Antifibrillatory action of the narcotic agonist fentanyl

Editor’s Choice- Sedation in the coronary intensive care unit: An adapted algorithm for critically ill cardiovascular patient

In the current era, cardiovascular intensive care units care for more complex patients who are far sicker than historical post-myocardial infarction patients, and sedation has become a common intervention in these units. Current sedation best practices derive mainly from non-cardiac units which limits their generalization to the critically ill cardiac patient. Thus, a great variability in sedation protocols, especially the selection of sedative agents, is commonly seen in daily practice across cardiac units. We present an updated review on sedation in cardiovascular critical care medicine with emphasis on the hemodynamic impact. The goal of this review is to generate a general sedation algorithm specific for the cardiac patient.

Activation of peripheral delta2 opioid receptors increases cardiac tolerance to ischemia/reperfusion injury Involvement of protein kinase C, NO-synthase, KATP channels and the autonomic nervous system

AIMS

This study aims to investigate the role of peripheral delta(2) opioid receptors in cardiac tolerance to ischemia/reperfusion injury and to examine the contribution of PKC, TK, K(ATP) channels and the autonomic nervous system in delta(2) cardioprotection.

MAIN METHODS

Deltorphin II and various inhibitors were administered in vivo prior to coronary artery occlusion and reperfusion in a rat model. The animals were monitored for the development of arrhythmias, infarct development and the effects of selected inhibitors.

KEY FINDINGS

Pretreatment with peripheral and delta(2) specific opioid receptor (OR) antagonists completely abolished the cardioprotective effects of deltorphin II. In contrast, the selective delta(1) OR antagonist 7-benzylidenenaltrexone (BNTX) had no effect. The protein kinase C (PKC) inhibitor chelerythrine and the NO-synthase inhibitor L-NAME (N-nitro-L-arginine methyl ester) also reversed both deltorphin II effects. The nonselective ATP-sensitive K+ (K(ATP)) channel inhibitor glibenclamide and the selective mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoic acid only abolished the infarct-sparing effect of deltorphin II. Inhibition of tyrosine kinase (TK) with genistein, the ganglion blocker hexamethonium and the depletion of endogenous catecholamine storage with guanethidine reversed the antiarrhythmic action of deltorphin II but did not change its infarct-sparing action.

SIGNIFICANCE

The cardioprotective mechanism of deltorphin II is mediated via stimulation of peripheral delta(2) opioid receptors. PKC and NOS are involved in both its infarct-sparing and antiarrhythmic effects. Infarct-sparing is dependent upon mitochondrial K(ATP) channel activation while the antiarrhythmic effect is dependent upon TK activation. Endogenous catecholamine depletion reduced antiarrhythmic effects but did not alter the infarct-sparing effect of deltorphin II.

Pharmacologic Evidence for the Involvement of Central and Peripheral Opioid Receptors in the Cardioprotective Effects of Fentanyl

BACKGROUND

We investigated the involvement of central and peripheral opioid receptors (OR) in the cardioprotective effects of fentanyl (FENT) in a model of myocardial ischemia/reperfusion injury associated with pharmacologically induced sympathetic overactivity in anesthetized rabbits.

METHODS

Central sympathetic stimulation was achieved through intracerebroventricular injection of l-glutamate in animals submitted to 35 min of coronary occlusion followed by 120 min of reperfusion. Rabbits received naloxone HCl intracerebroventricularly or naloxone methiodide IV, a quaternary compound that does not cross the blood-brain barrier, 5 min before FENT treatment (5 or 50 microg/kg, IV).

RESULTS

Infarct area was reduced only by FENT 50 (from 51% +/- 2% to 24% +/- 2%). This protective effect was abolished by peripheral (42% +/- 4%), but not central, OR blockade (32% +/- 3%). The number of premature ventricular complexes during the ischemic period (54 +/- 3) was reduced by FENT 50 (19 +/- 7), an effect blunted by central (40 +/- 3) but not peripheral (18 +/- 7) blockade of OR. During reperfusion, the number of premature ventricular complexes (134 +/- 50) was reduced to 9 +/- 5 by FENT 50 and was prevented by central (42 +/- 4) as well as peripheral (20 +/- 11) OR blockade. The mortality rate (50%) and incidence of ventricular tachycardia (55%) were completely abolished by FENT 50.

