The effects of psychological stress and vagal stimulation with morphine on vulnerability to ventricular fibrillation (VF) in the conscious dog

Neurovisceral interactions within the brain-heart axis as the basis of neurocardiology

The use of a systematic approach to the study of the etiology of a certain pathology makes it possible to improve the understanding of its pathogenesis, as well as to develop more effective diagnostic and therapeutic approaches, including improving the prediction of its risk. Within this review, we will consider such an area of interdisciplinary research as neurocardiology, which studies the brain-heart axis. Examples of cardiovascular diseases associated with organic and functional disorders of this axis will be considered, as well as the prospects for research in this area and their translational significance for clinical medicine.

Acute Stress Decreases but Chronic Stress Increases Myocardial Sensitivity to Ischemic Injury in Rodents

Cardiovascular disease (CVD) is the largest cause of mortality worldwide, and stress is a significant contributor to the development of CVD. The relationship between acute and chronic stress and CVD is well evidenced. Acute stress can lead to arrhythmias and ischemic injury. However, recent evidence in rodent models suggests that acute stress can decrease sensitivity to myocardial ischemia-reperfusion injury (IRI). Conversely, chronic stress is arrhythmogenic and increases sensitivity to myocardial IRI. Few studies have examined the impact of validated animal models of stress-related psychological disorders on the ischemic heart. This review examines the work that has been completed using rat models to study the effects of stress on myocardial sensitivity to ischemic injury. Utilization of animal models of stress-related psychological disorders is critical in the prevention and treatment of cardiovascular disorders in patients experiencing stress-related psychiatric conditions.

Sympathoneural and adrenomedullary responses to mental stress

This concept-based review provides historical perspectives and updates about sympathetic noradrenergic and sympathetic adrenergic responses to mental stress. The topic of this review has incited perennial debate, because of disagreements over definitions, controversial inferences, and limited availability of relevant measurement tools. The discussion begins appropriately with Cannon's "homeostasis" and his pioneering work in the area. This is followed by mental stress as a scientific idea and the relatively new notions of allostasis and allostatic load. Experimental models of mental stress in rodents and humans are discussed, with particular attention to ethical constraints in humans. Sections follow on sympathoneural responses to mental stress, reactivity of catecholamine systems, clinical pathophysiologic states, and the cardiovascular reactivity hypothesis. Future advancement of the field will require integrative approaches and coordinated efforts between physiologists and psychologists on this interdisciplinary topic.

Experimental studies of psychophysiological factors in sudden cardiac death

Earlier research in the field of sudden cardiac death is reviewed. Such studies have largely oriented towards the provocation of myocardial injury and asystole in normal animals. However, such investigations constitute an inadequate model to describe the clinical appearance of sudden death, where underlying coronary disease is often present and the precipitating event is usually ventricular fibrillation rather than asystole. This report describes a series of studies designed to investigate the processes underlying cardiac vulnerability and the influence upon it of various psychological stresses. It is concluded that the primary mediator of ventricular vulnerability is the sympathetic nervous system. The efferent vagus appears to exert some protective influence against arrhythmias due to adrenergic stimulation. An appropriate clinical strategy for the treatment of malignant arrhythmias would therefore involve attempts to decrease cardiac sympathetic drive whilst at the same time enhancing vagal tone. Treatments are described which aim to bring this situation about by the use of clonidine, morphine sulphate, l-tryptophan and tyrosine. The use of neurochemical agents in this context appears promising.

Can thromboembolism be the result, rather than the inciting cause, of acute vascular events such as stroke, pulmonary embolism, mesenteric ischemia, and venous thrombosis?: a maladaptation of the prehistoric trauma response

Thromboembolism is considered the inciting cause of many vascular disorders including acute coronary syndrome (ACS), ischemic stroke, pulmonary embolism (PE), deep vein thrombosis (DVT), and mesenteric ischemia. Adrenergia and inflammation are known to accompany these conditions, particularly among arterial thromboembolic disorders, but the teleologic basis of these associations remains poorly understood. We argue that thromboembolism may sometimes be the result, rather than the cause, of acute vascular events, and may be precipitated by underlying adrenergia. Thromboembolic events are most prone to occur during parts of the circadian, seasonal, lifespan, and reproductive cycles with sympathetic dominance, as well as during behavioral, exertional, physiologic, and iatrogenic activation of sympathetic stress. Molecular evidence suggests that adrenergia and inflammation can promote coagulation and lead to co-activation of the pathways. Acute vascular events that occur without angiographic evidence of occlusion suggest that some infarcts may be attributable to adrenergia alone. "Embolic" disorders may represent asynchronous systemic phenomena rather than clot migration. During acute thromboembolism, downstream tissue hypoxia can activate maladaptive self-propelling cycles of sympathetic bias, inflammation, and coagulation. The counterproductive co-activation of these pathways may reflect a maladaptive interlink forged during the primordial evolution of trauma physiology. Their rapid co-mobilization enables rapid control of hemorrhage, microbial defense, and perfusion maintenance during trauma, but the pathways may behave maladaptively in the setting of modern diseases where endothelial injury may be more often precipitated by smoking, diabetes, dyslipidemia, or hypertension. Sympathetic blockade is already employed in ACS, and beta-blockers are used as antihypertensives to prevent stroke. Our hypothesis suggests that the benefits of beta-blockers in stroke may be independent of antihypertensive effects, and that adrenergia may represent a target for managing all thromboembolic disorders, independent of anti-coagulative and thrombolytic therapies. Perhaps reducing adrenergia, rather than maintaining high cerebral perfusion pressure, may represent a counterintuitive strategy for treating stroke and for reducing reperfusion injury. Plausible mechanisms by which autonomic dysfunction may induce venous thrombosis are discussed, especially in those with baroreceptor dysfunction, immobilization, or dehydration. Unexplained hypercoagulability of cancer may also operate through tumor-induced adrenergia and inflammation.

