P1646Do Extracellular Vesicles repair chronic ischemic heart disease by replenishing the cardiomyocyte pool?

Introduction

Extracellular Vesicles (EV) seem to mediate the benefits of cell therapy for ischemic heart failure. Although their mechanism of action remains poorly understood, one hypothesis is that they might trigger the generation of new cardiomyocytes.

The doubly transgenic fate-mapping MerCreMer/ZEG mice model was thus used to distinguish whether these putative new cardiomyocytes originated from the division of preexisting ones (GFP+, Troponin T [TnT+], EdU+) or differentiated from endogenous progenitors, in which case they would stain positive for TnT+/EdU+ but negative for GFP.

Methods

Myocardial infarction was induced in 35 MerCreMer/ZEG mice by permanent occlusion of the left anterior descending coronary artery. Three weeks later, the surviving mice (n=18) with a left ventricular ejection fraction (LVEF) ≤45% received transcutaneous echo-guided injections in the peri-infarct myocardium of either EV (from 1.4 million human iPS-derived cardiovascular progenitor cells; 10 billion particles, n=9) or PBS (n=9); osmotic pumps were implanted to deliver EdU for 7 days in order to track the proliferation of new and native cardiomyocytes. Four-6 weeks after treatment all mice were evaluated by echocardiography (n=9 per group) and MRI (7 in each group), and then sacrificed for histological assessment, blindly.

Results

Based on echocardiography (MRI data pending), EV improved LVEF by 16% relative to baseline while a decrease of 4% was observed in the PBS group (p=0.46).

The number of new cardiomyocytes (TnT+/EdU+/GFP+) did not significantly differ between the EV-treated hearts and the controls, and averaged 0.54% of the total heart cell content in infarct, peri-infarct and remote areas. However, EV treatment better preserved preexisting GFP+/WGA+/TnT+ cardiomyocytes in the peri-infarct area as their number was greater by 5.15% compared to PBS (32 sections analyzed for each mouse). Compared to the PBS control group, EV delivery was also associated with a 2.5% decrease in fibrosis, a reduction of infarct size by 14.9%, and an increase in angiogenesis in the peri-infarct area (with a between-group absolute difference of 71 capillaries, on the basis of isolectin staining).

Conclusions

EV secreted by iPS-derived cardiovascular progenitors improve the function of chronically infarcted hearts. Preservation of the existing cardiomyocyte pool and limitation of adverse remodeling and scarred tissue, likely favored by increased neoangiogenesis, are the main mechanisms mediated by the EV, while fate mapping allowed to exclude the generation of new cardiomyocytes.

[Cardiac cellular therapy: from cells to the first clinical uses]

Despite the improvement in revascularisation techniques, coronary artery disease remains the principal aetiology of cardiac failure in developed countries. The therapeutic management of cardiac failure has been improved over recent years, yet cardiac failure is still associated with significant morbidity and mortality. As cardiac transplantation lacks donors, techniques that allow myocardial regeneration represent an attractive alternative. To date, several types of cells are under study and are suitable for implantation into infarcted myocardium (myoblasts, medullary stem cells...). Following good preclinical study results, the first human cell therapy trials, using the intramyocardial route, have begun, in the course of aorto-coronary bypass surgery in patients with chronic ischaemic cardiopathy and little altered left ventricular function, and then in those with ventricular dysfunction. Different modes of administration of these cell therapy products are under study and could be envisaged in clinical situations such as just after infarction in order to improve ventricular remodelling with an intracoronary injection technique. As for every new treatment, there are numerous problems to resolve, from understanding the relevant mechanisms of cellular transplantation, to the secondary effects that it could entail. Nevertheless, cardiac cellular transplantation is expanding rapidly and with the evolution of techniques it allows a glimpse of a new field of treatment for cardiac failure.

Cell transplantation for post-ischemic heart failure

Post-ischemic heart failure is becoming a major issue for public health in occidental countries and therapeutical options are limited. Therefore cell transplantation was developed as an alternative strategy to improve cardiac structure and function. This review describes the multiple cell types and clinical trials considered for use in this indication. The transplantation of fetal or neonatal cardiomyocytes has proven to be functionally successful, but ethical as well as technical reasons make their clinical use limited. Recent reports, however, suggested that adult autologous cardiomyocytes could be prepared from stem cells present in various mesenchymal tissues. Alternatively, endothelial progenitors originating from bone marrow or peripheral blood could promote the neoangiogenesis within the scar tissue. Finally, the transplantation of skeletal muscle cells (SMC) in the infarcted area improved myocardial function, in correlation with the development of skeletal muscle tissue in various animal models. The latter results paved the way for the development of a first phase I clinical trial of SMC transplantation in patients with severe ischemic heart failure. It required the scale-up of human cell production according to Good Manufacturing Procedures, it started in June 2000 in Paris and was terminated in November 2001, and it was followed by several others. The results were encouraging and prompted the onset of a blinded, multicentric phase II clinical trial for SMC transplantation. Meanwhile, clinical trials also evaluate the safety and efficacy of various cells types originating from the bone marrow.

[Anaphylactic reactions to aprotinin: intradermal diagnostic tests]

A 66-year-old patient, undergoing heart surgery, developed an anaphylactic reaction following the first administration of a test-dose of aprotinin. Skin tests were performed six months later. Prick-tests with 10(-2) and 10(-1) aprotinin dilutions were negative but intradermal reaction with a 10(-3) dilution was clearly positive. The level of aprotinin specific IgE was high, both in the serum obtained before surgery and in the one sampled on the day of the testing. As no reaction was observed during the tests, skin-testing and specific IgE appear to be an interesting alternative to a potentially dangerous test-dose, but they both need further evaluation.

