Presynaptic modulation of efferent sympathetic and vagal neurotransmission in the canine heart by hypoxia, high K+, low pH, and adenosine. Possible relevance to ischemia-induced denervation

Development of stimulus-sensitive electrospun membranes based on novel biodegradable segmented polyurethane as triggered delivery system for doxorubicin

In this work, redox-sensitive polyurethane urea (PUU) based electrospun membranes have been exploited to chemically tether a pH-sensitive doxorubicin derivative achieved by linking a lipoyl hydrazide to the drug via a hydrazone linkage. First, the lipoyl-hydrazone-doxorubicin derivative labelled as LA-Hy-Doxo has been synthesized and characterized. Then, the molecule has been tethered, via a thiol-disulfide exchange reaction, to the redox-sensitive PUU (PolyCEGS) electrospun membrane. The redox-sensitive PolyCEGS PUU has been produced by using PCL-PEG-PCL polyol and glutathione-tetramethyl ester (GSSG-OMe)₄ as a chain extender. The LA-Hy-Doxo tethered electrospun membrane has showed a dually controlled release triggered by acidic and reducing conditions, producing a significant cytotoxic effect in human breast cancer cell lines (MCF-7) which has validated the system for the post-surgical treatment of solid tumors to contrast recurrence.

Physiological control of fetal heart rate variability during labour: Implications and controversies

The interpretation of fetal heart rate (FHR) patterns is the only available method to continuously monitor fetal wellbeing during labour. One of the most important yet contentious aspects of the FHR pattern is changes in FHR variability (FHRV). Some clinical studies suggest that loss of FHRV during labour is a sign of fetal compromise so this is reflected in practice guidelines. Surprisingly, there is little systematic evidence to support this observation. In this review we methodically dissect the potential pathways controlling FHRV during labour-like hypoxaemia. Before labour, FHRV is controlled by the combined activity of the parasympathetic and sympathetic nervous systems, in part regulated by a complex interplay between fetal sleep state and behaviour. By contrast, preclinical studies using multiple autonomic blockades have now shown that sympathetic neural control of FHRV was potently suppressed between periods of labour-like hypoxaemia, and thus, that the parasympathetic system is the sole neural regulator of FHRV once FHR decelerations are present during labour. We further discuss the pattern of changes in FHRV during progressive fetal compromise and highlight potential biochemical, behavioural and clinical factors that may regulate parasympathetic-mediated FHRV during labour. Further studies are needed to investigate the regulators of parasympathetic activity to better understand the dynamic changes in FHRV and their true utility during labour. This article is protected by copyright. All rights reserved.

Feeling the Insight: Uncovering Somatic Markers of the "aha" Experience

Whether internal insight can be recognized by experiencing (somatic feeling) remains an unexplored problem. This study investigated the issue by examining potential somatic markers of the "aha" experience occurring at the moment of sudden insight. Participants were required to solve a set of compound remote associates (CRA) problems and were simultaneously monitored via electrodermal and cardiovascular recordings. The "aha"-related psychological components and somatic markers were determined by contrasting insightful solutions with non-insightful solutions. Results showed that the "aha" experience was an amalgam entailing positive affects and approached cognition accompanied by a greater mean skin conductance response (mSCR) amplitude and a marginally accelerated heart rate than the "no-aha" one. These results confirm and extend findings of the multidimensionality of the "aha" feeling and offer the first direct evidence of somatic markers, particularly an electrodermal signature of an "aha" feeling, which suggests a sudden insight could likely be experienced by individuals' external soma.

Cardiac metaiodobenzylguanidine imaging and heart failure

The autonomic nervous system has pivotal roles in pathophysiology and prognosis in patients with heart failure. Cardiac (123)I-labeled metaiodobenzylguanidine (MIBG) imaging enables noninvasive and quantitative assessment of cardiac sympathetic innervation in cardiology practice. Several investigations have demonstrated independent and incremental prognostic values of this imaging technique in combination with clinical information in patients with heart failure. Cardiac MIBG imaging may help cardiologists evaluate cardiac sympathetic nerve function and predict lethal event risk in heart failure. It can contribute not only to the identification of low-risk or high-risk probability for lethal events but also to the selection of the appropriate therapeutic strategy, such as medical and device therapy in patients at greater risk for lethal outcomes due to pump failure or sudden arrhythmic events. Thus, precise risk stratification through cardiac MIBG imaging may contribute to more effective use of medical resources and more appropriate selection of therapeutic strategy in heart failure patients.