Acute coronary syndromes and heart failure may reflect maladaptations of trauma physiology that was shaped during pre-modern evolution

We hypothesize that the pathophysiology of many cardiovascular diseases reflects a maladaptation of the triad of trauma response: adrenergia, inflammation, and coagulation. During biologic evolution, trauma has likely been a prevailing factor in natural selection. Components of the trauma triad act to limit hemorrhage, defend wounds against microorganisms, and initiate reconstruction. Response pathways that enable survival after trauma confer obvious adaptive advantages especially if the individual goes on to reproduce. Modern humans have shaped their own ecologic environment in such a way that the incidence of trauma has waned and previously unseen pathologies have emerged. Manifestations of modern diet, changing lifestyles, and extended lifespan have suddenly created new pathologic challenges to our prehistoric physiologic system. During our evolutionary heritage, endothelial injury and end-organ hypoxia were likely exclusively associated with physical trauma and the responses of the trauma triad were appropriate. Today, endothelial injury is more often precipitated by distinctly modern stressors such as hypertension, smoking, diabetes, and dyslipidemia. The once-adaptive trauma response can maladaptively initiate dangerous, self-propelling cycles of adrenergia, inflammation, and coagulation. Acute coronary syndromes perhaps best exemplify this phenomenon. Congestive heart failure, which often ensues, can similarly be seen as a maladaptation of the trauma triad. Whereas end-organ hypoxia was once commonly associated with trauma, now hypoxia is more often attributable to distinctly modern stressors such as pump failure. The fluid conservation and inflammation that results from the trauma triad was clearly adaptive in our prehistoric past, but in congestive heart failure the response is maladaptive, engendering self-propelling exacerbations of pump failure and vascular disease. Our maladaptive trauma response hypothesis portends new diagnostic and therapeutic paradigms for cardiovascular diseases and has ramifications for many other conditions such as stroke, venous thrombosis, vasculitis, aortic disease, arterial disease, pulmonary embolism, and restenosis.

Electrocardiographic criteria for vagotonia-validation with pharmacological parasympathetic blockade in healthy subjects

BACKGROUND

The importance of vagal tone on cardiac function and cardiovascular mortality is well established. Although the presence of an enhanced cardiac vagal tone (CVT) is frequently diagnosed using the 12-lead resting electrocardiogram (ECG) in daily practice, most of the proposed criteria have been determined on an empirical basis. Our objective was to evaluate the effects of pharmacological blockade of the parasympathetic component of the autonomic nervous system on resting ECG tracings.

METHODS

Nine healthy young adults (24+/-5 year-old) underwent parasympathetic blockade with atropine sulfate i.v. (0.04 mg kg(-1)) and resting ECGs were obtained before and 15 min thereafter. CVT was assessed by a dimensionless index, which measures the RR interval reduction caused by the vagal withdrawal induced by a 4-s exercise test performed on a cycle ergometer where the subjects pedal as fast as possible with no added resistance.

RESULTS

This index was 1.63+/-0.24 and 1.03+/-0.03, before and after atropine, respectively (P<0.0001). Atropine reduced the R-R intervals (P<0.0001), and the amplitude of T-waves in several leads (DII: P=0.03; V4: P=0.04; V5: P=0.03; V6: P=0.01), and abolished the appiculation of T-waves, J-point and ST-segment elevations (P<0.05), and U-waves (P<0.05), which were present in baseline ECG in all subjects in at least two leads. The R-wave amplitude in leads V4, V5, and V6 (all P>/=0.10) was not modified by atropine infusion.

CONCLUSION

The duration of the R-R intervals and the amplitude of T-waves in leads DII, V4, V5, and V6, and the presence of T-wave appiculation, U-waves, and elevation of J-point and ST-segment should be used to detect enhanced cardiac vagal tone in healthy subjects.

An alternative method to enhance vagal activities and suppress sympathetic activities in humans

Vagal withdrawal and/or sympathetic overactivity is always accompanied by various kinds of stress and is dangerous to the body. We proposed that mild acupuncture on the Sishencong points may effectively enhance vagal activities but suppress sympathetic regulations of the heart in humans. Experiments were carried out on nine healthy male volunteers, while they were lying in a quiet room during 2-4 P.M. Acupuncture was applied 2 mm deep into the skin using standard stainless acupuncture needles at the Sishencong points, which are located on the vertex of the head, each 1 cm away from Baihui (GV 20) in four directions. Four points around the temporal area were selected as control points. Forty minutes of precordial ECG signals before, during, and after acupuncture were recorded continuously. Frequency-domain analysis of the stationary RR intervals was performed to evaluate the total variance, high-frequency power (HF, 0.15-0.40 Hz) and low-frequency power (LF, 0.04-0.15 Hz) in normalized units (LF%). Acupuncture on the Sishencong points resulted in an increased HF but a decreased LF% compared with the before acupuncture stage. Such effects did not occur when manual acupuncture was applied to the control points. The differences in the heart rate dynamics between Sishencong and the control groups took place 10 min after initiation of acupuncture and persisted even after the removal of the needles. Based on these results, we concluded that manual acupuncture on the Sishencong points enhanced cardiac vagal and suppressed sympathetic activities in humans. The underlying mechanisms and potential applications warrant further investigations.

