Cardiac drugs antiarrhythmics

Drobuline (71) is a somewhat related cardiac-directed drug with antiarrhythmic action. Since both enantiomers have the... 

Antiarrhythmic drugs are substances that affect cardiac ionic channels or receptors, thereby altering the cardiac action potential or its generation or propagation. This results in changes of the spread of activation or the pattern of repolarization. Thereby, these drugs suppress cardiac arrhythmia. 

Antiarrhythmic Drugs. Figure 1 Transmembrane ionic currents of the cardiac action potential. In the middle of the figure, a typical cardiac action potential is shown as can be obtained from the ventricular myocardium (upper trace). Below, the contribution of the various transmembrane currents is indicated. Currents below the zeroline are inward currents above the zero line are outward fluxes. In the left column the name of the current is given and in the right column the possible clone redrawn and modified after [5]. 

Antiarrhythmic drugs are antagonists of the fast Na+ channel, which slow the propagation of the cardiac action potential. Class I drugs suppress the fast upstroke of the action potential. 

Ca2+ is an important intracellular second messenger that controls cellular functions including muscle contraction in smooth and cardiac muscle. Ca2+ channel blockers inhibit depolarization-induced Ca2+ entry into muscle cells in the cardiovascular system causing a decrease in blood pressure, decreased cardiac contractility, and antiarrhythmic effects. Therefore, these drugs are used clinically to treat hypertension, myocardial ischemia, and cardiac arrhythmias. 

The aiitiarrhytlimic drug s are primarily used to treat cardiac arrhythmias. A cardiac arrhy thmia is a disturbance or irregularity in the heart rate, rhythm, or both, which requires administration of one of the antiarrhythmic dragp. Some examples of cardiac arrhythmias are listed in Table 40-1. 

An arrhythmia may occur as a result of heart disease or from a disorder that affects cardiovascular function. Conditions such as emotional stress, hypoxia, and electrolyte imbalance also may trigger an arrhythmia An electrocardiogram (ECG) provides a record of the electrical activity of the heart. Careful interpretation of the ECG along with a thorough physical assessment is necessary to determine the cause and type of arrhythmia The goal of antiarrhythmic drug therapy is to restore normal cardiac function and to prevent life-threatening arrhythmias. 

The uses of the antiarrhythmic drug are given in the Summaiy Drug Table Antiarrhythmic Drug3. In general these drugp are used to prevent and treat cardiac arrhythmias, such as premature ventricular contractions (PVCs), ventricular tachycardia (VT), premature atrial contractions (PACs), paroxysmal atrial tachycardia (PAT), atrial fibrillation, and atrial flutter. Some of the antiarrhythmic dru are used for other... 

To discontinue use of the drug, the dosage should be gradually reduced during a period of 3 to 5 days. After administering the drug, the nurse observes the patient closely. An oral antiarrhythmic drug may be prescribed to provide continued stability to the cardiac muscle. 

Implantable cardioverter-defibrillators are more effective than antiarrhythmic drugs for reduction in the risk of sudden cardiac death due to VT or VF. 

ICDs have been found to be significantly more effective than antiarrhythmic agents such as amiodarone or sotalol for reducing the risk of sudden cardiac death 45,46 therefore, ICDs are preferred therapy.44 However, many patients with ICDs receive concurrent antiarrhythmic drug therapy to reduce the frequency with which patients experience the discomfort of shocks and to prolong battery life of the devices. Combined pharmacotherapy with amiodarone and a 3-blocker is more effective than monotherapy with sotalol or (i-blockers for reduction in the frequency of ICD shocks.47... 

Myocardium Cardiac action potential Class III antiarrhythmics block hERG Many noncardiac drugs block... 

Lacerda, A.E., Kramer, J., Shen, K.Z., Thomas, D. and Brown, A.M. (2001) Comparison of block among cloned cardiac potassium channels by non-antiarrhythmic drugs. European Heart Journal Supplements, 3, K23-K30. 

Is the drug likely to he co-prescribed with a drug of narrow therapeutic index For example, a drug for angina, cardiac failure or an antiarrhythmic agent is likely to be co-prescribed with warfarin. If there is any evidence of enzyme induction or inhibition, a clinical study with warfarin may be required. 

Propranolol is a prototype of this series of drugs and is the oldest and most widely used nonselective )3-adrenoblocker. It possesses antianginal, hypotensive, and antiarrhythmic action. Propranolol is a cardiac depressant that acts on the mechanic and electrophysio-logical properties of the myocardium. It can block atrioventricular conductivity and potential automatism of sinus nodes as well as adrenergic stimulation caused by catecholamines nevertheless, it lowers myocardial contractility, heart rate, blood pressure, and the myocardial requirement of oxygen. 

In addition to being used as antianginal and antiarrhythmic agents, calcium channel blockers are used to treat weak and moderate hypertension. These drugs prevent calcium ions from entering into the smooth muscle cells of peripheral vessels, and they cause relaxation of peripheral vessels, which leads to lowering of arterial blood pressure. In clinically used doses, calcium channel blockers relax smooth musculature of arteries and have little effect on veins. In doses that relax smooth musculature, calcium channel blockers have relatively little effect on cardiac contractility. 

Optimal therapy of cardiac arrhythmias requires documentation, accurate diagnosis, and modification of precipitating causes, and if indicated, proper selection and use of antiarrhythmic drugs. These drugs are classified according to their effects on the action potential of cardiac cells and their presumed mechanism of action. 

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. 

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