- Email: [email protected]
Is potassium a necessary component of cardioplegic solutions?
JOURNAL
OF SURGICAL
Is Potassium
RESEARCH
29,
62-70 (1980)
a Necessary
Component
of Cardioplegic
Solutions?1,2
FREDERICK L. GROVER, M.D.,3 JOHN G. FEWEL, B.A., JOHN J.GHIDoNI,M.D., KITV. AROM, M.D., AND J. KENTTRINKLE, M.D. Cardiothoracic Surgery Secton, and the Department of Pathology, Audie L. Murphy Veterans Administration Medical Center, 7400 Merton Minter Boulevard, San Antonio, Texas 78284, and the University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78284 Presented at the Annual Meeting of the Association for Academic Cleveland, Ohio, November 13- 15, 1978
Surgery,
Potassium-treated hearts were more completely arrested, usually did not require defibrillation, and had slightly less impairment of left ventricular contractility than those treated with hypothermia alone. There was more reactive hyperemia in non-potassium-treated hearts suggesting a greater oxygen debt. There were no significant differences however, in myocardial metabolism, as determined by myocardial lactate and ATP, myocardial lactate extraction, and electron microscopy.
nously. Arterial and central venous catheters were inserted. A median sternotomy was Left ventricular subendocardial necrosis performed, and catheters were inserted into continues to be a major finding in patients the left atrium, the left ventricle, and the who die following open heart operations coronary sinus (via the right atrium). Each 151. Considerable research has been peranimal was heparinized (3 mg/kg), the right formed to determine how to more effectively femoral artery was cannulated for inflow protect the myocardium during cardiac from the bypass pump, and both vena cava surgery. In 1973, Gay and Ebert [lo] rewere cannulated by separate right atriported experimental findings which demonotomies for flow from the animal to the strated adequate protection for 60 min of pump. The dogs were then subjected to ischemia following potassium-induced ar1’/2 hr of total cardiopulmonary bypass at a rest. Since then there has been considerable systemic temperature of 30°C with a flow controversy over the relative importance rate of 80 ml/kg/min. A Sarns modular pump of potassium and the temperature of the and Optiflow bubble oxygenator5 were cardioplegic solution. The following experiprimed with 20 ml/kg of 5% dextrose and ment was performed in an effort to better Plasmalyte and the remainder with fresh define their relative importance. heparinized blood. Sump catheters were inserted into both the right and left ventriMATERIALS AND METHODS cles and the pulmonary artery was ocEighteen adult mongrel dogs were anes- cluded. The right ventricular sump flow was thetized with 100 mg/kg of Chloralose and measured as coronary sinus flow. Arterial, 0.75 mg/kg of morphine sulfate intrave- central venous, and left ventricular pressures, cardiac output (dye-dilution), left 1 Supported by the Medical Research Service of the ventricular dpldt, arterial pH, p 02, and Veterans Administration. p COP, coronary sinus pH, p 02, p C02, and z The technical assistance of Ms. Cheryl Ellestad lactate, myocardial lactate and adenosine and Ms. Kay Ford is acknowledged and appreciated. triphosphate (ATP), and regional myocardial 3 Address reprint requests to Dr. Frederick L. blood flow (using the radioactive microGrover, Cardiothoracic Surgery Section, Audie L. INTRODUCTION
Murphy Veterans Administration Medical Center, 7400 Merton Minter Boulevard, San Antonio, Tex. 78284.
0022-4804/80/070062-09$01.00/O Copyright 0 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.
s Courtesy of Cobe Laboratories, Cola. 80215. 62
1201 Lakewood,
GROVER ET AL.: IS POTASSIUM NECESSARY IN CARDIOPLEGIC
SOLUTIONS?
63
sphere technique) were measured before bypass, the animals were cooled to 30°C. All bypass, sequentially during aortic cross- parameters were measured and then the clamping, for 30 min after release of the aorta was cross-clamped and the cardioaortic cross-clamp, and for 1 hr after the plegic solution was administered as dediscontinuation of cardiopulmonary bypass. scribed above over a period of 3 to 4 min. The specimens of myocardial tissue for Following the removal of the cross-clamp, lactate and ATP were obtained by left the hearts were observed for return to ventricular needle biopsy and were immedi- spontaneous coronary sinus rhythm. Folately frozen in liquid nitrogen (- 163°C). lowing the 5-min post-cross-clamp measureThe chemical analysis was done by the ments, the animals were rewarmed to 37°C. method of Lowry 1131. Sequential full Cardiopulmonary bypass was discontinued thickness needle biopsies for electron mi- 30 min after the release of the cross-clamps, croscope study were immediately immersed and the parameters were then measured for 1 hr after bypass. in a 2% buffered gluturaldehyde solution. Regional myocardial blood flow was measured by injecting 400,000 to 800,000 RESULTS radioactive microspheres, 15 2 5 microns in diameter (3M Company), which were la- Adequacy of Arrest beled with 14Ce, 1251,85Sr,and 46Scinto the All hearts in the potassium-treated group left atrium for determinations before and (10 of 10) arrested completely, whereas after pump bypass, and into the pump inflow none in the control group (0 of 8) completely line during bypass. At the completion of arrested, slow ventricular fibrillation pereach experiment, the animal was sacrificed sisting throughout the cross-clamp period and the heart removed and weighed. The (P < 0.003). Nine of ten of the potassiumleft ventricle was then divided into inner, treated group returned to spontaneous middle, and outer layers and the septum into normal sinus rhythm following release of right and left layers, and the right ventricle the aortic cross-clamp, whereas all of the into inner and outer layers. The tissue was control group remained in ventricular fibrilthen counted in a Packard gamma scintilla- lation following release of the clamp (P tion counter as described by Buckberg 1441. < 0.0005). Using this technique, the sequential regional distribution of coronary blood flow at each interval was calculated since a different Hemodynamics (Table 1) isotope tag had been used for each injection. Left atrial pressure rose from 4.0 * 0.3 The data were subjected to statistical mm Hg (mean + SEM) prior to bypass, to analysis comparing control to experimental 8.0 + 2.2 thirty minutes following bypass animals using the Student’s independent in the control group, whereas it remained t test. stable in the potassium group (P < 0.09). The animals were divided into two groups. Central venous pressure in the control group Group I (10 dogs) received 200 ml of 5% increased from 2.0 + 0.6 mm Hg prior to dextrose in 0.2% normal saline with 20 meq bypass, to 6.2 + 1.2 thirty minutes after of KC1 and 6 meq of NaHCOJ500 ml into the bypass, as compared to 2.8 + 0.6 in the KC1 aortic root proximal to the cross-clamp, at group (P < 0.05). The mean arterial presthe onset and at 20-min intervals during the sure of the potassium group was 75 it 3 mm anoxic period of 1 hr. Group II animals Hg 60 min following bypass as compared to (eight dogs) received the same solution 57 f 4 in the control group (P < 0.01). The without the potassium. Both solutions were systolic pressure of the potassium-treated administered at a temperature of 0-4°C. group increased significantly to 101 -t- 6 After the onset of total cardiopulmonary mm Hg 30 min after bypass (P < 0.09) and
* ** *** ****
P P P P
I (KCI) 2 (No KCI)
i < < <
0.09. 0.05. 0.01. 0. I I, independent
3.9 + 0.8’ 4.0 + 0.3
I (KCI) 2 (No KCI) cutput
55 + 10 69 i 23
57 2 8 66 2 12
65 T 5 66+4
2317 f 193 1925 z 512
2951 e 277 2138 f 369****
2781 2 247 2858 + 371
I test.
