In canine atria, rate adaptation of maximum diastolic potential and action potential duration are markedly reduced in both chronic and nonsustained atrial fibrillation compared to normal atria.
OBJECTIVE: Our goal was to study rate adaptation of atrial action potentials in non-steady and steady states to further our understanding of mechanisms determining inducibility and stability of atrial fibrillation. METHODS: We used standard microelectrode techniques to examine the characteristics of steady-state action potentials paced at regular cycle lengths (CL) and of nonsteady-state action potentials observed after an abrupt change of CL in atria from canine hearts that had been rapidly paced. RESULTS: We compared action potential characteristics among normal atria, atria in which chronic atrial fibrillation (cAF, lasting more than 3 days) had been induced and atria in which only nonsustained atrial fibrillation (nAF, lasting less than 12 h) had been induced. In steady-state, the rate adaptation of maximum diastolic potential (MDP) and action potential duration (APD) and markedly reduced in both cAF and nAF. Action potential characteristics did not differ between cAF and nAF atria, suggesting that factors other than electrophysiological properties determine the chronicity of AF. The time course of change in APD after an abrupt change of CL was altered in nAF/cAF atria; i.e., when CL was prolonged, APD also prolonged at the first beat, and then shortened during several subsequent beats (initial phase). Thereafter, APD slowly prolonged to a new steady-state (slow phase). In nAF/cAF atria, the initial phase was enhanced (greater shortening of APD) and the slow phase was reduced (less prolongation of APD). This latter phase was modified by ryanodine. CONCLUSIONS: Thus the reduced rate adaptation of steady-state APD is explained mainly by the loss of a slow phase of APD adaptation in nAF/cAF which is reversed in the presence of ryanodine. Therefore, in both nAF and cAF atria, rate adaptation of MDP as well as APD are reduced, nonsteady state as well as steady state, AP characteristics are markedly altered and these changes are partially explicable by Ca, -dependent processes.
M Hara (Sat,) conducted a other in Atrial fibrillation. Induced atrial fibrillation (chronic or nonsustained) vs. Normal atria was evaluated on Rate adaptation of maximum diastolic potential (MDP) and action potential duration (APD). In canine atria, rate adaptation of maximum diastolic potential and action potential duration are markedly reduced in both chronic and nonsustained atrial fibrillation compared to normal atria.