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(Circulation. 1974;49:32.)
© 1974 American Heart Association, Inc.

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The Effects of Cycle Length on Cardiac Refractory Periods in Man

PABLO DENES M.D.¹; DELON WU M.D.¹; RAMESH DHINGRA M.D.¹; RAYMOND J. PIETRAS M.D¹; KENNETH M. ROSEN M.D.¹

¹ From the Section of Cardiology, Department of Medicine, Abraham Lincoln School of Medicine and the University of Illinois College of Medicine, and the West Side Veterans Administration Hospital, Chicago, Illinois.

The effects of pacing-induced changes in cycle length on the refractory periods of the atrium, A-V node and His-Purkinje system were studied in 24 patients using the extra stimulus technique. Refractory period determinations were made at two or more cycle lengths in all patients. Slopes relating cycle length and refractory periods were calculated using the least squares method.

Both the effective and functional refractory periods (ERP and FRP) of the atrium shortened with decreasing cycle lengths, with a mean slope of +0.155 and +0.129 respectively. A-V nodal ERP lengthened (mean slope, –0.177) while A-V nodal FRP shortened slightly (mean slope, +0.126). Bundle branch refractory periods as well as relative refractory periods of the His-Purkinje system also decreased, with mean slopes of +0.270 and +0.360, respectively. The ERP of the A-V node at any cycle length was related to the A-H at that cycle length (r = +0.646, P < 0.001).

The responses of the human heart to changes in cycle length are generally similar to those previously described in the animal laboratory. Such information contributes to our understanding of electrocardiographic phenomena such as aberrant conduction.

Key Words: His bundle electrogram • Functional refractory period • Premature atrial impulses • Relative refractory period • Effective refractory period • Aberrant conduction

Submitted on May 4, 1973
Accepted on August 30, 1973

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