Effects of calcium in continuous cardioplegia on myocardial protection

The effects of calcium (Ca) on a hyperkalemic cardioplegic solution for continuous cardioplegia were examined in an isolated perfused working rat heart model. The coronary arteries were perfused with a modified Krebs-Henseleit bicarbonate buffer (K-H) solution, containing various concentrations of Ca(0.1, 0.6, 1.2, and 2.5 mmol/l) and a high concentration of potassium (20 mmol/l), for 180 min, after which cardiac arrest was induced at 37°C for 180 min. Cardiac function and creatine kinase (CK) were measured. In the control group, K-H solution was infused in place of the cardioplegic solution, and cardiac arrest was not induced. No significant differences were observed between the groups infused with the K-H solution containing Ca concentrations of 0.6, 1.2, and 2.5 mmol/l in the percent recovery of aortic flow (82.1±2.9%, 80.6±2.0%, and 71.5±3.7% (mean±SEM) respectively) or in the recovery of other indices of cardiac function, or in CK leakage. There were also no significant differences in the recovery of cardiac function and CK leakage between these groups and the control group. In the Ca 0.1 mmol/l group, however, the characteristic Ca paradox was observed. These findings suggest that if the Ca concentration in a cardioplegic solution is higher than 0.6 mmol/l during continuous cardioplegia, excellent cardioprotective effects will be achieved.     

Risk of low calcium and high magnesium in continuous warm hyperkalemic cardioplegia.

BACKGROUND: The recent introduction of operations on a warm heart has prompted clinical reports on the usefulness of continuous blood cardioplegia, but no in-depth basic evaluation of continuous cardioplegia has been done. The cardioprotective effects of magnesium (Mg) and calcium (Ca) in continuous warm hyperkalemic crystalloid cardioplegic solutions were investigated in an isolated rat heart model. METHODS: Isolated rat hearts were arrested for 180 minutes at 37 degrees C with a continuous warm hyperkalemic (20 mmol/L) modified Krebs-Henseleit bicarbonate buffer solution containing 1.2, 8.0, or 16.0 mmol/L of Mg and 0.1 to 2.5 mmol/L of Ca in different concentrations. Recovery of cardiac function and tissue damage were estimated. RESULTS: For each Mg concentration, the percentage recovery of aortic flow generated dose-response curves depending on Ca concentration. However, as Mg concentration increased, the recovery of aortic flow decreased in the groups with 0.5 mmol/L of Ca or less. CONCLUSIONS: In continuous warm cardioplegia the combination of low Ca and high Mg concentration caused severe cardiac injury, and normal Ca concentration avoids cardiac injury regardless of Mg concentrations.     

Experimental myocardial preservation study of adding perfluorochemicals (FC43) in lidocaine cardioplegia.

OBJECTIVE: Lidocaine exhibits a cardioplegic action via acute inhibition of sodium influx into the myocardial cells. In terms of the cardiac function and calcium dynamics in the myocardial cells, we investigated the myocardial protective effect of addition of FC43 of Perfluorochemicals, which has an excellent oxygen transport function to meet the myocardial oxygen demand, on lidocaine-induced cardioplegia. METHODS: Isolated rat hearts were perfused with Langendorff mode and were divided to three experimental groups. During of preservation, these hearts were perfused continuously with the next three solution, potassium chloride was added to Krebs-Henseleit bicarbonate buffer to make potassium concentration of 20 mM in the first group (Group A), 2 mM lidocaine was added to Krebs-Henseleit bicarbonate buffer in the second group (Group B), and 2 mM lidocaine and 20% FC43 were added to Krebs-Henseleit bicarbonate buffer in the third group (Group C). After 60 minutes of continuous perfusion, the cardiac function and the intracellular calcium concentration in Groups A and B during cardioplegia were measured. Furthermore, after 360 minutes of continuous coronary perfusion, the cardiac function were measured in Group B and Group C. RESULTS AND CONCLUSIONS: Lidocaine cardioplegia showed a good recovery of cardiac function, because lidocaine induced prompt cardiac arrest by blocking sodium influx and inhibited the intracellular calcium overload by the following inhibition of sodium-calcium channels. Moreover, our results suggested that combining Perfluorochemicals with lidocaine produced a more effective myocardial-preservation that meets the myocardial oxygen demand during long-term cardiac arrest.     

