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MYOCARDIAL METABOLISM IN THE HYPOTHERMIC BYPASSED HEART
MYOCARDIAL METABOLISM I N THE HYPOTHERMIC BYPASSED HEART Maurice C. Fuquay, M.D. (by invitation),
Charles N. Bucknam,
Walter J. Frajola, Ph.D. (by invitation),
Howard D. Sirak, M.D.,
H
(by invitation), Columbus,
M.D.
and
Ohio
has been extensively investigated in the laboratory and is now widely accepted as an adjunct to cardiovascular surgery during temporary interruption of coronary flow. However, the depth of cooling has varied. Total cardiopulmonary bypass is readily adaptable to the production of profound hypothermia by direct cooling of the blood, (lollan 1 produced cold-induced arrest by cooling dogs to 5° C. with a heat exchanger in the extracorporeal circuit. Complete recovery followed rewarming of the blood. More recently, surgeons2- 3 ' 4 have found extracorporeal cooling to 5° to 10° C. advantageous for the repair of difficult intracardiac defects. They believe the arrested heart is then maximally protected from anoxia. However, deep levels of cooling have often been associated with serious side effects.5' ° Although profound hypothermia may offer prolonged protection from anoxia, severe metabolic acidosis and acute circulatory failure may follow its use. This investigation was undertaken to evaluate in the bypassed heart the effects on the myocardium of potassium and/or cold-induced arrest at 37°, 30°, 20°, and 10° C. This study sought also to determine the temperature which affords the heart maximal protection during interruption of coronary flow. Determinations of gas content and pH, carbohydrate metabolites, and eight enzymes were obtained from samples of coronary sinus blood and used as indices for comparison. YPOTHERMIA
METHODS
Fifty-eight dogs were divided into five groups. Each group was placed on cardiopulmonary bypass and subjected to cardiac arrest at a specific temperatures level. The five groups were: (1) 37° C. with potassium arrest—7 dogs; From the Cardiovascular Service, Division of Thoracic Surgery and the Department of Physiological Chemistry, The Ohio State University Health Center, Columbus, Ohio. This investigation was supported by a research grant (No. H-5273) from the National Heart Institute, U. S. Public Health Service. Read at the Forty-second Annual Meeting of The American Association for Thoracic Surgery at St. Louis, Mo., April 16-18, 1962. 649
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J. Thoracic and Cardiovas. Surg.
(2) 30° C. with potassium arrest—13 dogs; (3) 20° C. with potassium arrest— 10 dogs; (4) 20° C. with cold arrest—10 dogs; and (5) 10° C. with cold arrest— 18 dogs. Adult dogs, weighing from 13 to 18 kilograms, were anesthetized with intravenous pentobarbital sodium. Endotracheal positive pressure respiration was maintained until cardiopulmonary bypass was established. A rotating disc oxygenator was used with a Brown-Harrison 7 heat exchanger placed in the
7.4 0
pH
PRE-COOLING
WM
PRE-ARREST
d ]
POST-ARREST
^B
7.35
NORMAL RANGE'.731-7.42
7.30
90
PRE-COOLING M PRE-ARREST CZI POST-ARREST M NORMAL RANGE: 60-64%
02 SATURATION
SO 70 60
7.25
50
7.20
40 7.1 5
30
7.10
1
37'K
20
30*K
2
Pig. 1.—Changes in pH of coronary sinus blood following normothermic arrest and after cooling and arrest a t various levels of hypothermia. Pig. 2.—Changes in oxygen saturation of coronary sinus blood following normothermic arrest and after cooling and arrest at various levels of hypothermia.
C0 2 CONTENT
PRE-COOLING PRE-ARREST _m _ POST-ARREST ^ NORMAL RANGE! 45-53 VOL.*
BLOOD GLUCOSE
PRE-COOLING PRE-ARREST
H ^
POST-TARREST
™
NORMAL RANGE'. 60-IOOmgX
Pig. 3.—Changes in carbon dioxide content of coronary sinus blood following normothermic arrest and after cooling and arrest at various levels of hypothermia. Pig. 4.—Changes in coronary sinus blood glucose levels following normothermic arrest and after cooling and arrest at various levels of hypothermia.
venous return line. The pump was primed with refrigerated donor blood less than 18 hours old. A No. 10 Poley catheter was inserted into the coronary sinus through a right atriotomy. After the animals in the hypothermic groups were cooled to the desired level, the ascending aorta was cross-clamped. In the 37°, 30°, and one of the 20° C. groups, the heart was arrested with potassium citrate injected into the aorta proximal to the point of occlusion. In the 10° and the
MYOCARDIAL METABOLISM
Vol. 44, No. 5 November, 1962
PRE-COOLING PRE-ARREST M POST-ARREST NORMAL RANGE 6-|6m«%
PYRUVIC ACID
Pig. 5.—Changes in coronary arrest and after cooling and arrest Fig. 6.—Changes in coronary arrest and after cooling and arrest GLUTAMIC
100 . OXALOACETIC TRANSAMINASE 90 80
651 PRE-COOLING PRE-ARREST POST-ARREST NORMAL RANGE!
[~~1 ■ ■ 1-2MG %
sinus blood levels of lactic acid following normothermic at various levels of hypothermia. sinus blood levels of pyruvic acid following normothermic at various levels of hypothermia.
PRE-COOLING PRE-ARREST C Z ] POST-ARREST I NORMAL RANGE
gggj*
PRE-COOLING PRE-ARREST
BBB □
TRANSAMINASE POST-ARREST ^ H NORMAL RANGE 0-20 UNITS
4 0 UNITS
ro 60 50 40 30 20 10 37'K
30-K
Fig. 7.—Changes in coronary sinus blood levels of glutamic oxaloacetlc transamlnase following normothermic arrest and after cooling and arrest at various levels of hypothermiaFig. 8.—Changes in coronary sinus blood levels of glutamic pyruvic transaminase following normothermic arrest and after cooling and arrest at various levels of hypothermia.
