Ultrastructural alterations during ischemia and reperfusion in human hearts during cardiac surgery

Induced cardiac pacemaker cells survive metabolic stress owing to their low metabolic demand

Cardiac pacemaker cells of the sinoatrial node initiate each and every heartbeat. Compared with our understanding of the constituents of their electrical excitation, little is known about the metabolic underpinnings that drive the automaticity of pacemaker myocytes. This lack is largely owing to the scarcity of native cardiac pacemaker myocytes. Here, we take advantage of induced pacemaker myocytes generated by TBX18-mediated reprogramming (TBX18-iPMs) to investigate comparative differences in the metabolic program between pacemaker myocytes and working cardiomyocytes. TBX18-iPMs were more resistant to metabolic stresses, exhibiting higher cell viability upon oxidative stress. TBX18-induced pacemaker myocytes (iPMs) expensed a lower degree of oxidative phosphorylation and displayed a smaller capacity for glycolysis compared with control ventricular myocytes. Furthermore, the mitochondria were smaller in TBX18-iPMs than in the control. We reasoned that a shift in the balance between mitochondrial fusion and fission was responsible for the smaller mitochondria observed in TBX18-iPMs. We identified a mitochondrial inner membrane fusion protein, Opa1, as one of the key mediators of this process and demonstrated that the suppression of Opa1 expression increases the rate of synchronous automaticity in TBX18-iPMs. Taken together, our data demonstrate that TBX18-iPMs exhibit a low metabolic demand that matches their mitochondrial morphology and ability to withstand metabolic insult.

The heart’s pacemaker cells contain mitochondria that are smaller than average and require less energy than other heart cells, properties that help make them naturally resilient to stress. Cardiac pacemaker cells constitute a tiny proportion of the heart’s cells, yet play a critical role in maintaining a steady heartbeat. However, quite how pacemaker cells maintain their automatic rhythm is unclear because their scarcity makes them difficult to study. To examine the cells’ metabolic state further, Hee Cheol Cho at Emory University, Atlanta, and Brian Foster at Johns Hopkins University School of Medicine, Baltimore, and co-workers therefore induced pacemaker cells by adding an embryonic protein to heart muscle cells. The induced pacemaker cells survived well under oxidative stress. The team identified a protein in the pacemakers’ mitochondrial membranes, the expression of which directly influences rhythm responses.

Cardioprotection of ginsenoside Rb1 against ischemia/reperfusion injury is associated with mitochondrial permeability transition pore opening inhibition

OBJECTIVE

To investigate the role of ginsenoside Rb1 (Gs-Rb1) in cardioprotection against ischemia/reperfusion (I/R) or hypoxia/reoxygenation (H/R) injury and to explore whether the cardioprotective action is mediated via attenuating the formation of mitochondrial permeability transition pore (mPTP).

METHODS

A Langendorff-perfused model of rat heart was employed. I/R injury was induced by breaking off perfusion for 40 min then reperfusion for 60 min. Gs-Rb1 (100 μmol/L) were administrated for 10 min before I/R. Infarct size was estimated by the 2,3,5-triphenyl tetrazolium chloride (TTC) staining. Lactate dehydrogenase (LDH) and creatine kinase (CK) released from effluents were measured. Transmission electron microscopy was performed to assess morphological difference between cardiac mitochondrial isolated from I/R rats and Gs-Rb1 pretreated rats. Western blot analysis was used to determine phosphorylation of protein kinase B/Akt, and its downstream target glycogen synthase kinase 3β (GSK-3β). Incubation isolated cardiac mitochondria with Gs-Rb1, Ca2+-induced opening of the mPTP was assessed by the reduction of absorbance at 520 nm (A520). Neonatal rat cardiomyocytes were subjected to hypoxia 9 h followed by reoxygenation 4 h to induce H/R injury. After pretreated with different concentration of Gs-Rb1 (6.25, 25, 100 μmol/L ), cell viability was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) method. The membrane potential was estimated by Rh123 fluorescence. mPTP opening was measured using the probe calcein-AM.

RESULTS

Gs-Rb1 100 μmol/L significantly reduced the infarct size of hearts (26.39%±11.67% vs. I/R group 56.68%±5.88%, P<0.01). Compared with the I/R group, Gs-Rb1 pretreatment decreased LDH and CK levels in the coronary effluent (P<0.05 or P<0.01) as well as attenuated destructive ultrastructure induced by I/R. The protective effect of Gs-Rb1 involved in phosphorylating protein kinase B/PKB (Akt) and GSK-3β. In mitochondria isolated from rat hearts, significant inhibition of Ca2+-induced swelling was observed in samples that were pretreated with Gs-Rb1 (6.25, 25, 100, 400 μmol/L) for 10 min. When cardiomyocytes were isolated from neonatal rat and subjected to H/R, cell viability was increased with treatment of Gs-Rb1 (6.25, 25, 100 μmol/L ). Gs-Rb1 inhibited mPTP opening and restored subsequent loss of mitochondrial membrane potential.

CONCLUSION

Gs-Rb1 presents cardioprotective effect against I/R or H/R injury which involves in activating Akt, phosphorylating GSK-3β and inhibiting mPTP opening.

