It has been shown that the inhibition of Na /H exchange

Transcription

1 The Contribution of Na /H Exchange to Ischemia-Reperfusion Injury After Hypothermic Cardioplegic Arrest Takashi Yamauchi, MD, Hajime Ichikawa, MD, Yoshiki Sawa, MD, Norihide Fukushima, MD, Koji Kagisaki, MD, Kazuhiro Maeda, PhD, Hikaru Matsuda, MD, and Ryota Shirakura, MD Department of Organ Transplantation and First Department of Surgery, Osaka University Medical School, Osaka, Japan Background. Na /H exchange has been reported to be one of the key mechanisms in myocardial ischemiareperfusion injury. However, the effect of temperature on Na /H exchange is not fully understood. Methods. Sodium-propionate induced cell swelling, an indicator of the function of the Na /H exchanger, was measured in rat thymic lymphocytes. A Langendorff perfused rat heart model was also employed to investigate the effect of the pharmacologic inhibition of Na /H exchange on the recovery of cardiac function after hypothermic ischemia. This was done using FR168888, an inhibitor of Na /H exchange. Results. In the in vitro study, rat lymphocytes were observed to swell at 17, 22, and 27 C, indicating that the Na /H exchanger remains functional even under hypothermic conditions. FR was found to significantly inhibit Na /H exchange induced cell swelling, even at 17 C. In the in vivo study, pretreatment with FR was found to prevent the deterioration of ventricular function, even after 5 hours of hypothermic cardioplegic arrest. This was associated with a decrease in the reperfusion-induced elevation in resting tension. Conclusions. These results suggest that Na /H exchange in the heart still occurs, even under hypothermic conditions, and contributes to reperfusion injury, even after hypothermic cardioplegic arrest. (Ann Thorac Surg 1997;63: ) 1997 by The Society of Thoracic Surgeons It has been shown that the inhibition of Na /H exchange is protective against ischemia-reperfusion injury because it inhibits the sudden restoration of intracellular ph and hence the Na and Ca 2 overload [1 4] mediated by Na /Ca 2 exchange. Na /H exchange can be inhibited either by lowering the extracellular ph during reperfusion or by administering amiloride derivatives. The initial acidic reperfusion theoretically suppresses the Na influx occurring via Na /H exchange during reperfusion [5, 6]. It is not, however, practical to apply this method clinically. The pharmacologic inhibition of Na /H exchange, which may be more practical for clinical use, has been shown to improve postischemic ventricular function after normothermic ischemia [1, 3, 7 10]. The question that needs to be answered, however, is whether this beneficial effect of Na /H exchange inhibition can be used in the clinical setting to protect the myocardium during cardiac surgical procedures. In the clinical situation, hypothermic cardioplegic arrest is normally used to protect the myocardium during aortic clamping. Therefore it must be determined whether the Na /H exchanger plays an important role under hypothermic conditions and whether the Na /H exchanger Accepted for publication Nov 5, Address reprint requests to Dr Ichikawa, Pediatric Cardiovascular Surgery, Michigan Congenital Heart Center, F7830 Mott Children s Hospital, 1500 East Medical Center Dr, Ann Arbor, MI can reduce the degree of ischemia-reperfusion injury occurring after hypothermic cardioplegic arrest. In the present study the temperature dependency of the Na /H exchanger and that of an inhibitor, FR168888, were investigated in vitro in rat thymic lymphocytes. Further, the effect of the inhibition of Na /H exchange on postischemic cardiac function was examined in isolated rat hearts subjected to normothermic or hypothermic arrest. Material and Methods Detection of Na /H Exchange Induced Cell Swelling by Electric Sizing Thymic lymphocytes were isolated from Male Sprague- Dawley rats (body weight, 250 to 300 g). To do this, the thymus was cut into small fragments in buffer solution (NaCl, 140 mmol/l; KCl, 1 mmol/l; CaCl 2, 1 mmol/l; MgCl 2, 1 mmol/l; glucose, 10 mmol/l; HEPES, 20 mmol/l; ph, 7.3 with NaOH) at room temperature and dissociated. This was then filtered and centrifuged at 1,000 g for 10 minutes at room temperature. The pellet was resuspended in 20 ml of buffer solution and centrifuged at 1,000 g for 10 minutes. The final pellet was resuspended in 10 ml of HEPES-buffered RPMI medium (RPMI 1640; Life Technologies Inc, Grand Island, NY) with 20-mmol/L HEPES (ph, 7.3; nominally HCO 3 free) 1997 by The Society of Thoracic Surgeons /97/$17.00 Published by Elsevier Science Inc PII S (96)