Acurácia de critérios para vagotonia no eletrocardiograma de repouso de 12 derivações: uma análise com curvas ROC

OBJETIVO: Determinar a sensibilidade, a especificidade, os valores preditivos positivo e negativo e a acurácia de diferentes critérios eletrocardiográficos para vagotonia. MÉTODOS: Foram avaliados 74 atletas olímpicos brasileiros (51 homens e 23 mulheres) com idade entre 16 e 42 anos (24 ± 5 anos), tendo sido realizados, entre outros exames, um ECG de repouso de 12 derivações e uma avaliação do tônus vagal cardíaco (TVC) pelo teste de exercício sem carga de quatro segundos (T4s), cujo índice B/C (indicativo da magnitude do TVC) foi utilizado como padrão-ouro. O T4s é um teste que se baseia no mecanismo da taquicardia inicial do exercício e foi anteriormente padronizado e validado como capaz de avaliar o TVC sem influência do componente simpático. Dados de 10 atletas foram excluídos devido à presença de critérios ecocardiográficos para hipertrofia ventricular esquerda, ainda que provavelmente fisiológica. Com o auxílio de curvas ROC (receiver operating characteristic), selecionou-se o ponto de corte com a melhor combinação entre sensibilidade (Sens) e especificidade (Esp) para cada variável do ECG, calculando-se os valores preditivos positivo (VPP) e negativo (VPN) e a acurácia (AC). Foram ainda correlacionados o índice B/C e as variáveis do ECG. RESULTADOS: Há fraca associação entre o índice B/C e as variáveis do ECG, à exceção da duração do intervalo R-R (r = 0,353; P = 0,004), que também apresentou curva ROC significativa (chi2= 0,863; P = 0,002), sendo que o critério intervalo R-R > ou = 990ms apresentou os seguintes resultados: Sens - 100%; Esp - 73%; VPP 20%; VPN 100%; AC 75%. As variáveis do ECG que apresentaram pontos de corte com acurácia > 80% foram: amplitude da onda T em V5 > ou = 8,0mm; amplitude da onda T em V6 > ou = 7,0mm; amplitude da onda Q em V5 > ou = 7,0mm; amplitude da onda R em V4 > ou = 50,0mm; presença de supradesnível de ponto J em duas ou mais derivações; presença de supradesnível de segmento S-T em cinco ou mais derivações e presença de transição precordial rápida. DISCUSSÃO E CONCLUSÃO: O desempenho dos critérios eletrocardiográficos em termos de VPP, VPN e AC foi muito limitado, com a exceção da duração do intervalo R-R. A combinação de outros critérios como amplitude da onda T em V5 e V6, amplitude da onda R em V4 e presença de supradesnível de ponto J e do segmento S-T em várias derivações pode auxiliar na predição de vagotonia.

Enhancement of heart rate variability by cholinergic stimulation with pyridostigmine in healthy subjects

The purpose of this study was to determine the effect of the oral administration of pyridostigmine bromide on indices of heart rate variability (HRV) in healthy young volunteers. Seventeen healthy participants (11 men, 6 women; aged 27 +/- 8 y) submitted to a randomized, crossover, double-blind protocol, in which they received 30 mg pyridostigmine bromide (PYR) or placebo orally at 8-hour intervals for 24 hours, on two separate days. Venous blood samples were collected 2 and 24 hours after the first dose for determination of serum cholinesterase activity. Holter tapes were recorded during the 24-hour period and analyzed using a semiautomatic technique to evaluate time- and frequency-domain indices of HRV and to build three-dimensional return maps for later quantification. Symptoms were mild and occurred similarly during administration of PYR and placebo (p = 0.140). Serum cholinesterase activity was reduced by 15% at 2 hours (p = 0.013) and by 14% at 24 hours (p = 0.010) after the first dose of PYR, but not after administration of placebo. Pyridostigmine administration caused a significant increase in the mean 24-hour R-R interval (placebo: 814 +/- 20 msec; PYR: 844 +/- 18 msec; p = 0.003) and in time-domain indices of HRV, such as the standard deviation of all R-R intervals (SDNN; placebo: 151 +/- 9 msec; PYR: 164 +/- 9 msec; p = 0.017), and the percentage of pairs of adjacent R-R intervals differing by more than 50 msec (pNN50; placebo: 12.8 +/- 1.8%; PYR: 13.9 +/- 1.5%; p = 0.029). Pyridostigmine had no significant effect on frequency-domain indices of HRV, but resulted in significant increase in P2, a parasympathetic index derived from the three-dimensional return map (placebo: 93 +/- 13 msec; PYR: 98 +/- 13 ms; p = 0.029). In conclusion, low-dose pyridostigmine reduced mean heart rate and increased HRV during a 24-hour period in healthy young subjects.

Living with an implantable cardioverter-defibrillator: a review of the current literature related to psychosocial factors

Sudden cardiac death (SCD) is responsible for 300,000 deaths annually. Lethal ventricular dysrhythmias account for the majority of SCDs. Implantable cardioverter-defibrillators (ICDs) are the emerging treatment for lethal dysrhythmias. Although reductions in SCD mortality with ICDs are clear, the psychologic and social consequences of these devices reveal a mixed success. Patients with ICDs have high levels of anxiety and depressive symptoms. Conversely, most studies of quality of life in patients with ICDs report that the device is well accepted despite fears of being shocked. The ICD shocks are a unique aspect of treatment and have the potential to cause psychologic distress. Nursing needs to provide care from a holistic perspective. Support groups provide reassurance and allow patients to discuss expectations and fears related to the ICD. Research needs to be conducted to explore the impact of these devices on the lives of patients and their families.