60 mitt after
30 mitt after
Before
(ml/mitt/kg)
60 min after
Cardiac
30 min after
max. (mm H&cc)
78 f 6 6825
95 * 4 101 i 6
2.1 + 0.6 4.2 2 0.8**
pressure
Before
arterial 30 min after
Mean
60 min after
(mm Hg)
Before
dpldt
2.8 -t 0.6 6.2 + 1.2.’
1.7 2 0.5 2.0 + 0.6
4.3 2 0.9 5.8 + 1.0
pressure
Before
venous 30 min after
Central
60 min after
(mm Hg)
Left ventricular
4.0 + 0.9 8.0 2 2.2’
Before
ChUP
pressure
30 min after
Left atrial
HEMODYNAMICS
TABLE 1
75 k 3 57 * 4***
60 min after
(mm Hg)
159 + 6 158 + 8
Before
Heart
30 mitt after
rate (beatdmin)
114k6 141 + 10’1
64 mitt after
99k5 73 e 4.8’
60 min after
BP (mm Hg)
101 + 6 85 -t 5’
30 min after
arterial
120 * 5 133 -t 10
114 f 6 116 2 5
Before
Systolic
a A = Anoxia; b SEM. *P
I (KC11 2 (No KCI)
45 f 3b 39 + 2
1 (KC11 2 (No KCl)
coronary
63 f 8 78 -c 16
bypass.
52 2 5 55 2 6
30 min after A
g)
62 _c 9 108 c 28’
60 min after CPB
g)
Septal flow (mllminllO0
I5 min of CPB
53 c 5 53 f 5
30 min after A
Row (mWmin/lOO
65 2 7 76 2 14
I5 min of CPB”
CPB = cardiopulmonary
48 2 3 41 + 2
Before
Before
GKWp
Total
2
58 f 7 % + 22’
60 min a&-r CPB
1.01 2 0.05 1.03 _t 0.05
Before
IS min of CPB
ventricular
ratio
51 f 5 50 + 5
30 min after A
Row (mllminl
1.08 -c_0.07 1.12 2 0.15
30 min after A
endoxpi
63 -t_ 7 725 13
IS min of CPB
ventricular
1.09 * 0.07 0.99 _f 0.09
Left
51 -c_ 4 43 + 3
Before
Left
MYOCARDIAL BLOOD FLOW-MICROSPHERE
TABLE
60 min after CPB
I ..M 2 0.05 0.98 _f 0.12
60 min after CPB
61 k8 90 _f 19***
100 g)
1.75 c_ 0.25 2.17 + 0.21
Before
Coronary
33 + 3 30 _f 1
Before
resistance
73 t 8 79 t 13
I5 min of CPB
ventricular
1.22 + 0.19 0.99 c 0.20
15 min of CPB
vascular
Right
L.00 ? 0.13 1.03 f 0.11
30 min after A
(mm Hg/ml/lOO
55 + 4 58 2 6
30 min after A
flow (ml/min/lOO
0.93 0.48
f 0.13 -t 0.09**
60 min after CPB
timin)
49 t 6 93 t- 23”
60 min after CPB
g)
66
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
99 + 5 sixty minutes after bypass (P < 0.01) as compared to control values of 85 k 5 and 73 + 4. Left ventricular dpldt max in the control group decreased to 2138 c 369 and 1925 f 512 mm Hglsec 30 and 60 min following bypass in contrast to the potassium-treated group which increased to 2951 + 277 (P < 0.11) before decreasing to 2317 + 193 sixty minutes after bypass. Myocardial
control group as compared to 0.93 + 0.13 in the KC1 group (P < 0.05). The coronary sinus flow was significantly greater 10, 15, and 30 min following the release of the cross-clamp in the control group as compared to the KC1 group, and was slower to return to preischemic levels than in the potassium group (Fig. 1). Respective values for control vs KC1 flows at those intervals were 147 + 13 ml/mm/ 100 g, 120 + 19, 80 4 8 vs 70 k 8, 61 k 5, and 61 + 4 (P < 0.001, P < 0.01, P < 0.05). The flow in the KC1 group returned to preanoxic arrest values by 10 min after the release of the cross-clamp, as compared to 30 min in the control group.