LACTIC DEHYDROGENASE
PRE-COOLING mm. MALIC PRE-ARREST CZ DEHYDROGENASE POST-ARREST H NORMAL RANGE: 150-250 UNITS
PRE-COOLING PRE-ARREST POST-ARREST
■ ■
NORMAL RANGE: 150-250 UNITS
200
Fig. 9.—Changes in coronary sinus blood levels of lactic dehydrogenase following normothermic arrest and after cooling and arrest at various levels of hypothermia. Fig. 10.—Changes in coronary sinus blood levels of malic dehydrogenase following normothermic arrest and after cooling and arrest a t various levels of hypothermia.
FUQTJAY ET AL.
652
J. Thoracic and Cardiovas. Surg.
other 20° C. group, cardioplegia was accomplished by anoxic or cold arrest. The animals were rewarmed while the aorta was cross-clamped, but the excluded heart was maintained at the desired temperature as confirmed by an intramyocardial thermistor. Following 30 minutes of arrest, the aorta was undamped and coronary circulation was restored. PRE- COOLING PRE-ARREST POST-ARREST NORMAL RANGE:
100 50-150 UNITS
90
PRE-COOLING PRE-ARREST POST-ARREST
PHOSPHOHEXOSE ISOMERASE ^ H
NORMAL RANGE! 10-20 UNITS
80 70 60 50 40 30 20 10 0
12
Fig. 11.—Changes in coronary sinus blood levels of aldolase following arrest and after cooling and arrest at various levels of hypothermia.
normothermic
Pig. 12.—Changes in coronary sinus blood levels of phosphohexase isomerase following normothermic arrest and after cooling and arrest at various levels of hypothermia.
400
PRE-COOLING « LEUCINE PRE-ARREST CH AMINOPEPTIDASE POST-ARREST * NORMAL RANGE: 100- 310 UNITj]
PRE-COOLING WM ACETYL I I CHOUNESTERASE PRE-ARREST POST-ARREST ^ H NORMAL RANGE! 130 - 260 UNITS
350 300 250 200 I 50
13
37*K
30*K
Fig. 13.—Changes in coronary sinus blood levels of leucine aminopeptidase normothermic arrest and after cooling and arrest a t various levels of hypothermia. Fig. 14.—Changes in coronary sinus blood levels of acetyl cholinesterase normothermic arrest and after cooling and arrest at various levels of hypothermia.
following following
Rectal and direct myocardial temperatures and arterial and venous pressures were monitored continuously. Rates of cooling varied from 1° to 2° C. per minute. Perfusion rates ranged from 60 to 100 ml. per kilogram per minute. Blood samples were obtained from the following sources at five intervals: (1) oxygenated pump blood before perfusion; (2) pre-perfusion sample—from the superior vena cava upon opening the chest; (3) pre-cooling sample—from the coronary sinus immediately following cannulation; (4) pre-arrest sample—from the coronary sinus after the desired level of hypothermia had been attained;
Vol. 44, No. 5
November, 1962
MYOCARDIAL METABOLISM
653 "
u o
and (5) post-arrest sample—from the coronary sinus immediately following release of the aortic clamp after 30 minutes of cardiac arrest. The following determinations were made on each blood sample: (1) blood pH, (2) carbon dioxide content, 8 (3) oxygen saturation, 8 (4) blood glucose,9 (5) lactic acid,10 (6) pyruvic acid,11 (7) glutamic oxaloacetic transaminase, 12 (8) glutamic pyruvic transaminase, 13 (9) lactic dehydrogenase, 13 (10) malic dehydrogenase, 13 (11) aldolase," (12) phosphohexose isomerase,15 (13) leucine aminopeptidase, 16 and (14) acetyl cholinesterase.17 The results are shown in Figs. 1 through 14. DISCUSSION
Even though deep hypothermia has certain advantages, it is productive of metabolic acidosis.5- "•18 This selective study of coronary sinus blood confirmed the occurrence of myocardial metabolic acidosis under the conditions of these experiments. The metabolic acidosis was of comparable severity after temporary interruption of the coronary circulation when deep hypothermia (10° C. coldarrest group) was used as there was with potassium arrest at 37° C. In the 10° C. cold-arrest group, restoration of coronary flow after a 30 minute arrest produced a coronary sinus blood pH fall to 7.15 and a lactic acid rise to 68 mg. per cent. Less marked acidosis occurred in the 30° and 20° C. groups. These changes in coronary sinus blood occurred following cardiac arrest in all groups except the 10° C. cold-arrest dogs in which metabolic acidosis developed also during the cooling phase. It was expected that the coronary sinus blood would be acidotic after interruption of coronary flow in the normothermic dogs. This is due to the accumulation of anaerobic glycolysis products during the period of myocardial anoxia. Lactic acid is the principal product of the anaerobic process,19 the lowered p H being inversely related to the rise in lactic acid. However, with the reduced myocardial metabolism produced by hypothermia, one would not expect such marked myocardial acidosis. One would assume that the deeper the hypothermia, the less the acidosis. Contrary results were obtained from the lactic acid and p H data of the 10° C. cold-arrest dogs. Several factors may be responsible for this finding. First, during cooling there would be a shift to the left in the oxygen-hemoglobin dissociation curve that would make less oxygen available to the tissues. However, this would be partially offset by a shift to the right caused by the acidosis.20 Differential cooling6 may be an important factor contributing to the metabolic acidosis. During rapid total-body cooling, there is a temperature lag in certain regions. The skeletal muscle mass may be as much as 10° C. warmer than the myocardium. This will produce acidosis in those tissues with the greater oxygen demand. In the present study, during rapid cooling, differences between the myocardial and rectal temperatures varied from 7° to 12° C , but the two temperatures were essentially equal when the aorta was cross-clamped. A third factor which contributed to the myocardial metabolic acidosis in the 10° C. cold-arrest group is that, even at 10° C , there is still a basic oxygen
654
FUQUAY ET AL.