Myocardial preservation related to magnesium content of hyperkalemic cardioplegic solutions at 8 degrees C

This study investigates whether the addition of magnesium to a hyperkalemic cardioplegic solution containing 0.1 mM ionized calcium improves myocardial preservation, and whether there is an optimal magnesium concentration in this solution. Isolated perfused rat hearts were arrested for two hours by this cardioplegic solution, which was fully oxygenated and infused at 8 degrees C every 15 minutes to simulate clinical conditions. The cardioplegic solution contained either 0, 2, 4, 8, 16, or 32 mM magnesium. At end-arrest, the myocardial creatine phosphate concentration (nanomoles per milligram of dry weight) was 20.7 +/- 2.1, 22.9 +/- 1.7, 24.8 +/- 2.0, 31.3 +/- 1.4, 33.1 +/- 1.8, and 31.6 +/- 0.8, respectively, in hearts given cardioplegic solution containing these magnesium concentrations. Thus, the concentration of creatine phosphate was significantly higher at end-arrest when the cardioplegic solution contained 8, 16, or 32 mM than 0 or 2 mM magnesium (p less than 0.002) or 4 mM magnesium (p less than 0.02), and highest with 16 mM magnesium. Also, creatine phosphate was more sensitive to the magnesium concentration of the cardioplegic solution than was end-arrest adenosine triphosphate levels, which did not differ among the experimental groups. Aortic flow, expressed as a percentage of prearrest aortic flow, was 60.3 +/- 5.0, 70.2 +/- 5.5, 71.6 +/- 4.4, 71.8 +/- 4.8, 81.0 +/- 5.0, and 71.8 +/- 5.3, respectively. The addition of magnesium to the cardioplegic solution improved recovery of aortic flow (p less than 0.05, 16 mM versus 0 mM magnesium). We conclude from these data that with deep myocardial hypothermia and at an ionized calcium concentration of 0.1 mM, the addition of magnesium, over a broad concentration range, improved preservation of myocardial creatine phosphate and, at a concentration of 16 mM, improved aortic flow. The optimal magnesium concentration in the cardioplegic solution was 16 mM.     

Non-depolarizing cardioplegia activates Ca-ATPase in sarcoplasmic reticulum after reperfusion

Objectives: Depolarizing cardioplegia is the most common method for myocardial preservation in cardiac operations. However, depolarizing cardioplegia causes depolarization of the membrane potential by extracellular hyperkalemia, resulting in depletion of energy stores and calcium overload. This study examined the hypothesis that non-depolarizing cardioplegia would provide superior protection compared with depolarizing cardioplegia. Methods: In an isolated rat heart Langendorff model, hearts were perfused for 10 min with St. Thomas' Hospital cardioplegic solution (Group I: n=20), St. Thomas' Hospital cardioplegic solution+Lidocaine 1 mM (Group II: n=20) or non-depolarizing cardioplegia (Group III: n=20). The hearts then were subjected to 60 min of normothermic global ischemia, after which they were perfused with Krebs–Henseleit buffer at 37 °C for 30 min. The percent recovery of functional data, myocardial cyclic AMP contents, and myocardial cyclic GMP contents were recorded at each time point (base, after the administration of cardioplegia, after global ischemia, and after 30 min of reperfusion). Ca²⁺-ATPase in sarcoplasmic reticulum was measured at pre-ischemia and 30 min of reperfusion. Results: The percent recovery of developed pressure and ±dp/dt were significantly higher in Group III than in other groups. Myocardial cyclic AMP and GMP contents were elevated after reperfusion in all groups. However, in Group III, myocardial cyclic AMP contents after 30 min of reperfusion were significantly higher than in other groups (Group III: 14.7±1.6 vs. Group I: 8.7±1.0, Group II: 8.3±0.2 pmol/mg dry weight, P=0.05) but not cGMP. The sarcoplasmic reticulum Ca²⁺-ATPase activities at 30 min of reperfusion significantly increased in Group III compared with Groups II and I (Group III: 70.3±3.6 vs. Group I: 46.8±3.4, Group II: 53.9±6.1 μmol Pi/mg per h, P=0.025 and P=0.030). Conclusions: Non-depolarizing cardioplegia induced the activity of Ca²⁺-ATPase in sarcoplasmic reticulum after reperfusion. The activity would be increased by the cyclic AMP pathway. These findings suggested that non-depolarizing cardioplegia prevented calcium overload after reperfusion, especially decreased cytosolic calcium during the diastolic phase.     

Successful rewarming technique of isolated rat hearts following a long term preservation--calcium increase in a step-wise fashion

This study was designed to evaluate the successful rewarming technique of isolated rat hearts which was preserved for 24 hour. Isolated rat hearts preserved with hydroxy ethyl starch (3g/dl) solution at 15 degrees C, was rewarmed and calcium concentration of the perfusate was increased in a step-wise fashion from 0.25 to 2.5mM every 5 minutes. Other hearts were also rewarmed and perfused with normal calcium (2.5mM) solution, throughout the rewarming period. The hearts perfused with normal calcium solution contracted a few times, and then severely contractured. The heart lost its color and acquired a pale and mottled appearance. On the other hand, the hearts perfused low calcium solution started beating spontaneously, and their heart rate and left ventricular pressure was increased gradually according to the calcium increase. In addition, re-introduction of normal calcium concentration did not change the cardiac parameters. This results indicated that step-wise increase of calcium concentration of the perfusate prevented heart contracture after rewarming and was a useful rewarming technique.     

