Arrhythmias etiology

Treatment of sinus bradycardia is only necessary in patients who become symptomatic. If the patient is taking any med-ication(s) that may cause sinus bradycardia, the drug(s) should be discontinued whenever possible. If the patient remains in sinus bradycardia after discontinuation of the drug(s) and after five half-lives of the drug(s) have elapsed, then the drugs(s) can usually be excluded as the etiology of the arrhythmia. In certain circumstances, however, discontinuation of the medication(s) may be undesirable, even if it may be the cause of symptomatic sinus bradycardia. For example, if the patient has a history of myocardial infarction or HF, discontinuation of a (3-blocker is undesirable, because (3-blockers have been shown to reduce mortality and prolong life in patients with those diseases, and the benefits of therapy with... 

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. 

Heart disease is the leading cause of death in the United States and is responsible for approximately 870,000 deaths per year (1). Sudden cardiac death (SCD) is responsible for almost half of these deaths, claiming 350,000 to 400,000 lives per year (2). SCD is defined by the World Health Organization as death due to any cardiac disease that occurs out of hospital, in an emergency room, or a patient who is dead on arrival to a care facility. Of note, the death must occur within one hour after the onset of symptoms. The majority of SCD is likely arrhythmic in etiology. In women, up to 88% of sudden cardiac arrests may be due to arrhythmic causes (3). Of SCD due to cardiac arrhythmias, greater than 80% of events are due to ventricular tachycardia (VT) and ventricular fibrillation (VF), with the remainder due to bradyarrhythmias and asystole (4). Coronary artery disease (CAD), manifesting acutely as ischemic ventricular arrhythmias or chronically as scar-mediated... 

Class III indications for an ICD (i.e., NOT indicated) (1) Syncope of unclear etiology when an electrophysiology study fails to induce any ventricular arrhythmia. (2) Ventricular arrhythmias secondary to transient or reversible disorders. (3) Elderly patients with projected life expectancy less than 1 year due to major comorbidities. (4) Terminal illnesses with projected life expectancy < 12 months. 

Sudden, unexpected death is usually classified as cardiac in etiology, assumed to be due to ischemic heart disease or an arrhythmia. Death Irom asphyxia caused by acute bronchospasm could be erroneously classified as a cardiac cause of death. In addition, exacerbations of COPD can precipitate cardiac arrhythmias or myocardial infarction in patients with significant underlying heart disease (6,42). Severe COPD is often complicated by cor pulmonale, or chronic failure of the right ventricle caused by pulmonary hypertension and hypoxemia. Deaths caused by cor pulmonale may be misclassified as primary cardiac deaths, although the precipitating event may be a pulmonary insult. 

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