Cholinergic stimulation with pyridostigmine blunts the cardiac responses to mental stress

Mental stress may induce myocardial ischemia and ventricular arrhythmia in patients with coronary artery disease, and cholinergic stimulation is a potential protective mechanism. The purpose of this study was to determine the effect of pyridostigmine bromide (PYR), a reversible cholinesterase inhibitor, on the cardiac responses to a mental stress challenge. Twelve healthy young volunteers were submitted to a mental stress test (arithmetic test) 2 hours after the oral administration of either placebo or PYR (45 mg) on two separate days, following a randomized crossover double-blind protocol. Heart rate was reduced after both placebo and PYR (p < 0.05), but the cardiac responses to the mental stress were lower with PYR (p < 0.05): mean RR interval (mean +/- SE)-placebo: 730 +/- 19 msec; PYR: 769 +/- 21 msec; Peak systolic pressure-placebo: 129 +/- 4 mmHg; PYR: 124 +/- 3 mmHg; Peak diastolic pressure-placebo: 92 +/- 3 mmHg; PYR: 89 +/- 4 mmHg; Mean rate-pressure product-placebo: 10,496 +/- 412 bpm x mmHg; PYR: 9,746 +/- 383 bpm x mmHg. In conclusion, 45 mg of pyridostigmine blunted the pressor and chronotropic responses to mental stress in healthy young subjects.

Autonomic control of heart rate in dogs treated chronically with morphine

The vagotonic effect of chronic morphine on the parasympathetic control of the heart was examined in dogs treated with morphine for 2 wk. Because normal vagal function is critical to myocardial stability, the study was conducted to evaluate for potential impairments following chronic vagal stimulation. The hypothesis that persistent vagal outflow would result in a loss of vagal reserve and reduced vagal control of heart rate was tested. Heart rate and the high-frequency variation in heart rate (power spectral analysis) declined shortly after initiation of subcutaneous morphine infusion. A progressive bradycardia correlated well with the rising plasma morphine. The resting bradycardia (57 beats/min) was maintained through day 2 and was accompanied by a significant parallel increase in vagal effect and a decline in the intrinsic heart rate (160 vs. 182 beats/min). A compensatory increase in the ambient sympathetic control of heart rate was evident on day 2 and was supported by an increase in circulating catecholamines. The lowered intrinsic heart rate and elevated sympathetic activity were maintained through day 10 despite a return of the resting heart rate and plasma catecholamines to pretreatment values. These observations suggested that chronic morphine alters either the intrinsic function of the sinoatrial node or reduces the postvagal tachycardia normally attributed to nonadrenergic, noncholinergic agents. Both acute and chronic morphine depressed the rate of development of bradycardia during direct vagal nerve stimulation without altering the rate of recovery afterward. This last observation suggests that acute morphine reduces the rate of acetylcholine release. Results provide insight into the mechanisms that maintain vagal responsiveness. The results are also relevant clinically because opiates are increasingly prescribed for chronic pain and opiate abuse is currently in resurgence.

Stress and endogenous opioids: behavioral and circulatory interactions

Endogenous opioid peptides are the basis of a diverse system of complex neuroregulatory and endocrine mechanisms. While relatively quiescent in the resting state, these peptides are released during intense stimulation and modify, in a number of ways, circulatory homeostatic mechanisms. The endogenous opioids, primarily via endorphins and enkephalins, are capable of influencing circulatory responses to stress at the behavioral, the endocrinological, and the neural level. Recent research in humans and animals has described several roles for opioids in regulation of the circulatory stress response, and has also provided clues about the significance of opioid dysregulation in the pathophysiology of stress. Increased understanding of the basic mechanisms of stress and endogenous opioids will clarify the potential roles of opioids in important pharmacologic and behaviorally based therapeutics.

Morphine and morphiceptin increase the threshold for epinephrine-induced cardiac arrhythmias in the rat through brain mu opioid receptors

1. To determine whether morphine modulates the development of cardiac arrhythmias through mu opioid receptors by an action within the central nervous system (CNS). Catecholamine-induced ventricular arrhythmias were produced, in the rat, by continuous infusion of epinephrine at incremental doses until the development of fatal arrhythmias, usually ventricular fibrillation. 2. Morphine, 0.1 mg/kg i.v., significantly suppressed (P < 0.05) the development of epinephrine-induced arrhythmias compared with the control group. This was opposed by the mu opioid antagonist naloxone (1 or 2 mg/kg) in a dose-dependent manner. 3. To determine whether these effects were operative in the brain, rats received an injection of either morphine 50 micrograms/kg or its diluent (control) into the lateral cerebral ventricle intracerebroventricularly (i.c.v.). Morphine significantly increased (P < 0.05) the threshold for the development of arrhythmias. 4. To further explore whether this effect was operative at the mu opioid receptor, a more specific mu opioid receptor agonist morphiceptin (50 micrograms/kg) was administered i.c.v. and produced a significant increase (P < 0.05) in the threshold for cardiac arrhythmias compared with controls. 5. The action of morphine was further established to be operating through mu opioid receptors from experiments with the i.c.v. administration of naloxone (+) and naloxone (-) followed by morphine showing that the action of morphine in the brain was prevented by the opioid antagonist naloxone but not by its stereo-isomer that is not a mu opioid receptor antagonist. 6. These data suggest a role for morphine to modulate cardiac arrhythmias, specifically to increase arrhythmia threshold, through an action within the CNS at mu opioid receptors.

Morphine and the Endogenous Opioid Dynorphin in the Brain Attenuate Digoxin-Induced Arrhythmias in Guinea Pigs

