Class la antiarrhythmics

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. 

Pirmenol. Pirmenol hydrochloride, a pyridine methanol derivative, is a racemic mixture. It has Class lA antiarrhythmic activity, ie, depression of fast inward sodium current, phase 0 slowing, and action potential prolongation. The prolongation of refractory period may be a Class III property. This compound has shown efficacy in converting atrial arrhythmias to normal sinus rhythm (34,35). 

Paul, A.A., Witchel, H.J. and Hancox, J. C. (2001) Inhibition of HERG potassium channel current by the class la antiarrhythmic agent disopyramide. Biochemical and Biophysical Research Communications, 280, 1243—1250. 

Pharmacology Quinidine, a class lA antiarrhythmic, depresses myocardial... 

Pharmacology Procainamide, a class lA antiarrhythmic, increases the effective refractory period of the atria, and to a lesser extent the bundle of His-Purkinje system and ventricles of the heart. 

Concurrent antiarrhythmic agents Concurrent antiarrhythmic agents may produce enhanced prolongation of conduction or depression of contractility and hypotension, especially in patients with cardiac decompensation. Reserve concurrent use of procainamide with other Class lA antiarrhythmic agents (eg, quinidine, disopyramide) for patients with serious arrhythmias unresponsive to a single drug and use only if close observation is possible. 

Mechanism of action - Disopyramide is a class lA antiarrhythmic agent that decreases the rate of diastolic depolarization (phase 4), decreases the upstroke velocity (phase 0), increases the action potential duration of normal cardiac cells, and prolongs the refractory period (phases 2 and 3). It also decreases the disparity in refractoriness between infarcted and adjacent normally perfused myocardium and does not affect alpha- or beta-adrenergic receptors. 

Concomitant antiarrhythmic therapy Reserve concomitant use of disopyramide with other class lA antiarrhythmics or propranolol for life-threatening arrhythmias unresponsive to a single agent. Such use may produce serious negative inotropic effects or may excessively prolong conduction, particularly with cardiac decompensation. 

Quinidine Similar class lA antiarrhythmic effect, leading to EKG parameter changes (e.g., longer QRS) Palpitations, bradycardia Need frequent monitoring of EKG parameters when drugs are used in combination Glassman and Preud homme, 1993... 

Class la antiarrhythmic agents block fast sodium channels and prolong the action potential (class III effect), thereby lengthening the effective refractory period. They can cause QT interval prolongation, which may in turn be proarrhythmic, promoting re-entry. In the horse, they are useful for the treatment of a wide variety of arrhythmias, including both supraventricular and ventricular tachycardias. 

Chemicae/Pharmaceutical/Other Class Class lA antiarrhythmic... 

Diprosone betamethasone. diprOtin A is a tripeptide that is an ENZYME INHIBITOR with selectivity as an aminopeptidase inhibitor active against dipeptidylpeptidase IV (EC 3.4.11). It can be used as a pharmacological tool in experimental analytical studies, dipyridamole [ban, inn, usan] (Persantin ) is a pyrimidine derivative, a coronary VASODILATOR, a (class la) ANTIARRHYTHMIC, an adenosine UPTAKE INHIBITOR causing indirect adenosine receptor activation, and enhances effects of anticoagulants and is a platelet AGGREGATION INHIBITOR. 

The oscillatory afterpotentials seen post-repolarization give the first clue that the drug is quinidine. Quinidine blocks sodium channels, which is consistent with the blunting of the amplitude or phase 0, and also potassium channels, which is consistent with the lengthening of phase 2 and the decrease in the slope of phase 3. The drug is thus identified as quinidine, a class la antiarrhythmic. 

Answer E. Increased sympathetic activity is a major problem in hyperthyroidism and is best managed by use of beta blockers, which can offset cardiac stimulatory effects. Propranolol has an ancillary action in thyrotoxicosis in that it prevents conversion of T to Tj via its inhibition of 5 deiodinase. Amiodarone causes difficult-to-predict adverse effects on thyroid function and would not be appropriate in a patient with hyperthyroidism. Quinidine is a class lA antiarrhythmic, which is associated with tachycardia as a side effect. Digoxin is not ideal because of its complex actions on the heart, which include both inhibition and stimulation. 

Class lA antiarrhythmic drug short half-life, metabolized by A-acetyltrans-ferase. Similar to quinidine but more cardiodepressant and may cause lupus erythematosus. 

Class lA antiarrhythmic prototype used in atrial and ventricular arrhythmias. Tox cinchonism, GI upset, thrombocytopenic purpura, arrhythmogenic (torsade de pointes). 

Not treated if asymptomatic. If symptomatic, treat with Class la antiarrhythmics Quinidine Procainamide Disopyramide... 

Amiodarone is a class III antiarrhythmic and can prolong the QT interval. Disopyramide is a class la antiarrhythmic and also prolongs the QT interval. Their additive effects can result in the development of torsade de pointes arrhythmias. 

Class lA antiarrhythmic agents Class III antiarrhythmic agents Calcium antagonists Antihypertensives Antidepressant agents... 

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