Arrhythmias tachyarrhythmias

Normal rhythmic activity is the result of the activity of the sinus node generating action potentials that are conducted via the atria to the atrioventricular node, which delays further conduction to the His-Tawara-Purkinje system. From the Purkinje fibres, action potentials propagate to the ventricular myocardium. Arrhythmia means a disturbance of the normal rhythm either resulting in a faster rhythm (tachycardia, still rhythmic) or faster arrhythmia (tachyarrhythmia) or slowed rhythm (bradycardia, bradyarrhythmia). 

Treat coma (p 19) and arrhythmias (pp 12-15) if they occur. Caution avoid use of epinephrine or other sympathomimetic amines because they may induce or aggravate arrhythmias. Tachyarrhythmias caused by increased myocardial sensitivity may be treated with propranolol, 1-2 mg IV in adults (see p 496), or esmolol, 0.025-0.1 mg/kg/min IV (see p 443). Monitor patients for at least 4-6 hours after exposure, and longer if symptomatic. 

Lethal Arrhythmias. Arrhythmias are a second significant source of cardiovascular problems. An arrhythmia is an abnormal or irregular heart rhythm. Bradyarrhythmias result in heart rates that are too slow tachyarrhythmias cause abnormally fast rates. A bradyarrhythmia can be debiUtating, causing a person to be short of breath, unable to climb stairs, black out, or even to go into cardiac arrest. Tachyarrhythmias can be un settling and painful at best, life-threatening at worst. 

There is a close correlation between myocardial infarctions and tachyarrhythmias, illustrated by the presence of complex ventricular arrhythmias among heart attack victims which are estimated to affect one-third of the survivors each year. Frequendy, the immediate cause of sudden death is ventricular fibrillation, an extreme arrhythmia that is difficult to detect or treat. In the majority of cases, victims have no prior indication of coronary heart disease. 

Implantable tachyrhythmia devices, available for some years, address far less dangerous atrial tachyarrhythmias and fibrillation. The technical barriers to counteracting ventricular tachyarrhythmias and fibrillation using massive shocks have been formidable and are compounded by the possibiUty of causing the very problem the shock is designed to overcome. Newer tachyrhythmia devices are being readied that can safely regulate arrhythmias across the hiU spectmm. 

Propafenone. Propafenone hydrochloride, an arylketone, is stmcturaHy similar to the P-adrenoceptor blocking agents. It has been in use in the former West Germany since 1977 and was introduced in the United States in 1990. Its effects may result from a combination of weak calcium channel blocking, weak nonselective -adrenoceptor blocking, and sodium channel blocking activity. Propafenone is effective in treating supraventricular tachyarrhythmias, ventricular ectopic beats, and ventricular arrhythmias. It is the most frequendy prescribed medication for ventricular arrhythmias in Europe (32). 

Propranolol. Propranolol hydrochloride, considered the prototype of the P-adrenoceptor blocking agents, has been in use since 1964. It is a nonselective, highly Hpid-soluble P-adrenoceptor blocker having no ISA. It is a mixture of (+) and (—) enantiomers, and the (—) enantiomer is the active moiety. The local anesthetic effects of propranolol are equipotent to those of Hdocaine [137-58-6] C 4H22N20, (see Anesthetics). Therapeutic effects include termination of catecholamine-induced arrhythmias, conversion of SA nodal tachycardias (including flutter and fibrillation) and AV nodal tachyarrhythmias to normal sinus rhythm, digitahs-induced arrhythmias, and ventricular arrhythmias (1,2). The dmg also has cardioprotective properties (37,39). 

Dmgs that mimic or inhibit the actions of neurotransmitters released from parasympathetic or sympathetic nerves innervating the heart may also be used to treat supraventricular bradyarrhythmias, heart block, and supraventricular tachyarrhythmias. Those used in the treatment of arrhythmias may be found in Table 1. 

Supraventricular bradycardia is treated by implantation of a pacemaker device or has been treated pharmacologically with atropine. Supraventricular paroxysmal tachycardia is treated with aj marine or praj marine. Supraventricular tachyarrhythmias or AV reentrant arrhythmia typically can be terminated using adenosine. 

Normal cardiac contraction depends on the conduction of electrical impulses through the myocardium in a highly coordinated fashion. Any abnormality of the initiation or propagation of the impulse is referred to as an arrhythmia. These disorders are the most common clinical problem encountered by a cardiologist. There is a wide range of types of arrhythmias with multiple etiologies and a variety of symptoms. In this section, two types of cardiac tachyarrhythmias are discussed. The most common treatment for these conditions is drug therapy. 

First, drug-induced lengthening of the QT interval has been associated with the occurrence of ventricular tachyarrhythmias, namely TdP, a polymorphous ventricular arrhythmia that may cause syncope and degenerate into ventricular fibrillation and sudden death although the incidence of TdP is a rare event (usually, less than 1 in 100 000) [32], even a low risk is not justified for drugs with uncertain benefits or drugs providing only symptomatic improvement of a mild disease. 

Arrhythmias can range from isolated PVC s, coupled beats, non-sustained ventricular tachyarrhythmias (NSVT), sustained ventricular tachyarrhythmias (SVT) and, ultimately, ventricular fibrillation (VF). It is generally... 

Amiodarone (11), a benzofuran derivative, was initially developed as a coronary vasodilator in the early 1960 s [11,12]. Several years later, the efficacy of the compound as an antiarrhythmic agent began to be exploited. The first clinical trials with amiodarone were reported in 1974 [13]. Amiodarone was effective in controlling the tachyarrhythmias of eleven patients with Wolff-Parkinson-White syndrome. Since that time the compound has been studied extensively [14,15]. Recently, in the Canadian Amiodarone Myocardial Infarction Arrhythmia Trial (CAMIAT), amiodarone was shown to reduce mortality during a mean 18 month period following myocardial infarction (13.8% deaths in placebo group vs. 2.1 % deaths in the treatment group) [16]. 

