Does a prolonged QT peak identify left ventricular hypertrophy in hypertension?

BACKGROUND

Left ventricular hypertrophy is a powerful predictor of death. Hypertensive subjects with left ventricular hypertrophy can have increased QT (end) dispersion, which is associated with cardiac death. Despite its prognostic value, QT (end) dispersion is not widely used. QTp (i.e. start of QRS to peak of T wave) is easier to measure. Therefore, we tested the hypothesis that long QT peak was associated with left ventricular hypertrophy and assessed its cost-effectiveness at diagnosing left ventricular hypertrophy.

METHODS

ECGs and echocardiograms were recorded in 47 hypertensive patients. The onset of the QRS complex and peak of T wave of lead I of each subject's ECGs were digitised by one observer blind to results of the echocardiogram. Receiver-operator characteristics curves were plotted to determine the sensitivity and specificity of different cut-off values of QT peak at predicting left ventricular hypertrophy (defined as left ventricular mass index> or =134 g/m2 in male, > or =110 g/m2 in female).

RESULTS

The heart-rate corrected QT peak of lead I correlated with left ventricular mass index (r=0.45, P=0.002). If all patients with a prolonged QT peak (> or =300 ms) had an echocardiogram, then no cases of left ventricular hypertrophy would be missed (100% sensitive). This novel ECG criterion not only had better positive and negative predictive values than the Sokolow-Lyon voltage criteria, but also resulted in more cost-effective resource use (< pound 370 vs. pound 1750/case of left ventricular hypertrophy detected).

CONCLUSION

If the results of this small pilot study are confirmed in larger studies, then measuring QT peak of lead I may become a cost-effective way of identifying hypertensives who are likely to have echocardiographic left ventricular hypertrophy.