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European Heart Journal 1989 10(5):409-416;
Copyright © 1989 by the European Society of Cardiology.
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© 1989 The European Society of Cardiology

Effect of paced cycle length on sinus node effective refractory period before and after autonomic blockade in patients with sick syndrome

I. OMORI, D. INOUE, T. SHIRAYAMA, J. ASAYAMAM, H. KATSUME and M. NAKAGAWA

Department of Internal Medicine, Kyoto Prefectural University of Medicine Kyoto Japan

Received 23 February 1988; revised 28 June 1988; .

Address for correspondence: Itsuki Omori, M.D., Second Department of Internal Medicine, Kyoto Prefectural University of Medicine, Kawaramachi Hirokoji, Kamikyo-ku, Kyoto 602, Japan.

Abstract

Effect of basic paced cycle length on sinus node effective refractory period was studied in 22 patients with sick sinus syndrome. Sinus node effective refractory period was measured using three different paced cycle lengths before and after pharmacologic autonomic blockade. Sinus node effective refractory period could be measured at one cycle length, at least, in 59% of the patients before blockade, however, it could be measured at two or more cycle lengths in only 18% of patients because of the chaotic response of sinus node against premature stimuli. It could be measured after pharmacologic autonomic blockade in 68% of the patients at two or more paced cycle lengths. On the other hand, the rest of the patients showed no measurable sinus node effective refractory period at any cycle length, for their sinus node effective refractory periods were shorter than their right atrial effective refractory periods. The comparison of sinus node effective refractory period at different paced cycle lengths was unsuccessful before pharmacologic autonomic blockade, while the refractory period was significantly prolonged as cycle length was shortened after blockade. We concluded that (1) sinus node effective refractory period in humans is prolonged as paced cycle length decreases, (2) the autonomic reflex is the major disturbing factor in measuring sinus node effective refractory period, and pharmacologic autonomic blockade can be usefully employed to eliminate a chaotic sinus nodal response, (3) when sinus node effective refractory period is shorter than right atrial effective refractory period, a shorter paced cycle length should be used for definite measurement of the former.

Key Words: Sinus node effective refractory period • paced cycle length • pharmacologic autonomic blockade • sick sinus syndrome.


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