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Premature Ventricular Beat Information
Ventricular premature beats are characterized by wide QRS complexes that differ in morphology from the patient's normal beats. They are usually not preceded by a P wave, although retrograde ventriculoatrial conduction may occur. Unless the latter is present, there is a fully compensatory pause (ie, without change in the PP interval). Bigeminy and trigeminy are arrhythmias in which every second or third beat is premature; these patterns confirm a reentry mechanism for the ectopic beat. Exercise generally abolishes premature beats in normal hearts, and the rhythm becomes regular. The patient may or may not sense the irregular beat, usually as a skipped beat. Ambulatory electrocardiographic monitoring or monitoring during graded exercise may reveal more frequent and complex ventricular premature beats than occur in a single routine ECG. An increased frequency of ventricular premature beats during exercise is associated with a higher risk of cardiovascular mortality, though there is no evidence that specific therapy has a role.
Sudden death occurs more frequently (presumably as a result of ventricular fibrillation) when ventricular premature beats occur in the presence of organic heart disease but not in individuals with no known cardiac disease. If no associated cardiac disease is present and if the ectopic beats are asymptomatic, no therapy is indicated. If they are frequent, electrolyte abnormalities (especially hypo- or hyperkalemia and hypomagnesemia), hyperthyroidism, and occult heart disease should be excluded. Pharmacologic treatment is indicated only for patients who are symptomatic. Because of concerns about worsening arrhythmia and sudden death with most antiarrhythmic agents, -blockers are the agents of first choice. If the underlying condition is mitral prolapse, hypertrophic cardiomyopathy, left ventricular hypertrophy, or coronary disease—or if the QT interval is prolonged—-blocker therapy is appropriate. The class I and III agents are all effective in reducing ventricular premature beats but often cause side effects and may exacerbate serious arrhythmias in 5–20% of patients. Therefore, every attempt should be made to avoid using class I or III antiarrhythmic agents in patients without symptoms.
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