Left ventricular function following aortic valve replacement

J

THoRAc CARDIOVASC SURG

79:121-124, 1980

Left ventricular function following aortic valve replacement Assessment by radionuclide ventriculography Left ventricular function following aortic valve replacement has been evaluated in 15 consecutive patients. Cold potassium cardioplegia was utilized for myocardial preservation. Left ventricular function was assessed by radionuclide ventriculography performed preoperatively and 3 months postoperatively. The predominant lesion was aortic insufficiency in 10 patients and aortic stenosis in five patients. All patients demonstrated improved ejection fractions at 3 months. The mean increases of ejection fraction in the aortic insufficiency group were 20% from the anterior (Ant.) position and 12.5% from the left anterior oblique (LAO) position; in the aortic stenosis group they were 15.2% (Ant.) and 14.8% (LAO). It is our contention that cold potassium cardioplegia is an effective means of myocardial preservation and that it showed no measurable deleterious effect on left heart function in this group of patients.

Frederick B. Parker, Jr., M.D., F. Deaver Thomas, M.D., Robert A. Poirier, M.D., Alan H. M. Markowitz, M.D., and Robert H. Eich, M.D., Syracuse, N. Y.

Although the technical aspects of aortic valve replacement are well standardized, the method of myocardial preservation is not. Successful myocardial preservation remains the key to long-term beneficial results. Normothermic arrest, hypothermia, coronary perfusion, and cold cardioplegia all have their proponents. The patient's operative survival alone does not adequately prove the efficacy of the preservation technique. All too often postoperative results focus solely on clinical course and pay little heed to myocardial function. More complete studies are necessary. The invasive nature of cardiac catheterization often precludes routine postoperative studies and noninvasive methods such as the electrocardiogram and echocardiography may not provide the necessary information. Computerized radionuclide cineangiocardiography allows assessment of both regional and global left ventricularfunction. Comparison of preoperative and postFrom the Departments of Surgery, Nuclear Medicine, and Medicine, State University of New York, Upstate Medical Center, Syracuse, N. Y. Received for publication April 14, 1979. Accepted for publication Sept. 6, 1979. Address for reprints: Frederick B. Parker, Jr., M.D., Department of Surgery, SUNY Upstate Medical Center, 750 E. Adams St., Syracuse, N. Y. 13210. 0022-5223/80/010121+04$00.40/0

operative results of left ventriculography by this method affords quantitative assessment of the method of myocardial preservation. In addition, the method does not interfere with left ventricular function, and it is less expensive and safer than invasive contrast ventriculography. Ejection fraction, rate, and duration are easily calculated. Visualization of the moving myocardium allows determination of deficiencies in segmental wall motion. By performing these studies in the preoperative and postoperative periods, the effects of the myocardial preservation technique can be analyzed carefully. We have utilized cold potassium cardioplegia for myocardial preservation in aortic valve replacement for several years. To assess its effect on left ventricular function, we have studied such patients utilizing radionuclide cineangiocardiography. Patients and methods Fifteen consecutive patients, aged 25 to 64 years, were studied with radionuclide angiography 1 day prior to and 3 months following aortic valve replacement. No patient was in congestive heart failure at the time of study. There were 11 men and four women. Preoperative and postoperative electrocardiograms were taken for all patients. In addition to aortic valve replacement, one patient underwent mitral commissurotomy, one

© 1980 The C. V. Mosby Co.

121

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Parker et al.

Surgery

Table I. Cardioplegic solution utilized I L lactated Ringer's solution I gm methylprednisolone (Solu-Medrol) 25 mEq potassium chloride 4 cc 10% calcium chloride 4 cc 8.4% sodium bicarbonate 10 U insulin

Table II. The preoperative /postoperative changes in ejection fraction (percent) and aortic cross-clamp time in the aortic stenosis group Preoperative (%)

Patient H. N.

J. C. W.K.

P. O. T. B.

Ant.

