Myocardial Changes in Malignant Hyperthermia John J. Fenoglio, Jr., MD, Maj, MC, USA, and Nelson S. Irey, MD
Although consideral information is available concerning the structural and biochemical changes in the skeletal muscles of patients with malignant hyperthemia, little is known of the cardiac changes in this disease. However, ventricular fibrillation and cardiac arrest are frequent in these patients. In 3 patients with malignant hyperthermia, contraction bands and foci of myofiberlysis were found in the heart at necropsy. Ultrastructurally, areas of mvofiber overstretching adjacent to contraction bands and foci of extensive myofiberlysis were associated with disruptions of the sarcolemma. Similar ultrastructural findings have been reported in the skeletal muscles of these patients and are thought responsible for the hyperkalemia which is a constant feature of malignant hvperthermia. Our findings suggest that the ventricular arrhythmias, frequent in this disease, are the result of direct damage to cardiac muscle rather than secondary to elevated plasma levels of potassium. (Am J Pathol 89:51-58, 1977)
MALIGNANT HYPERTHERMIA is a rare condition characterized by fever and muscle rigidity during general anesthesia. The mortality rate is extremely high, 64% in the recent survey of Britt et al.,I and in the majority of patients death is the result of cardiac arrest. Ventricular tachvcardias are recorded in 72% and cardiac arrhvthmias are noted in 36% of patients with malignant hyperthermia. In spite of these findings and the frequent statements in the literature that patients with malignant hvperthermia often die in ventricular fibrillation,' little attention has been paid to morphologic changes in the heart. Although extensive investigations of the ultrastructural and biochemical changes in the skeletal muscles of these patients have been published,2A no description of cardiac ultrastructure in malignant hyperthermia is available. The purpose of this report is to report the changes, especially the ultrastructural ones, in the myocardium of patients with malignant hyperthermia. These alterations in myocardial structure reflect alterations in mvocardial biochemistrv and, we believe, are crucial to the understanding and effective treatment of this disease. From the Department of Cardiovascular Pathologp and the Registrv of Tissue Reactions to Drugs. -krmed Forces Institute of Pathology. Washington, DC The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the view-s of the Department of the Arms or of Defense or of the sponsors of the Registry of Tissue Reactions to Drugs. The Registry of Tissue Reactions to Drugs is sponsored by the Food and Drug Akdministration (under Contract FDA 223-73-3178), Department of Health, Education, and Welfare. and b%- the Armed Forces Institute of Pathologp. Accepted for publication May 30, 1977. Address reprint requests to Dr Nelson S. Irev, Division of Tissue Reactions to Drugs, Armed Forces Institutes of Pathology. Washington, DC 20(306. 51
52
FENOGLIO AND IREY
American Journal of Pathology
Materials and Methods Three patients with proven malignant hvperthermia and complete clinical histories, autopsy protocols, and tissue from the heart or the gross heart were selected from the files of the Armed Forces Institute of Pathology for this study. Case Histories Case 1
This 22-year-old white male was admitted to the hospital with the clinical picture of acute appendicitis. The patient was given Demerol, atropine, and Thorazine and taken to the operating room. During the operation, succinyl chloride was administered by intravenous drip, and the patient experienced severe generalized muscle fasciculations. This subsided, and the operation was continued. Tachycardia was noted at the beginning of the anesthesia (120 beats/min), and the patient's pulse rose to 144 shortly after the first incision was made. Temperature was not monitored during the operation, but at termination of the procedure, the patient's temperature was noted to be over 106 F. The hyperpyrexia persisted and was followed by hypotension, shock, and coma. The patient expired about 3 hours after leaving the operating room. His terminal temperature was 102 F. At autopsy the heart was of normal size and configuration. Several small hemorrhages noted on the pericardium measured up to 0.2 cm in diameter, and were located mainly along the distribution of the left anterior descending coronary artery. On sectioning the posterior papillary muscles, a small ill-defined area of reddening about 0.3 cm in diameter was noted. The aorta was unremarkable, and the coronary arteries are free of atherosclerosis. The cardiac valves appeared normal. The lungs were congested but otherwise unremarkable. Case 2
