| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Ann Thorac Surg 1998;66:2037-2043
© 1998 The Society of Thoracic Surgeons
a Division of Cardiothoracic Surgery and Biometrics Center, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
Accepted for publication June 11, 1998.
Address reprint requests to Dr McCully, Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, Harvard Institutes of Medicine, 77 Avenue Louis Pasteur, Room 144, Boston, MA 02115
 |
Abstract |
|---|
 Top Abstract IntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Methods. The efficacy of APC was investigated in senescent rabbit hearts and compared with magnesium-supplemented potassium cardioplegia (K/Mg) and IPC. Global ischemia (GI) hearts were subjected to 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts received 5 minutes of global ischemia and 5 minutes of reperfusion before global ischemia. Magnesium-supplemented potassium cardioplegia hearts received cardioplegia just before global ischemia. Adenosine-enhanced ischemic preconditioning hearts received a bolus injection of adenosine in concert with IPC. To separate the effects of adenosine from that of APC, a control group (ADO) received a bolus injection of adenosine 10 minutes before global ischemia.
Results. Infarct size was significantly decreased to 18.9% ± 2.7% with IPC (p < 0.05 versus GI); 17.0% ± 1.0% with ADO (p < 0.05 versus GI); 7.7% ± 1.3% with K/Mg (p < 0.05 versus GI, IPC, and ADO); and 2.1% ± 0.6% with APC (p < 0.05 versus GI, IPC, ADO, and K/Mg; not significant versus control). Only APC and K/Mg significantly enhanced postischemic functional recovery (not significant versus control).
Conclusions. Adenosine-enhanced ischemic preconditioning provides similar protection to K/Mg cardioplegia, significantly enhancing postischemic functional recovery and decreasing infarct size in the senescent myocardium.
|
Introduction |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
With the development of novel cardiac surgical techniques, the use of cardioplegia, generally accepted as the standard for use in cardiac surgery, may not always be appropriate, and the use of alternative protocols has been suggested to allow for optimization of surgical outcome. One such protocol is ischemic preconditioning (IPC), in which the imposition of one or more brief periods of ischemia (3 to 5 minutes) followed by reperfusion "preconditions" the heart such that infarct size and myocardial necrosis is significantly reduced during the subsequent induction of sublethal ischemia [5, 6]. The induction of endogenous myocardial protection by preconditioning would appear to be common in all species studied in reducing myocardial infarct volume. However, the effects of preconditioning on postischemic myocardial functional recovery have been shown to vary among species, in contrast to the protection afforded by cardioplegia [5–10]. In the rat heart, the use of preconditioning has been shown to both reduce myocardial infarction and enhance postischemic myocardial functional recovery [7, 9]. In contrast, in the rabbit heart, whereas preconditioning has been shown to reduce myocardial infarction, no enhancement of postischemic myocardial functional recovery occurs [8, 10].
Recently we have developed an alternative cardioprotective protocol, adenosine-enhanced ischemic preconditioning (APC), which extends the protection afforded by ischemic preconditioning by both decreasing postischemic infarct size and enhancing myocardial functional recovery in the rabbit heart [11]. In addition we have shown that APC is as effective as K/Mg cardioplegia in the mature heart. The efficacy of APC in providing for enhanced postischemic myocardial function and infarct size reduction in the aged heart, however, was unknown.
With the increased incidence of elderly patients as candidates for complex cardiac surgery, the investigation into methods that will increase survivability and enhance cardiac protection are of paramount importance. In this article we compare APC, IPC, and K/Mg cardioplegia on the ability to ameliorate infarct size and enhance postischemic functional recovery in the senescent myocardium.
|
Material and methods |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Langendorff perfusion
All rabbits were anesthetized with sodium pentobarbital (Veterinary Laboratories, Inc, Lenexa, KS; 100 mg/kg intravenously), and heparin (200 U/kg intravenously) was administered by a marginal ear vein. The heart was excised and used for Langendorff perfusion as previously described [3, 11]. Left ventricular (LV) systolic pressure, LV peak developed pressure, LV end-diastolic pressure, and coronary flow were continuously recorded [3, 11]. Hemodynamic variables were acquired using a PO-NE-MAH digital data acquisition system (Gould, Valley View, OH), with an Acquire Plus processor board and left ventricular pressure analysis software.
