Nature Of Arrhythmias Research Articles

Computational biology of propagation in excitable media models of cardiac tissue

Biophysically detailed models of the electrical activity of single cardiac cells are modular, stiff, high order, differential systems that are continually being updated by incorporating new formulations for ionic fluxes, binding and sequestration. They are validated by their representation of the ionic flux and concentration data they summarise, and by their ability to reproduce cell action potentials, their stability to perturbations, structural stability and robustness. They can be used to construct discrete or continuous, one- (1D), two- (2D) or three-dimensional (3D) virtual cardiac tissues, with heterogeneities, anisotropy and realistic cardiac geometry. These virtual cardiac tissues are being applied to understand the propagation of excitation in the heart, provide insights into the generation and nature of arrhythmias, aid the interpretation of electrical signs of arrhythmia, to develop defibrillation and antiarrhythmic strategies, and to prescreen potential antiarrhythmic agents.

Effects of antihypertensive therapy with lercanidipine and verapamil on cardiac electrical activity in patients with hypertension: a randomized, double-blind pilot study

ObjectiveThe aim of this study was to compare the effects of prolonged (2 weeks) administration of lercanidipine with those of sustained-release (SR) verapamil on cardiac excitation and conduction in patients with mild to moderate essential hypertension. BackgroundLercanidipine is a new dihydropyridine calcium channel blocker that has demonstrated efficacy in the treatment of hypertension. The effects of lercanidipine on cardiac conduction in hypertensive patients have not been studied. MethodsAfter a 1-week washout period and a 2-week placebo run-in period, 37 patients were randomized to receive 20 mg lercanidipine (n = 18) or 240 mg verapamil SR (n = 19) once daily for 2 weeks. Electrocardiographic variables, including heart rate (HR), duration of QRS, and the PR, QT, and QTc intervals, were measured by Holter monitoring. ResultsNo significant changes in HR, QRS duration, or PR, QT, and QTc intervals were observed in either group. However, the PR interval in patients receiving verapamil SR showed a modest but not statistically significant prolongation. The number and nature of cardiac arrhythmias did not change in either group after 2 weeks of treatment. Systolic and diastolic blood pressures were significantly reduced after 1 week of treatment with lercanidipine or verapamil SR (P< 0.05), and were further reduced after 2 weeks of treatment, with no statistically significant difference between treatments. ConclusionsResults of this study suggest that at therapeutic doses, lercanidipine does not interfere with normal cardiac excitation and conduction in patients with mild to moderate essential hypertension.

Cisapride: a survey of the frequency of use and adverse events in premature newborns.

This survey estimated the frequency of use and adverse events associated with cisapride treatment of premature newborns in intensive care units. It was initiated in response to a warning issued in Canada cautioning against cisapride treatment of premature infants of <36 weeks' gestation and <3 months of age. Surveys were mailed to 105 neonatology training program directors to obtain the total number of neonatal intensive care unit (NICU) admissions, the number of admissions of infants of <36 weeks' gestation, the number of years that cisapride had been used, the estimated percent/number of premature patients treated with cisapride per year, and the frequency and nature of arrhythmias or other adverse events associated with cisapride treatment. Of 105 programs, 46 responded to a single mailing of the first survey. A second survey mailed to the 45 respondents to the first survey sought to determine the indications, diagnostic tests, and dosages used with cisapride treatment of premature newborns. Of the 45 programs, 26 responded to the second survey. More than 58 000 premature newborns of <36 weeks' gestation were admitted to the NICUs we surveyed, and approximately 19% were treated with cisapride. No deaths attributable to cisapride were reported among >11 000 preterm newborns treated. Three nonfatal arrhythmias were reported; two associated with 10-fold dosing errors and one with co-treatment with erythromycin, a macrolide antibiotic that reduces the metabolism of cisapride. Diarrhea was reported in 12 patients, and reversible liver enzyme changes were noted in one patient. Typically, cisapride treatment was started in dosages of 0.1 to 0.2 mg/kg/dose, repeated every 6 to 8 hours. Treatment usually was begun empirically, without a preceding study to document gastroesophageal reflux. The most frequent indications for cisapride treatment were choking or gagging, with associated apnea, bradycardia, and desaturation. Approximately 50% of patients had discontinued cisapride treatment before discharge. Eighty-four percent of clinicians judged cisapride to be effective for the problems being treated. Cisapride treatment of premature infants of <36 weeks' gestation and <3 months of age in NICUs appears to be widespread in the United States. Complications and adverse events were seen when cisapride was administered in excessive dosages or in combination with a drug that inhibits its metabolism and leads to increased serum concentrations. Severe toxicities such as arrhythmias were reported with a frequency of <1/11 000 NICU admissions. However, in a retrospective survey, episodes of toxicity, including mortality, attributable to cisapride may not have been recognized or reported.