2 1108 YAMAUCHI ET AL Ann Thorac Surg Na /H EXCHANGE AND HYPOTHERMIA 1997;63: and preserved in ice-cold water. The total counts of the cells were adjusted to cells/ml. Na-propionate buffer (Na-propionate, 140 mmol/l; KCl, 1 mmol/l; CaCl 2, 1 mmol/l; MgCl 2, 1 mmol/l; glucose, 10 mmol/l; HEPES, 20 mmol/l; ph, 6.7) was used to induce intracellular acid loading. Using a multichannel particle counter (TA2; Coulter Corp, Miami, FL) equipped with a 50- m aperture, the cell swelling was measured 1, 2, 3, 4, and 5 minutes after acid loading. FR (C 4 H 4 NC 6 H 3 CH 2 [OH]CONC(NH 2 ) 2 CH 3 SO 3 H; molecular weight, ; Fujisawa Pharmaceutical Company, Tokyo, Japan) was dissolved in dimethysulfoxide solvent. Isolated Rat Heart Preparation Male Sprague-Dawley rats weighing around 350 g were anesthetized by an intraperitoneal injection of sodium pentobarbital (50 mg/g body weight) and heparin (2 U/g body weight). Hearts were then excised, and a retrograde aortic perfusion was started with Krebs Henseleit buffer (NaCl, mmol/l; NaHCO mmol/l; KCl, 4.5 mmol/l; MgSO 4, 1.2 mmol/l; KH 2 PO 4, 1.2 mmol/l; CaCl 2, 2.5 mmol/l; glucose, 10.0 mmol/l, aerated with 5% carbon dioxide and 95% oxygen to maintain a ph of 7.4) at a pressure of 100 cm H 2 O. The temperature of the hearts was kept at 37 C by a temperature-regulated water-jacketed glass chamber. Experimental Protocol A left ventricular (LV) balloon was inserted during 30 minutes of stabilization, and the LV systolic pressure at an end-diastolic pressure of 10 mm Hg, coronary flow rate, and heart rate were measured at the end of the stabilization period using a pressure transducer (AP641G; Nihon Koden Co, Tokyo, Japan). St. Thomas Hospital cardioplegic solution (NaCl, mmol/l; KCl, 16.0 mmol/l; MgCl 2, 1.2 mmol/l; CaCl 2, 1.2 mmol/l; NaHCO 3, 10.0 mmol/l, with the ph adjusted to 7.8 with HCl) at each temperature (37 or 17 C) was then infused for 3 minutes at 60 cm H 2 O to obtain cardioplegic arrest. The myocardial temperature during ischemia was kept at 37 C for 35 minutes in the normothermic experiment and at 17 C for 4 or 5 hours in the hypothermic experiment. FR was given before (FRpre), during the infusion of St. Thomas Hospital solution (FRcp), or during reperfusion (FRrep) in the normothermic experiment and before ischemia in the hypothermic experiment. The total amount of FR given was 1 mg ( mole) in all experimental groups, whereas the control group received only normal saline solution (Fig 1). During the ischemic period the LV balloon was kept inflated to detect the time to the onset and the peak amplitude of the ischemic contracture. The time to the onset of the ischemic contracture was defined to occur when the left ventricular resting tension increased by 1 mm Hg. Hearts were then reperfused for 20 minutes and the hemodynamic indices again measured at the end of reperfusion, with the balloon volume readjusted to keep the enddiastolic pressure at 10 mm Hg. The postischemic hemodynamic recoveries were expressed as a percentage of the preischemic value of each index. Fig 1. The experimental protocol. The administration of FR is denoted by the black boxes. (CP the period of the infusion of cardioplegia; FRpre, FRcp, and FRrep the drug-treated groups during the preischemic period, the infusion of cardioplegic solution, and the reperfusion phase, respectively.) Tissue Drug Concentration The hearts were removed from the Langendorff perfusion apparatus 30 seconds after the onset of reperfusion to determine the tissue drug concentration. Hearts were frozen quickly in liquid nitrogen and kept at 80 C. Humane Animal Care Animals were treated in accordance with the Guide for the Care and Use of Laboratory Animals (NIH publication 85-23, revised 1985). Data Analysis Results are expressed as the mean the standard error of the mean. The inhibition constant (K i ) was calculated using the following procedure: The velocity of the change in the cell volume induced by Na-propionate was calculated when FR was added in a concentration of 0, , , and mol/l at each temperature. By linear regression analysis, data were fitted to the following formula: 1/ V a S b, where V is the velocity of the change in the cell volume, S is the concentration of FR168888, and the X intercept