Monophasic action potentials in patients with coronary artery disease: reproducibility and electrical restitution and conduction at different stimulation rates.

Monophasic action potentials were recorded in the outflow tract of the right ventricle in patients with coronary artery disease during ventricular pacing at different basic cycle lengths and programmed stimulation. During continuous pacing (basic cycle length 600 ms) the time for 90% repolarisation (MAP90) and the QTa interval decreased exponentially during the first 1.5-2 min of pacing to 90% of control values. The reproducibility of the monophasic action potential signals and the ventricular effective refractory period were assessed as good when studied after repetitive trains of 8 beats for more than 1.5 min. The reproducibility of conduction, however, was less good. Electrical restitution of MAP90 duration of the premature beats determined at three different basic cycle lengths was different from that in single muscle preparations. The curves showed two phases with unchanged MAP90 durations despite longer coupling intervals. The first phase was close to the ventricular effective refractory period, probably because subnormal conduction left the diastolic interval constant for the earliest premature beats. This indicates that subnormal conduction may influence the premature dispersion of repolarisation.