The monophasic action potential upstroke: a means of characterizing local conduction

J H Levine, E N Moore, A H Kadish, T Guarnieri, J F Spear
1986 Circulation  
The upstrokes of monophasic action potentials (MAPs) recorded with an extracellular pressure electrode were characterized in isolated canine tissue preparations in vitro. The characteristics of the MAP upstroke were compared with those of the local action potential foot as well as with the characteristics of approaching electrical activation during uniform and asynchronous conduction. The upstroke of the MAP was exponential during uniform conduction. The time constant of rise of the MAP
more » ... of the MAP upstroke (TMAP) correlated with that of the action potential foot (Tf,o0): TMAP + 1.01 TfO,t + 0.50; r2 = .80. Furthermore, changes in Tf0Ot with alterations in cycle length were associated with similar changes in TMAP: Tfoot = 1.06 TMAP -0. 1 1; r2 = .78. In addition, TMAP and Tfo,o both deviated from exponential during asynchronous activation; the inflections that developed in the MAP upstroke correlated in time with intracellular action potential upstrokes that were asynchronous in onset in these tissues. Finally, the field of view of the MAP was determined and was found to be dependent in part on tissue architecture and the space constant. Specifically, the field of view of the MAP was found to be greater parallel compared with transverse to fiber orientation (6.02 + 1.74 vs 3.03 + 1.10 mm; p < .01). These data suggest that the MAP upstroke may be used to define and characterize local electrical activation. The relatively large field of view of the MAP suggests that this technique may be a sensitive means to record focal membrane phenomena in vivo. Circulation 74, No. 5, 1147-1155, 1986 MONOPHASIC action potentials (MAPs) have been recorded from the surface of myocardium in animals and man with extracellular electrodes that induce local injury via suction or pressure.'The close correlation between the time courses of repolarization of intracellular and monophasic action potentials during electrolyte and cycle length changes has been confirmed in vitro." 3'7 The upstroke of the MAP, however, has received little attention. Although it is well known that its rate of rise is significantly slower than that of neighboring action potentials,' its characteristics and determinants during both uniform and asynchronous conduction have not been well studied. In addition, the "field of view" of monophasic action potentials, that is, the distance from the recording electrode that an
doi:10.1161/01.cir.74.5.1147 pmid:3769172 fatcat:vjmk5iiiovcjhepvd35k2etsri