Blood Flow (Table 2)
Total coronary flow in the control group increased to 96 2 22 ml/min/lOO g 60 min following bypass, whereas corresponding values in the potassium-treated group remained constant (P < 0.09). Left ventricular flow also increased in the control group Myocardial Metabolism to 90 _t 19 sixty minutes after bypass as There were no significant differences in compared to 61 + 8 in the potassium group (P < 0.13). Right ventricular flow also myocardial tissue lactate between groups increased to 93 + 23 in the controls 60 min (Fig. 2). The lactates steadily increased to a after bypass, in contrast to 49 + 6 in the high of 13pmol/g in both groups after 60 min potassium-treated animals (P < 0.05). Sim- of arrest. These values dropped sharply in ilar increases in septal flow in the control both groups following the release of the group were noted. Coronary vascular re- aortic cross-clamp. The myocardial adenosine triphosphate sistance decreased with the onset of bypass in both groups, remained relatively stable (ATP) measurements were also quite similar 30 min after the release of cross-clamp but between the two groups (Fig. 3), decreasing then decreased to 0.48 2 0.09 mm Hg/ml/ only slightly during the arrest period, but 100 g/min 60 min following bypass in the then dropping to 3.72 + 0.5 and 4.04 + 0.40
X0160OJ l60E g 1408 ‘20 2 loog 68s E 604020-
, I 6don
pg.05
X-Cbmp
l
C-P lb
30’
4
ByparS 6is
I 90’
105’
3OB
1 6dp
FIG. 1. Coronary sinus flow. The coronary sinus flow of the nonpotassium-treated hearts was significantly greater following release of the aortic cross-clamp, and remained so for 30 mitt of reperfusion. Note, also, the delay in returning to preanoxic flows in this group as compared to the group receiving potassium. This is indicative of a sustained hyperemic response in the hearts which did not receive potassium.
GROVER ET AL.: IS POTASSIUM NECESSARY IN CARDIOPLEGIC
I3
SOLUTIONS?
67
KClo--o Controls
12 II
I c , eefor.15’
C-P Bypass I 36
60’
I so’
105’
30’1
, 60’0
FIG. 2. Myocardial lactate. Myocardial lactate values were almost identical in the two groups, rising to a high of 13 pmol/g at the end of the arrest period, and quickly decreasing during the reperfusion period, although remaining higher than preanoxic levels throughout the experiment.
pmol/g in the control and KC1 groups 5 min after the release of the cross-clamp. Very little recovery of ATP to prearrest levels occurred in the ensuing 90 min. Lactate extraction was not significantly different between the groups (Fig. 4). Lactate production, rather than extraction occurred at 1 and 3 min following release of the cross-clamp in the control group, and at 1, 3, and 5 min in the KC1 group. Electron Microscopy The specimens were studied ultrastructurally without knowing which were from potassium or non-potassium-treated animals. Slight mitochondrial swelling and slight cytoplasmic edema were commonly encountered and highly variable in extent. In some animals, an increase in cytoplasmic lysosomes and/or myelin figures occurred in the post-cross-clamp period. The specimens taken 60 min after the dog came off bypass showed varying evidence of turnover of debris by interstitial macrophages. Contraction banding appeared while on cardiopulmonary bypass but before cross-clamping, did not occur in tissue obtained during
cross-clamping, but reappeared during the reperfusion interval. No significant differences in ultrastructure were noted between the two groups. DISCUSSION Preservation of the myocardium during cardiac operative procedures has come under increasing scrutiny during the past decade. Since 1973 when Gay and Ebert [lo] introduced potassium cardioplegia there has been increasing interest in the effects of various cardioplegia solutions and the method of their administration. There has been considerable discussion regarding the most effective composition of cardioplegic solutions. Follette et al. 181have advocated a cardioplegic solution containing procaine hydrochloride for membrane stabilization, with potassium, glucose, insulin, THAM, plasma, and albumin, and have also stressed the importance of reperfusing with alkaline-buffered blood following the anoxic arrest. O’Donoghue et al. [14] noted that solutions containing potassium consistently provided the best overall function following anoxic arrest.
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
2 ,j
X-Clomp C-P Bypass
’ 1
Before
15’
30’
8
60’
-I 9d
lob
3&p
1 6dp
FIG. 3. Myocardial adenosine triphosphate. Myocardial ATP levels were very similar in the two groups throughout the experiment, decreasing slightly during the period of arrest, decreasing more markedly following the removal of the aortic cross-clamp, and then remaining relatively stable for the remainder of the experiment.
Laks et al. [12] compared a cold potassium cardioplegic solution to intermittent infusion of cold blood and found the cardioplegic solution to be superior. Follette et al. [9] investigated a blood cardioplegia solution and found that this reduced left ventricular compliance only slightly, and resulted in normal postischemic ATP, water, and contractility. Harlan et al. [ll] compared Krebs - Henseleit buffer (KHB) , KHB with potassium, and KHB with procaine, administered at 15 and 5°C. The authors noticed that the solutions to which potassium and procaine were added caused a more rapid arrest and a greater incidence of spontaneous recovery of sinus rhythm. Engelman et al. [7] found that myocardial preservation was inadequate with a myocardial perfusate which was normokalemic or hypokalemic, and that adequate preservation occurred only with hypothermia and multidose potassium cardioplegia. Roberts et al. [15] found that the addition of potassium to hypothermic cardioplegic solutions resulted in better preservation of left ventricular performance and high energy myocardial stores than hypothermic perfusion without potassium. Behrendt and Jochim [2] found that no deterioration in function was observed in hearts protected with cardioplegic solutions including potassium chloride and mannitol when administered at either 4 or 28°C. However, they found severe myocardial depression in hearts
perfused with a 28°C solution without potassium chloride and mannitol, and concluded that the potassium cardioplegic solutions exerted a protective effect beyond that which was afforded by hypothermia. They found their best results occurred when a combination of hypothermia and potassium was used, and felt that these effects were additive. There has been some controversy about the relative importance of potassium versus the temperature of the perfusate. Ellis et al. [6] found that the coronary sinus creatine phosphokinase (CPK) was similar during the reperfusion period in animal hearts
FIG. 4. Myocardiai lactate extraction. Myocardial lactate extraction was similar between the two groups, decreasing somewhat during arrest, and then quite markedly following the release of the aortic crossclamp. There was lactate production rather then extraction in both groups following the release of the cross-clamp.
