Epinephrine-induced changes in serum potassium and cardiac repolarization and effects of pretreatment with propranolol and diltiazem

Cold pressor stress effects on cardiac repolarization

The cold pressor test (CPT) elicits strong cardiovascular reactions via activation of the sympathetic nervous system (SNS), yielding subsequent increases in heart rate (HR) and blood pressure (BP). However, little is known on how exposure to the CPT affects cardiac ventricular repolarization. Twenty-eight healthy males underwent both a bilateral feet CPT and a warm water (WW) control condition on two separate days, one week apart. During pre-stress baseline and stress induction cardiovascular signals (ECG lead II, Finometer BP) were monitored continuously. Salivary cortisol and subjective stress ratings were assessed intermittently. Corrected QT (QTc) interval length and T-wave amplitude (TWA) were assessed for each heartbeat and subsequently aggregated individually over baseline and stress phases, respectively. CPT increases QTc interval length and elevates the TWA. Stress-induced changes in cardiac repolarization are only in part and weakly correlated with cardiovascular and cortisol stress-reactivity. Besides its already well-established effects on cardiovascular, endocrine, and subjective responses, CPT also impacts on cardiac repolarization by elongation of QTc interval length and elevation of TWA. CPT effects on cardiac repolarization share little variance with the other indices of stress reactivity, suggesting a potentially incremental value of this parameter for understanding psychobiological adaptation to acute CPT stress.

Comparison of TWA and PEP as indices of α2- and ß-adrenergic activation

RATIONALE

Pre-ejection period (PEP) and T-wave amplitude (TWA) have been used to assess sympathetic nervous system (SNS) activity. Here we report two single-blinded, placebo-controlled intravenous (IV) drug application studies in which we pharmacologically modified SNS activity with epinephrine (study 1) as well as dexmedetomidine (alpha2-agonist) and yohimbine (alpha2-antagonist) (study 2). Restricted heart rate (HR) intervals were analyzed to avoid confounding effects of HR changes.

OBJECTIVE

Study 1 served to replicate previous findings and to validate our approach, whereas study 2 aimed to investigate how modulation of central SNS activity affects PEP and TWA.

METHODS

Forty healthy volunteers (58% females) participated in study 1 (between-subject design). Twelve healthy men participated in study 2 (within-subject design). TWA and PEP were derived from ECG and impedance cardiography, respectively.

RESULTS

Epinephrine shortened PEP and induced statistically significant biphasic TWA changes. However, although the two alpha2-drugs significantly affected PEP as expected, no effects on TWA could be detected.

CONCLUSION

PEP is better suited to reflect SNS activity changes than TWA.

Hypokalemic Cardiac Arrest: Narrative Review of Case Reports and Current State of Science

PURPOSE

Hypokalemic cardiac arrest is an uncommon occurrence in the emergency department. Electrocardiogram findings related to hypokalemic cardiac arrest include prolonged QT, U waves, and preventricular contractions leading to Torsades de Pointes and then arrest. Literature evaluating the prevalence of hypokalemic cardiac arrest is scarce, and its management is lacking. This review provides a summary of current literature, recommendations from current guidelines, and proposed management strategies of hypokalemic cardiac arrest.

SUMMARY

Intravenous potassium administration is the treatment for hypokalemic cardiac arrest. Although the treatment for hypokalemic cardiac arrest is known, there is limited evidence on the proper procedure for administering intravenous potassium appropriately and safely. Owing to the time-sensitive nature of treating hypokalemic cardiac arrest, rapid administration of intravenous potassium (10 mEq/100 mL of potassium chloride over 5 minutes) is warranted. Concerns regarding rapid potassium administration are not without merit; however, a risk-benefit analysis and potential mitigation strategies for unwanted side effects need to be considered if hypokalemic cardiac arrest is to remain a reversible cause. It is imperative to identify hypokalemia as the cause for arrest as soon as possible and administer potassium before systemic acidosis, ischemia, and irreversible cell death.

CONCLUSIONS

More evidence is necessary to support treatment recommendations for hypokalemic cardiac arrest; however, it is the authors' opinion that, if identified early during cardiac arrest, intravenous potassium should be administered to treat a reversible cause for cardiac arrest.

Stress and the "extended" autonomic system

This review updates three key concepts of autonomic neuroscience-stress, the autonomic nervous system (ANS), and homeostasis. Hans Selye popularized stress as a scientific idea. He defined stress variously as a stereotyped response pattern, a state that evokes this pattern, or a stimulus that evokes the state. According to the "homeostat" theory stress is a condition where a comparator senses a discrepancy between sensed afferent input and a response algorithm, the integrated error signal eliciting specific patterns of altered effector outflows. Scientific advances since Langley's definition of the ANS have incited the proposal here of the "extended autonomic system," or EAS, for three reasons. (1) Several neuroendocrine systems are bound inextricably to Langley's ANS. The first to be described, by Cannon in the early 1900s, involves the hormone adrenaline, the main effector chemical of the sympathetic adrenergic system. Other neuroendocrine systems are the hypothalamic-pituitary-adrenocortical system, the arginine vasopressin system, and the renin-angiotensin-aldosterone system. (2) An evolving body of research links the ANS complexly with inflammatory/immune systems, including vagal anti-inflammatory and catecholamine-related inflammasomal components. (3) A hierarchical network of brain centers (the central autonomic network, CAN) regulates ANS outflows. Embedded within the CAN is the central stress system conceptualized by Chrousos and Gold. According to the allostasis concept, homeostatic input-output curves can be altered in an anticipatory, feed-forward manner; and prolonged or inappropriate allostatic adjustments increase wear-and-tear (allostatic load), resulting in chronic, stress-related, multi-system disorders. This review concludes with sections on clinical and therapeutic implications of the updated concepts offered here.