J. Thoracic and Cardiovas. Surg.
need and when coronary flow is interrupted, the resulting anaerobic cellular metabolism causes an accumulation of glycolytic products and an oxygen debt.18 Ventricular fibrillation is another factor which probably contributed to acidosis. In the 10° C. cold-arrest dogs, acidosis developed during the cooling phase in contrast to the other groups in which acidosis occurred principally after arrest. There was a high incidence of ventricular fibrillation during cooling of the 10° C. cold-arrest dogs, whereas fibrillation seldom occurred during cooling in the other groups. This would suggest that the relative increase in oxygen consumption associated with ventricular fibrillation contributes to acidosis at lower temperatures. Edwards and associates21 have stated that hypothermia does not result in a discrepancy between myocardial oxygen demand and supply. However, in our 10° C. cold-arrest dogs, metabolic acidosis of the coronary sinus blood developed in the face of adequate coronary perfusion with well-oxygenated blood. The high oxygen content of the coronary sinus blood suggests that hypothermia alters myocardial cellular function in such a manner that the cell is unable to utilize the available oxygen. The accumulation of anaerobic glycolysis products also indicates that the metabolic demands of the myocardium are unsatisfied by the usual oxidative process. Increased oxygen consumption, in the normothermic group while on cardiopulmonary bypass prior to arrest, is in agreement with results found by Wallace.22 The reduction in oxygen consumption, as shown in the hypothermic groups, has been well documented. There were no consistent significant changes in glucose levels in the hypothermic groups. In the 37° C. potassium-arrest group there was a marked elevation following arrest. This suggests poor utilization of glucose by the myocardium while in the hypoxic state. Similar findings have been reported by Michel23 in regard to lactate. Enzyme Metabolism—Transaminases.—Serum transaminases catalyze the intermolecular transfer of amino groups from amino acids to keto acids. There are two major transaminating enzymes in heart muscle: glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase. These enzymes are present in lesser concentration in skeletal muscle, brain, liver, and kidney. Serum glutamic oxaloacetic transaminase (SGOT) levels are significantly elevated following myocardial injury. This was reported by La Due and associates24 and Agress. 25 It has since been confirmed by numerous authors. SGOT elevation is the most specific enzyme change associated with myocardial damage. 26 While it is true that elevated SGOT levels have been reported following major abdominal surgery, cardiac surgery and the use of cardiopulmonary bypass, it should be emphasized that these changes were not immediate and did not develop until several hours after the surgical procedure. This study is concerned only with the changes which occur during cooling or during the 30 minutes of coronary flow interruption. In the present study, the lowest elevations were found in the 20° and 10° C. cold-arrest groups. The cooling process did not have any appreciable effect on
Vol. 44, No. 5 November, 1962
MYOCARDIAL METABOLISM
655
SGOT levels. That cooling may have a protective effect is contradicted by Blair 27 who found that elevated levels of SGOT followed prolonged periods of hypothermia. He reported significant changes after periods of surface cooling up to 12 hours in duration. Snyder 28 reported a correlation between the degree of SGOT elevation and length of time on bypass. This was not confirmed in this study, since the 10° C. cold-arrest group was on bypass for the longest period of time and had the lowest SGOT levels. The two potassium-arrest groups had higher levels of SGOT than the coldarrest groups. This suggests that the harmful effects of potassium arrest, now well documented in the literature, 29 ' 30 is a cause of enzyme elevation. Elevated SGOT levels following potassium arrest agree with the findings of Quinn and associates.31 The results in this study indicate that SGPT is a less sensitive test than SGOT. The fact that the dehydrogenases had higher levels at 10° C. suggests that they are less depressed by cold. Aldolase behaved as expected with the lower values occurring with cold. The response of other enzymes were not particularly informative. CONCLUSIONS
Myocardial metabolic acidosis results from tissue hypoxia that follows temporary interruption of coronary flow even when hypothermia is used. The acidosis is less at moderate levels of cooling (20° C.). However, severe metabolic acidosis may develop if the hypothermia reaches 10° C. Temporary coronary flow interruption produced less disturbance in the coronary sinus blood p H and lactic acid values during hypothermic arrest at 20° C. than at 30° C. or 10° C. Paradoxically, the p H was most pronouncedly lowered when the hearts were cooled to 10° C , suggesting the presence of significant anaerobic metabolism and the development of an oxygen debt. In this group, immediately following restoration of coronary circulation, the coronary sinus blood was highly saturated with oxygen. The oxygen debt indicated by the marked acidosis should have produced lowering of oxygen saturation. Perhaps the severely cooled myocardial cell was unable to utilize oxygen because of impairment of its enzyme system. Some of the enzyme values were low while others were unaffected, suggesting that the levels of cold used in these experiments does not have an equal effect on all enzymes. Higher enzyme values were always obtained whenever potassium citrate was added to the arrest procedure. This suggests that the drug itself has a specific injurious effect. SUMMARY
1. Changes in the coronary sinus blood were studied after a 30 minute interval of cardiac arrest. Hypothermia-induced arrests at 20° C. and 10° C. were compared with each other and with potassium citrate-induced arrest at normothermia (37° C.) and at 30° C. and 20° C. 2. Metabolic acidosis occurred in all groups, but it was most marked with cold arrest at 10° C. and whenever potassium citrate was used.
FUQUAY E T AL.
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J. Thoracic and Cardiovas. Surg.
