second-degree heart block


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Related to second-degree heart block: First degree heart block, Third degree heart block

second-degree heart block

A form of atrioventricular block in which only some atrial impulses are conducted to the ventricles. Two variants exist: Mobitz I (Wenckebach) and Mobitz II. In Mobitz I, the P-R intervals become progressively longer until a QRS complex is dropped. Because of the dropped beats, the QRS complexes appear to be clustered (grouped beating) on the electrocardiogram. In Mobitz II, P-R intervals have a constant length, but QRS complexes are dropped periodically, usually every second, third, or fourth beat.
See also: heart block