GROVER
ET AL.: IS POTASSIUM
NECESSARY
which were perfused with either a potassium solution at 4°C or with Ringers lactate without potassium at 4°C. They concluded that the myocardial injury was less in the groups perfused with hypothermic solution regardless of whether potassium chloride was added, and that the hypothermic perfusion was the major factor in the myocardial preservation. There are therefore three viewpoints in the literature: (1) that the potassium is the most important component of cardioplegic solutions, (2) that the cold temperature is the most important, and (3) that the effects of both are additive so that a combination of hypothermia and potassium best enhances myocardial preservation. All of the hearts in our experiment that were treated with potassium had complete arrest, whereas all of the control group were in a very slow ventricular fibrillation. This supports the findings of the above authors who have emphasized the importance of the solution containing potassium. This was further evident by the fact that 9 out of 10 potassium-treated hearts returned to a spontaneous normal sinus rhythm following the release of the aortic cross-clamp, whereas all of the control group remained in ventricular fibrillation, necessitating electrical defibrillation. The potassium-treated hearts demonstrated slightly less impairment of left ventricular function following arrest, the left atria1 and central venous pressures being somewhat lower, and the left ventricular dpldt max somewhat higher than in the non-potassium-treated group. The arterial pressure was also significantly higher in the potassium group, but there was no difference in cardiac output. A greater reactive hyperemia was noted in the control group following anoxic arrest than in the potassium-treated group. Coronary sinus flow was significantly greater following the release of the cross-clamp in the control group and was slower to return to preischemic levels than in the potassium group. Coronary vascular resistance was
IN CARDIOPLEGIC
SOLUTIONS?
69
also less in the control group at 60 min following bypass. This greater reactive hyperemia of the nonpotassium cardioplegia group may indicate a greater oxygen debt. There were no significant changes, however, in myocardial tissue lactate between the two groups, both increasing similarly during the period of anoxic arrest and then decreasing rapidly following the release of the cross-clamp. Similarly, no significant differences were noted between groups in myocardial adenosine triphosphate (ATP). The values decreased slightly during the period of anoxic arrest, then dropped markedly following the release of the cross-clamp, and 5 min later began to rise slowly. Lactate extraction was also similar in both groups. Electron microscopy did not reveal any sign&ant difference between the two groups, both showing some swelling of the mitochondria during and following the anoxic arrest period. The mildly degenerative alterations in ultrastructure appeared to be randomly distributed among our animals, and must be attributed to factors other than the presence or absence of KCl. The cytologic changes in any given animal generally worsened during cross-clamping and improved appreciably during reperfusion. The appearance of contraction banding in viable cells is consistent with the recent publications of Adomian et al. [l], in which they reported contraction banding as a routine in tissue obtained by endomyocardial biopsy and fixed immediately. We have observed similar phenomena in tissue obtained from live normal baboon hearts. The contraction banding noted in this experiment was almost exclusively “minor” contraction banding as outlined by Bloom and Cancilla [3]. Of significance was the universal lack of minor contraction banding during cross-clamping and reappearance of it during reperfusion. It is evident from this study, therefore, that both solutions offer considerable protection to the myocardium, supporting the importance of the deep hypothermia of the
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
solution. However, the complete arrest and spontaneous return of sinus rhythm of the potassium-treated hearts, and the greater hyperemia and the more pronounced decrease in hemodynamic parameters of the non-potassium-treated group point to extra protection afforded by the potassium. REFERENCES 1. Adomian, G. E., Laks, M. M., and Billingham, M. E. The incidence and significance of contraction banding in endomyocardial biopsies from normal human hearts. Amer. Heart J95: 348,1978. 2. Behrendt, D. M., and Jochim, K. E. Effect of temperature of cardioplegic solution. J. Thorac. Cardiovasc. Surg. 76: 353, 1978. 3. Bloom, S., and Cancilla, P. Myocytolysis and mitochondrial calcification in rat myocardium after low doses of isoproterenol. Amer. J. Pathol. 54: 373, 1969. 4. Buckberg, G. D. Studies of regional coronary flow using radioactive microspheres. Ann. Thorac. Surg. 20: 46, 1975. 5. Buckberg, G. D. Left ventricular subendocardial necrosis. Ann. Thorac. Surg. 24: 379, 1977. 6. Ellis, R. J., Pryor, W., and Ebert, P. A. Advantages of potassium cardioplegia and perfusion hypothermia in left ventricular hypertrophy. Ann. Thorac. Surg. 24: 299, 1977. 7. Engelman, R. M., Levitsky, S., O’Donoghue, M. J., and Auvil, J. Cardioplegia and myocardial preservation during cardiopulmonary bypass. Circulation (Suppl. 1) 58: I-108, 1978. 8. Follette, D., Fey, K., Mulder, D., Maloney,
J. V., Jr., and Buckberg, G. D. Prolonged safe aortic clamping by combining membrane stabilization, multidose cardioplegia, and appropriate pH reperfusion. J. Thorac. Cardiovasc. Surg. 74: 682, 1977. 9. Follette, D. M., Steed, D. L., Foglia, R., Fey, K., and Buckberg, G. D. Advantages of intermittent blood cardioplegia over intermittent ischemia during prolonged hypothermic aortic clamping. Circulation (Suppl. 1) 58: I-200, 1978. 10. Gay, W. A., Jr., and Ebert, P. A. Functional, metabolic, and morphologic effects of potassiuminduced cardioplegia. Surgery 74: 284, 1973. 11. Harlan, B. J., Ross, D., Macmanus, Q., Knight, R., Luber, J., and Starr, A. Cardioplegic solutions for myocardial preservation; Analysis of hypothermic arrest, potassium arrest, and procaine arrest. Circulation (Suppl. 1) 58: I-l 14, 1978. 12. Laks, H., Barner, H. B., Standeven, J. W., Hahn, J. W., Jellinek, M., and Menz, L. J. Myocardial protection by intermittent perfusion with cardioplegic solution versus intermittent coronary perfusion with cold blood. J. Thorac. Cardiovasc. Surg. 76: 158, 1978. 13. Lowry, 0. H., and Passonneau, J. V. A Flexible System of Enzymatic Analysis. New York: Academic Press, 1972. 14. O’Donoghue, M. J., Engelman, R. M., and Auvil, J. Multidose cardioplegia for myocardial preservation during prolonged ischemic arrest. Surg. Forum 29: 274, 1978. 15. Roberts, A. J., Abel, R. M., Subramanian, V. A., Paul, J., Alonso, D. A., and Gay, W. A., Jr. Effects of multidose potassium-induced cardioplegia during prolonged aortic cross-clamping: Comparison of continuous and intermittent clamping techniques. Surg. Forum 27: 279, 1978.