[Towards an integrated protection of heart grafts]

In an attempt to provide a consistent protection of cardiac allografts during the sequence of events inherent in transplantation procedures, we developed two preservation solutions of which one is used for initial arrest, storage and cardioplegia during graft implantation, whereas the other serves as initial reperfusate. The formulations of these solutions are closely interrelated and their design has integrated the basic principles of organ preservation with those of myocardium-specific metabolism. Based upon experimental studies in the isolated rat heart model, this integrated approach has yielded better functional recoveries than conventional preservation protocols.

[Early constrictive pericarditis after coronary revascularization. Apropos of a case]

The authors report a case of severe constrictive pericarditis occurring 6 weeks after coronary bypass surgery and in the absence of any other predisposing factor. The diagnosis was confirmed by CT scan and cardiac catheterisation which showed signs of a diastole. The patient died despite early surgical reoperation because of the severity of the pericardial fibrosis.

Cardioplegia by way of the coronary sinus for valvular and coronary surgery

Retrograde coronary sinus perfusion has recently reemerged as an attractive means of delivering cardioplegic solutions during open heart procedures. In patients undergoing aortic valve or aortic root surgery, there is no evidence that coronary sinus cardioplegia results in a better myocardial protection than that achieved with the use of standard methods of anterograde cardioplegia delivery. However, the retrograde approach provides distinct technical advantages that might favor its use as an alternative to direct coronary ostial cannulation. In select subgroups of patients undergoing coronary bypass procedures, there is a growing body of evidence that the coronary sinus route may be more effective than the anterograde route because of its superior capacity to ensure homogeneous distribution of cooling and cardioplegia in myocardial areas supplied occluded arteries. The well established safety of coronary sinus cardioplegia in the clinical setting further justifies its inclusion among techniques for ensuring adequate myocardial preservation during surgically induced ischemic arrest.

[The surgical section of the bundle of Kent as an operative treatment of the Wolff-Parkinson-White syndrome: apropos a series of 82 operated cases]

Eighty two patients diagnosed of the Wolff-Parkinson-White syndrome (WPW) underwent operation for the surgical section of the Kent-His bundle. In these cases, posteroseptal localization (PS) occurred in 32, left lateral (LL) in 25, right lateral (RL) in six, anteroseptal (AS) in one, posteroseptal and left lateral in 14, right and left posteroseptal in two, anteroseptal and left lateral in one, and left lateral and right and left posteroseptal in one. All of the patients presented an invalidating clinical of palpitations and/or loss of consciousness, and episodes of atrial fibrillation and/or reciprocal rhythm were registered in all cases. The mean anterograde refractory period in the accessory pathways was 244 +/- 60 msec, and the shortest RR in atrial fibrillation was 190 +/- 36 msec. A mitral commissurotomy was carried out in 3 patients during surgery, mitral prostheses were implanted in two, a double aorto-coronary bypass was made in three and an interventricular communication was closed in one. After a follow-up of 36 +/- 18 months, the surgical section of the Kent bundle was found to be effective in 77 out 82 patients (94%). (In 70 out of 77 cases, both anterograde and retrograde conduction were totally abolished and in seven out of 77 obtunded. All patients were asymptomatic during the follow-up period). In 5 out of 82 patients, surgical treatment was ineffective all five showed a PS Kent-His and two presented a second Kent-His fascicle (LL).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of the acyl azide method for cross-linking collagen-rich tissues such as pericardium

Collagen biomaterials should be cross-linked in order to prevent biodegradation when they are used as implants. We have compared the cross-linking efficiencies of glutaraldehyde and acyl azide in pericardium. Glutaraldehyde is used currently, but it elicits a cytotoxic effect which reduces the biocompatibility of cross-linked tissue. We have attempted to overcome this problem by developing a cross-linking method that obviates incorporation of foreign agents. Our process involves transformation of free carboxyl groups on collagen into acyl azide groups, which react with free amino groups on adjacent side chains. We have shown that the greatest increase in the thermal stability of collagen, as measured by differential scanning calorimetry, is achieved when tissue swelling is inhibited by the addition of sodium chloride (1 M) during acyl azide formation. Under these conditions, the denaturation temperature (Td) of pericardial collagen treated with acyl azide is raised to 83.4 degrees C and that of tissue treated with glutaraldehyde to 85.1 degrees C. Moreover, acyl-azide-treated tissues have the same resistance as glutaraldehyde-treated tissues to chemical solubilization by cyanogen bromide and to enzymatic digestion by collagenase.

[Aortic and mitral endocarditis caused by Haemophilus paraphrophilus with abscess of the aortic ring and cerebral embolism]

We report the first case of aortic and mitral Haemophilus paraphrophilus endocarditis complicated by abscess of the aortic annulus in a 30-year old man with post-rheumatic mitral regurgitation. We recall the peculiar clinical features and course of this bacterial endocarditis of uncommon origin. We insist, in particular, on the occurrence of cerebral embolism and on the two-dimensional echocardiographic diagnosis of an aortic annulus abscess confirmed at surgery. Cure was obtained by aortic and mitral valve replacement and by the prolonged antibiotic therapy made necessary by the presence of cerebral lesions. After 3 months, there were no neurological sequelae, but doppler-echocardiography showed a persistent washed out pouch the reports of which with the surrounding structures were determined by transoesophageal echocardiography: moderate aortic regurgitation was detected at that level.