Cold continuous antegrade blood cardioplegia: high versus low hematocrit.

OBJECTIVE: Cold continuous antegrade blood cardioplegia (CCABCP) is used with different hematocrit values. We investigated the consequences of CCABCP with low hematocrit (LH: 20-25%) versus high hematocrit (HH: 40-45%). METHODS: Anesthetized open chest pigs (25 kg) were placed on cardiopulmonary bypass (CPB). The hearts were arrested for 30 min by 6 degrees C CCABCP with either LH or HH (n=8, each): After an initial 3 min application of high potassium (20 mEq) BCP the hearts were arrested for subsequent 27 min by normokalemic 6 degrees C cold blood delivered continuously antegradely. Thereafter the hearts underwent perfusion with warm systemic blood for an additional 30 min on CPB. Biochemical cardiac data (MVO(2) (ml min(-1)100 g(-1)), release of creatine kinase (CK; units min(-1)100 g(-1))) and lactate (mg min(-1)100 g(-1))) and the coronary vascular resistance index (CVRI (mmHg ml(-1)ming)) were measured during CPB. Total tissue water content (%) and left and right ventricular stroke work indices (LV-and RV-SWI (g m kg(-1))) were assessed 30 min after discontinuation of CPB and compared to pre-CPB controls. RESULTS: The hearts of the LH group had no biochemical or functional disturbance. The HH group showed marked CK leakage (0.6+/-0.2* vs. 0.1+/-0.1, *P<0.05 for comparison of LH vs. HH with Student's t-test for unpaired data), impaired initial oxygen consumption (4+/-1* vs. 7+/-1) after cardiac arrest, an increased CVRI (82+/-12* vs. 50+/-8), the formation of myocardial edema (81.0+/-1.3* vs. 77.5+/-1.2), and poor functional recovery (LVSWI 0.2+/-0.1* vs. 1.0+/-0.1; RVSWI 0.1+/-0.1* vs. 0.5+/-0.1). The absence of lactate production in both groups was in accord with the non-ischemic protocol. CONCLUSIONS: CCABCP with a low hematocrit of 20-25% is cardioprotective. In contrast, CCABCP with a high hematocrit of 40-45% jeopardizes the heart despite avoiding ischemic periods, and should be avoided.     

Magnesium ion is beneficial in hypothermic crystalloid cardioplegia

The role of magnesium ion and its relation to the calcium concentration of cardioplegic solutions was reexamined in this study. Isolated rat hearts were used with an oxygenated modified Krebs-Henseleit bicarbonate buffer as perfusion medium. The hearts were arrested for 20 minutes at 37 degrees C or 90 minutes at 24 degrees C. Treatment groups received one dose of nine possible cardioplegic solutions containing magnesium (0, 1.2, or 15 mmol/L) and calcium (0.05, 1.5, or 4.5 mmol/L). Ninety-six percent of the 75 magnesium-treated hearts recovered, regardless of the calcium concentration, in contrast to a 52% recovery rate in the 69 hearts that did not receive magnesium. The addition of 15 mmol/L Mg2+ to a cardioplegic solution containing no magnesium but 0.05 mmol/L Ca2+ significantly increased (p less than 0.01) the percent recovery of the following parameters of cardiac function: systolic pressure, 74% to 93% (37 degrees C), 64% to 98% (24 degrees C); cardiac output, 76% to 101% (37 degrees C), 71% to 102% (24 degrees C); stroke work, 64% to 104% (37 degrees C), 52% to 99% (24 degrees C); and adenosine triphosphate level, 75% to 83% (37 degrees C), 58% to 90% (24 degrees C). There were significant reductions (p less than 0.03) in percent recovery (37 degrees C and 24 degrees C) of cardiac output, stroke work, and adenosine triphosphate level in the groups that contained 0 or 15 mmol/L Mg2+ as the calcium concentration was increased from 0.05 to 4.5 mmol/L.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of epidural insertion site and surgical procedure on plasma lidocaine concentration

