’ The maximum reduction appears to be obtained rather early after operation, while no marked improvement can later be achieved, regardless of valve type. Thus, the preoperative heart size is the main determinant also for the postoperative size, which again stresses the importance of myocardial function for the late results. The most marked reduction was found in patients with isolated aortic valvular lesions, indicating that additional heart disease may negatively influence size,” and coexisting valvular, coronary, or other heart disease was the cause of the slight average increase in heart volumes from the first to the second examination. The less favorable development of heart size in patients who received smaller valves instead of larger ones reflects the importance of a wide orifice in the implanted valve, although part of t,he reduction observed can be explained by the preoperative heart enlargement. The minimal improvement in patients with smaller ball valves of series 2300 is in accordance with the high systolic gradients found across these valves.‘” Surprisingly, the larger disc valves did not appear to be superior to the ball valves even with regard to heart size reduction, as would have been expected from the higher gradients across the ball valves, in type 2300 in particular.‘i Peak and mean systolic gradients valves, especially the heart volume reduction

are low across

aortic disc and the does not fully

BS prothesis,“’ therefore

Aortic

reflect the hemodynamic advantage of the BS prosthesis, Possibly the slight leakage in diastole through the disc valves, particularly the BS prosthesis,ZX might have some influence. It appears, however, than an enlarged heart can be reduced only to a certain extent, and that the condition of the myocardium is the limiting factor which determines the improvement that can be obtained even with the best prosthesis. Similar considerations can be made regarding the clinical improvement that occurred. The patients with disc valves were on an average in a slightly poorer condition than those with ball valves, as judged from the NYHA group classification. Functional class assessment is, however, subjective, and the criteria are not equally easy to apply to all symptoms the patients experienced before operation, most frequently dyspnea and angina on exertion, fatigue, and syncope. After valve replacement, syncope no longer occurred, angina or dyspnea had disappeared or was less easily precipitated, while fatigue and dizziness were the most common complaints. These symptoms may be due to anesthesia or altered blood flow during operation, especially the effect of extracorporeal circulation. Continued microembolization may contribute,‘” or the symptoms may be unmasked by the disappearance of others. The clinical improvement was considerable, and corresponded to a reduction of one functional class in most patients, slightly less in those with ball than in those with disc prostheses. The clinical effect appeared to be greater than could be expected from the heart size reduction. The considerable initial improvement did, however, not continue, and a quite stable clinical condition was reached in most patients, while a slight deterioration was noted in several others. Even if a less favorable development often could be attributed to coexisting heart disease, the results indicate certain long-term limitations to the effect of aortic valve replacement. The less pronounced clinical improvement in individuals with smaller ball valves, especially of type 2300, is in accordance with the minimal heart size reduction found, and could be anticipated from the high systolic gradients across such valves. The equally satisfactory effect on functional capacity of larger and smaller disc valves and of larger ball valves indicates that the clinical course is less influenced by valve modifications than by myocardial function. American

Heart

Journal

value replacement

with four prostheses

Although more sensitive criteria might reveal a clinical advantage of the hemodynamically better BS valves, our results suggest that more can be gained by earlier valve replacement than by further refinement of valve design. Summary

The long-term results after implantation of isolated aortic ball and disc prostheses were studied. The Starr-Edwards ball valve type 1200 was first used in 80 patients, thereafter type 2300 was used in 173, later the Bjork-Shiley and the Lillehei-Kaster disc valves were implanted in 99 and 97 patients according to randomization. The surviving patients with the oldest ball valve were examined after 4.7 and 6.7 years on an average, the others after approximately 2.5 and 4.5 years. The early mortality rate was 15%, and did not differ between the four groups. Even the late mortality rate was quite similar in the patient groups, the five-year survival rate being 65% in patients with ball valves and 68% in those with disc valves, as estimated with the actuarial method. The average reduction of heart size was moderate and quite similar in the four groups, most pronounced in patients with isolated aortic valve The reduction was greater in involvement. patients who received larger rather than smaller valves of all types. Aortic valve replacement resulted in a considerable clinical improvement in patients with all valve types; it corresponded largely to one functional group according to the NYHA classification. The heart size reduction and functional improvement was most moderate in patients with smaller ball valves, which could be anticipated from higher peak systolic gradients than across the other valves used. No significant differences appeared between patients with the larger valves of the four types. The initial improvement, as recorded either by reduction of heart size or increase in functional capacity, had reached its maximum at the first follow-up examination in most patients. The preoperative myocardial function appeared to be the limiting factor which determined what late results could be obtained regardless of the type of valve implanted. The results therefore indicate that more can be achieved by earlier valve replacement than by improving the prostheses. 161

Dale,

Levang,

and

Enge

REFERENCES

17.

1.