This 42-year-old white female developed jaw rigidity 1 hour after she had received preliminary hypnotics for surgery. She was administered Pentothal sodium, nitrous oxide, halothane, and Sucrostin, and a gynecologic pelvic examination was done. During the course of this examination she developed an irregular pulse, with premature ventricular contractions, and surgery was then cancelled. After anesthesia, the serum creatine phosphokinase and the serum SGOT levels were found to be markedly elevated. She was readmitted for surgery, and appeared to tolerate this procedure (a 1-hour operation). However, on the patient's arrival in the recovery room, her lips were cyanotic and her temperature rectally was 104 F. An irregular pulse and respiratory depression were also present. She was unconscious throughout the postoperative period. Treatment of the cardiac arrhythmias, acidosis, and hyperpyrexia over the next hour and a half was of no avail. At autopsy the heart weighed 210 g. The external surface and cardiac valves were not remarkable. The left ventricular wall measured 1.2 cm and the right ventricular wall, 0.3 cm in thickness. The myocardium was reddish-brown and homogeneous, without evidence of hemorrhage or fibrosis. The coronary arteries were patent and free of atherosclerosis. The remainder of the autopsy was unremarkable. Case 3 This 24-year-old white male was admitted to the hospital complaining of abdominal pain, which finally localized to the right lower quadrant. Physical examination revealed rebound pain and tenderness in the right lower quadrant. An appendectomy was performed under general anesthesia. Immediately after the operation, the patient's temperature rose to 108 F. His blood pressure was 180/110 mm Hg. Tachycardia (to 140 beats/
Vol. 89, No. 1 October 1977
MALIGNANT HYPERTHERMIA
53
min) and occasional premature ventricular contractions were noted. The patient suddenly became hvpotensise, and he suffered cardiac arrest. At autopsy. the heart w-eighed 310 g and was of normal size and shape. The heart valsves were normal. The mvocardium w-as red-brown and homogeneous and without evidence of hemorrhage or fibrosis. The coronarv arteries were patent and free of atherosclerosis. The lungs were congested but otheru-ise unremarkable.
Tssue Techniques Multiple blocks w-ere taken from the formalin-fixed cardiac tissue of each patient and included blocks from both atria and ventricles. Selected blocks were cut to include the distal subendocardial Purkinje cell network and or the bundle branches. The major conduction system (atrioventricular node, His bundle, and right and left bundle branches) %vas excised en bloc and cut in serial sections. All tissue u-as embedded in paraffin. Sections w-ere cut at 4 u thickness and stained with hematoxvlin and eosin, the Movat pentachrome stain, and phosphotungstic acid-hematoxylin. The five blocks from the conduction svstem w-ere seriallv sectioned, collecting every 25th section. In each case, tissue was taken from the formalin-fixed heart for electron microscopy. Representative blocks were taken from the ventricular septum, left ventricular free w-all, anterior papillary muscle, right ventricular free wall, and both atria. In addition, blocks were taken from the subendocardium of the ventricular septum to include the subendocardial Purkinje netmvork.2 These blocks w-ere processed to preserve the endocardium.5 The tissue blocks X ere rinsed in phosphate buffer, pH 7.4. refixed in 2% phosphatebuffered (pH 7.4) osmium tetroxide, and embedded in Epon 812. Thick sections (I1 ) were cut on glass knises and stained with toluidine blue, and thin sections were cut on diamond knives and stained with uran\l acetate and lead citrate."
ResuKts Light Microp
There Xwere extensive areas of m ofibrolvsis throughout the heart in all :3 cases. These areas of mN ofiber clearing alternated with areas of contraction bands (Figure IA) and were especially prominent in the Purkinje fibers of the distal bundle branches and subendocardial Purkinje network; they were also present in both atria and ventricles. At higher magnification, areas of cytoplasmic clearing were striking and there were apparent breaks in the sarcolemma (Figure IB). The mvofibers were widely separated by edema fluid, but inflammatorv cells were absent in spite of apparent focal distributions of the sarcolemma. There was no evidence of significant coronary artery disease (luminal obstruction 30% or greater) in any of our patients. The major conduction system was traced in over 100 sections from each heart. No evidence of fibrosis in the distribution of the conduction pathways was apparent in the atrioventricular node or His bundle by light microscopy. Ultrastucture
Contraction bands were dramatically visualized by electron microscopy. The areas of contraction (Figure 2) were confined to single mvo-
54
FENOGLIO AND IREY
American Journal of Pathology
