TOXICOLOGY
AND
APPLIED
PHARMACOLOGY
s&383-385
(1979)
Letters to the Editor
To the Editor: There may be ambiguities in interpretation of the illustrated tracings in Figs. 3, 6 and 7 of the article, “The Normal Electrocardiogram of the Conscious Beagle Dog” (Toxicol. Appl. Pharmacol. 41, 567-584, 1979). In each, long R-R intervals are twice the previous interval (in Figs. 3, 6), or the following R-R interval (Fig. 7), with great variation in the other intervals represented. Figure 5 might be a better candidate for “block” because the shorter R-R intervals are more nearly equal and the longer R-R interval is two times the shorter. (The first long interval could represent a change in
rate; thus a longer strip is needed to demonstrate a differentiation between a block and a respiratory arrhythmia which occasionally simulates a block.) Perhaps longer segments of reduced size would better demonstrate the differences that the authors are trying to represent. Figure 9 seems to fit the WHO/I SFC definition of a Wenckebach-type block, but the figure presented is not exactly a classical form with the successive lengthening of the P-R interval before the “dropped” QRS complex. The difference between Figs. 13 and 14 may need clarification. WILLIAM C. VAN ARSDEL III
1000 6th Street, Southwest, Apt. 609 Washington, D.C. 20024
Dear Sir: Enclosed are our comments on the “Letter to the Editor” of William C. van Arsdel III, concerning our article “The Normal Electrocardiogram of the Conscious Beagle Dog” (Toxicol.
Appl.
Pharmacol. 47, 567-584,
1979). Figures 3,, 6, and 7, as* we described on page 572 of the article, surely show, overall, more or less signs of respiratory influenced sinus arrhythmia. The differences between the examples are merely in degree. As we concluded on page 581 even a sinus block and/or sinus arrest can occur as a physiological ex-
tension or strengthening of a respiratorymediated sinus arrhythmia in the dog. The difference between respiratory-mediated sinus arrhythmia and respiratory and vagal-mediated sinus block is more of an academic problem than one of real clinical difference in this special case. In respiratory-mediated sinus arrhythmia, which is very common in the dog, every exaggeration in degree and every concomitant sign we reported in our article can exist alongside the others in a particular dog. In single cases, however, it may be difficult to decide whether there is a 383
004-008X/79/140383-03$02.00/0 Copyright 0 1979 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain
AND
APPLIED
PHARMACOLOGY
s&383-385
(1979)
Letters to the Editor
To the Editor: There may be ambiguities in interpretation of the illustrated tracings in Figs. 3, 6 and 7 of the article, “The Normal Electrocardiogram of the Conscious Beagle Dog” (Toxicol. Appl. Pharmacol. 41, 567-584, 1979). In each, long R-R intervals are twice the previous interval (in Figs. 3, 6), or the following R-R interval (Fig. 7), with great variation in the other intervals represented. Figure 5 might be a better candidate for “block” because the shorter R-R intervals are more nearly equal and the longer R-R interval is two times the shorter. (The first long interval could represent a change in
rate; thus a longer strip is needed to demonstrate a differentiation between a block and a respiratory arrhythmia which occasionally simulates a block.) Perhaps longer segments of reduced size would better demonstrate the differences that the authors are trying to represent. Figure 9 seems to fit the WHO/I SFC definition of a Wenckebach-type block, but the figure presented is not exactly a classical form with the successive lengthening of the P-R interval before the “dropped” QRS complex. The difference between Figs. 13 and 14 may need clarification. WILLIAM C. VAN ARSDEL III
1000 6th Street, Southwest, Apt. 609 Washington, D.C. 20024
Dear Sir: Enclosed are our comments on the “Letter to the Editor” of William C. van Arsdel III, concerning our article “The Normal Electrocardiogram of the Conscious Beagle Dog” (Toxicol.
Appl.
Pharmacol. 47, 567-584,
1979). Figures 3,, 6, and 7, as* we described on page 572 of the article, surely show, overall, more or less signs of respiratory influenced sinus arrhythmia. The differences between the examples are merely in degree. As we concluded on page 581 even a sinus block and/or sinus arrest can occur as a physiological ex-
tension or strengthening of a respiratorymediated sinus arrhythmia in the dog. The difference between respiratory-mediated sinus arrhythmia and respiratory and vagal-mediated sinus block is more of an academic problem than one of real clinical difference in this special case. In respiratory-mediated sinus arrhythmia, which is very common in the dog, every exaggeration in degree and every concomitant sign we reported in our article can exist alongside the others in a particular dog. In single cases, however, it may be difficult to decide whether there is a 383
004-008X/79/140383-03$02.00/0 Copyright 0 1979 by Academic Press, Inc. All rights of reproduction in any form reserved. Printed in Great Britain