We compared the plasma lidocaine concentrations associated with continuous epidural infusion at different insertion sites in patients during surgery using epidural plus general anesthesia. In Study 1, there were 12 patients in each of four surgical groups in whom blood loss was expected to be <400 mL. The four groups were as follows: the lower extremity, the lower abdomen, the upper abdomen, and the lung. Liver surgery was excluded from Study 1. Study 2 comprised patients undergoing radical hysterectomy or radical prostatectomy (a radical operation group, n = 12) and hepatectomy (a hepatectomy group, n = 12) in whom the expected surgical blood loss was more than 1500 mL. All patients initially received 0.1 mL/kg followed by a continuous infusion of 0.1 mL. kg(-1). h(-1) of 1.5% lidocaine, and plasma concentrations of lidocaine were measured at 15, 30, 60, 90, and 120 min and every 60 min thereafter to 300 min. The plasma lidocaine concentration during surgery did not change regardless of the infusion site or the surgical site, other than the liver. The plasma concentrations of lidocaine in the hepatectomy group increased significantly at 180 min (2.9 +/- 0.6 microg/mL, P < 0.01), 240 min (3.5 +/- 0.7 microg/mL, P < 0.01), and 300 min (3.6 +/- 0.74 microg/mL, P < 0.01) compared with that at 15 min (2.0 +/- 0.3 microg/mL), and these values were significantly larger than those in all other groups.     

Potential deleterious effect of beta-adrenergic stimulation during warm-blood cardioplegia in rabbit hearts.

We hypothesized that beta-adrenergic stimulation with isoproterenol during continuous normothermic cardioplegic arrest would enhance the regenerative and regulatory function of the myocardium, resulting in improved cardiac function. We studied isolated rabbit hearts paced at approximately 200 beats per minute (bpm) and perfused by a support rabbit. We measured ventricular pressure over a range of ventricular volumes to determine maximal elastance (Emax) at baseline and 20 and 45 min after discontinuation of cardioplegia. Myocardial oxygen consumption (MVO2) measurements were performed simultaneously and during cardioplegic arrest. Hearts were prospectively randomized to receive either isoproterenol at 0.1 M or control in blinded fashion for 10 min during a 1-h continuous warm-blood cardioplegic arrest. Compared to control hearts, isoproterenol-treated hearts had trends toward longer time to first spontaneous heartbeat (control 141 +/- 43 vs. isoproterenol 200 +/- 74 s, p = .07), and longer time to capture of atrial pacing (control 214 +/- 52 vs. isoproterenol 288 +/- 91 s, p = .06). There was no difference observed in the MVO2 between isoproterenol-treated and control groups of hearts. MVO2 decreased during cardioplegia (p < .01), but there was no significant change in MVO2 during isoproterenol infusion during cardioplegic arrest. There was a significant reduction in Emax compared to baseline 20 min after discontinuation of cardioplegic arrest in both groups (control 7.3 +/- 1.7 mm Hg/microL vs. 9.0 +/- 1.7 mm Hg/microL, p = .02, isoproterenol-treated 6.8 +/- 2.8 mm Hg/microL vs. 8.2 +/- 2.6 mm Hg/microL, p = .01, respectively), with recovery of Emax by 45 min in control hearts only. We conclude that exposure of hearts to isoproterenol during warm cardioplegic arrest has a deleterious effect that may be mediated through mechanisms independent of increased myocardial oxygen consumption.     

Transient hypocalcemic reperfusion does not improve postischemic recovery in the rat heart after preservation with St. Thomas' Hospital cardioplegic solution.

We used the isolated perfused working rat heart to investigate the effects of transient hypocalcemic reperfusion after cardioplegic arrest with the St. Thomas' Hospital cardioplegic solution and 25 minutes of global normothermic (37 degrees C) ischemia. Hearts were reperfused (Langendorff mode) transiently (20 minutes) with solutions containing various concentrations of calcium; this was followed by 30 minutes of reperfusion with standard (1.4 mmol/L, the physiologic concentration) calcium buffer (10 minutes in the Langendorff mode and 20 minutes in the working mode). Recovery of cardiac output in control hearts (calcium concentration 1.4 mmol/L throughout) was 51.7% +/- 4.6%; in hearts transiently reperfused with hypocalcemic buffer (0.25, 0.5, 0.75, or 1.0 mmol/L) the recoveries of cardiac output were 49.3% +/- 6.4%, 52.2% +/- 7.2%, 58.7% +/- 3.2%, and 47.2 +/- 4.7%, respectively (all not significant), whereas recovery was only 14.7% +/- 2.8% (p less than 0.05) in hearts transiently reperfused with calcium 0.1 mmol/L. Creatine kinase leakage was significantly (p less than 0.05) greater in the group reperfused with calcium 0.1 mmol/L, but it did not vary significantly between the other groups. Tissue high-energy phosphate content was similar and in the normal range in all groups except for the group reperfused with calcium 0.1 mmol/L. In further experiments, the duration of hypocalcemic (0.5 mmol/L) reperfusion was varied (0, 5, 10, 15, 20, or 30 minutes). No significant differences in recovery of cardiac output were observed (58.2% +/- 5.0%, 52.3% +/- 5.7%, 52.0% +/- 8.2%, 61.2% +/- 5.0%, 62.2% +/- 4.3%, and 66.2% +/- 3.2%, respectively). In additional studies, the standard calcium concentration (1.4 mmol/L) used before and after ischemia was replaced by hypercalcemic solution (2.5 mmol/L). Despite this, transient (10 minutes) hypocalcemic (0.5 mmol/L) reperfusion did not improve recovery. Finally, studies were undertaken with a longer duration of ischemia (40 minutes), and although recovery of cardiac output in the hypocalcemic group (0.5 mmol/L for 10 minutes) tended to be higher than in the control group (29.7% +/- 4.8% versus 18.5% +/- 4.9%, respectively), statistical significance was not achieved. We conclude that in these studies transient hypocalcemic reperfusion did not afford any additional protection over and above that afforded by cardioplegia alone.     