Dilated cardiomyopathy in a 32-year-old woman with Russell-Silver syndrome

INTRODUCTION

Russell-Silver Syndrome (RSS) is a genetically determined condition characterized by severe intrauterine and postnatal growth retardation; relative macrocephaly; a small, triangular face; and fifth-finger clinodactyly. The etiology of RSS involves epigenetic regulation through either uniparental disomy or genomic imprinting via DNA methylation. There has been no documented association between RSS and cardiomyopathy.

METHODS

We present an original case of a 32-year-old woman with RSS with dilated a cardiomyopathy who on cardiac biopsy showed occasional hypertrophic and atrophic myocytes with no evidence of inflammation, abnormal sarcomeres and disintegration of the Z bands on ultrastructural analysis, abnormal desmin, and normal C9 immunoreactivity.

CONCLUSION

This case represents the first reported association between RSS and cardiomyopathy. Given the complex mechanisms of disease etiology in RSS, this novel case provides insights into the mechanism of progressive dilated cardiomyopathy in an older individual with RSS.

Reperfusion injury intensifies the adaptive human T cell alloresponse in a human-mouse chimeric artery model

OBJECTIVE

Perioperative nonimmune injuries to an allograft can decrease graft survival. We have developed a model for studying this process using human materials.

METHODS AND RESULTS

Human artery segments were transplanted as infrarenal aortic interposition grafts into an immunodeficient mouse host, allowed to "heal in" for 30 days, and then retransplanted into a second mouse host. To induce a reperfusion injury, the healed-in artery segments were incubated for 3 hours under hypoxic conditions ex vivo before retransplantation. To induce immunologic rejection, the animals receiving the retransplanted artery segment were adoptively transferred with human peripheral blood mononuclear cells or purified T cells from a donor allogeneic to the artery 1 week before surgery. To compare rejection of injured versus healthy tissues, these manipulations were combined. Results were analyzed ex vivo by histology, morphometry, immunohistochemistry, and mRNA quantitation or in vivo by ultrasound. Our results showed that reperfusion injury, which otherwise heals with minimal sequelae, intensifies the degree of allogeneic T cell-mediated injury to human artery segments.

CONCLUSIONS

We developed a new human-mouse chimeric model demonstrating interactions of reperfusion injury and alloimmunity using human cells and tissues that may be adapted to study other forms of nonimmune injury and other types of adaptive immune responses.

Immunohistological basis of the late gadolinium enhancement phenomenon in tako-tsubo cardiomyopathy

AIMS

Tako-tsubo cardiomyopathy is characterized by transient contractile dysfunction after emotional or physical stress. Only few patients show late gadolinium enhancement (LGE) in cardiovascular magnetic resonance imaging (MRI). It was the purpose of this study to elucidate the histological basis of this phenomenon.

METHODS AND RESULTS

The study included 15 patients. Tako-tsubo cardiomyopathy was diagnosed by coronary angiography and ventriculography. Cardiac MRI was performed within 24 h of admission. Endomyocardial biopsies were taken during the acute phase and after recovery. The content of fibrosis was determined by immunohistochemical staining of collagen-1. In the acute phase, cardiac MRI revealed LGE in five patients. This was completely reversed at follow-up [14, inter-quartile range (IQR) 11-14.5 days]. All patients showed a significant increase of collagen-1 compared with control tissue. Moreover, the amount of collagen-1 was significantly higher in LGE positive patients (LGE positive: 18.84, IQR 13.82-19.75 AU/microm(2); LGE negative: 7.57, IQR 5.41-9.19 AU/microm(2), P = 0.001). The presence of LGE was not associated with poorer left ventricular function.

CONCLUSION

The presence of LGE cannot rule out tako-tsubo cardiomyopathy. Instead it defines a special subgroup of patients with a disproportionate increase of extracellular matrix.

Effects on Reperfusion Injury of Adding Diltiazem to Tepid Blood Cardioplegia

BACKGROUND

Although the present techniques of myocardial preservation for limiting ischemia/reperfusion injury in open heart operations yield excellent results for most patients, certain subgroups of patients with advanced coronary artery disease present a challenge in terms of intraoperative safety.

METHODS

In a prospective, randomized, controlled study, we assessed the myocardial protective effects of a total dose of 150 +/- 150 = 300 microg/kg diltiazem added to induction and terminal (reperfusion) doses of tepid blood cardioplegia. We determined the myocardial morphological (ultrastructural) and enzymatic (serum assays for the cardiospecific isoenzyme of creatine kinase [CK-MB]) changes and functional recovery (atrioventricular [AV]-node recovery time and postoperative need for inotropic support) in patients undergoing elective coronary artery bypass operations. The determinations were made with respect to values for control patients, who received the same cardioplegia but without the addition of diltiazem.

RESULTS

The mean isoenzyme CK-MB levels and semiquantitative ultrastructural score values of the diltiazem group were significantly less than those of the control group. Although AV-node recovery time was significantly prolonged (P < .05), this factor did not have major clinical impact.

CONCLUSIONS

We concluded that the addition of 150 +/- 150 microg/kg diltiazem to the induction and terminal doses of tepid cardioplegia enhanced myocardial protection in elective aortocoronary bypass surgery in high-risk patients and presented no significant additional operative risk.