Experimental protocol
Hearts were perfused for 20 minutes to establish equilibrium hemodynamics. Equilibrium was ceased when heart rate, coronary flow, left ventricular pressure, and diastolic pressure were maintained at the same level for three continuous measurement periods timed 5 minutes apart. Hearts not meeting this criterion were eliminated from this study. After 20 minutes of equilibrium perfusion, the hearts were divided into six groups. Control hearts (n = 6) were perfused without global ischemia at 37°C for 180 minutes. Global ischemia hearts (GI; n = 6) were subjected to 30 minutes of ischemia and 120 minutes of reperfusion. Global ischemia was achieved by cross-clamping of the aorta. Magnesium-supplemented potassium cardioplegia hearts (K/Mg; n = 6), were infused with magnesium-supplemented potassium cardioplegia (20 mmol/L each KCl and MgSO4), then subjected to 30 minutes of ischemia and 120 minutes of reperfusion. Cardioplegia was perfused at a constant pressure of 75 cm H2O at 37°C for 5 minutes before the onset of 30 minutes of global ischemia and 120 minutes of reperfusion. Ischemic preconditioning hearts (IPC; n = 6) received 5 minutes of zero-flow global ischemia followed by 5 minutes of reperfusion before 30 minutes of global ischemia and 120 minutes of reperfusion. Adenosine-enhanced preconditioning hearts (APC, n = 6) received a 10-mL bolus injection of 1 mmol/L adenosine in Krebs buffer, coincident with preconditioning (5 minutes of zero-flow global ischemia followed by 5 minutes of reperfusion). The concentration of adenosine used for bolus injection was determined by preliminary investigation [11]. To separate the effects of adenosine from that of APC, a control group (ADO; n = 6) received a 10-mL bolus injection of 1 mmol/L adenosine in Krebs buffer 10 minutes before global ischemia and reperfusion. The bolus was injected into the aortic root through a sidearm cannula located proximal to the perfusion cannula. All hearts were paced continuously through the right atrium at 180 ± 3 beats/min throughout the experiment, using a Medtronic rapid atrial pacer (Medtronic 5330 Minneapolis, MN).
Comparison of wet and dry weights
Left ventricular tissue samples (approximately 0.1 g) from all experimental groups were weighed (wet weight) and dried at 80°C for 24 hours for reweighing (dry weight) and then used for the determination of wet weight/dry weight ratios, as previously described [3].
Measurement of infarct size
After reperfusion, hearts were rapidly removed and sliced across the long axis of the left ventricle, from apex to base, into 2-mm-thick transverse sections and incubated in 1% triphenyl tetrazolium chloride (Sigma Chemical Co, St. Louis, MO) in phosphate buffer (pH 7.4) at 38°C for 20 minutes [12]. Infarct areas were enhanced by storage in 10% formaldehyde solution for 24 hours before final measurement [8, 12]. In the globally ischemic heart, the whole ventricle is at risk of infarction and therefore collateral flow and estimation of the area at risk was not required [8, 12]. A copy of the stained heart slices was traced onto a clear acetate sheet over a glass plate under room light. The area of left ventricle and the area of infarcted tissue were measured by an independent, blinded observer using planimetry. The volumes of the infarcted zone and the area at risk were calculated by multiplying the planimetered areas by the slice thickness [8, 12]. Infarct volume was expressed as a percentage of left ventricular volume for each heart [8, 12].
