BMH Med. J. 2019; 6(4):145-146.   Interesting ECG

Masquerading Bundle Branch Block

Johnson Francis, MBBS, MD, DM, FACC, FRCP

Baby Memorial Hospital, Kozhikode, Kerala, India

Address for Correspondence: Prof. Dr. Johnson Francis, Senior Consultant Cardiologist, Baby Memorial Hospital, Kozhikode, Kerala, India, PIN 673017. Email: pulikkottil2002@hotmail.com

Abstract

Masquerading bundle branch block can be either of the standard type or the precordial type. In the standard type, precordial leads show right bundle branch block pattern and frontal plane leads show left bundle branch block pattern. Precordial type of masquerading bundle branch block is characterised by right bundle branch block pattern in anterior leads and left bundle branch block in leads V4 to V6. Several authors have reported a poor prognosis for masquerading bundle branch block.

Keywords: Masquerading Bundle Branch Block

The term masquerading bundle branch block was coined by Richman JL and Wolff in 1954 [1]. Two types of masquerading bundle branch block has been described: (a) standard type and  (b) precordial type [2]. In the standard type, precordial leads V1-V6 are suggestive of right bundle branch block, while frontal plane leads (limb leads) resemble that left bundle branch block. The ECG shown in Figure 1 is suggestive of the standard type of masquerading bundle branch block. Lead I and aVL shows left bundle branch block pattern while V1 shows right bundle branch block pattern. In addition to these, this ECG shows atrial fibrillation and left axis deviation with rS complexes in the inferior leads (left anterior hemiblock pattern).

Figure 1: Masquerading bundle branch block

In the precordial type, leads V4 to V6 shows left bundle branch block pattern while right precordial leads V1 to V3 shows right bundle branch block pattern. Masquerading bundle branch block is considered to be a marker of poor prognosis, as reported by several authors [3-5].

Masquerading bundle branch block is thought to be caused by presence of high grade left anterior fascicular block with right bundle branch block when associated with severe left ventricular enlargement [5]. This implies extensive disease of the left ventricle and hence the poor prognosis. There is reorientation of terminal electrical forces of the QRS complex upwards and to the left so that the slurred S wave in lead I expected in right bundle branch block becomes diminutive or disappears.

References

1. Richman JL, Wolff L. Left bundle branch block masquerading as right bundle branch block. Am Heart J. 1954 Mar;47(3):383-93.

2. Choudhary D, Namboodiri N, Tharakan JA. A case of 'Masquerading' bundle branch block: a forgotten concept. Indian Heart J. 2014 Jan-Feb;66(1):139-40.

3. Kaimoto S, Kawasaki T, Taniguchi T, Kawasaki S, Kamitani T, Sugihara H. Masquerading bundle branch block as a marker of poor prognosis. J Cardiol Cases. 2013 May 16;8(1):e57-e59.

4. Dhanse S, Kareem H, Devasia T, Rao MS. Masquerading Bundle Branch Block: A Poor Prognostic Sign Revisited. J Clin Diagn Res. 2016 Sep;10(9):OD01-OD02.

5. Elizari MV, Baranchuk A, Chiale PA. Masquerading bundle branch block: a variety of right bundle branch block with left anterior fascicular block. Expert Rev Cardiovasc Ther. 2013 Jan;11(1):69-75.