was defined as K i. The LV static pressure during the early phase of reperfusion after normothermic ischemia was fitted to two exponentials using a personal computer program (Sigma Plot; Jandel Scientific, San Rafael, CA) to evaluate the time constants of the pressure decay occurring during reperfusion, the scaling factors, and the asymptotic pressure. The repeated-measure analysis of variance was used to assess the LV static pressure after hypothermic ischemia. Student s t test was used for the other parameters. A p value of less than 0.05 was defined as significant. Results Temperature Dependency of Na /H Exchange Induced Cell Swelling The activity of Na /H exchange was gauged by the amount of swelling of thymic lymphocytes induced by

3 Ann Thorac Surg YAMAUCHI ET AL 1997;63: Na /H EXCHANGE AND HYPOTHERMIA 1109 the acid load [11]. The diameter of lymphocytes started to increase when they were mixed with propionate buffer. Five minutes after the start of acid loading, the cell diameter increased by approximately 500 nm in normothermia (37 C). Although this swelling was slightly attenuated at lower temperatures (17, 22, and 27 C), considerable cell swelling was still detected (Fig 2A). At each temperature, FR ( nmol/l) caused the percentage of cell swelling to be reduced. The percentage of the inhibition of cell swelling was highest at 17 C. The K i values were 3.03, 6.42, and 3.23 nmol/l at 17, 22, and 27 C, respectively (Fig 2B). Isolated Rat Heart Experiment Ischemic contracture started after the induction of normothermic cardioplegic arrest. No significant difference was observed between groups in the time to the onset or the peak amplitude of ischemic contracture ( min, min, min, and min and mm Hg, mm Hg, mm Hg, and mm Hg in the control, FRpre, FRcp, and FRrep groups, respectively). During the very early stage of reperfusion, the resting tension increased and peaked within 15 seconds, which then decreased with time (Fig 3). This change in the LV Fig 2. Temperature dependency of Na /H exchange and its inhibitor. (A) The acid load induced swelling of rat thymic lymphocytes for 5 minutes. (B) Percentage of inhibition of cell swelling by FR The drug concentration was mol/l. The K i values were 3.03, 6.42, and 3.23 nmol/l at 17, 22, and 27 C, respectively. Fig 3. The raw trace of a representative pressure recording during early reperfusion. At the onset of reperfusion in the normothermic experiment, the resting tension started to increase. After peaking, it gradually decreased. The trace was from the control group (e exponential.) static pressure during the early reperfusion period was fit to two exponentials (e), as follows: LV static pressure Ae ( t/t1) Be ( t/t2) C where is the time from the onset of reperfusion, T1 and T2 are the time constants of each exponential component, A and B are the scaling factors, and C is the asymptotic pressure. There was no significant difference in A, B, T1, or T2 between groups. However, the asymptotic pressure was significantly lower in the FRcp group than in the other groups (Table 1). The LV end-diastolic pressures at 20 minutes of reperfusion were mm Hg, mm Hg, mm Hg, and mm Hg, and the percentages of the recovery of LV systolic pressure were 35.4% 3.2%, 80.8% 7.3%, 103.3% 4.1%, and 73.0% 3.7% in the control, FRpre, FRcp, and FRrep groups, respectively (p versus the control group for both variables in all three drug-treated groups; Fig 4A). The percentage of the recovery of coronary flow in the FRpre, FRcp, and FRrep groups was also significantly higher than that in the control group by 24.2%, 32.7%, and 15.6%, respectively. Reperfusion-induced ventricular fibrillation occurred in 5, 4, 0, and 4 of the 5 animals in the control, FRpre, FRcp, and FRrep groups, respectively. In a different set of experiments, the tissue drug concentration was measured at 30 seconds after the onset of reperfusion and was found to be the highest in the FRcp group ( , , and [micrograms per gram of dry heart weight] in the FRpre, FRcp, and FRrep groups, respectively). During hypothermic ischemia with cardioplegia, no significant difference was seen in the time to the onset or peak amplitude of the ischemic contracture between the control and drug-treated groups at each duration of ischemia ( minutes versus minutes, mm Hg versus mm Hg and minutes versus minutes, mm Hg versus mm Hg in the control versus the FR treated group at 4 and 5 hours, respectively).

