Right bundle branch block with left posterior hemiblock

Right bundle branch block with left posterior hemiblock

Right bundle branch block with left posterior hemiblock
Right bundle branch block with left posterior hemiblock

Right bundle branch block is evident as wide QRS (160 msec), slurred S wave in lead I and slurred R in V1. In V1 there is qR pattern suggesting anterior wall infarction with right bundle branch block (qRBBB).  The QRS shows right axis deviation (dominant negative deflection in leads I and aVl) with dominant positive deflection in aVf along with rS pattern in lead I and qR pattern leads III and aVf, suggesting left posterior hemiblock. This combination is bifascicular block. The PR interval is borderline at 200 msec. If PR interval is prolonged in this combination, it becomes trifascicular block.

Left posterior hemiblock is the rarest of the fascicular blocks as it is spared in most cases due to the dual blood supply from left anterior descending coronary artery and right coronary artery [1]. For the same reason, left posterior hemiblock carries a poorer prognosis. Since the left posterior fascicle is a broad fascicle compared with the anterior fascicle and has dual blood supply, it is involved only in more extensive myocardial infarction. This would mean  more severe left ventricular dysfunction. The combination of left posterior hemiblock with right bundle branch block carries a still worse outcome. The very wide QRS for an RBBB in this case also indicates more extensive myocardial damage. The T wave inversion in leads V1 to V3 could be explained either by the old myocardial infarction or by the right bundle branch block.

In a study of 21 patients with chronic right bundle branch block and left posterior hemiblock, 48% had hypertensive cardiovascular disease and 33% had primary conduction disease. Three patients needed a permanent pacemaker during a mean follow up period of 671 days. One patient died suddenly and two others died of noncardiac causes [2].

Left posterior hemiblock can mask the Q waves of an inferior wall myocardial infarction. This has been demonstrated in a case with inferior wall infarction and transient left posterior hemiblock during an episode of angina [3].

References

  1. PĂ©rez-Riera AR, Barbosa-Barros R, Daminello-Raimundo R, de Abreu LC, Tonussi Mendes JE, Nikus K. Left posterior fascicular block, state-of-the-art review: A 2018 update. Indian Pacing Electrophysiol J. 2018 Nov-Dec;18(6):217-230.
  2. Dhingra RC, Denes P, Wu D, Chuquimia R, Amat-Y-Leon F, Wyndham C, Rosen KM. Chronic right bundle branch block and left posterior hemiblock. Clinical, electrophysiologic and prognostic observations. Am J Cardiol. 1975 Dec;36(7):867-79.
  3. Elizari MV, Acunzo RS, Ferreiro M. Hemiblocks revisited. Circulation. 2007 Mar 6;115(9):1154-63.
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