Simultaneous recording of monophasic action potentials and contractile force from the human heart.

Cardiac monophasic action potentials (MAPs) and contractility have been simultaneously measured in man while the heart rate was being changed by right atrial pacing. A new non-suction electrode was used for safe and long-term recording of MAPs from the endomyocardium. Abrupt changes in cycle-length were followed first by a fast, then a slow response in the adaptation of MAP-duration and of contractility (LV dp/dt max) to the new steady state. After increasing the heart rate then slow phase of MAP shortening appears to be related to the slow staircase of contractility, whereas after the step decrease of frequency no such a relation could be observed. The consistency of these results with those obtained in corresponding in-vitro experiments indicates that this methodical approach may be suitable for assessing the process of E-C coupling in the human heart.