ECG Prediction of LVH in LBBB
abstract & commentary
Synopsis: Left atrial abnormality is diagnostic of LVH in patients with LBBB and that older age, larger body size, left axis deviation, and QRS duration greater than 155 ms are also significant predictors of LV mass.
Source: Mehta A, et al. Am J Cardiol 2000;85:354-359.
The presence of left bundle branch block (LBBB) on the ECG makes diagnosing left ventricular hypertrophy (LVH) problematic because conduction delays augment electrocardiographic wave (QRS) voltage and disturb repolarization in ways that mimic LVH. However, LBBB and LVH are frequently associated in autopsy studies. Thus, Mehta and colleagues from the West Virginia University School of Medicine evaluated left atrial abnormality (LAA) on ECG and other clinical factors for their ability to predict LVH by echocardiography. In 220 patients with ECG LBBB, 120 had LAA and they were compared with 100 matched controls without LAA. All patients had LV mass measured by echocardiography. Six conventional ECG criteria for LVH detected LVH in 10% of the patients, whereas LAA accurately predicted increased LV mass (x2 =10; P < 0.001) with a sensitivity of about 80% and a specificity of about 90%. Multivariate analysis showed that LAA was an independent predictor of LV mass after adjusting for age, body mass index (BMI), body surface area (BSA), left axis deviation, and QRS duration, which were also significant predictors of LV mass. Left axis deviation was more common in the patients with LAA (48% vs 30%; P < 0.04) and correlated with LV mass (r = 0.84) in the patients with LAA. Also, QRS duration was more prolonged (> 155 ms) in patients with LAA (61% vs 9%; P < 0.02) and correlated with LV mass (r = 0.82) in patients with LAA. Mehta et al conclude that LAA is diagnostic of LVH in patients with LBBB and that older age, larger body size, left axis deviation, and QRS duration greater than 155 ms are also significant predictors of LV mass.
Comment by Michael H. Crawford, MD
The presence of LBBB in adults usually means cardiomyopathy, which can be ischemic, as it was in about half of the patients in this study. Thus, it is not surprising that autopsy series have shown a high correlation between cardiac enlargement and LBBB. The actual incidence of LVH among patients with LBBB could not be determined in this study since they chose to contrast two groups of patients with LBBB—those with and those without LAA. Clearly, those with LAA had a high incidence of LVH and those without LAA did not, as evidenced by the high predictive value of LAA (88%). Other ECG factors, such as left axis deviation and QRS duration greater than 155 ms, were also independent predictors of LV mass, but only in patients with LAA, not in those without. The same is true for other factors such as age and body size. Thus, LAA seems to be the most important factor.
LAA was evaluated using six criteria: three based upon the P terminal force in V1 and three based upon P-wave duration characteristics. A P terminal force in V1 greater than 0.04 mV/s or one ECG box at normal paper speed was the most common and consistent criterion. Also, the reproducibility of two observers for identifying LAA was high, at 91% agreement. Conventional criteria for LVH by ECG in patients with LBBB were worthless in this study, which is well known.
The proposed mechanism of this observation seems obvious, but has never been proven: LVH leads to increased LV diastolic and left atrial pressure, which produces LAA on ECG. Whether left atrial dilation is required is unknown and was not evaluated in this study. Conventional teaching is that increased LA size or pressure can cause LAA on ECG. How useful this ECG pearl will be clinically is unknown, since almost all patients with LBBB have a diseased LV and should have an echocardiogram done. I can’t imagine restricting the work-up to only those with LAA, but who knows where managed care will take us.
In the presence of LBBB, LVH by ECG is best determined by:
a. left axis deviation.
b. QRS greater than 155 ms.
c. left atrial abnormality.
d. "U" waves.
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