Enzyme release and mitochondrial activity in reoxygenated cardiac muscle: relationship with oxygen-induced lipid peroxidation

The aim of this work was to precisely determine the sites of the peroxidative action on unsatured lipids by oxygen-derived free radicals and the lytic cell damage on reoxygenated perfused hearts. The cellular load of lipid peroxidation products (malondialdehyde) during the reoxygenation was dependent on PO2. This unfavorable biochemical response was linked to creatine kinase leakage, alteration of coronary flow and mitochondrial injury. When an enzymatic (superoxide dismutase, 290 IU/minute) or tripeptide scavenger of oxygen radicals (reduced glutathione, 0.5 mmol/l) was administered at the end of hypoxia and during reoxygenation, the abnormal intolerance of hypoxic heart to molecular oxygen was significantly weakened; the load of lipid peroxides load, enzyme release, and vascular alteration were all reduced. Moreover, mitochondrial activity was enhanced and the oxygen-induced uncoupling of mitochondrial remained limited: both the respiratory control ratio (RCR) and the ADP/O ratio were higher than in control reoxygenated hearts. The inhibition by rotenone (100 mumol/l) of reoxidation of electron chain transfer during oxygen readmission also reduced the unfavorable cardiac accumulation of lipid peroxidation products and the release of creatine kinase. These data demonstrate that in the oxygen paradox, the peroxidative attack on lipids plays an important role in inducing alterations of sarcolemmal permeability and mitochondrial activity. An uncontrolled reactivation of oxidative function of mitochondria during reoxygenation enhances the synthesis of oxygen-derived free radicals and triggers the peroxidation of cardiac lipids resulting in irreversible injury to cellular and intracellular membranes.

[Role of calcium blockers in protecting the myocardium in cardiac surgery]

Calcium plays an essential role in ischemic events observed during cardiac surgery. Many experiments have studied the effects of calcium channel blockers on intracellular calcium overload during the periods of cardiac ischemia and reperfusion. Calcium channel blockers are no longer used before and during cardiac surgery because hypothermia inhibits their pharmacological action. However, during the post-operative period, calcium channel blockers are the drugs of choice to control coronary spasm, and arterial hypertension which is secondary to peripheral vasoconstriction.

Rupture of the right ventricular free wall. An unusual complication of mediastinitis after cardiac surgery

Of 2171 patients who underwent open heart surgery between 1981 and 1986, 41 (1.8%) developed postoperative mediastinitis and were treated by closed irrigation drainage or open chest therapy. Six patients, (mean age 59 years) developed rupture of the right ventricular free wall. The primary procedures were: resection of akinetic fibrous plaque (2), mitral valve replacement (1), coronary bypass grafting (1), removal of a left atrial myxoma (1) and repair of post-infarction rupture of the left ventricle (1). In 2 patients, rupture occurred in the operating theatre during revision of the irrigation drainage. Both patients died after repair. In 4 patients, rupture occurred during coughing. One died before surgery. In the 3 other cases, the defects were repaired either by direct suture (2 patients) or with a pericardial patch (1 patient) with the aid of normothermic extracorporeal circulation. Three days later, a muscular flap (pectoral or dorso-lumbar) was mobilized to protect the mediastinal viscera. All 3 patients are alive and well. When bleeding occurs during treatment of mediastinitis, an immediate exploration with extracorporeal circulation to close the defect should be considered.

Prevention of hydroxyl radical formation: a critical concept for improving cardioplegia. Protective effects of deferoxamine

The hydroxyl radical is one of the most damaging oxygen metabolites that are thought to be produced during ischemia and reperfusion of cardiac tissue. Therefore, we used the isolated, isovolumetric, buffer-perfused rat heart preparation of cardioplegic arrest to assess the effects of interventions targeted at inhibiting production of the hydroxyl radical by decreasing either the availability of one of its precursors (hydrogen peroxide) or that of the metal catalyst (ferric iron) involved in the radical formation. Sixty hearts were studied and, except for nonischemic controls, were subjected to 3 hr of hypothermic (15 degrees to 18 degrees C) cardioplegic arrest, followed by 45 min of reperfusion. The following interventions were tested: pretreatment with peroxidase, a scavenger of hydrogen peroxide, pretreatment with a combination of peroxidase and the iron chelator deferoxamine, pretreatment with peroxidase followed by supplementation of the cardioplegic solution with deferoxamine, and supplementation of the cardioplegic solution with deferoxamine without preischemic enzymatic treatment. Based on comparisons of postreperfusion pressure development, maximal ventricular dP/dt, left ventricular compliance, and coronary flow, deferoxamine-containing cardioplegic solution alone afforded the best myocardial protection. This may be due to the ability of deferoxamine to act both as an iron chelator and as a direct scavenger of superoxide anion, an activated oxygen species that participates in hydroxyl radical formation. This study confirms that an important component of the cardiac damage sustained during global ischemia and reperfusion may involve injury caused by the hydroxyl radical. Furthermore, our results point out the potential therapeutic usefulness of deferoxamine in the context of cardioplegic protection during open-heart procedures.

Enhancement of cardioplegic protection with the free-radical scavenger peroxidase

This study assesses the ability of the free-radical scavenger peroxidase to enhance cardioplegic protection when given during or before myocardial ischemia. Forty-four isolated isovolumetric buffer-perfused rat hearts were studied. In a first series of experiments that consisted of three groups, hearts were subjected to 90 min of normothermic global ischemia followed by 45 min of reperfusion. One group received a crystalloid cardioplegic solution given as a single dose at the onset of arrest. A second group received cardioplegic solution supplemented with superoxide dismutase (200,000 U/liter), and a third group received cardioplegic solution supplemented with peroxidase (6000 U/liter). Based on comparisons of postreperfusion coronary flow, left ventricular developed pressure, maximum dP/dt, and diastolic pressure, we found that the best protection was provided by peroxidase-enriched cardioplegia. A second series of experiments was then undertaken to assess the effects of the latter enzyme given as a pretreatment. Hearts were subjected to 3 hr of global ischemia, during which myocardial protection was provided by hypothermia (15 degrees C) along with multidose cardioplegia. The treatment group was given peroxidase (10,000 U/liter) added to the perfusate fluid for 15 min before the onset of cardioplegic arrest without further enzyme supplementation during ischemia or reperfusion. Hearts perfused with standard buffer for an equal period of time served as controls. While the two groups demonstrated the same degree of postischemic increase in myocardial stiffness, peroxidase-pretreated hearts had a significantly better recovery of contractile indexes at 30 and 45 min of reflow.(ABSTRACT TRUNCATED AT 250 WORDS)

[Free radical scavenging agents in myocardial protection during cardiac surgery]

Oxygen free radicals are very unstable metabolites which are produced in abundant quantity during the reoxygenation of an ischemic organ. Oxidation, by these radicals, of the structural lipids of the membranes, is at the origin of cellular lesions all the more extensive as the ischemia, by itself, decreases the ischemic tissue content in "trapping" molecules which usually inactivate those free radicals. Thus, was introduced the concept of an exogenous supply of trappers intended to bring under control the production of radicals and consequently preserve the membrane integrity in the revascularized tissue. This review summarizes, in light of our experience, the results obtained with free radicals trappers in the scope of myocardial preservation, especially in cardiac surgery, and analyzes some of the problems that remain to be resolved before considering the clinical use of these trappers.

