Ventricular tachyarrhythmias

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Ventricular premature complexes are commonly seen in the critically ill and are not usually treated unless the patient develops ventricular tachycardia. In the setting of acute myocardial infarction, premature ventricular contractions are considered as warning arrhythmias and may progress to ventricular tachycardia. However, unless this develops, the current recommendation is not to treat isolated premature ventricular contractions as the toxic effects of antiarrhythmic drugs do not warrant the potential benefits. During the first 48 h following myocardial infarction, most episodes of ventricular tachycardia are non-sustained asymptomatic events that do not alter prognosis.

Occasionally, an accelerated idioventricular rhythm occurs with rates between 50 and 100 beats/min. More commonly seen after acute myocardial infarction, it is not associated with lethal ventricular arrhythmias and does not alter short- or long-term prognosis. It is frequently seen during episodes of sinus bradycardia, and the administration of 0.5 to 1 mg atropine will usually restore normal conduction by increasing the sinus rate. However, atropine possesses arrhythmogenic properties and may also result in sinus tachycardia which will increase myocardial oxygen consumption. Therefore this rhythm is not treated unless there is hemodynamic compromise.

Treatment of ventricular tachycardia depends on the condition of the patient. Frequently, short runs of non-sustained ventricular tachycardia are not treated if asymptomatic, and treatment of the underlying problem may be all that is necessary. Lidocaine is usually the drug of choice with symptomatic non-sustained or sustained ventricular tachycardia. However, if it is injected too quickly, transient toxic levels may cause atrioventricular block or central nervous system abnormalities. Amiodarone may be administered as a continuous infusion, giving additional 150-mg boluses over 10 min for breakthrough ventricular tachycardia/fibrillation to a total of 1000 mg in the first 24 h. Other medications that can be used include intravenous procainamide and bretylium. If the patient is stable, an alternative would be ventricular pacing to interrupt the re-entry circuit. Occasionally, however, artificial pacing may increase the ventricular rate and degenerate into ventricular fibrillation. If medications are ineffective in converting the ventricular tachycardia and ventricular pacing is not available, elective d.c. synchronized cardioversion, starting as low as 50 J, may be effective. The patient should be adequately sedated prior to this procedure. If the patient becomes unstable at any point, immediate synchronized d.c. cardioversion (100-360 J) is indicated.

Beta-blockers may be helpful in acute myocardial infarction, as ventricular tachycardia during this time period may be due to an automatic focus. Antiarrhythmic agents may be proarrhythmic when used in this setting and the patient must be observed closely. Non-pharmacological intervention, such as intra-aortic balloon counterpulsation, emergency coronary artery bypass surgery, or angioplasty, may be necessary to stabilize arrhythmias related to ischemia.

Patients with torsade de pointes respond poorly to lidocaine, procainamide, and bretylium, and actually may be made worse by class IA, IC, or III antiarrhythmics. Treatment requires prompt correction of any metabolic abnormalities, and particular attention should be given to potassium and magnesium replacement. Any potentially offending medications should be withheld, and intravenous catecholamines or rapid rate pacing may help prevent recurrence.

Ventricular fibrillation or flutter requires immediate electrical cardioversion at 360 J. If this is ineffective, administering a 100-mg lidocaine bolus followed by repeat d.c. cardioversion is indicated. Bretylium and procainamide are other agents that may be used. As with any arrhythmia, metabolic abnormalities such as acidosis, hypoxemia, hypokalemia, and hypomagnesemia should be corrected. Prophylaxis for recurrent ventricular fibrillation is similar to that for ventricular tachycardia, and care must be taken to search for any precipitating factors.

Ventricular fibrillation or flutter requires immediate electrical cardioversion at 360 J. If this is ineffective, administering a 100-mg lidocaine bolus followed by repeat d.c. cardioversion is indicated. Bretylium and procainamide are other agents that may be used. As with any arrhythmia, metabolic abnormalities such as acidosis, hypoxemia, hypokalemia, and hypomagnesemia should be corrected. Prophylaxis for recurrent ventricular fibrillation is similar to that for ventricular tachycardia, and care must be taken to search for any precipitating factors.

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