4 1110 YAMAUCHI ET AL Ann Thorac Surg Na /H EXCHANGE AND HYPOTHERMIA 1997;63: Table 1. The Profile of Left Ventricular Static Pressure During Early Reperfusion in Normothermia a Variable Control FRpre FRcp FRrep A (mm Hg) B (mm Hg) C (mm Hg) b T1 (s) T2 (s) a T1, T2, A, B, and C were derived by the curve fitting of the resting tension trace in the normothermic experiment, as follows: Left ventricular static pressure Ae ( t/t1) Be ( t/t2) C, where T1 and T2 are the exponential time constants, A and B are the scaling factors, and C is the asymptotic pressure. b p 0.05 versus control. FRpre, FRcp, and FRrep the drug-treated groups during the preischemic period, the infusion of cardioplegia, and the reperfusion phase, respectively. Upon reperfusion, the myocardial temperature was not fully restored for 2 minutes. The resting tension increased and peaked in about 10 seconds, then stayed at this level or decreased for about 1 minute. In the 4-hour experiment, no significant difference was observed in the profile of the resting tension. In the 5-hour experiment, the resting tension was significantly lower in the FR treated group than in the control group (Fig 5). There was a significant difference in the percentages of the recovery of LV systolic pressure after 4 hours of ischemia between the control and the FR treated groups (72.2% 4.3% and 98.1% 4.0%, respectively; p 0.01). However, the difference was more prominent in the 5-hour experiment (38.4% 2.5% and 74.7% 5.4%, respectively; p 0.001) (see Fig 4B). FR also improved the percentage of the recovery of coronary flow by 16.3% after 4 hours and by 12.9% after 5 hours of ischemia and decreased the incidence of ventricular fibrillation (3/5 versus 0/5 in the 4-hour groups and 3/5 versus 1/5 in the 5-hour groups). In the FRpre group in the hypothermic experiment, the tissue drug concentration at early reperfusion after 5 hours of ischemia was g/g, which was significantly higher than that of the FRpre group in the normothermic experiment. Comment The present study showed that Na /H exchange occurs even under hypothermic conditions and can be inhibited by FR168888, a newly synthesized inhibitor of Na /H exchange [12]. This inhibition of Na /H exchange with FR improved the postischemic functional recovery in isolated rat heart after both normothermic and prolonged hypothermic cardioplegic arrest. It has been established that reperfusion injury caused by Na overload resulting from Na /H exchange occurs after normothermic ischemia in the very early stage of reperfusion [6, 13] and can be inhibited by suppressing Fig 4. Percentage of recovery of left ventricular systolic pressure in the normothermic (A) and hypothermic (B) experiments. It was significantly higher in the FR treated groups (FR) than in the control group at both temperatures. (FRpre, FRcp, and FRrep the drug-treated groups during the preischemic period, the infusion of cardioplegic solution, and the reperfusion phase, respectively; *p 0.01; **p ) Fig 5. The change in the resting tension during early reperfusion after hypothermic arrest for 5 hours. The resting tension started to increase and peaked at about 10 seconds. After this it remained at this level in the control group and decreased in the FR treated group (FR). (*p 0.05.)