The effects of the opioid receptor agonists morphine and dynorphin on digoxin-induced arrhythmias were examined in guinea pigs that had received intravenous digoxin (50 mu/kg bolus plus 500 mu/kg/hr intravenously). Animals received either morphine (50 or 100 micrograms/kg) or dynorphin A(1-13) (50 or 100 micrograms/kg) or saline (the diluent) into the lateral cerebral ventricle (intracerebroventricularly) prior to digoxin. Morphine and dynorphin produced significant (P < 0.05) dose-dependent increases in the threshold of digoxin-induced arrhythmias. The mean digoxin dose at the development of fatal arrhythmias was 775 +/- 42 micrograms/kg in the control group but was significantly higher namely 958 +/- 45 micrograms/kg after 100 micrograms/kg of morphine ICV, and 984 +/- 47 micrograms/kg after 100 micrograms/kg of dynorphin A (1-13) intracerebroventricularly. In the absence of digoxin, the highest doses of each of these opioids did not produce arrhythmias. Changes in blood pressure and heart rate were unlikely explanations for the observed actions of these opioids as morphine accentuated the increase in blood pressure that accompanied digoxin while dynorphin was associated with a lower blood pressure with digoxin, despite similar effects on arrhythmias. In the control group, fatal digoxin-induced arrhythmias were ventricular tachyarrhythmias in two-thirds of cases and complete heart block in the rest. Morphine and dynorphin reduced the development of ventricular tachyarrhythmias. The role of the cholinergic system was explored, with morphine, utilizing atropine sulfate which crosses the blood brain barrier and atropine methylnitrate which does not enter the CNS. Atropine sulfate but not atropine methylnitrate reversed the effects of morphine on digoxin-induced arrhythmias.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of life-threatening arrhythmias by pharmacologic stimulation of the muscarinic receptors with oxotremorine

The potential antiarrhythmic efficacy of pharmacologic parasympathetic activation is still controversial. This study assessed the antiarrhythmic effect of saline solution (n = 9) and of the muscarinic agonist oxotremorine (1.5 micrograms/kg administered intravenously) (n = 17) in a feline animal model in which malignant arrhythmias were reproducibly elicited by the combination of acute myocardial ischemia and left stellate ganglion stimulation. Although saline solution had no effect, oxotremorine significantly decreased heart rate, blood pressure, the incidence of ventricular fibrillation from 47% to 0% (p = 0.004), and the incidence of malignant arrhythmias (either ventricular tachycardia or ventricular fibrillation) from 88% to 12% (p less than 0.001). When reduction in heart rate was prevented by means of atrial pacing (n = 15), the incidence of malignant arrhythmias was still significantly reduced from 87% to 27% (p = 0.001). Arrhythmias were also graded as follows: 0 = no premature ventricular contractions; 1 = 1 to 10 premature ventricular contractions; 2 = 11 to 50 premature ventricular contractions; 3 = ventricular tachycardia; 4 = ventricular fibrillation. Arrhythmia severity was 3.29 +/- 0.16 (SEM) in the control trials and was reduced to 0.76 +/- 0.26 (p less than 0.001) by oxotremorine and to 1.53 +/- 0.34 by oxotremorine and pacing (p = 0.002). Therefore a muscarinic agonist can significantly reduce malignant arrhythmias during acute myocardial ischemia and may represent a novel approach to the prevention of sudden cardiac death.

Effects of enflurane on inducibility of ventricular tachycardia

The effects of enflurane on cardiac electrophysiologic parameters and on inducibility of ventricular tachycardia (VT) by programmed stimulation were studied in 12 patients (11 men, 1 woman, mean age +/- standard deviation 55 +/- 8 years) with drug refractory sustained monomorphic VT who underwent transcatheter ablation with high-energy direct-current shocks. One catheter ablation procedure was performed in 10 patients, whereas 2 ablation sessions were necessary in 2 patients. Programmed ventricular stimulation was performed on 2 separate days (mean interval 19). There were 2 baseline studies, 1 several days before ("baseline study I") and the second at the beginning of the ablation procedure ("baseline study II") while the patient was awake and nonsedated. The third programmed stimulation study was done 15 to 30 minutes after administration of anesthesia with enflurane, oxygen and nitrous oxide ("enflurane study"). Rate of sinus rhythm, QRS duration, PQ interval and ventricular effective refractory period were unaltered, whereas QTc interval increased significantly after initiation of anesthesia. Before and after induction of general anesthesia, clinical VT was inducible in all patients. However, in 1 patient, induction of VT was only possible by pacing in the left ventricle after enflurane administration. Based on these data, it is concluded that general anesthesia with enflurane, oxygen and nitrous oxide has no marked influence on inducibility of clinical VTs. Therefore, this type of anesthesia may be useful for nonpharmacologic, ablative procedures requiring general anesthesia.

High-dose fentanyl reduces intraoperative ventricular fibrillation in neonates with hypoplastic left heart syndrome

STUDY OBJECTIVE

To determine retrospectively the effect of high-dose opiate-oxygen (O2) anesthetic technique on intraoperative ventricular fibrillation in high-risk neonates.

DESIGN

Retrospective chart review of different anesthetic techniques in a partially contemporaneous patient group (1981 to 1983).

SETTING

Cardiac anesthesia service at a university pediatric hospital.

PATIENTS

Forty neonates undergoing Norwood Stage I repair of hypoplastic left heart syndrome.

INTERVENTIONS

High-dose fentanyl-O2 anesthesia in 30 neonates and low-dose morphine sulfate 50%-nitrous oxide (N2O) in 10 neonates.

MEASUREMENTS AND MAIN RESULTS

Clinical condition assessed by preoperative and intraoperative arterial blood gases, requirements for sodium bicarbonate (NaHCO3), need for inotropic and pressor support, and vital signs. Outcome assessments by intraoperative ventricular fibrillation (frequency before and after bypass) and hospital mortality. Clinical condition and hospital mortality were no different. The frequency of intraoperative ventricular fibrillation was significantly different: 3% with high-dose fentanyl and 50% with morphine-N2O (p less than 0.005).

CONCLUSIONS

High-dose opiate-O2 anesthesia in these patients markedly decreased intraoperative ventricular fibrillation. Other clinical reports and recent experimental work suggest that this finding is due to high-dose opiates rather than the avoidance of N2O.