3. Anaerobic metabolism producing an oxygen debt occurred even with 10° C. cold-induced arrest. Immediately following restoration of coronary circulation, the coronary sinus blood remained fully saturated suggesting that the myocardial cells were unable to use the available oxygen. This may be due to depression of this enzyme system. 4. The enzyme levels in the coronary sinus blood were usually decreased by cold, but a few appeared to be unaffected. This suggests that all the enzyme systems are not depressed equally by the hypothermic levels used in these experiments. REFERENCES
1. Gollan, F., Grace, J. T., Schell, M. W., Tysinger, D. S., and Feaster, L. B . : Left Heart Surgery in Dogs During Respiratory and Cardiac Arrest at Body Temperatures Below 10° C , Surgery 3 8 : 363, 1955. 2. Young, W. G., Sealy, W. C , Brown, I. W., Jr., Smith, W., Calloway, H. A., and Harris, J . S.: Metabolic and Physiologic Observations on Patients Undergoing Extracorporeal Circulation in Conjunction "With Hypothermia, Surgery 46: 175, 1959. 3. Dubost, C , and Blondeau, P . : The Association of the Artificial Heart-Lung With Deep Hypothermia in Open H e a r t Surgery, J . Cardiov. Surg. 1 : 85, 1960. 4. Sealy, W. C , Young, W. G., Brown, I. W., Smith, W. W., and Lesage, A. M.: Profound Hypothermia Combined With Extracorporoal Circulation for Open Heart Surgerv, Surgery 48: 432, 1960. 5. Stephen, C. R., Dent, S., Sealy, W. C , and Hull, K . : Anesthetic and Metabolic Factors Associated With Combined Extracorporeal Circulation and Hypothermia, Am. J . Cardiol. 6 : 737, 1960. 6. Neville, W. E., Kameya, S., Oz, M., Bloor, B., and Clowes, G. H. A., J r . : Profound Hypothermia and Complete Circulation Interruption, A. M. A. Arch. Surg. 82: 108, 1961. 7. Brown, I . W., Smith, W. W., and Emmons, W. O.: An Efficient Blood Heat Exchanger for Use With Extracorporeal Circulation, Surgery 44: 372, 1958. 8. Van Slyke, D. D., and Neil, J . M.: Determination of Gasses in Blood and Other Solutions by Vacuum Extraction and Manometric Measurement, J . Biol. Chem. 6 1 : 523, 1924. 9. Hagedorn, H . C , and Jensen, B . N . : Zur Microbestimmung des Blutzuckers Mittels Ferrieyanid, Biochcm. Ztschr. 135: 46, 1923. 10. Barker, S. B., and Summerson, W. A.: Colorimetric Determination of Lactic Acid in Biological Material, J . Biol. Chem. 138: 535, 1941. 11. Friedemann, T. E., and Haugcn, G. E . : Pyruvic Acid: Determination of Keto Acids in Blood and Urine, J . Biol. Chem. 147: 415, 1943. 12. Karman, A. J., Wroblewski, F., and La Due, J. S.: Transaminase Activitv in Human Blood, Clin. Invest. 34: 126, 1955. 13. Wroblewski, F., and Cabaud, P . : Colorimetric Measurement of Serum Glutamic Pyruvic Transaminase, Am. J . Clin. Path. 2 7 : 235, 1957. 14. Beisenherz, G., Bucher, T., and Garbade, K . : Methods of Enzymology. I, edited by S. P . Colowich and N. O. Kaplan, New York, 1955, Academic Press, Inc. 15. Bodansky, M., and Bodansky, O.: Serum Phosphohexose Isomerase in Cancer. I . Method of Determination and Establishment of Normal Values, Cancer 7 : 1191, 1954. 16. Goldberg, J . A., and Rutenberg, A. M.: The Colorimetric Determination of Leucine Aminopeptidase in Urine and Serum of Normal Subject and Patients With Cancer and Other Diseases, Cancer 11: 283, 1958. 17. De la Huerga, J., Yesinick, G., and Popper, H . : Colorimetric Method for the Determination of Serum Cholinesterase, Am. J . Clin. Path. 2 2 : 1126, 1952. 18. Padhi, R., and Rainbow, R.: Some Observations on Deep Hypothermia Using Extracorporeal Circulation, Angiology 12: 12, 1961. 19. Litwin, M. S., Panico, F . G., Rubini, C , Harken, D. E., and Moore, F . D . : Acidosis and Lactic Acidemia in Extracorporeal Circulation, Ann. Surg. 149: 188, 1959. 20. Best, C. H., and Taylor, N . B . : The Physiological Basis of Medical Practice, ed. 7, Baltimore, 1961, Williams & Wilkins Co. 21. Edwards, W. S., Tuluy, S., Reber, W. E., Siegel, A., and Bing, R. J . : Coronary Blood Flow and Myocardial Metabolism in Hypothermia, Ann. Surg. 139: 275, 1954. 22. Wallace, H. W . : Cardiac Metabolism, New England J . Med. 261: 26, 1959.
Vol. 44, No. 5
November, 1962
MYOCARDIAL METABOLISM
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23. Michel, G., Beuren, A., Hagancamp, C. E., and Bing, E. J . : Effect of Interruption of Coronary Circulation on Metabolism of Arrested Heart, Am. J . Physiol. 195: 417, 1958. 24. L a Due, J . S., Wroblewski, F., and Karman, A.: Serum Glutamic Oxaloacetic Transaminase Activity in Human Acute Transmural Myocardial Infarction, Science 120: 497, 1954. 25. Agress, C. M.: Evaluation of the Transaminase Test, Am. J . Cardiol. 3 : 74, 1959. 26. Hamolsky, M., and Kaplan, N . : Measurements of Enzymes in the Diagnosis of Acute Myocardial Infarction, Circulation 2 3 : 102, 1961. 27. Blair, E., Hook, R., and Bunce, G.: Serum Glutamic Oxaloacetic Transaminase Content in Hypothermia, Science 133: 105, 1961. 28. Snyder, D. D., Barnard, C. N., Varco, R. L., and Lillihei, C. W . : Serum Transaminase Patterns Following Intracardiac Surgery, Surgery 44: 1083, 1958. 29. Helmsworth, J . A., Kaplan, S., Clark, L. C , Jr., McAdams, A. J., Matthews, E. C , and Edwards, F . K . : Myocardial Injury Associated With Asystole Induced With Potassium Citrate, Ann. Surg. 149: 200, 1959. 30. Greenberg, J . J., Edmunds, L. H., and Brown, R. B . : Myocardial Metabolism and Postarrest Function in the Cold and Chemically Arrested Heart, Surgery 48: 31, 1960. 31. Quinn, J . W., Sirak, H. D., Shabanah, E. H., and Frajola, W. J . : Transaminase Values Following Open-Heart Surgery, Ann. Surg. 152: 45, 1960. (For Discussion,
see page
695)
Charles N. Bucknam,
Walter J. Frajola, Ph.D. (by invitation),
Howard D. Sirak, M.D.,
H
(by invitation), Columbus,
M.D.