fibers and were sharply delimited by the intercalated discs. Sarcomeres in adjacent myofibers, separated from the areas of contraction by the intercalated disc, were markedly overstretched. I bands and H zones were prominent in overstretched myofibers, and Z bands were no longer in registry (Figure 2). Away from areas of marked contraction, foci of loss of myosin, and actin filaments, were seen. Many of these foci were so extensive that only fragments of the sarcomere remained, and there was an apparent aggregation of mitochondria (Figure 3). In other areas, thick and thin filaments appeared lysed from single, scattered sarcomeres, while the surrounding sarcomeres appeared normal and were in register. Focal disruptions of the sarcolemma were found, especially in areas of extensive myocytolysis and overstretched myofibers (Figure 4). The intercalated discs appeared normal throughout the material examined. These ultrastructural changes were observed in atrial and ventricular myocardial cells as well as in subendocardial Purkinje fibers from the left ventricular septum. We are unable to comment on the sarcoplasmic tubular system, the mitochondria, or the nuclei because of the nature of the fixation of our material; however, the alteration in fine structure observed in these structures was no more extensive than would be expected from autolysis. Discussion
The possibility that ischemia or autolysis is responsible for the ultrastructural changes in the myocardium of patients with malignant hyperthermia must be considered. Contraction bands are not seen in the center of an infarct 7-9 or in autolyzed myocardium,9- 1 although they are prominent when contracting cardiac muscle cells are cut and allowed to undergo unopposed contraction. In the early stages of ischemia and reversible injury and during the first hours of autolysis, the sarcomeres are uniformly relaxed, and I bands, H zones, and M bands are clearly identifiable. Contraction bands are present in a wide variety of types of cardiac injury 12 in association with myofibrillar degeneration or myofiberlysis. Ultrastructurally, myofiberlysis is characterized by dissolution of myofilaments, disruption of sarcomeres, and sarcolemmal breaks. Dissolution of myofilaments and disruption of sarcomeres can be observed following prolonged autolysis; however, even after 12 hours of autolysis, sarcolemmal breaks were not seen.13 The contraction bands and sarcolemmal breaks in the myocardium of patients with malignant hyperthermia are therefore not consistent with changes secondary to autolysis or ischemia. Similar myocardial ultrastructural changes have been described in potas-
Vol. 89, No. 1 October 1977
MALIGNANT HYPERTHERMIA
55
sium deficiency, hemorrhagic shock, and hypothermia.U2 In these conditions, the contraction bands and sarcolemmal breaks are associated with extensive myofiberlysis. Although it seems likely that the foci of myofiberlysis present in patients with malignant hyperthermia are also secondary to the disease process, we cannot exclude the possibility that myofiberlysis, in our material, is secondary to autolysis. Contraction bands and foci of myofiberlysis are a prominent ultrastructural feature of the skeletal muscle in patients with malignant hyperthermia,34 and the changes in the hearts of our patients are similar to those described in the skeletal muscles. The biochemical mechanisms which result in the structural changes have been partially elucidated in skeletal muscle.2'o There is a reduction in activity of sarcoplasmic ATPase, and the sarcoplasmic reticulum's ability to accumulate calcium is impaired. This defect is further impaired by the anesthetic. As a result, the concentration of myoplasmic calcium is increased, and myosin ATPase is stimulated, troponin is inhibited, and phosphorylase kinase is activated. A rapid catabolism of glycogen with a subsequent depletion of creatine phosphate stores results. This process is responsible for the myofibrillar contracture. In addition, ATPase production falls. ATPases are necessary to maintain sarcolemmal integrity and sarcomere structure. The relative lack of ATPases results in myofiber dissolution and disruption of the sarcolemma. Presumably this mechanism also applies to cardiac muscle and would account for the ultrastructural changes seen in these hearts. Recent developments in the therapy of malignant hyperthermia crisis have stressed the use of procainamide to lower myoplasmic calcium levels,15 and this mode of therapy has been successful in a number of patients. Procainamide also effectively elevates the threshold of the ventricular myocardium to electrically induced ventricular fibrillation. Ventricular arrhvthmias and, in particular, ventricular fibrillation, are important and frequently fatal complications of malignant hyperthermia. The disruption of the cardiac sarcolemma observed in these patients must result in large shifts in potassium, with increased extracellular and decreased intracellular potassium. Such shifts, both in the heart and skeletal muscles, are reflected in the hyperkalemia that is well recognized in these patients. Intracellular myocardial changes in potassium concentration and hyperkalemia are extremely important in the genesis of ventricular arrhythmias, as are intracellular shifts in calcium concentration. It would appear that the fatal ventricular fibrillation of patients with malignant hyperthermia maybe secondary to changes, both structural and biochemical, within the heart rather than secondary to changes in the levels of circulating Ca2+ and K+.
