Transient ventricular fibrillation and myosin heavy chain isoform profile.

The present paper deals with spontaneous ventricular defibrillation in mammals and the possibility to facilitate its occurrence. Clinical and experimental evidence suggest that in the majority of cases, ventricular fibrillation (VF) is permanent, requiring defibrillation by electric shock. However, a growing number of reports show that VF can terminate spontaneously in various mammals, including human beings. The mechanisms involved in spontaneous ventricular defibrillation are controversial. Available reports imply that intracellular Ca2+ overload is the key event triggering VF and preventing its reversal. Since the sarcoplasmatic reticulum is the main intracellular Ca2+ regulating organelle and the activity of the cardiac SR Ca2+ ATPase (SERCA 2a) is its prime element of Ca2+ sequestration, spontaneous ventricular defibrillation likely requires high level of SERCA 2a activity. We suggest that mammalian hearts with high SERCA 2a activity defibrillate spontaneously and those with low activity only after its enhancement. Since high SERCA 2a activity is co-expressed with the myosin heavy chain (MHC) isoform V1, we assumed that those hearts preferentially expressing V1 MHC are able to defibrillate spontaneously. Hearts with small amounts of V1 MHC and correspondingly lower level of SERCA 2a activity can only defibrillate following administration of compounds that augment SERCA 2a activity and prevent intracellular Ca2+ overload.

Role of ischemia and of hypoxia-inducible genes in arteriogenesis after femoral artery occlusion in the rabbit.

Vascular endothelial growth factor (VEGF) is known to play an important role in angiogenesis. Its place in collateral artery growth (arteriogenesis), however, is still debated. In the present study, we analyzed the expression of VEGF and its receptors (Flk-1 and Flt-1) in a rabbit model of collateral artery growth after femoral artery occlusion. Hypoxia presents the most important stimulus for VEGF expression. We therefore also investigated the expression level of distinct hypoxia-inducible genes (HIF-1alpha, LDH A) and determined metabolic intermediates indicative for ischemia (ATP, creatine phosphate, and their catabolites). We found that arteriogenesis was not associated with an increased expression of VEGF or the mentioned hypoxia-inducible genes. Furthermore, the high-energy phosphates and their catabolites were entirely within normal limits. Despite the absence of an increased expression of VEGF and its receptors, collateral vessels increased their diameter by a factor of 10. The speed of collateral development could be increased by infusion of the chemoattractant monocyte chemotactic protein-1 but not by infusion of a 30 times higher concentration of VEGF. From these data, we conclude that under nonischemic conditions, arteriogenesis is neither associated with nor inducible by increased levels of VEGF and that VEGF is not a natural agent to induce arteriogenesis in vivo.

Signaling from beta-adrenoceptor to L-type calcium channel: identification of a novel cardiac protein kinase A target possessing similarities to AHNAK.

A novel calcium channel-associated protein of approximately 700 kDa has been identified in mammalian cardiomyocytes that undergoes substantial cAMP-dependent protein kinase (PKA) phosphorylation. It was therefore designated as phosphoprotein 700 (pp700). The pp700 interacts specifically with the beta(2) subunit of cardiac L-type calcium channels as revealed by coprecipitation experiments using affinity-purified antibodies against different calcium channel subunits. It is surprising that amino acid sequence analysis of pig pp700 revealed homology to AHNAK-encoded protein, which was originally identified in human cell lines of neural crest origin as 700-kDa phosphoprotein. Cardiac AHNAK expression was assessed on mRNA level by reverse transcriptase-polymerase chain reaction. Sequence-directed antibodies raised against human AHNAK recognized pp700 in immunoblotting and immunoprecipitation experiments, confirming the homology between both proteins. Anti-AHNAK antibodies labeled preferentially the plasma membrane of cardiomyocytes in cryosections of rat cardiac tissue and isolated cardiomyocytes. Sarcolemmal pp700/AHNAK localization was not influenced by stimulation of either the PKA or the protein kinase C pathway. In back-phosphorylation studies with cardiac biopsies, we identified distinct pp700 pools. The membrane-associated fraction of pp700 underwent substantial in vivo phosphorylation on beta-adrenergic receptor stimulation by isoproterenol, whereas the cytoplasmic fraction of pp700 was not accessible to endogenous PKA. It is important that in vivo phosphorylation occurred in that pp700 fraction which coprecipitated with the calcium channel beta subunit. We hypothesize that both phosphorylation of pp700 and its coupling to the beta subunit play a physiological role in cardiac beta-adrenergic signal transduction. Haase, H., Podzuweit, T., Lutsch, G., Hohaus, A., Kostka, S., Lindschau, C., Kott, M., Kraft, R., Morano, I. Signaling from beta-adrenoceptor to L-type calcium channel: identification of a novel cardiac protein kinase A target that has similarities to AHNAK.

