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At least 1,711 records · Page 95Linked to original sources
PubMed1989

Effect of altered repolarization course induced by antiarrhythmic drugs and constant current pulses on duration of premature action potentials in canine cardiac Purkinje fibers.

The purpose of this study was to elucidate the mechanism of the upward shift of the electrical restitution curve, i.e., the lengthening of premature action potential duration (APDt) expressed as percentage of basic APD, induced by class I antiarrhythmic drugs in dog Purkinje fibers. In this study, six class I antiarrhythmic drugs lengthened APDt at a diastolic interval of 20 ms by 2.5-14.1%. The drugs also decreased the ratio of APD at 50% to APD at 90% of repolarization from 70.8 +/- 1.8% (n = 60) to 47.4-60.8%. The relation between the decrease in the ratio of APD50 to APD90 of the basic AP and lengthening of the normalized APDt was linear (r = 0.92; p less than 0.01). We attributed the lengthening of normalized APDt to the decreased ratio of APD50 to APD90, and applied repolarizing current pulses in short (less than or equal to 2 mm) fibers to simulate the drug-induced decrease in the ratio of APD50 to APD90. The altered repolarization course of basic AP by the current pulse during late plateau and early phase 3 caused APDt lengthening. The relation between the current-induced decrease in the ratio of APD50 to APD90 of the basic AP and the lengthening of normalized APDt was linear (r = 0.91; p less than 0.01). The slope of regression line describing this relation was similar to that in the presence of drugs. These results suggest that lengthening of the normalized APDt by class I antiarrhythmic drugs results from a more rapid repolarization during phase 2 of the preceding basic AP, possibly due to lesser influence of the delayed outward rectifying current. The lengthening of APDt by class I drugs may contribute to their antiarrhythmic action.

Action Potentials↗
PubMed1998

Ostensible day-night difference of QT prolongation during long-term treatment with antiarrhythmic drugs: reappraisal of the law of "regression to the mean".

This study was designed to test whether the law of regression to the mean explains the diurnal variation in the modulation of electrocardiographic variables during the treatment with antiarrhythmic agents. In part 1, in 34 subjects, ambulatory ECG monitorings were repeated twice, and the corrected QT interval (QTc) at a heart rate of 60 beats/min was calculated separately for the daytime and night. The individual diurnal QTc variation (day-night difference) of the first recording (4.4 +/- 3.3%) was significantly correlated with that of the second recording (5.0 +/- 3.1%; r = 0.61; p < 0.0001), and naturally, the second measurement tended to be lower than the first value in those with relatively greater baseline diurnal QTc variation and vice versa (p < 0.005). In part 2, 30 subjects undertook ambulatory ECG recordings before and during treatment with class Ia antiarrhythmic drugs. Mean QTc changes in the daytime and in the night with the drugs were comparable (18 +/- 17 ms and 19 +/- 15 ms). However, the day-night difference of postdrug QTc changes in each subject was inversely correlated with baseline diurnal QTc variation (r = -0.64; p < 0.0001). These observations in part 2 were comparable with those in part 1, and individual day-night difference in QT prolongation with antiarrhythmic drugs seemed to be a chance occurrence. It was suggested that the law of regression to the mean is appreciably reflected in the ostensible intraday variation of pharmacologic modulation of electrocardiographic variables.

Anti-Arrhythmia Agents↗
PubMed1982

Pharmacology of commonly used antiarrhythmic drugs and comments on the use of therapeutic drug monitoring.

Five commonly used antiarrhythmic agents are examined with regard to their pharmacokinetics, pharmacology, electrophysiology, and clinical utility. The effective, nontoxic plasma levels are noted, and important drug--drug interactions with these agents are noted. Monitoring plasma levels of these agents serves a useful function in that it identifies patients who are not compliant, who are taking too little drug, or who are taking too much drug. Current techniques do not allow rapid, reproducible, and inexpensive measurements of free (vs. bound) drug in the plasma, a quantity that is likely to be substantially more valuable in determining drug effect than total plasma concentration. Previous studies on drug effectiveness may not have taken into account natural fluctuations in arrhythmia frequencies that mimic drug effect.

Anti-Arrhythmia Agents↗
PubMed1992

Recurrent unexplained syncope in the elderly: the use of head-upright tilt table testing in evaluation and management.

OBJECTIVE: To investigate the usefulness of head-upright tilt table testing for vasovagal episodes in the evaluation and management of elderly patients with recurrent idiopathic syncope. DESIGN: Prospective survey. SETTING: Electrophysiology laboratory of a university hospital. PATIENTS: Twenty-five patients (11 male, 14 female; mean age 73 +/- 6 years) with recurrent unexplained syncope and seven control subjects with other causes of syncope (4 male, 3 female; mean age 70 +/- 4 years). METHODS: Each patient underwent head-upright tilt table testing for 30 minutes with or without an infusion of isoproterenol (1-3 micrograms/min given intravenously) in an attempt to provoke bradycardia, hypotension, or both. MAIN RESULTS: Syncope occurred in nine patients (36%) during the baseline tilt and in seven patients (28%) during isoproterenol infusion (total positives 64%). None of the controls had syncope during the test. All of the patients who had positive test results eventually became tilt table negative with therapy, and over a mean follow-up period of 24 months, no further syncopal episodes have occurred. CONCLUSIONS: Head-upright tilt table testing combined with isoproterenol infusion may be a useful tool in the diagnosis of vasovagal syncope in the elderly and in the evaluation of preventive therapy.

