Poor Estimation of Echocardiographic Left Atrial Linear Dimension From Electrocardiographic Assessment in an Outpatient Cohort

Left atrial (LA) dilatation on transthoracic echocardiograms (TTEs) can be estimated in inpatients by the formula LA dimension (mm) = 2.47 + 0.29 x P wave duration (ms). This association, however, has not been assessed among outpatients who are perhaps "less sick." The authors applied blinded P wave measurements to this formula among 35 consecutive outpatients with valid TTEs (electrocardiograms obtained within 60 days of initial assessment). Fifteen patients (42.9%) had P wave measurements above the normal cutoff (110 ms), but no patients had P wave measurements that exceeded 130 ms. Mean (108.6+/-11 ms) and mode (100 ms) durations were considerably shorter than those of previously studied hospitalized cohorts. Estimated LA dimension by formula was comparable with TTE LA dimension in 29 patients (82.9%), all of whom were among those without LA dilatation on TTE. The regression formula is therefore useful in predicting normal LA linear dimension but is insensitive for estimating LA dilatation on TTE among outpatients in whom P waves rarely exceeded 130 ms.