Cardiovascular crisis after use of epinephrine: a case report and review of the literature

Diluted epinephrine is often locally used to provide hemostasis and improve visualization. However, rapid absorption or inadvertent intravascular injection of epinephrine can cause unexpected cardiovascular effects. A 28-year-old man was scheduled to undergo a nasal septoplasty. After local application of 0.01% epinephrine-soaked nasal pledgets and infiltration of 3 mL 0.001% epinephrine, the patient developed a severe hypertension of 205/126 mmHg, followed by ventricular tachycardia. Cardiac arrest ensued after intravenous injection of lidocaine and esmolol in an attempt to control ventricular arrhythmia. After successful resuscitation, the patient was transferred to the intensive care unit (ICU) and fully recovered in 5 days. While another two epinephrine-induced hypertension cases were treated smoothly without β-blockers. Although the plausible explanation of this precipitating event is the usage of β-blocker, we reviewed the previous published similar clinical reports and proposed other possible explanations and differential diagnosis. It is important to recognize this potential cardiovascular side-effect in patients administrated with topical and/or submucosal epinephrine. Drugs used to treat hypertension and/or arrhythmia needed to be appreciated.

Hydroelectrolytic Disorder in COVID-19 patients: Evidence Supporting the Involvement of Subfornical Organ and Paraventricular Nucleus of the Hypothalamus

Multiple neurological problems have been reported in coronavirus disease-2019 (COVID-19) patients because severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) likely spreads to the central nervous system (CNS) via olfactory nerves or through the subarachnoid space along olfactory nerves into the brain's cerebrospinal fluid and then into the brain's interstitial space. We hypothesize that SARS-CoV-2 enters the subfornical organ (SFO) through the above routes and the circulating blood since circumventricular organs (CVOs) such as the SFO lack the blood-brain barrier, and infection of the SFO causes dysfunction of the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON), leading to hydroelectrolytic disorder. SARS-CoV-2 can readily enter SFO-PVN-SON neurons because these neurons express angiotensin-converting enzyme-2 receptors and proteolytic viral activators, which likely leads to neurodegeneration or neuroinflammation in these regions. Considering the pivotal role of SFO-PVN-SON circuitry in modulating hydroelectrolyte balance, SARS-CoV-2 infection in these regions could disrupt the neuroendocrine control of hydromineral homeostasis. This review proposes mechanisms by which SARS-CoV-2 infection of the SFO-PVN-SON pathway leads to hydroelectrolytic disorder in COVID-19 patients.

The extended autonomic system, dyshomeostasis, and COVID-19

The pandemic viral illness COVID-19 is especially life-threatening in the elderly and in those with any of a variety of chronic medical conditions. This essay explores the possibility that the heightened risk may involve activation of the “extended autonomic system” (EAS). Traditionally, the autonomic nervous system has been viewed as consisting of the sympathetic nervous system, the parasympathetic nervous system, and the enteric nervous system. Over the past century, however, neuroendocrine and neuroimmune systems have come to the fore, justifying expansion of the meaning of “autonomic.” Additional facets include the sympathetic adrenergic system, for which adrenaline is the key effector; the hypothalamic-pituitary-adrenocortical axis; arginine vasopressin (synonymous with anti-diuretic hormone); the renin-angiotensin-aldosterone system, with angiotensin II and aldosterone the main effectors; and cholinergic anti-inflammatory and sympathetic inflammasomal pathways. A hierarchical brain network—the “central autonomic network”—regulates these systems; embedded within it are components of the Chrousos/Gold “stress system.” Acute, coordinated alterations in homeostatic settings (allostasis) can be crucial for surviving stressors such as traumatic hemorrhage, asphyxiation, and sepsis, which throughout human evolution have threatened homeostasis; however, intense or long-term EAS activation may cause harm. While required for appropriate responses in emergencies, EAS activation in the setting of chronically decreased homeostatic efficiencies (dyshomeostasis) may reduce thresholds for induction of destabilizing, lethal vicious cycles. Testable hypotheses derived from these concepts are that biomarkers of EAS activation correlate with clinical and pathophysiologic data and predict outcome in COVID-19 and that treatments targeting specific abnormalities identified in individual patients may be beneficial.

Severe iatrogenic hypoglycaemia requiring medical assistance is associated with concurrent prolongation of the QTc interval

AIMS

Hypoglycaemia has been shown to exert arrhythmogenic effects. Herein, we explore the association between severe hypoglycaemia requiring medical assistance and the length of the QT interval in patients with diabetes.

METHODS

Data from a prospective study, conducted in eight tertiary hospitals, which recorded cases of hypoglycaemia from patients with diabetes seeking treatment at emergency departments (ED) were analyzed. The patients' electrocardiograms (ECGs), were compared to those of non-hypoglycaemic diabetic individuals, matched for age, gender and duration of diabetes, obtained during their scheduled follow-up visits. The corrected QT intervals (QTc) were calculated blindly by two cardiologists.