Digitoxin is used for chronic cardiac insufficiency, tachyarrhythmia form of atrial fibrillation, paroxysmal ciliary arrhythmia, and paroxysmal supraventricular tachycaria. Synonyms of this drag are cardigin, cordalin, crystodigin, purodigin, and others. 

Cardiovascular Specifically, screen and evaluate patients with coronary heart disease, serious cardiac arrhythmias or vasospastic diseases before nicotine is prescribed. There have been occasional reports of tachyarrhythmias associated with nicotine use therefore, if an increase in cardiovascular symptoms occurs, discontinue the drug. 

The cardiac toxicity of quinidine includes A-V and intraventricular block, ventricular tachyarrhythmias, and depression of myocardial contractility. Ventricular arrhythmia induced by quinidine leading to a loss of consciousness has been referred to as quinidine syncope. This devastating side effect is more common in women than in men and may occur at therapeutic or subtherapeutic plasma concentrations. 

Clinically, tachyarrhythmias associated with digitalis excess (including supraventricular and ventricular extrasystoles) and ventricular tachycardia have been suppressed by propranolol. Although propranolol is highly effective in the treatment of digitalis-induced arrhythmias, phenytoin and Udocaine are preferred. 

Dofetilide is approved for the treatment of atrial fibrillation and atrial flutter. Because of the lack of significant hemodynamic effects, dofetilide may be useful in patients with CHF who are in need of therapy for supraventricular tachyarrhythmias. Dofetilide is not indicated for use in the setting of ventricular arrhythmias. 

Verapamil is useful for slowing the ventricular response to atrial tachyarrhythmias, such as atrial flutter and fibrillation. Verapamil is also effective in arrhythmias supported by enhanced automaticity, such as ectopic atrial tachycardia and idiopathic left ventricular tachycardia. 

Magnesium sulfate may be effective in terminating refractory ventricular tachyarrhythmias, particularly polymorphic ventricular tachycardia. DigitaUs-induced arrhythmias are more likely in the presence of magnesium deficiency. Magnesium sulfate can be administered orally, intramuscularly, or, preferably, intravenously,... 

The prominent depressant action of verapamil and diltiazem at the SA and A-V nodes finds use in specific arrhythmias. They are of proven efficacy in acute control and long-term management of paroxysmal supraventricular tachycardia (see Chapter 16).Their ability to inhibit conduction at the A-V node is employed in protecting ventricles from atrial tachyarrhythmias, often in combination with digitalis or propranolol. 

It includes anorexia, vomiting which may be of central origin. Headache, visual disturbance, xanthopsia (yellow vision), white vision, diplopia, drowsiness, disorientation, delirium and psychotic behaviour. Cardiac related effects include cardiac arrhythmias e.g. tachyarrhythmias, ventricular arrhythmias, supraventricular arrhythmia, AV block and bradycardia. 

Adverse effects include SA block or arrest, high grade AV block, ventricular tachycardia, arrhythmia or ventricular asystole, polymorphic ventricular tachyarrhythmia, hypotension (particularly when given IV), cinchonism, tinnitus, loss of hearing, gastrointestinal upset, severe headache, diplopia, photophobia, etc. 

It is indicated in prophylaxis or treatment of ventricular arrhythmias associated with Ml, digitalis intoxication, ventricular tachyarrhythmia, in patients predisposed to ventricular arrhythmias during general anaesthesia. 

It is indicated in tachyarrhythmias associated with WPW syndrome, atrial flutter and fibrillation, paroxysmal tachyarrhythmias not responding to other agents. Ventricular tachycardia and ventricular arrhythmia refractory to other treatment. 

These are class IC drugs with similar pharmacological profiles and with the same indication range and adverse effects. They are mainly used for the treatment of severe, lifethreatening ventricular tachyarrhythmias, and non-sustained ventricular tachycardia or high-frequency premature ventricular beats. The main adverse effects are cardiovascular, including proarrhythmic actions and severe negative inotropic effects, especially in patients with impaired cardiac function. Both flecainide and encainide increase the risk of sudden death in patients with myocardial infarction and asymptomatic unsustained ventricular arrhythmias. 

Flecainide is very effective in suppressing premature ventricular contractions. However, it may cause severe exacerbation of arrhythmia even when normal doses are administered to patients with preexisting ventricular tachyarrhythmias and those with a previous myocardial... 

In addition to angina, calcium channel blockers have well-documented efficacy in hypertension (see Chapter 11 Antihypertensive Agents) and supraventricular tachyarrhythmias (see Chapter 14 Agents Used in Cardiac Arrhythmias). They also show promise in a wide variety of other conditions, including hypertrophic cardiomyopathy, migraine, and Raynaud s phenomenon. 

Flecainide is very effective in suppressing premature ventricular contractions. However, it may cause severe exacerbation of arrhythmia even when normal doses are administered to patients with preexisting ventricular tachyarrhythmias and those with a previous myocardial infarction and ventricular ectopy (see The Cardiac Arrhythmia Suppression Trial). The drug is well absorbed and has a half-life of approximately 20 hours. Elimination is both by hepatic metabolism and by the kidney. The usual dosage of flecainide is 100-200 mg twice a day. 

Therapeutic uses Quinidine is used in the treatment of a wide variety of arrhythmias, including atrial, AV junctional, and ventricular tachyarrhythmias. Quinidine is used to maintain sinus rhythm after direct current cardioversion of atrial flutter or fibrillation and to prevent frequent ventricular tachycardia. 

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