Ischemic preconditioning and the beta-adrenergic signal transduction pathway.

BACKGROUND: Previous studies from our laboratory showed cyclic increases in tissue cAMP during a multiple-cycle preconditioning (PC) protocol, followed by attenuated cAMP accumulation during sustained ischemia. The aim of this study was to determine whether ischemia-induced activation of the beta-adrenergic signaling pathway could act as a trigger in eliciting protection. METHODS AND RESULTS: Isolated perfused rat hearts were preconditioned by 3x5 minutes of global ischemia, interspersed by 5 minutes of reperfusion. beta-Adrenergic responsivity was assessed by measurement of tissue cAMP generation after beta-adrenergic agonist administration at the end of the PC protocol. Tissue cAMP, adenylyl cyclase, and protein kinase A (PKA) activities and beta-adrenergic receptor characteristics were assessed at different times. The role of cAMP generation in eliciting PC was studied by investigation of functional recovery during reperfusion after 25 minutes of global ischemia after (1) cAMP increases in the trigger period were prevented with the beta-adrenergic blocker alprenolol 7.5x10(-5) mol/L and (2) increases in cAMP were elicited by administration of forskolin 10(-7) and 10(-6) mol/L or isoproterenol 10(-8), 10(-7), and 10(-6) mol/L. Intermittent ischemia resulted in reduced beta-adrenergic responsivity at the end of the protocol, although B(max) and K(d) values of the beta-adrenergic receptor population and adenylyl cyclase and PKA activities were increased. Abolishment of cyclic increases in cAMP before sustained ischemia attenuated myocardial protection against ischemia, whereas agonists elicited protection. No clear correlation between protection and beta-adrenergic desensitization was observed. CONCLUSIONS: Ischemia-induced activation of the beta-adrenergic signaling pathway during preconditioning should also be considered a trigger in eliciting preconditioning.

Transmyocardial laser revascularisation has no beneficial effect on high energy phosphates and lactate content during acute myocardial ischaemia in pigs.

OBJECTIVE: Transmyocardial laser revascularisation (TMLR) is used to treat endstage coronary heart disease. There is evidence that angina is significantly reduced after TMLR. However, the precise mechanism by which symptoms disappear remains unknown. The objective of the present study was to examine the potential effects of TMLR on high-energy phosphates and myocardial perfusion in an acute ischaemic model. METHOD: Five male landrace pigs (42 +/- 1.8 kg) had TMLR of the anterolateral wall of the left ventricle using a 1000 W CO2 laser (PLC, USA). Thereafter the anterior descending coronary artery was occluded with a tourniquet. After 90 min of ischaemia, drill-biopsies were taken from ischaemic and non-ischaemic areas as well as from laser channels. The specimens were snap-frozen in liquid nitrogen. Subsequently, methylene blue was injected into the left atrium to study tissue distribution. The hearts were excised and the patency of channels was examined visually. RESULTS: Coronary artery occlusion resulted in immediate blue discoloration in both TMLR and control areas. There was no subendocardial methylene blue staining around laser channels. Inspection of hearts showed occlusion of laser channels due to thrombus formation at both endo- and epicardial levels. ATP-metabolites significantly increased in ischaemic areas compared to non-ischaemic areas. Furthermore there was significant upregulation of purine-content in ischaemic regions even in areas with laser channels. CONCLUSIONS: In our acute model there was early occlusion of the channels after TMLR. We suggest that clinical improvement after this procedure is not due to increased myocardial oxygen delivery, since high energy phosphate levels and lactate content remained unchanged.