RESULTS

ECGs from 154 patients presenting with hypoglycaemia were analyzed and compared to 95 matched controls. The mean QTc interval was significantly longer in patients with hypoglycaemia than in controls (441.9 ± 48.2 vs. 401.0 ± 29.6 ms, p < 0.001) A significantly higher proportion of hypoglycaemic patients had an abnormally prolonged QTc (≥440 ms) compared to controls (49.4% vs. 11.6%, p < 0.001). Among patients with hypoglycaemia, there was a statistically significant but rather weak negative correlation between QTc interval and plasma glucose at presentation (r: -0.183, p = 0.02).

CONCLUSIONS

In diabetic patients, hypoglycemia requiring medical assistance is associated with a significant prolongation of the QTc interval. The degree of this prolongation is associated with hypoglycaemia severity.

The effects of diltiazem and metoprolol in QTc prolongation due to amitriptyline intoxication

Background and objective:

Amitriptyline, a frequently used tricyclic antidepressant agent, has powerful cardiotoxic effects especially in high doses. Serum and urine levels of amitriptyline dosages are not correlated with severity of toxicity; therefore, it increases the importance of electrocardiography (ECG) abnormalities. The prolongation of QTc can be a predictive marker for cardiotoxicity. Hence, in this study, it is aimed to evaluate possible effects of metoprolol and diltiazem in amitriptyline toxicity.

Materials and methods:

The rats were separated into four groups. First one was control group, the second was the amitriptyline + saline group, third one was the amitriptyline + metoprolol group, and forth one was the amitriptyline + diltiazem group. ECG were recorded on rats under anesthesia.

Results:

In amitriptyline group, QTc duration was prolonged compared with all other groups. The prolongation of QTc was shorter in amitriptyline + metoprolol group and amitriptyline + diltiazem group than amitriptyline group ( p < 0.01 and p < 0.01, respectively).

Conclusion:

According to the results, it is possible to report ameliorating effects of both metoprolol and diltiazem on QTc prolongation related with amitriptyline intoxication. With further studies, these agents may be used for amitriptyline toxicity and besides, they may be used for patients in cardiovascular risk groups who take amitriptyline treatment regularly.

The value of adrenaline in the induction of supraventricular tachycardia in the electrophysiological laboratory

AIMS

The most commonly used drug for the facilitation of supraventricular tachycardia (SVT) induction in the electrophysiological (EP) laboratory is isoprenaline. Despite isoprenaline's apparent indispensability, availability has been problematic in some European countries. Alternative sympatomimethic drugs such as adrenaline have therefore been tried. However, no studies have determined the sensitivity and specificity of adrenaline for the induction of SVT. The objective of this study was to determine the sensitivity and specificity of adrenaline for the induction of SVT.

METHODS AND RESULTS

Between February 2010 and July 2013, 336 patients underwent an EP study for prior documented SVT. In 66 patients, adrenaline was infused because tachycardia was not induced under basal conditions. This group was compared with 30 control subjects with no history of SVT. Programmed atrial stimulation was carried out during baseline state and repeated after an infusion of adrenaline (dose ranging from 0.05 mcg/kgc to 0.3 mcg/kgc). The endpoint was the induction of SVT. Among 66 patients with a history of SVT but no induction under basal conditions, adrenaline facilitated induction in 54 patients (82%, P < 0.001). Among the 30 control subjects, SVT was not induced in any patient (0%) after infusion. Adrenaline was generally well tolerated, except for two patients (3.0%), where it had to be discontinued due to headache and high blood pressure or lumbar pain.

CONCLUSION

Adrenaline infusion has a high sensitivity (82%) and specificity (100%) for the induction of SVT in patients with prior documented SVT. Therefore, it could serve as an acceptable alternative to isoprenaline, when the latter is not available.

Prevention of Pazopanib-Induced Prolonged Cardiac Repolarization and Proarrhythmic Effects

Background

Pazopanib (PZP) may induce prolonged cardiac repolarization and proarrhythmic effects, similarly to other tyrosine kinase inhibitors.

Objectives

To demonstrate PZP-induced prolonged cardiac repolarization and proarrhythmic electrophysiological effects and to investigate possible preventive effects of metoprolol and diltiazem on ECG changes (prolonged QT) in an experimental rat model.

Methods

Twenty-four Sprague-Dawley adult male rats were randomly assigned to 4 groups (n = 6). The first group (normal group) received 4 mL of tap water and the other groups received 100 mg/kg of PZP (Votrient^® tablet) perorally, via orogastric tubes. After 3 hours, the following solutions were intraperitoneally administered to the animals: physiological saline solution (SP), to the normal group and to the second group (control-PZP+SP group); 1 mg/kg metoprolol (Beloc, Ampule, AstraZeneca), to the third group (PZP+metoprolol group); and 1mg/kg diltiazem (Diltiazem, Mustafa Nevzat), to the fourth group (PZP+diltiazem group). One hour after, and under anesthesia, QTc was calculated by recording ECG on lead I.

Results

The mean QTc interval values were as follows: normal group, 99.93 ± 3.62 ms; control-PZP+SP group, 131.23 ± 12.21 ms; PZP+metoprolol group, 89.36 ± 3.61 ms; and PZP+diltiazem group, 88.86 ± 4.04 ms. Both PZP+metoprolol and PZP+diltiazem groups had significantly shorter QTc intervals compared to the control-PZP+SP group (p < 0.001).

Conclusion

Both metoprolol and diltiazem prevented PZP-induced QT interval prolongation. These drugs may provide a promising prophylactic strategy for the prolonged QTc interval associated with tyrosine kinase inhibitor use.

