Failure of primary negativity to predict dominant pacemaker
location: implications for sinoatrial conduction.
Bromberg, Burt I., Dwight E. Hand, Richard B. Schuessler, John P.
Boineau.
Department of Pediatrics and *Division of Cardiothoracic Surgery,
Department of Surgery, Washington University School of Medicine, St.
Louis, MO
APStracts 2:0119H, 1995.
Activation sequence maps derived during normal sinus rhythm from
extracellular potentials in the canine right atrium exhibit widely
separated sites of origin. The objectives of this study were to
characterize the distribution of pacemakers within the right atrium
and to determine the relationship of pacemaker action potentials to
sites of earliest surface activation as well as to local
extracellular electrograms. The right atria of six adult mongrel dogs
were rapidly excised under deep pentobarbital anesthesia and perfused
with 95% O2/5% CO2 Krebs-Henseleit solution. Action potentials from
the epicardial surface were recorded throughout the region bounded by
the crista terminalis laterally and the atrial septum medially.
Simultaneously, unipolar extracellular electrograms were recorded
from 250 endocardial sites. The earliest pacemakers preceded the
earliest electrogram by 63 +/- 34 msec, the latest pacemakers
followed the earliest electrogram by 71 +/- 40 ms. Primary negativity
in the extracellular electrogram did not predict the site of the
earliest or dominant pacemaker, and in some cases was associated with
the latest pacemakers. We conclude that primary negativity and/or the
sites of earliest activation reflect the point at which the impulse
engages atrial myocardium, not the site of earliest pacemaker
activity. As such, early extracellular activation appears to
represent sites of exit from a relatively insulated sinus node.
Received 26 August 1994; accepted in final form 2 March 1995.
APS Manuscript Number H772-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 4 April 1995.