Class III Antiarrhythmic Drugs (class + iii_antiarrhythmic_drug)

Distribution by Scientific Domains

Selected Abstracts

Steady-State versus Non-Steady-State QT-RR Relationships in 24-hour Holter Recordings

The aim of the present study was to investigate the QT-RR interval relationship in ambulatory ECG recordings with special emphasis on the physiological circumstances under which the QT-RR intervals follow a linear relation. Continuous ECG recordings make it possible to automatically measure QT duration in individual subjects under various physiological circumstances. However, identification of QT prolongation in Holter recordings is hampered by the rate dependence of QT duration. Comparison of QT duration and QT interval rate dependence between different individuals implies that the nature of the QT-RR relationship is defined in ambulatory ECG. Holter recordings were performed in healthy volunteers at baseline and after administration of dofetilide, a Class III antiarrhythmic drug. After dofetilide, beat-to-beat automated QT measurements on Holter tapes were compared with manually measured QT intervals on standard ECGs matched by time. The QT-RR relationship was analyzed at baseline in individual and group data during three different periods: 24-hour, daytime, and nighttime. Data were collected under steady-state or non-steady-state conditions of cycle length and fitted with various correction formulae. Our study demonstrated an excellent agreement between manually and automated measurements. The classic Bazett correction formula did not fit the QT-RR data points in individual or group data. When heart beats were selected for a steady rhythm during the preceding minute, QT-RR intervals fit a linear relationship during the day and night periods, but not during the 24-hour period in both individual and group data. In contrast, in the absence of beat selection, data fit a more complex curvilinear relationship irrespective of the period. Our study provides the basis for comparison of QT interval durations and QT-RR relationships between individuals and between groups of subjects. [source]

Differences between Ventricular Repolarization in Men and Women: Description, Mechanism and Implications

Borys Surawicz M.D., M.A.C.C.
The purpose of this review article is to discuss the differences between ventricular repolarization in males and females in terms of morphology, possible mechanism, and practical significance. The interest in the subject increased when it became known that in comparison to men, women have a higher incidence of torsade de pointes (tdp) and a greater lengthening of QT-interval after administration of class III antiarrhythmic drugs. Before puberty, the QT intervals and the patterns of ventricular repolarization in boys and girls are similar. At puberty, in boys the QT interval shortens, and a typical male pattern of ventricular repolarization develops. This pattern is characterized by a higher amplitude of the J-point, a shorter and steeper ST segment course, a steeper ascent, and a higher amplitude of the T wave. This pattern is prevalent in >90% of young males. With increasing age the prevalence of the male pattern in males declines gradually and drops to 14% in the oldest age group. The rise and fall of the prevalence of the male pattern appears to parallel the rise and decline of testosterone in males. The female pattern of ventricular repolarization is prevalent in about 80% of females in all age groups. The hormonal effects on ventricular repolarization have been studied in normal and castrated rabbits of both sexes. The available evidence indicates that the females have greater divergence of L calcium current among different layers of the myocardium and a lower density of the repolarizing Kr and Ks currents. The clinical significance of the repolarization differences among genders remains to be determined. Of particular interest is the question whether the males with female pattern are at the same risk of tdp as the females or whether the females with male pattern are at lower risk of tdp than the females with female pattern. [source]

Prevention of Atrial Fibrillation in Cardiac Surgery: Time to Consider a Multimodality Pharmacological Approach

Kwok M. Ho
Atrial fibrillation (AF) is very common within the first 5 days of cardiac surgery. It is associated with significant morbidity including stroke, ventricular arrhythmias, myocardial infarction, heart failure, acute kidney injury, prolonged hospital stay, and also short- and long-term mortality. The underlying mechanisms of developing AF after cardiac surgery are multifactorial; risk factors may include advanced age, withdrawal of beta-blockers and angiotensin-converting-enzyme inhibitors, valve surgery, obesity, increased left atrial size, and diastolic dysfunction. There are many pharmacological options in preventing AF, but none of them are effective for all patients and they all have significant limitations. Beta-blockers may reduce the incidence of AF by more than a third, but bradycardia, hypotension, or exacerbation of heart failure often limit their utility postoperatively. Recent evidence suggests that class III antiarrhythmic drugs, sotalol and amiodarone, are more effective than beta-blockers, but they both share similar hemodynamic side effects of beta-blockers. Magnesium, antiinflammatory drugs such as statins, omega fatty acids, and low-dose corticosteroids also have some efficacy and they have the advantages of not causing significant hemodynamic side effects. Data on effectiveness of calcium channel blockers, digoxin, alpha-2 agonists, sodium nitroprusside, and N-acetylcysteine are more limited. Because the pathogenesis of AF is multifactorial, a combination of drugs with different pharmacological actions may have additive or synergistic effect in preventing AF after cardiac surgery. Randomized controlled trials evaluating the effectiveness of a multimodality pharmacological approach in patients at high-risk of AF after cardiac surgery are needed. [source]

Update on atrial fibrillation: Part II

Irina Savelieva MD
Abstract Antiarrhythmic drugs are an essential tool in the management of atrial fibrillation (AF). Although we are already on the threshold of a large expansion in the use of ablation therapies, these will not, however, be appropriate for all patients, and pharmacological therapies will continue to have an important place in the management of atrial fibrillation. The plethora of antiarrhythmic drugs currently available for the treatment of atrial fibrillation is a reflection that none is wholly satisfactory, each having limited efficacy combined with poor safety and tolerability. Improved class III antiarrhythmic drugs, such as dronedarone, new classes of antiarrhythmic agents, such as atrial repolarization delaying agents, and upstream therapies dealing with substrate, represent potential sources of new pharmacological therapies. Copyright 2008 Wiley Periodicals, Inc. [source]