Cation interdependency in acute stressor states

Acute stressor states are inextricably linked to neurohormonal activation which includes the adrenergic nervous system. Consequent elevations in circulating epinephrine and norepinephrine unmask an interdependency that exists between K+, Mg2+ and Ca2+. Catecholamines, for example, regulate the large number of Mg2+-dependent Na/K ATPase pumps present in skeletal muscle. A hyperadrenergic state accounts for a sudden translocation of K+ into muscle and rapid appearance of hypokalemia. In the myocardium, catecholamines promote Mg2+ efflux from cardiomyocytes, whereas intracellular Ca2+ influx and overloading account for the induction of oxidative stress and necrosis of these cells with leakage of their contents, including troponins. Accordingly, acute stressor states can be accompanied by nonischemic elevations in serum troponins, together with the concordant appearance of hypokalemia, hypomagnesemia and ionized hypocalcemia, causing a delay in myocardial repolarization and electrocardiographic QTc prolongation raising the propensity for arrhythmias, including atrial fibrillation and polymorphic ventricular tachycardia. In this review, we focus on the interdependency between K+, Mg2+ and Ca2+ which are clinically relevant to acute stressor states.

Neurocardiology: therapeutic implications for cardiovascular disease

The term "neurocardiology" refers to physiologic and pathophysiological interplays of the nervous and cardiovascular systems. This selective review provides an update about cardiovascular therapeutic implications of neurocardiology, with emphasis on disorders involving primary or secondary abnormalities of catecholamine systems. Concepts of scientific integrative medicine help understand these disorders. Scientific integrative medicine is not a treatment method or discipline but a way of thinking that applies systems concepts to acute and chronic disorders of regulation. Some of these concepts include stability by negative feedback regulation, multiple effectors, effector sharing, instability by positive feedback loops, allostasis, and allostatic load. Scientific integrative medicine builds on systems biology but is also distinct in several ways. A large variety of drugs and non-drug treatments are now available or under study for neurocardiologic disorders in which catecholamine systems are hyperfunctional or hypofunctional. The future of therapeutics in neurocardiology is not so much in new curative drugs as in applying scientific integrative medical ideas that take into account concurrent chronic degenerative disorders and interactions of multiple drug and non-drug treatments with each other and with those disorders.

Miliaria rubra and thrombocytosis in pseudohypoaldosteronism: case report

Pseudohypoaldosteronism type 1 (PHA1) is a disease involving a state of renal tubular unresponsiveness to the action of aldosterone and characterized by excessive salt loss in the urine, hyperkalemia, and metabolic acidosis. In kidney, PHA1 may occur primarily by mutations in the subunits of the sodium channel or in the mineralocorticoid receptors, and secondarily by several renal disorders. Miliaria rubra and thrombocytosis are reported in a 6-month-old girl with PHA1. In patients with PHA1, miliaria rubra-like cutaneous eruptions are suggested to occur due to obstruction of eccrine sweat glands through inflammation caused by excessive sodium excretion in sweat during hyponatremic crises. The presence of thrombocytosis in patients with PHA1 has not been previously reported. A hypothesis is proposed suggesting that sympathetic activation which provides vascular tonus during sodium excretion in sweat and salt-depletion crisis may play a role in the development of eruptions and thrombocytosis in patients with PHA1.

Epinephrine bolus test in detecting long QT syndrome mutation carriers with indeterminable electrocardiographic phenotype

BACKGROUND

In long QT syndrome (LQTS), prolonged and heterogeneous ventricular repolarization predisposes to serious arrhythmias. We examined how QT intervals are modified by epinephrine bolus in mutation carriers of three major LQTS subtypes with indefinite QT interval.

METHODS

Genotyped, asymptomatic subjects with LQTS type 1 (LQT1; n = 10; four different KCNQ1 mutations), type 2 (LQT2; n = 10; three different HERG mutations), and type 3 (LQT3; n = 10; four different SCN5A mutations), and healthy volunteers (n = 15) were examined. Electrocardiogram was recorded with body surface potential mapping system. After an epinephrine 0.04 μg/kg bolus QT end, QT apex, and T-wave peak-to-end (Tpe) intervals were determined automatically as average of 12 precordial leads. Standard deviation (SD) of the 12 channels was calculated.

RESULTS

Heart rate increased 26 ± 10 bpm with epinephrine bolus, and similarly in all groups. QT end interval lengthened, and QT apex interval shortened in LQTS and normals, leading to lengthening of Tpe interval. However, the lengthening in Tpe was larger in LQTS than in normals (mean 32 vs 18 ms; P < 0.05) and SD of QT apex increased more in LQTS than in normals (mean 23 vs 7 ms; P < 0.01). The increase in Tpe was most pronounced in LQT2, and in SD of QT apex in LQT1 and LQT2.

CONCLUSIONS

Abrupt adrenergic stimulation with a moderate dose of exogenous epinephrine affects ventricular repolarization in genotype-specific fashion facilitating distinction from normals. This delicate modification may help in diagnosing electrocardiographically silent mutation carriers when screening LQTS family members.

The effect of patient-controlled intravenous analgesia on postoperative hypokalemia in patients undergoing laparoscopic cholecystectomy

PURPOSE

We investigated whether hypokalemia developed during the postoperative period and whether the use of intravenous patient-controlled analgesia (IV-PCA) could decrease the incidence of postoperative hypokalemia in patients who underwent laparoscopic cholecystectomy.