A comparative study of free radical scavengers in cardioplegic solutions. Improved protection with peroxidase

Oxygen-derived free radicals play an important role in the myocardial injury associated with ischemia and reperfusion. This study was designed to assess whether the protection afforded by a K+ rich, Mg2+ rich cardioplegic solution could be enhanced by the addition of free radical scavengers acting at different levels of the radical generating pathway. Forty isolated isovolumic rat hearts were divided into five groups (n = 8). Four groups of hearts were subjected to 90 minutes of normothermic cardioplegic arrest followed by 45 minutes of reperfusion. Hearts were given an initial bolus of either unmodified cardioplegic solution or cardioplegic solution enriched with superoxide dismutase (200,000 U/L) reduced glutathione (0.1 mmol/L), or peroxidase (6,000 U/L). One group of hearts was aerobically perfused throughout the experimental protocol and served as nonischemic controls. Based on comparisons of postreperfusion ventricular pressure development, maximal ventricular dP/dt, left ventricular compliance and coronary flow, peroxidase-containing cardioplegic solution afforded the best myocardial protection, with values of these indicators not significantly different from those of nonischemic perfused control heart. Glutathione afforded protection slightly inferior to that of peroxidase but still markedly better than in groups receiving superoxide dismutase or unmodified cardioplegic solution. This study confirms that cardioplegic protection can be enhanced by the addition of free radical scavengers, in particular peroxidase.

Increased injury of hypertrophied myocardium with ischemic arrest: preservation with hypothermia and cardioplegia

Many patients undergoing cardiac surgery have some degree of myocardial hypertrophy. To assess the response of hypertrophied myocardium to simulated cardiac surgery, left ventricular hypertrophy was induced in rats by aortic banding, and ventricular function was measured by means of the isolated, isovolumic heart perfusion technique. The hypertrophied hearts had a greater susceptibility to ischemic injury than nonhypertrophied control hearts, as manifested by a greater degree of diastolic contracture during the recovery period after 30 minutes of ischemic arrest at 37 degrees C. Hypothermia without cardioplegia during a 2-hour arrest did not completely preserve diastolic function in the hypertrophied hearts, but cardioplegia combined with hypothermia completely protected the hypertrophied hearts against 2 hours of ischemia. The results suggest a need for both hypothermic and cardioplegic preservation techniques in patients with myocardial hypertrophy who have cardiac surgical procedures requiring a significant period of myocardial ischemia.

31P-NMR study of high-energy phosphorylated compounds metabolism and intracellular pH in the perfused rat heart

Using 31P-NMR and haemodynamical measurements, this work assesses different aspects of myocardial preservation improvement during a global ischaemia, based on a simultaneous and correlated study of high-energy phosphorylated compounds, intracellular pH and left ventricular function. Isolated perfused working rat hearts were subjected to 2 or 3 h of hypothermic ischaemia followed by 30 or 45 min of reperfusion. A study of the influence of pH and buffer used in cardioplegic solutions has demonstrated a better preservation of high-energy phosphates and an improved functional recovery when using a pH 7.0, glutamate - containing solution. Protection provided by cardioplegia can be enhanced by the appropriate use of a fluorocarbon-oxygenated cardioplegic reperfusate. The use of nifedipine, a calcium antagonist, in the cardioplegic solutions, does not provide any additional protection under hypothermic conditions.

Enhanced cardioplegic protection by a fluorocarbon-oxygenated reperfusate: a phosphorus-31 nuclear magnetic resonance study

Prolonged global ischemia results in a defect in oxygen extraction during early reperfusion. This study was thus undertaken to assess the effects of maintaining cardioplegia at the onset of reoxygenation in view of channeling available energy toward reparative cell processes rather than mechanical activity. Twenty-four isolated perfused rat hearts were subjected to 120 min of 15 degrees C ischemia. Group I (control) was reperfused with the standard Krebs perfusion medium whereas in groups II and III the initial reperfusate consisted of an oxygenated alkaline cardioplegic solution prior to the resumption of Krebs perfusion. Oxygenation of the cardioplegic reperfusate was ensured by fluorocarbons at a concentration of 10% (O2 content: 5.5 vol %; group II) or 20% (O2 content: 9 vol %; group III). In addition to hemodynamical determinations, high-energy phosphates and intracellular pH were monitored serially by phosphorus-31 nuclear magnetic resonance spectroscopy. After 30 min of reperfusion postischemic recovery of aortic flow was better in group II (74.0 +/- 5.9% of control) than in group I (59.1 +/- 5.4% of control, P less than 0.05). This functional improvement correlated with a higher postischemic increase in phosphocreatine levels (103.21 +/- 11.21% vs 74.12 +/- 3.59%, at 3 min of reperfusion, P less than 0.05) without significant differences in total ATP content. Group III hearts exhibited a slow recovery as evidenced by a severe depression in aortic flow, coronary arteriovenous difference, and total phosphate content during the 15 initial minutes of reperfusion. These results show that the protection provided by cardioplegia can be improved by a fluorocarbon-oxygenated cardioplegic reperfusate.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of the pH of cardioplegic solutions on intracellular pH, high-energy phosphates, and postarrest performance. Protective effects of acidotic, glutamate-containing cardioplegic perfusates