Statistical analysis
Statistical analysis was performed using the SAS (version 6.12) software package (SAS Institute, Cary, NC). The mean plus or minus the standard error of the mean was calculated for all variables. Statistical significance was determined using repeated measures analysis of variance with group as a between-subjects factor and time as a within-subjects factor. Post hoc comparisons between groups for both the average effect and at individual time points were made using a Bonferroni correction to adjust for the multiplicity of tests. A one-way analysis of variance was used for area of infarction. Significant values at p less than 0.05 are noted.
|
Results |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
Left ventricular end-diastolic pressure
The effects of GI, IPC, ADO, K/Mg, and APC on LVEDP in the senescent myocardium during equilibrium, 30 minutes of normothermic global ischemia, and 120 minutes of reperfusion are shown in Figure 1. Left ventricular end-diastolic pressure in IPC and APC hearts decreased to 0 mm Hg during ischemic preconditioning and then returned to control levels during the 5 minutes of reperfusion before the induction of global ischemia. No significant difference in LVEDP was found between groups before the 30 minutes of global ischemia. Both K/Mg and APC hearts maintained LVEDP at control levels throughout 120 minutes of reperfusion after 30 minutes of global ischemia. After 30 minutes of normothermic global ischemia LVEDP was significantly increased (p < 0.05) in GI, IPC, and ADO hearts compared with control, K/Mg, and APC hearts throughout 120 minutes of reperfusion, reaching 36.3 ± 11.8, 34.4 ± 8.0, and 43.3 ± 4.8 mm Hg, respectively at 120 minutes of reperfusion (p < 0.05 versus control, K/Mg and APC hearts).
|
|
|
|
|
|
Comment |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
In this report we show that APC enhances postischemic functional recovery in the senescent myocardium equally as well as K/Mg cardioplegia (Figs 3, 4). In addition our results indicate that both APC and K/Mg cardioplegia significantly decrease infarct size in the senescent myocardium (Fig 5; p < 0.05 versus GI, IPC, and ADO), but that APC is superior to K/Mg cardioplegia (p < 0.05), decreasing infarct size such that no significant difference from control hearts was observed.
The mechanisms leading to decreased infarct size remain controversial. Kloner and associates [15] have previously suggested that myocyte injury occurs before vascular injury, whereas Hearse and colleagues [16] have proposed that altered (increased) vasoconstriction precedes and contributes to myocyte injury and necrosis. Our data indicate that infarct size in the senescent myocardium was significantly decreased with APC, IPC, ADO, and K/Mg; however, infarct size was more significantly decreased p < 0.05) in APC and K/Mg hearts compared with ADO and IPC hearts. Our data also show that APC was superior (p < 0.05) to K/Mg in decreasing infarct size (Fig 5). Coronary flow in K/Mg and ADO hearts was decreased compared with APC and IPC hearts throughout reperfusion (Fig 4). These data agree with our previous investigation using the mature heart in which no correlation between coronary flow during reperfusion and infarct size was observed [11].
Our data indicate that IPC or adenosine alone improve postischemic functional recovery in proportion to their infarct-limiting capacity, which was significantly less than that of K/Mg or APC. Both APC and K/Mg cardioplegia significantly decreased infarct size and enhanced postischemic functional recovery in the senescent rabbit heart and were superior to both IPC and ADO alone. No significant difference in postischemic functional recovery was observed between GI hearts and ADO and IPC hearts. These data are consistent with that of Kolocassides and coworkers [9], who have reported that after ischemia and reperfusion coronary vascular resistance is significantly attenuated with both preconditioning (IPC) and cardioplegia in the rat heart. In our investigations we have not investigated coronary vascular resistance using vasodilators or vasoconstrictors; however, our results would agree with those of Kolocassides and associates [9] in that the observed differences in coronary flow after global ischemia are unrelated to decreased myocardial infarction or enhanced postischemic functional recovery in the senescent myocardium. The relatively decreased coronary flow observed with K/Mg cardioplegia in the senescent myocardium may be associated with the previously noted impairment of microvascular relaxation after cold potassium cardioplegia [17].