CONCLUSIONS

We conclude that fentanyl's effects for limiting myocardial ischemic injury are mediated via peripheral ORs while opioid's antiarrhythmic actions are mediated via central OR agonism.

Heparin-induced transient prolongation of the QT interval during endovascular embolisation of intracranial aneurysm

Prolonged QT interval and increased QT(C) dispersion have been described immediately following rupture of intracranial aneurysm, due to increased sympathetic activity. Here, we report a patient with transient prolongation of the QT interval, probably due to heparin-induced hypocalcaemia, which occurred during coiling of a right internal carotid aneurysm, 54 days after ictus. Correction of the hypocalcaemia led to resolution of the electrocardiogram and blood pressure abnormalities.

Conscious sedation with intermittent midazolam and fentanyl in electrophysiology procedures

OBJECTIVES

To determine the safety and efficacy of intermittent midazolam and fentanyl conscious sedation for electrophysiology procedures (EP).

BACKGROUND

Intermittent midazolam and fentanyl conscious sedation was administered in 700 consecutive cases (175 radiofrequency ablations, 163 EP studies, 261 pacemakers, and 101 implantable cardioverter-defibrillators) for 471 patients (239 males, 51%) mean age 65 +/- 15 years. The mean dose of midazolam was 0.063 mg/kg/hr and fentanyl was 0.591 microgram/kg/hr.

METHODS

Cardiac rate and rhythm were monitored continuously, while blood pressure and arterial oxygen saturation were noninvasively assessed every 5 minutes. Drugs were administered in aliquots of 0.5 to 2.0 mg of midazolam and 6.25 to 25 micrograms of fentanyl as determined by clinical condition every 15 to 30 minutes.

RESULTS

There were no deaths. In no case was endotracheal intubation required. Mild hypoxemia (SaO2 > 80%, but < 90%) occurred in 17 cases (2.4%) and was easily reversed with verbal stimulation and oropharyngeal repositioning (12 cases, 1.7%), increased F1O2 (3 cases, 0.4%), or intravenous naloxone (2 cases, 0.3%). Reversible hypotension (systolic blood pressure < 90, but > 60 mmHg) occurred in 14 patients (2.0%) and was corrected with intravenous crystalloid bolus or flumazenil (10 cases, 1.4%) or inotrope infusion (4 cases, 0.6%). No patient stay was prolonged due to sedation. Only five patients (0.7%) had any recollection of the procedure, while two (0.3%) were aware of pain. All hypoxemic episodes occurred during the first hour, whereas 43% (6/14) of hypotensive episodes occurred after the first hour.

CONCLUSION

Conscious sedation with intermittent midazolam and fentanyl is safe and efficacious for a broad range of EP procedures.

Phenylephrine increases T wave shock energy required to induce ventricular fibrillation

INTRODUCTION

Previous reports in experimental models have suggested that ventricular fibrillation threshold (VFT) can be changed by manipulating cardiac neural tone using agents such as phenylephrine. The purpose of this study was to determine whether phenylephrine increased the energy required to induce VF in humans undergoing such induction using DC energy applied to the T wave.

METHODS AND RESULTS

In this prospective investigation, 18 consecutive patients with previously implanted cardioverter defibrillators had induction of VF by placing DC monophasic shocks into the T wave coupled 310 msec after the eighth paced ventricular complex at 400 msec. The T wave shock energy was titrated from 0.2 to 12 J until sustained VF or ventricular tachycardia was induced. Phenylephrine was infused either before the first or second VF induction in a randomized fashion to increase systolic blood pressure by more than 20 mmHg. The mean energy required to induce VF was 1.1 J at baseline and increased to 1.7 J during phenylephrine infusion (P = 0.036). The mean arterial pressure increased from 88 to 114 mmHg (P < 0.001), and the mean sinus cycle length increased from 850 to 1070 msec (P < 0.001). Ten of 13 (77%) patients with sinus cycle length prolongation had increased energy requirements to induce VF compared with only 1 of 5 patients (20%) without sinus cycle length prolongation (P < 0.05).