Effects of the anesthetics heptanol, halothane and isoflurane on gap junction conductance in crayfish septate axons: A calcium- and hydrogen-independent phenomenon potentiated by caffeine and theophylline, and inhibited by 4-aminopyridine

This study has monitored junctional and nonjunctional resistance, [Ca2+]i and [H+]i, and the effects of various drugs in crayfish septate axons exposed to neutral anesthetics. The uncoupling efficiency of heptanol and halothane is significantly potentiated by caffeine and theophylline. The modest uncoupling effects of isoflurane, described here for the first time, are also enhanced by caffeine. Heptanol causes a decrease in [Ca2+]i and [H+]i both in the presence and absence of either caffeine or theophylline. A similar but transient effect on [Ca2+]i is observed with halothane. 4-Aminopyridine strongly inhibits the uncoupling effects of heptanol. The observed decrease in [Ca2+]i with heptanol and halothane and negative results obtained with different [Ca2+]o, (Ca2+)-channel blockers (nisoldipine and Cd2+) and ryanodine speak against a Ca2+ participation. Negative results obtained with 3-isobutyl-1-methylxanthine, forskolin, CPT-cAMP, 8Br-cGMP, adenosine, phorbol ester and H7, superfused in the presence and absence of caffeine and/or heptanol, indicate that neither the heptanol effects nor their potentiation by caffeine are mediated by cyclic nucleotides, adenosine receptors and kinase C. The data suggest a direct effect of anesthetics, possibly involving both polar and hydrophobic interactions with channel proteins. Xanthines and 4-aminopyridine may participate by influencing polar interactions. The potentiating effect of xanthines on cell-to-cell uncoupling by anesthetics may provide some clues on the nature of cardiac arrhythmias in patients treated with theophylline during halothane anesthesia.

COMPARISON OF THE INCIDENCE AND NATURE OF CARDIAC ARRHYTHMIAS OCCURRING DURING ISOFLURANE OR HALOTHANE ANAESTHESIA: Studies During Dental Surgery

Seventy-six Chinese patients aged between 15 and 30 yr, undergoing 3rd molar extraction, were randomly allocated to two groups. One group received halothane and the other isoflurane. The incidence of arrhythmia during surgery under anaesthesia with isoflurane was significantly less than with halothane. Sinus tachycardia was a significant feature under anaesthesia with isoflurane. Under anaesthesia with halothane, the arrhythmias occurring most frequently during surgery were ventricular ectopics, the commonest being ventricular bigeminy. The frequency and nature of arrhythmias during surgery on right and left sides were similar. In three patients a slight decrease in arterial pressure was recorded in association with the arrhythmia, but on stopping the stimulus, both rhythm and arterial pressure returned to normal. The incidence of arrhythmia with halothane in the Chinese population in this study was significantly higher than that reported previously in non-Chinese patients.

Some theoretical and clinical aspects of electrical impulse therapy for cardiac arrhythmias

Based on modern ideas about the nature of cardiac arrhythmias, about the role in their development of changes in the transmembrane potential caused by shifts in the permeability of cytoplasmic membranes and extra- and intracellular concentrations of the main potential-forming ions, it can be assumed that a high-voltage discharge of a capacitor restores sinus rhythm by affecting the indicated parameters heart muscle.

Prevalence and nature of cardiac arrhythmias in apparently normal well-trained runners

Sixty well-conditioned runners were evaluated for arrhythmias by Holter monitor during both a distance run and a maximal treadmill test. Twenty-seven percent of subjects had ventricular arrhythmias during treadmill testing, only 3% having grades higher than just an occasional isolated premature ventricular complex (PVC), compared with 60% during the monitored run, of which ventricular bigeminy occurred in 10%, ventricular couplets in 10%, and multiform PVCs in 5%. Treadmill testing significantly underestimated the frequency and grade of both atrial and ventricular arrhythmias: 57% of subjects who had ventricular arrhythmias while running had none on the treadmill, and 11 of 16 who had ventricular arrhythmias on the treadmill had up to 3 grades higher on the run. The discovery of frequent high-grade atrial and ventricular arrhythmias in subjects considered to be completely fit and healthy suggests that such variations in heart rhythm are a normal phenomenon and no more specific for heart disease or risk than ventricular arrhythmias during maximal treadmill exercise testing.

Nature of cardiac arrhythmias and electrolyte disturbances. Role of potassium in atrial fibrillation.

Atrial fibrillation is highly favoured by an accelerated atrial muscle repolarization. In hyperthyroidism, this occurs without changes in resting membrane potential level of the atrial muscle cells and without changes in the ionic composition of the cell. In patients prone to atrial fibrillation but without signs of hyperthyroidism, accelerated atrial repolarization can also be demonstrated. In such patients, a decreased atrial muscle potassium content seems responsible for the electrophysiological changes that highly favours the occurrence of atrial fibrillation.

Evaluation of arrhythmias in the late hospital phase of acute myocardial infarction compared to coronary care unit ectopy.

To evaluate the prevalence and nature of arrhythmias during the entire three-week period in hospital after myocardial infarction, the results of coronary care unit monitoring (initial 3 to 5 days) were compared with continuous 8-hour portable monitoring during the ambulatory phase (second and third weeks) in 83 consecutive survivors. Arrhythmias were detected in 84.3 per cent (70/83) of patients while in the coronary care unit and in 85.5 per cent (71/83) during hospital stay after the coronary care unit. Ventricular ectopic depolarizations were classified as complicated (multifocal, paired, R on T, or five or more a minute) or uncomplicated. Importantly, the high frequency of complicated ventricular extrasystoles and tachycardia persisted during the entire period in hospital (early 34.9% and late 42.5% of all patients). However, only 16.9 per cent (14/83)had these ventricular arrhythmias during both coronary care unit and ward monitoring. Thus, the absence of complicated ventricular ectopic depolarization and ventricular tachycardia in the coronary care unit did not exclude their subsequent occurrence in the majority of the large number of patients with late hospital complicated ventricular ectopy.

Incidence and nature of arrhythmias in the early hospital post-coronary care unit phase of acute myocardial infarction

Incidence and nature of arrhythmias in the early hospital post-coronary care unit phase of acute myocardial infarction