56
FENOGLIO AND IREY
American Journal of Pathology
References 1.
2. 3. 4. 5.
6. I.
8. 9. 10. 11.
12.
13. 14. 15.
Britt BA, Kalow W: Malignant hyperthermia: A statistical review. Can Anaesth Soc J 17:293-315, 1970 Britt BA, Kalow W: Malignant hyperthermia: Aetiology unknown. Can Anaesth Soc J 17:316-330, 1970 Isaacs H, Frere G, Mitchell J: Histological, histochemical and ultramicroscopic findings in muscle biopsies from carriers of the trait for malignant hyperpyrexia. Br J Anaesth 45:860-867, 1973 Reske-Nielsen E: Ultrastructpre of human muscle in malignant hyperthermia. Acta Pathol Microbiol Scand [A] 81 :585-587, 1973 Friedman PL, Fenoglio JJ Jr, Wit AL: Time course for reversal of electrophysiological and ultrastructural abnormalities in subendocardial Purkinje fibers surviving extensive myocardial infarction in dogs. Circ Res 36:127-144, 1975 Reynolds ES: The use of lead citrate at high pH as an electron opaque stain in electron microscopy. J Cell Biol 17:208-212, 1963 Bahr GF, Jennings RB: Ultrastructure of normal and asphyxic myocardium of the dog. Lab Invest 10:548-571, 1961 Jennings RB: Symposium on the pre-hospital phase of acute myocardial infarction. Part II. Early phase of nmyocardial ischemic injury and infarction. Am J Cardiol 24:753-765, 1969 Herdson PB, Kaltenbach JP, Jennings RB: Fine structural and biochemical changes in dog mvocardium during autolysis. Am J Pathol 57:539-557, 1969 Fenoglio JJ Jr, Albala A, Silva FG, Friedman PL, Wit AL: Structural basis of ventricular arrhythmias in human myocardial infarction: A hypothesis. Hum Pathol 7:547-563, 1976 Burch GE, Tsui CY, Harb JM: Postmortem chapges in the rat myocardium: A histologic and electron microscopic study. Pathol Microbiol 38:233-249, 1972 Ferrans VJ, Buja LM, Maron BJ: Myofibrillar abnormalities following cardiac muscle cell injurv. Pathophysiology and Morphology of Myocardial Cell Alterations: Recent Advances in 'Studies pp Cardiac Structure and Metabolism Series: Vol 6. Edited bv NI Fleckenstein. Baltimore, University Park Press, 1975, pp 367-382 Buja LM, Roberts WC: The coronary arteries and myocardium in acute myocardial infarction and shock: Pathologic aspects. Shock in Myocardial Infarction. Edited by RF Gunnar. New York, Grunt & Stratton, 1974, pp 1-21 Gordon RA, Britt BA, Kalow W (editors). Proceedings of the International Symposium on Malignant Hyperthermia. Springfield, Ill., Charles C Thomas, Publisher, 1973 Britt BA: Malignant hyperthermia: A pharmacogenetic disease of skeletal and cardiac muscle (editorial). N Engl J NIed 290:1140-1142, 1974
lB
Figur IA-Areas of myofibertysis (Ml) and contraction bands (arrows) in the left ventricular myocardium, alternating with areas of normal muscle in which distinct cross-gtriations are dlearly seen (Toluidine blue, X 305). B-High magnification of anarea of contraction bands (C)ywnVmyofibertysis (M); there is apparent disruption of the cell membrane (arrow) in an area of extensive myofiber clearing (Toluidine blue, X 750). Figure 2-The contraction bands (C) involve entire myofibers and a're sharply deliminated by the intercalated disc (arrows). The intercalated discs are intact. The myofibers adjacent to contraction bands are overstretched, and sarcomeres are no longer in register. T = mitochondria, Z = Z band. (x 5775)
4
Figure 3-Focal areas of overstretched sarcomeres are frequent in the center of otherwise normal myofibers Many of the sarcomeres in these areas are disrupted (arrows) and aggregates of mitochondria (T) are promi nent. Z = Z band. (x 5775) Figure 4-In areas of markedly overstretched sarcomeres adjacent to contractior bands (C), the Z bands (Z) are distorted and not in register, and sarcomeres are disrupted (arrow). Areas o complete lysis of myofilaments appear replaced by aggregates of mitochondria (T). D = intercalated disc. (> 5775) Inset-Breaks (arrows) in the sarcolemma (S) are frequent in overstretched myofibers (X 24,870)
Although consideral information is available concerning the structural and biochemical changes in the skeletal muscles of patients with malignant hyperthemia, little is known of the cardiac changes in this disease. However, ventricular fibrillation and cardiac arrest are frequent in these patients. In 3 patients with malignant hyperthermia, contraction bands and foci of myofiberlysis were found in the heart at necropsy. Ultrastructurally, areas of mvofiber overstretching adjacent to contraction bands and foci of extensive myofiberlysis were associated with disruptions of the sarcolemma. Similar ultrastructural findings have been reported in the skeletal muscles of these patients and are thought responsible for the hyperkalemia which is a constant feature of malignant hvperthermia. Our findings suggest that the ventricular arrhythmias, frequent in this disease, are the result of direct damage to cardiac muscle rather than secondary to elevated plasma levels of potassium. (Am J Pathol 89:51-58, 1977)