Synergistic prognostic values of cardiac sympathetic innervation with left ventricular hypertrophy and left atrial size in heart failure patients without reduced left ventricular ejection fraction: a cohort study

OBJECTIVES

This study tested whether cardiac sympathetic innervation assessed by metaiodobenzylguanidine (MIBG) activity has long-term prognostic value in combination with left ventricular hypertrophy (LVH) and left atrial size in heart failure (HF) patients without reduced left ventricular ejection fraction (LVEF).

DESIGN

A single-centre prospective cohort study.

SETTING/PARTICIPANTS

With primary endpoints of cardiac death and rehospitalisation due to HF progression, 178 consecutive symptomatic HF patients with 74% men, mean age of 56 years and mean LVEF of 64.5% were followed up for 80 months. The entry criteria consisted of LVEF more than 50%, completion of predischarge clinical evaluations including cardiac MIBG and echocardiographic studies and at least more than 1-year follow-up when survived.

RESULTS

Thirty-four patients with cardiac evens had larger left atrial dimension (LAD), increased LV mass index, reduced MIBG activity quantified as heart-to-mediastinum ratio (HMR) than did the others. Multivariable Cox analysis showed that LAD and HMR were significant predictors (HR of 1.080 (95% CI 1.00 to 1.16, p=0.044) and 0.107 (95% CI 0.01 to 0.61, p=0.012, respectively). Thresholds of HMR (1.65) and LAD (37 mm) were closely related to identification of high-risk patients. In particular, HMR was a significant determinant of cardiac events in both patients with and without LV hypertrophy. Reduced HMR with enlarged LAD or LV hypertrophy identified patients at most increased risk; overall log-rank value, 11.5, p=0.0032 for LAD and 17.5, p=0.0002, respectively.

CONCLUSIONS

In HF patients without reduced LV ejection fraction, impairment of cardiac sympathetic innervation is related to cardiac outcomes independently and synergistically with LA size and LV hypertrophy. Cardiac sympathetic innervation assessment can contribute to better risk-stratification in combination with evaluation of LA size and LV mass but is needed to be evaluated for establishing aetiology-based risk assessment in HF patients at increased risk.

Silent myocardial ischemia

Although much progress has been made in reducing mortality from ischemic cardiovascular disease, this condition remains the leading cause of death throughout the world. This might in part be due to the fact that over half of patients have a catastrophic event (heart attack or sudden death) as their initial manifestation of coronary disease. Contributing to this statistic is the observation that the majority of myocardial ischemic episodes are silent, indicating an inability or failure to sense ischemic damage or stress on the heart. This review examines the clinical characteristics of silent myocardial ischemia, and explores mechanisms involved in the generation of angina pectoris. Possible mechanisms for the more common manifestation of injurious reductions in coronary flow; namely, silent ischemia, are also explored. A new theory for the mechanism of silent ischemia is proposed. Finally, the prognostic importance of silent ischemia and potential future directions for research are discussed.

Predicting the need for an implantable cardioverter defibrillator using cardiac metaiodobenzylguanidine activity together with plasma natriuretic peptide concentration or left ventricular function

Despite widespread use of implantable cardioverter defibrillators (ICDs), their cost and the fact that only a certain group of patients fully benefits from the devices require appropriate risk stratification of patients. This study investigated whether altered cardiac autonomic function is associated with the occurrence of ICD discharge or lethal cardiac events.

METHODS

Fifty-four ICD-treated patients were prospectively followed after assessment of cardiac metaiodobenzylguanidine (MIBG) activity, quantified as the heart-to-mediastinum ratio (HMR), plasma concentration of brain natriuretic peptide (BNP), and left ventricular ejection fraction (LVEF). Patients were divided into 2 groups based on the presence (group A, n = 21) or absence (group B, n = 33) of appropriate ICD discharge during a 15-mo period.

RESULTS

Group A had a significantly lower level of MIBG activity and a higher plasma BNP level than did group B. Univariate analysis revealed BNP level, any medication, and late HMR to be significant predictors, and multivariate analysis showed late HMR to be an independent predictor. An HMR of less than 1.95 with a plasma BNP level of more than 187 pg/mL or an LVEF of less than 50% had significantly increased power to predict ICD shock: positive predictive values, 82% (HMR + BNP) and 58% (HMR + LVEF); negative predictive values, 73% (HMR + BNP) and 77% (HMR + LVEF); sensitivities, 45% (HMR + BNP) and 67% (HMR + LVEF); and specificities, 94% (HMR + BNP) and 70% (HMR + LVEF).

CONCLUSION

When combined with plasma BNP concentration or cardiac function, cardiac MIBG activity is closely related to lethal cardiac events and can be used to identify patients who would benefit most from an ICD.