Vagal stimulation and prevention of sudden death in conscious dogs with a healed myocardial infarction

The interest for the antifibrillatory effect of vagal stimulation has been largely limited by the fact that this concept seemed restricted to acute experiments in anesthetized animals. To explore the potentially protective role of vagal stimulation in conscious animals we developed a chronically implantable device to be placed around the cervical right vagus. An anterior myocardial infarction was produced in 161 dogs; 1 month later an exercise stress test was performed on the 105 survivors. Toward the end of the test the circumflex coronary artery was occluded for 2 minutes. Fifty-nine (56%) dogs developed ventricular fibrillation and, before this test was repeated, were assigned either to a control group (n = 24) or to be instrumented with the vagal device (n = 35). Five dogs were excluded because of electrode malfunction. Compared with the heart rate level attained after 30 seconds of occlusion during exercise in the control test, vagal stimulation led to a decrease of approximately 75 beats/min (from 255 +/- 33 to 170 +/- 36 beats/min, p less than 0.001). In the control group 22 (92%) of 24 dogs developed ventricular fibrillation during the second exercise and ischemia test. By contrast, during vagal stimulation ventricular fibrillation occurred in only 3 (10%) of the 30 dogs tested and recurred in 26 (87%) during an additional exercise and ischemia test in the control condition (p less than 0.001 versus the vagal stimulation test; internal control analysis). Combined analysis of the tests performed in the control condition showed that ventricular fibrillation was reproducible in 48 (89%) of the 54 dogs tested. The protective effect of vagal stimulation was also significant in the group comparison analysis and even after exclusion of those four dogs in which ventricular fibrillation was not reproducible (92% versus 11.5%, control versus vagal stimulation, p less than 0.001). When heart rate was kept constant by atrial pacing, the vagally mediated protection was still significant (p = 0.015) as five (55%) of nine dogs survived the test. This study shows that vagal stimulation, performed shortly after the onset of an acute ischemic episode in conscious animals with a healed myocardial infarction, can effectively prevent ventricular fibrillation. This striking result seems to depend on multiple mechanisms having a synergistic action. The decrease in heart rate is an important but not always essential protective mechanism. The electrophysiological effects secondary to the vagally mediated antagonism of the sympathetic activity on the heart are likely to play a major role.

Stress and the heart: biobehavioral aspects of sudden cardiac death

Stress has been implicated as a developmental factor in atherosclerotic heart disease, essential hypertension, and sudden cardiac death. This article reviews the mechanisms and biobehavioral effects of stress on the heart, focusing on its relation to sudden cardiac death. Epidemiologic evidence, cultural studies, animal experiments, and human research are reviewed to better understand the biobehavioral aspects of stress on the heart. Emphasis is placed on understanding the interaction of the central nervous system's frontal cortex and hypothalamus with cardiovascular control areas. With today's understanding of the frontal cortex and the interaction of hormones and neurotransmitters with the cardiovascular system, clinical interventions utilizing psychotherapy and psychopharmacology are needed, particularly since both approaches are underutilized in combating arrhythmias.

Hemodynamic and arrhythmogenic effects of aversive stress during myocardial ischemia

Pavlovian conditioning was accomplished in two groups of dogs by following a 30-s tone (the CS+) with a short (less than or equal to 1 s) electric shock). An inflatable occluder was implanted around the left circumflex coronary artery in all animals. The CS+ was presented to Group I dogs (n = 6) during control (i.e., no coronary occlusion) and at 30 s and 3 min after the onset of a 4-min left circumflex coronary occlusion. The CS+ evoked a robust increase in heart rate and blood pressure in the control state. A conditional cardiovascular response was still evoked during the acute coronary occlusion despite the evolving myocardial ischemia. No increase in ventricular ectopic beats occurred during the CS+. An anterior myocardial infarction (16.8 +/- 1.7% of left ventricular mass, mean +/- SEM) was created in Group II dogs (n = 8) at the time of surgery. A CS+ was presented, as above, both alone and 1 min after the beginning of a 2-min left circumflex coronary occlusion. There were significant differences in the conditional response in heart rate, left ventricular (systolic) pressure (LVP) and d(LVP)/dt for trials given during the coronary occlusion compared with no occlusion. These dogs were then classified as 'resistant' or 'susceptible' to ventricular arrhythmias approx. 4 weeks later using an exercise and coronary occlusion test. Three of five susceptible dogs, but none of three resistant dogs, evidenced increased severity of arrhythmias during the CS+. We conclude that the nature of the cardiovascular response to behavioral stress during myocardial ischemia depends in part upon the timing of the CS+, the presence or absence of a resident myocardial infarction and the status of the autonomic reflexes controlling the heart.

Abolition of clonidine's effects on ventricular refractoriness by naloxone in the conscious dog

The interaction between opiate and adrenergic receptors on cardiac electrophysiologic function in the conscious dog was addressed in our study. We examined the effects of opiate receptor blockade with naloxone on clonidine-induced changes in refractoriness of the cardiac ventricle. Nine dogs were chronically instrumented for recording mean arterial blood pressure, administration of drugs and for measurement of effective refractory period of the ventricle. Clonidine (10 micrograms/kg, i.v.) significantly (p less than 0.05) decreased heart rate to 72 +/- 5 beats/minute from 108 +/- 8 beats/minute; mean arterial pressure decreased significantly (p less than 0.05) to 83 +/- 3 mmHg from 91 +/- 4 mmHg. Ventricular refractoriness was increased significantly (p less than 0.05) at current levels of 7 and 10 mA and pacing rates 180 and 200 beats/minute. Naloxone (3-10 mg/kg, i.v.) abolished clonidine's effects on heart rate, mean arterial pressure and ventricular refractoriness. We conclude that ventricular refractoriness may be regulated in part by interactions between central adrenergic and opioidergic systems.

