[Recording of monophasic action potentials of the right ventricle in a case of long QT and isolated alternation of the U wave].

Monophasic action potentials (MAP) of the right ventricle were recorded with suction electrodes in a case of long QTU, electrical alternans of the U wave and "torsades de pointe" by hypocalcaemia. Two electrophysiological features were observed:--a notable difference in the duration of MAPs of different zones of the right ventricle;--a change in the length and appearances of phase 3 of the longest MAPs with an inconstant bulge (delayed repolarisation) in the terminal portion of these same MAPs. These changes, which favourise focal reentry phenomena and/or reciprocal conduction are the probable explanation of the pathogenesis of episodes of "torsades de pointe". A reduction in the conductance of potassium associated or related to hypocalcaemia probably explains the second of the two changes.