Effects of dietary phytoestrogen on global myocardial ischemia-reperfusion injury in isolated female rat hearts

We investigated the effects of phytoestrogen on global myocardial ischemia-reperfusion injury in five groups of female rats. A high-phytoestrogen group (HPE) was ovariectomized (Ovx) and fed a diet containing soybean protein and a high-isoflavone soy extract. Another Ovx group of rats was fed the same diet as the HPE group but treated with the estrogen receptor blocker ICI-182,780 (HPE + ICI). A third group of Ovx rats was fed a diet containing soybean protein alone (low-phytoestrogen content; LPE). A fourth Ovx group was fed a diet free of phytoestrogen (Ovx). The fifth group of rats was sham ovariectomized (sham). Hearts from all rats were subjected to 30 min of global, hypothermic (4 degrees C), cardioplegic ischemia and 120 min of normothermic (37 degrees C) reperfusion with oxygenated Krebs-Henseleit buffer. Compared with either the sham or the HPE group, the Ovx and HPE + ICI groups had significantly decreased first derivative of left ventricular pressure (dP/dt), coronary flow rate (CFR), nitrite production and mitochondrial respiratory function and significantly increased Ca2+ accumulation and myocardial histological and ultrastructural injury. The CFR of the LPE group was significantly different from that of either Ovx or HPE + ICI group but the dP/dt, nitrite production, Ca2+ accumulation, and mitochondrial function were not. Our results indicate that diets containing phytoestrogen extract play a cardioprotective role in global myocardial ischemia-reperfusion in female rats.

The influence of hypoxia on the myocardium of experimentally diabetic rats with and without protection by Ginkgo biloba extract. III: Ultrastructural investigations on mitochondria

Completing our preceding ultrastructural studies on diabetes and additional acute hypoxia of rat myocardium and the protective effect of Ginkgo extract (EGb) we investigated specific ultrastructural-morphometric parameters of corresponding mitochondria. Aim of the study was to answer the question whether mitochondria of diabetic myocardium are more sensitive to hypoxia than in normal condition, and whether antioxidative protection by EGb is effective. Further we compared the ultrastructural reactions of mitochondria of different intracellular locations. Voluminal parameters of mitochondria indicated a moderate swelling after diabetes and a further slight swelling after additional hypoxia, which was slightly reduced after EGb pretreatment. Decrease of volume density of mitochondrial cristae was less expressed after diabetes and much stronger after additional hypoxia; slight protection by EGb was only visible after diabetes. Degenerative intramitochondrial areas increased significantly after diabetes and after hypoxia; EGb was protective only after additional hypoxia. The relative number of ATPase particles (F1-coupling factors) at the inner mitochondrial membranes was slightly but significantly reduced after diabetes and stronger reduced after additional hypoxia; only in the latter condition Ginkgo extract was slightly protective. The product of volume density of mitochondria x volume density of cristae x relative number of ATPase particles at the inner mitochondrial membrane (as structural equivalent of the myocardial capacity for ATP production) indicated better than single parameters the increasing mitochondrial damage after diabetes of 4 months duration and subsequent acute hypoxia of 20 min duration. After hypoxia this capacity amounted only to 46% of the normal and was improved by EGb to 53%.

Effect of estrogen on global myocardial ischemia-reperfusion injury in female rats

We investigated the effects of estrogen on global myocardial ischemia-reperfusion injury in rats that were ovariectomized (Ovx), sham-operated, or ovariectomized and then given 17beta-estradiol (E(2)beta) supplementation (Ovx+E(2)beta). Hearts were excised, cannulated, perfused with and then immersed in chilled (4 degrees C) cardioplegia solution for 30 min, and then retrogradely perfused with warm (37 degrees C), oxygenated Krebs-Henseleit bicarbonate buffer for 120 min. The coronary flow rate, first derivative of left ventricular pressure, and nitrite production were all significantly lower in Ovx than in sham-operated or Ovx+E(2)beta hearts. However, coronary flow rates or nitrate production were not consistently different throughout the entire reperfusion period. Ca(2+) accumulated more in Ovx rat hearts than in sham-operated or Ovx+E(2)beta hearts, and mitochondrial respiratory function was lower in Ovx hearts than in hearts from the other two groups. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of Ovx rat hearts but not in hearts from either of the other groups. Hematoxylin-basic fuchsin-picric acid-stained sections revealed fewer viable myocytes in hearts from the Ovx group than from the sham or Ovx+E(2)beta group. Transmission electron microscopy demonstrated more severely damaged mitochondria and ultrastructural damage to myocytes in Ovx rat hearts. Our results indicate that estrogen plays a cardioprotective role in global myocardial ischemia-reperfusion injury in female rats.