Cardiac metaiodobenzylguanidine activity can predict the long-term efficacy of angiotensin-converting enzyme inhibitors and/or beta-adrenoceptor blockers in patients with heart failure

PURPOSE

Although the benefits of treatment with angiotensin-converting enzyme (ACE) inhibitors and beta-blockers are well known, no method has as yet been established to predict the efficacy of drug therapy. This study tested whether cardiac 123I-metaiodobenzylguanidine (MIBG) activity is of prognostic value and can predict the improvement in heart failure patients resulting from treatment with ACE inhibitors and/or beta-blockers.

METHODS

Following quantification of the heart-to-mediastinum ratio (HMR) of MIBG activity, 88 patients with heart failure who were treated with ACE inhibitors and/or beta-blockers (treated group) and 79 patients with heart failure who were treated conventionally without the aforementioned agents, and who served as controls, were followed up for 43 months with a primary endpoint of cardiac death.

RESULTS

The treated group had a significantly lower prevalence of cardiac death and a significantly lower mortality at 5 years compared with the control group (15% vs 37% and 21% vs 42%, p<0.05, respectively). Multivariate analysis revealed that significant predictors were HMR, age, nitrate use and ventricular tachycardia for the treated group, and HMR, nitrate use and NYHA class for the control group. The drug treatment significantly reduced mortality from 36% to 12% when HMR was 1.53 or more and from 53% to 37% when HMR was less than 1.53. The reduction in risk of mortality within 5 years in patients without a severe MIBG defect (67%) was twice that in patients with such a defect (32%) (p<0.05).

CONCLUSION

The reduction in mortality risk achieved by using ACE inhibitors and/or beta-blockers is associated with the severity of impairment of cardiac MIBG uptake. Cardiac MIBG activity can consequently be of long-term prognostic value in predicting the effectiveness of such treatment in patients with heart failure.

Prognostic implications of an initial loss of cardiac metaiodobenzylguanidine uptake and diabetes mellitus in patients with left ventricular dysfunction

BACKGROUND

Although altered cardiac sympathetic innervation is related to fatal outcome, the mechanisms and prognostic value of an initial cardiac metaiodobenzylguanidine (MIBG) defect are not known.

METHODS AND RESULTS

After quantitative cardiac MIBG imaging, 205 patients with left ventricular ejection fraction <50% were prospectively followed up with a primary end-point of cardiac death for 35 months. In regard to 38 cardiac deaths, consisting of 25 pump failure deaths, 11 sudden deaths, and 2 fatal acute myocardial infarctions, multivariate analysis identified diabetes mellitus as a significant independent predictor as well as reduced cardiac MIBG activity, use of nitrate, and New York Heart Association functional status. Independent of washout kinetics and cardiac function, patients with profound loss of initial MIBG uptake and those with late-phase MIBG activity of 1.74 or less had significantly greater mortality rates than did their counterparts. Initial cardiac MIBG activity closely correlated inversely with annual cardiac death rate.

CONCLUSIONS

An initial cardiac MIBG defect and presence of diabetes mellitus indicate a low probability of long-term survival. The profound loss of initial MIBG activity is likely to be due to structural deficit of sympathetic neurons themselves, rather than accelerated sympathetic function, suggesting that denervation is one of mechanisms of cardiac sympathetic dysfunction leading to lethal clinical outcomes.

Disruption of vagal efferent axon and nerve terminal function in the postischemic myocardium

Despite the importance of vagal control over the ventricle, little is known regarding vagal efferent conduction and nerve terminal function in the postischemic myocardium. To elucidate postischemic changes in the cardiac vagal efferent neuronal function, we measured myocardial interstitial acetylcholine (ACh) levels by using in vivo cardiac microdialysis and examined the ACh responses to electrical stimulation of the vagi or local administration of ouabain in anesthetized cats. Sixty-minute occlusions of the left anterior descending coronary artery (LAD) followed by 60-min reperfusion abolished electrical stimulation-induced ACh release (20.4 +/- 3.9 vs. 0.9 +/- 0.4 nmol/l; means +/- SE, P < 0.01). In different groups of animals, 60-min LAD occlusion followed by 60-min reperfusion decreased but did not completely abolish ouabain-induced release of ACh (9.2 +/- 1.8 vs. 3.9 +/- 0.7 nmol/l; P < 0.05). These results indicate that function of the vagal efferent axon was completely interrupted, whereas the local ACh release was partially suppressed in the postischemic myocardium. The postischemic disruption of vagal efferent neuronal function might exert deleterious effects on cardiac regulation.

Effect of the final coronary arterial diameter after coronary angioplasty on heart rate variability responses

BACKGROUND

Autonomic nervous system dysfunction and reduced heart rate variability (HRV) after percutaneous transluminal coronary angioplasty (PTCA) were reported in patients with coronary artery disease. However, factors related to reduced HRV are not clearly demonstrated. The aim of the present study was to assess the relationship between HRV indices and the final coronary arterial luminal diameter after PTCA.