and
Ohio
has been extensively investigated in the laboratory and is now widely accepted as an adjunct to cardiovascular surgery during temporary interruption of coronary flow. However, the depth of cooling has varied. Total cardiopulmonary bypass is readily adaptable to the production of profound hypothermia by direct cooling of the blood, (lollan 1 produced cold-induced arrest by cooling dogs to 5° C. with a heat exchanger in the extracorporeal circuit. Complete recovery followed rewarming of the blood. More recently, surgeons2- 3 ' 4 have found extracorporeal cooling to 5° to 10° C. advantageous for the repair of difficult intracardiac defects. They believe the arrested heart is then maximally protected from anoxia. However, deep levels of cooling have often been associated with serious side effects.5' ° Although profound hypothermia may offer prolonged protection from anoxia, severe metabolic acidosis and acute circulatory failure may follow its use. This investigation was undertaken to evaluate in the bypassed heart the effects on the myocardium of potassium and/or cold-induced arrest at 37°, 30°, 20°, and 10° C. This study sought also to determine the temperature which affords the heart maximal protection during interruption of coronary flow. Determinations of gas content and pH, carbohydrate metabolites, and eight enzymes were obtained from samples of coronary sinus blood and used as indices for comparison. YPOTHERMIA
METHODS
Fifty-eight dogs were divided into five groups. Each group was placed on cardiopulmonary bypass and subjected to cardiac arrest at a specific temperatures level. The five groups were: (1) 37° C. with potassium arrest—7 dogs; From the Cardiovascular Service, Division of Thoracic Surgery and the Department of Physiological Chemistry, The Ohio State University Health Center, Columbus, Ohio. This investigation was supported by a research grant (No. H-5273) from the National Heart Institute, U. S. Public Health Service. Read at the Forty-second Annual Meeting of The American Association for Thoracic Surgery at St. Louis, Mo., April 16-18, 1962. 649
FUQUAY E T AL.
650
J. Thoracic and Cardiovas. Surg.
(2) 30° C. with potassium arrest—13 dogs; (3) 20° C. with potassium arrest— 10 dogs; (4) 20° C. with cold arrest—10 dogs; and (5) 10° C. with cold arrest— 18 dogs. Adult dogs, weighing from 13 to 18 kilograms, were anesthetized with intravenous pentobarbital sodium. Endotracheal positive pressure respiration was maintained until cardiopulmonary bypass was established. A rotating disc oxygenator was used with a Brown-Harrison 7 heat exchanger placed in the
7.4 0
pH
PRE-COOLING
WM
PRE-ARREST
d ]
POST-ARREST
^B
7.35
NORMAL RANGE'.731-7.42
7.30
90
PRE-COOLING M PRE-ARREST CZI POST-ARREST M NORMAL RANGE: 60-64%
02 SATURATION
SO 70 60
7.25
50
7.20
40 7.1 5
30
7.10
1
37'K
20
30*K
2
Pig. 1.—Changes in pH of coronary sinus blood following normothermic arrest and after cooling and arrest a t various levels of hypothermia. Pig. 2.—Changes in oxygen saturation of coronary sinus blood following normothermic arrest and after cooling and arrest at various levels of hypothermia.
C0 2 CONTENT
PRE-COOLING PRE-ARREST _m _ POST-ARREST ^ NORMAL RANGE! 45-53 VOL.*
BLOOD GLUCOSE
PRE-COOLING PRE-ARREST
H ^
POST-TARREST
™
NORMAL RANGE'. 60-IOOmgX
Pig. 3.—Changes in carbon dioxide content of coronary sinus blood following normothermic arrest and after cooling and arrest at various levels of hypothermia. Pig. 4.—Changes in coronary sinus blood glucose levels following normothermic arrest and after cooling and arrest at various levels of hypothermia.
venous return line. The pump was primed with refrigerated donor blood less than 18 hours old. A No. 10 Poley catheter was inserted into the coronary sinus through a right atriotomy. After the animals in the hypothermic groups were cooled to the desired level, the ascending aorta was cross-clamped. In the 37°, 30°, and one of the 20° C. groups, the heart was arrested with potassium citrate injected into the aorta proximal to the point of occlusion. In the 10° and the
MYOCARDIAL METABOLISM
Vol. 44, No. 5 November, 1962
PRE-COOLING PRE-ARREST M POST-ARREST NORMAL RANGE 6-|6m«%
PYRUVIC ACID
Pig. 5.—Changes in coronary arrest and after cooling and arrest Fig. 6.—Changes in coronary arrest and after cooling and arrest GLUTAMIC
100 . OXALOACETIC TRANSAMINASE 90 80
651 PRE-COOLING PRE-ARREST POST-ARREST NORMAL RANGE!
[~~1 ■ ■ 1-2MG %
sinus blood levels of lactic acid following normothermic at various levels of hypothermia. sinus blood levels of pyruvic acid following normothermic at various levels of hypothermia.
PRE-COOLING PRE-ARREST C Z ] POST-ARREST I NORMAL RANGE
gggj*
PRE-COOLING PRE-ARREST
BBB □
TRANSAMINASE POST-ARREST ^ H NORMAL RANGE 0-20 UNITS
4 0 UNITS
ro 60 50 40 30 20 10 37'K
30-K
Fig. 7.—Changes in coronary sinus blood levels of glutamic oxaloacetlc transamlnase following normothermic arrest and after cooling and arrest at various levels of hypothermiaFig. 8.—Changes in coronary sinus blood levels of glutamic pyruvic transaminase following normothermic arrest and after cooling and arrest at various levels of hypothermia.