The common practice of using alkalotic cardioplegic solutions is not supported by experimental evidence. The present study was conducted to assess the effects of varying the pH (7.00, 7.40, and 7.70 at 20 degrees C) of a glutamate-containing cardioplegic solution on intracellular pH, high-energy phosphate content, and postarrest functional recovery and to compare the effects of various buffers (glutamate, bicarbonate, TRIS, and histidine) at a given pH (7.00 and 7.40). Isolated perfused rat hearts were subjected to 2 hours of cardioplegic arrest at 15 degrees C followed by 30 minutes of reperfusion. Intracellular pH and high-energy phosphate content were measured at 4 minute intervals by phosphorus 31 nuclear magnetic resonance spectroscopy. These data were correlated with postischemic recovery of function. There was no significant difference between the intracellular pH values recorded at the end of arrest in the three glutamate-containing groups. However, the acidotic solution (pH 7.00) resulted in better preservation than the alkalotic solution (pH 7.70), as evidenced by a higher creatine phosphate content at the end of arrest (61% +/- 9% of control values versus 30% +/- 9% [mean +/- standard error of the mean], p less than 0.05), a higher adenosine triphosphate content at the end of reperfusion (102% +/- 5% versus 82% +/- 6%, p less than 0.05), and a faster recovery of aortic flow (at 3 minutes of reperfusion, 91% +/- 11% versus 51% +/- 11%, p less than 0.05). Subsequent comparison of buffers showed that bicarbonate, TRIS, and histidine were equally effective in maintaining intracellular pH close to control values during arrest. Conversely, the use of glutamate resulted in a more pronounced fall in intracellular pH, which correlated with a better preservation of adenosine triphosphate and a better functional recovery than in the other groups. Overall, the greatest extent of preservation was provided by the pH 7.00 glutamate-containing cardioplegic solution. We conclude that additional protection can be conferred to the cold, chemically arrested heart by combining mild intracellular acidosis, which lowers metabolic needs during arrest, most likely through a limitation of calcium overload, and provision of glutamate, which may act as a substrate for anaerobic energy production while allowing intracellular pH to be kept within the appropriate range.

Limitations of fluorocarbons in reducing myocardial infarct size

The effects of the oxygen-carrier fluorocarbons on myocardial infarct size were assessed in non-exchange-transfused dogs subjected either to a 3-hour occlusion of the left anterior descending coronary artery (LAD) followed by 2 hours of reperfusion (protocol I) or to a 5-hour permanent LAD occlusion (protocol II). Fluorocarbon administration was begun 30 minutes after LAD occlusion and was continued over the entire period of ischemia. After 5 hours, the hearts were excised and areas of necrosis were visualized by triphenyl tetrazolium chloride staining while risk regions were assessed by radiolabeled microspheres injected after coronary occlusion just before the onset of therapy, and further, in protocol I, by thallium-201 perfusion imaging performed at the end of fluorocarbon administration. In protocol I experiments, the ratio of necrotic area to area at risk was 81 +/- 35% (mean +/- standard deviation) in control saline-treated dogs (n = 6) and 67 +/- 27% in fluorocarbon-treated dogs (n = 6) (difference not significant). There was no significant difference between risk regions measured after and before fluorocarbon treatment. In protocol II, the ratio of necrotic area to area at risk was 47 +/- 30% in control dogs (n = 5) and 63 +/- 29% in fluorocarbon-treated dogs (n = 5) (difference not significant). However, in control dogs, the ratio of necrotic area to area at risk increased from 47 +/- 30% in the dogs that underwent permanent occlusion to 81 +/- 35% in the group that underwent reperfusion (p less than 0.001) while this ratio was similar in the corresponding subsets of fluorocarbon-treated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of arrhythmias within hours after a single oral dose of amiodarone and relation to plasma and myocardial concentrations

In 65 patients a single oral dose of amiodarone (30 mg/kg) produced an antiarrhythmic effect on supraventricular or ventricular arrhythmias within 3 to 8 hours and lasted for 17 to 19 hours. On the second day a 15-mg/kg dose reproduced this effect within 3 to 9 hours. Plasma concentration of amiodarone increased to a maximum (2.2 +/- 1.7 mg/liter) mean +/- standard deviation) at 6 +/- 3.5 hours and plasma levels of N-desethylamiodarone (NDA) rose to 0.2 +/- 0.08 mg/liter at 12 +/- 6.4 hours. Sixty-one other patients were given a single 30-mg/kg dose 7 hours to 4 days before open heart surgery. Biopsies of the right atrial and left ventricular walls were taken during surgery. Myocardial concentration of amiodarone was maximal in the atrium after 7 hours (13 +/- 8 mg/kg) and in the ventricle after 24 hours (17 +/- 11 mg/kg). NDA myocardial concentration increased progressively until 24 hours and then remained stable over 4 days (1.5 mg/kg). The amiodarone myocardial to plasma concentration ratio was similar in the atrium and in the ventricle and averaged 22 and 10 for amiodarone and NDA, respectively. A significant relation existed between amiodarone concentration and the effect on ventricular premature complexes (r = 0.74, p less than 0.001) and between amiodarone plasma concentration and the effect on the atrioventricular conduction (r = 0.58, p less than 0.001). The plasma concentration of amiodarone corresponding to a 60% decrease in arrhythmias averaged 1.5 to 2 mg/liter.(ABSTRACT TRUNCATED AT 250 WORDS)

Protective effects of cardioplegia on diastolic function of hypertrophied rat hearts after hypothermic ischaemic arrest