METHODS

Twenty-seven patients (23 male, 4 female, mean age: 52.5 +/- 7.1 years) with single vessel disease were included in the study. PTCA was performed in all patients. Low-frequency power (LFP), high-frequency power (HFP), and total power (TP) were calculated by using frequency-domain analysis of HRV. All examinations were performed 24 hours before, and 24 hours, 10 days, and 30 days after PTCA. The patients were divided into groups according to the PTCA restenosis risk score, the degree of dilatation, and revascularization after coronary angioplasty.

RESULTS

The groups were comparable for age, gender, and coronary artery risk factors. HRV was found to be reduced in 76% of patients. Reduction in HRV after PTCA was significantly related to the PTCA risk score and the degree of revascularization (r = 0.48, P < 0.01 and r = 0.50, P < 0.008). Reduction in HRV was more significant in patients with previous myocardial infarction (P < 0.05). Recovery of HRV occurred on the tenth day after PTCA.

CONCLUSION

Transient and rapidly recovered, especially parasympathetically modulated HRV reduction occurred after PTCA in patients with single-vessel disease. HRV reduction is associated with PTCA restenosis risk score and the degree of revascularization as invasive feature of angioplasty, hence it may be related to reperfusion.

Differential effects of acidosis, high potassium concentrations, and metabolic inhibition on noradrenaline release and its presynaptic muscarinic regulation

It was the aim of the present study to characterize the effect of single components of ischaemia, such as inhibition of aerobic and anaerobic energy production by combined anoxic and glucose-free perfusion (metabolic inhibition), high extracellular potassium concentrations (hyperkalaemia), and acidosis, on (1). the stimulated release of noradrenaline from the in situ perfused guinea-pig heart and (2). its presynaptic modulation by the muscarinic agonist carbachol. The release of endogenous noradrenaline from efferent cardiac sympathetic nerve endings was induced by electrical stimulation of the left stellate ganglion (1 min, 5 V, 12 Hz) and quantified in the coronary venous effluent by high-performance liquid chromatography. Under control conditions, two consecutive electrical stimulations (S1, S2) elicited a similar noradrenaline overflow (S2/S1: 0.98 plus minus 0.05). After 10 min of global myocardial ischaemia overflow of endogenous noradrenaline was significantly reduced (S2/S1: 0.18 plus minus 0.03; P< 0.05). When studied separately, metabolic inhibition, hyperkalaemia (16 mM), and acidosis (pH 6.0) each markedly attenuated stimulated noradrenaline overflow (S2/S1: 0.65 plus minus 0.05, 0.43 plus minus 0.14, and 0.37 plus minus 0.09, respectively; P< 0.05). The muscarinic agonist carbachol (10 microM) inhibited stimulated noradrenaline release under normoxic conditions (S2/S1: 0.41 plus minus 0.07; P< 0.05). However, after 10 min of global myocardial ischaemia the inhibitory effect of carbachol on noradrenaline overflow was completely lost. Single components of ischaemia had a differential effect on presynaptic muscarinic modulation. Whereas hyperkalaemia (8-16 mM) did not affect muscarinic inhibition of noradrenaline release, carbachol lost its inhibitory effect during acidosis and metabolic inhibition. In conclusion, hyperkalaemia, metabolic inhibition, and severe acidosis each contribute to reduced overflow of noradrenaline after 10 min of myocardial ischaemia. However, presynaptic muscarinic inhibition of noradrenaline release was not affected by hyperkalaemia, but was sensitive to metabolic inhibition and low degrees of acidosis.

Wavelet transform analysis of heart rate variability during myocardial ischaemia

Analysis of heart rate variability (HRV) is a valuable, non-invasive method for quantifying autonomic cardiac control in humans. Frequency-domain analysis of HRV involving myocardial ischaemic episodes should take into account its non-stationary behaviour. The wavelet transform is an alternative tool for the analysis of non-stationary signals. Fourteen patients have been analysed, ranging from 40 to 64 years old and selected from the European Electrocardiographic ST-T Database (ESDB). These records contain 33 ST episodes, according to the notation of the ESDB, with durations of between 40s and 12 min. A method for analysing HRV signals using the wavelet transform was applied to obtain a time-scale representation for very low-frequency (VLF), low-frequency (LF) and high-frequency (HF) bands using the orthogonal multiresolution pyramidal algorithm. The design and implementation using fast algorithms included a specially adapted decomposition quadrature mirror filter bank for the frequency bands of interest. Comparing a normality zone against the ischaemic episode in the same record, increases in LF (0.0112 +/- 0.0101 against 0.0175 +/- 0.0208 s2 Hz(-1); p<0.1) and HF (0.0011 +/- 0.0008 against 0.00 17 +/- 0.0020 s2 Hz(-1); p<0.05) were obtained. The possibility of using these indexes to develop an ischaemic-episode classifier was also tested. Results suggest that wavelet analysis provides useful information for the assessment of dynamic changes and patterns of HRV during myocardial ischaemia.

