Echocardiography may not improve accuracy of acute MI diagnosis in the presence of LBBB
Early echocardiography for suspected acute MI in the presence of left bundle branch block may not increase diagnostic accuracy in differentiating chest pain from other causes in hemodynamically stable patients, researchers reported.
According to data published in the Journal of the American Heart Association, the proportion of patients with wall motion abnormalities in the presence of left bundle branch block (LBBB) was similar, regardless of whether there was a final diagnosis of acute MI or not.
“Patients with suspected acute MI in the setting of LBBB present an important diagnostic and therapeutic challenge to clinicians, as altered ventricular depolarization might mask changes in ventricular repolarization associated with acute MI,” Thomas Nestelberger, MD, research fellow at the Cardiovascular Research Institute Basel and the department of cardiology at the University Hospital Basel, Switzerland, and the GREAT Network, Rome, and the division of cardiology at Vancouver General Hospital at the University of British Columbia, Canada, and colleagues wrote. “We hypothesized that the use of early echocardiography may provide value in the differentiation of acute MI from other causes of acute chest pain.”
Researchers evaluated three international, prospective studies to assess the diagnostic accuracy of echocardiography in patients presenting with suspected acute MI and LBBB at 26 EDs. In this analysis, final diagnoses were adjudicated by two independent cardiologists according to the fourth universal definition of acute MI using available ECGs, serial troponin measurement, echocardiography, MRI and coronary angiography performed before and after the index event. Patients underwent echocardiography if indicated by the treating physician and were included in the analysis if echocardiography was performed prior to revascularization.
Acute MI diagnosis with echocardiography
Of 10,959 patients who presented to the ED with acute chest pain, LBBB was identified in 2.6% of patients. Of those, transthoracic echocardiography was performed in 35%. According to the study, acute MI was the final diagnosis in 41% of patients with confirmed LBBB.
Wall motion abnormalities were documented in 77% of the cohort, with comparable incidence among patients with a final diagnosis of acute MI or other diagnoses (80% vs. 75%; P = .49). The results were similar when evaluations were isolated to motion abnormalities of the anterior wall.
According to the study, the prevalence of anterior wall abnormalities (54% in both groups; P = .95) and septum wall abnormalities (acute MI, 66%; no acute MI, 58%; P = .41) were similar among patients with LBBB and a final diagnosis of acute MI compared with other diagnoses.
Moreover, the prevalence of other structural and/or functional abnormalities such as left atrium dilation, left ventricular hypertrophy or LV dilation did not differ among patients with a final diagnosis of acute MI compared with patients with other diagnoses.
“These findings have important and immediate clinical consequences, as they falsified the assumption underlying our hypothesis regarding the utility of echocardiography in patients with suspected acute MI and LBBB as recommended in current guidelines,” the researchers wrote. “As these data were derived from large international diagnostic studies using central adjudication by independent cardiologists, their validity and generalizability seem high.”
Lingering questions about acute MI diagnosis
In a related editorial, Yochai Birnbaum, MD, FAHA, FACC, professor of cardiology and the John S. Dunn Chair in Cardiology Research and Education at Baylor College of Medicine, and colleagues discussed some of the lingering questions left by this study.
“This study does not answer well the question we most want to know: Does a wall motion abnormality have high sensitivity for [occlusion MI]? If a patient has no wall motion abnormality, can we wait for the troponin diagnosis and avoid emergent catheterization laboratory activation? What is its sensitivity (or negative predictive value or negative likelihood ratio) for occlusion MI,” the editorial authors wrote. “They have certainly shown that wall motion abnormalities has low sensitivity for any acute MI, but many non-occlusion MI acute MI are very small and would not be expected to have a wall motion abnormalities.
“If echocardiography does not improve the diagnosis of occlusion MI and can cause delays in reperfusion therapy, we would need to continue using a combination of clinical evaluation, ECG scores, and serial troponin tests,” the editorial authors wrote. “It should be emphasized that if the patient continues to have symptoms despite initial medical therapy, is hemodynamically unstable, or develops sustained ventricular arrhythmia, an immediate invasive strategy is recommended even if the diagnosis of STEMI equivalent is uncertain.”