This study was undertaken to assess the effects of hypothermia and chemical cardioplegia on the functional recovery of hypertrophied non-failing rat hearts subjected to an extended period of global ischaemia. Left ventricular hypertrophy was produced by constriction of the abdominal aorta. Hearts were studied an average of 8 weeks following this procedure. Sham-operated animals served as controls. Twenty-nine isolated isovolumic perfused rat heart preparations were then subjected to 2 h of ischaemic arrest at 15-18 degrees C followed by 45 min of normothermic reperfusion. In one series of hearts (8 sham, 8 hypertrophied), myocardial protection consisted of hypothermia alone. In another series (6 sham, 7 hypertrophied), repeated infusions of cardioplegic solution at 30-min intervals throughout arrest were added to hypothermia. Hypothermia alone resulted in a similar preservation of contractility as evidenced by the recovery of dp/dtmax/left ventricular (LV) systolic pressure after 45 min of reperfusion (91.6 +/- 5.9% of control values in sham vs 78.6 +/- 6.5% in hypertrophied hearts). Conversely, the recovery of compliance was much more impaired in hypertrophied hearts as indicated by a significantly higher percentage of increase in post-ischaemic LV diastolic pressure (DP) (at 45 min of reperfusion: 243.8 +/- 27.5% of control values vs 167.1 +/- 23.8% in sham, P less than 0.05). The addition of cardioplegia improved the preservation of contractility in both groups but its major effect was to normalize the recovery of compliance in hypertrophied hearts so that post-ischaemic LVDP values were no longer different from those recorded in normal hearts (at 45 min of reperfusion: 102.1 +/- 32.8% vs 98.5 +/- 14.2% of pre-ischaemic values respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Collagen vascular grafts: a step towards improved compliance in small-calibre bypass surgery; preliminary report

This study assesses the static compliance of a 4-mm-calibre collagen vascular graft. The graft was prepared by extrusion from a gel of collagen obtained from the skin of grown calves. To allow easy surgical handling, the prosthesis was reinforced by embedding a polyester mesh between two concentric tubes of collagen. Compliance was determined in vitro by filling the graft with increasing volumes of saline while intraluminal pressure and longitudinal stretching were simultaneously recorded. A 4-mm polytetrafluoroethylene prosthesis and a freshly-harvested human saphenous vein served as references. In the range of physiological pressures (100 to 200 mmHg), the collagen graft was only half as stiff as the polytetrafluoroethylene graft (5.6 vs 2.7 mm3/mb/m) and, in spite of its reinforcement, yet slightly more compliant than the vein itself (4.5 mm3/mb/m). Thus, from a mechanical viewpoint, a collagen prosthesis seems to be a valuable alternative for small-vessel bypass grafting, but further studies of its flow-surface characteristics are now warranted to assess its potential usefulness in the clinical setting.

An asanguineous reperfusion solution. An effective adjunct to cardioplegic protection in high-risk valve operations

The protection afforded by cardioplegia during elective ischemic arrest can be partly compromised by a reperfusion injury, which may impede the recovery of cardiac function. We previously showed experimentally that this postischemic damage could be largely avoided by an appropriate crystalloid reperfusate. The present study was thus undertaken to assess the effects of this "reperfusion solution" clinically. One hundred twelve patients undergoing valve replacement with the aid of hypothermic cardioplegia (K+ 12 mEq, Mg2+ 26 mEq) were prospectively divided in two groups: Group I (n = 49) received an unmodified blood reperfusate. In Group II (n = 63), 1 L of the reperfusion solution was delivered just prior to removal of the aortic clamp. The formulation of the reperfusion solution adhered to the following principles: (1) maintenance of cardioplegia (K+ = 15 mEq), (2) replenishment of Ca2+ stores (Ca2+ = 2.5 mEq), (3) substrate provision (glutamate = 2,942 gm), (4) buffering (pH = 7.70 at 28 degrees C), and (5) hyperosmolarity (370 mOsm). The two groups were matched for preoperative data except for a higher incidence of isolated aortic valve replacement (p = 0.01) in Group II. Also, the cross-clamp time (mean +/- standard error of the mean) was longer in Group II (94 +/- 4 minutes versus 63 +/- 4 minutes, p less than 10(-6]. The reperfusion solution was found to increase both the rate and extent of postischemic functional recovery, as evidenced by (1) a lower proportion of catecholamine-supported patients 48 hours after operation (9/63 [14.28%] versus 16/49 [32.6%] in the control group [p less than 0.03]) and (2) a lower amount (gamma/kg/min) of dobutamine required to achieve stable hemodynamics (11 +/- 1 versus 26 +/- 6 in the control group [p less than 0.03]). A similar recovery pattern was noted in the high-risk subgroup of patients with mitral valve disease. Further, serial postoperative hemodynamic measurements were performed in 31 randomly selected patients (10 control and 21 reperfused). Although the reperfused patients were found to be at higher risk because of lower preoperative cardiac indices and longer cross-clamp times, they consistently achieved better postoperative hemodynamics with a lower incidence of catecholamine support. This hemodynamic improvement was particularly reflected by a higher left ventricular stroke work index throughout the postoperative course, the difference being significant 6 hours and 12 hours postoperatively.(ABSTRACT TRUNCATED AT 400 WORDS)

Radionuclide assessment of cardiac function. Pre-operative evaluation of patients with abdominal aortic occlusive disease undergoing aortobifemoral bypass grafting

Pre-operative radionuclide angiography, a non-invasive technique for evaluating ventricular function, was performed on 34 consecutive patients undergoing aortobifemoral bypass grafting for abdominal aortic occlusive disease, to determine whether pre-existing coronary artery disease causes significant modification of cardiac function. Patients were divided into two groups according to medical history. Group I had 23 patients with no symptoms of coronary artery disease and Group II had 11 patients, six with previous myocardial infarction and five with angina pectoris. There was a significant difference in left ventricular ejection fraction and in cardiac output between these two groups. A flow-directed pulmonary artery catheter was inserted in eight patients in Group II who had an ejection fraction less than 50% and a nitroglycerin infusion was used in six cases to maintain pulmonary capillary wedge pressure below 20 mmHg. In the other patients, only central venous pressure was monitored. All patients had uneventful operative courses. It is concluded that left ventricular function is significantly altered in patients with symptoms of both abdominal aortic occlusive disease and coronary artery disease. By contrast, cardiac function is normal in patients free from symptoms of coronary artery disease, and central venous pressure monitoring seems sufficient in the management of these patients during aortobifemoral bypass grafting.