5 Ann Thorac Surg YAMAUCHI ET AL 1997;63: Na /H EXCHANGE AND HYPOTHERMIA 1111 this exchanger [4, 7, 9]. However, it is still unclear whether Na /H exchange plays an important role during reperfusion after hypothermic ischemia in which the myocardial temperature is not fully restored. The study in which Na /H exchange was assessed in lymphocytes showed that Na /H exchange is still considerably functional, even at low temperatures, which implies that inhibition of the Na /H exchanger protects against myocardial reperfusion injury, even at low temperatures. In the isolated rat heart perfusion study, the inhibition of Na /H exchange did not change the development of ischemic contracture in either the normothermic or the hypothermic experiment. In the early stage of reperfusion, the LV static pressure increased as the consequence of the change in the intracellular Ca 2 concentration, which may be affected by the intracellular ph and Na activity. After normothermic ischemia, the inhibition of Na /H exchange with FR did not cause the peak amplitude or the exponential time constant of the decay in the LV static pressure to be altered during early reperfusion but did cause the asymptotic pressure to be changed. This parallel and downward shift of the LV static pressure indicates that FR may cause a decrease in the intracellular Ca 2 activity but does not affect the speed of the Ca 2 -extruding mechanism, such as Na /Ca 2 exchange or Ca 2 sequestration by sarcoplasmic reticulum [14 17]. This is compatible with the conventional concept that the inhibition of Na /H exchange shows its beneficial effect mainly in the early stage of reperfusion [18]. The improvement in functional recovery coincided well with the tissue drug concentration during the early reperfusion phase. In the hypothermic experiments, the better functional recovery and the downward shift in the profile of the resting tension in the early stage of reperfusion were observed in the FR treated group in the 5-hour experiment, indicating that FR may cause the reperfusion injury to be reduced, even in the setting of low myocardial temperature. In the 4-hour experiment the downward shift of the resting tension during early reperfusion was not observed in the FR treated group, whereas the postischemic functional recovery was significantly greater in the FR treated group than in the control group. It can be assumed that the beneficial effect of the inhibition of Na /H exchange on the change in the resting tension appears only when ischemia-reperfusion injury is severe. The protective effect of FR became prominent when the ischemic insult was severe as the result of prolonged arrest, indicating that the Na /H exchanger may play an important role in the pathogenesis of severe myocardial ischemia-reperfusion injury. It is possible that the severe intracellular acidification induced during extended ischemia causes the Na overload occurring as the result of Na /H exchange to be exaggerated, and hence Ca 2 overload in myocytes. A better functional recovery was associated with a lower incidence of ventricular fibrillation after hypothermic arrest, which is consistent with reports that various inhibitors of Na /H exchange protect myocardium against reperfusion-induced arrhythmia after normothermic ischemia [19]. In cardiac surgical procedures, hypothermic, multidose cardioplegic infusion is widely employed to obtain a better oxygen supply and washout of the metabolites. However, such multidose cardioplegia necessitates multitime reperfusion [20, 21] to alter the ph gradient between the inside and outside of the cells and at the same time causes ions to move through the Na /H exchanger during every infusion. It has also been reported that multidose cardioplegia is harmful to neonatal myocardium because of the Na /H exchange related mechanism triggered [22, 23]. Therefore a single-dose cardioplegic infusion was employed in this series of experiment to enable the simple interpretation of the data. Although the present study has its limitations because of its experimental nature, the results did show the importance of inhibiting Na /H exchange after hypothermic ischemia, which implies the possibility of its future use in cardiovascular surgical procedures. We thank the Fujisawa Pharmaceutical Company for the supply of FR References 1. Tani M, Neely JR. Role of intracellular Na in Ca 2 overload and depressed recovery of ventricular function of reperfused ischemic rat hearts. Possible involvement of H -Na and Na -Ca 2 exchange. Circ Res 1989;65: Pike MM, Luo CS, Clark MD, et al. NMR measurements of Na and cellular energy in ischemic rat heart: role of Na ( ) -H exchange. Am J Physiol 1993;265:H Hendrikx M, Mubagwa K, Verdonck F, et al. New Na ( ) -H exchange inhibitor HOE 694 improves postischemic function and high-energy phosphate resynthesis and reduces Ca 2 overload in isolated perfused rabbit heart. Circulation 1994; 89: Faes FC, Sawa Y, Ichikawa H, et al. Inhibition of Na /H exchanger attenuates neutrophil-mediated reperfusion injury. Ann Thorac Surg 1995;60: Matsuda N, Kuroda H, Mori T. Beneficial actions