Of significance is the finding that APC is superior to K/Mg in significantly decreasing myocardial infarct size in the senescent myocardium (Fig 5). This finding is noteworthy, because earlier investigation in the mature heart indicated that APC and K/Mg were both equally effective in reducing infarct size and enhancing postischemic functional recovery [11]. The age-related difference observed herein does not appear to be associated with the differences in coronary flow between APC and K/Mg hearts observed during reperfusion. It is possible that owing to the level of the significant difference (p < 0.05) in infarct size observed in APC and K/Mg hearts compared with IPC and ADO hearts, the effect of decreased coronary flow on postischemic function and myocardial viability in the senescent myocardium was obfuscated by the relative levels of infarct size reduction observed with the different protocols. It is also possible that whereas no correlative difference was evident within the 120 minutes of reperfusion used in our protocol, the significance of these observations may be made apparent with more protracted investigation.
Recently, Faris and colleagues [19] have reported that IPC cardioprotection was not enhanced when endogenous adenosine levels were increased with draflazine, a nucleoside transport inhibitor. This finding would suggest that the mode by which interstitial adenosine is augmented is of importance. The mechanism by which a bolus injection of adenosine when used coincident with IPC confers superior cardioprotection remains to be fully elucidated; however, we speculate that exogenous rather than endogenous adenosine supplementation is of primary importance.
We speculate that the bolus injection of adenosine allows for the rapid binding and activation of myocardial adenosine receptors during the ischemic phase of IPC, thus allowing for maximal IPC conditioning of the myocardium. Support for this hypothesis is derived from the observations of Mullane and associates [18], who have previously noted that although endogenous adenosine accumulation is central to the cardioprotection afforded by ischemic preconditioning, endogenous concentration is not sufficient to allow for maximal cardioprotection because the administration of exogenous adenosine or its analogs increases the degree of cardioprotection. This would agree with the observations of Lasley and coworkers [12], who have suggested that it is the interstitial fluid levels of adenosine that attenuate infarct size. Although we have not determined the effect of APC on interstitial adenosine levels, we speculate that APC rapidly increases interstitial adenosine levels greater than that able to be achieved by either IPC induction or steady-state adenosine infusion, allowing for the rapid saturation of myocardial adenosine receptors and, further, that the level of adenosine receptor saturation may be directly correlated with both the reduction of myocardial infarct size and the degree of postischemic functional recovery attained.
The inability of adenosine or IPC alone to enhance postischemic myocardial functional recovery concurrent with the reduction of myocardial infarct size would suggest that both endogenous adenosine levels and priming of adenosine receptors may be required for cardioprotection. Our results indicate that the use of an intracoronary bolus adenosine (1 mmol/L) by itself significantly decreases myocardial infarct volume in the rabbit heart but does not enhance postischemic myocardial functional recovery. This would agree with previous reports showing no direct inotropic effects are associated with adenosine [13, 14]. Our results indicate that the effects of a bolus injection of adenosine when used in concert with IPC are additive and, when used alone, neither IPC nor a bolus injection of adenosine enhance postischemic functional recovery or significantly reduce (compared with APC and K/Mg) infarct size (Fig 5). The exact mechanisms by which APC enhanced cardioprotection is afforded, however, will require further investigation.
Intrinsic to the development of new myoprotective protocols for use in cardiac surgery are the requirements of new protocols to be equal to or better than conventional cardioplegia in providing for (1) enhanced postischemic functional recovery and (2) decreased myocardial infarct size. Our results indicate that APC and K/Mg cardioplegia significantly decrease infarct size and enhance postischemic functional recovery in the senescent rabbit heart. Our results also indicate that APC is superior to K/Mg cardioplegia in significantly decreasing infarct size in the senescent heart. These results may be clinically important to reduce morbidity and mortality in the senescent myocardium.
Certain limitations must be acknowledged in this report, the main and major limitation being that these results were obtained in the isolated crystalloid-perfused heart preparation and do not account for the intervening variables incurred with in situ blood-perfused heart preparations. In addition, normothermic cardioplegia infusion and global ischemia were used in this study to allow for comparison with previous results [3, 4, 8, 10].