Effect of the potassium-channel opener nicorandil as an adjunct to cardioplegia on myocardial preservation in isolated rabbit hearts

We studied the effect of nicorandil on the hemodynamic, biochemical, and ultrastructural changes in rabbit hearts (n=50) rendered cardioplegic with a single injection of Bretschneider's HTK solution over 30min or 60min at 37°C or 15°C, followed by reperfusion at 37°C for 60min. Particular attention was focused on the aspects of doseresponse relationship, temperature sensitivity, and ischemic tolerance. Isolated hearts were prepared for modified Langendorff circulation using modified Krebs-Henseleit bicarbonate solution bubbled with a 95% O₂-5% CO₂ gas mixture, to which nicorandil (0, 0.1, 1, and 5 mM) was added. The optimal concentration of nicroandil was 1 mM, which increased the recovery of left ventricular (LV) function, affecting coronary flow and the myocardial cyclic adenosine monophosphate, but not the myocardial concentrations of adenine nucleotide compounds or total calcium. These effects were abolished by the addition of glibenclamide to the HTK, but they were not diminished by a high potassium (K⁺) concentration of 20 mM. The addition of nicorandil 1 mM to the HTK at 15°C did not improve the recovery of LV function. Our result suggested that nicorandil used adjunctly prevents LV functional depression after 30 min, and possibly 60 min of cardioplegia at 37°C, and that this effect is not disturbed by a high K⁺ concentration up to 20 mM. However, nicorandil has temperature sensitivity whereby it loses its efficacy at 15°C.     

Experimental Conditions Are Important Determinants of Cardiac Inotropic Effects of Propofol

Background: The rationale for this study is that the depressant effect of propofol on cardiac function in vitro is highly variable but may be explained by differences in the temperature and stimulation frequency used for the study. Both temperature and stimulation frequency are known to modulate cellular mechanisms that regulate intracellular free Ca2+ concentration ([Ca2+]i) and myofilament Ca2+ sensitivity in cardiac muscle. The authors hypothesized that temperature and stimulation frequency play a major role in determining propofol-induced alterations in [Ca2+]i and contraction in individual, electrically stimulated cardiomyocytes and the function of isolated perfused hearts.

Methods: Freshly isolated myocytes were obtained from adult rat hearts, loaded with fura-2, and placed on the stage of an inverted fluorescence microscope in a temperature-regulated bath. [Ca2+]i and myocyte shortening were simultaneously measured in individual cells at 28[degrees] or 37[degrees]C at various stimulation frequencies (0.3, 0.5, 1, 2, and 3 Hz) with and without propofol. Langendorff perfused hearts paced at 180 or 330 beats/min were used to assess the effects of propofol on overall cardiac function.

Results: At 28[degrees]C (hypothermic) and, to a lesser extent, at 37[degrees]C (normothermic), increasing stimulation frequency increased peak shortening and [Ca2+]i. Times to peak shortening and rate of relengthening were more prolonged at 28[degrees]C compared with 37[degrees]C at low stimulation frequencies (0.3 Hz), whereas the same conditions for [Ca2+]i were not altered by temperature. At 0.3 Hz and 28[degrees]C, propofol caused a dose-dependent decrease in peak shortening and peak [Ca2+]i. These changes were greater at 28[degrees]C compared with 37[degrees]C and involved activation of protein kinase C. At a frequency of 2 Hz, there was a rightward shift in the dose-response relation for propofol on [Ca2+]i and shortening at both 37[degrees] and 28[degrees]C compared with that observed at 0.3 Hz. In Langendorff perfused hearts paced at 330 beats/min, clinically relevant concentrations of propofol decreased left ventricular developed pressure, with the effect being less at 28[degrees]C compared with 37[degrees]C. In contrast, only a supraclinical concentration of propofol decreased left ventricular developed pressure at 28[degrees]C at either stimulation frequency.     

