Local myocardial biochemical and ionic alterations during myocardial ischaemia and reperfusion

Mechanisms of sudden cardiac death: oxidants and metabolism

Ventricular arrhythmia is the leading cause of sudden cardiac death (SCD). Deranged cardiac metabolism and abnormal redox state during cardiac diseases foment arrhythmogenic substrates through direct or indirect modulation of cardiac ion channel/transporter function. This review presents current evidence on the mechanisms linking metabolic derangement and excessive oxidative stress to ion channel/transporter dysfunction that predisposes to ventricular arrhythmias and SCD. Because conventional antiarrhythmic agents aiming at ion channels have proven challenging to use, targeting arrhythmogenic metabolic changes and redox imbalance may provide novel therapeutics to treat or prevent life-threatening arrhythmias and SCD.

Controlled Reperfusion Versus Conventional Treatment of the Acutely Ischemic Limb

Background—

Amputation rates and mortality in patients with severe acute limb ischemia remain high. The protective effect of controlled reperfusion (CR) on tissue damage because of local and systemic reperfusion injury is unclear.

Methods and Results—

A total of 174 patients from 14 centers were randomized between conventional treatment (CT) by thrombembolectomy and normal blood reperfusion and thrombembolectomy followed by CR. The primary end point was amputation-free survival (AFS) after 4 weeks (CT, 82.4%; CR, 82.6%). Secondary end points were AFS (CT, 62.4%; CR, 63.1%) and overall survival (CT, 71.6%; CR, 76.3%) after 1 year. Analysis of the prognostic effects of preoperative factors revealed a strong adverse effect of bilateral involvement on AFS. In the subgroup with unilateral ischemia (n=160), age >80 years and central localization of the occlusion had independent negative prognostic effects on AFS. In the per-protocol population of 104 patients with unilateral ischemia, treatment per protocol, and successful revascularization, amputation or death within 4 weeks occurred in only 8% as compared with 33% in patients not fulfilling these criteria. No differences between treatment groups CT and CR were found, neither overall nor in the per-protocol population nor in patient subgroups defined by other pre- and intraoperative factors.

Conclusions—

Similar AFS in patients with CT or with CR was observed in this large randomized multicenter trial.

Clinical Trial Registration—

URL: http://www.drks.de . Unique identifier: DRKS00000579.

Trimetazidine protective effect against ischemia-induced susceptibility to ventricular fibrillation in pigs

PURPOSE

Ventricular fibrillation (VF) is a possible consequence of brief myocardial ischemia. Such a short ischemia does not provoke cell damage, but induces changes in intracellular cardiac metabolism due to diminished oxygen supply to the heart. Trimetazidine (TMZ) is a drug able to restore the metabolic balance between fatty acid and glucose oxidation in ischemic myocardial cells. The aim of this double-blind study was to investigate TMZ effect on VF in pigs during short-term ischemia.

METHODS

Ischemia was induced after thoracotomy by complete, but brief (1 min) occlusion of the left anterior descending coronary artery under electrical stimulation. The ventricular fibrillation threshold (VFT), heart rate (HR), various hemodynamic parameters and malondialdehyde (MDA) blood levels were measured before and during ischemia in two groups of eight anesthetized pigs. The mass of ischemic myocardial tissue was also evaluated.

RESULTS

No effects on either the HR or the hemodynamic parameters were observed during myocardial ischemia, whereas TMZ increased the VFT and decreased both MDA blood levels (an index of lipid peroxidation) and the ischemic area.

CONCLUSIONS

TMZ limited ischemia-induced electrical dysfunction leading to cardiac susceptibility to VF by decreasing lipid peroxidation and maintaining ionic homeostasis. TMZ could therefore provide protection against ischemia-induced VF.