MALIGNANT HYPERTHERMIA is a rare condition characterized by fever and muscle rigidity during general anesthesia. The mortality rate is extremely high, 64% in the recent survey of Britt et al.,I and in the majority of patients death is the result of cardiac arrest. Ventricular tachvcardias are recorded in 72% and cardiac arrhvthmias are noted in 36% of patients with malignant hyperthermia. In spite of these findings and the frequent statements in the literature that patients with malignant hvperthermia often die in ventricular fibrillation,' little attention has been paid to morphologic changes in the heart. Although extensive investigations of the ultrastructural and biochemical changes in the skeletal muscles of these patients have been published,2A no description of cardiac ultrastructure in malignant hyperthermia is available. The purpose of this report is to report the changes, especially the ultrastructural ones, in the myocardium of patients with malignant hyperthermia. These alterations in myocardial structure reflect alterations in mvocardial biochemistrv and, we believe, are crucial to the understanding and effective treatment of this disease. From the Department of Cardiovascular Pathologp and the Registrv of Tissue Reactions to Drugs. -krmed Forces Institute of Pathology. Washington, DC The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the view-s of the Department of the Arms or of Defense or of the sponsors of the Registry of Tissue Reactions to Drugs. The Registry of Tissue Reactions to Drugs is sponsored by the Food and Drug Akdministration (under Contract FDA 223-73-3178), Department of Health, Education, and Welfare. and b%- the Armed Forces Institute of Pathologp. Accepted for publication May 30, 1977. Address reprint requests to Dr Nelson S. Irev, Division of Tissue Reactions to Drugs, Armed Forces Institutes of Pathology. Washington, DC 20(306. 51
52
FENOGLIO AND IREY
American Journal of Pathology
Materials and Methods Three patients with proven malignant hvperthermia and complete clinical histories, autopsy protocols, and tissue from the heart or the gross heart were selected from the files of the Armed Forces Institute of Pathology for this study. Case Histories Case 1
This 22-year-old white male was admitted to the hospital with the clinical picture of acute appendicitis. The patient was given Demerol, atropine, and Thorazine and taken to the operating room. During the operation, succinyl chloride was administered by intravenous drip, and the patient experienced severe generalized muscle fasciculations. This subsided, and the operation was continued. Tachycardia was noted at the beginning of the anesthesia (120 beats/min), and the patient's pulse rose to 144 shortly after the first incision was made. Temperature was not monitored during the operation, but at termination of the procedure, the patient's temperature was noted to be over 106 F. The hyperpyrexia persisted and was followed by hypotension, shock, and coma. The patient expired about 3 hours after leaving the operating room. His terminal temperature was 102 F. At autopsy the heart was of normal size and configuration. Several small hemorrhages noted on the pericardium measured up to 0.2 cm in diameter, and were located mainly along the distribution of the left anterior descending coronary artery. On sectioning the posterior papillary muscles, a small ill-defined area of reddening about 0.3 cm in diameter was noted. The aorta was unremarkable, and the coronary arteries are free of atherosclerosis. The cardiac valves appeared normal. The lungs were congested but otherwise unremarkable. Case 2
This 42-year-old white female developed jaw rigidity 1 hour after she had received preliminary hypnotics for surgery. She was administered Pentothal sodium, nitrous oxide, halothane, and Sucrostin, and a gynecologic pelvic examination was done. During the course of this examination she developed an irregular pulse, with premature ventricular contractions, and surgery was then cancelled. After anesthesia, the serum creatine phosphokinase and the serum SGOT levels were found to be markedly elevated. She was readmitted for surgery, and appeared to tolerate this procedure (a 1-hour operation). However, on the patient's arrival in the recovery room, her lips were cyanotic and her temperature rectally was 104 F. An irregular pulse and respiratory depression were also present. She was unconscious throughout the postoperative period. Treatment of the cardiac arrhythmias, acidosis, and hyperpyrexia over the next hour and a half was of no avail. At autopsy