I

LAO

67 74 27 77 44

72

70 25 64 50

Mean increase: Ant.

Postoperative (%)

Cross-clamp time (min)

Ant.

60 49 47 55 68

78 76 71 86 54

15.2%; LAO

=

=

I

LAO



75 75 68 74 63

+11 +2 +44 +9 +10

+3 +5 +43 +10 +13

14.8%. P < 0.2.

Table III. The preoperative /postoperative changes in ejection fraction (percent) and aortic crossclamp time in the aortic insufficiency group Postoperative (%)

Preoperative (%)

Patient

Ant.

M.G. H. S. D. P. E. M. J. C. C. S. D. K. H.M. B. M. D. C.

44 54

I

LAO

72

49 74 68 76 59 32 59

Mean increase: Ant.

38 55 69 42 67 59 81 67 43 61

=

Cross-clamp time (min.)

42 53 65 70 48 45

67 69 73 76 80 73 78 82 46 63

72

73 50 42 12%; LAO

Ant.

=

I

LAO

66 64 74 77 67 71 83 86 53 66


+23 +15 +1 +27 +6 +5 +2 +23 +14 +4

+28 +9 +5 +35 0 +12 +2 +19 +10 +5

12.5%. P < 0.01.

mitral valve replacement, and three patients coronary artery bypass grafting (one single, one double, and one triple). The radionuclide method consisted of injecting 20 mCi 99mTc-Iabeled autologous red blood cells into an antecubital vein just prior to positioning the patient under a 10 inch, single-crystal scintillation camera (Ohio Nuclear Model Sigma 400) equipped with a high-resolution collimator. Multiple-frame, electrocardiogram-gated studies were acquired in the anterior (Ant.) and left anterior oblique (LAO, 45 degree) posi-

tions. Ten-minute acquisition time for each view resulted in images containing approximately 5 million total counts. Image processing using a Gamma-II system (Digital Equipment Corporation) produced II frames of gated images spanning the cardiac cycle. Regions of interest were generated around the entire left ventricle in each view and in a background region along the free left ventricular margin. Care was taken to avoid large blood pools (i.e., spleen, aorta, pulmonary artery) in selecting the background region. Net ventricular volume curves (subtracting normalized background activity) were produced and ejection fractions were calculated. Ejection fractions exceeding 50% are considered normal in this technique. In 10 patients aortic insufficiency was predominant and in five patients aortic stenosis. All patients except one had left ventricular enlargement or hypertrophy by electrocardiogram. Aortic valve replacement was performed utilizing cardiopulmonary bypass and hypothermia at 28° C. Venous return was instituted via the superior and inferior vena cavae and arterial perfusion was through the ascending aorta. The left ventricle was vented at the apex. When esophageal temperature of 28° C was reached, the aorta was cross-clamped and 1,000 cc cold potassium cardioplegic solution, containing 30 mEq KCI/L (Table I) in a pressurized bag at 4° C, was injected into the aortic root. Care was taken to keep the heart beating while the cardioplegic solution was injected. The heart was packed in a lactated Ringer's iced-slush solution, protecting the left phrenic nerve with a pad. An intramyocardial temperature probe in the intraventricular septum was a help in maintaining temperatures between 10° and 15° C. Temperature was maintained by adding slush both inside the left ventricle and outside the heart as needed. Aortic cross-clamp times averaged 55 ± 10.7 minutes (standard deviation, SD). In the patient undergoing mitral and aortic valve replacement, the mitral valve was replaced under intermittent aortic cross-clamping at 28° C with the heart beating, prior to aortic valve replacement. The aortic valve was then replaced using the cold cardioplegia technique. In an attempt to minimize aortic cross-clamp time, the coronary artery bypass graft procedures were performed under ventricular fibrillation, with intermittent aortic cross-clamping or localized vessel occlusion, either prior to or following the aortic valve replacement. Myocardial temperature during these periods was maintained at 28° C. No cardioplegic solution was utilized during this period. The Lillehei-Kaster valve was used for replacement. Postoperative filling pressures were monitored with a left atrial pressure line. Three months following discharge