METHODS

Sixty patients undergoing laparoscopic cholecystectomy were randomly assigned to either IV-PCA (n = 30) or control (n = 30) groups. We measured serum potassium concentration at the outpatient department (T1), at 8:00 a.m. on the day of surgery (T2), at 6 h after the end of surgery (T3), and at 8:00 a.m. on the first (T4), second (T5), and third (T6) postoperative days. Serum potassium concentration, incidence of hypokalemia, mean blood pressure, heart rate, respiratory rate, and the patient-reported visual analogue scale score were compared within each group and between groups at each time point.

RESULTS

Serum potassium concentrations in all patients showed a significant decrease at T2-T4 compared to the preoperative concentration (T1). Serum potassium concentrations at T3 and T4 in the IV-PCA group were significantly higher than those in the control group. Also, the incidence of hypokalemia at T3 and T4 was significantly lower in the IV-PCA group. Mean blood pressure and heart rate were significantly lower in the IV-PCA group than in controls at T3 and T4.

CONCLUSIONS

The results show that hypokalemia developed during the perioperative period and the use of IV-PCA in patients undergoing laparoscopic cholecystectomy effectively decreased the degree and incidence of postoperative hypokalemia on the day of the operation and postoperative day one.

The case for hypoglycaemia as a proarrhythmic event: basic and clinical evidence

Recent clinical studies show that hypoglycaemia is associated with increased risk of death, especially in patients with coronary artery disease or acute myocardial infarction. This paper reviews data from cellular and clinical research supporting the hypothesis that acute hypoglycaemia increases the risk of malignant ventricular arrhythmias and death in patients with diabetes by generating the two classic abnormalities responsible for the proarrhythmic effect of medications, i.e. QT prolongation and Ca(2+) overload. Acute hypoglycaemia causes QT prolongation and the risk of ventricular tachycardia by directly suppressing K(+) currents activated during repolarisation, a proarrhythmic effect of many medications. Since diabetes itself, myocardial infarction, hypertrophy, autonomic neuropathy and congestive heart failure also cause QT prolongation, the arrhythmogenic effect of hypoglycaemia is likely to be greatest in patients with pre-existent cardiac disease and diabetes. Furthermore, the catecholamine surge during hypoglycaemia raises intracellular Ca(2+), thereby increasing the risk of ventricular tachycardia and fibrillation by the same mechanism as that activated by sympathomimetic inotropic agents and digoxin. Diabetes itself may sensitise myocardium to the arrhythmogenic effect of Ca(2+) overload. In humans, noradrenaline (norepinephrine) also lengthens action potential duration and causes further QT prolongation. Finally, both hypoglycaemia and the catecholamine response acutely lower serum K(+), which leads to QT prolongation and Ca(2+) loading. Thus, hypoglycaemia and the subsequent catecholamine surge provoke multiple, interactive, synergistic responses that are known to be proarrhythmic when associated with medications and other electrolyte abnormalities. Patients with diabetes and pre-existing cardiac disease may therefore have increased risk of ventricular tachycardia and fibrillation during hypoglycaemic episodes.

Micellar liquid chromatographic determination of five antianginals in pharmaceuticals

A procedure was developed for the determination of five antianginals (diltiazem, nadolol, nifedipine, propranolol and verapamil), using hybrid micellar mobile phases of sodium dodecyl sulphate (SDS) and pentanol, a C18 column and UV detection. All possible combinations of antianginals were resolved and determined using a mobile phase of 0.05 M SDS-5% pentanol with an analysis time of 9 min. Repeatabilities and intermediate precision were evaluated at four different drug concentrations in the 2-20 microg/ml (n=5) range. Limits of detection were in the range 0.028 microg/ml for diltiazem and 0.130 microg/ml for verapamil. The range of the limit of quantitation was from 0.092 to 0.431 microg/ml for the same compounds. Antianginal drugs were studied in pharmaceuticals with no interference from related compounds. The results of the analyses of pharmaceuticals formulations were in agreement with the declared compositions.

Absence of QTc-Interval-Prolonging or Hemodynamic Effects of a Single Dose of Bitter-Orange Extract in Healthy Subjects

STUDY OBJECTIVE

To evaluate the hemodynamic and electrocardiographic effects of a single dose of commercially available bitter-orange dried-fruit extract, which is increasingly being used in dietary supplements.

DESIGN

Randomized, double-blind, placebo-controlled, crossover study.

SETTING

University of Connecticut, Storrs Campus.

SUBJECTS

Eighteen healthy volunteers aged 18 years or older.

INTERVENTION

Subjects were given either placebo or bitter-orange dried-fruit extract (450 mg standardized to 27 mg of m- or p-synephrine) in phase 1. The opposite treatment was given during phase 2 after a washout period of at least 7 days.

MEASUREMENTS AND MAIN RESULTS

The rate-corrected QT (QTc) interval and blood pressure were measured before dosing and at 1, 3, 5, and 8 hours after dosing. Mean+/-SD values of the maximum postdose values were compared between groups. Subjects receiving bitter-orange extract versus those receiving placebo had similar postdose QTc intervals (402+/-29 vs 403+/-24 msec, p=0.653), systolic blood pressure (114+/-10 vs 115+/-8 mm Hg, p=0.686) and diastolic blood pressure (68+/-9 vs 68+/-8, p=0.879).

CONCLUSION

Bitter-orange dried-fruit extract standardized to m- or p-synephrine 27 mg did not significantly alter the QTc interval or blood pressure after a single dose was administered. Future studies are necessary to ensure the safety of this herbal product with multiple doses.