Low pH modulation of recombinant vanilloid receptors and perivascular capsaicin-sensitive sensory neurotransmission

The effect of low pH on capsaicin-sensitive sensory neurotransmission in the rat isolated mesenteric arterial bed and at recombinant (rVR1) vanilloid receptors was investigated. Mesenteric sensory neurogenic vasorelaxation elicited by electrical field stimulation was reversibly inhibited by lowering pH from 7.4 to 6.9 and 6.3. Capsaicin-induced vasorelaxation was not different at pH 6.9, but was attenuated at pH 6.3. Vasorelaxation to calcitonin gene-related peptide, the principal sensory motor neurotransmitter in rat mesenteric arteries, was not different at pH 6.9 or pH 6.3. In rVR1-transfected HEK293 cells, acidic conditions enhanced the affinities of capsaicin and capsazepine at rVR1, but did not affect the potency of carbachol at endogenous muscarinic receptors. Following inactivation of endogenous acid-sensitive ion channels, lowering pH (6.0-4.5) directly increased [Ca2+]i in rVR1-HEK293 cells (EC50 5.5). This response was abolished by 1 microM capsazepine. In conclusion, a decrease in pH (to 6.9 and 6.3) enhances the affinity of capsaicin at rVR1, but inhibits sensory neurotransmission in the rat mesenteric arterial bed. This likely explains why there is no evidence of an enhancement of sensitivity to capsaicin at endogenous vanilloid receptors, as observed with rVR1. When pH is reduced still further (6.0-5.5) there is direct activation of rVR1.

Attenuation of ischemia-induced activation of cardiac sympathetic afferents following brief myocardial ischemia in cats

OBJECTIVE

We have previously shown that brief myocardial ischemia impairs neural conduction in cardiac sympathetic efferent fibers. However, attenuation of the activity of afferent sympathetic nerves, which may contribute to impaired ischemic nociception and reflex hemodynamic responses, is not well understood. Therefore, we studied the electrophysiological effects of brief myocardial ischemia on the mechano-, chemo- and ischemia-sensitive properties of cardiac sympathetic afferent fibers.

METHODS

Single unit activity of sympathetic afferent A delta and C fibers innervating the left ventricle (LV) was recorded from the thoracic chain or rami communicantes in 16 anesthetized cats. We tested the response of impulse activity to (1) mechanical LV probing, (2) epicardial application of bradykinin (10 microg), H2O2 (1.5%) or adenosine (500 microg), and (3) 1 min of coronary occlusion. Repeat tests were performed in 11 of 16 fibers after 15 min of coronary occlusion and 15 min of reperfusion. Control responses were measured in five fibers before and after a 30-min interval without ischemia.

RESULTS

Afferent fibers responded with increased activity to LV probing (16/16 fibers), bradykinin (13/16 fibers), H2O2 (7/11 fibers), adenosine (1/11 fibers), and to a 60 s period of coronary occlusion (11/16 fibers). The unit impulse activity to 1 min of coronary occlusion was markedly attenuated after 15 min of myocardial ischemia and 15 min of reperfusion (P < 0.05). This attenuation was associated with reduced sensitivity to mechanical and chemical stimuli, while in separate time-control studies (n = 5) no attenuation was observed in absence of ischemia.

CONCLUSION

A brief period of myocardial ischemia is capable of attenuating mechano-, chemo- and ischemia-sensitive activity of cardiac afferent sympathetic nerves. This may have important implications for the mechanism of silent myocardial ischemia.

Relationship Between Components of Heart Rate Variability and Doppler Echocardiographic Indices of Left Ventricular Systolic Performance in Patients with Coronary Artery Disease

