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Dressler beat

[drĕs′lər]
n.
  1. A fusion beat interrupting a ventricular tachycardia and, on an electrocardiogram, producing a narrow wave complex.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.