Critical differences among beta-adrenoreceptor antagonists in myocardial failure: debating the MERIT of COMET

In the United States, carvedilol and metoprolol (tartrate or succinate) are the most commonly employed beta-adrenoreceptor antagonists for the treatment of heart failure. However, use of these agents in patients with heart failure remains extremely low despite overwhelming evidence of their beneficial short- and long-term effects. Because the myocardial pathophysiology associated with heart failure involves not only beta-1 adrenoreceptors but also beta-2 and alpha-1 adrenoreceptors, this indicates a more complex disease process that may require pan-receptor antagonism to provide optimal clinical benefit. Relative to metoprolol (tartrate or succinate), carvedilol represents an extremely complex molecular entity that not only possesses the ability to antagonize all of the principle adrenoreceptors involved in heart failure but also reduces oxidative stress and provides an antiarrhythmic benefit independent of beta-adrenoreceptor antagonism. Taken together, an interesting pharmacologic premise for the superiority of carvedilol relative to metoprolol (tartrate) may exist, but the lack of clinical trials comparing an optimal dose of either extended-release metoprolol (ie, succinate) or immediate-release metoprolol (ie, tartrate) to carvedilol limits the clinical application of the pharmacologic differences between the agents.

Gender disparities in serum electrolytes levels after subarachnoid hemorrhage

We retrospectively studied 133 patients with subarachnoid hemorrhage (SAH) to assess whether there was any gender disparity in serum electrolytes levels throughout the clinical course. Serum concentrations of sodium and potassium were measured in all patients, while catecholamines or antidiuretic hormone were assessed in a number of cases. Female SAH-patients had lower potassium level (3.29 +/- 0.47 mEq/L) than did male patients (3.68 +/-0.38) on the first day of SAH. This gender disparity continued to the beginning of the chronic phase and disappeared several months later. Mean serum sodium level was lower in the male group than in the female group throughout the clinical course. Mean serum levels of adrenaline and antidiuretic hormone were characterized by their prominent high value on the first day. Serum potassium levels were inversely related to serum levels of catecholamines, especially adrenaline, during the acute and subacute phases, particularly on the first day.

Experimental hyperkalaemia in rabbits: effects of salbutamol and norepinephrine treatments on blood biochemistry and electrocardiography

The effects of salbutamol and norepinephrine on the electrocardiogram (ECG), serum potassium level and enzyme activities were studied in rabbits with hyperkalaemia; norepinephrine and salbutamol may be therapeutically useful. For induction of hyperkalaemia, 300 mM KCl solution was used and then isotonic saline solution containing 6 microg salbutamol and 3.9 microg norepinephrine per ml were administered. Norepinephrine and salbutamol decreased the serum potassium from 7.36 +/- 0.26 and 7.21 +/- 0.31 mmol/L to 5.62 +/- 0.27 and 4.35 +/- 0.33 mmol/L, respectively, and caused the ECG changes (flatness of P wave, widening of QRS complex and bradycardia) to return to the control conditions (time 0). Norepinephrine, but not salbutamol, decreased the activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) to the control levels. These results suggest that monitoring of the enzyme activities might be useful as it yields indexes suitable for evaluating the therapeutic approach with norepinephrine in hyperkalaemia.

Epinephrine unmasks latent mutation carriers with LQT1 form of congenital long-QT syndrome

OBJECTIVES

This study was designed to test the hypothesis that epinephrine infusion may be a provocative test able to unmask nonpenetrant KCNQ1 mutation carriers.

BACKGROUND

The LQT1 form of congenital long QT syndrome is associated with high vulnerability to sympathetic stimulation and appears with incomplete penetrance.

METHODS

The 12-lead electrocardiographic parameters before and after epinephrine infusion were compared among 19 mutation carriers with a baseline corrected QT interval (QTc) of > or =460 ms (Group I), 15 mutation carriers with a QTc of <460 ms (Group II), 12 nonmutation carriers (Group III), and 15 controls (Group IV).

RESULTS

The mean corrected Q-Tend (QTce), Q-Tpeak (QTcp), and Tpeak-end (Tcp-e) intervals among 12-leads before epinephrine were significantly larger in Group I than in the other three groups. Epinephrine (0.1 microg/kg/min) increased significantly the mean QTce, QTcp, Tcp-e, and the dispersion of QTcp in Groups I and II, but not in Groups III and IV. The sensitivity and specificity of QTce measurements to identify mutation carriers were 59% (20/34) and 100% (27/27), respectively, before epinephrine, and the sensitivity was substantially improved to 91% (31/34) without the expense of specificity (100%, 27/27) after epinephrine. The mean QTce, QTcp, and Tcp-e before and after epinephrine were significantly larger in 15 symptomatic than in 19 asymptomatic mutation carriers in Groups I and II, and the prolongation of the mean QTce with epinephrine was significantly larger in symptomatic patients.

CONCLUSIONS

Epinephrine challenge is a powerful test to establish electrocardiographic diagnosis in silent LQT1 mutation carriers, thus allowing implementation of prophylactic measures aimed at reducing sudden cardiac death.