OF SURGICAL
Is Potassium
RESEARCH
29,
62-70 (1980)
a Necessary
Component
of Cardioplegic
Solutions?1,2
FREDERICK L. GROVER, M.D.,3 JOHN G. FEWEL, B.A., JOHN J.GHIDoNI,M.D., KITV. AROM, M.D., AND J. KENTTRINKLE, M.D. Cardiothoracic Surgery Secton, and the Department of Pathology, Audie L. Murphy Veterans Administration Medical Center, 7400 Merton Minter Boulevard, San Antonio, Texas 78284, and the University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, Texas 78284 Presented at the Annual Meeting of the Association for Academic Cleveland, Ohio, November 13- 15, 1978
Surgery,
Potassium-treated hearts were more completely arrested, usually did not require defibrillation, and had slightly less impairment of left ventricular contractility than those treated with hypothermia alone. There was more reactive hyperemia in non-potassium-treated hearts suggesting a greater oxygen debt. There were no significant differences however, in myocardial metabolism, as determined by myocardial lactate and ATP, myocardial lactate extraction, and electron microscopy.
nously. Arterial and central venous catheters were inserted. A median sternotomy was Left ventricular subendocardial necrosis performed, and catheters were inserted into continues to be a major finding in patients the left atrium, the left ventricle, and the who die following open heart operations coronary sinus (via the right atrium). Each 151. Considerable research has been peranimal was heparinized (3 mg/kg), the right formed to determine how to more effectively femoral artery was cannulated for inflow protect the myocardium during cardiac from the bypass pump, and both vena cava surgery. In 1973, Gay and Ebert [lo] rewere cannulated by separate right atriported experimental findings which demonotomies for flow from the animal to the strated adequate protection for 60 min of pump. The dogs were then subjected to ischemia following potassium-induced ar1’/2 hr of total cardiopulmonary bypass at a rest. Since then there has been considerable systemic temperature of 30°C with a flow controversy over the relative importance rate of 80 ml/kg/min. A Sarns modular pump of potassium and the temperature of the and Optiflow bubble oxygenator5 were cardioplegic solution. The following experiprimed with 20 ml/kg of 5% dextrose and ment was performed in an effort to better Plasmalyte and the remainder with fresh define their relative importance. heparinized blood. Sump catheters were inserted into both the right and left ventriMATERIALS AND METHODS cles and the pulmonary artery was ocEighteen adult mongrel dogs were anes- cluded. The right ventricular sump flow was thetized with 100 mg/kg of Chloralose and measured as coronary sinus flow. Arterial, 0.75 mg/kg of morphine sulfate intrave- central venous, and left ventricular pressures, cardiac output (dye-dilution), left 1 Supported by the Medical Research Service of the ventricular dpldt, arterial pH, p 02, and Veterans Administration. p COP, coronary sinus pH, p 02, p C02, and z The technical assistance of Ms. Cheryl Ellestad lactate, myocardial lactate and adenosine and Ms. Kay Ford is acknowledged and appreciated. triphosphate (ATP), and regional myocardial 3 Address reprint requests to Dr. Frederick L. blood flow (using the radioactive microGrover, Cardiothoracic Surgery Section, Audie L. INTRODUCTION
Murphy Veterans Administration Medical Center, 7400 Merton Minter Boulevard, San Antonio, Tex. 78284.
0022-4804/80/070062-09$01.00/O Copyright 0 1980 by Academic Press, Inc. All rights of reproduction in any form reserved.
s Courtesy of Cobe Laboratories, Cola. 80215. 62
1201 Lakewood,
GROVER ET AL.: IS POTASSIUM NECESSARY IN CARDIOPLEGIC
SOLUTIONS?
63
sphere technique) were measured before bypass, the animals were cooled to 30°C. All bypass, sequentially during aortic cross- parameters were measured and then the clamping, for 30 min after release of the aorta was cross-clamped and the cardioaortic cross-clamp, and for 1 hr after the plegic solution was administered as dediscontinuation of cardiopulmonary bypass. scribed above over a period of 3 to 4 min. The specimens of myocardial tissue for Following the removal of the cross-clamp, lactate and ATP were obtained by left the hearts were observed for return to ventricular needle biopsy and were immedi- spontaneous coronary sinus rhythm. Folately frozen in liquid nitrogen (- 163°C). lowing the 5-min post-cross-clamp measureThe chemical analysis was done by the ments, the animals were rewarmed to 37°C. method of Lowry 1131. Sequential full Cardiopulmonary bypass was discontinued thickness needle biopsies for electron mi- 30 min after the release of the cross-clamps, croscope study were immediately immersed and the parameters were then measured for 1 hr after bypass. in a 2% buffered gluturaldehyde solution. Regional myocardial blood flow was measured by injecting 400,000 to 800,000 RESULTS radioactive microspheres, 15 2 5 microns in diameter (3M Company), which were la- Adequacy of Arrest beled with 14Ce, 1251,85Sr,and 46Scinto the All hearts in the potassium-treated group left atrium for determinations before and (10 of 10) arrested completely, whereas after pump bypass, and into the pump inflow none in the control group (0 of 8) completely line during bypass. At the completion of arrested, slow ventricular fibrillation pereach experiment, the animal was sacrificed sisting throughout the cross-clamp period and the heart removed and weighed. The (P < 0.003). Nine of ten of the potassiumleft ventricle was then divided into inner, treated group returned to spontaneous middle, and outer layers and the septum into normal sinus rhythm following release of right and left layers, and the right ventricle the aortic cross-clamp, whereas all of the into inner and outer layers. The tissue was control group remained in ventricular fibrilthen counted in a Packard gamma scintilla- lation following release of the clamp (P tion counter as described by Buckberg 1441. < 0.0005). Using this technique, the sequential regional distribution of coronary blood flow at each interval was calculated since a different Hemodynamics (Table 1) isotope tag had been used for each injection. Left atrial pressure rose from 4.0 * 0.3 The data were subjected to statistical mm Hg (mean + SEM) prior to bypass, to analysis comparing control to experimental 8.0 + 2.2 thirty minutes following bypass animals using the Student’s independent in the control group, whereas it remained t test. stable in the potassium group (P < 0.09). The animals were divided into two groups. Central venous pressure in the control group Group I (10 dogs) received 200 ml of 5% increased from 2.0 + 0.6 mm Hg prior to dextrose in 0.2% normal saline with 20 meq bypass, to 6.2 + 1.2 thirty minutes after of KC1 and 6 meq of NaHCOJ500 ml into the bypass, as compared to 2.8 + 0.6 in the KC1 aortic root proximal to the cross-clamp, at group (P < 0.05). The mean arterial presthe onset and at 20-min intervals during the sure of the potassium group was 75 it 3 mm anoxic period of 1 hr. Group II animals Hg 60 min following bypass as compared to (eight dogs) received the same solution 57 f 4 in the control group (P < 0.01). The without the potassium. Both solutions were systolic pressure of the potassium-treated administered at a temperature of 0-4°C. group increased significantly to 101 -t- 6 After the onset of total cardiopulmonary mm Hg 30 min after bypass (P < 0.09) and
* ** *** ****
P P P P
I (KCI) 2 (No KCI)
i < < <
0.09. 0.05. 0.01. 0. I I, independent
3.9 + 0.8’ 4.0 + 0.3
I (KCI) 2 (No KCI) cutput
55 + 10 69 i 23
57 2 8 66 2 12
65 T 5 66+4
2317 f 193 1925 z 512
2951 e 277 2138 f 369****
2781 2 247 2858 + 371
I test.