Myocardial ischemia-reperfusion injury in estrogen receptor-alpha knockout and wild-type mice

We investigated the function of estrogen receptor-alpha in global myocardial ischemia and reperfusion injury in male estrogen receptor-alpha knockout (ERKO) and wild-type mice. Mouse hearts were subjected to 45 min of global ischemia followed by 180 min of reperfusion. The hearts were excised, cannulated, and maintained in a chilled (4 degrees C) cardioplegia solution until warm (37 degrees C) oxygenated Krebs-Henseleit bicarbonate buffer was perfused through the coronary arteries. ERKO hearts started beating later and had a higher incidence of ventricular fibrillation and/or tachycardia than control hearts. Coronary flow rate was significantly lower in ERKO hearts during the 90- and 120-min periods of reperfusion. Ca(2+) accumulation was significantly greater following 30, 90, 120, 150, and 180 min of reperfusion in ERKO hearts. Nitrite production was significantly less in ERKO hearts following 90, 120, and 150 min of reperfusion. Myocardial reduction of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide was significantly lower in experimental ERKO hearts. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of ischemia-reperfused ERKO hearts but not in control tissues. Hematoxylin-basic fuchsin-picric acid-stained sections from experimental ERKO hearts had fewer viable myocytes compared with controls. Transmission electron microscopy revealed swollen and fragmented mitochondria with amorphous and granular bodies, loss of matrix, and rupture of cristae in experimental ERKO hearts. This is the first demonstration that estrogen receptor-alpha plays a cardioprotective role in ischemia-reperfusion injury in males.

Functional and ultrastructural evidence of myocardial stunning after acute carbon monoxide poisoning

OBJECTIVE

To study human myocardial ultrastructural changes after carbon monoxide (CO) poisoning inducing reversible cardiac failure.

DESIGN

CASE REPORT

clinical, functional and morphologic findings.

SETTINGS

Public university-affiliated hospital and electron microscopy laboratory.

PATIENT

A 25-yr-old woman with functional evidence of cardiac failure after acute CO poisoning.

INTERVENTIONS

Hyperbaric and intensive care treatment over 10 days. Scintigraphic and cardiac angiography with endomyocardial biopsy.

MEASUREMENTS AND MAIN RESULTS

Scintigraphy with 99mTc hexakis 2-methoxy-2-isobutyl isonitrile (sestaMIBI) showed an uptake defect in the left anterior descending artery territory. The cardiac angiography demonstrated a slight hypokinesis of the superior two thirds of the anterior wall and of the septal region with completely normal coronary angiograms. Electron microscopy of left ventricular biopsies showed slight ultrastructural changes in the myocytes. In addition, large glycogen deposits were mostly associated with swollen mitochondria. The patient was discharged in good clinical condition on day 10.

CONCLUSIONS

Presence of glycogen deposits associated with abnormal mitochondria may be signs of the incapability of myocardial cells in utilizing energy substrata. In the presence of normal myocardial perfusion, our findings are consistent with the presence of a stunned myocardium-like syndrome. Early recognition and treatment of this clinical syndrome allow the prevention of myocardial infarction.

The role of amrinone in treating heart failure during and after coronary artery surgery supported by cardiopulmonary bypass

Amrinone and dobutamine compare favorably in the treatment of chronic congestive heart failure. There is increasing evidence that amrinone alone or in combination with a catecholamine may be used with considerable success in treating patients who are difficult to wean from cardiopulmonary bypass or who have a low cardiac output syndrome after coronary artery bypass grafting surgery. Amrinone increases intramyocardial cyclic adenosine monophosphate and exerts positive inotropic activity in addition to being a potent vasodilator. It may also improve diastolic function by increasing sarcoplasmic reticulum reuptake of calcium during diastole. It has been administered to patients prior to weaning from cardiopulmonary bypass and has improved hemodynamics and oxygen transport. When compared with dobutamine as primary treatment for depressed myocardial function in patients being weaned from cardiopulmonary bypass after coronary artery bypass grafting surgery, it was more effective in achieving primary treatment objectives. Patients given dobutamine had a higher incidence of myocardial infarction, ventricular fibrillation, supraventricular tachyarrhythmias, sinus tachycardia, and hypertension compared to those given amrinone. It is concluded that amrinone compares favorably with dobutamine and may even be superior when used as primary treatment for treating myocardial depression in patients having coronary artery surgery supported by cardiopulmonary bypass.

Amrinone and dobutamine as primary treatment of low cardiac output syndrome following coronary artery surgery: a comparison of their effects on hemodynamics and outcome

This study was undertaken in order to compare the effectiveness of amrinone and dobutamine as primary treatment of a low cardiac output (CO) after coronary artery bypass graft (CABG) surgery. Thirty patients with preoperative left ventricular dysfunction participated in this open-label randomized study. Patients were included if they failed to separate from cardiopulmonary bypass (CPB) without inotropic support or if they had a cardiac index (CI) less than 2.4 L/min/m2 after CPB regardless of the blood pressure, in the presence of adequate filling pressures. The treatment objectives were to separate from CPB and achieve a CI > or = 2.4 L/min/m2 and a mean arterial pressure > or = 70 mmHg. Patients treated with amrinone received 0.75 mg/kg followed by 10 micrograms/kg/min; when the objectives were not achieved within five minutes, another 0.75 mg/kg was given. Patients treated with dobutamine received an initial infusion of 5 micrograms/kg/min increased stepwise to 15 micrograms/kg/min if necessary. Eleven of 15 amrinone versus 6 of 15 dobutamine patients achieved the predefined treatment objectives with the test drug alone (P = NS). Comparisons of hemodynamics in patients treated solely with amrinone (n = 7) or dobutamine (n = 6) after CPB showed no significant differences between the treatment groups. The incidence of myocardial ischemia as detected by Holter monitor was 36% with amrinone and 33% with dobutamine. Two patients suffered ventricular fibrillation and two had significant supraventricular tachyarrhythmias (heart rate > 130/min) during treatment with dobutamine alone, whereas no significant arrhythmias occurred in the amrinone group (P = NS). Six dobutamine patients (40%) had postoperative myocardial infarction (MI) as opposed to none among the amrinone patients (P = 0.017). These results indicate that amrinone compares favorably with dobutamine as a primary treatment of low CO after CABG. Further study in a larger number of patients will be required in order to determine if the lower incidence of MI in the amrinone group was due to the treatment drug.