Optimal temperature of continuous lidocaine perfusion for the heart preservation

Objective: During cardiovascular surgery, lidocaine is administered to the cardioplegic system to stabilize cell membrenes and prevent arrhythmia. Lidocaine is also commonly used in hypothermia Both lidocaine and hypothermia are myocardially protective. Under normothermia, lidocaine displays its full pharmacological effects, which are apt, however, to be suppressed under hypothermia. We conducted experiments to determine the optimal temperature for myocardial protection in continuous lidocaine cardioplegia. Methods: In Langendorff mode, rat hearts were continuously perfused with 1 mMol/l of lidocaine solution at 36±0.5°C (Group A), 24±0.5°C (Group B), or 7±0.5°C (Group C) during preservation. Cardiac function and intracellular calcium concentration were measured during both preservation and reperfusion. Heat shock protein 70 (HSP70) was subsequently analyzed by Western blotting. Results: Rapid cardiac arrest was obtained in Groups A and C. Heart rate recovery was good and ultimately the best in Group B, but worst in Group A. During lidocaine perfusion, the volume of coronary perfusion flow decreased gradually in all groups. After reperfusion, Group A showed only a slight increase in coronary perfusion, While Groups B and C showed a marked increase. Left ventricular contractility showed good recovery in all groups. The calcium concentration increased slightly in Group A, but decreased in Groups B and C. No calcium overload was evident in Group A. The same HSP70 level was detected in all groups. Conclusion: Lidocaine used in normothermia does not decrease cardiac metabolism or oxygen consumption, and displays full, pharmacological effectiveness in preventing ischemic injury. We found 36°C to be the optimal temperature for heart preservation by coronary perfusion with lidocaine cardioplegia.     

The effect of graft perfusion with warm blood cardioplegia for cadaver heart transplantation

This study was designed to verify the effect of reperfusion of donor hearts in a perfusion apparatus after 60 min of global ischemia prior to heart transplantation. Thirteen dogs were exsanguinated from the femoral artery and cardiac arrest was achieved. The hearts were left in situ at room temperature (25°C)for 60 min. In group A (n=7), the hearts were excised and reperfused 60 min after cardiac arrest in the perfusion apparatus with substrate-enriched warm blood cardioplegia (WBCP) containing a hydroxyl radical scavenger, EPC, followed by 45 min of blood perfusion, Next, the hearts were preserved in cold (4°C) University of Wisconsin (UW) solution. In group B (n=6), the hearts were perfused with cold (4°C) St. Thomas' solution 60 min after cardiac arrest and preserved in cold UW solution. Thereafter, all hearts in both groups were transplanted orthotopically to recipient dogs. In group A, 6 of 7 dogs were weaned from cardiopulmonary bypass (CPB). In group B, only 2 of 6 dogs were weaned from CPB. Moreover, 3 of the 6 hearts in group B did not start beating after transplantation (stone heart). This study suggested reperfusion of the donor heart in the perfusion apparatus with WBCP to be a beneficial preconditioning method when utilizing 60-min arrested hearts for transplantation. This study was supported in part by Senju Pharmaceutical Co. Ltd., Osaka, Japan     

Experimental conditions are important determinants of cardiac inotropic effects of propofol

BACKGROUND: The rationale for this study is that the depressant effect of propofol on cardiac function in vitro is highly variable but may be explained by differences in the temperature and stimulation frequency used for the study. Both temperature and stimulation frequency are known to modulate cellular mechanisms that regulate intracellular free Ca2+ concentration ([Ca2+]i) and myofilament Ca2+ sensitivity in cardiac muscle. The authors hypothesized that temperature and stimulation frequency play a major role in determining propofol-induced alterations in [Ca2+]i and contraction in individual, electrically stimulated cardiomyocytes and the function of isolated perfused hearts. METHODS: Freshly isolated myocytes were obtained from adult rat hearts, loaded with fura-2, and placed on the stage of an inverted fluorescence microscope in a temperature-regulated bath. [Ca2+]i and myocyte shortening were simultaneously measured in individual cells at 28 degrees or 37 degrees C at various stimulation frequencies (0.3, 0.5, 1, 2, and 3 Hz) with and without propofol. Langendorff perfused hearts paced at 180 or 330 beats/min were used to assess the effects of propofol on overall cardiac function. RESULTS: At 28 degrees C (hypothermic) and, to a lesser extent, at 37 degrees C (normothermic), increasing stimulation frequency increased peak shortening and [Ca2+]i. Times to peak shortening and rate of relengthening were more prolonged at 28 degrees C compared with 37 degrees C at low stimulation frequencies (0.3 Hz), whereas the same conditions for [Ca2+]i were not altered by temperature. At 0.3 Hz and 28 degrees C, propofol caused a dose-dependent decrease in peak shortening and peak [Ca2+]i. These changes were greater at 28 degrees C compared with 37 degrees C and involved activation of protein kinase C. At a frequency of 2 Hz, there was a rightward shift in the dose-response relation for propofol on [Ca2+]i and shortening at both 37 degrees and 28 degrees C compared with that observed at 0.3 Hz. In Langendorff perfused hearts paced at 330 beats/min, clinically relevant concentrations of propofol decreased left ventricular developed pressure, with the effect being less at 28 degrees C compared with 37 degrees C. In contrast, only a supraclinical concentration of propofol decreased left ventricular developed pressure at 28 degrees C at either stimulation frequency. CONCLUSION: These results demonstrate that temperature and stimulation frequency alter the inhibitory effect of propofol on cardiomyocyte [Ca2+]i and contraction. In isolated cardiomyocytes, the inhibitory effects of propofol are more pronounced during hypothermia and at higher stimulation frequencies and involve activation of protein kinase C. In Langendorff perfused hearts at constant heart rate, the inhibitory effects of propofol at clinically relevant concentrations are more pronounced during normothermic conditions.     