Decreased heart rate variability (HRV) has been reported as prognostic predictor in coronary artery disease population. The aim of the study was to assess the relationship between cardiac autonomic tone disturbances and the degree of left ventricular dysfunction, estimated by 2-dimensional and Doppler echocardiography, in patients with coronary artery disease. Forty patients with angiographically proven coronary artery disease and 15 age-and sex-matched healthy subjects were included into the study (Group I and II, respectively). Routine clinical examinations, electrocardiography, coronary angiography, and 2-dimensional and Doppler echocardiography with assessment of LV systolic performance were done in all the patients and control subjects. Cardiac autonomic function was assessed by means of frequency-domain analysis of heart rate variability. The powers of LF and HF bands (P1 and P2), their ratio (P1/P2), and the logarithmic expression of powers were measured. The patients (Group I) had lower values of parasympathetic band of HRV and higher sympathetic activity than the healthy population (Group II) (p < 0.0002 for P2 and p < 0.04 for P1/P2 ratio). A positive significant correlation was seen between parasympathetic band of HRV and ejection fraction (r = 0.61, p < 0.0001), and mean acceleration of aortal flow (r = 0.56, p < 0.0001), whereas P1/P2 ratio inversely and significantly correlated with the same parameters (r = -0.46, p < 0.002 and r = -0.41, p < 0.008).

The seventh annual Gordon K. Moe Lecture. Atrial fibrillation: from cell t bedside

Atrial fibrillation is the most common sustained tachyarrhythmia and, as such, has become the recent focus of intense clinical and experimental interest. Because of its associated morbidity and mortality, there is a multidisciplinary effort to understand the pathophysiology that may ultimately lead to improved therapeutic options. This review concentrates on three aspects of atrial fibrillation that influence contemporary choices for treatment: an electrophysiologic basis for initiation of atrial fibrillation, anatomic and electrophysiologic remodeling, and concepts regarding its termination or prevention.

Effects of trimetazidine on heart rate variability and left ventricular systolic performance in patients with coronary artery disease after percutaneous transluminal angioplasty

Fifty-one patients (mean age 51.6 +/- 7.1 years) with angiographically proven coronary artery disease (CAD) entered the study. In 26 patients (Group I), trimetazidine treatment started twenty-four hours after percutaneous transluminal coronary angioplasty (PTCA). Another 25 patients (Group II) without trimetazidine treatment were kept as controls. The groups were comparable by age, gender, risk factors of CAD, coronary anatomy, left ventricular performance, and heart rate variability indices at baseline state. Power spectral analysis of heart rate variability and two-dimensional and Doppler echocardiographic examinations were performed before PTCA, and twenty-four hours, ten days, thirty days, and three months after PTCA. A statistically significant improvement of left ventricular systolic performance (P < 0.001), augmentation of the parasympathetic band of heart rate variability (P < 0.001), and decline of P1/P2 ratio (P < 0.01) were evident in patients treated with trimetazidine, while no apparent changes were observed in controls. The intergroup analysis also showed marked difference between groups as recorded on the day 30 and month 3 of observation (P < 0.001). During follow-up period recurrences of angina pectoris and ischemia were registered in Group II, while no evidence of ischemia was discerned in Group I patients. In conclusion, trimetazidine modulates the autonomic control of heart rate, ie, reduces sympathetic overactivity and augments vagal influences, improves left ventricular contractility, and diminishes the clinical manifestations of ischemia in patients with CAD after PTCA.

Interactive effects of K+, acid, norepinephrine, and ischemia on the heart: implications for exercise

We tested the hypothesis that cardiac ischemia uncouples the beneficial interaction among hyperkalemia, acidosis, and raised plasma catecholamines when these chemicals are changed to mimic their exercise levels. Potassium chloride, lactic acid, and norepinephrine (NE) were infused intravenously for 2 min into anesthetized, artificially ventilated, thoracotomized rabbits during either occlusion of the left circumflex artery (3 min; n = 10) or after a period of prolonged ischemia (20 min; n = 7) that led to a small infarction. NE (1 microg x kg(-1) x min(-1) iv) offset the negative cardiac effects of hyperkalemia (up to 8.7 +/- 0.7 mM) and acidosis (arterial pH 7.09 +/- 0.03) in normal hearts. Cardiac performance was not significantly depressed by either acute or chronic ischemia before any infusions. However, the protective effect of NE during acute ischemia or after prolonged ischemia with hyperkalemia and acidosis was substantially reduced. These results show that cardiac ischemia attenuates the protective action of NE and increases the depressive effects of hyperkalemia and acidosis. Whether myocardial ischemia amplifies the cardiotoxic effects of hyperkalemia and acidosis during vigorous exercise by attenuating the beneficial effect of catecholamines remains to be determined.