Recently, Birnbaum and associates [20] have suggested that 3 hours of reperfusion is required to allow for the proper estimation of infarct size in the in situ rabbit heart after 30 minutes of regional ischemia. In our investigation we have used 2 hours of reperfusion after 30 minutes of normothermic global ischemia before estimation of infarct size by triphenyl tetrazolium chloride staining. It is possible that our results may underestimate infarct size after 30 minutes of global ischemia; however, we must assume that this underestimate would be proportional and therefore would not bias the overall import of our findings. Of importance, our results indicate that APC provides for both significantly decreased infarct size and enhanced postischemic functional recovery after global ischemia and reperfusion in the senescent rabbit heart.
|
Acknowledgments |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
|
References |
|---|
|
TopAbstractIntroductionMaterial and methodsResultsCommentAcknowledgmentsReferences |
|---|
This article has been cited by other articles:
|
|
 |
|
  J. D. O'Brien and S. E. Howlett Simulated ischemia-induced preconditioning of isolated ventricular myocytes from young adult and aged Fischer-344 rat hearts Am J Physiol Heart Circ Physiol, August 1, 2008; 295(2): H768 - H777. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 M. Loubani, S. Ghosh, and M. Galinanes The aging human myocardium: tolerance to ischemia and responsiveness to ischemic preconditioning J. Thorac. Cardiovasc. Surg., July 1, 2003; 126(1): 143 - 147. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Vinten-Johansen, Z.-Q. Zhao, J. S. Corvera, C. D. Morris, J. M. Budde, V. H. Thourani, and R. A. Guyton Adenosine in myocardial protection in on-pump and off-pump cardiac surgery Ann. Thorac. Surg., February 1, 2003; 75(2): S691 - 699. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Suematsu, T. Ohtsuka, H. Horimoto, K. Maeda, Y. Nakai, S. Mieno, and S. Takamoto Long-term treatment with nipradilol, a nitric oxide-releasing {beta}-adrenergic blocker, enhances postischemic recovery and limits infarct size Ann. Thorac. Surg., January 1, 2002; 73(1): 173 - 179. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 K. Przyklenk, G. Li, and P. Whittaker No loss in the in vivo efficacy of ischemic preconditioning in middle-aged and old rabbits J. Am. Coll. Cardiol., November 15, 2001; 38(6): 1741 - 1747. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Kloner Preinfarct angina and exercise: yet another reason to stay physically active J. Am. Coll. Cardiol., November 1, 2001; 38(5): 1366 - 1368. [Full Text] [PDF]
|
|
|
|
|
|
B. Stadler, J. Phillips, Y. Toyoda, M. Federman, S. Levitsky, and J. D. McCully Adenosine-enhanced ischemic preconditioning modulates necrosis and apoptosis: effects of stunning and ischemia-reperfusion Ann. Thorac. Surg., August 1, 2001; 72(2): 555 - 563. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y. Suematsu, T. Ohtsuka, Y. Hirata, K. Maeda, K. Imanaka, and S. Takamoto L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts Eur. J. Cardiothorac. Surg., June 1, 2001; 19(6): 873 - 879. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. D. McCully, Y. Toyoda, M. Uematsu, R. D. Stewart, and S. Levitsky Adenosine-enhanced ischemic preconditioning: adenosine receptor involvement during ischemia and reperfusion Am J Physiol Heart Circ Physiol, February 1, 2001; 280(2): H591 - H602. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Toyoda, I. Friehs, R. A. Parker, S. Levitsky, and J. D. McCully Differential role of sarcolemmal and mitochondrial KATP channels in adenosine-enhanced ischemic preconditioning Am J Physiol Heart Circ Physiol, December 1, 2000; 279(6): H2694 - H2703. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. Abete, C. Calabrese, N. Ferrara, A. Cioppa, P. Pisanelli, F. Cacciatore, G. Longobardi, C. Napoli, and F. Rengo Exercise training restores ischemic preconditioning in the aging heart J. Am. Coll. Cardiol., August 1, 2000; 36(2): 643 - 650. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ANN THORAC SURG | ASIAN CARDIOVASC THORAC ANN | EUR J CARDIOTHORAC SURG |
| J THORAC CARDIOVASC SURG | ICVTS | ALL CTSNet JOURNALS |