Role of cyclic nucleotide phosphodiesterases in ischemic preconditioning.

Several signal transduction pathways have been implicated in the mechanism of protection induced by ischemic preconditioning (PC). For example, stimulation of a variety of G-protein coupled receptors results in stimulation of protein kinase C (PKC) which has been suggested to act as common denominator in eliciting protection. PC also significantly attenuated cAMP accumulation during sustained ischemia, suggesting involvement of an anti-adrenergic mechanism. The aim of this study was to evaluate the beta-adrenergic signal transduction pathway (as evidenced by changes in tissue cAMP and cAMP- and cGMP-phosphodiesterase) during the PC protocol as well as during sustained ischemia. Isolated perfused rat hearts were preconditioned by 3 x 5 min global ischemia (PC1,2,3) interspersed by 5 min reperfusion, followed by 25 min global ischemia. Tissue cAMP- and cGMP-PDE activity as well as cAMP and cGMP levels were determined at different time intervals during the PC protocol and sustained ischemia. Tissue cAMP increased with each PC ischemic event and normalized upon reperfusion, while PDE activity showed the opposite, viz a reduction during ischemia and an increase during reperfusion. Except for PC1, tissue cGMP showed similar fluctuations. Throughout 25 min sustained ischemia, cAMP- and cGMP-PDE activities were higher in PC than in nonpreconditioned hearts, associated with a significantly lesser accumulation in cAMP and higher cGMP levels in the former. Fluctuations in cyclic nucleotides during preconditioning were associated with concomitant changes in PDE activity, while the attenuated beta-adrenergic response of preconditioned hearts during sustained ischemia may partially be due to increased PDE activity.

Intramyocardial infusion of tool drugs for the study of molecular mechanisms in ischemic preconditioning.

Many of the new tool drugs useful for the study of molecular mechanisms of ischemic preconditioning (IP) are very valuable in in vitro systems but produce undesired side-effects after systemic injection in intact animals that limit their applicability. Our aim was to develop an experimental in vivo model that allows the use of said drugs in sufficiently high local concentrations, but avoiding at the same time the systemic side-effects. Several techniques were combined to study regional damage or protection as a result of local drug infusion such as nuclear staining, NADH fluorescence, fluorescent microspheres and tetrazolium salts. In open-chest pigs, the intramyocardial infusion (20 microliters/min) of the adenosine A1-receptor agonist N6-cyclohexyladenosine (0.3 mmol) for 10 min prior to a 60-min LAD-occlusion and 120-min reperfusion mimicked IP by exerting a local protection (n = 9, p < 0.001). Krebs-Henseleit buffer (negative control) was without protective effect. IP's cardioprotection was locally prevented by the intramyocardial application of the adenosine A1-receptor antagonist cyclopentyltheophylline (1 mmol, infused during IP; n = 6, p < 0.001) but not by KHB. The protein kinase C (PKC)-inhibitors staurosporine (100 nmol, n = 6) or bisindolylmaleimide (BIS, 25 mumol, n = 9) did not prevent IP locally. The PKC activator phorbol myristate acetate (PMA, 1 mumol, n = 6) was ineffective in preventing ischemic injury and increased the amount of necrosis in IP, whereas BIS exerted a local myocardial protection (n = 9, p < 0.001). In conclusion, the new model of intramyocardial infusion appears to be useful for the investigation of IP's signal transduction. Our data support the role of the adenosine A1-receptor in IP, but suggest that inhibition instead of activation of PKC may protect ischemic myocardium from infarction.

Role of nitric oxide and phosphodiesterase isoenzyme II for reduction of endothelial hyperpermeability.