LACTIC DEHYDROGENASE
PRE-COOLING mm. MALIC PRE-ARREST CZ DEHYDROGENASE POST-ARREST H NORMAL RANGE: 150-250 UNITS
PRE-COOLING PRE-ARREST POST-ARREST
■ ■
NORMAL RANGE: 150-250 UNITS
200
Fig. 9.—Changes in coronary sinus blood levels of lactic dehydrogenase following normothermic arrest and after cooling and arrest at various levels of hypothermia. Fig. 10.—Changes in coronary sinus blood levels of malic dehydrogenase following normothermic arrest and after cooling and arrest a t various levels of hypothermia.
FUQTJAY ET AL.
652
J. Thoracic and Cardiovas. Surg.
other 20° C. group, cardioplegia was accomplished by anoxic or cold arrest. The animals were rewarmed while the aorta was cross-clamped, but the excluded heart was maintained at the desired temperature as confirmed by an intramyocardial thermistor. Following 30 minutes of arrest, the aorta was undamped and coronary circulation was restored. PRE- COOLING PRE-ARREST POST-ARREST NORMAL RANGE:
100 50-150 UNITS
90
PRE-COOLING PRE-ARREST POST-ARREST
PHOSPHOHEXOSE ISOMERASE ^ H
NORMAL RANGE! 10-20 UNITS
80 70 60 50 40 30 20 10 0
12
Fig. 11.—Changes in coronary sinus blood levels of aldolase following arrest and after cooling and arrest at various levels of hypothermia.
normothermic
Pig. 12.—Changes in coronary sinus blood levels of phosphohexase isomerase following normothermic arrest and after cooling and arrest at various levels of hypothermia.
400
PRE-COOLING « LEUCINE PRE-ARREST CH AMINOPEPTIDASE POST-ARREST * NORMAL RANGE: 100- 310 UNITj]
PRE-COOLING WM ACETYL I I CHOUNESTERASE PRE-ARREST POST-ARREST ^ H NORMAL RANGE! 130 - 260 UNITS
350 300 250 200 I 50
13
37*K
30*K
Fig. 13.—Changes in coronary sinus blood levels of leucine aminopeptidase normothermic arrest and after cooling and arrest a t various levels of hypothermia. Fig. 14.—Changes in coronary sinus blood levels of acetyl cholinesterase normothermic arrest and after cooling and arrest at various levels of hypothermia.
following following
Rectal and direct myocardial temperatures and arterial and venous pressures were monitored continuously. Rates of cooling varied from 1° to 2° C. per minute. Perfusion rates ranged from 60 to 100 ml. per kilogram per minute. Blood samples were obtained from the following sources at five intervals: (1) oxygenated pump blood before perfusion; (2) pre-perfusion sample—from the superior vena cava upon opening the chest; (3) pre-cooling sample—from the coronary sinus immediately following cannulation; (4) pre-arrest sample—from the coronary sinus after the desired level of hypothermia had been attained;
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and (5) post-arrest sample—from the coronary sinus immediately following release of the aortic clamp after 30 minutes of cardiac arrest. The following determinations were made on each blood sample: (1) blood pH, (2) carbon dioxide content, 8 (3) oxygen saturation, 8 (4) blood glucose,9 (5) lactic acid,10 (6) pyruvic acid,11 (7) glutamic oxaloacetic transaminase, 12 (8) glutamic pyruvic transaminase, 13 (9) lactic dehydrogenase, 13 (10) malic dehydrogenase, 13 (11) aldolase," (12) phosphohexose isomerase,15 (13) leucine aminopeptidase, 16 and (14) acetyl cholinesterase.17 The results are shown in Figs. 1 through 14. DISCUSSION
Even though deep hypothermia has certain advantages, it is productive of metabolic acidosis.5- "•18 This selective study of coronary sinus blood confirmed the occurrence of myocardial metabolic acidosis under the conditions of these experiments. The metabolic acidosis was of comparable severity after temporary interruption of the coronary circulation when deep hypothermia (10° C. coldarrest group) was used as there was with potassium arrest at 37° C. In the 10° C. cold-arrest group, restoration of coronary flow after a 30 minute arrest produced a coronary sinus blood pH fall to 7.15 and a lactic acid rise to 68 mg. per cent. Less marked acidosis occurred in the 30° and 20° C. groups. These changes in coronary sinus blood occurred following cardiac arrest in all groups except the 10° C. cold-arrest dogs in which metabolic acidosis developed also during the cooling phase. It was expected that the coronary sinus blood would be acidotic after interruption of coronary flow in the normothermic dogs. This is due to the accumulation of anaerobic glycolysis products during the period of myocardial anoxia. Lactic acid is the principal product of the anaerobic process,19 the lowered p H being inversely related to the rise in lactic acid. However, with the reduced myocardial metabolism produced by hypothermia, one would not expect such marked myocardial acidosis. One would assume that the deeper the hypothermia, the less the acidosis. Contrary results were obtained from the lactic acid and p H data of the 10° C. cold-arrest dogs. Several factors may be responsible for this finding. First, during cooling there would be a shift to the left in the oxygen-hemoglobin dissociation curve that would make less oxygen available to the tissues. However, this would be partially offset by a shift to the right caused by the acidosis.20 Differential cooling6 may be an important factor contributing to the metabolic acidosis. During rapid total-body cooling, there is a temperature lag in certain regions. The skeletal muscle mass may be as much as 10° C. warmer than the myocardium. This will produce acidosis in those tissues with the greater oxygen demand. In the present study, during rapid cooling, differences between the myocardial and rectal temperatures varied from 7° to 12° C , but the two temperatures were essentially equal when the aorta was cross-clamped. A third factor which contributed to the myocardial metabolic acidosis in the 10° C. cold-arrest group is that, even at 10° C , there is still a basic oxygen
