Circulation, Vol 86, 1223-1232, Copyright © 1992 by American Heart Association
SM Hardman, MI Noble and WA Seed
BACKGROUND. Beat-to-beat variations in the pulse during atrial fibrillation
(AF) have conventionally been attributed to time-dependent changes in
filling. We have explored the possibility that they are dependent on the
intrinsic myocardial interval force relation. METHODS AND RESULTS. Left
ventricular (LV) contractility (maximum rate of rise of pressure, LV
dP/dtmax) and ascending aortic blood velocity were measured during cardiac
catheterization in 15 patients with AF. Beats preceded by an interval of
less than 500 msec were excluded from analysis to reduce the confounding
influence of incomplete mechanical restitution. The LV dP/dtmax was then
related to the prepreceding interval. An inverse relation consistent with
postextrasystolic potentiation was obtained in all 15 patients (Spearman's
rank correlations, -0.56 to -0.86; p less than or equal to 0.0001). This
relation was confirmed in three patients during pacing that overrode the AF
and introduced single-interval variations into steady-state pacing. The ECG
sequences from six of the AF patients were used to drive isometrically
contracting guinea pig papillary muscle and human right ventricular tissue
(n = 7); the same inverse relation was demonstrated. On a beat-by-beat
basis, the maximum rate of rise of force in the isolated muscle correlated
well with LV dP/dtmax in the patients (r = 0.50-0.86, p less than or equal
to 0.0001). The relation of the integral of aortic velocity (AVI,
proportional to stroke volume) to prepreceding interval was also inverse,
whereas important correlations were demonstrated between LV dP/dtmax and
AVI (Spearman's rank correlations, 0.27-0.95; p less than or equal to
0.0001). CONCLUSIONS. This study demonstrates that postextrasystolic
potentiation contributes to the characteristic beat-to-beat variation of
the pulse in AF.
ARTICLES
Postextrasystolic potentiation and its contribution to the beat-to-beat variation of the pulse during atrial fibrillation
Academic Unit of Cardiovascular Medicine, Charing Cross and Westminster Medical School, London.
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