Arrhythmias types

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]. 

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). 

The term anaphylactic shock describes a severe generalized type I allergic reaction associated with cardiovascular shock, airway constriction and heart arrhythmias, which, if left untreated, may cause death. 

In the Long QT Syndrome (LQTS), the repolarization phase of the cardiac muscle is delayed, rendering the heart vulnerable to an arrhythmia known as torsade de pointes. LQTS is associated with five genes encoding ion channels. LQTS type 3 (LQT3) results from mutations of Nav1.5, which cause persistent sodium cunent. In contrast, sodium channel mutations associated with Biugada syndrome reduce the expression level of cardiac sodium channels. 

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. 

Antiarrhythmic dragp are used to treat various types of cardiac arrhythmias. There are initial preadministration assessments the nurse performs before starting therapy that are the same for all antiarrhythmic drags. These assessments include ... 

One eritical factor that has been neglected in considering mechanisms of cardiac fatalities is the timeframe for various types of toxicities. For example, a majority of cocaine-related fatalities and near fatalities reported from emergency rooms are attributed to one or more types of cardiac ischemic or hypertensive episodes (Isner et al. 1986). Thus, these studies may discount the cocaine-induced arrhythmias and conduction defects as important direct causes of fatalities. Yet, if coroner reports are used as data sources (Virmani et al. 1988 Wetli and Wright 1979 Mittleman and Wetli 1984), there are great numbers of deaths in which pulmonary effusion and lack of evidence for coronary occlusion, acute myocardial infarction, or... 

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. 

Proarrhythmia refers to development of a significant new arrhythmia (such as VT, ventricular fibrillation [VF], or TdP) or worsening of an existing arrhythmia. Proarrhythmia results from the same mechanisms that cause other arrhythmias or from an alteration in the underlying substrate due to the antiarrhythmic agent. TdP is a rapid form of polymorphic VT associated with evidence of delayed ventricular repolarization due to blockade of potassium conductance. TdP may be hereditary or acquired. Acquired forms are associated with many clinical conditions and drugs, especially type la and type III IKr blockers. 

The most frequently used classification system is that proposed by Vaughan Williams (Table 6-1). Type la drugs slow conduction velocity, prolong refractoriness, and decrease the automatic properties of sodium-dependent (normal and diseased) conduction tissue. Type la drugs are broad-spectrum antiarrhythmics, being effective for both supraventricular and ventricular arrhythmias. 

Although categorized separately, type lb drugs probably act similarly to type la drugs, except that type lb agents are considerably more effective in ventricular than supraventricular arrhythmias. 

Type Ic drugs profoundly slow conduction velocity while leaving refractoriness relatively unaltered. Although effective for both ventricular and supraventricular arrhythmias, their use for ventricular arrhythmias has been limited by the risk of proarrhythmia. 

---