Types of Arrhythmias

Ca waves in systems [ike Xenopus laevis oocytes and pancreatic (3 cells fall into this category Electrochemical waves in cardiac and nerve tissue have this origin and the appearance and/or breakup of spiral wave patterns in excitable media are believed to be responsible for various types of arrhythmias in the heart [39, 40]. Figure C3.6.9 shows an excitable spiral wave in dog epicardial muscle [41]. 

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. 

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. 

Exercise-induced ventricular tachycardia in persons without overt cardiac disease is an example of delayed after-depolarizations and is characterized by an increase in intracellular ionized calcium. This type of arrhythmia is known to often respond well to which of the following combinations ... 

In the following paragraphs several types of arrhythmia will be discussed with regard to the underlying mechanisms. Since it would be out of the scope of this book on gap junction channels to discuss all possible mechanisms of arrhythmia in detail, readers interested in a complete detailed review of the pathophysiology and clinics of arrhythmia are referred to the reviews by Janse and Wit [1989] and Pogwizd and Corr [1987, 1990] and to the specialized literature. 

An arrhythmia can be broadly defined as any significant deviation from normal cardiac rhythm.6 Various problems in the origination and conduction of electrical activity in the heart can lead to distinct types of arrhythmias. If untreated, disturbances in normal cardiac rhythm result in impaired cardiac pumping ability, and certain arrhythmias are associated with cerebrovascular accidents, cardiac failure, and other sequelae that can be fatal.1,2 16 Fortunately, a variety of drugs are available to help establish and maintain normal cardiac rhythm. 

Individual beta blockers are presented in Chapter 20. Beta blockers shown to be effective in treating arrhythmias include acebutolol, atenolol, esmolol, metoprolol, nadolol, propranolol, sotalol, and timolol (see Table 23-2). Choice of a specific beta blocker depends to a large extent on the exact type of arrhythmia present and the individual patient s response to the drug. 

Cardiotoxicity is a very well known side effect of phenothiazine drug (see Fig. 1) administration. The main cardiotoxic effect is the induction of different types of arrhythmia, which are mostly the result of QT interval prolongation [242], This prolongation can be associated with a potentially lethal ventricular arrhythmia known as torsades de pointes [242,243]. The mechanism of the influence of phenothiazines on QT interval prolongation is complex, but on the molecular level there is increasing evidence that different types of myocardial ion channels are involved [243]. 

It is evident that during all types of cardiac catheterization (Table I) atrial fibrillation (AF) can occur and that several patients will present with preexisting AF It is the most common type of arrhythmia in adults (I), The prevalence goes from less than I % in persons younger than 60 years of age to more than 8% in those olderthan 80 years of age (2). The age-adjusted incidence for women is about half that of men. 

Amiodarone, for example (Fig. 1.12), was introduced as a coronary dilator for angina, but concern about comeal deposits, discoloration of skin exposed to sunlight and thyroid disorders led to the withdrawal of the drug in 1967. However, in 1974 amiodarone was found to be highly effective in the treatment of a rare type of arrhythmia known as the Wolff-Parkinson-White syndrome. Accordingly, amiodarone was reintroduced specifically for that purpose [22]. 

On the other hand, with other types of arrhythmias, digitalis may be used primarily for the sake of its action on pacemaker cells. 

As it happens with all types of arrhythmias the incidence in the acute MI phase, of RBBBs and LBBBs, has decreased very much since the introduction of reperfusion therapy, because this treatment improves intraventricular conduction system perfusion. Furthermore, the prognosis is better, as in general the ventricular function is also more preserved (Roth et al, 1993). 

Another study compared the toxicity of trichloroacetic acid (TGA) and phenol (Baker s solution) the conclusion was that it would appear advisable to set up a cardiac monitor during a ftill-face peel with Baker s solution, whereas TGA does not cause any type of arrhythmia. 

A major limitation of AEM is the amount of data collected with ECG abnormalities that are of unknown clinical significance. High day-to-day variability of frequency and type of arrhythmias means that repeat AEM may demonstrate as much as a 90% difference in... 

There are many dmgs available to treat arrhythmias and the choice of drug often depends on the type of arrhythmia. Anti-arrhythmic drugs have been classified according to their mode of action into the so-called Vaughan-Williams classification. (See Table 4.2.)... 

The Vaughan—Williams classification is of academic interest. Clinically, the type of arrhythmia against which the drugs are effective is of more importance than their mode of action. 

P-blockers are useful in all types of arrhythmia because they block the conducting system in the heart and reduce heart rate. 

Quinidine can suppress all types of arrhythmia, but also cause them. Because of this, it is rarely used without specialist guidance. 

Ischaemic heart disease can be treated with nitrates, potassium channel activators, P-blockers and calcium channel blockers. All these drugs either improve the blood supply to the myocardium or reduce its metabolic demand for oxygen, or both. Beta blockers are also useful in treating hypertensive patients who do not respond adequately to other antihypertensive drugs, and some types of arrhythmia because they slow the heart rate. 

Quinidine is used in the therapy of atrial arrhythmias, particularly atrial flutter and atrial fibrillation. It is also useful in other types of arrhythmias (e.g., v-tac), and is also useful in the treatment of malaria, when given intravenously. 

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