CONCLUSION

Phenylephrine increases VFT in humans presumably by reflex activation of the baroreceptors decreasing sympathetic and/or increasing parasympathetic cardiac efferent effects.

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.

Lack of arrhythmogenicity of aminophylline in dogs

This study was designed to determine if doses of aminophylline up to 10 mg/kg given i.v. would produce ventricular arrhythmias in seven healthy dogs anaesthetized with fentanyl-droperidol-pentobarbital. Arrhythmias were sought by inspection of ECGs before and after attempts at provoking them with 5 micrograms/kg boluses of epinephrine given i.v., or by programmed electrical stimulation. After cumulative doses of 10 mg aminophylline/kg body weight, producing an estimated plasma concentration of greater than 30 micrograms/ml, no ventricular ectopia other than escape depolarizations were observed. We were unable to document an arrhythmogenic effect of aminophylline when given rapidly by the i.v. route. It is possible that the anaesthetic regimen reduced the arrhythmogenic property of aminophylline, or that arrhythmias might be produced in either obese or ill dogs; but it is unlikely that chronic administration of aminophylline would be more arrhythmogenic.

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.

The calcium antagonist diltiazem has antiarrhythmic effects which are mediated in the brain through endogenous opioids

The purpose of this study was to examine the hypothesis that the calcium channel blocker, diltiazem, modulates catecholamine-induced arrhythmias through CNS mechanisms. Rats, that had catheters previously inserted into the lateral cerebral ventricle and femoral artery, received diltiazem, 10 or 50 micrograms/kg or the diluent, into the lateral cerebral ventricle (i.c.v.). Epinephrine was infused to produce arrhythmias. The onset of ventricular arrhythmias, premature ventricular complexes, occurred at a significantly (P less than 0.05) greater dose of epinephrine, after diltiazem, compared to the control group and in a dose-dependent manner, with the mean (+/- 1 SEM) dose of epinephrine being 198 +/- 5, 175 +/- 13 and 115 +/- 15 micrograms/kg in the groups treated with 50 and 10 micrograms/kg of diltiazem and the control groups, respectively. The development of fatal arrhythmias, mainly ventricular tachyarrhythmias, occurred at significantly (P less than 0.05) greater concentrations of epinephrine with diltiazem, 50 and 10 micrograms/kg, 225 +/- 5 and 183 +/- 13 micrograms/kg, respectively, compared to controls, 131 +/- 15 micrograms/kg. Endogenous opioids of the mu-type were implicated in this action of diltiazem, because the mu opioid antagonist naloxone, 1 mg/kg (i.v.), significantly (P less than 0.05) antagonized the antiarrhythmic effects of centrally administered diltiazem and the mu opioid agonist DAGO (i.c.v.), did not further enhance the suppression of epinephrine-induced arrhythmias, produced by diltiazem, 50 micrograms/kg. Atropine sulfate, which crosses the blood-brain barrier and atropine methylnitrate, which does not enter the brain, each at 1 mg/kg (i.v.), produced an equal and significant antagonism of the effect of diltiazem, 50 micrograms/kg, that was less than that of naloxone. The combination of naloxone plus atropine sulfate completely prevented the effect of diltiazem, 50 micrograms/kg, on arrhythmias. The antiarrythmic action of diltiazem could not be explained by alteration of the blood pressure or heart rate response to epinephrine. The results suggest that: (a) calcium channels on neurons in the CNS play an important role in the modulation of epinephrine-induced cardiac arrhythmias, (b) diltiazem can suppress arrhythmias through CNS mechanisms, (c) activation of the parasympathetic nervous system mediates some of the effect of diltiazem, but (d) the mechanism of action of diltiazem is modulated through endogenous opioids.

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.

The neuroanatomy, neurophysiology, and neurochemistry of pain, stress, and analgesia in newborns and children

Beginning with a brief description of mature anatomic pathways and neurotransmitters in the "pain system," this article details their development in the human fetus, neonate, and child. Special emphasis is given to the basic mechanisms and physiologic effects of opioid analgesia. The clinical implications of these data are described, particularly with regard to the maintenance of cardiovascular stability and hormonal-metabolic homeostasis in newborns and children undergoing surgery or other forms of stress.