Myocardial protection by coronary washout during global ischemic cardiac arrest

The effect of intermittent coronary washout (WO) during global ischemic cardiac arrest (ICA) was evaluated in isolated blood perfused dog hearts undergoing 90 min normothermic ICA and 90 min reperfusion. WO consisted of infusion of 100 ml normothermic dog plasma at 100 mm Hg every 10 min during ICA. Systolic and diastolic pressures were measured at constant volume with a left ventricular balloon. Coronary blood flow (CBF) was measured, and transmyocardial oxygen, lactate, and glucose differences were calculated. Adenosine triphosphate (ATP), creatine phosphate (CP), calcium (Ca²⁺), glycogen, and water content were measured from left ventricular biopsies. During 90 min of WO, hearts extracted glucose (15 ± 4 mg/g dry wt LV) and lost lactate (90 ± 5 μmole/g dry wt LV). ATP and CP were significantly depressed at arrest in both groups although WO resulted in significantly higher levels of ATP and CP. CP returned to control levels at 90 min reperfusion in the WO group but remained depressed in the ICA group. Calcium accumulation was greater in hearts with ICA. With reperfusion, both ICA and WO groups demonstrated early hyperemia and rapid lactate washout. There were no differences in total CBF, AVO₂, MOV₂, and myocardial glycogen or water content. Systolic performance was equally depressed in both groups at 90 min of reperfusion. Diastolic compliance, while still impaired, was better preserved in WO when measured in the arrested heart at 90 min ICA (P < 0.01) and in the contracting heart after 90 min reperfusion (P < 0.02). Normothermic coronary washout during 90 min of normothermic ischemic arrest without cardioplegic agents produces improved ventricular compliance and energy metabolism, and reduces myocardial calcium accumulation.     

Superior myocardial protection with nicorandil cardioplegia.

OBJECTIVE: The ATP-sensitive potassium channel (K(ATP)) activator nicorandil used as cardioplegic agent may protect the left ventricle during cardiac arrest. Nicorandil in cold blood was compared with standard hyperkalemic blood and crystalloid cardioplegia. METHODS: Twenty-one pigs were randomly assigned to three groups: (1) cold hyperkalemic crystalloid (n=7); (2) cold hyperkalemic blood (n=7); and (3) nicorandil as cardioplegia in cold blood (n=7). Left ventricular mechanical performance, pressure-volume area (PVA) and myocardial oxygen consumption (MVO(2)) were measured before and at 1 and at 2 h after 60 min of cold global ischemia on cardiopulmonary bypass using intraventricular pressure-volume conductance catheters, coronary flow probes and O(2)-content difference. RESULTS: The slope (M(w)) of the stroke work end-diastolic volume relationship, the preload recriutable stroke work relationship, was unchanged after ischemia in the nicorandil group, but was reduced to averaged 62.5% (standard deviation 14) of baseline values in both hyperkalemic perfusions (P<0.05). The slope of the MVO(2)-PVA relationship was unchanged after nicorandil cardioplegia while the slope after hyperkalemic blood and crystalloid cardioplegia increased with 33% (P<0.02) and 52% (P<0.02) of baseline values, respectively. CONCLUSIONS: Nicorandil as sole cardioplegic agent in cold blood given intermittently preserves left ventricular contractility and myocardial energetics significantly better than traditional forms of cardioplegia after cardiac arrest.     