Systemic and cardiac catecholamines during elective PTCA and during immediate PTCA for acute myocardial infarction

This study investigated arterial and coronary venous catecholamine concentrations in patients undergoing either elective coronary angioplasty (PTCA) or direct PTCA for acute myocardial infarction. We included 17 patients with stenoses of the left anterior descending coronary artery (LAD) and 10 patients with acute anterior myocardial infarction (AMI) undergoing PTCA. During the initial balloon dilatation arterial and coronary venous plasma concentrations of norepinephrine and epinephrine were determined. In elective PTCA, coronary occlusion (2 min) resulted in a transient increase of arterial concentrations of norepinephrine (2.04 +/- 0.30 vs. 1.26 +/- 0.13 nmol/L before dilatation) and epinephrine (0.52 +/- 0.08 vs. 0.34 +/- 0.04 nmol/L) in the first minute of reperfusion, whereas coronary venous concentrations of catecholamines were not changed after dilatation. Among the 10 patients with AMI, immediate reperfusion of the LAD (TIMI grade 3) was achieved in 6 patients. In these patients, baseline arterial concentrations for norepinephrine (3.91 +/- 1.16 nmol/L) and epinephrine (4.68 +/- 2.07 nmol/L) were elevated and no transcardiac gradient for catecholamines was found. In the first minute after successful reopening of the LAD we detected a distinct rise of the transcardiac norepinephrine gradient from -0.10 +/- 0.53 to 85.02 +/- 24.64 nmol/L, which declined in the fifth minute of reperfusion of 4.36 +/- 2.30 nmol/L. Conversely, venous epinephrine and arterial concentrations for both catecholamines remained unchanged within the observation period. In the four patients with incomplete (TIMI 0-2) reopening of the LAD, we found no cardiac washout of norepinephrine. In summary, a transient rise of systemic catecholamines, but no cardiac release of norepinephrine was observed in patients after brief coronary occlusion. Conversely, a massive washout of norepinephrine from the infarcted myocardium occurred during AMI.

Regional cardiac sympathetic nerve dysfunction and the diagnostic efficacy of metaiodobenzylguanidine tomography in stable coronary artery disease

The present study endeavors to correlate regional myocardial sympathetic nerve dysfunction with reversible and persistent perfusion abnormalities and depressed regional wall motion, and to determine the diagnostic efficacy of radio-iodinated metaiodobenzylguanidine (MIBG) tomography for detecting coronary artery disease. In 28 consecutive patients with stable coronary artery disease and 7 patients with atypical chest pain but no coronary stenosis, regional MIBG uptake was semiquantitatively evaluated in 13 left ventricular segments early (30 minutes) and late (4 hours) after injection. Regional MIBG uptake was reduced in 68 of 90 segments (76%) showing reversible perfusion abnormality and 72 of 81 segments (89%) showing persistent abnormality 4 hours after injection. Although the sensitivity and negative predictive values of late MIBG scanning for detecting myocardial perfusion abnormalities were relatively high (82% and 85%, respectively), the specificity, positive predictive value, and kappa value were low (63%, 57%, and 0.41, respectively). Right coronary lesions were detected by late MIBG scanning with a high sensitivity (85%) but a low specificity (41%). Conversely, the sensitivities for detecting lesions in the other 2 major left coronary arteries were low (55%). The overall diagnostic accuracy of late MIBG scanning was 66% and the positive and negative predictive values and kappa value were low; 60%, 70%, and 0.31, respectively. Similarly, regional sympathetic dysfunction was observed in 42 of 49 asynergic segments (86%) on late MIBG scans, of which 32 segments were viable and 10 nonviable; but the low specificity (73%) and positive predictive value (44%) reduced the kappa value (0.43). Thus, regional cardiac sympathetic innervation is impaired in ischemic, asynergic but noninfarcted myocardium as well as in myocardium which is infarcted or has a persistent perfusion abnormality. The diagnostic efficacy of MIBG tomography to detect coronary artery disease, however, is limited probably because of nonspecific reductions of MIBG uptake in the inferior and posterolateral regions.

Role of the sympathetic nervous system in cardiac performance during hyperkalaemia in the anaesthetized pig

Cardiovascular performance was studied in 18 alpha-chloralose anaesthetized pigs when arterial potassium ([K+]a) was raised to levels observed in heavy exercise. The effects of hyperkalaemia were then studied during cardiac sympathetic nerve stimulation or during an infusion of noradrenaline. Elevation of [K+]a up to ca. 10 mM caused a progressive decline in cardiovascular performance. However, right cardiac sympathetic nerve stimulation elevated all cardiovascular parameters in the presence of raised [K+]a and offset the negative cardiac effects of hyperkalaemia. Electrical pacing of the right atrium to heart rates (HRs) equivalent to those observed during right cardiac sympathetic nerve stimulation did not offset the depressive effects of hyperkalaemia and, indeed, hastened the decline in cardiovascular performance. Infusion of noradrenaline (1 microgram kg min-1 i.v.) during hyperkalaemia caused an increase in all cardiovascular parameters similar to that seen during sympathetic nerve stimulation. After propranolol (0.5 mg kg-1 i.v.), sympathetic nerve stimulation slightly increased HR, systolic blood pressure (SBP) and dP/dtmax. Elevation of [K+]a occurred more rapidly after propranolol, but the heart was still protected from hyperkalaemia during cardiac sympathetic stimulation. Infusion of noradrenaline elicited arrhythmias in six pigs. Infusion of KCl reduced the incidence of arrhythmias and in some cases abolished them. These findings may be related to how the heart is protected from exercise-induced changes in potassium and catecholamines.