Regulation of endothelial permeability is poorly understood. Previous studies have shown that endothelial cells contain phosphodiesterase (PDE) isoenzymes II-IV and that simultaneous adenylate cyclase activation and/or PDE inhibition blocked endothelial hyperpermeability (J.Clin.Invest. 91: 1421-1428, 1993). We now focused on a possible role for guanosine 3',5'-cyclic monophosphate (cGMP)-dependent mechanisms and studied H2O2-exposed porcine pulmonary artery endothelial cell monolayers. Pretreatment of cells with different nitric oxide (NO) donors or atrial natriuretic peptide (ANP) increased endothelial cGMP-content severalfold and blocked H2O2-related effects on permeability; opposite results were obtained with a NO synthase inhibitor. Determination of cGMP degradation in nitroprusside-exposed endothelial cells identified PDE II as the major cGMP metabolizing pathway, whereas PDE III and IV contributed little or nothing. Inhibition of PDE II reduced H2O2-related endothelial hyperpermeability, an effect that could be enhanced synergistically by simultaneous guanylate cyclase activation. In summary, these studies indicate that cGMP-dependent mechanisms (NO donors, ANP, and dibutyryl-cGMP) blocked H2O2-related increases in endothelial permeability. The major cGMP degrading pathway in endothelial cells was PDE II, thereby substituting the missing PDE V in these cells. Simultaneous guanylate cyclase activation and/or PDE II inhibition may be a valuable approach to treat endothelial hyperpermeability.

Isozyme selective inhibition of cGMP-stimulated cyclic nucleotide phosphodiesterases by erythro-9-(2-hydroxy-3-nonyl) adenine.

Erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA), a potential inhibitor of adenosine deaminase (ADA), was tested as an inhibitor of the soluble cyclic nucleotide phosphodiesterase (PDE) isoenzymes from pig and human myocardium. Four soluble PDE activities were resolved from human papillary muscle extracts using anion exchange chromatography (DEAE Sepharose CL-6B). These activities were designated PDE I-IV according to the nomenclature of Beavo. PDE I was stimulated by Ca(2+)-calmodulin and PDE II by cGMP (1 microM). PDE III was inhibited by cGMP (1 microM) as well as SK&F 94120, and PDE IV by both rolipram and Ro 20-1724. Enzyme kinetics and inhibition constants were similar with the PDE isoenzymes from pig heart. However, porcine myocardium lacked Ca(2+)-calmodulin-stimulated soluble PDE I activity. The present data reveal that EHNA exerted a concentration-dependent inhibition of the cGMP-stimulated PDE II (cGs-PDE) (IC50: 0.8 microM (human), 2 microM (pig)) but did not inhibit the other PDE isoenzymes (IC50 > 100 microM). These findings indicate that EHNA is a potent and, as far as cytosolic PDEs are concerned, selective inhibitor of cGMP-stimulated PDEs. The compound may lend itself for the rational design of other isozyme selective PDE II inhibitors and for examining the specific biological functions of cGs-PDEs. EHNA may be used in systems in which inhibition of ADA is of no concern. Conversely, dual inhibition of both ADA and cGs-PDE by EHNA may cause accumulation of two inhibitory metabolites, adenosine and cGMP, which may act in synergy to mediate diverse pharmacological responses, including antiviral, antitumour and antiarrhythmic effects.

Potential arrhythmogenic role of cyclic adenosine monophosphate (AMP) and cytosolic calcium overload: implications for prophylactic effects of beta-blockers in myocardial infarction and proarrhythmic effects of phosphodiesterase inhibitors.

Activation of the adrenergic nervous system appears to play a crucial role in the genesis of fatal arrhythmias associated with the very early stages of acute myocardial infarction. The second messenger of beta-adrenergic catecholamine stimulation, cyclic adenosine monophosphate (AMP), has established arrhythmogenic qualities, acting by an increase in cytosolic calcium, which potentially has three adverse electrophysiologic effects. First, stimulation of the transient inward current by excess oscillations of cytosolic calcium can invoke delayed afterdepolarizations, so that triggered automaticity can develop in otherwise quiescent ventricular muscle. Second, cyclic AMP can evoke calcium-dependent slow responses in depolarized fibers, so that conditions for reentry are favored. Third, excess cytosolic calcium can cause intercellular uncoupling with conduction slowing. Focal changes in cyclic AMP and cytosolic calcium promote the development of ventricular fibrillation. Beta-adrenergic blockade can limit the formation of cyclic AMP in ischemic tissue. Furthermore, by reducing sinus tachycardia it can lessen cytosolic calcium overload. Hence, beta-adrenergic blockade helps to prevent ventricular fibrillation in the early stages of acute myocardial infarction and protects from sudden death in the postinfarction phase. In congestive heart failure, abnormalities of cytosolic calcium patterns exist with cytosolic calcium overload. It is proposed that the adverse effects of phosphodiesterase inhibitors on the mortality rate in patients with congestive heart failure can be explained by increased rates of formation of cyclic AMP and the development of calcium-dependent arrhythmias. Because calcium is the ultimate messenger of cyclic AMP-induced arrhythmias and because cytosolic calcium is increased in heart failure, it will be difficult to develop positive inotropic agents that are free of the risk of sudden death.