Effect of D-Ala-2-Me-Phe-4-Gly-ol-5 enkephalin on epinephrine-induced arrhythmias in the rat and the interrelationship to the parasympathetic nervous system

The purpose of this study was to evaluate the effects of the millimicrons opioid agonist D-Ala-2-Me-Phe-4-Gly-ol enkephalin (DAGO) on catecholamine-induced arrhythmias. Arrhythmias were produced, in the rat, by continuous infusion of epinephrine until the development of fatal arrhythmias that were usually ventricular fibrillation. Intracerebroventricular (ICV) administration of DAGO, 3 nmol, significantly (p less than 0.05) shifted to the right the relationship between epinephrine and both the onset of ventricular arrhythmias and the development of fatal arrhythmias. Naloxone, 1 mg/kg i.v., prevented these effects of DAGO. Atropine, 1 mg/kg i.v. or 20 micrograms/kg ICV, prevented the shift in these dose response relationships. Antagonism of DAGO's effects on arrhythmias could not be explained by an alteration of the blood pressure response to epinephrine. However, DAGO significantly increased blood pressure and decreased heart rate in separate experiments in animals that did not receive epinephrine and atropine prevent the heart rate and blood pressure effects of DAGO. These data show that 1) the millimicrons opioid receptor agonist DAGO suppresses epinephrine-induced arrhythmias, 2) the site of action can be within the CNS, 3) there is a role for the central parasympathetic nervous system to mediate the effect of DAGO and 4) endogenous opioids could modulate catecholamine-induced cardiac arrhythmias.

The interrelationship of morphine and the parasympathetic nervous system in digoxin-induced arrhythmias in the guinea-pig

1. The role of the parasympathetic nervous system and the effect of morphine on cardiac arrhythmias induced by digitalis was assessed in guinea-pigs that had digitalis arrhythmias produced by digoxin 50 micrograms/kg intravenously plus 500 micrograms/kg per h. 2. Morphine produced a dose-dependent rightward shift in the relationship between digoxin dose and arrhythmias. Morphine 5 mg/kg subcutaneously (s.q.) was associated with significantly (P less than 0.05) higher digoxin doses both at the onset of ventricular arrhythmias and at development of fatal arrhythmias compared with the control group that received saline s.q. 3. Vagotomy and atropine prevented the effect of morphine so that the dose-response relationships and the mean digoxin dose at onset of ventricular arrhythmias and the development of fatal arrhythmias were not significantly different from the control group receiving saline. 4. These data indicate that morphine limits the development of digitalis arrhythmias and this effect is, at least in part, mediated through the parasympathetic nervous system.

Comparison of effects of three anesthetic agents on induction of ventricular tachycardia in a canine model of myocardial infarction

The effects of three anesthetic agents on the inducibility of ventricular tachycardia by programmed stimulation were investigated in dogs with a surgically induced left ventricular infarct. Endocardial catheter electrodes were placed at the right ventricular apex under general anesthesia at least 2 weeks after infarction, and the dogs were allowed to recover for 24 hours before undergoing programmed stimulation in the conscious state on two occasions 2 hours apart. A protocol of programmed stimulation with up to seven ventricular extrastimuli was used. In 15 animals, ventricular tachycardia was inducible on both occasions with 3.4 +/- 0.4 (mean +/- SEM; range, 1-5) extrastimuli. Two hours after baseline conscious induction, the dogs were anesthetized with either halothane, pentobarbital, or a fixed combination of fentanyl-droperidol plus nitrous oxide. Halothane prolonged the PR interval from 99 +/- 4 to 117 +/- 6 msec (p = 0.001) and the ventricular effective refractory period from 140 +/- 4 to 157 +/- 6 msec (p = 0.008). The ability to induce ventricular tachycardia was abolished in five of 10 animals (p less than 0.05). In the animals that remained inducible, the cycle length of tachycardia increased from 153 +/- 10 to 168 +/- 10 msec (p = 0.015), while the number of extrastimuli required was unaltered. Pentobarbital prolonged the PR interval from 104 +/- 6 to 124 +/- 6 msec (p = 0.004) and the QTc interval from 270 +/- 10 to 310 +/- 6 msec (p = 0.006). Ventricular tachycardia remained inducible in only six of 10 dogs (p less than 0.05) with no change in cycle length or the number of extrastimuli required. Ventricular fibrillation was inducible in an additional three dogs with a number of extrastimuli similar to that required to induce ventricular tachycardia before anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Night terrors and sudden unexplained nocturnal death

A high incidence of sudden unexplained nocturnal deaths has been reported among young Asian males. These deaths are known as Pokkuri in Japan, Bangungut in the Philippines and Sudden Unexplained Nocturnal Death in the United States. Post mortem analysis has demonstrated cardiac conduction defects in many of the victims. Careful review of the terminal events surrounding these deaths suggests that the victims suffered from night terrors. Night terrors are a sleep disorder characterized by vocalization, motor activity, a nonarousable state, and severe autonomic discharge. The proposed recognition of both night terrors and cardiac anomalies in these patients offers a pathophysiologic mechanism for their sudden death.

Antifibrillatory action of the narcotic agonist fentanyl

Morphine, an opiate alkaloid with mixed mu- and delta-agonist properties, raises the ventricular fibrillation threshold in anesthetized dogs by altering autonomic tone. To elucidate further underlying structure-activity relationships, the effect of fentanyl, a nonalkaloid, mu-selective agonist in wide clinical use, was studied. Fentanyl (30 micrograms/kg) was given intravenously to 27 chloralose-anesthetized dogs, and ventricular fibrillation threshold was measured by means of the single-stimulus technique. In the baseline state fentanyl raised the ventricular fibrillation threshold by 14%. When the dogs were subjected to hemorrhagic stress, this effect was amplified to 29% (p less than 0.0001). Bilateral cervical vagotomy abolished fentanyl's antifibrillatory effect, but neither atropine sulfate (0.4 mg/kg/hr) nor atropine methylnitrate (0.5 mg/kg/hr) did so. Fentanyl's influence on the fibrillation threshold during hemorrhage was significantly reduced by bilateral stellate ganglionectomy (p less than 0.005). It is concluded that fentanyl raises the ventricular fibrillation threshold by its known sympathoinhibitory action rather than by its vagal efferent activating effect. The facts that an intact vagus is required and that hemorrhage amplifies the effect suggest that the antifibrillatory effect of fentanyl is mediated through the afferent component of the baroreflex arc.