The effects of paeonol on the electrophysiological properties of cardiac ventricular myocytes

Previous studies have shown that "Mudanpi", a Chinese herbal medicine, has a significant cardioprotective effect against myocardial ischaemia. Based on these findings we hypothesised that paeonol, the main component of Mudanpi, might have an effect on the cellular electrophysiology of cardiac ventricular myocytes. The effects of paeonol on the action potential and ion channels of cardiac ventricular myocytes were studied using the standard whole-cell configuration of the patch-clamp technique. Ventricular myocytes were isolated from the hearts of adult guinea-pig by enzymic dispersion. The myocytes were continuously perfused with various experimental solutions at room temperature and paeonol applied in the perfusate. Action potentials and membrane currents were recorded using both current and voltage clamp modes of the patch-clamp technique. Paeonol, at concentrations 160 microM and 640 microM, decreased the action potential upstroke phase, an action associated with the blockade of the voltage-gated, fast sodium channel. The effects of paeonol on both action potential and Na(+) current were concentration dependent. Paeonol had a high affinity for inactivated sodium channels. Paeonol also shortened the action potential duration, in a manner not associated with the blockade of the calcium current, or the enhancement of potassium currents. These findings suggest that paeonol, and therefore Mudanpi, may possess antiarrhythmic activity, which may confer its cardioprotective effects.

Involvement of extracellular signal-regulated protein kinase in gliosis induced during recovery from metabolic inhibition

Brain reperfusion may be of particular importance in the etiology of periventricular leukomalacia, of which the common findings are gliosis and ventricular dilatation. To investigate the mechanism of this pathogenesis, we used a metabolic inhibition (MI) model using cyanide plus deoxyglucose treatment of cultured glia isolated from fetal rat brain and examined the activity of extracellular signal-regulated protein kinase (ERK) during MI and also during the recovery from MI of 30 min. ERK activation was stimulated during MI and the recovery from MI. The time course and extent of activation of ERK during MI and the recovery from MI, however, were distinctly different. Activation of ERK was stimulated within 5 min of MI and declined thereafter. Activation of ERK was sustained during the recovery phase from MI and the extent of the activation was much greater than that during MI. Pretreatment with EGTA to eliminate extracellular Ca(2+), or with APV, an NMDA receptor antagonist, to inhibit Ca(2+) influx through the NMDA receptor, attenuated the activation of ERK. Moreover, pretreatment with PMA to downregulate PKC abolished the activation of ERK. PD98059, an inhibitor of ERK kinase, attenuated the cell proliferation induced by MI followed by recovery from MI. These results suggest that ERK is involved in gliosis during the recovery phase from MI and may play a role in the etiology of periventricular leukomalacia.

Cardiac ionic currents and acute ischemia: from channels to arrhythmias

The aim of this review is to provide basic information on the electrophysiological changes during acute ischemia and reperfusion from the level of ion channels up to the level of multicellular preparations. After an introduction, section II provides a general description of the ion channels and electrogenic transporters present in the heart, more specifically in the plasma membrane, in intracellular organelles of the sarcoplasmic reticulum and mitochondria, and in the gap junctions. The description is restricted to activation and permeation characterisitics, while modulation is incorporated in section III. This section (ischemic syndromes) describes the biochemical (lipids, radicals, hormones, neurotransmitters, metabolites) and ion concentration changes, the mechanisms involved, and the effect on channels and cells. Section IV (electrical changes and arrhythmias) is subdivided in two parts, with first a description of the electrical changes at the cellular and multicellular level, followed by an analysis of arrhythmias during ischemia and reperfusion. The last short section suggests possible developments in the study of ischemia-related phenomena.

Magnesium--a profibrillatory or antifibrillatory drug depending on plasma concentration, heart rate and myocardial perfusion

BACKGROUND

The opinions on the efficacy of magnesium as an antiarrhythmic drug vary considerably. The action of magnesium on vulnerability to fibrillation was therefore investigated in anaesthetized, open-chest pigs under different conditions as regards plasma concentration, heart rate and myocardial perfusion.

METHODS

Vulnerability to fibrillation was assessed by electrical fibrillation threshold (EFT), measured with 100-ms duration diastolic impulses. These stimuli were delivered to the heart normally perfused, at a usual (90 and 120 beats/min) or accelerated (180 beats/min) rate. Vulnerability to fibrillation was also assessed at the high rate (180 beats/min) in the heart made ischaemic by complete occlusion of the left anterior descending coronary artery near its origin. EFT was then measured at the end of occlusion periods which were of increasing duration (30, 60, 90, 120 s). Monophasic action potential (MAP) duration, intraventricular conduction time, left ventricular dP/dt max (LVdP/dt max) and mean blood pressure were concurrently measured.