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need and when coronary flow is interrupted, the resulting anaerobic cellular metabolism causes an accumulation of glycolytic products and an oxygen debt.18 Ventricular fibrillation is another factor which probably contributed to acidosis. In the 10° C. cold-arrest dogs, acidosis developed during the cooling phase in contrast to the other groups in which acidosis occurred principally after arrest. There was a high incidence of ventricular fibrillation during cooling of the 10° C. cold-arrest dogs, whereas fibrillation seldom occurred during cooling in the other groups. This would suggest that the relative increase in oxygen consumption associated with ventricular fibrillation contributes to acidosis at lower temperatures. Edwards and associates21 have stated that hypothermia does not result in a discrepancy between myocardial oxygen demand and supply. However, in our 10° C. cold-arrest dogs, metabolic acidosis of the coronary sinus blood developed in the face of adequate coronary perfusion with well-oxygenated blood. The high oxygen content of the coronary sinus blood suggests that hypothermia alters myocardial cellular function in such a manner that the cell is unable to utilize the available oxygen. The accumulation of anaerobic glycolysis products also indicates that the metabolic demands of the myocardium are unsatisfied by the usual oxidative process. Increased oxygen consumption, in the normothermic group while on cardiopulmonary bypass prior to arrest, is in agreement with results found by Wallace.22 The reduction in oxygen consumption, as shown in the hypothermic groups, has been well documented. There were no consistent significant changes in glucose levels in the hypothermic groups. In the 37° C. potassium-arrest group there was a marked elevation following arrest. This suggests poor utilization of glucose by the myocardium while in the hypoxic state. Similar findings have been reported by Michel23 in regard to lactate. Enzyme Metabolism—Transaminases.—Serum transaminases catalyze the intermolecular transfer of amino groups from amino acids to keto acids. There are two major transaminating enzymes in heart muscle: glutamic-oxaloacetic transaminase and glutamic-pyruvic transaminase. These enzymes are present in lesser concentration in skeletal muscle, brain, liver, and kidney. Serum glutamic oxaloacetic transaminase (SGOT) levels are significantly elevated following myocardial injury. This was reported by La Due and associates24 and Agress. 25 It has since been confirmed by numerous authors. SGOT elevation is the most specific enzyme change associated with myocardial damage. 26 While it is true that elevated SGOT levels have been reported following major abdominal surgery, cardiac surgery and the use of cardiopulmonary bypass, it should be emphasized that these changes were not immediate and did not develop until several hours after the surgical procedure. This study is concerned only with the changes which occur during cooling or during the 30 minutes of coronary flow interruption. In the present study, the lowest elevations were found in the 20° and 10° C. cold-arrest groups. The cooling process did not have any appreciable effect on
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SGOT levels. That cooling may have a protective effect is contradicted by Blair 27 who found that elevated levels of SGOT followed prolonged periods of hypothermia. He reported significant changes after periods of surface cooling up to 12 hours in duration. Snyder 28 reported a correlation between the degree of SGOT elevation and length of time on bypass. This was not confirmed in this study, since the 10° C. cold-arrest group was on bypass for the longest period of time and had the lowest SGOT levels. The two potassium-arrest groups had higher levels of SGOT than the coldarrest groups. This suggests that the harmful effects of potassium arrest, now well documented in the literature, 29 ' 30 is a cause of enzyme elevation. Elevated SGOT levels following potassium arrest agree with the findings of Quinn and associates.31 The results in this study indicate that SGPT is a less sensitive test than SGOT. The fact that the dehydrogenases had higher levels at 10° C. suggests that they are less depressed by cold. Aldolase behaved as expected with the lower values occurring with cold. The response of other enzymes were not particularly informative. CONCLUSIONS
Myocardial metabolic acidosis results from tissue hypoxia that follows temporary interruption of coronary flow even when hypothermia is used. The acidosis is less at moderate levels of cooling (20° C.). However, severe metabolic acidosis may develop if the hypothermia reaches 10° C. Temporary coronary flow interruption produced less disturbance in the coronary sinus blood p H and lactic acid values during hypothermic arrest at 20° C. than at 30° C. or 10° C. Paradoxically, the p H was most pronouncedly lowered when the hearts were cooled to 10° C , suggesting the presence of significant anaerobic metabolism and the development of an oxygen debt. In this group, immediately following restoration of coronary circulation, the coronary sinus blood was highly saturated with oxygen. The oxygen debt indicated by the marked acidosis should have produced lowering of oxygen saturation. Perhaps the severely cooled myocardial cell was unable to utilize oxygen because of impairment of its enzyme system. Some of the enzyme values were low while others were unaffected, suggesting that the levels of cold used in these experiments does not have an equal effect on all enzymes. Higher enzyme values were always obtained whenever potassium citrate was added to the arrest procedure. This suggests that the drug itself has a specific injurious effect. SUMMARY
1. Changes in the coronary sinus blood were studied after a 30 minute interval of cardiac arrest. Hypothermia-induced arrests at 20° C. and 10° C. were compared with each other and with potassium citrate-induced arrest at normothermia (37° C.) and at 30° C. and 20° C. 2. Metabolic acidosis occurred in all groups, but it was most marked with cold arrest at 10° C. and whenever potassium citrate was used.