Rapid changes in myofibrillar proteins after reperfusion of ischemic myocardium in dogs

The effect of reperfusion on cardiac myofibrillar proteins in the irreversibly injured ischemic myocardium was studied in dogs. Ischemia of the myocardium was produced by complete occlusion of the left anterior descending coronary artery for 90 min (the group of 90I). Occlusion of the coronary artery was then released (reperfusion) for 0.5 min (the group of 90I + 0.5R), 5 min (the group of 90I + 5R), or 20 min (the group of 90I + 20R). In control dogs, the coronary artery was not occluded (the group of no ischemia). Myofibrils (Mfp) were prepared from the myocardium (with centrifugation) in each of the groups, and subjected to electrophoretic analysis in terms of myofibrillar proteins. The yield of Mfs in the groups of 90I, 90I + 0.5R, 90I + 5R, and 90I + 20R was lower than that in the group of no ischemia. There were no marked differences, however, in the electrophoretic pattern of Mfp among the five groups. These results suggest that myofibrils are broken down during reperfusion after ischemia. Therefore, supernatant solution after the first stage of homogenization during the course of preparation of myofibrils (mfs) was also examined. There were many unidentified bands in Mfs, being assumed to be originated from myofibrillar proteins, in the groups of both 90I + 0.5R and 90I + 5R, although these bands were not observed in the group of 90I. These results indicate that degradation of myofibrillar proteins occurs rapidly after reperfusion of the irreversibly injured myocardium. It is uncertain, however, whether reperfusion has a detrimental effect on the reversibly injured myocardium, too.

Ultrastructural myocardial preservation during coronary artery surgery: a controlled, prospective, randomized study in humans

Potassium cardioplegia was compared with normothermic, intermittent ischemic arrest in 30 patients undergoing multiple coronary artery bypass grafts. Group 1 comprised 15 patients in whom cold potassium cardioplegia with St. Thomas' Hospital solution was used. In Group 2 were 15 patients who underwent intermittent ischemic arrest during the construction of the distal anastomoses. Two myocardial transmural left ventricular biopsies were done in each patient. There was no operative mortality. Electron microscopical examination showed normal myocardial ultrastructure in both groups. In particular, mitochondria were well preserved in all samples. The postoperative electrocardiogram demonstrated a new Q wave in 1 patient in Group 2 whose level of the myocardial isoenzyme of creatine phosphokinase (CPK-MB) was within the normal range. The peak CPK-MB release in Group 1 was 23.2 +/- 20.1 IU and in Group 2, 19.9 +/- 15.1 IU. This difference was not statistically significant. The mean period of anoxic arrest in Group 1 was 49.5 +/- 15 minutes and in Group 2, 25.5 +/- 8 minutes (p less than 0.001). Total cardiopulmonary bypass time in Group 1 was 114.5 +/- 20 minutes and in Group 2, 90.2 +/- 16 minutes (p less than 0.01). It is concluded that both techniques can preserve myocardial subcellular architecture during multiple coronary artery bypass grafting in patients with normal left ventricular function.

Effect of prostacyclin infusion during low-flow ischaemia in the isolated perfused rat heart

Although prostacyclin (PGI2) has been shown to exert a protective effect on ischaemic hearts its precise mode of action remains obscure. Possible explanations include protection of the high energy phosphate stores (ATP and CP), maintenance of homeostasis with respect to Ca2+, and an antiaggregatory effect. The following experiments were undertaken to investigate these possibilities, using isolated, spontaneously beating rat hearts perfused with Krebs-Henseleit solution. Ischaemia was induced at 37 degrees C for 30 min by reducing the flow rate from 10.0 to 0.1 ml/min, and was followed by reperfusion. PGI2 was given as a constant infusion (20 ng/ml). The hearts were frozen and assayed for ATP and CP, or digested in HNO3 and assayed for Ca2+. Peak developed tension was recorded throughout. The results show that PGI2 slowed the rate of decline of developed tension during low flow perfusion, and hastened the recovery of contractions on reperfusion. These effects could not be accounted for in terms of an improved supply of ATP or CP, or an altered tissue Ca2+. The protective effect of PGI2 on isolated, buffer-perfused hearts may be a reflection of a generalized, but undefined, mechanism of cell preservation which has also been observed in other systems.