RESULTS

In the absence of ischaemia, 5 mumol.kg-1.min-1 magnesium i.v. infusion, which raised plasma concentration to 1.78 +/- 0.14 mmol/L, lowered EFT, measured at the rate of 116 beats/min, from 14.0 +/- 1.1 to 6.8 +/- 1.0 mA (P < 0.001), without significant variation of the other parameters. Administered as previously or in a markedly higher dose (400 mumol.kg-1 loading dose and 10 mumol.kg-1.min-1 infusion) which raised plasma concentration up to 4.84 +/- 0.52 mmol/L, magnesium significantly influenced neither EFT nor MAP duration, reduced by the high rate (180 beats/min) to 6.2-6.7 mA and 212-220 ms respectively. Under the same conditions, at the same 180 beats/min rate, ischaemia brings about a fall of EFT, from 6.9 down to nearly 0 mA, with occurrence of fibrillation, in approximately 120 s. Magnesium failed to slow this fall and to delay the onset of fibrillation. In contrast, within the minutes following the end of occlusion, magnesium increased EFT to a great extent (from 7.1 +/- 0.4 to 13.5 +/- 0.7 mA, P < 0.001), with a significant prolongation of MAP duration (212 +/- 6 to 234 +/- 8 ms, P < 0.01).

CONCLUSION

Magnesium may develop profibrillatory or antifibrillatory effects depending on plasma concentration, heart rate and myocardial perfusion.

Ischaemia-induced loss or reversal of the effects of the class I antiarrhythmic drugs on vulnerability to fibrillation

1. In the last decade, a number of clinical observations have questioned the efficacy of certain class I antiarrhythmic drugs against ischaemia-induced ventricular fibrillation. The effects of three drugs of this class, disopyramide (Ia), lignocaine (Ib) and flecainide (Ic) on the vulnerability to fibrillation during experimental ischaemia were investigated. 2. The study was carried out in anaesthetized, open-chest pigs (n = 8 for each of the drugs, in addition to the control group, n = 6). Vulnerability to fibrillation was evaluated by measuring electrical fibrillation threshold (EFT) by means of stepwise increased intensity of wide (100 ms) diastolic impulses applied to the ischaemic tissue at a 180 beats min-1 rate. Monophasic action potential (MAP) duration and conduction time in the ischaemic region were also measured. 3. EFT determinations were performed before and during periods of ischaemia induced by complete occlusion of the left anterior descending coronary artery near its origin. Ischaemic periods of increasing duration (30, 60, 90, 120, 150 s) were induced to determine the electrophysiological changes, of EFT especially, leading to fibrillation. 4. In the absence of ischaemia, all three drugs, administered by intravenous route (1 mg kg-1 plus 0.04 mg kg-1 min-1) increased EFT to a similar extent (from approximately 7 to 10 mA), despite a 25% prolongation of conduction time. 5. During ischaemia, none of the drugs prevented the fall in EFT towards 0 mA, resulting in spontaneous fibrillation. After 30 s of ischaemia, they no longer had any capacity for raising EFT and, after 60, 90 and 120 s of ischaemia, the decrease in EFT was exacerbated. This accelerated reduction in EFT shortened the time to onset of fibrillation (after 120 s of ischaemia, 62.5% of fibrillations with flecainide instead of 12.5 under control conditions, 75% instead of 25 with lignocaine and 50% instead of 25 with disopyramide). The reduction in MAP duration due to ischaemia was also significantly accelerated (at 60 s, 178 +/- 5 ms instead of 192 +/- 4 with flecainide, 175 +/- 3 ms instead of 194 +/- 5 with lignocaine and 180 +/- 5 ms instead of 196 +/- 3 with disopyramide) and the slowing of conduction was made worse (prolongation of conduction time by 70% instead of 50). 6. In conclusion, the antifibrillatory properties normally manifested by these drugs are first suppressed, then inverted by ischaemia, depending on oxygen debt varying with severity and duration of ischaemia.

