Repolarization prolongators

Prolong repolarization. Prolonged repolarization is the time when the electrical impulse returns to normal and is ready to fire again. These include bretyhum (Bretylol) and amiodarone (Cordarone). 

C. Cardiotoxicity with impaired ventricular depolarization (as evidenced by a prolonged QRS interval) caused by tricyclic antidepressants, type la or type Ic antiarrhythmics, and other membrane-depressant dmgs (see Table 11-7, p 88). Note Not effective for dysrhythmias associated with abnormal repolarization (prolonged QT interval and torsade de pointes). 

Glass lA Antiarrhythmic Agents. Class lA antiarrhythmic agents decrease automaticity, ie, depress pacemaker rates, especially ectopic foci rates produce moderate depression of phase 0 depolarization and thus slow conduction in atria, A-V node, His-Purkinje system, and ventricles prolong repolarization, ie, lengthen action potential duration increase refractoriness and depress excitabiHty. These electrophysiological effects are manifested in the ECG by increases in the PR, QRS, and QT intervals. 

Glass IG Antiarrhythmic Agents. Class IC antiarrhythmic agents have marked local anesthetic effects. They slow the rapid inward sodium current producing marked phase 0 depression and slow conduction. Action potential duration of ventricular muscle is increased, ie, prolonged repolarization, but decreased in the His-Purkinie system by these agents. The effects on the ECG are increased PR interval, marked prolongation of the... 

Fleca.inide, Elecainide acetate, a fluorobenzamide, is a derivative of procainamide, and has been reported to be efficacious in suppressing both supraventricular and ventricular arrhythmias (26—29). The dmg is generally reserved for patients with serious and life-threatening ventricular arrhythmias. Elecainide depresses phase 0 depolarization of the action potential, slows conduction throughout the heart, and significantly prolongs repolarization (30). The latter effect indicates flecainide may possess some Class III antiarrhythmic-type properties (31). 

III Block of repolarizing potassium channels, prolongation of action potential Amiodarone, Dronedarone, Sotalol, Dofetilide, Ibutilide... 

A cell may produce early afterdepolarizations that are depolarization during incomplete repolarization. This is possible if the action potential is considerably prolonged. This is the typical mechanism for elicitation of Torsade de Pointes arrhythmia, a typical complication of class III antiarrhythmics and many other drugs. 

Kvl.5 In human atria, the Kvl.5 presents the ultrarapid delayed rectifier that contributes to the repolarization in the early phase of cardiac action potential. Selective blockers of Kvl.5 channels could be potentially beneficial in the treatment of atrial fibrillation because blocking Kvl. 5 could delay repolarization and prolong refractoriness selectively in cardiac myocytes. Examples for Kvl.5 blockers include AVE0118, S9947, and analogs of diphenyl phosphine oxide (DPO). 

STB The Non-Clinical Evaluation of the Potential for Delayed Ventricular Repolarization (QT Interval Prolongation) by Human Pharmaceuticals Immunotoxicology Studies... 

The Vaughan-Williams classification of antiarrhythmic drugs has been criticized for a number of reasons. The classification is based on the effects of drugs on normal, rather than diseased, myocardium. In addition, many of the drugs may be placed into more than one class. For example, the class IA drugs prolong repolarization/refractoriness, either via the parent drug8,9 or an active metabolite,10 and therefore also maybe placed in class III. Sotalol is also a 3-blocker, and therefore fits into class II. Amiodarone inhibits sodium and potassium channels, is a non-competitive inhibitor of 3-receptors, and inhibits calcium... 

Procainamide (Class IA antiarrhythmic drug) is an effective agent for ventricular tachycardia. Its mechanism of action involves blockade of the fast Na+ channels responsible for phase 0 in the fast response tissue of the ventricles. Therefore, its effect is most pronounced in the Purkinje fibers. The effects of this drug s activity include a decrease in excitability of myocardial cells and in conduction velocity. Therefore, a decrease in the rate of the phase 0 upstroke and a prolonged repolarization are observed. As a result, duration of the action potential and the associated refractory period is prolonged and the heart rate is reduced. These effects are illustrated by an increase in the duration of the QRS complex. 

I88-E89. The answers arc 188-g 189-b. (Hardman, pp 858-859, 864-865.) It is widely accepted that anti arrhythmic drugs are best classified according to their electro physio logic attributes. This is best accomplished by relating the effects of the different drugs to their actions on Na and Ca channels, which are reflected by changes in the monophasic action potential. Amiodarone blocks Na, Ca, and K currents and markedly prolongs repolarization, particularly in depolarized cells. Hecainide is related... 

Type III drugs specifically prolong refractoriness in atrial and ventricular fibers and include very different drugs that share the common effect of delaying repolarization by blocking potassium channels. 

In conclusion, QT prolongation by hERG channel blockers is per se dose dependent, whereas actual occurrence of TdP depends on the repolarization reserve, which is variable among subjects and over time. The exception to the mle are those hERG blockers with multiple, sometimes complementary electrophysiological actions, which lead to a bell-shaped concentration-response curve [109]. 

ICH E14 provides recommendations to sponsors concerning the design, conduct, analysis and interpretation of clinical studies to assess the potential of a drug to delay cardiac repolarization. Specifically, it calls for a clinical thorough QT/QTc study (typically conducted in healthy volunteers), which is intended to determine whether a drug has a threshold pharmacological effect on cardiac repolarization, as detected by QT/QTc interval prolongation. 

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