Absence of xanthine oxidoreductase activity in human myocardium.

STUDY OBJECTIVE: The aim was to examine whether or not xanthine oxidase activity may be a significant source of oxygen derived free radicals in the human heart. DESIGN: Xanthine oxidoreductase activity of human myocardium was assayed in vitro. In addition, tests were performed to assess whether or not endogenous inhibitors of the enzyme were present in myocardial homogenates. The enzyme assay was based on high performance liquid chromatography with electrochemical and/or radiochemical detection of hypoxanthine, xanthine, and urate. SUBJECTS: Measurements were done on (a) isolated perfused rat myocardia and (b) left ventricular needle biopsies and papillary muscles obtained during elective cardiac surgery (chiefly aortic and/or mitral valve replacement and aortocoronary bypass) (n = 105 patients). MEASUREMENTS AND MAIN RESULTS: Homogenisation of human papillary muscles in buffer caused significant accumulation of hypoxanthine but not xanthine or urate. In addition, during incubation of crude myocardial homogenates with exogenous xanthine or hypoxanthine in the presence of NAD+ and/or O2 no production of urate was detected. Likewise, following aerobic incubation of papillary muscle homogenates with 14C-hypoxanthine neither 14C-xanthine nor 14C-urate were formed. Absence of xanthine oxidising activity was also observed with human papillary muscle extracts that were subjected to either ultrafiltration or gel filtration. In contrast, the rat heart was found to contain abundant xanthine oxidoreductase activity. The rat heart enzyme was inhibited by both allopurinol and oxypurinol but remained active when mixed with human papillary muscle homogenates. CONCLUSIONS: These findings show absence of xanthine oxidase and xanthine dehydrogenase activities in human myocardium, indicating that xanthine oxidase is not a source of oxygen derived free radicals in the human heart.

Factors determining ventricular fibrillation after induced cardiac arrest.

Ventricular fibrillation following release of the aortic cross clamp is not uncommon. In 38 patients undergoing aortic valve replacement we investigated if this disturbance of rhythm is due to perioperative myocardial ischemia or due to deterioration of myocardial function prior to surgery. In all cases hypothermic cardioplegic arrest (Bretschneider) was used. The mean duration of ischemia was 49.39 +/- 10.46 minutes. After release of the aortic cross clamp in 17 of 38 patients ventricular fibrillation occurred. To find out which factors are responsible for the occurrence of ventricular fibrillation we performed a statistical analysis. Thereby we found out that the occurrence of ventricular fibrillation did not correlate with ischemia, the maximal level of myocardium-bound creatine kinase, the NYHA stage, or the left ventricular end diastolic pressure. The left-ventricular concentration of noradrenaline determined just before release of the aortic cross clamp showed a significant negative correlation with the occurrence of ventricular fibrillation. From our results we conclude that ischemic injury was not the determining factor for the occurrence of ventricular fibrillation in our study. We suggest that the significant correlation with reduced myocardial noradrenaline content demonstrates that myocardial deterioration prior to surgery is the determining factor for the occurrence of ventricular fibrillation.

[Effect of the duration of reperfusion on metabolic recovery during unloading of the hypertrophic heart following induced heart arrest]. / Einfluss der Reperfusionsdauer auf die metabolische Erholung während Entlastung des hypertrophen Herzens nach induziertem Herzstillstand.