Herr, R. H., Starr, A., Pierie, W. R., Wood. J. A., and Bigelow, J. C.: Aortic valve replacement. A review of six years’ experience with the ball valve prosthesis, Ann, Thorac. Surg. 3:199, 1968. 2. Chin, H. P., Harrison, E. C., Blankenhorn, D. H., and Moacanin, J.: Lipids in silicone rubber valve prostheses after human implantation, Circulation 43 and 44(Suppl. 1):55, 1971. I3 Fleming, J., Hamer, J., Hayward, G., Tubbs, 0. S., and Hill, I.: Long-term results of aortic valve replacement with the Starr-Edwards valve, Br. Med. J. 1:139, 1969. 4. Friedli, B., Acrichide, N., Grondin, P., and Campeau, L.: Thromboembolic complications of heart valve prostheses, A&f. HEART J. 81:702, 1971. 5. Matloff, J. M., Collins, J. J., Sullivan, J. M., Gorlin, R.. and Harken, D.: Control of thromboembolism from prosthetic heart valves, Ann. Thorac. Surg. 8: 133, 1969. 6. Dale, d.: Arterial thromboembolic complications in patients with Starr-Edwards aortic ball valve prostheses, AM. HEART J. 91:653, 1976. 7. Barnhorst, D. A., Oxman, H. A., Connolly, D. C., Pluth, .J. R., Danielson, G. K., Wallace, R. B.. and McGoon, D. C.: Long-term follow-up of isolated replacement of the aortic or mitral valve with the Starr-Edwards prosthesis, Am. J. Cardiol. 35:228, 1975. E., Dale, J., and Rasmussen, K.: Erythrocyte 8. Myhre, destruction in different types of Starr-Edwards aortic ball valves, Circulation 42:515, 1970. 9 . Bjork, V. O., Olin, C., and Rodriguez, L.: Comparative results of aortic valve replacement with different prosthetic heart valves, J. Cardiovasc. Surg. 13:268, 1972. R. L., Lillehei, C. W., and Starek, P. J. K.: The 1U. Kaster, Lillehei-Kaster pivoting disc aortic prosthesis and a comparative study of its pulsatile flow characteristics with four other prostheses, Am. Sot. Artif. Intern. Organs 16:233, 1970. 11. Dale, J.: Arterial thromboembolic complications in patients with Bjork-Shiley and Lillehei-Kaster aortic disc valve prostheses, AM. HEART J. 94: 101, 1977. J., Hildner, F. d., Chandraratna, P. A., and 12. Ben-Zvi. Samet, P.: Thrombosis on Bjork-Shiley aortic valve prosthesis, Am. J. Cardiol. 34:538. 1974. R.. Beck. W.. and Barnard. C. N.: Results of 13. Forman. valve replacement’with the Lillehei-Kaster disc prosthesis, AM. HEART J. 94:282, 1978. 14. Dale, J., and Myhre, E.: Intravascular hemolysis in the late course of aortic valve replacement. Relation to valve type, size and function, AM. HEART J. 96:24, 1978. 15. Dale, J., Myhre. E., Storstein, O., Stormorken, H., and Efskind, L.: Prevention of arterial thromboembolism with acetylsalicylic acid. A controlled study in patients with aortic ball valves, AM. HEART J. 94:101, 1977. 16. Jonsell, S.: A method for determination of the heart size by teleroentgenography (A heart volume index), Acta Kadiol. 20: 325, 1939.

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Amundsen, P.: The diagnostic valve of conventional radiological examination of the heart in adults, BostonOslo-London,1959, Oslo University Press. New York Heart Association: Nomenclature and criteria for diagnosis of the heart and blood vessels, ed. .5, New York, 1953. Rubin, d. W., Moore, H. V., Hillson, R. F., and Ellison, H. G.: Thirteen years’ experience with aortic valve replacement, Am. .J. Cardiol. 40:345, 1977. Pellegrini, A., Marcazzan. E., Peronace, B., de Gasperis, D., Gordini, F., and Mombelloni. G.: Ten years’ experience in heart valve replacement with artificial prostheses: Immediate and long-term results in 1.812 cases, d. Cardiovasc. Surg. 16:612, 1975. Rossiter. S. J., Hultgren, H. N., Kosek, J. C., Wuerflein. R. D., and Angel], W. W.: Ischemic myocardial injury with aortic valve replacement and coronary bypass, Arch. Surg. 109:652. 1974. Ison, 0. W., Williams, C. D., Falk, E. A., Glassman, E., and Spencer, F. C.: Long-term evaluation of clothcovered metallic ball prostheses, .J. Thorac. Cardiovasc. Surg. 64:354, 1972. Storstein. O., and Efskind, L.: Immediate and late results of aortic valve replacement, Stand. ,J. Thorac. Cardiovast. Surg. 6:114, 1972. Kloster, F. E., Herr, R. H., Starr, A., and Griswold, H. E.: Hemodynamic evaluation of a cloth-covered StarrEdwards valve prosthesis, Circualtion 39 and 4O(Suppl I): 119, 1969. Reis, R. I,., Glancy, D. L.. O’Brien, K., Epstein, S. E., and Morrow, A. G.: Clinical and hemodynamic assessment of fabric-covered Starr-Edwards prosthetic valves, J. Thorat. Cadiovasc. Surg. 59:84, 1970. Bryant, I,. R., Trinkle, J. K., Spencer, F. C., Danielson, G. K., Shabetai. R., and Reeves, J. T.: Cardiac valve replacement. Results in patients with advanced disability, J.A.M.A. 216:996, 1971. Sullivan, ,J. M., Harken, D. E., and Gorlin. R.: Pharmacologic control of thromboembolic complications of cardiac-valve replacement, N. Engl. J. Med. 284: 1391. 1971. Nitter-Hauge. S., Hall, K.-V., Frhysaker, T., and E&kind, I,.: Aortic valve replacement. One-year results with Lillehei-Kaster and Bjork-Shiley disc prosthesis, AM. HEART. J. 88:23, 1974. Biork. V. 0.. Holmeren. A.. Olin. C.. and Ovenfors. C.-O.: Clinical and hemodinakc results of aortic valve replacement with the Bjork-Shiley tilting disc valve prosthesis, Stand. .I. Thorac. Cardiovasc. Surg. 5:177, 1971. Levang, 0.. Nitter-Hauge, S., Levorstad, K., and Froysaker, T.: Aortic valve replacement. A comparative study between Lillehei-Kaster and Bjork-Shiley disc valve prosthesis. Central hemodynamic and its relation to clinical results and left ventricular function, Stand. J. Thorac. Cardiovasc. Surg. (In press)

Fehruarv.

1980, Vol. 99, No. 2