Protective effect of an asanguineous reperfusion solution on myocardial performance following cardioplegic arrest

This study assesses whether an appropriately designed asanguineous initial reperfusate effectively reduces the reperfusion injury following prolonged global ischemia and improves the recovery of cardiac performance after cardioplegic arrest. Forty-eight isolated perfused working rat hearts underwent two hours of hypothermic (15 degrees to 18 degrees C) ischemic arrest followed by 30 minutes of normothermic reperfusion. During ischemic injury, multidose cardioplegia was delivered at 30-minute intervals. The reperfusion solution under study was infused during the last 3 minutes of ischemia, just prior to release of the aortic clamp. The usual hemodynamic variables of this preparation (heart rate, aortic pressure, aortic flow, coronary flow, and stroke volume) were serially recorded and expressed as percent of recovery of control values. The influence of the concentration of Ca2+, pH, and buffer was more specifically investigated. A reperfusate containing 1 mM of Ca2+ was found to result in higher postischemic hemodynamic values than a Ca2+-poor (0.25 mM) reperfusate. The best functional recovery was provided by an alkalotic (pH 7.70 at 28 degrees C), glutamate-enriched initial reperfusate, which, by 30 minutes of reperfusion, yielded a 93.5 +/- 2.3% recovery of aortic flow versus 83.6 +/- 1.8% in the control group receiving unmodified reperfusion (p less than 0.01). We conclude that an appropriate composition of the initial reperfusate can improve the recovery of cardiac function significantly following two hours of cardioplegic arrest and that such an improvement can be achieved by an asanguineous reperfusate provided its composition is properly designed with respect to electrolytes, pH, and substrates.

The influence of non-coronary collateral blood supply on the electively arrested heart during ischemia and reperfusion

To study the influence of non-coronary collateral blood circulation (NCCBC) on the integrity of the ischemic myocardium a right-sided thoracotomy was performed on 15 anesthetized dogs. Following a total cardiopulmonary bypass (CPB), ventricular fibrillation was induced, during which 2,000 ml calcium-free cardioplegic solution LK 352 was given at the aortic root over an 8-10 min period. Precautions were taken to prevent retrograde blood flow into the coronary system via the coronary sinus. After 90 min of ischemia, ten of the dog hearts were reperfused with systemic blood for the next 30 min. Transmural biopsies were taken from the apex of the left ventricle at the following intervals: (1) before CPB, (2) immediately after the infusion of LK 352, (3) following 90 min of ischemia, (4) after 5 min, (5) after 15 min, and finally (6) after 30 min of reperfusion and were then studied ultrastructurally. The presence of NCCBC was documented by the observation of erythrocyte-filled blood vessels in the biopsies corresponding to nos. 2 and 3 of the above. To assess the degree of ischemic injury and the extent of myocardial recovery during reperfusion, a scoring system based on a semiquantitative assessment of the characteristic morphological changes was used. The average result of the separately assessed subendo- and subepicardial layers represented the score, which was plotted on the ischemic injury and the recovery scale, thus making a direct comparison of the hearts possible. All the hearts generously supplied with blood via extracoronary routes during ischemia showed minimal and reversible ischemic injuries. They recovered more quickly and more completely following reperfusion than those hearts without NCCBC. From these results we conclude that despite its warming-up effect on the myocardium and its tendency to wash out the cardioplegic solution, the NCCBC generally protects the myocardium from serious ischemic injuries and shortens the period of recuperation during the reperfusion.

Magnesium and the calcium paradox: the occurrence of "spasmodic contractions" during Ca2+-Mg2+ -free perfusion of isolated rat heart

The effects of omission of Mg2+ during Ca2+-free perfusion (3 min) of either spontaneously beating and electrically stimulated rat hearts were studied. Ca2+-free perfusion per se induced cardiac arrest and coronary vasodilation, and increased intrinsic pulse rate of the heart. Upon reperfusion with Ca2+, cardiac function was lost and parallelled by a sudden and massive release of cellular constituents ("calcium paradox"). Mg2+-free perfusion evoked effects opposite from Ca2+-free, with exception of heart rate which was increased. During Ca2+-Mg2+-free perfusion the electrocardiogram became irregular within 30 s, and this effect was followed by transient "spasmodic contractions". The effects of normal reperfusion were indistinguishable from those observed after Ca2+-free perfusion in the presence of Mg2+. Addition of Mn2+ or La3+ to the Ca2+-Mg2+-free perfusion medium completely inhibited the induction of electrical irregularities and spasmodic contractions. The typical effects of Ca2+-Mg2+-free perfusion are discussed in terms of Mg-Ca and Mg-K interactions at the sarcolemmal surface. It was concluded that our results may contribute indirectly to an explanation of the protective effect of high Mg2+-concentrations during Ca2+-free as well as ischemic perfusion of mammalian hearts.

Delayed recovery following hypothermic arrest in rabbit myocardium

The purpose of this investigation was to determine the relationship between the duration of myocardial ischemia at 15 degrees C and the time required for the myocardium to recover maximum contractile function following the ischemia. The isolated blood perfused rabbit heart was used as a model of myocardial ischemia. Hearts from 22 New Zealand white rabbits were divided into four groups. In Group I seven hearts were subjected to 15 minutes of ischemia at 15 degrees C. In Group II five hearts were subjected to 30 minutes of ischemia at 15 degrees C. In Group III and IV the ischemia time was extended to 60 and 120 minutes, respectively. Following the ischemia each heart was reperfused at normothermia and papillary muscle contractility was measured and used as an index of myocardial recovery. Hearts in Group I recovered their maximum contractile function after an average of 22.5 minutes. Those in Groups II, III, and IV were fully recovered after 31.7, 38.2, and 45.5 minutes, respectively. The study indicates that the time required for the maximum recovery of myocardial contractility following myocardial ischemia increases at a decreasing rate with an increase in the duration of the ischemia at 15 degrees C.