Effect of oxygenated crystalloid cardioplegia on the functional and metabolic recovery of the isolated perfused rat heart

The use of an oxygenated crystalloid cardioplegic solution to improve myocardial preservation during elective cardiac arrest was evaluated with the isolated perfused rat heart used as a model. Experiments were conducted at 4 degrees C and 20 degrees C. The oxygen tension of the nonoxygenated and oxygenated cardioplegic solutions averaged 117 and 440 mm Hg, respectively. At 4 degrees C, the adenosine triphosphate content of hearts subjected to 120 minutes of oxygenated cardioplegia was significantly higher than that of the nonoxygenated cardioplegia group. However, functional recovery during reperfusion was similar for both groups. At 20 degrees C, the myocardial adenosine triphosphate concentration decreased at a significantly faster rate during ischemia in the group receiving nonoxygenated cardioplegia compared with the oxygenated cardioplegia group. Hearts subjected to 180 minutes of ischemia with oxygenated cardioplegia had a normal ultrastructural appearance whereas hearts subjected to 120 minutes of nonoxygenated cardioplegia showed severe ischemic damage. Myocardial functional recovery in the group receiving oxygenated cardioplegia exceeded that of the group receiving nonoxygenated cardioplegia. The use of myocardial adenosine triphosphate concentration at the end of the ischemic period to predict subsequent cardiac output, peak systolic pressure, and total myocardial work showed significant positive correlations.     

左西孟旦乌司他丁与其联合用药对幼兔离体心脏的保护作用

目的 通过幼兔离体心脏Langendorff模型,探讨左西孟旦、乌司他丁及二者联合应用对幼兔离体心脏缺血再灌注损伤的保护作用.方法 建立新西兰幼兔离体心Langendorff模型,经左心房、二尖瓣置入左室测压管.K-H液平衡灌注10 min,分别用K-H液(C组)、乌司他丁5万单位/kg(U组)、小剂量左西孟旦0.1 μmoL/L(L1组)、大剂量左西孟旦0.3 μmol/L(L2 组)、乌司他丁5万单位/kg和左西孟旦0.1 μmol/L(L+U组)灌注10 min.应用St.Thomas停跳液使心脏停跳,全心缺血30 min,然后分别以上述液体复灌30 min.于缺血前和复灌即刻、10 min、20 min、30 min记录心率(HR)、左室内压(LVP)、左室内压最大上升速率(LVdp/dt)、冠脉流量(CF);同时测定冠状静脉流出液中肌酸激酶(CK)、肌钙蛋白(cTnI)、肿瘤坏死因子(TNF-α)、白细胞介素6(IL-6)的浓度.结果 L1 组、L2组和L+U组复灌后LVP、LVdp/dt与对照组(C组)和U组差异有统计学意义,但L2组的心率明显高于其他组.与其他各组比较,左西孟旦和乌司他丁联合用药组复灌后冠脉流量(CF)升高(P<0.05);冠状静脉流出液CK、cTnI,TNF-α、IL-6的浓度明显低于其他组.结论 左西孟旦和乌司他丁通过不同机制均能较好地减轻幼兔心肌缺血再灌注损伤,其联合用药对未成熟心肌的保护作用强于单独应用.

Abstract：

Objective Levosimendan,a new calcium ion sensitizer,is currently used in the treatment of heart failure and as an option for patients with injury to the left heart or at high risk for surgery.The study tried to evaluate the effects of levosimendan and ulinastain for protecting myocardium from ischemia-reperfusion (I/R) injury to the isolated immature rabbit hearts and investigate the possible mechanism.Methods Fifty New Zealand long-ear white immature rabbits were anesthetized and heparinized.Their hearts were rapidly removed and mounted on modified Langendorff apparatus.A left ventricle pressure monitoring line was inserted through the left atrial and mitral valve.The hearts were equilibrated with oxygenated K-H solution at 37℃ for 10 minutes.The rabbit hearts were randomly divided into 5 groups with 10 hearts in each group.Hearts in group C were perfused with K-H solution,in group U were perfused with ulinastain (50000 U/kg),in group LI were perfused with Levosimendan 0.1 μmol/L,in group L2 were perfused with Levosimendan 0.3 μmol/L,and in group L + U were perfused with Ulinastain (50 000 U/kg) and Levosimendan 0.1μmol/L.The hearts were arrested with St-Thomas solution for 30 min.Hearts in each group underwent 30 min-reperfusion with the same solutions after 30 min-global myocardial ischemia.Heart rate ( HR) Jeft ventricular pressure ( LVP) and LVdp/dtMax were monitored.Effluent from coronary sinus was collected at time of ischemia /reperfusion for measuring the concentration of TNF-α,IL-6,CK and cTnI.Results LVP and LVdp/dt in group L1,L2 and L + U were better than those in group C and U.But the heart rates in group L2 were higher than in other groups.Concentrations of CK,cTnI,TNF-α and IL-6 in the effluent from coronary sinus at 0、10 and 30 min of reperfusion were significantly lower in group L + U than in the other groups.Conclusion Levosimendan may have the similar effects with ulinastain in reducing the reperfusion injury to the immature myocardium.The protective effect of levosimendan (0.1 μmol/L) in combination with ulinastain (50 000 U/kg) was better than that of levosimendan or ulinastain alone.