The methods of cardioplegia used today are not always able to sufficiently protect the hypertrophied heart. The present study investigated if a recovery period of 30 min before the end of ECC improves metabolic recovery of the heart in comparison to a recovery period of 15 min before terminating extracorporeal circulation. A clinical study was performed of patients undergoing aortic valve replacement. In one group reperfusion was performed for 15 min and in the second group for 30 min before the conclusion of extracorporeal circulation. The concentration of high energy phosphates in the left ventricle was determined at the end of the ischemic period, after 15 min and after 30 min of reperfusion. The behavior of the myocardial metabolites of the two groups showed no differences. Creatinephosphate increased continuously in both groups, while adenosine triphosphate and the adenonucleotide pool did not change during the reperfusion period. From our results we conclude that under the conditions given in our study a recovery period of 15 min is sufficient for metabolic recovery and prolongation of reperfusion before termination of extracorporeal circulation do not improve metabolic recovery.

The anti-arrhythmic effects of myocardial ischaemia. Relation to reperfusion arrhythmias?

Ventricular tachycardia was induced in the intact non-ischaemic pig heart by intramyocardial or intracoronary infusions of noradrenaline or N6, O2'-dibutyryl-cAMP. The chemically induced tachycardia was consistently stopped within 10 to 30 s by occluding the coronary artery supplying the infusion area. This ischaemic effect was readily reversed by coronary reperfusion, with ventricular tachycardia resuming within seconds after release of the occlusion. In contrast to the immediate effect of myocardial ischaemia, it took several minutes for the tachycardia to cease after the infusion of arrhythmogenic compounds was stopped. Pacing experiments showed that the effect of myocardial ischaemia on ventricular tachycardia was probably not due to a conduction block. The anti-arrhythmic property of myocardial ischaemia was separate from its known effect of decreasing the ventricular fibrillation threshold for electrical stimulation. The increased vulnerability of the acutely ischaemic myocardium to fibrillation was apparent in experiments in which ectopic activity was induced in the non-ischaemic part of the myocardium. In these experiments ventricular fibrillation consistently ensued within 6 min following distal occlusion of the anterior descending coronary artery. By contrast, ventricular fibrillation was not precipitated by coronary artery occlusion or local infusion of arrhythmogenic compounds alone. Cyclic AMP was shown to accumulate in ischaemic myocardium. An association existed between cAMP accumulation and the intensity of early ischaemic arrhythmias as well as reperfusion arrhythmias. The highest incidence of ventricular fibrillation was found during reperfusion, at peak myocardial cAMP levels. These findings suggest: (1) Noradrenaline and dibutyryl-cAMP exert arrhythmogenic effects preferentially in the intact, non-ischaemic myocardium, the effects being attenuated in ischaemic myocardium by a paradoxical anti-arrhythmic effect of ischaemia. (2) In the acutely ischaemic heart, ventricular fibrillation may be precipitated by the emergence of ectopic activity outside the ischaemic area. (3) Arrhythmias and fibrillation occurring early after reperfusion may be caused by unmasking the effects of excitants (eg, noradrenaline or cAMP) arising during the antecedent period of ischaemia.

Preservation of myocardial energy-rich phosphates by retrograde application of Bretschneider cardioplegia during aortocoronary bypass surgery.

The efficacy of myocardial protection obtained by antegrade application of a cardioplegic solution was compared with that obtained by retrograde application via the coronary sinus. Myocardial preservation was assessed using biochemical parameters, i.e. tissue content of lactate, creatine phosphate, nucleotides, nucleosides and hypoxanthine. Nineteen patients undergoing routine aortocoronary bypass surgery were randomly allocated to a study group. During cardiac arrest induced by antegrade Bretschneider cardioplegia, myocardial tissue content of creatine phosphate dropped to 52% of its pre-ischemic value and degradation of nucleotides occurred, characterized mainly by an accumulation of adenosine. Retrograde cardioplegia prevented this catabolism of energy-rich phosphates completely during ischemic cardiac arrest and is therefore considered to be superior to antegrade cardioplegia.

Arrhythmias and infarction in the ischemic pig heart are not mediated by xanthine oxidase-derived free oxygen radicals.