Delay by a calcium antagonist, amlodipine, of the onset of primary ventricular fibrillation in myocardial ischemia

Calcium antagonists have been reported to counteract the increase by ischemia of vulnerability to ventricular fibrillation. This ability might be especially of interest in the prevention of sudden death subsequent to a major, but transitory, inadequacy between myocardial oxygen requirements and available coronary blood flow produced by exercise, emotion, etc., because death is then not related to irreversible damage of myocardial fibers. This study has been undertaken to examine the protective effect of a calcium antagonist on an animal model of this type of ischemia. This model used complete, but transient occlusion of the left anterior descending coronary artery near its origin during pacing at a constant high rate (180 beats/min) in anesthetized, open-chest pigs, most often resulting in fibrillation within 1-2 minutes after a progressive fall of the electrical fibrillation threshold. Amlodipine was the preferred calcium antagonist for this study because it is only moderately negatively inotropic. The results of the preventive administration of amlodipine was assessed by the time to onset of fibrillation. Amlodipine 0.30 mg/kg prolonged this time by 50-100% (p < 0.05) without appreciable impairment of blood pressure or myocardial contractility. Concurrently, amlodipine delayed the shortening of the monophasic action potential duration, the lengthening of conduction time, and the alterations of ST segments and T waves linked to ischemic depolarization. Consequently, when given experimentally before the occurrence of major, but transitory ischemia, amlodipine protected against fibrillation. Similarly, in clinical settings it ought to delay sudden death that may occur as a result of a major but transitory inadequacy between myocardial oxygen requirements and available coronary blood flow.

Change of a beneficial effect into an untoward effect by ischaemia: effect of quinidine-like drugs on vulnerability to ventricular fibrillation

The effects of three quinidine-like drugs, disopyramide, lidocaine and flecainide were investigated in anaesthetized, open-chest pigs on vulnerability to ventricular fibrillation under normal conditions and under myocardial ischaemia conditions. Vulnerability to fibrillation was evaluated by electrical ventricular fibrillation threshold (VFT), measured with 100 ms duration diastolic impulses the intensity of which was increased by steps of 1.0 or 0.5 mA. Impulses were delivered at the rate of 180 beats · min(-1). The ventricles were subjected to pacing at the same rate before the VFT determination, particularly throughout periods of ischaemia of increasing duration (30, 60, 90, 120, 150 s), separated by appropriate intervals for reproducibility of the results. Monophasic action potential (MAP) duration and conduction time were monitored in the ischaemic area under pacing. Ischaemia was obtained by complete occlusion of the left anterior descending coronary artery near its origin. The three drugs were i.v. administered in clinical dose range (1.00 mg · kg(-1) plus 0.04 mg · kg(-1) · min(-1)). In the absence of ischaemia, they increased almost equally VFT (from about 7 to 10 mA), despite 25% prolongation of conduction time. But, none of them was able to impede the increasingly marked fall of VFT caused by ischaemia: at 30 s, they had already lost any capacity for raising VFT and, beyond this time, they even aggravated its fall which led to spontaneous fibrillation when VFT approached 0 mA. The faster fall of VFT shortened time to onset of fibrillation (20 24 fibrillations for the three drugs at 150 s as against 12 24 in control period), the ischaemia-induced reduction of MAP duration (by 20%) being also hastened and slowing of conduction enhanced, given the addition of the depressant effects of ischaemia and drugs on conduction. Consequently, the antifibrillatory properties normally manifested by the studied drugs are first suppressed, then inverted by ischaemia.

Effects of a 100% perfluorooctylbromide emulsion on ischemia/reperfusion injury following cardioplegia

Protective effects of a perfluorooctylbromide emulsion on myocardial ischemia and reperfusion (MI/R) injury were evaluated in a modified Langendorff rat heart preparation. Isolated rat hearts were equilibrated in Krebs-Henseleit solution (KH) for 35 minutes and perfused with either cardioplegic solution (CPS) or a 100% perfluorooctylbromide (PFOB) emulsion in CPS for 3 minutes. Hearts were then bathed in the emulsion or CPS. Both groups were subjected to 30 minutes of ischemia. Following 30 minutes of ischemia and 30 minutes of reperfusion with KH solution, hearts subjected to the 100% PFOB emulsion showed improved recovery of left ventricular function. Tissue activities of the antioxidant enzymes glutathione peroxidase, superoxide dismutase, and catalase were not affected by the emulsion in this model. Activity of lactate dehydrogenase (LDH) in the bathing medium was elevated at the end of the experimental period in both control and PFOB-treated hearts. The PFOB emulsion reduced the decline in ATP and GSH levels produced by cardioplegia and subsequent reperfusion. No differences were noted in oxidized glutathione (GSSG) levels. These data suggest that the PFOB emulsion provides some protection for the myocardium against injury associated with cardioplegia.

