EKG of the Week

A 44 yo male presents c/o palpitations.

Q1. What does the EKG demonstrate?

Q2. What is the correct management?

A1. Second-degree type I AV block

A2. Supportive care

Second-degree AV block is characterized by one or more (but not all) sinus impulses failing to reach the ventricles. The conduction ratio is defined as the ratio of the number of P waves to the number of QRS complexes over a period of time (e.g., 3 : 2, 2 : 1). Second-degree AV block can be further classified into two types on the basis of the underlying pathophysiology and ECG appearance. Type I second-degree AV block, also called Wenckebach or Mobitz I AV block, is associated with a conduction disturbance within the AV node. The surface ECG is characterized by a progressive lengthening of the PR interval until an impulse is not conducted (“dropped beat”). The progressive lengthening of the PR interval gives the appearance of successive P waves retreating into the preceding QRS complexes. By definition, the longest R-R interval (i.e., following the dropped beat) is less than twice the length of the shortest. On a rhythm strip, type I second-degree AV block gives the appearance of “grouped beating,” especially pairs or trios (i.e., 3 : 2 or 4 : 3 block), but occasionally in larger multiples. This EKG represents grouped beatin gin trios. Grouped beating is not unique to type I second-degree AV block; it occurs in a variety of other conditions, including SA exit block, type II second-degree AV block, and extrasystoles with or without block. Type I second-degree AV block occurs in acute and chronic conditions associated with increased vagal tone and usually requires no treatment. In well-conditioned adults, type I second-degree AV block may be a normal variant. In the setting of an acute inferior myocardial infarction, this type of AV block is generally transient and is associated with a good outcome.

(Yealy, Kosowsky. Dysrrhythmias. In Rosen’s Emergency Medicine, 8th ed. Ch. 79)