Significance of cardiac innervation on spontaneous ventricular arrhythmias elicited by left stellate ganglion stimulation in dogs 4 days after myocardial infarction: comparison of two experimental models

The effects of cardiac sympathetic overactivity on spontaneous arrhythmias and transmural left ventricular effective refractory period (LVERP) were assessed by left stellate stimulation (LSS) in 16 anesthetized dogs. The experiments were performed 4 days after proximal occlusion of the left anterior descending (LAD) coronary artery produced by either ligation (9 dogs) or embolization with histoacryl (7 dogs). The innervation of left ventricular myocardium was studied by light and electron microscopies. Synaptophysin (SYN)- and neuropeptide Y (NPY)-immunoreactive nerve fibers and terminals were thereby detected. In dogs subjected to ligation, LSS elicited negligible arrhythmias in spite of a decrease in LVERP by 6.9 +/- 2.2% (mean +/- SD, p < 0.001). However, dogs with intravascular occlusion were more susceptible to LSS, as indicated by development of sustained ventricular rhythms. In these animals, the LVERP decreased with LSS by 14.6 +/- 3.4% (p < 0.001). The innervation of the anterior left ventricular wall distal to the place of occlusion revealed a higher reduction of SYN- and NPY-immunoreactive nerves in infarcted myocardium and a more heterogeneous distribution of nerves in undamaged regions after ligation, compared to intravascular occlusion. Ultrastructurally, nerve terminals containing small agranular and large dense-core vesicles were found innervating ischemically damaged myocardiocytes. Our findings indicate a higher preservation of nerves in infarcted and noninfarcted myocardium of animals subjected to embolic occlusion of the LAD. Because LSS apparently elicited more arrhythmias in these animals, we suggested a proarrhythmic effect of intact myocardial innervation after infarction.

Simulated ischemia does not protect against efferent sympathetic denervation following acute myocardial infarction in canine hearts

INTRODUCTION

Preconditioning the myocardium with brief episodes of ischemia preserves efferent autonomic responsiveness of noninfarcted myocardium apical to a site of acute transmural ischemia by mechanism(s) still unknown. We hypothesized that repeated brief exposure of the myocardium to a simulated ischemic milieu including hypoxia, high K+, low pH, and adenosine would be as effective as brief coronary occlusions in creating this protection.

METHODS AND RESULTS

Open chest anesthetized dogs received an extracorporeal bypass between the left carotid artery and a diagonal branch of the left anterior descending coronary artery. We analyzed the effects of simulated ischemia on the time course and extent of efferent sympathetic denervation during a subsequent 3-hour sustained ischemia in three groups of dogs: two groups of dogs underwent four cycles of 5-minute intracoronary perfusion with either hypoxic altered Tyrode's solution (12 mM K+, 6.8 pH, and 10 microM adenosine; n = 11) or normal Tyrode's solution (n = 11). Each Tyrode's perfusion was separated by 5 minutes of blood perfusion prior to permanent coronary occlusion by latex embolization of the cannulated coronary artery. A third group received a continuous 3-hour blood perfusion before the final ischemic episode (n = 5). Shortening of effective refractory periods (ERPs) induced by bilateral ansae subclaviae stimulation (2 to 4 Hz) basal and apical to the intervention site was determined before and after perfusions and 20, 60, 120, and 180 minutes after sustained occlusion. In all groups, sympathetically-induced ERP shortening was unchanged at basal sites throughout the experiment. ERP shortening at apical sites was unchanged after perfusions with either the altered or normal Tyrode's solution or after a continuous 3-hour blood perfusion. However, ERP shortening became significantly attenuated at apical sites after coronary occlusion in all groups. Neither the size in reduction of sympathetically-induced ERP shortening at apical test sites nor the cumulative percentage of denervated apical test sites (< or = 2-msec shortening) during a 3-hour period of permanent ischemia differed significantly among groups (P = 0.052 and P = 0.752, respectively). The degree of subepicardial involvement in the myocardial infarction was comparable among groups.

CONCLUSION

Thus, brief exposure of the left ventricular myocardium to ischemic metabolites prior to a subsequent permanent coronary occlusion does not trigger mechanism(s) that are responsible for protection against efferent sympathetic denervation apical to an area of transmural myocardial infarction/ischemia.