Volume 79 Number 1 January. 1980

Left ventricular fun ction after A VR

I 23

from the hospital , radionuclide cineangiography was repeated to assess left ventricular function. Results All patients survived operation without complication. Two patients developed late complications-one developed a small, asymptomatic paravalvular leak and the other cardiac tamponade at 2 weeks postoperatively which required drainage . Postoperative electrocardiograms taken after operation revealed no change in 10 patients. One patient developed left anterior hemiblock, one patient first-degree heart block , one patient left bundle branch block, one patient right bundle branch block, and one a possible inferior wall infarction. Every patient demonstrated improved left ventricular ejection fraction by radionuclide ventriculogram. Preoperatively the mean left ventricular ejection fractions ±SD were 58.4% ± 16.3% (Ant.) and 57.5% ± 15.3% (LAO) . At 3 months the mean ejection fractions increased to 71.5% ± 10.6% (Ant.) , p < 0.02, and 70.8% ± 8.3% (LAO), P < 0.01. No patient had a decreased ejection fraction in either projection. In the aortic stenosis group the mean increases were 15.2% (Ant.) and 14.8% (LAO) , p < 0.2 (Table II). In the aortic insufficiency group the mean increases were 12.0% (Ant.) and 12.5% (LAO), P < 0.01 (Table III). In those patients (five) with subnormal «50%) ejection fractions preoperatively, the average increases were 23.6% (Ant.) and 25.6% (LAO) . The patient with the lowest preoperative ejection fractions had the greatest improvement postoperatively, 43% (Ant.) and 43% (LAO) (Fig . I). All patients have returned to normal activity and are symptomatically improved.

Discussion This study demonstrated that the aortic valve replacement technique described preserved myocardial function and improved left ventricular performance in all patients of this consecutive series. The beneficial results of aortic valve replacement in this group of patients continue to support cold potassium cardioplegia as a myocardial preservation technique. Potassium cardioplegia was used during the early years of cardiac surgery to allow ease in difficult intramyocardial repairs because of improved exposure due to the resultant ventricular flaccidity. 1 This method was abandoned due to a high incidence of postoperative myocardial necrosis and fibrosis. The cause of the fibrosis was never ascertained although the high-dose potassium citrate utilized has been implicated ." Formerly , regional hypothermia was not performed in

Fig. lA. Preoperat ive and postoperative radionuclide ventriculograms (45% , LAO) in patient with 35% improvement in ejection fraction . Note the improvement in ejection fraction in addition to a decrease in size of the left ventricle .

DIASTOLE

post-op~

SYSTOLE

RA UI

RV

~

~

Fig. lB. Diagram corresponding to radionuclide study . (RV . Right ventricle. LV. Left ventricle. RA. Right atrium. SP. Spleen .

conjunction with the potassium arrest. As cardiac procedures have become more extensive, the need for improved myocardial protection has become obvious . This has led to further investigation combining hypothermia with a much less concentrated potassium solution . The resultant metabolic arrest markedly reduces myocardial oxygen requirements . Early results have encouraged widespread use. Low-dose cold potassium cardioplegia appears to have little or no immediate effect upon left ventricular function. Work by several

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The Journal of Thoracic and Cardiovascular Surgery

Parker et at.