Effects of adrenaline and potassium on QTc interval and QT dispersion in man

BACKGROUND

Hypoglycaemia alters cardiac repolarization acutely, with increases in rate-corrected QT (QTc) interval and QT dispersion (QTd) on the electrocardiogram (ECG); such changes are related to the counterregulatory sympatho-adrenal response. Adrenaline produces both QTc lengthening and a fall in plasma potassium (K+) when infused into healthy volunteers. Hypokalaemia prolongs cardiac repolarization independently however, and therefore our aim was to determine whether adrenaline-induced repolarization changes are mediated directly or through lowered plasma K+.

MATERIALS AND METHODS

Ten healthy males were studied on two occasions. At both visits they received similar l-adrenaline infusions but on one occasion potassium was also administered; infusion rates were adjusted to maintain circulating K+ at baseline. The QTc interval, QTd, peripheral physiological responses and plasma adrenaline and potassium concentrations were measured during both visits.

RESULTS

The QTc interval and QTd increased both with and without potassium clamping. Without K+ replacement, mean (SE) QTc lengthened from 378 (5) ms to a final maximum value of 433 (10) ms, and QTd increased from 36 (5) ms to 69 (8) ms (both P < 0.001). During K+ replacement, QTc duration at baseline and study end was 385 (7) ms and 423 (11) ms, respectively (P < 0.001), and QTd 38 was (4) ms and 63 (5) ms (P = 0.001).

CONCLUSIONS

These data suggest that disturbed cardiac repolarization as a result of increases in circulating adrenaline occurs independently of extracellular potassium. A direct effect of adrenaline upon the myocardium appears the most likely mechanism.

Multivariate analysis of risk factors for QT prolongation following subarachnoid hemorrhage

BACKGROUND

Subarachnoid hemorrhage (SAH) often causes a prolongation of the corrected QT (QTc) interval during the acute phase. The aim of the present study was to examine independent risk factors for QTc prolongation in patients with SAH by means of multivariate analysis.

METHOD

We studied 100 patients who were admitted within 24 hours after onset of SAH. Standard 12-lead electrocardiography (ECG) was performed immediately after admission. QT intervals were measured from the ECG and were corrected for heart rate using the Bazett formula. We measured serum levels of sodium, potassium, calcium, adrenaline (epinephrine), noradrenaline (norepinephrine), dopamine, antidiuretic hormone, and glucose.

RESULTS

The average QTc interval was 466 +/- 46 ms. Patients were categorized into two groups based on the QTc interval, with a cutoff line of 470 ms. Univariate analyses showed significant relations between categories of QTc interval, and sex and serum concentrations of potassium, calcium, or glucose. Multivariate analyses showed that female sex and hypokalemia were independent risk factors for severe QTc prolongation. Hypokalemia (<3.5 mmol/l) was associated with a relative risk of 4.53 for severe QTc prolongation as compared with normokalemia, while the relative risk associated with female sex was 4.45 as compared with male sex. There was a significant inverse correlation between serum potassium levels and QTc intervals among female patients.

CONCLUSION

These findings suggest that female sex and hypokalemia are independent risk factors for severe QTc prolongation in patients with SAH.

Epinephrine-induced QT interval prolongation: a gene-specific paradoxical response in congenital long QT syndrome

OBJECTIVE

To determine the effect of epinephrine on the QT interval in patients with genotyped long QT syndrome (LQTS).

PATIENTS AND METHODS

Between May 1999 and April 2001, 37 patients (24 females) with genotyped LQTS (19 LQT1, 15 LQT2, 3 LQT3, mean age, 27 years; range, 10-53 years) from 21 different kindreds and 27 (16 females) controls (mean age, 31 years; range, 13-45 years) were studied at baseline and during gradually increasing doses of intravenous epinephrine infusion (0.05, 0.1, 0.2, and 0.3 microg x k(-1) x min(-1)). The 12-lead electrocardiogram was monitored continuously, and heart rate, QT, and corrected QT interval (QTc) were measured during each study stage.

RESULTS

There was no significant difference in resting heart rate or chronotropic response to epinephrine between LQTS patients and controls. The mean +/- SD baseline QTc was greater in LQTS patients (500+/-68 ms) than in controls (436+/-19 ms, P<.001). However, 9 (47%) of 19 KVLQT1-genotyped LQT1 patients had a nondiagnostic resting QTc (<460 milliseconds), whereas 11 (41%) of 27 controls had a resting QTc higher than 440 milliseconds. During epinephrine infusion, every LQT1 patient manifested prolongation of the QT interval (paradoxical response), whereas healthy controls and patients with either LQT2 or LQT3 tended to have shortened QT intervals (P<.001). The maximum mean +/- SD change in QT (AQT [epinephrine QT minus baseline QT]) was -5+/-47 ms (controls), +94+/-31 ms (LQT1), and -87+/-67 ms (LQT2 and LQT3 patients). Of 27 controls, 6 had lengthening of their QT intervals (AQT >30 milliseconds) during high-dose epinephrine. Low-dose epinephrine (0.05 microg x kg(-1) x min(-1)) completely discriminated LQT1 patients (AQT, +82+/-34 ms) from controls (AQT, -7+/-13 ms; P<.001). Epinephrine-triggered nonsustained ventricular tachycardia occurred in 2 patients with LQTS and in 1 control.

CONCLUSIONS

Epinephrine-induced prolongation of the QT interval appears pathognomonic for LQT1. Low-dose epinephrine infusion distinguishes controls from patients with concealed LQT1 manifesting an equivocal QTc at rest. Thus, epinephrine provocation may help unmask some patients with concealed LQTS and strategically direct molecular genetic testing.

