Anterior infarction and right bundle branch block appearance

ECG 1A: Sinus rhythm, normal PR interval; complete right bundle branch block (QRS duration 120 ms, QR pattern in V1, delayed intrinsicoid deflection in V1, wide S wave in V6); wide and deep Q-wave from V1 to V3; elevation from V2 to V5;

ECG 1B: The coronary angiogram revealed thrombosis of the proximal LAD treated by angioplasty + stenting; ECG recorded 2 days later; intermittent right bundle branch block (1 complex with narrower QRS); identical repolarization pattern (elevation from V2 to V4) whether the QRS is wide or narrow;

ECG 1C: ECG recorded 2 hours later; QRS narrowing (disappearance of the right bundle branch block pattern);

Comments: the occurrence of a right bundle branch block is mainly observed in anterior infarctions by occlusion of the proximal LAD before the first septal branch which supplies the right bundle branch. The right block may be transient or permanent depending on the delay in coronary reperfusion with prognosis seemingly better in the former instance. As explained on the previous tracing, the right bundle branch block causes very little interference with changes in the QRS pattern and in the repolarization induced by the acute coronary syndrome. In this patient, the elevation characteristic of the acute phase remains visible from V2 to V4, whereas a right bundle branch block is rather usually accompanied by a depression in these leads. Similarly, this anteroseptal infarction is accompanied by a QR complex in V1, V2 followed by a wide and slurred necrosis Q-wave and a late R wave with delayed intrinsicoid deflection corresponding to the late depolarization of the right ventricle. Remotely, there is a persistent elevation from V2 to V3 possibly suggesting the presence of a developing left ventricular aneurysm.

Various studies have shown that

1. a right bundle branch block is observed in about 5-6% of patients with acute coronary syndrome;
2. the right bundle branch block occurs preferentially in a relatively extended coronary syndrome in conjunction with a proximal LAD thrombosis;
3. association with a left anterior fascicular block is relatively frequent;
4. as in the case of the left bundle branch block, when a right bundle branch block is highlighted in the course of an acute coronary syndrome, prognosis is guarded with a significantly increased mortality; it would further appear that the combination of right bundle branch block + left anterior fascicular block has the most pejorative prognosis; the risk of heart failure and complete atrioventricular block is also significantly increased;
5. the presence of a block reflects an extensive infarction worsening the prognosis of the patient and must hence encourage the decision of invasive reperfusion or emergency thrombolysis.

Take-home message: the onset of a right bundle branch block in the course of an acute anterior coronary syndrome reflects the presence of a proximal LAD lesion and alters the prognosis to at least the same extent as the onset of a left bundle branch block.