The effects of global ischemia and reperfusion on human myocardium: quantitative evaluation by electron microscopic morphometry

During open-heart operation, myocardial biopsies were taken from 31 patients undergoing aortic valve replacement during total cardiopulmonary bypass. The first needle biopsy was taken before induction of cardiac arrest (Kirsch cardioplegia), the second at the end of global ischemia, and the third during the reperfusion period. Teh tissue was investigated by electron microscopy, in both a qualitative and a quantitative manner (morphometry). Ultrastructural morphometry revealed cellular and especially mitochondrial swelling that occurred during the reperfusion phase, but not after ischemia alone. On the basis of morphological measurements, this study shows the occurrence of postischemic cellular and mitochondrial edema that possibly might be avoided by the use of improved techniques of myocardial protection during operation.

St. Thomas cardioplegia versus topical cooling: ultrastructural and biochemical studies in humans

Transmural left ventricular biopsies were studied from 28 patients undergoing cardiopulmonary bypass with anoxic cardiac arrest. The myocardium was protected by topical cooling (20 degrees C) (Group 1, 15 patients) or by cardioplegia with St. Thomas' solution (Group 2, 13 patients). Biopsies were taken at the start of bypass and 3 to 5 minutes after unclamping of the aorta. Mean cross-clamp time was not significantly different between the groups (50 minutes for Group 1 and 53 minutes for Group 2; p greater than 0.05). The ultrastructural changes induced by ischemia and subsequent reperfusion were almost exclusively related to the mitochondria. The degree of mitochondrial damage was evaluated by a semiquantitative analysis based on mitochondrial fine structure. The frequency of severe postischemic mitochondrial damage was significantly higher in Group 1 (20.1% versus 2.7% in Group 2; p less than 0.05). Biochemical analysis of the biopsies indicates that the myocardial concentration of creatine phosphate decreases by about 50% after topical cooling (p less than 0.05). With St. Thomas cardioplegia, no significant change in the tissue level of this high-energy phosphate takes place. The results show evidence of the superiority of the St. Thomas cardioplegia to topical cooling alone.

Electron microscopic visible ischemic changes of the mitochondrial ATPases in human myocardial cells during extracorporal circulation

During open heart surgery, needle biopsy material was obtained in four patients, and electron microscopic preparations of the mitochondrial ATPases (coupling factors 1) in human myocardial cells were performed. The pre-ischemic, normal structure of the mitochondrial ATPases and the changes which occur during the ischemic interval were described. An increase in the center-to-center space was shown in the post-ischemic phase. This result was discussed for the pathogenesis of subcellular injuries due to ischemia.

Determination of maximal ischemic tolerance of the human heart by ultrastructural recording of preischemic degree of myocardial hypertrophy and degeneration

Three biopsies were taken transmurally in different time intervals (before and after ischemia and during the reperfusion phase) from 20 patients undergoing open-heart operation for acquired valvular heart disease, and the myocardial cylinders were examined with the electron microscope. They were scrutinized to see if there is a relationship between the degree of hypertrophy and degeneration before ischemia and the extent of ischemic damage after a certain ischemia period, and between the damage before ischemia and the postoperative outcome of the patients. Our results show that the ischemic changes are not dependent on the preischemic extent of hypertrophy and degeneration. It seems that they are mainly dependent on the duration of ischemia because the degree of ischemic damage increases with prolongation of the ischemia interval. However, a good correlation was found between the preischemic changes and the postoperative outcome. Especially the combination of marked hypertrophy and the appearance of degenerative signs in the biopsy taken before ischemia seems to predestine a bad postoperative course. Therefore, it can be concluded that the total damage to the myocardial cells, which results from the sum of previous damage (hypertrophy and degeneration) and ischemic alterations, is responsible for the postoperative outcome.

Salvage of acutely ischemic myocardium by emergency coronary artery bypass grafting

After cardiac catheterization a 53-year old patient developed widespread myocardial ischemia that produced electromechanical dissociation and cardiogenic shock. The administration of methylprednisolone, the initiation of cardiopulmonary bypass and hypothermia within 40 min of the onset of ischemia, and reperfusion within 90 min of the onset of ischemia were sufficient to salvage a major portion of the ischemic myocardium.

[Factors affecting the post-ischemic recuperation of isolated perfused rat heart]

A number of cardioplegic solutions have been described for the reduction of cellular damage during ischemic cardiac arrest. Using an isolated working rat heart model, we have attempted to precise some of the factors affecting the post-ischemic recovery of myocardial tissue after a 30-min period of total ischemia at 37 degrees C. The results indicate that procaine (1 mM) is able to afford some protective against normothermic ischemia while this protective effect remains consistently lower than that of the St. Thomas' Hospital solution (procaine + high K+ + high Mg2+; JYNGE et al., 1977). On the other hand, hearts from rats of the Wistar strain consistently exhibit a significantly better degree of recovery than do hearts from rats of the Shermann strain. When hearts were perfused at different levels of preload (1 or 2 kPa) and afterload (8 or 10 kPa), post-ischemic recovery was better in hearts with lower levels of cardiac work. Glucose, insulin and DL-propranolol which have been shown to exert a protective effect in isolated rat hearts with regional ischemia failed to protect the heart in the present experimental conditions. No clear correlation does exist between the post-ischemic recovery and the enzymatic assessment of myocardial cell damage.