Aged↗
PubMed1980

Ventricular tachycardia initiated by both normally and aberrantly conducted atrial premature beats.

Electrophysiologic studies were performed in a 72-year-old female with recurrent ventricular tachycardia in whom all documented spontaneous episodes were initiated by atrial premature beats. These studies confirmed the diagnosis of ventricular tachycardia and its initiation by atrial premature beats. Both normally and aberrantly conducted atrial premature beats were capable of initiating the tachycardia. With aberrant prematures the onset of the tachycardia was delayed in proportion to the delay in the right bundle branch. Triggered automaticity and re-entry were equally plausible as underlying mechanisms for this arrhythmia.

Aged↗
PubMed1984

Failure to pace following high dose antiarrhythmic therapy--reversal with isoproterenol.

A patient with resistant ventricular tachycardia treated with a combination of antiarrhythmic agents is described. Sudden onset of a wide complex ventricular rhythm with periods of asystole and failure to achieve transvenous pacing were observed, presumably due to antiarrhythmic drug toxicity. Inability to pace was reversed by the infusion of isoproterenol.

Amiodarone↗
PubMed1986

Combination antiarrhythmic drug therapy for ventricular tachyarrhythmias.

New antiarrhythmic drug regimens are constantly being sought because of the relatively low efficacy rates of standard antiarrhythmic agents in preventing induction of ventricular tachyarrhythmias; the application of these agents is also limited due to serious or debilitating side-effects. The combination of two antiarrhythmic agents with complimentary electrophysiologic activities and differing toxicities might offer significant advantages in overcoming the drawbacks of standard antiarrhythmic drug therapy. A knowledge of the pharmacodynamics of the major classes of antiarrhythmic agents will allow informed choices of drugs for use in combination therapy. Judging antiarrhythmic drug efficacy is a complex problem, requiring an understanding of the influence of the arrhythmia monitoring technique, arrhythmia morphology and the response to previous drugs on drug efficacy rates, so that accurate comparisons of drug effectiveness can be made among different agents or combinations. A number of combination therapies have been tested for suppression of complex ventricular ectopy, nonsustained ventricular tachycardia and sustained ventricular tachycardia and ventricular fibrillation. The most successful combinations have been those using class IA and IB agents and class IA and II agents. In general, these combinations tend to show higher efficacy rates in suppressing all forms of ventricular ectopy and ventricular tachyarrhythmias, and usually have a lower incidence of toxic side-effects compared with individual agents alone. On the basis of these initial results, it seems warranted to perform further studies to explore these combinations in larger populations and to test new combinations developed on the basis of pharmacodynamic principles.

Adrenergic beta-Antagonists↗
PubMed1991

Effects of transcatheter cardioversion on chronic lone atrial fibrillation.

The effectiveness and safety of internal transcatheter cardioversion on chronic lone atrial fibrillation were examined in ten patients resistant to external electrical (400 joules) and pharmacological cardioversion. Transcatheter cardioversion was performed by pulling back the atrioventricular junction catheter just inferior to the site of the His-bundle recording and delivering the shock between a proximal electrode (cathode) and backplate (anode). Transcatheter cardioversion restored sinus rhythm in all of the ten patients. The only complication observed was transient atrioventricular block after the shock and this was treated by temporary pacing. However, atrial fibrillation recurred in five patients at 30, 27, 52, 1, and 6 days, respectively. A second attempt at transcatheter cardioversion was performed in those patients an was successful in three patients. During a follow-up period ranging from 12 to 22 months, eight patients continued in sinus rhythm. Thus, transcatheter cardioversion is considered effective and safe in selected patients with chronic lone atrial fibrillation in whom external cardioversion was unsuccessful.

Atrial Fibrillation↗
PubMed1995

Postpartum syncope.

Recurrent unexpected syncope may have severe consequences and result in serious injury. This is especially the case in the immediate postpartum period when maternal syncope may have a disastrous effect on the infant as well as the mother. We report on 12 women who developed episodic hypotension resulting in syncope in the immediate postpartum period and describe the distinguishing characteristics of their presentation, tilt table results, and responses to therapy. Postpartum syncope represents a unique subgroup of syncopal patients who need to be recognized and treated in order to prevent potentially serious injury to both mother and infant.

1-Naphthylamine↗
PubMed1997

Unexplained syncope: clinical management.

The management of unexplained syncope begins with the patient's history and physical examination, which are oriented to help separate benign from serious causes. Malignant etiologies are more likely to occur with exertional syncope. Cardiac causes should be considered, particularly cardiomyopathy, postoperative congenital heart disease, right ventricular dysplasia, anomalous coronary artery, pulmonary artery hypertension, myocarditis, long QT syndrome, and Wolff-Parkinson-White syndrome. Neurological and metabolic disorders may underlie a syncope episode. After malignant causes of syncope have been excluded and the diagnosis of neurocardiac syncope has been established, treatment strategies include behavior modification, salt and increased fluids, and pharmacological agents. Efficacious agents include beta-blockers, dysopyramide, fludrocortisones, and alpha agents. Yet, behavior modification alone may be as effective as salt or pharmacological therapy. Because the natural history of neurocardiac syncope in children is spontaneous resolution, it is appropriate to try the simple measures before introducing drug therapy.

Adrenergic alpha-Agonists↗