Evaluation of drug-induced QT interval prolongation: implications for drug approval and labelling

Assessment of proarrhythmic toxicity of newly developed drugs attracts significant attention from drug developers and regulatory agencies. Although no guidelines exist for such assessment, the present experience allows several key suggestions to be made and an appropriate technology to be proposed. Several different in vitro and in vitro preclinical models exist that, in many instances, correctly predict the clinical outcome. However, the correspondence between different preclinical models is not absolute. None of the available models has been demonstrated to be more predictive and/or superior to others. Generally, compounds that do not generate any adverse preclinical signal are less likely to lead to cardiac toxicity in humans. Nevertheless, differences in likelihood offer no guarantee compared with entities with a preclinical signal. Thus, the preclinical investigations lead to probabilistic answers with the possibility of both false positive and false negative findings. Clinical assessment of drug-induced QT interval prolongation is crucially dependent on the quality of electrocardiographic data and the appropriateness of electrocardiographic analyses. An integral part of this is a precise heart rate correction of QT interval, which has been shown to require the assessment of QT/RR relationship in each study individual. The numbers of electrocardiograms required for such an assessment are larger than usually obtained in pharmacokinetic studies. Thus, cardiac safety considerations need to be an integral part of early phase I/II studies. Once proarrhythmic safety has been established in phase I/II studies, large phase III studies and postmarketing surveillance can be limited to less strict designs. The incidence of torsade de pointes tachycardia varies from 1 to 5% with clearly proarrhythmic drugs (e.g. quinidine) to 1 in hundreds of thousands with drugs that are still considered unsafe (e.g. terfenadine, cisapride). Thus, not recording any torsade de pointes tachycardia during large phase III studies offers no guarantee, and the clinical premarketing evaluation has to rely on the assessment of QT interval changes. However, since QT interval prolongation is only an indirect surrogate of predisposition to the induction of torsade de pointes tachycardia, any conclusion that a drug is safe should be reserved until postmarketing surveillance data are reviewed. The area of drug-related cardiac proarrhythmic toxicity is fast evolving. The academic perspective includes identification of markers more focused compared with simple QT interval measurement, as well as identification of individuals with an increased risk of torsade de pointes. The regulatory perspective includes careful adaptation of new research findings.

Molecular autopsy of sudden unexplained death in the young

Sudden unexplained death (SUD) claims over 4,000 persons between the age of 1 and 22 each year in the United States. Nearly half of all pediatric SUD cases have a normal structural autopsy evaluation and are dismissed without a diagnosis. With the discovery of the genetic basis for potentially fatal arrhythmias associated with the inherited long QT syndrome (LQTS), postmortem molecular diagnosis of this disorder is possible. The authors describe the results of a molecular autopsy performed on a 17-year-old boy found dead in bed. A novel clinical test involving an epinephrine challenge in the decedent's mother implicated a potential defect in the phase 3 potassium current encoded by the gene KVLQT1. Exon-specific amplification by polymerase chain reaction and direct DNA sequencing of KVLQT1 revealed a 5-base pair deletion in the genetic material recovered from the decedent's paraffin-embedded heart tissue. The ability to perform molecular autopsies on archived necropsy material undoubtedly will transform the forensic evaluation of SUD. The combination of catecholamine provocation testing in survivors and a postmortem LQTS gene analysis may unmask families with "concealed" LQTS and establish the cause and manner of death in SUDS.

Abnormalities of the QT interval in primary disorders of autonomic failure

BACKGROUND

Experimental evidence shows that activation of the autonomic nervous system influences ventricular repolarization and, therefore, the QT interval on the ECG. To test the hypothesis that the QT interval is abnormal in autonomic dysfunction, we examined ECGs in patients with severe primary autonomic failure and in patients with congenital dopamine beta-hydroxylase (DbetaH) deficiency who are unable to synthesize norepinephrine and epinephrine.

SUBJECTS AND METHODS

Maximal QT and rate-corrected QT (QTc) intervals and adjusted QTc dispersion [(maximal QTc - minimum QTc on 12 lead ECG)/square root of the number of leads measured] were determined in blinded fashion from ECGs of 67 patients with primary autonomic failure (36 patients with multiple system atrophy [MSA], and 31 patients with pure autonomic failure [PAF]) and 17 age- and sex-matched healthy controls. ECGs of 5 patients with congenital DbetaH deficiency and 6 age- and sex-matched controls were also analyzed.

RESULTS

Patients with MSA and PAF had significantly prolonged maximum QTc intervals (492+/-58 ms(1/2) and 502+/-61 ms(1/2) [mean +/- SD]), respectively, compared with controls (450+/-18 ms(1/2), P < .05 and P < .01, respectively). A similar but not significant trend was observed for QT. QTc dispersion was also increased in MSA (40+/-20 ms(1/2), P < .05 vs controls) and PAF patients (32+/-19 ms(1/2), NS) compared with controls (21+/-5 ms(1/2)). In contrast, patients with congenital DbetaH deficiency did not have significantly different RR, QT, QTc intervals, or QTc dispersion when compared with controls.

CONCLUSIONS

Patients with primary autonomic failure who have combined parasympathetic and sympathetic failure have abnormally prolonged QT interval and increased QT dispersion. However, QT interval in patients with congenital DbetaH deficiency was not significantly different from controls. It is possible, therefore, that QT abnormalities in patients with primary autonomic failure are not solely caused by lesions of the sympathetic nervous system, and that the parasympathetic nervous system is likely to have a modulatory role in ventricular repolarization.