Is Left Bundle Branch Block Associated with In-hospital Mortality Rates Similar to those Associated with ST-Elevation Myocardial Infarction (STEMI)?

Does the evidence support the guidelines that recommend immediate reperfusion therapy for patients presenting with a new or presumed new left bundle branch block (LBBB)? A study presented during the "Women, STEMI, and PCI Trials" Abstract Oral Session Tuesday morning at the American Heart Association Scientific Sessions 2009 provided a surprising answer to that question.

Kimble Poon, from the Harbor-UCLA Medical Center, presented "Does a New or Presumed New Left Bundle Branch Block have Equivalent Mortality to an Acute ST-Elevation Myocardial Infarction?" which sought to determine "if a new or presumed new left bundle branch block carries the same in-hospital mortality as a STEMI." Researchers conducted a retrospective study of the National Registry of Myocardial Infarction (NRMI) database and identified nearly 107,000 patients who had been diagnosed with a STEMI and nearly 17,000 additional patients who had a presumed new LBBB. After excluding patients with previously diagnosed LBBB, the researchers used a multivariate linear regression model to adjust for "53 independent variables representing patient demographics, previous medical history, clinical presentation, and treatments received, including reperfusion therapy."

Analysis of data showed that unadjusted mortality was significantly higher for patients presenting with new or presumed new LBBB compared to patients with STEMI (19% vs. 10%). Mortality associated with new or presumed new LBBB was also higher than that experienced by patients with anterior STEMI (12%) and non-ST elevationmyocardial infarction (NSTEMI; 10.5%).

These numbers did not provide the whole picture however, because, the researchers reported, "patients with new or presumed new LBBB were older with more comorbidities," and were less likely to receive aspirin, statins, ACE inhibitors, beta blockers, or anticoagulation. Only 10% of patients with new or presumed new LBBB received any form of reperfusion therapy; the rate for STEMI patients was 67%.

So, after adjusting for a host of variables, including patient demographics, medical history, clinical presentation, and treatments received, "the picture reversed," said Poon. Now in-hospital mortality for new or presumed new LBBB patients was lower than mortality rates for STEMI and anterior STEMI, but still higher than rates for NSTEMI.

This data showed that new or presumed new LBBB is associated with significantly lower in-hospital mortality than a STEMI; "a patient with presumed new LBBB has a markedly better prognosis than a patient with a STEMI," said Poon. He also said that the difference in prognosis of patients with presumed new LBBB suggests "a different disease process than a STEMI," and that clinicians should not view a new LBBB as being quivalent to a STEMI. Thus, conclude the researchers, "the ACC/AHA recommendation for immediate reperfusion therapy for these patients should be reconsidered."