Potentially Fatal Ventricular Arrhythmias
Ventricular arrhythmias are potentially fatal depending on the setting in which they occur. It has long been recognized that a single premature ventricular beat may initiate ventricular fibrillation in the presence of an acute myocardial infarction or an acute ischemic episode. Such depolarization will initiate ventricular fibrillation most often if it occurs on the apex of the T wave (the vulnerable zone), but in the presence of an acute infarction the single ectopic ventricular beat can initiate ventricular fibrillation during any portion of the cardiac cycle. Evidence has accumulated to document the increased hazard of: (a) two consecutive ventricular beats, (b) “R on T” ventricular beats, and (c) multifocal or multiform ventricular beats. The number of ventricular beats per minute (or preferably per 100 beats) may be a factor in predicting fibrillation, but data are not available to define what that number is. Data on the duration of the vulnerable period following acute infarction are also lacking. After the acute infarction there is an exponential decrease in the prevelance of ventricular fibrillation with time, but vulnerability to ectopic ventricular beats may continue for as long as 3–6 months. It is the purpose of this chapter to classify the types of ectopic ventricular beats and to suggest an approach to their treatment, and most importantly, to define a rational approach to the prevention of these potentially lethal ventricular rhythms in the setting of an acute ischemic episode or infarction.
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