of acidotic initial reperfusate in stunned myocardium of rat hearts. Basic Res Cardiol 1991;86: Kitakaze M, Weisfeldt ML, Marban E. Acidosis during early reperfusion prevents myocardial stunning in perfused ferret hearts. J Clin Invest 1988;82: Lazdunski M, Frelin C, Vigne P. The sodium/hydrogen exchange system in cardiac cells: its biochemical and pharmacological properties and its role in regulating internal concentrations of sodium and internal ph. J Mol Cell Cardiol 1985;17: Murphy E, Perlman M, London RE, Steenbergen C. Amiloride delays the ischemia-induced rise in cytosolic free calcium. Circ Res 1991;68: Dennis SC, Coetzee WA, Cragoe EJ Jr, Opie LH. Effects of proton buffering and of amiloride derivatives on reperfusion arrhythmias in isolated rat hearts. Possible evidence for an arrhythmogenic role of Na ( ) -H exchange. Circ Res 1990;66: Yasutake M, Ibuki C, Hearse DJ, Avkiran M. Na /H exchange and reperfusion arrhythmias: protection by intracoronary infusion of a novel inhibitor. Am J Physiol 1994;267: H

6 1112 YAMAUCHI ET AL Ann Thorac Surg Na /H EXCHANGE AND HYPOTHERMIA 1997;63: Grinstein S, Goetz JD, Cohen S, Rothstein A, Gelfand EW. Regulation of Na /H exchange in lymphocytes. Ann NY Acad Sci 1985;456: Yamauchi T, Sawa Y, Ichikawa H, et al. FR168888, an inhibitor of Na /H exchange attenuates reperfusion injury after 5 hours of hypothermic cardioplegic arrest in isolated rat heart. J Mol Cell Cardiol 1995;27:A Kusuoka H, Kitakaze M, Koretsune Y, Inoue M, Marban E. Pathophysiology and pathogenesis of contractile failure in stunned myocardium. Jpn Circ J 1991;55: Bers DM, Lederer WJ, Berlin JR. Intracellular Ca transients in rat cardiac myocytes: role of Na-Ca exchange in excitation-contraction coupling. Am J Physiol 1990;258:C Bers DM, Christensen DM. Functional interconversion of rest decay and ryanodine effects in rabbit and rat ventricle depends on Na/Ca exchange. J Mol Cell Cardiol 1990;22: DiFrancesco D, Noble D. A model of cardiac electrical activity incorporating ionic pumps and concentration changes. Philos Trans R Soc Lond [Biol] 1985;307: Mullins LJ. An electrogenic saga: consequences of sodiumcalcium exchange in cardiac muscle. Soc Gen Physiol Ser 1984;38: Avkiran M, Ibuki C. Reperfusion-induced arrhythmias. A role for washout of extracellular protons? Circ Res 1992;71: Yasutake M, Avkiran M. Exacerbation of reperfusion arrhythmias by alpha 1 adrenergic stimulation: a potential role for receptor mediated activation of sarcolemmal sodiumhydrogen exchange. Cardiovasc Res 1995;29: Ichikawa H, Yamamoto F. Proton gradient during cardiac arrest: oxygenation of St. Thomas Hospital cardioplegic solution and carbon dioxide level [Letter]. J Thorac Cardiovasc Surg 1993;105: Von Oppell UO, King LM, Du Toit EF, Owen P, Reichart B, Opie LH. Effect of oxygenation and consequent ph changes on the efficacy of St. Thomas Hospital cardioplegic solution. J Thorac Cardiovasc Surg 1991;102: Murashita T, Hearse DJ. Temperature-response studies of the detrimental effects of multidose versus single-dose cardioplegic solution in the rabbit heart. J Thorac Cardiovasc Surg 1991;102: Artman M, Ichikawa H, Avkiran M, Coetzee WA. Na /Ca 2 exchange current density in cardiac myocytes from rabbits and guinea pigs during postnatal development. Am J Physiol 1995;268:H The Society of Thoracic Surgeons: Thirty-fourth Annual Meeting Mark your calendars for the Thirty-fourth Annual Meeting of The Society of Thoracic Surgeons, which will be held at the Ernest N. Morial Convention Center in New Orleans, Louisiana, January 26 28, Members may register for the Scientific Sessions at no charge. There will be a $250 registration fee for nonmember physicians except for Scientific and Poster Session presenters and residents. Registration for the Postgraduate Course is separate from the Annual Meeting. There will be a $70 registration fee for attendees of the Postgraduate Program, which will be held Sunday, January 25. The Postgraduate Course will provide in-depth coverage of thoracic surgical topics selected to enhance and broaden the knowledge of practicing thoracic and cardiac surgeons. Advance registration forms, hotel reservation forms, and details regarding transportation arrangements, as well as the complete meeting program, will be mailed to Society members this fall (1997). Also, complete meeting information will be available as early as possible on The Society s Web site located at Nonmembers wishing to receive information on attending the meeting should write to the Society s Secretary, Peter C. Pairolero. The abstract submission form for the Thirty-fourth Annual Meeting will be sent to all Society members in May and July, will be published in the May, June, and July issues of The Annals, and will also be available as early as possible on the STS Web site. The abstracts will be due on August 4, Films will be due on July 31, Peter C. Pairolero, MD Secretary The Society of Thoracic Surgeons 401 N Michigan Ave Chicago, IL (312) Fax: (312) by The Society of Thoracic Surgeons Ann Thorac Surg 1997;63: /97/$17.00 Published by Elsevier Science Inc PII S (97)