the heart weighed 210 g. The external surface and cardiac valves were not remarkable. The left ventricular wall measured 1.2 cm and the right ventricular wall, 0.3 cm in thickness. The myocardium was reddish-brown and homogeneous, without evidence of hemorrhage or fibrosis. The coronary arteries were patent and free of atherosclerosis. The remainder of the autopsy was unremarkable. Case 3 This 24-year-old white male was admitted to the hospital complaining of abdominal pain, which finally localized to the right lower quadrant. Physical examination revealed rebound pain and tenderness in the right lower quadrant. An appendectomy was performed under general anesthesia. Immediately after the operation, the patient's temperature rose to 108 F. His blood pressure was 180/110 mm Hg. Tachycardia (to 140 beats/
Vol. 89, No. 1 October 1977
MALIGNANT HYPERTHERMIA
53
min) and occasional premature ventricular contractions were noted. The patient suddenly became hvpotensise, and he suffered cardiac arrest. At autopsy. the heart w-eighed 310 g and was of normal size and shape. The heart valsves were normal. The mvocardium w-as red-brown and homogeneous and without evidence of hemorrhage or fibrosis. The coronarv arteries were patent and free of atherosclerosis. The lungs were congested but otheru-ise unremarkable.
Tssue Techniques Multiple blocks w-ere taken from the formalin-fixed cardiac tissue of each patient and included blocks from both atria and ventricles. Selected blocks were cut to include the distal subendocardial Purkinje cell network and or the bundle branches. The major conduction system (atrioventricular node, His bundle, and right and left bundle branches) %vas excised en bloc and cut in serial sections. All tissue u-as embedded in paraffin. Sections w-ere cut at 4 u thickness and stained with hematoxvlin and eosin, the Movat pentachrome stain, and phosphotungstic acid-hematoxylin. The five blocks from the conduction svstem w-ere seriallv sectioned, collecting every 25th section. In each case, tissue was taken from the formalin-fixed heart for electron microscopy. Representative blocks were taken from the ventricular septum, left ventricular free w-all, anterior papillary muscle, right ventricular free wall, and both atria. In addition, blocks were taken from the subendocardium of the ventricular septum to include the subendocardial Purkinje netmvork.2 These blocks w-ere processed to preserve the endocardium.5 The tissue blocks X ere rinsed in phosphate buffer, pH 7.4. refixed in 2% phosphatebuffered (pH 7.4) osmium tetroxide, and embedded in Epon 812. Thick sections (I1 ) were cut on glass knises and stained with toluidine blue, and thin sections were cut on diamond knives and stained with uran\l acetate and lead citrate."
ResuKts Light Microp
There Xwere extensive areas of m ofibrolvsis throughout the heart in all :3 cases. These areas of mN ofiber clearing alternated with areas of contraction bands (Figure IA) and were especially prominent in the Purkinje fibers of the distal bundle branches and subendocardial Purkinje network; they were also present in both atria and ventricles. At higher magnification, areas of cytoplasmic clearing were striking and there were apparent breaks in the sarcolemma (Figure IB). The mvofibers were widely separated by edema fluid, but inflammatorv cells were absent in spite of apparent focal distributions of the sarcolemma. There was no evidence of significant coronary artery disease (luminal obstruction 30% or greater) in any of our patients. The major conduction system was traced in over 100 sections from each heart. No evidence of fibrosis in the distribution of the conduction pathways was apparent in the atrioventricular node or His bundle by light microscopy. Ultrastucture
Contraction bands were dramatically visualized by electron microscopy. The areas of contraction (Figure 2) were confined to single mvo-
54
FENOGLIO AND IREY
American Journal of Pathology
fibers and were sharply delimited by the intercalated discs. Sarcomeres in adjacent myofibers, separated from the areas of contraction by the intercalated disc, were markedly overstretched. I bands and H zones were prominent in overstretched myofibers, and Z bands were no longer in registry (Figure 2). Away from areas of marked contraction, foci of loss of myosin, and actin filaments, were seen. Many of these foci were so extensive that only fragments of the sarcomere remained, and there was an apparent aggregation of mitochondria (Figure 3). In other areas, thick and thin filaments appeared lysed from single, scattered sarcomeres, while the surrounding sarcomeres appeared normal and were in register. Focal disruptions of the sarcolemma were found, especially in areas of extensive myocytolysis and overstretched myofibers (Figure 4). The intercalated discs appeared normal throughout the material examined. These ultrastructural changes were observed in atrial and ventricular myocardial cells as well as in subendocardial Purkinje fibers from the left ventricular septum. We are unable to comment on the sarcoplasmic tubular system, the mitochondria, or the nuclei because of the nature of the fixation of our material; however, the alteration in fine structure observed in these structures was no more extensive than would be expected from autolysis. Discussion