Regulation of fos and jun immediate-early genes by redox or metabolic stress in cardiac myocytes

We have previously demonstrated coordinate inductions of c-fos, c-jun, jun B, and jun D in cardiac myocytes exposed to hypoxia for 2 to 4 hours. Induction of these transcripts occurred before any significant loss of intracellular ATP. In the present study, the origin of the signal(s) that regulates immediate-early gene induction was investigated by comparing the effects of hypoxia with those of the metabolic inhibitors cyanide, deoxyglucose and cyanide combined, and iodoacetic acid. Cyanide, an inhibitor of oxidative metabolism, closely mimicked the metabolic effects of hypoxia, with elimination of oxygen consumption, increased lactate production, and minimal decline in ATP levels under both conditions. Compared with hypoxia, cyanide mediated small transient inductions of fos and jun transcripts that followed a different time course. The combination of cyanide and deoxyglucose resulted in inhibition of lactate production as well as respiration, and ATP dropped rapidly to 20% of control levels. The loss of intracellular ATP was followed by fourfold inductions of c-fos and c-jun with minor changes in jun B and jun D transcript levels. Similarly, iodoacetic acid caused a major (90%) loss of ATP and irreversible cell damage as measured by leakage of creatine phosphokinase enzyme and loss of membrane arachidonic acid; ATP loss was followed by fivefold to sevenfold inductions of c-fos, c-jun and jun B transcripts.(ABSTRACT TRUNCATED AT 250 WORDS)

Gallopamil. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic potential in ischaemic heart disease

Gallopamil is a methoxy derivative of verapamil. As is typical of the phenylalkylamine class of calcium antagonists, it acts on the vascular system, and on the heart and its nodal structures. In the treatment of stable angina pectoris, gallopamil is at least as effective as nifedipine and diltiazem, though apparently better tolerated than nifedipine. Typical of calcium antagonists there is little or no tolerance to the antiischaemic effects of gallopamil. Preliminary studies indicate that gallopamil, like other calcium antagonists, has cardioprotective potential. However, further investigation is required to explore the clinical relevance of the improved myocardial regional perfusion and free fatty acid utilisation in reversibly ischaemic regions, and the potential of delayed ischaemia during angioplasty that is observed during gallopamil administration. Gallopamil is well tolerated, exhibiting a low propensity for causing cardiovascular and gastrointestinal adverse effects, thus making it a suitable alternative to other calcium antagonists for the treatment of patients with ischaemic heart disease.

Attenuation of the ischaemia-induced fall of electrical ventricular fibrillation threshold by a calcium antagonist, diltiazem

Calcium antagonists have been reported to decrease the incidence of sudden death in postinfarction management and vulnerability to fibrillation secondary to experimental coronary occlusion. In order to confirm such beneficial results regarding ischaemic ventricular fibrillation, the threshold intensity for fibrillation electrically induced with impulses of 100 ms and 180 beats.min-1 was measured during the course of ischaemias obtained by total occlusion of the left anterior descending coronary artery near its origin in open-chest pigs. The variations of electrical fibrillation threshold with ischaemia duration (30, 60, 120, 180, 240, 360 s) were compared under control conditions and after i.v. diltiazem (0.50 mg.kg-1 plus 0.02 mg.kg-1.min-1 over 25 min). Electrical fibrillation threshold was not influenced by diltiazem before, but raised during ischaemia, particularly from the 60th s (1.7 to 4.0 mA), with delay in the triggering of fibrillation which occurs when the fibrillation threshold falls down to the pacing threshold (0.2 to 0.3 mA). In 6 pigs out of 8, fibrillation was even avoided in the longest of the ischaemic periods considered (360 s), for fibrillation threshold ceased falling before reaching the critical level. These experimental results obtained with diltiazem are consistent with the clinical effectiveness of calcium antagonists recently observed in the prevention of postinfarction sudden death, provided that myocardial contractility is not too much adversely affected. But, left ventricular dP/dtmax was not reduced by more than 6.8% in the present experiments.