[The long QT syndrome: importance of phonocardiography and ergometry]

The chronological relationship between the S2 of the phonocardiogram and the T wave of the ECG, and the behaviour of the QT and QTc intervals, have been investigated in two cases of idiopathic long QT syndrome (LQTS) at rest and during effort. At rest and during effort with heart rates (HR) under 120/min, the S2 is always abnormal before the end of the T wave where the QTc interval is generally prolonged, but is sometimes within normal range (less than or equal to 440 msec). In cases where the QTc interval falls within normal range, the use of Bazett's formula to calculate the QTc interval may mislead and cause the existence of LQTS to be overlooked. Study of the chronological relationship (timing) between S2 and T wave is a reliable method of detecting LQTS even with a normal QTc interval. During ergometer exercise, if we observe (as in our two cases) not only a normal acceleration of the HR but a shortening and even a normalization of the QTc interval, therapeutic abstention (betablockers) may be recommended in asymptomatic LQTS. It is concluded that (1) in LQTS at rest and with HR under 120/min, S2 is always abnormal before the end of the T wave, (2) study of the timing S2/T wave is a reliable method of detecting the existence of LQTS even with a normal QTc interval, (3) in asymptomatic LQTS where the QTc interval shortens or falls within normal range during effort with S2 appearing at the end of the T wave, as reported in our first case, therapeutic abstention (betablockers) may be recommended.