60 mitt after
30 mitt after
Before
(ml/mitt/kg)
60 min after
Cardiac
30 min after
max. (mm H&cc)
78 f 6 6825
95 * 4 101 i 6
2.1 + 0.6 4.2 2 0.8**
pressure
Before
arterial 30 min after
Mean
60 min after
(mm Hg)
Before
dpldt
2.8 -t 0.6 6.2 + 1.2.’
1.7 2 0.5 2.0 + 0.6
4.3 2 0.9 5.8 + 1.0
pressure
Before
venous 30 min after
Central
60 min after
(mm Hg)
Left ventricular
4.0 + 0.9 8.0 2 2.2’
Before
ChUP
pressure
30 min after
Left atrial
HEMODYNAMICS
TABLE 1
75 k 3 57 * 4***
60 min after
(mm Hg)
159 + 6 158 + 8
Before
Heart
30 mitt after
rate (beatdmin)
114k6 141 + 10’1
64 mitt after
99k5 73 e 4.8’
60 min after
BP (mm Hg)
101 + 6 85 -t 5’
30 min after
arterial
120 * 5 133 -t 10
114 f 6 116 2 5
Before
Systolic
a A = Anoxia; b SEM. *P
I (KC11 2 (No KCI)
45 f 3b 39 + 2
1 (KC11 2 (No KCl)
coronary
63 f 8 78 -c 16
bypass.
52 2 5 55 2 6
30 min after A
g)
62 _c 9 108 c 28’
60 min after CPB
g)
Septal flow (mllminllO0
I5 min of CPB
53 c 5 53 f 5
30 min after A
Row (mWmin/lOO
65 2 7 76 2 14
I5 min of CPB”
CPB = cardiopulmonary
48 2 3 41 + 2
Before
Before
GKWp
Total
2
58 f 7 % + 22’
60 min a&-r CPB
1.01 2 0.05 1.03 _t 0.05
Before
IS min of CPB
ventricular
ratio
51 f 5 50 + 5
30 min after A
Row (mllminl
1.08 -c_0.07 1.12 2 0.15
30 min after A
endoxpi
63 -t_ 7 725 13
IS min of CPB
ventricular
1.09 * 0.07 0.99 _f 0.09
Left
51 -c_ 4 43 + 3
Before
Left
MYOCARDIAL BLOOD FLOW-MICROSPHERE
TABLE
60 min after CPB
I ..M 2 0.05 0.98 _f 0.12
60 min after CPB
61 k8 90 _f 19***
100 g)
1.75 c_ 0.25 2.17 + 0.21
Before
Coronary
33 + 3 30 _f 1
Before
resistance
73 t 8 79 t 13
I5 min of CPB
ventricular
1.22 + 0.19 0.99 c 0.20
15 min of CPB
vascular
Right
L.00 ? 0.13 1.03 f 0.11
30 min after A
(mm Hg/ml/lOO
55 + 4 58 2 6
30 min after A
flow (ml/min/lOO
0.93 0.48
f 0.13 -t 0.09**
60 min after CPB
timin)
49 t 6 93 t- 23”
60 min after CPB
g)
66
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
99 + 5 sixty minutes after bypass (P < 0.01) as compared to control values of 85 k 5 and 73 + 4. Left ventricular dpldt max in the control group decreased to 2138 c 369 and 1925 f 512 mm Hglsec 30 and 60 min following bypass in contrast to the potassium-treated group which increased to 2951 + 277 (P < 0.11) before decreasing to 2317 + 193 sixty minutes after bypass. Myocardial
control group as compared to 0.93 + 0.13 in the KC1 group (P < 0.05). The coronary sinus flow was significantly greater 10, 15, and 30 min following the release of the cross-clamp in the control group as compared to the KC1 group, and was slower to return to preischemic levels than in the potassium group (Fig. 1). Respective values for control vs KC1 flows at those intervals were 147 + 13 ml/mm/ 100 g, 120 + 19, 80 4 8 vs 70 k 8, 61 k 5, and 61 + 4 (P < 0.001, P < 0.01, P < 0.05). The flow in the KC1 group returned to preanoxic arrest values by 10 min after the release of the cross-clamp, as compared to 30 min in the control group.
