Anterior infarction in a patient with a prior right bundle branch block

ECG 1A: Sinus rhythm, normal PR interval; complete right bundle branch block (QRS duration 120 ms, RsR’ pattern in V1, wide S wave in V6); elevation from V2 to V5;

ECG 1B: The coronary angiogram revealed a thrombosis of the mid-LAD treated with angioplasty + stenting; tracing recorded 2 days after angioplasty; minimal Q-waves from V3 to V6; inverted T-waves from V3 to V6 and in the inferior leads; negative, deep and symmetrical T-waves from V3 to V5;

Comments: A right bundle branch block schematically corresponds to a normal activation of the left ventricle and a delayed activation of the right ventricle. The electrocardiogram thus reveals a wide QRS, a delayed intrinsicoid deflection in V1 with a delayed R’ wave and a wide and slurred S wave in V6. Primary septal activation and the direction of endocardial-epicardial activation of the left ventricular mass are unchanged. The second part of the QRS is modified while its initial part is relatively preserved. It is frequent to observe repolarization disorders limited to the right precordial leads with presence of a moderate depression from V1 to V3.

Unlike left bundle branch block, which alters all activation and repolarization vectors and renders the diagnosis of acute coronary syndrome much more difficult, the presence of a right bundle branch block interferes very little with the occurrence of signs of ischemia.

Since the right bundle branch block does not modify the first milliseconds of depolarization, it does not prevent the recording of necrosis Q-waves regardless of their territory; the Q-waves are followed by the late deformation of the QRS-complex. A few cases of false positives (Q-wave in V1-V2 without anteroseptal necrosis) or false negatives (decrease or disappearance of Q-waves in leads II, III, aVF in a prior inferior infarction) have been described in patients with right bundle branch block.

Unlike the left bundle branch block where it is acknowledged that the depolarization pattern is completely altered, the usual electrocardiographic criteria cannot be applied to the diagnosis of acute coronary syndrome since, theoretically, the presence of a right bundle branch block does not mask the repolarization phase. In the acute phase, the presence of a right bundle block therefore does not in itself represent a sign of acute coronary syndrome and thus investigating for a significant elevation or depression is necessary. There can be a risk of false negative in an anteroseptal infarction. Indeed, the depression in V1 to V3 observed during a right block can completely or partially compensate for the elevation generated by the acute coronary syndrome. Hence, a few cases of undiagnosed massive anteroseptal infarctions and therefore untreated in the absence of characteristic elevation in V1-V3 have been described in the literature. On the other hand, a right bundle branch block does not in itself induce a significant rise in the ST-segment and, thus, an evocative elevation (two contiguous leads ≥ 1 mm) in the setting of chest pain should lead to suspect a diagnosis of acute coronary syndrome. Similarly, a ST-segment depression ≥ 1 mm in two contiguous frontal leads or in the V4-V6 leads is highly suspicious, this pattern being very unusual in patients with right bundle branch block.

Take-home message:The presence of a right bundle branch block incurs little or no interference with the diagnosis of coronary syndrome both in the acute or chronic stages. A few cases of false negative in instances of anteroseptal infarction have been described.