Reduction of myocardial infarct size by a fluorocarbon-oxygenated reperfusate

This investigation assesses whether the size of an acutely revascularized myocardial infarct (MI) could be reduced by altering the composition of the initial reperfusate. Nineteen open-chest dogs underwent 4-hour occlusion of the left anterior descending coronary artery and were then assigned to a treatment group: 12 dogs to selective intracoronary infusion of the modified reperfusate over 30 minutes before resumption of blood flow for 60 minutes and 7 to a control group (90 minutes of unmodified blood reperfusion). The modified reperfusate consisted of 500 ml of a fluorocarbon-oxygenated crystalloid solution (PO2 650 mm Hg; total O2 content 5.5 vol%) whose composition was adjusted by decreasing Ca++ (0.25 mM), increasing pH (7.60) and adding glucose (1.8 g/liter). Four hours after occlusion, technetium-99m-labeled microspheres were injected into the left atrium. After 90 minutes of reperfusion, the heart was removed and sliced transversely. Areas not perfused by microspheres (areas at risk) were traced, planimetered and compared with the areas of necrosis after incubation in triphenyltetrazolium chloride. Areas were then converted into weights. In control dogs, the weight of necrotic myocardium was not significantly different from the weight at risk (5.0 +/- 0.7 vs 7.0 +/- 0.8 g, respectively [mean +/- standard error of the mean]), whereas it was markedly reduced in treated dogs (5.9 +/- 0.5 vs 9.4 +/- 0.7 g, respectively, p less than 0.001). The weight of salvaged myocardium was 3.4 +/- 0.5 g in treated dogs vs 1.9 +/- 0.4 g in the control group (p less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

[Ionic bases of cardioplegic solutions. II. Influence of the ionic composition of a cardioplegic solution on the metabolic and functional preservation of ischemic myocardium. Experimental evaluation with phosphorus 31 nuclear magnetic resonance and applications to cardiac surgery]

The object of this study was to establish whether the protective effects of a cardioplegic solution could be improved by ionic or pharmacological intervention aimed at reducing cellular Ca++ overload resulting from myocardial ischaemia. The experimental model was the isolated perfused working heart of the rat submitted to 60 or 120 minutes of hypothermic ischaemia (15 degrees C) followed by 30 minutes of reperfusion at 37 degrees C. The high energy phosphates were measured every 2,5 or 5 minutes by Phosphorus 31 (P31) nuclear magnetic resonance and correlated with haemodynamic data. Our results showed that the best metabolic (75,5 +/- 9,7 p. 100 preservation of ATP after 60 minutes ischaemia) and functional protection (91,8 +/- 4,7 p. 100 recovery of aortic output after 30 minutes reperfusion) was obtained with a solution with the following ionic properties: 1) high Mg++ concentration (13 mM); 2) low Ca++ concentration (0,25 mM); 3) high Na+ concentration (100 mM). The protective effects of this solution were further improved by the addition of a calcium blocking agent (nifedipine 0,2 micrograms/ml). This preserved 85,5 +/- 3,2 p. 100 of basal ATP values after 120 minutes of ischaemia and was associated with a 92,9 +/- 2,8 p. 100 recovery of aortic output at the end of reperfusion. We conclude that: 1) limitation of cellular Ca++ overload is one of the major objectives to be considered when making up cardioplegic solutions; 2) the use of P 31 nuclear magnetic resonance on the isolated working heart is the technique of choice for comparing methods of myocardial protection because it provides a non-invasive, sequential and simultaneous assessment of the parameters of metabolic and haemodynamic function.

Evaluation of high-energy phosphate metabolism during cardioplegic arrest and reperfusion: a phosphorus-31 nuclear magnetic resonance study

Hypothermic potassium cardioplegia is now commonly used to protect the myocardium during surgically induced ischemia. Because the potassium-related membrane depolarization has been shown to increase calcium influx, we undertook this study to define the effects of varying the calcium content in hyperkalemic perfusates and the effects of using magnesium instead of or in addition to potassium as the arresting agent on the ability of hearts to recover normal function after ischemic arrest. We subjected isolated perfused working rat hearts to 60 minutes of cardioplegic arrest followed by 30 minutes of reperfusion, and measured high-energy phosphate levels every 2 1/2 minutes by phosphorus-31 nuclear magnetic resonance spectroscopy. These data were correlated with postischemic recovery of function. Our results show that potassium cardioplegia may be harmful when the calcium concentration is greater than 1 mM. The kalemic injury is significantly reduced when the calcium content is lowered to 0.25 mM and the greatest extent of preservation is provided by a calcium-poor perfusate (0.25 mM) containing 13 mM magnesium. The beneficial effects of magnesium are not enhanced by subsequent addition of potassium. Close correlations were found between all observed metabolic changes during arrest and the degree of recovery of contractile performance after reperfusion. We conclude that the ability of the myocardium to maintain or resynthesize high-energy phosphate after cardioplegic arrest may be an important determinant of postischemic mechanical performance. These results show that phosphorus-31 nuclear magnetic resonance spectroscopy is a valuable method for evaluating interventions to reduce the severity of ischemic damage.

Coronary artery spasm during non-cardiac surgical procedure

A case of coronary artery spasm during a non-cardiac surgical procedure is presented. Two paroxysmal episodes of ST segment elevation in lead 11 and aVF without changes in V5 developed during general anaesthesia. These changes were not preceded by increases in heart rate or arterial pressure. The second episode was associated with a ventricular bigeminal rhythm. This case demonstrates the importance of monitoring several leads in patients likely to develop peroperative spasm of the coronary arteries. Intravenous nitroglycerin was effective in treating the second episode of coronary artery spasm. However, this episode occurred in spite of nitroglycerin administered intravenously at a rate of 0.25 microgram/kg min.