The possibility that ischemia or autolysis is responsible for the ultrastructural changes in the myocardium of patients with malignant hyperthermia must be considered. Contraction bands are not seen in the center of an infarct 7-9 or in autolyzed myocardium,9- 1 although they are prominent when contracting cardiac muscle cells are cut and allowed to undergo unopposed contraction. In the early stages of ischemia and reversible injury and during the first hours of autolysis, the sarcomeres are uniformly relaxed, and I bands, H zones, and M bands are clearly identifiable. Contraction bands are present in a wide variety of types of cardiac injury 12 in association with myofibrillar degeneration or myofiberlysis. Ultrastructurally, myofiberlysis is characterized by dissolution of myofilaments, disruption of sarcomeres, and sarcolemmal breaks. Dissolution of myofilaments and disruption of sarcomeres can be observed following prolonged autolysis; however, even after 12 hours of autolysis, sarcolemmal breaks were not seen.13 The contraction bands and sarcolemmal breaks in the myocardium of patients with malignant hyperthermia are therefore not consistent with changes secondary to autolysis or ischemia. Similar myocardial ultrastructural changes have been described in potas-
Vol. 89, No. 1 October 1977
MALIGNANT HYPERTHERMIA
55
sium deficiency, hemorrhagic shock, and hypothermia.U2 In these conditions, the contraction bands and sarcolemmal breaks are associated with extensive myofiberlysis. Although it seems likely that the foci of myofiberlysis present in patients with malignant hyperthermia are also secondary to the disease process, we cannot exclude the possibility that myofiberlysis, in our material, is secondary to autolysis. Contraction bands and foci of myofiberlysis are a prominent ultrastructural feature of the skeletal muscle in patients with malignant hyperthermia,34 and the changes in the hearts of our patients are similar to those described in the skeletal muscles. The biochemical mechanisms which result in the structural changes have been partially elucidated in skeletal muscle.2'o There is a reduction in activity of sarcoplasmic ATPase, and the sarcoplasmic reticulum's ability to accumulate calcium is impaired. This defect is further impaired by the anesthetic. As a result, the concentration of myoplasmic calcium is increased, and myosin ATPase is stimulated, troponin is inhibited, and phosphorylase kinase is activated. A rapid catabolism of glycogen with a subsequent depletion of creatine phosphate stores results. This process is responsible for the myofibrillar contracture. In addition, ATPase production falls. ATPases are necessary to maintain sarcolemmal integrity and sarcomere structure. The relative lack of ATPases results in myofiber dissolution and disruption of the sarcolemma. Presumably this mechanism also applies to cardiac muscle and would account for the ultrastructural changes seen in these hearts. Recent developments in the therapy of malignant hyperthermia crisis have stressed the use of procainamide to lower myoplasmic calcium levels,15 and this mode of therapy has been successful in a number of patients. Procainamide also effectively elevates the threshold of the ventricular myocardium to electrically induced ventricular fibrillation. Ventricular arrhvthmias and, in particular, ventricular fibrillation, are important and frequently fatal complications of malignant hyperthermia. The disruption of the cardiac sarcolemma observed in these patients must result in large shifts in potassium, with increased extracellular and decreased intracellular potassium. Such shifts, both in the heart and skeletal muscles, are reflected in the hyperkalemia that is well recognized in these patients. Intracellular myocardial changes in potassium concentration and hyperkalemia are extremely important in the genesis of ventricular arrhythmias, as are intracellular shifts in calcium concentration. It would appear that the fatal ventricular fibrillation of patients with malignant hyperthermia maybe secondary to changes, both structural and biochemical, within the heart rather than secondary to changes in the levels of circulating Ca2+ and K+.