Blood Flow (Table 2)
Total coronary flow in the control group increased to 96 2 22 ml/min/lOO g 60 min following bypass, whereas corresponding values in the potassium-treated group remained constant (P < 0.09). Left ventricular flow also increased in the control group Myocardial Metabolism to 90 _t 19 sixty minutes after bypass as There were no significant differences in compared to 61 + 8 in the potassium group (P < 0.13). Right ventricular flow also myocardial tissue lactate between groups increased to 93 + 23 in the controls 60 min (Fig. 2). The lactates steadily increased to a after bypass, in contrast to 49 + 6 in the high of 13pmol/g in both groups after 60 min potassium-treated animals (P < 0.05). Sim- of arrest. These values dropped sharply in ilar increases in septal flow in the control both groups following the release of the group were noted. Coronary vascular re- aortic cross-clamp. The myocardial adenosine triphosphate sistance decreased with the onset of bypass in both groups, remained relatively stable (ATP) measurements were also quite similar 30 min after the release of cross-clamp but between the two groups (Fig. 3), decreasing then decreased to 0.48 2 0.09 mm Hg/ml/ only slightly during the arrest period, but 100 g/min 60 min following bypass in the then dropping to 3.72 + 0.5 and 4.04 + 0.40
X0160OJ l60E g 1408 ‘20 2 loog 68s E 604020-
, I 6don
pg.05
X-Cbmp
l
C-P lb
30’
4
ByparS 6is
I 90’
105’
3OB
1 6dp
FIG. 1. Coronary sinus flow. The coronary sinus flow of the nonpotassium-treated hearts was significantly greater following release of the aortic cross-clamp, and remained so for 30 mitt of reperfusion. Note, also, the delay in returning to preanoxic flows in this group as compared to the group receiving potassium. This is indicative of a sustained hyperemic response in the hearts which did not receive potassium.
GROVER ET AL.: IS POTASSIUM NECESSARY IN CARDIOPLEGIC
I3
SOLUTIONS?
67
KClo--o Controls
12 II
I c , eefor.15’
C-P Bypass I 36
60’
I so’
105’
30’1
, 60’0
FIG. 2. Myocardial lactate. Myocardial lactate values were almost identical in the two groups, rising to a high of 13 pmol/g at the end of the arrest period, and quickly decreasing during the reperfusion period, although remaining higher than preanoxic levels throughout the experiment.
pmol/g in the control and KC1 groups 5 min after the release of the cross-clamp. Very little recovery of ATP to prearrest levels occurred in the ensuing 90 min. Lactate extraction was not significantly different between the groups (Fig. 4). Lactate production, rather than extraction occurred at 1 and 3 min following release of the cross-clamp in the control group, and at 1, 3, and 5 min in the KC1 group. Electron Microscopy The specimens were studied ultrastructurally without knowing which were from potassium or non-potassium-treated animals. Slight mitochondrial swelling and slight cytoplasmic edema were commonly encountered and highly variable in extent. In some animals, an increase in cytoplasmic lysosomes and/or myelin figures occurred in the post-cross-clamp period. The specimens taken 60 min after the dog came off bypass showed varying evidence of turnover of debris by interstitial macrophages. Contraction banding appeared while on cardiopulmonary bypass but before cross-clamping, did not occur in tissue obtained during
cross-clamping, but reappeared during the reperfusion interval. No significant differences in ultrastructure were noted between the two groups. DISCUSSION Preservation of the myocardium during cardiac operative procedures has come under increasing scrutiny during the past decade. Since 1973 when Gay and Ebert [lo] introduced potassium cardioplegia there has been increasing interest in the effects of various cardioplegia solutions and the method of their administration. There has been considerable discussion regarding the most effective composition of cardioplegic solutions. Follette et al. 181have advocated a cardioplegic solution containing procaine hydrochloride for membrane stabilization, with potassium, glucose, insulin, THAM, plasma, and albumin, and have also stressed the importance of reperfusing with alkaline-buffered blood following the anoxic arrest. O’Donoghue et al. [14] noted that solutions containing potassium consistently provided the best overall function following anoxic arrest.
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
2 ,j
X-Clomp C-P Bypass
’ 1
Before
15’
30’
8
60’
-I 9d
lob
3&p
1 6dp
FIG. 3. Myocardial adenosine triphosphate. Myocardial ATP levels were very similar in the two groups throughout the experiment, decreasing slightly during the period of arrest, decreasing more markedly following the removal of the aortic cross-clamp, and then remaining relatively stable for the remainder of the experiment.
Laks et al. [12] compared a cold potassium cardioplegic solution to intermittent infusion of cold blood and found the cardioplegic solution to be superior. Follette et al. [9] investigated a blood cardioplegia solution and found that this reduced left ventricular compliance only slightly, and resulted in normal postischemic ATP, water, and contractility. Harlan et al. [ll] compared Krebs - Henseleit buffer (KHB) , KHB with potassium, and KHB with procaine, administered at 15 and 5°C. The authors noticed that the solutions to which potassium and procaine were added caused a more rapid arrest and a greater incidence of spontaneous recovery of sinus rhythm. Engelman et al. [7] found that myocardial preservation was inadequate with a myocardial perfusate which was normokalemic or hypokalemic, and that adequate preservation occurred only with hypothermia and multidose potassium cardioplegia. Roberts et al. [15] found that the addition of potassium to hypothermic cardioplegic solutions resulted in better preservation of left ventricular performance and high energy myocardial stores than hypothermic perfusion without potassium. Behrendt and Jochim [2] found that no deterioration in function was observed in hearts protected with cardioplegic solutions including potassium chloride and mannitol when administered at either 4 or 28°C. However, they found severe myocardial depression in hearts
perfused with a 28°C solution without potassium chloride and mannitol, and concluded that the potassium cardioplegic solutions exerted a protective effect beyond that which was afforded by hypothermia. They found their best results occurred when a combination of hypothermia and potassium was used, and felt that these effects were additive. There has been some controversy about the relative importance of potassium versus the temperature of the perfusate. Ellis et al. [6] found that the coronary sinus creatine phosphokinase (CPK) was similar during the reperfusion period in animal hearts
FIG. 4. Myocardiai lactate extraction. Myocardial lactate extraction was similar between the two groups, decreasing somewhat during arrest, and then quite markedly following the release of the aortic crossclamp. There was lactate production rather then extraction in both groups following the release of the cross-clamp.