Ventricular fibrillation

Ventricular fibrillation is the most common mechanism of sudden unexpected cardiac death in persons with asymptomatic or symptomatic coronary artery disease. The electrophysiologic mechanisms reviewed in this article include: automaticity of pacemaker fibers, transformation of nonpacemaker into pacemaker fibers, "injury" currents and reentry. Some of the conditions facilitating ventricular fibrillation include bradycardia, long QT syndrome, electrocution, electrolyte imbalance, drugs, sympathetic stimulation and myocardial ischemia. Electrophysiologic studies during acute myocardial ischemia suggest that the earliest activity at the onset of arrhythmia may originate at the sites of the surviving Purkinje fibers or at the epicardial rim. Reentrant arrhythmias arising in ischemic myocardium are attributed to nonhomogeneous distribution of local hyperkalemia and acidosis.

Effects of acetyl-strophanthidin on left ventricular function and ventricular arrhythmias

Digitalis drugs can suppress ventricular arrhythmias. It is uncertain whether this effect results from improved left ventricular (LV) function. We utilized radionuclide scanning techniques to evaluate changes in LV ejection fraction (EF) after an infusion of acetyl-strophanthidin in 43 patients with frequent ventricular premature beats (VPBs) (44 to 2400/hr). Acetyl-strophanthidin suppressed ventricular arrhythmia in 17 patients, but LVEF increased in only six of these patients (57% to 67%), while it was unaltered in 11 patients (28% to 30%). In 26 patients ventricular arrhythmia was not suppressed. Fifteen of these patients had an increase in LVEF (60% vs 71%), while this was unchanged in 11 patients (27% vs 29%). Thus no correlation was observed between the positive inotropic and antiarrhythmic action of acetyl-strophanthidin on ventricular arrhythmia and LVEF. We conclude that the suppression of VPBs by acetyl-strophanthidin is independent of the drug's effects on LV function. Evidence is reviewed suggesting that the antiarrhythmic effect of acetyl-strophanthidin on ventricular ectopic activity is due to its vagotonic action.

Factors related to the induction of ventricular fibrillation in the normal canine heart by programmed electrical stimulation

Programmed electrical stimulation was performed in eight normal dogs using a stimulator and endocardial electrode catheters identical to those used in human studies. The right and left ventricular apex were paced at a drive cycle length of 400 ms and, in some cases, 500 ms, with a pacing sequence of single (S1S2), double (S1S2S3) and triple (S1S2S3S4) premature impulses introduced after eight paced complexes. Pacing sequences were performed using combinations of pulse width (1, 2 and 4 ms) and current strengths of 2, 5 and 10 times diastolic threshold, and in three dogs, 15 times diastolic threshold. Twenty-two episodes of ventricular fibrillation were initiated in five dogs in 170 pacing sequences using current strengths up to 10 times diastolic threshold, and six episodes of ventricular fibrillation in the two of three remaining dogs tested at 15 times diastolic threshold. Ventricular fibrillation was reproducible on seven of nine occasions. Ventricular fibrillation was never induced by S1S2 at up to 15 times diastolic threshold; it was induced by S1S2S3 in 3 (1.8%) of 170 sequences, but only at 10 times diastolic threshold. It was induced by S1S2S3S4 in 19 (11.4%) of 167 sequences using 2 to 10 times diastolic threshold, although 20 of 28 episodes only occurred with S1S2S3S4 at 10 or more times diastolic threshold.(ABSTRACT TRUNCATED AT 250 WORDS)

Psychological stress and fatal heart attack: the Athens (1981) earthquake natural experiment

The effects of acute and subacute psychological stress caused by a sudden general disaster on mortality from atherosclerotic heart disease (underlying cause) and cardiac events (proximate cause) were investigated by comparing total and cause-specific mortality during the days after a major earthquake in Athens in 1981 with the mortality during the surrounding month and the corresponding periods of 1980 and 1982. There was an excess of deaths from cardiac and external causes on the days after the major earthquake, but no excess of deaths from cancer and little, if any, excess of deaths from other causes. The excess mortality was more evident when atherosclerotic heart disease was considered as the underlying cause (5, 7, and 8 deaths on the first three days, respectively; background mean deaths per day 2.6; upper 95th centile 5) than when cardiac events in general were considered as the proximate cause (9, 11, and 14 deaths on the first three days, respectively; background mean 7.1, upper 95th centile 12).

Psychosocial and behavioral influences in the pathogenesis of acquired cardiovascular disease

When taken together, studies relating psychosocial and behavioral factors to cardiovascular disease phenomena provide justification for the conclusion that such factors are importantly involved. We would emphasize the need to study and evaluate the interaction of environmental and biological factors in both laboratory studies of pathogenesis as well as in clinical studies of management. Indeed, upon careful scrutiny, even the accepted "nonbehavioral" risk factors such as hypercholesterolemia, hypertension, cigarette smoking, obesity, and sedentary lifestyles are each composite manifestations rather than single pathogens whose identities are powerfully impregnanted and bolstered by varieties of behavioral and psychosocial underpinnings. In view of the awesome impact of contemporary cardiovascular disease, both in terms of its increasing socioeconomic importance and its biologic devastation, we can not long afford comprehensive public health programs without increased and improved attention to psychosocial and behavioral influences in the pathogenesis of acquired cardiovascular disease.