56
FENOGLIO AND IREY
American Journal of Pathology
References 1.
2. 3. 4. 5.
6. I.
8. 9. 10. 11.
12.
13. 14. 15.
Britt BA, Kalow W: Malignant hyperthermia: A statistical review. Can Anaesth Soc J 17:293-315, 1970 Britt BA, Kalow W: Malignant hyperthermia: Aetiology unknown. Can Anaesth Soc J 17:316-330, 1970 Isaacs H, Frere G, Mitchell J: Histological, histochemical and ultramicroscopic findings in muscle biopsies from carriers of the trait for malignant hyperpyrexia. Br J Anaesth 45:860-867, 1973 Reske-Nielsen E: Ultrastructpre of human muscle in malignant hyperthermia. Acta Pathol Microbiol Scand [A] 81 :585-587, 1973 Friedman PL, Fenoglio JJ Jr, Wit AL: Time course for reversal of electrophysiological and ultrastructural abnormalities in subendocardial Purkinje fibers surviving extensive myocardial infarction in dogs. Circ Res 36:127-144, 1975 Reynolds ES: The use of lead citrate at high pH as an electron opaque stain in electron microscopy. J Cell Biol 17:208-212, 1963 Bahr GF, Jennings RB: Ultrastructure of normal and asphyxic myocardium of the dog. Lab Invest 10:548-571, 1961 Jennings RB: Symposium on the pre-hospital phase of acute myocardial infarction. Part II. Early phase of nmyocardial ischemic injury and infarction. Am J Cardiol 24:753-765, 1969 Herdson PB, Kaltenbach JP, Jennings RB: Fine structural and biochemical changes in dog mvocardium during autolysis. Am J Pathol 57:539-557, 1969 Fenoglio JJ Jr, Albala A, Silva FG, Friedman PL, Wit AL: Structural basis of ventricular arrhythmias in human myocardial infarction: A hypothesis. Hum Pathol 7:547-563, 1976 Burch GE, Tsui CY, Harb JM: Postmortem chapges in the rat myocardium: A histologic and electron microscopic study. Pathol Microbiol 38:233-249, 1972 Ferrans VJ, Buja LM, Maron BJ: Myofibrillar abnormalities following cardiac muscle cell injurv. Pathophysiology and Morphology of Myocardial Cell Alterations: Recent Advances in 'Studies pp Cardiac Structure and Metabolism Series: Vol 6. Edited bv NI Fleckenstein. Baltimore, University Park Press, 1975, pp 367-382 Buja LM, Roberts WC: The coronary arteries and myocardium in acute myocardial infarction and shock: Pathologic aspects. Shock in Myocardial Infarction. Edited by RF Gunnar. New York, Grunt & Stratton, 1974, pp 1-21 Gordon RA, Britt BA, Kalow W (editors). Proceedings of the International Symposium on Malignant Hyperthermia. Springfield, Ill., Charles C Thomas, Publisher, 1973 Britt BA: Malignant hyperthermia: A pharmacogenetic disease of skeletal and cardiac muscle (editorial). N Engl J NIed 290:1140-1142, 1974
lB
Figur IA-Areas of myofibertysis (Ml) and contraction bands (arrows) in the left ventricular myocardium, alternating with areas of normal muscle in which distinct cross-gtriations are dlearly seen (Toluidine blue, X 305). B-High magnification of anarea of contraction bands (C)ywnVmyofibertysis (M); there is apparent disruption of the cell membrane (arrow) in an area of extensive myofiber clearing (Toluidine blue, X 750). Figure 2-The contraction bands (C) involve entire myofibers and a're sharply deliminated by the intercalated disc (arrows). The intercalated discs are intact. The myofibers adjacent to contraction bands are overstretched, and sarcomeres are no longer in register. T = mitochondria, Z = Z band. (x 5775)
4
Figure 3-Focal areas of overstretched sarcomeres are frequent in the center of otherwise normal myofibers Many of the sarcomeres in these areas are disrupted (arrows) and aggregates of mitochondria (T) are promi nent. Z = Z band. (x 5775) Figure 4-In areas of markedly overstretched sarcomeres adjacent to contractior bands (C), the Z bands (Z) are distorted and not in register, and sarcomeres are disrupted (arrow). Areas o complete lysis of myofilaments appear replaced by aggregates of mitochondria (T). D = intercalated disc. (> 5775) Inset-Breaks (arrows) in the sarcolemma (S) are frequent in overstretched myofibers (X 24,870)
