Bundle branch block during primary angioplasty: reperfusion success remains encrypted in the ECG!

It has been known for years that the finding of bundle branch block (BBB) in patients with ST-segment elevation myocardial infarction (STEMI) is associated with a high mortality rate [1]. In the prethrombolytic era, several studies demonstrated that the presence of left BBB (LBBB) and right BBB (RBBB) was associated with large infarct sizes often accompanied by heart failure, ventricular arrhythmias or cardiovascular death [2]. Although thrombolytic reperfusion decreased mortality in STEMI patients, the appearance of BBB was still associated with a poor short- and long-term prognosis [3–6]. Current guidelines recommend primary percutaneous coronary intervention (PCI) as the gold- standard therapy for the management of patients with STEMI [7–9]. There are some reports addressing the incidence and prognosis of BBB in this setting, but hardly anyone addresses the importance of different kinds of BBB; is it the same as a previous (already known) BBB or a de novo (transient vs persistent after reperfusion) BBB? Why are BBBs associated with such a poor prognosis? The mechanisms explaining why BBBs are asso ciated with such a dismal prognosis remain poorly understood. Previous studies have speculated that the high mortality might be related to the bundle branches’ blood supply. Interestingly, both right and left bundle branches are irrigated by branches arising from proximal coronary arteries, and their occlusion induces large infarctions unless reperfusion therapy is carried out promptly [10]. It is worth noting that the right bundle branch often has a dual blood supply and therefore the involvement of the two main coronary arteries is theor etically required for the appearance of RBBB. Therefore, the association between BBB and an acute myocardial infarction reveals a poor prognosis. However, if the patient presents the BBB before the onset of the STEMI, it is possible that this finding is not associated with the same poor prognosis (Figure 1).