Reappraisal of inhibition and summation with a single conditioning stimulus in man.
A noncapturing conditioning stimulus is known to exert inhibitory effect on a subsequent suprathreshold stimulus, while summation occurs rarely in man. The present study was conducted to revaluate whether conditioning stimulus at a relatively low intensity produced inhibition and summation in man. Thirteen patients with various arrhythmias, 47 +/- 19 years old, were studied. Basic ventricular driving stimuli (S1S1 = 600 msec), a conditioning stimulus (Sc), and extrastimulus (S2) were introduced from a catheter electrode. Sc at an intensity of twice the late diastolic threshold inhibited suprathreshold S2 from evoking a response in all 13 patients. The ScS2 interval producing inhibition was from 11 +/- 4 to 38 +/- 26 msec. When Sc preceded S2 by 5 msec, effective refractory period was shortened by 16 +/- 7 msec in 7 of 13 patients, a phenomenon of summation. The present study demonstrates that inhibition and summation are common phenomena with a single conditioning stimulus at relatively low intensities.
Second Department of Internal Medicine, Tokyo University Hospital, Japan.
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S
Saihara
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H
Inoue
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I
Toda
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M
Usui
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T
Sugimoto
D000293:Adolescent; D000328:Adult; D000368:Aged; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D003971:Diastole; D004558:Electric Stimulation; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D012032:Refractory Period, Electrophysiological / Q000502:physiology; D013997:Time Factors