Challenges in the terminology of second-degree atrioventricular block

In 1873, using an isolated frog heart preparation, the Italian physiologist Luigi Luciani was the first to demonstrate group beating [1]. In 1899, Wenckebach credited Luciani with this discovery and called the phenomenon “Luciani periods” [2]. This form of group beating has become known as Wenckebach periodicity in second-degree atrioventricular block (AVB). Thus, Wenckebach AVB is sometimes called Luciani–Wenckebach periodicity/AVB.

“Wenckebach” is one of the most common eponyms in medicine. The form of AVB described by Wenckebach is now called traditional or classic. The mathematical characteristics of the classic form are well-known. The atypical type has also been called “common” since it is far more frequent than the traditional form. Atypical Wenckebach AVB has never been clearly defined by professional organizations. It can be considered a form of Wenckebach AVB that deviates in any way from the traditional form. Wenckebach AVB is often labeled as Wenckebach type I AVB, but it is an example of tautology, given that there is no need to add “type I” since the term “Wenckebach AVB” is self-evident. Furthermore, using the label of type I incorrectly suggests to the beginner that in Wenckebach AVB, there might also be a type II Wenckebach AVB.

In 1924, using the electrocardiograph, Mobitz classified the well-known Wenckebach form of second-degree AVB as type I and characterized the form of AV block originally described by Hay in 1906 as type II second-degree AVB [3, 4]. This led to an alternative appellation of Wenckebach AVB as Mobitz type I AVB. Unfortunately, use of the term “Mobitz block” in the literature, presumably referring to type II block, is potentially misleading without specifying whether it refers to Mobitz type I or type II AVB. Mobitz did not specifically indicate that sustained 2:1 AVB was a form of type II AVB. Rather, he showed that 2:1 AVB may be associated with sequences showing intermittent typical type II AVB. Unfortunately, to this day, sustained 2:1 AVB is not infrequently called Mobitz type II AVB in the literature. Furthermore, high grade or advanced second-degree AVB with constant PR intervals before and after the non-conducted P waves is called Mobitz II AVB by purists, who cite Mobitz’s original article showing more than one blocked P wave, thereby defying the present codified definition requiring the block of a single P wave. In other words, apart from Mobitz type I and II AVB, any other form of second-degree narrow QRS AVB should not be automatically called Mobitz type I block, while any form of wide QRS complex second-degree AVB should not automatically be labeled as Mobitz type II block.

The term “apparent Mobitz AVB” has been used to describe some cases of vagally induced AVB associated with sinus slowing. “Pseudo-Mobitz type II AVB” has been used to describe a manifestation of concealed extrasystoles mimicking true Mobitz type II AVB [5]. It has also been applied to a sequence of Wenckebach AVB with constant PR intervals in its terminal part before the non-conducted beat mimicking true Mobitz type II AVB. The term “pseudo-Mobitz type II AVB” seems preferable to “apparent.”