groups of investigators":" attests to this. In a study similar to ours, Ellis and colleagues" performed preoperative and 48 hour postoperative radionuclide ventriculography in patients undergoing coronary artery bypass. No deleterious effects on ventricular performance resulting from cold cardioplegia could be found, although long-term studies were lacking. In this similar study utilizing patients with aortic valve disease, we repeated the preoperative study 3 months postoperatively. Again, there appeared to be no deleterious effects from the cold potassium solution, even though the patients had hypertrophied, dilated ventricles as a result of advanced aortic valve disease. Whether the potassium ion is the most significant factor in myocardial protection remains unproven. Studies have shown that cold alone provides equal protection in some patients. 7 A question that must be addressed is the degree of ventricular improvement secondary to the immediate effect of valve replacement alone, particularly in the aortic insufficiency group. Is it possible that improvement in the resting hemodynamic state, secondary to reduction of preload or afterload or resulting from valve replacement, masks a deleterious effect of cardioplegic solution on ventricular function? This has to be considered, but will be difficult to prove. It would appear that continued metabolic, anatomic, and functional studies may eventually answer this question. The conduction changes present postoperatively in the electrocardiograms of four of the patients may represent mechanical damage incurred during valve removal or insertion and presumably are not secondary to the cold cardioplegia. We have seen similar conduction defects in aortic valve replacements prior to utilization of cardioplegia techniques. We feel this assumption needs more thorough evaluation as transient conduction defects do occur with utilization of cold cardioplegia. Radionuclide angiography for left heart imaging has been available in its current form for only a short time.": 9 For evaluation of the results of operative intervention, the method is of little inconvenience to the patient, although ejection fraction is the only measurement introduced. Ejection fraction depends upon many variables including preload, afterload, and exercise .'" Due to the noninvasiveness of this technique, these measurements are not available, although no patient was in congestive heart failure at the time of evaluation and all were evaluated in a similar resting state.

In summary, it can be said that radionuclide ventriculography is a satisfactory noninvasive method to assess left ventricular ejection fraction. It appears to be particularly useful to the surgeon and cardiologist who are interested in estimating left heart function in the postoperative state. At early assessment, our method of myocardial preservation utilizing cold potassium cardioplegia in aortic valve replacement appears to be satisfactory. It is obvious that further long-range postoperative studies must be performed to continue this evaluation.

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3

4 5 6 7

8

9

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REFERENCES Melrose DG, Dreyer B, Bentall HH, Baker JBE: Elective cardiac arrest. Lancet 2:21-22, 1955 Helmsworth JA, Kaplan S, Clark LC, McAdams AJ, MatthewsEC, Edwards FK: Myocardial injury associated with asystole induced with potassium citrate. Ann Surg 149:200, 1959 MundthED, Goel IP, Morgan RJ, McEnany MT, Austen WG: Effect of potassium cardioplegia and hypothermia on left ventricular function in hypertrophied and nonhypertrophied hearts. Surg Forum 26:257-258, 1975 Gay WA Jr, Ebert PA: Functional, metabolic and morphologic effects of potassium-induced cardioplegia. Surgery 75:284-290, 1973 Ellis RJ, Pryor W, Ebert PA: Advantages of potassium cardioplegiaand perfusion hypothermiain left ventricular hypertrophy. Ann Thorac Surg 24:299-306, 1977 Ellis RJ, Born M, Feit T, Ebert PA: Potassium cardioplegia. Early assessment by radionuclide ventriculography. Circulation 58:Suppl 1:57-61, 1978 Tucker WY, Ellis RJ, Mangano D, Ryan CJM, Ebert PA: Questionable importance of high potassium concentrations in cardioplegic solutions. J THoRAc CARDIOVASC SURG 77:183-190, 1979 Borer JS, BacharachSL, Green MY, et al: Application of real time radionuclide cineangiography in the noninvasiveevaluation of global and regional left ventricular function at rest and during exercise in patients with coronary artery disease. N Engl J Med 296:839-844, 1977 Green MY, Ostrow HG, Douglas MA, Myers RW, Scott RN, Bailey JJ, Johnston GS: High temporal resolution ECG-gated scintigraphic angiocardiography. J Nucl Med 16:95-98, 1975 Ross J, McCollogh WH: Natureof enhancedperformance of the dilated left ventricle in the dog during chronic volume overloading. Circ Res 30:549-556, 1972