GROVER
ET AL.: IS POTASSIUM
NECESSARY
which were perfused with either a potassium solution at 4°C or with Ringers lactate without potassium at 4°C. They concluded that the myocardial injury was less in the groups perfused with hypothermic solution regardless of whether potassium chloride was added, and that the hypothermic perfusion was the major factor in the myocardial preservation. There are therefore three viewpoints in the literature: (1) that the potassium is the most important component of cardioplegic solutions, (2) that the cold temperature is the most important, and (3) that the effects of both are additive so that a combination of hypothermia and potassium best enhances myocardial preservation. All of the hearts in our experiment that were treated with potassium had complete arrest, whereas all of the control group were in a very slow ventricular fibrillation. This supports the findings of the above authors who have emphasized the importance of the solution containing potassium. This was further evident by the fact that 9 out of 10 potassium-treated hearts returned to a spontaneous normal sinus rhythm following the release of the aortic cross-clamp, whereas all of the control group remained in ventricular fibrillation, necessitating electrical defibrillation. The potassium-treated hearts demonstrated slightly less impairment of left ventricular function following arrest, the left atria1 and central venous pressures being somewhat lower, and the left ventricular dpldt max somewhat higher than in the non-potassium-treated group. The arterial pressure was also significantly higher in the potassium group, but there was no difference in cardiac output. A greater reactive hyperemia was noted in the control group following anoxic arrest than in the potassium-treated group. Coronary sinus flow was significantly greater following the release of the cross-clamp in the control group and was slower to return to preischemic levels than in the potassium group. Coronary vascular resistance was
IN CARDIOPLEGIC
SOLUTIONS?
69
also less in the control group at 60 min following bypass. This greater reactive hyperemia of the nonpotassium cardioplegia group may indicate a greater oxygen debt. There were no significant changes, however, in myocardial tissue lactate between the two groups, both increasing similarly during the period of anoxic arrest and then decreasing rapidly following the release of the cross-clamp. Similarly, no significant differences were noted between groups in myocardial adenosine triphosphate (ATP). The values decreased slightly during the period of anoxic arrest, then dropped markedly following the release of the cross-clamp, and 5 min later began to rise slowly. Lactate extraction was also similar in both groups. Electron microscopy did not reveal any sign&ant difference between the two groups, both showing some swelling of the mitochondria during and following the anoxic arrest period. The mildly degenerative alterations in ultrastructure appeared to be randomly distributed among our animals, and must be attributed to factors other than the presence or absence of KCl. The cytologic changes in any given animal generally worsened during cross-clamping and improved appreciably during reperfusion. The appearance of contraction banding in viable cells is consistent with the recent publications of Adomian et al. [l], in which they reported contraction banding as a routine in tissue obtained by endomyocardial biopsy and fixed immediately. We have observed similar phenomena in tissue obtained from live normal baboon hearts. The contraction banding noted in this experiment was almost exclusively “minor” contraction banding as outlined by Bloom and Cancilla [3]. Of significance was the universal lack of minor contraction banding during cross-clamping and reappearance of it during reperfusion. It is evident from this study, therefore, that both solutions offer considerable protection to the myocardium, supporting the importance of the deep hypothermia of the
JOURNAL OF SURGICAL RESEARCH: VOL. 29, NO. 1, JULY 1980
solution. However, the complete arrest and spontaneous return of sinus rhythm of the potassium-treated hearts, and the greater hyperemia and the more pronounced decrease in hemodynamic parameters of the non-potassium-treated group point to extra protection afforded by the potassium. REFERENCES 1. Adomian, G. E., Laks, M. M., and Billingham, M. E. The incidence and significance of contraction banding in endomyocardial biopsies from normal human hearts. Amer. Heart J95: 348,1978. 2. Behrendt, D. M., and Jochim, K. E. Effect of temperature of cardioplegic solution. J. Thorac. Cardiovasc. Surg. 76: 353, 1978. 3. Bloom, S., and Cancilla, P. Myocytolysis and mitochondrial calcification in rat myocardium after low doses of isoproterenol. Amer. J. Pathol. 54: 373, 1969. 4. Buckberg, G. D. Studies of regional coronary flow using radioactive microspheres. Ann. Thorac. Surg. 20: 46, 1975. 5. Buckberg, G. D. Left ventricular subendocardial necrosis. Ann. Thorac. Surg. 24: 379, 1977. 6. Ellis, R. J., Pryor, W., and Ebert, P. A. Advantages of potassium cardioplegia and perfusion hypothermia in left ventricular hypertrophy. Ann. Thorac. Surg. 24: 299, 1977. 7. Engelman, R. M., Levitsky, S., O’Donoghue, M. J., and Auvil, J. Cardioplegia and myocardial preservation during cardiopulmonary bypass. Circulation (Suppl. 1) 58: I-108, 1978. 8. Follette, D., Fey, K., Mulder, D., Maloney,
J. V., Jr., and Buckberg, G. D. Prolonged safe aortic clamping by combining membrane stabilization, multidose cardioplegia, and appropriate pH reperfusion. J. Thorac. Cardiovasc. Surg. 74: 682, 1977. 9. Follette, D. M., Steed, D. L., Foglia, R., Fey, K., and Buckberg, G. D. Advantages of intermittent blood cardioplegia over intermittent ischemia during prolonged hypothermic aortic clamping. Circulation (Suppl. 1) 58: I-200, 1978. 10. Gay, W. A., Jr., and Ebert, P. A. Functional, metabolic, and morphologic effects of potassiuminduced cardioplegia. Surgery 74: 284, 1973. 11. Harlan, B. J., Ross, D., Macmanus, Q., Knight, R., Luber, J., and Starr, A. Cardioplegic solutions for myocardial preservation; Analysis of hypothermic arrest, potassium arrest, and procaine arrest. Circulation (Suppl. 1) 58: I-l 14, 1978. 12. Laks, H., Barner, H. B., Standeven, J. W., Hahn, J. W., Jellinek, M., and Menz, L. J. Myocardial protection by intermittent perfusion with cardioplegic solution versus intermittent coronary perfusion with cold blood. J. Thorac. Cardiovasc. Surg. 76: 158, 1978. 13. Lowry, 0. H., and Passonneau, J. V. A Flexible System of Enzymatic Analysis. New York: Academic Press, 1972. 14. O’Donoghue, M. J., Engelman, R. M., and Auvil, J. Multidose cardioplegia for myocardial preservation during prolonged ischemic arrest. Surg. Forum 29: 274, 1978. 15. Roberts, A. J., Abel, R. M., Subramanian, V. A., Paul, J., Alonso, D. A., and Gay, W. A., Jr. Effects of multidose potassium-induced cardioplegia during prolonged aortic cross-clamping: Comparison of continuous and intermittent clamping techniques. Surg. Forum 27: 279, 1978.