Effects of perfusion pressure on coronary flow, myocardial Ca2+-washout, and the occurrence of calcium paradox in isolated perfused rat heart ventricles

The influence of perfusion pressure (5-8 kPa) on coronary flow and myocardial Ca2+-washout during Ca2+-free perfusion, and on the occurrence of calcium paradox after subsequent Ca2+-reperfusion, was studied in isolated, stimulated, rat heart ventricles. During the Ca2+-free perfusion period (3 min) the following changes were observed: 1. Rapid cessation of ventricular contractions. 2. A pressure-dependent increase in diastolic rest tension. 3. A pressure-dependent increase increase in coronary flow rate. 4. A pressure-dependent increase in myocardial Ca2+-washout. Upon Ca2+-reperfusion all hearts failed to recover fully and the incidence of complete loss of ventricular contractility ("complete calcium paradox") increased with increasing perfusion pressure. Furthermore, a clear relationship between coronary flow and effluent-Ca2+-concentration (during Ca2+-free perfusion) and the occurrence of calcium paradox (upon Ca2+-reperfusion) was observed. The results suggested that the processes underlying the calcium paradox mechanism are influenced by the perfusion pressure, mainly via an effect on coronary flow during the Ca2+-free perfusion phase and through this effect on the rate and extent of myocardial Ca2+-washout.

Ultrastructural integrity of human ventricular myocardium following cardioplegic arrest

The appearance of the ventricular myocardium in 6 patients electing coronary bypass operation was evaluated by electron microscope before and after aortic cross-clamping. Bypassing protocol included the induction of hypothermic cardioplegia by intermittent aortic root perfusion, with potassium chloride added to cold blood serving as the cardioplegic agent. Cross-clamp intervals ranged from 66 to 125 minutes. Ultrastructural alterations following bypass manipulations, and distinct from those observed before cross-clamping, were limited to the presence of extensive myocardiocytic pooling of glycogen. Scrutiny of the intramyocardial capillary bed following perfusion with the cardioplegic solution revealed no abnormalities attributable to, or intensified by, the bypass maneuver. These findings indicate that hypothermic potassium cardioplegia, as specified, is not injurious to human myocardial ultrastructure.

[Ultrastructural morphometric analysis of hypertrophied human myocardial left ventricles (author's transl)]

Biopsies of hypertrophied human myocardial left ventricles were investigated morphometrically. The diagnoses of the patients were stenosis of the aortic valve, aortic insufficiency or a combination of both lesions. The results were compared with those from normally loaded human left ventricles. There are no differences on light microscopical level between the volume densities of interstitial tissue and of heart muscle cells in the three groups of patients. A significant diminution of the volume density of the nuclei (P less than 0.001) and the number of nuclei per test area (P less than 0.001) when compared with normal groups suggests an increase in volume of the single heart muscle cell. The ultrastructural study shows marked increase in volume density of myofibrils (P less than 0.0001), with accompanying decrease in the volume densities of mitochondria (P less than 0.0001) and the remaining cytoplasm (P less than 0.001). A gross decrease in the surface area of mitochondria (P less than 0.001) and of cristae mitochondriales (P less than 0.0001) is found. The morphological equivalents of this result are numerous stages of mithochondrial destruction including cristolysis. All myocardial weights were beyond the "critical heart weight".

Calcium in isolated mitochondria from the left ventricular wall

The content of calcium per mg mitochondrial protein has been measured by conventional biochemical methods in myocardial tissue of some mammalian species. In addition, a method is presented for (1) the analysis of mitochondrial volumes in the same tissues and (2) calculating the amount of calcium in units of 10(6) mitochondria. It appears that a highly significant correlation exists between the calcium content and the number of mitochondria, with a positive correlation coefficient of 0.92. The mean mitochondrial volume in fractions of the rabbit myocardium was found to be 1.3386 micron3. Electron microscopic studies demonstrate pure mitochondrial fractions and only moderate structural alterations. The method described may represent a useful supplement for the estimation of calcium fluxes in mitochondria and of alterations in their volume, number and structure under conditions of myocardial ischemia.

Tolerance to ischemia of hypertrophied human hearts during valve replacement

This study evaluates the tolerance to ischemia during induced cardiac arrest in patients undergoing aortic valve replacement. In all patients cardiac standstill was of 45 minutes duration. Biopsies for electron microscopic study were taken from the left ventricle before induction of arrest, at the end of the ischemic period and 20 minutes after coronary perfusion had been reestablished. Structural ischemic damage was more pronounced in patients with severe hypertrophy and structural reconstitution was delayed. Degenerative changes of the myocardial cells, although observed frequency, apparently did not influence the tolerance to ischemia. It is concluded from this study that patients with severe hypertrophy represent a high-risk group in cardiac surgery because of their reduced tolerance to induced myocardial ischemia during cardiopulmonary bypass.