[Acute rupture of the left ventricle 12 hours after an anteroseptal myocardial infarct. Successful surgical repair]

Acute rupture of the left ventricular free wall was suspected in a 53 year old hypertensive patient at the 12th hour of primary antero-septo-apical myocardial infarction. He developed acute tamponade with severe cardiogenic shock during his transfer to hospital. Cardiac compression due to hemopericardium was confirmed by M mode echocardiography (pericardial effusion), right heart catheterisation (adiastole and low cardiac output) and pericardial puncture during which several ccs of blood were aspirated leading to a slight improvement in the patient's condition. At operation under cardiopulmonary bypass 2,5 hours after hospital admission, the surgeon found a hemopericardium related to fissuration of an acute apical infarct which was sutured on a Teflon support. The initial postoperative course was complicated by unexplained gastro-intestinal hemorrhage, transient functional renal failure, cardiac failure and mediastinitis, but the final outcome was successful with a follow-up of 24 months. This appears to be the 9th reported case of long-term survival after surgical repair of rupture of the heart in the acute phase of myocardial infarction.

Acute left ventricular rupture secondary to myocardial infarction. Report of long-term survival after early surgical repair

The case of a 53-year-old male patient is presented who experienced acute left ventricular rupture 12 hours after a myocardial infarct. Immediately following emergency right heart catheterization and pericardiocentesis the patient was operated upon after preliminary institution of femoro-femoral partial heart-lung bypass. Left ventricular rupture in the area of an apical infarct was found which was successfully treated by direct closure. The patient made a complete recovery subsequent to a complicated postoperative course.

[Aorto-left ventricular discontinuity of infectious origin. Problems of surgical repair]

Aorto-left ventricular discontinuity may result from destruction of the aortic ring in aortic valve endocarditis, making solid implantation of a valvular prosthesis difficult. We believe the best technique to be the insertion of a valved Dacron tube from a noninfected area of the left ventricle to the ascending aorta distal to the coronary ostia, the coronary arteries being reimplanted in the tube. This technique implies a relatively dilated aortic ring and the integrity of the supra-annular aortic wall. When these conditions are not fulfilled, the problem has to be solved by supra coronary implantation of an aortic prosthesis with double aorto-coronary bypass grafts. Valved tubes from the left ventricular apex to the abdominal aorta is complex major surgery, the indications for which should be limited to the most mutilating forms of endocarditis causing such severe annular and periannular lesions that the two preceding techniques are impossible. Despite the advances in surgical technique, operative mortality remains high, a problem that could undoubtedly be reduced by early surgery before the association of hemodynamic and infectious complications lead to severe cardiac failure and widespread local lesions.

[Nuclear magnetic resonance. Applications to medicine and biology (author's transl)]

Nuclear magnetic resonance (NMR) is a non-invasive exploratory technique based on a principle radically different from those of radiography, radionuclide exploration and ultrasonography. Signals coming from atomic nuclei and reflecting their density and chemical/biochemical environment are collected, thus providing information of the physiological and pathological state of tissues. The technique has multiple applications, either practical (tomographic imaging of the brain, thyroid gland and liver) or in the field of research, e.g. investigating ischaemic myocardial areas and pathological fluid composition, measuring intracellular pH, diagnosing the nature of a tumour and, broadly speaking, understanding the biochemical changes associated with malignant degeneration.

Limitations of potassium cardioplegia during cardiac ischemic arrest: a phosphorus 31 nuclear magnetic resonance study

Cold K+ cardioplegia is commonly used to preserve the myocardium during surgical ischemia. Since the K+-induced membrane depolarization could cause a Ca2+-mediated breakdown of adenosine triphosphate, this study compared the influence of different electrolytes on high-energy phosphate metabolism during cardioplegic arrest phosphate metabolism during cardioplegic arrest and subsequent recovery of mechanical function. An isolated working heart was subjected to hypothermic ischemia for one hour. Metabolic studies were assessed on phosphorus 31 nuclear magnetic resonance (NMR). Results show that (1) K+ cardioplegia is harmful when the Ca2+ content is equal to 2 mEq/I; (2) deleterious effects of K+ are markedly reduced by lowering the Ca2+ content; (3) the most adequate preservation is provided by a Mg2+-rich-Ca2+-poor perfusate; (4) this protection is not enhanced by addition of K+. Finally, 31P NMR appears particularly appropriate for evaluating myocardial protection techniques since it allows noninvasive serial monitoring of high-energy phosphate content and subsequent correlation with functional recovery after ischemia.

[Postoperative haemodynamic evaluation of myocardial protection by physicochemical cardioplegia. Hyperkaliemic, hyperosmolar and acid solution at 4 degrees C (author's transl)]

Myocardial protection by a combination of cardiac hypothermia and chemical cardioplegia (high concentration of K+ and Mg++, hyperosmolarity, acid pH), was studied during 20 valve replacements. Essentially assessed on the basis of repeated measurements of postoperative cardiac output, the results were compared with those obtained previously using local hypothermia only (20 patients) and hypothermic cardioplegia using Ringer Lactate (20 patients). Analysis of haemodynamic data, which thus involved 60 patients, indicated the superiority of physicochemical cardioplegia, and this for clamping periods of up to 2 hours, but also showed the desirability of changes in the protection protocol during the ischaemia phase and during reperfusion which might improve the results.

[Surgical treatment of Prinzmetal's syndrome. Report of sixty operated cases (author's transl)]

The results of the surgical treatment of Prinzmetal's angina are reported in this study of 60 patients. The operative mortality is 3,3 percent and the incidence of post-operative infarction is 20 percent. 53 patients were followed over an average period of 2,7 years. The global survival rate is 91 percent at 5 years, the infarction rate is 24 percent. 76 percent of the sublims are asymptomac. The patients can be classified in three group : isolated lesions, multiple lesions and spasms.