Xanthine oxidase activities of pig myocardium and blood during and following myocardial ischemia were measured using HPLC, and electrochemical detection of hypoxanthine, xanthine and uric acid. Myocardial ischemia was produced by occluding the anterior descending coronary artery two-thirds of the way from its origin. There was no accumulation of either xanthine or urate in the ischemic pig myocardium during occlusion periods of 90 min, but there was a substantial accumulation of hypoxanthine. Similarly, there was no increase in myocardial xanthine or urate during the 30 min reperfusion following coronary artery occlusion periods of 15, 30, 60 or 90 min. Following in vitro incubation at pH 8 of myocardial homogenates or blood with either hypoxanthine or xanthine and NAD, no urate production was detectable. In contrast, significant amounts of xanthine and/or urate were produced, following addition of xanthine oxidase to the reaction mixtures. Additional in vitro experiments showed that the following pig tissues were lacking xanthine oxidase activity: left and right atrial appendage, left and right ventricle, interventricular septum, anterior descending and circumflex coronary arteries, ascending aorta, lung, and blood. Large amounts of xanthine oxidase (9.3 +/- 1.8 SEM mU/g wet weight, n = 7) were found in pig liver. In the ischemic pig heart, transmural infarction developed within 60 min of ischemia. Ventricular arrhythmias and fibrillation occurred most frequently within 45 min of ischemia and within seconds after reperfusion. These results showed that the pig heart and blood were xanthine oxidase deficient, suggesting that xanthine oxidase-derived free oxygen radicals were not involved in the cytotoxic and arrhythmogenic effects brought about by myocardial ischemia and/or reperfusion in the pig.

Protection of the hypertrophied human heart by adjusting regional myocardial temperature to a safe level.

Uneven distribution of temperature and the persistence of electro-mechanical activity after aortic cross-clamping are 2 factors limiting the myocardial protection during cardioplegic arrest, especially in hypertrophied hearts which are known to be extremely vulnerable to ischemia. In the present study regional myocardial temperature (T) was continuously controlled, and the time until arrest occurred (delta t) was determined in 61 patients undergoing aortic valve replacement. In addition, the myocardial contents of high energy phosphates and lactate were assessed. Three different cardioplegic solutions were employed: In the first group we used Bretschneider solution (Br), in the second group St. Thomas' solution (St), and in the third group the so-called "Hamburg cardioplegia" (H). During cardiac arrest the regional myocardial temperature was adjusted to temperatures not exceeding 15 degrees C by intermittent infusions of cold cardioplegic solution. We found a positive correlation between left ventricular muscle mass (LVMM) and delta t. A negative correlation existed between LVMM and adenosine triphosphate (ATP) contents at the end of the ischemic period. The cooling characteristics and delta t were significantly longer and the cooling to 15 degrees C was less rapid when H was used. Adenosine-triphosphate contents were well preserved during ischemia in all 3 groups. We conclude that all 3 cardioplegic solutions tested protect the hypertrophied myocardium adequately if the regional myocardial temperature does not increase above 15 degrees C during cardiac arrest. Hearts with a higher LVMM showed a decreased myocardial ATP content at the end of the ischemic period. Therefore, the LVMM may limit myocardial protection.

Preservation of high energy phosphates in hypertrophied human myocardium.

Hypertrophied hearts are extremely vulnerable to ischemia. In 61 patients with aortic valve disease undergoing surgery we investigated the quality of myocardial protection obtained with three different methods of crystalloid cardioplegia. To exclude the influence of temperature differences the regional myocardial temperatures were continuously measured and adjusted to the same level in all patients. Before and after ischemia and after 10 minutes reperfusion myocardial biopsies were taken and the high energy phosphates and lactic acid determined. In one group St. Thomas cardioplegia was used, in another Bretschneider cardioplegia and in the third the Hamburg method. There were no significant differences between the three groups at the end of ischemia and after 10 minutes reperfusion. After 10 minutes reperfusion the metabolic alterations caused by ischemia were in part reversible. From our results we conclude that each of the cardioplegias used is able to protect a hypertrophied heart adequately against ischemia during cardiac arrest.