Incomplete Bundle Branch Block: Distinction of types 1a and 2 from our classification (1948)

 Quintiliano H. de Mesquita, MD 

In the year of 1948 we have had the opportunity to register and publish an exceptional and inedited electrocardiographical picture which led us to record the Wenckeback phenomenon in the right bundle branch, showing successive QRS complex of identical morphology but with variable and progressive variation in duration: from <_ 0.10 seconds in the first cycle; from < 0.12 sec. in the second cycle; and from >_ 0.12 sec. in the third cycle with patterns of complete block in the right bundle branch, repeated in a long and continuous ECG, identified as right bundle branch block 3:2.

Such Wenckebach phenomenon has been recorded again by us, along the time, with fascinating aspects of spontaneous normalization of QRS complex, like after atrial or ventricular extrasystole, resulting from the effect and facilitation of Wedensky and also as a phenomenology of dependent bradycardia (Arq.Bras.Cardiol 1948; 1:175, 1958;11:143, 1963; 16:187, 1971;24:15).

In literature are registered similar cases published by Vitolo, E and Rossi, L (Minerva Cardioangiol., 1961;9:254), Friedberg, H.D. and Schamroth, L (Am. J. Cardiol., 1969;24:591) and Rosenbaum, M.B. et al. (Circulation, 1969;40:79).

Over the first cycle of various periods recording Wenckeback phenomenon in the ECG, we have had the chance to capture the incomplete right bundle branch block type 1a, according our classification, characterized by QRS complex with normal duration but morphologically with patterns of right bundle branch block (QRS of <_ 0.10 sec. with double peak of R deflection, in ‘M’, at the right precordial area (V4R, V1); with thick and notched deflections S1, S2, SaVL, V4-V6 and R3, R in aVR and aVF. In the same occasion we obtained recordings of incomplete bundle branch block type 1a alternating with complete RBBB.

Regarding the type 1a of incomplete left bundle branch block we passed to present it with the following characteristics: QRS complex with a duration of <_ 0.10 sec. with a pure deflection R, thick and/or notched, without Q wave at D1, aVL and precordial leads V5 and V6.

In both left and right bundle branch blocks the intrinsecoid deflections varies from 0.04 – 0.08 sec. in the referred precordial leads.

Thus, we established a new incomplete bundle branch block classification joining the already existing type 1 and type 2 as Wenckeback phenomenon at the ‘His’ bundle branch.

In the year of 1949, Sodi Pallares, D ( book, Edition del Instituto N. de Cardiologia, Mexico) adopted a new position coincident with ours related to the incomplete bundle branch block type 1a, including our paper of 1948 in the book bibliography, without justifying his sudden change about the concepts issued in a paper with Friedland, C. (Am. Heart J., 1947;34:930).

Note:  In 1984, we published cases with ECG aspects of conversion of incomplete left bundle branch block type 1a in complete block and vice-versa. (Arq.Bras.Cardiol, 1984;42/2:)

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