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3. Anaerobic metabolism producing an oxygen debt occurred even with 10° C. cold-induced arrest. Immediately following restoration of coronary circulation, the coronary sinus blood remained fully saturated suggesting that the myocardial cells were unable to use the available oxygen. This may be due to depression of this enzyme system. 4. The enzyme levels in the coronary sinus blood were usually decreased by cold, but a few appeared to be unaffected. This suggests that all the enzyme systems are not depressed equally by the hypothermic levels used in these experiments. REFERENCES
1. Gollan, F., Grace, J. T., Schell, M. W., Tysinger, D. S., and Feaster, L. B . : Left Heart Surgery in Dogs During Respiratory and Cardiac Arrest at Body Temperatures Below 10° C , Surgery 3 8 : 363, 1955. 2. Young, W. G., Sealy, W. C , Brown, I. W., Jr., Smith, W., Calloway, H. A., and Harris, J . S.: Metabolic and Physiologic Observations on Patients Undergoing Extracorporeal Circulation in Conjunction "With Hypothermia, Surgery 46: 175, 1959. 3. Dubost, C , and Blondeau, P . : The Association of the Artificial Heart-Lung With Deep Hypothermia in Open H e a r t Surgery, J . Cardiov. Surg. 1 : 85, 1960. 4. Sealy, W. C , Young, W. G., Brown, I. W., Smith, W. W., and Lesage, A. M.: Profound Hypothermia Combined With Extracorporoal Circulation for Open Heart Surgerv, Surgery 48: 432, 1960. 5. Stephen, C. R., Dent, S., Sealy, W. C , and Hull, K . : Anesthetic and Metabolic Factors Associated With Combined Extracorporeal Circulation and Hypothermia, Am. J . Cardiol. 6 : 737, 1960. 6. Neville, W. E., Kameya, S., Oz, M., Bloor, B., and Clowes, G. H. A., J r . : Profound Hypothermia and Complete Circulation Interruption, A. M. A. Arch. Surg. 82: 108, 1961. 7. Brown, I . W., Smith, W. W., and Emmons, W. O.: An Efficient Blood Heat Exchanger for Use With Extracorporeal Circulation, Surgery 44: 372, 1958. 8. Van Slyke, D. D., and Neil, J . M.: Determination of Gasses in Blood and Other Solutions by Vacuum Extraction and Manometric Measurement, J . Biol. Chem. 6 1 : 523, 1924. 9. Hagedorn, H . C , and Jensen, B . N . : Zur Microbestimmung des Blutzuckers Mittels Ferrieyanid, Biochcm. Ztschr. 135: 46, 1923. 10. Barker, S. B., and Summerson, W. A.: Colorimetric Determination of Lactic Acid in Biological Material, J . Biol. Chem. 138: 535, 1941. 11. Friedemann, T. E., and Haugcn, G. E . : Pyruvic Acid: Determination of Keto Acids in Blood and Urine, J . Biol. Chem. 147: 415, 1943. 12. Karman, A. J., Wroblewski, F., and La Due, J. S.: Transaminase Activitv in Human Blood, Clin. Invest. 34: 126, 1955. 13. Wroblewski, F., and Cabaud, P . : Colorimetric Measurement of Serum Glutamic Pyruvic Transaminase, Am. J . Clin. Path. 2 7 : 235, 1957. 14. Beisenherz, G., Bucher, T., and Garbade, K . : Methods of Enzymology. I, edited by S. P . Colowich and N. O. Kaplan, New York, 1955, Academic Press, Inc. 15. Bodansky, M., and Bodansky, O.: Serum Phosphohexose Isomerase in Cancer. I . Method of Determination and Establishment of Normal Values, Cancer 7 : 1191, 1954. 16. Goldberg, J . A., and Rutenberg, A. M.: The Colorimetric Determination of Leucine Aminopeptidase in Urine and Serum of Normal Subject and Patients With Cancer and Other Diseases, Cancer 11: 283, 1958. 17. De la Huerga, J., Yesinick, G., and Popper, H . : Colorimetric Method for the Determination of Serum Cholinesterase, Am. J . Clin. Path. 2 2 : 1126, 1952. 18. Padhi, R., and Rainbow, R.: Some Observations on Deep Hypothermia Using Extracorporeal Circulation, Angiology 12: 12, 1961. 19. Litwin, M. S., Panico, F . G., Rubini, C , Harken, D. E., and Moore, F . D . : Acidosis and Lactic Acidemia in Extracorporeal Circulation, Ann. Surg. 149: 188, 1959. 20. Best, C. H., and Taylor, N . B . : The Physiological Basis of Medical Practice, ed. 7, Baltimore, 1961, Williams & Wilkins Co. 21. Edwards, W. S., Tuluy, S., Reber, W. E., Siegel, A., and Bing, R. J . : Coronary Blood Flow and Myocardial Metabolism in Hypothermia, Ann. Surg. 139: 275, 1954. 22. Wallace, H. W . : Cardiac Metabolism, New England J . Med. 261: 26, 1959.
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23. Michel, G., Beuren, A., Hagancamp, C. E., and Bing, E. J . : Effect of Interruption of Coronary Circulation on Metabolism of Arrested Heart, Am. J . Physiol. 195: 417, 1958. 24. L a Due, J . S., Wroblewski, F., and Karman, A.: Serum Glutamic Oxaloacetic Transaminase Activity in Human Acute Transmural Myocardial Infarction, Science 120: 497, 1954. 25. Agress, C. M.: Evaluation of the Transaminase Test, Am. J . Cardiol. 3 : 74, 1959. 26. Hamolsky, M., and Kaplan, N . : Measurements of Enzymes in the Diagnosis of Acute Myocardial Infarction, Circulation 2 3 : 102, 1961. 27. Blair, E., Hook, R., and Bunce, G.: Serum Glutamic Oxaloacetic Transaminase Content in Hypothermia, Science 133: 105, 1961. 28. Snyder, D. D., Barnard, C. N., Varco, R. L., and Lillihei, C. W . : Serum Transaminase Patterns Following Intracardiac Surgery, Surgery 44: 1083, 1958. 29. Helmsworth, J . A., Kaplan, S., Clark, L. C , Jr., McAdams, A. J., Matthews, E. C , and Edwards, F . K . : Myocardial Injury Associated With Asystole Induced With Potassium Citrate, Ann. Surg. 149: 200, 1959. 30. Greenberg, J . J., Edmunds, L. H., and Brown, R. B . : Myocardial Metabolism and Postarrest Function in the Cold and Chemically Arrested Heart, Surgery 48: 31, 1960. 31. Quinn, J . W., Sirak, H. D., Shabanah, E. H., and Frajola, W. J . : Transaminase Values Following Open-Heart Surgery, Ann. Surg. 152: 45, 1960. (For Discussion,
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