The restitution portrait: a new method for investigating rate-dependent restitution.
BACKGROUND
Electrical restitution, relating action potential duration (APD) to diastolic interval (DI), was believed to determine the stability of heart rhythm. However, recent studies demonstrate that stability also depends on long-term APD changes caused by memory. This study presents a new method for investigation of rate- and memory-dependent aspects of restitution and for assessment of mapping models of APD.


RESULTS
Bullfrog ventricular myocardium was paced with a "perturbed downsweep protocol." Starting from a basic cycle length (BCL) of 1,000 ms, the tissue was paced until steady state was achieved, followed by single beats of longer and shorter cycle lengths. BCL was decreased by 50 to 100 ms and the process repeated. All APDs were plotted as a function of the preceding DI, which allowed simultaneous observation of dynamic, S1-S2, and two constant-BCL restitution curves in a "restitution portrait." Responses were classified as 1:1 (stimulus:response), transient 2:2, or persistent 2:2 (alternans) and were related to the slopes of the restitution curves. None of these slopes approached unity for the persistent 2:2 response, demonstrating that the traditional restitution condition does not predict alternans. The restitution portrait was used to evaluate three mapping models of APD. The models with no memory and with one-beat memory did not produce restitution portraits similar to the experimental one. A model with two-beat memory produced a qualitatively similar portrait.


CONCLUSIONS
The restitution portrait allows a more comprehensive assessment of cardiac dynamics than methods used to date. Further study of models with memory may result in a clinical criterion for electrical instability.
Kalb
Soma S
SS
Department of Biomedical Engineering, Duke University, Durham, North Carolina 27708, USA. ss49@duke.edu
Dobrovolny
Hana M
HM
Tolkacheva
Elena G
EG
Idriss
Salim F
SF
Krassowska
Wanda
W
Gauthier
Daniel J
DJ
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002304:Cardiac Pacing, Artificial; D003971:Diastole / Q000502:physiology; D004558:Electric Stimulation; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000502:physiology* / Q000503:physiopathology; D006339:Heart Rate / Q000502:physiology; D006352:Heart Ventricles / Q000503:physiopathology; D023421:Models, Animal; D008955:Models, Cardiovascular; D008962:Models, Theoretical; D009200:Myocardial Contraction / Q000502:physiology; D011237:Predictive Value of Tests; D011892:Rana catesbeiana; D016276:Ventricular Function