During cardiology conference one of the senior cardiology fellows mentioned that we have seen several cases of patients presenting with new right bundle branch block in the setting of acute MI who had complete arterial occlusion requiring coronary reperfusion (PCI or thrombolytics). While the traditional teaching is that new left bundle branch block in the setting of a clinical presentation suggestive of myocardial infarction mandates immediate reperfusion therapy, the point was made that a new RBBB may also suggest significant myocardial infarct territory, and coronary reperfusion in this setting should be considered.
This reminded me of a conversation I had a few years ago about guidelines for coronary reperfusion in the setting of ACS. The gist of that conversation was that only 1 of the major societies that issues these guidelines suggests consideration of a new RBBB for immediate reperfusion — ACEP.
I pulled the major guidelines to determine why they differed on this issue, and more importantly, why ACEP felt it necessary to broaden the indication for coronary reperfusion to include new RBBB. The first thing to note is that ACEP certainly does not enthusiastically endorse reperfusion therapy in the setting of RBBB given that it is given only a level C recommendation (based on preliminary, inconclusive, or conflicting evidence or expert opinion). Here is their rationale as quoted from the ACEP Clinical Policy:
…only 6 of the 9 trials included in the FTT analysis included BBB as an entry criteria and none of these studies made a distinction from right, left, or atypical, and from new or old. There were only 2,146 (4%) patients with BBB out of a total of 58,600 patients. In this undifferentiated group of BBB, mortality was 18.7% in the fibrinolytic treated patients versus 23.6% in controls…Due to the relatively small number of these patients included in the FTT report, it suggests that these patients with undifferentiated BBB most likely had symptoms strongly suggestive of AMI in order to be enrolled in these clinical trials. Studies since the FTT report have failed to clarify this issue, and it has become commonplace for clinical trials in AMI to either exclude all BBB patients or to include only patients with new or presumably new LBBB as one of the entry criteria.
In essence, ACEP concludes that the FTT analysis (PMID: 7905143) reviewed trials in which the BBB included was undifferentiated, and given that those patients did better with reperfusion therapy and that more recent trials exclude patients with RBBB, evidence is inconclusive to support excluding patients with new RBBB from consideration for reperfusion therapy. Given the acknowledged evidentiary weakness of the this claim, it is given a level C recommendation.
Reviewing the AHA/ACC Practice Guidelines and the European Society of Cardiology Guidelines, there is consensus recommendations on the use of reperfusion therapy for new LBBB or ECG-demonstrated STEMI. The AHA/ACC guidelines do not ever mention the case of new RBBB, and while the ESC guidelines mention the same shortcomings (patients with undifferentiated BBB) in the data reviewed in the FTT analysis, they stop short of recommending consideration of reperfusion therapy for new RBBB (at least in the text, although there is an ambiguous chart on page 38).
The bottom line is that ACEP has put this into a clinical policy which may hold medicolegal weight, although in clinical practice the entire controversy may be moot. This is because unlike in a LBBB, it is still possible to decipher true, ischemic ST elevations in the setting of a RBBB. Thus patients with new RBBB resulting from complete occlusion of a coronary vessel will have ST elevations that should be interpretable despite the right bundle and therefore qualify for reperfusion based on that well-accepted criteria.
